Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
532 AM AST Sun Sep 17 2023

...New SYNOPSIS, AVIATION, MARINE...

.SYNOPSIS...
Issued at 454 AM AST Sun Sep 17 2023

Abundant moisture will bring heavy showers and some thunderstorms--mainly
during the afternoons during the week. Although the tropical
systems Lee and Margot are still active, only residual moisture
and marine hazards are expected at this time from their distant presence.
But, this moisture will contribute to the excessive heat that
will continue to be felt for the next several days.

&&

.SHORT TERM...Tonight through Monday...

Tonight, mostly cloudy skies prevailed over Puerto Rico and the U.S.
Virgin Islands, in addition to periods of passing showers. The
minimum temperatures along the PR and USVI coastal areas varied
between the upper 70s to low 80s, while in the mountains, they
stayed in the upper 60s to lower 70s. Like previous nights, the
wind flow across the islands was mostly land breezes. However,
some easterly components once again were seen.

Today, expect a combination of sunny and cloudy skies across the
islands. Daily maximum temperatures along the coasts should
fluctuate in the upper 80s to low 90s, while in the mountains, they
will range in the upper 70s to low 80s. The warm temperatures will
be accompanied by heat indices above 108 and 112 degrees Fahrenheit
in the low areas of the islands. An Excessive Heat Warning was
issued for north-central PR, Culebra, and Vieques due to expected
heat indices above 112 degrees. A Heat Advisory was issued for
northwestern, northeastern, eastern, and eastern interior PR and the
island of St. Croix. In the morning, we anticipate periods of
isolated to scattered showers to move across the islands.
Nonetheless, in the afternoon, expect most of the rainfall activity
to focus on the interior and western sections of Puerto Rico as
easterly winds prevail. Models continue to suggest a weak ridge
building across the Caribbean. This weather feature will limit the
heavy rainfall to the afternoon hours, where the diurnal heating,
orographic lifting, and sea breeze effects will contribute to
thunderstorm development. Like in previous days, expect frequent
lightning and gusty winds across the affected areas. The latest
model guidance suggests fluctuating precipitable water values to
around average and below average by Sunday into the beginning of the
workweek. This fluctuation in moisture content was observed in the
latest 00Z sounding, which showed 1.50 inches of precipitable
water, and the 12Z 09/16 sounding, which reported 1.96 inches.
Overall, expect similar weather conditions to prevail throughout
the period.

The National Hurricane Center continues to monitor the now-named
Tropical Storm Nigel, located about 980 miles northeast of the
Lesser Antilles at 5 AM AST and it is expected to become a
hurricane by Monday. Even though this system is not forecast to
impact Puerto Rico and the U.S. Virgin Islands directly, the wind
flow and marine conditions across the region will be influenced by
the storm as it continues to move northeast of the forecast
area.

&&

.LONG TERM...Wednesday through Saturday...

Tropical Storm Nigel is expected to be a hurricane by early
Monday morning and around 935 miles northeast of Saint Marten on
Monday afternoon. By Wednesday morning it is forecast to be 1135
miles north northeast of Saint Thomas. This will still place the
col between the weak trough over the Leeward Islands and the
tropical cyclone, but much further away. Hence winds across the
local area will be outside of any influence of the wind field
surrounding the hurricane and local winds and will be generally be
10 to 15 mph from the east northeast with gentle sea breezes.
Moisture will be near normal with patches and bands of excess
moisture being produced by perturbations out of the cross-
Atlantic easterly flow at tropical latitudes on Friday and Sunday.
Currently this is when the heavier rains are expected, but heavy
rain and thunderstorms are likely each afternoon in mostly
interior locations and scattered night and morning showers can be
expected from this pattern each morning.

At upper levels a TUTT low will be approaching the area along 20
degrees north, but will pull away and dissipate before it can
have any effect. Therefore a ridge of high pressure is expected to
hold over the area with high pressure building north of us
beginning on Friday.

&&

.AVIATION...
(06Z TAFS)
Issued at 454 AM AST Sun Sep 17 2023

All terminals will experience VFR conditions. Aft 17/18Z
SHRA/TSRA are expected to dvlp over interior and western PR with
mtn obscurations and brief MVFR conds. MVFR conditions may affect
TJMZ/TJBQ briefly but should not prevail. Sfc winds less than 5 kt
bcmg E-NE and incrg to 10-15 kt with hir gusts in sea breezes and
near TSRA.

&&

.MARINE...
Issued at 454 AM AST Sun Sep 17 2023

A pulse of energy from the recent passage of the tropical systems Lee
and Margot will move through the Atlantic waters in nearly north
swell that will cause seas to be hazardous today and Monday with
seas up to 7 feet. A second pulse will move through the area on
Wednesday from the northeast, but will be weaker. At this time
only precautionary statements are expected to be needed then.
Isolated thunderstorms may occur over the local waters from time
to time throughout the week.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
452 AM AST Mon Sep 18 2023

.SYNOPSIS...Diurnal heating and local effects will promote
afternoon shower and thunderstorm activity mainly across interior
to western Puerto Rico over the next few days. Excessive heat risk
will persist each late morning to early afternoon across urban,
coastal and lower elevation areas.

Northerly swells from Lee and Margot are promoting hazardous seas
across the Atlantic Waters. Because of this, Small Craft
Advisories is in effect for the offshore Atlantic Waters, and the
coastal waters of northern and northwestern Puerto Rico, through
at least this evening. High Surf Advisories and High Risk of Rip
Currents are in effect for the northern coastline of PR.

&&

.SHORT TERM...Today through Wednesday...

Mostly clear to partly cloudy skies were observed across the islands
during the overnight hours. Minimum temperatures were from the mid
60s across the higher elevations of Puerto Rico to the upper 70s and
low 80s across the coastal areas of the islands. Light passing
showers were noted across the coastal Atlantic waters of PR with
some leaving minor rainfall accumulations over land areas. The land
breeze prevailed across PR and the USVI, with wind speeds at less
than 10 mph.

For today, sunny to partly cloudy skies should prevail through the
morning hours across the region. A weak surface high pressure over
the western Atlantic and TC Nigel over the central Atlantic will
promote a weak northeasterly wind flow across the region. Embedded
in this flow, a patch of low-level moisture is expected to reach the
local area through the day. This will aid in the formation of
showers and isolated thunderstorms during the afternoon hours over
portions of the interior, southern, and western Puerto Rico. Urban
and small stream flooding is expected with these thunderstorms. Due
to the light steering winds showers could drift over coastal areas
after the sea breeze decreases before sunset.

For Tuesday and Wednesday, an upper level ridge is forecast to build
over the area, increasing stability. However, the precipitable water
content is expected to remain between 1.50 and 1.75 inches,
sufficient to aid in the development of afternoon convection over
the interior of PR each day. The wind direction is expected to
become more easterly, but relative weak trades will continue to
prevail. Also, the change in wind direction may cause showers to
develop over the north-northwestern sections of PR. Across the USVI,
overall fair weather conditions should prevail through the short-
term period, with limited shower activity.

Maximum temperatures should range from the upper 80s to low 90s
across the lower elevations, and the usual urban and coastal areas o
the islands should experience heat indices between 105-110 degrees
or higher, before the onset of afternoon convection.

&&

.LONG TERM...Thursday through Tuesday...

Easterly winds will prevail over the long term period as a surface
ridge builds across the eastern Atlantic. This will drive a
pattern of passing windward showers across eastern Puerto Rico and
the USVI followed by afternoon convection mainly across the
interior to western section of PR. The main driver of how much
rain is to be expected is the content of precipitable water each
day that becomes abundant at the end of the term. On Friday
moisture increases, which will support good rainfall. Then on
Sunday afternoon, a large tropical airmass will move into the
region. This has the potential to bring soggy conditions into next
week. However, a mid to upper level ridge begins to form north of
the eastern Caribbean at this time. This could possible limit
most of the rainfall to afternoon convection. Heavy rain can be
expected on Sunday, Monday, and Tuesday due to this increase of
moisture. Also, the seasonal pattern of hot afternoons will
continue each day, especially across northern coastal areas of
Puerto Rico which is likely to continue the trend of record
breaking high temperature across some parts of our islands.

&&

.AVIATION...Mainly VFR conditions expected to prevail across all
terminals during the next 24 hours. However, diurnally induced
afternoon SHRA/TSRA may cause tempo MVFR conds at TJPS and VCTS at
TJBQ. Elsewhere, VCSH possible at times thru the period. Surface
winds E-ENE at 8-12 kt with sea breeze variations and higher gusts
aft 18/15z.

&&

.MARINE...Recent observation across the northern coastlines are
showing seas up to 8 feet with periods between 12 to 14 seconds
reflecting the lingering swell action from Lee and Margot. As a
result, a small craft advisory for the Atlantic waters is in place
through at least this evening. High surf Advisories and High rip
current risk statements will continue due to breaking waves around
10 feet. The southern coastlines are much tamer with 2 to 4 foot
breaking waves. Swell will continue later this week due to
Hurricane Nigel.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
443 AM AST Tue Sep 19 2023

.SYNOPSIS...Diurnal and local effects will promote afternoon
shower and thunderstorm activity mainly across the interior to
western sections of Puerto Rico over the next several days.
Moisture from a tropical wave will increase rain chances for the
second half of the workweek with Sunday onward also looking wet.
Hot conditions will persist each late morning to early afternoon
across urban, coastal and lower elevation areas. Northerly swells
generated from previous storms Lee and Margot and now Hurricane
Nigel will continue to affect the Atlantic waters, nearshore
northern and northwestern waters of Puerto Rico, and the Mona
Passage.

&&

.SHORT TERM...Today through Thursday...

Afternoon thunderstorms with gusty winds and periods of heavy
rainfall leading to urban and small stream flooding can be expected
each day over portions of Puerto Rico. Also, heat indices higher
than 108 degrees Fahrenheit will remain possible across the urban
and lower elevations of the coastal municipalities of the islands.

ASCAT Scatterometer wind data suggests northeast trades persisting
across the Atlantic waters, and embedded in this flow there is a
surge in low-level moisture, likely from an induced trough to our
northeast in response to a short wave trough at the upper levels.
Therefore, passing showers could continue to move at times across
the U.S. Virgin Islands and north-northeastern sections of Puerto
Rico through the early morning hours. Minimum temperatures were from
the mid 60s across the higher elevations of Puerto Rico to the upper
70s and low 80s across the coastal areas of the islands. Winds were
light from the northeast.

At least for the next day or so, the induced trough to our northeast
will slowly stream westwards, and passing showers will continue
across the Atlantic waters with some reaching portions of the
islands during the night and early morning hours. Meanwhile, the mid-
level ridge is currently forecast to be weaker than previously
expected, and the short-wave trough will remain positioned between
the islands and the Anegada Passage. This pattern will promote SW
flow aloft and areas of divergence to favor convective development
over the interior and western PR each afternoon, including over the
San Juan metro area today. In addition, convective activity may last
once again through the evening hours due to the environmental
conditions and the weak steering winds. A small area of drier air
and increasing trade winds are expected early on Thursday ahead of a
tropical wave, but locally induced afternoon showers and
thunderstorms are still expected to develop over the interior and
western PR.

&&

.LONG TERM...Friday through Tuesday...

A seasonal day of weather is expected on Friday as moisture
increases, which will support afternoon thunderstorms once diurnal
heating and local effects promote convection. Precipitable water
values drop a bit on Saturday yet and active afternoon across Puerto
Rico is forecast. Then on Sunday afternoon, a large tropical airmass
will move into the region. This has the potential to bring muggy
conditions into next week. However, a mid to upper level ridge
begins to form north of the eastern Caribbean at this time. This
could possible limit most of the rainfall to afternoon convection
and quick passing showers. Thunderstorms can be expected each
afternoon on Sunday through Wednesday mainly across the interior to
western sections of Puerto Rico as easterly flow continues. Due to
the abundance of moisture, this activity may be long lasting at
times, potential providing lots of rain. Also, the high RH values
will make it feel extra hot across the islands, with high heat
indices especially for urban coastal areas.


&&

.AVIATION...Mainly VFR conditions expected to prevail across all
terminals during the next 24 hours. However, diurnally induced
afternoon SHRA/TSRA may cause tempo MVFR conds at TJSJ/TJPS/TJBQ btw
19/16z-21z. Surface winds from the east at 8-12 kt with sea breeze
variations and higher gusts aft 19/15z.

&&

.MARINE...Fading northerly swells generated from previous storms
Lee and Margot, will be replaced by a northeasterly swell from
Hurricane Nigel. This will continue to affect the Atlantic waters
through the week causing seas up to 6 feet, occasionally greater. Recent
buoy observations along the north coast of PR and the Rincon buoy
suggest wave heights between 4-6 feet with 11-13 seconds periods.
High rip current risk continues due to this across the northern
coastline of PR.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
507 AM AST Sat Sep 23 2023

.SYNOPSIS...The persistent hot weather pattern we have observed
across the islands will continue today. Therefore, several heat
related advisories and warnings are in effect from 10 AM to 5 PM.
This diurnal heating, along with sea breeze convergence and local
effects will promote strong showers and thunderstorms mainly
across interior to western Puerto Rico. A tropical wave will
increase shower and thunderstorm activity across the region on
Sunday into Monday. Model guidance continues to lean towards the
current AL90 staying over the tropical Atlantic next week. Please
continue to monitor the latest updates from the National Hurricane
Center (NHC) and WFO San Juan regarding this system.

&&

.SHORT TERM...Today through Monday...

Western Puerto Rico had clear skies overnight, while eastern
Puerto Rico, Culebra, Vieques, and the U.S. Virgin Islands had
variably cloudy skies with occasional passing showers that moved
inland. Low temperatures dropped into the low 80s and upper 70s
across the coastal areas and into the mid-70s or upper 60s across
the mountain sites—winds were mainly from the east to east-
southeast at less than ten mph.

The persistent hot weather pattern we have observed across
the islands will continue today, with heat index values surpassing
107 degrees Fahrenheit across the urban and coastal areas in Puerto
Rico and the U.S. Virgin Islands. Therefore, an Excessive Heat
Warning is in effect for Vieques, Culebra, and St Croix, and the
rest of the lower elevations are under a Heat Advisory from 10 am to
5 pm this afternoon. Strong thunderstorms will again develop across
the mountain areas and western coastal sections due to the local
effects, excessive heating, and sea breeze variations during the
afternoon. This activity may result in urban and small-stream
flooding, frequent cloud-to-ground lightning, and gusty winds across
the interior, western, and northeast PR, including the SJ Metro.

It's possible that the Total Precipitable Water (TPW) may rise by 2
to 2.35 inches between Sunday and Monday thanks to a tropical wave
moving into the area. The GFS GDI indicates that there is a chance
for scattered to numerous showers and thunderstorms every day,
especially in the afternoons. As a result, the weather could be wet
and unstable, with heavy rains, strong winds, and intense
thunderstorms early next week.

&&

.LONG TERM...Tuesday through Saturday...

Northeasterly winds are forecast to prevail during most of the long
term forecast period. Current model guidance indicates a drying
trend on Tuesday as a tropical wave, and moisture associated with
it, moves away from the islands. Patches of moisture will continue
to filter into the region on Wednesday through Saturday, maintaining
precipitable water (PWAT) values at up to normal values. During the
night and early morning hours, passing showers affect windward
sectors of the islands, particularly across northern and eastern
Puerto Rico, and across Vieques, Culebra and the USVI. NE wind flow
will help promote afternoon shower activity, induced by sea breeze
convergence, diurnal heating and local effects, mainly over sectors
of interior to southern Puerto Rico each day. Afternoon activity
could also be observed downwind of El Yunque, Vieques, Culebra, and
the USVI. Maximum temperatures should be in the upper 80s to low 90s
across lower elevations of the islands. Minimums should range in the
upper 70s to low 80s across lower elevations of the islands, and in
the upper 60s to lower 70s across higher elevations of Puerto Rico.
At least a limited excessive heat risk will persist each late
morning to early afternoon across urban, coastal and lower elevation
areas. A tropical wave (AL90), currently several hundred miles west
of the Cabo Verde Islands, has a high chance of development. The
NHC's 2 AM EDT TWOAT mentions that this system will likely become
a tropical depression during the next couple of days. With model
consensus now leaning towards this system staying over the
Atlantic, the main hazard from this system would be swells
reaching our local waters and coastlines. Please continue to
monitor the latest updates from the NHC and WFO San Juan regarding
this system.

&&

.AVIATION...Mainly VFR conditions will prevail during the morning.
Afternoon TSRA/SHRA could result in brief MVFR conditions, mainly
across PR terminals btwn 23/17-23z. After that, SHRA may affect
USVI terminals and TJSJ, without significant impacts. Surface
winds will remain from the east-southeast at 5 to 10 kt but will
then range between 10- 15 knots with higher gusts after 23/13z.

&&

.MARINE...Seas should remain favorable for small craft at 2 to 5
feet through early next week. Light to moderate east winds will
continue before becoming more northeasterly by mid next week. The
next tropical wave is expected by tomorrow into Monday and we
anticipate shower and thunderstorm activity across the regional
waters. Seas are forecast to increase by midweek next week with
swells from a tropical cyclone over the open Atlantic, well east
northeast of the islands.

Today, there is a moderate risk of rip currents for north oriented
beaches of Puerto Rico, from Aguadilla to Fajardo, as well as the
northern beaches of Culebra. There is also a moderate risk of rip
currents today today for the northeastern beaches of St. Thomas
and the easternmost beaches of St. Croix. Low risk elsewhere
across the islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
551 AM AST Sat Sep 30 2023

.SYNOPSIS...Tropical Storm Philippe is not an immediate threat to
Puerto Rico and the U.S. Virgin Islands. Nevertheless, the outer
bands of Philippe will extend over the area, resulting in a
persistent wet and unstable weather pattern for most of the
forecast period. Even though there is an anticipated increase in
shower activity, warm-to-hot conditions will persist, potentially
leading to heat-related issues like heat exhaustion or heat stroke
with prolonged exposure. Additionally, there will be ongoing risks
of hazardous seas for small craft and life-threatening rip
currents for beachgoers, particularly for offshore Atlantic waters
and Atlantic-facing beaches.


&&

.SHORT TERM...Today through Monday...

The weather was characterized by a variable pattern throughout the
night, with frequent light to moderate passing showers across most
local waters and some inland areas. The most significant rainy
activity was observed across northeast sectors, moving further
south-southwestward towards the interior. However, rainfall
accumulations were insignificant, with the Radar Doppler rainfall
estimates indicating less than an inch. Due to some cloud cover
and moisture presence, minimum temperatures were relatively high,
ranging from the upper 70s to lower 80s across coastal areas and
dropping to the lower to mid 70s across the interior.

As we move into the day, residents can expect a continuation of the
variable weather pattern, with a prevailing northeasterly wind
flow. This wind flow is generated from a surface high pressure
over the central Atlantic and Tropical Storm Philippe, located
approximately 500 miles east of the region. As a result, the
islands will likely receive moisture from an external band of
Philippe. According to the GOES Satelite-derived PWAT, the
moisture values now fluctuate between 2.0 to 2.7 inches and above
climatological levels. In the morning, there will be some good
periods of sunshine with clear to partly cloudy skies, which will
favor daytime heating and cause heat index values to climb again
to heat advisory criteria. As a result, a Heat Advisory is in
effect for all the U.S. Virgin Islands and all coastal areas of
Puerto Rico, including the vicinity of Caguas, from 10 AM to 5 PM
AST. As the day progresses, local effects and diurnal heating will
trigger another quite active day, especially over the northern
sections during the late morning hours, followed by more severe
activity over the southwestern quadrant and the interior in the
afternoon. There is a higher likelihood of lightning and flooding
threats, especially over the southwest, as suggested by the
Gálvez-Davison Index (GDI).

Although conditions may improve at nighttime with the arrival of a
slightly drier airmass slot, another external band from Tropical
Storm Philippe will likely reach the islands on Sunday, inducing
another wet and variable day. Therefore, residents should
anticipate an increase in the frequency of passing showers, with
the bulk of the showers around the northeastern and northern
sections in the morning and over the south and southwestern in the
afternoon. On Monday, as Philippe moves northward as the official
track from the National Hurricane Center suggests, the local
pressure gradient will relax, favoring lighter and variable winds
across the region. This pattern will support slow-moving shower
activity that will cluster across the interior, potentially
inducing urban and small stream flooding.

.LONG TERM...Tuesday through Saturday...

Based on the latest model guidance and in close alignment with
the projected track of Tropical Storm Philippe, there will be
fluctuations in the prevailing wind patterns over the extended
forecast period. Initially, the winds will be gentle, measuring
below ten miles per hour, and variable on Tuesday before shifting
to a more southerly direction on Wednesday. As Philippe rapidly
moves northward, distancing itself from the region, the winds are
expected to increase, reaching speeds of 10-15 knots, while
gradually backing from the southeast on Thursday to the east by
Saturday. Emphasizing this transition is crucial because the
steering flow will determine the focus of both advective and
convective-generated showers. Regarding moisture levels, southerly
winds on Tuesday and Wednesday will bring increasing amounts of
tropical moisture from the same outer bands projected to cross the
local islands during the weekend. Then, between Thursday and
Saturday, Philippe's feeder band will likely sweep across the
region from the east, again bringing abundant tropical moisture.
During peak moisture periods, precipitable water values are
projected to peak close to two standard deviations above normal
moisture levels, around 2.3-2.5 inches, by Wednesday afternoon and
Friday morning.

In summary, anticipate variable weather conditions, with periods
of increased shower and thunderstorm activity producing moderate
to locally heavy rainfall. This activity should focus on the
southern and eastern regions of Puerto Rico and the U.S. Virgin
Islands during the nighttime, followed by afternoon convective
development following the general steering flow, if influential.
Afternoon convective development will first cluster across the
interior and spread northward on Tuesday and Wednesday and the
west-northwestern from Thursday onwards. The risk of excessive
heat will persist, with higher risk levels as southerly winds
become more dominant by the latter part of the workweek. Some
relief may be possible in areas or days experiencing extended
periods of rain.


&&

.AVIATIONS...SHRA could occasionally move across the local area
through Saturday morning. This may cause tempo MVFR conditions at
TJSJ, & TIST TSRA is expected to develop between 30/16-22z over
the interior and southern sections of PR, driving tempo MVFR
conditions at TJPS. Lower ceilings are expected across TJPS and
the vicinity, with the TS activity. Winds will prevail at 10 knots
or less until 30/14Z, increasing with sea breeze variations.


&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated steady seas between 2
and 6 feet, with the highest wave heights across bouys with east-
northeast exposure. Swells generated by Philippe will maintain
hazardous seas of up to 8 feet through at least Monday, mainly
across the offshore Atlantic waters, where a Small Craft Advisory
remains in effect. Small craft should exercise caution elsewhere,
particularly across the coastal waters and local passages with
eastern exposure.

There is a high rip current risk for the northern and eastern
beaches of Puerto Rico and Culebra. Life-threatening rip currents
are possible elsewhere, including the U.S. Virgin Islands and
Vieques.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Sun Oct 1 2023

.SYNOPSIS...Although the National Hurricane Center adjusted
Tropical Storm Philippe's track a few miles closer, Philippe is
not an immediate threat to Puerto Rico and the U.S. Virgin
Islands. Nevertheless, Philippe's core moisture field and feeding
band will likely extend over the area, resulting in a persistent
wet and unstable weather pattern for most of the forecast period.
Even though there is an anticipated increase in shower activity,
warm- to-hot conditions will persist, potentially leading to heat-
related issues like heat exhaustion or heat stroke with prolonged
exposure. Additionally, there will be ongoing risks of hazardous
seas for small craft and life- threatening rip currents for
beachgoers, particularly for the Atlantic waters and Atlantic-
facing beaches.


&&

.SHORT TERM...Today through Tuesday...

PWAT-derived data from GOES Satellite imagery shows a plumb of
abundant tropical moisture currently impacting our region due to a
nearby tropical storm, Philippe. This moisture surge has generated
frequent light to strong showers across the northeastern sections
of Puerto Rico, drifting west-southwestward into the north-central
areas. Rainfall accumulations so far were less than one inch.
Overnight temperatures were in the low 80s over the coastal areas
and in the low to upper 70s for the rest of the island.

For the rest of the day, wet and warm weather conditions will
persist due to the continuous flow of tropical moisture from
Philippe, embedded in northeasterly winds. Another warm day is
expected, with the humidity and the diurnal heating allowing heat
indices to reach 108-111 degrees across the northern, western, and
eastern PR coastal areas, Culebra Vieques, and the U.S. Virgin
Islands. Although abundant moisture is present in the CWA, stable
conditions aloft, with warmer (two standard deviations above the
normal) temperatures at 500 Mb and subsidence aloft, will limit
somewhat widespread long-live activity. Nevertheless, residents
can expect strong showers with possible isolated thunderstorms
across the southwestern quadrant of Puerto Rico and the northern
areas, especially in the afternoon. The activity could result in
ponding water in roadways, urban flooding, and the threat of
lightning with the heaviest activity.

A few changes were introduced between Monday and Tuesday, as the
official track of the National Hurricane Center places Philippe a
few miles closer from the area. Despite the effects of this new
trajectory, favoring increased tropical moisture moving into the
region, model global guidances suggest PWAT values decrease to
near or slightly below climatological normals. This scenario could
result in a lower frequency of passing showers, especially at
nighttime, and convective development in the afternoon. Regardless
of the model solutions, external rain bands from Philippe could
reach the islands, inducing shower activity.

.LONG TERM...Wednesday through Sunday...

Based on the latest model guidance and consistent with the newly
forecasted track of Tropical Storm Philippe, anticipate some
variations in the prevailing wind patterns during the extended
forecast period. Initially, expect light winds below ten mph,
which will gradually shift to a south-southwesterly direction on
Wednesday across most areas, excluding portions of the U.S. Virgin
Islands and surrounding waters where wind speeds of 10-20 mph with
higher gusts are likely due to Philippe's proximity. As Philippe
rapidly moves northward and away from the region starting
Thursday, the wind speed pattern will persist but with a more
southerly direction. Subsequently, the winds will weaken while
gradually backing from the southeast on Friday and from the east-
southeast on Saturday and Sunday.

It's important to emphasize this transition, as the steering flow
will determine the areas prone to advective and convective-
generated showers. Concerning moisture levels, Philippe's core
moisture field may continue bringing increased moisture on
Wednesday, peaking around two standard deviations above
climatological moisture levels, with precipitable water values
around 2.3-2.5 inches. Then, Philippe's feeder band will likely
extend across the region from Thursday to Saturday, bringing
additional tropical moisture, with precipitable water values
reaching above-normal climatological levels by late Friday night
into Saturday. By Sunday, precipitable water values should remain
around climatological moisture levels, coinciding with the arrival
of a tropical wave.

In summary, anticipate variable weather conditions, with showers
affecting southern and eastern sections of Puerto Rico and the
U.S. Virgin Islands during nighttime, followed by afternoon
convective development, with possible isolated thunderstorms,
clustering across the interior and spreading northward on
Wednesday and Thursday and more northwestward to westward from
Friday onward. In this scenario, expect an increased flooding
risk, particularly during high- moisture periods. There will also
be ongoing concerns about excessive heat hazards, with an
increased risk as winds become more south-southeasterly during the
latter part of the workweek and into the weekend. Some areas may
experience relief from prolonged periods of rain.


&&

.AVIATION...SHRA would continue across the local area through
Sunday morning, especially over TJSJ, TIST, and TISX. This is
causing brief MVFR conditions, mainly at TJSJ and TIST. After
01/16Z, TSRA is expected to develop over the interior and southern
sections of PR, driving brief MVFR conditions at TJPS. Lower
ceilings are expected across TJPS and the vicinity, linked to the
TS activity. Winds will prevail at 10 knots or less from the NE
until 01/14Z, increasing up to 12 knots with sea breeze
variations. He


&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated subsiding seas between
2 and 5 feet, with the highest wave heights across buoys with
eastern and northern exposure. Swells generated by Philippe will
maintain hazardous seas of up to 7 feet through at least Monday
afternoon, mainly across the Atlantic waters, where a Small Craft
Advisory remains in effect. Small craft should exercise caution
elsewhere, particularly across the coastal waters and local
passages with eastern exposure.

There is a high rip current risk for the northern and eastern
beaches of Puerto Rico and Culebra through this afternoon. Life-
threatening rip currents are possible elsewhere, including beaches
of the U.S. Virgin Islands and Vieques.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Mon Oct 2 2023

.SYNOPSIS...While Tropical Storm Philippe is forecast to track
well east-northeast of the local islands, thus not posing a
direct threat to Puerto Rico or the U.S. Virgin Islands,
Philippe's outer and feeder bands will likely extend over the
area. This extension will result in a continued pattern of
persistent wet and unstable weather for most of the forecast
period. Even though an increase in shower activity is anticipated,
warm-to-hot conditions will persist, potentially giving rise to
heat-related problems such as heat exhaustion or heatstroke,
especially with prolonged exposure. Furthermore, there will be
ongoing concerns regarding hazardous seas for small craft and
life-threatening rip currents for beachgoers, particularly in the
Atlantic waters and on beaches facing the Atlantic.


&&

.SHORT TERM...Today through Wednesday...

Surface ridge extending into the southwest Atlantic and the broad
circulation around Tropical Storm Philippe will maintain a moderate
northeast wind flow through at least Tuesday. Thereafter it is then
forecast to become light and more southerly by Wednesday onwards as
Phillipe continues it's present and expected forecast track well
northeast of the region. Consequently expect the outer bands from
Philippe to occasionally propagate west and southwest across the
region. This will bring periods of moderate to locally heavy rains
along with brief wind gust accompanying the stronger shower
activity, especially during the overnight and early morning hours.
Afternoon activity today should later shift and be focused over the
central and southwest quadrant Puerto Rico, and mainly downwind of
the adjacent islands and the USVI. This overall showery and
advective weather pattern will continue through Tuesday, especially
during the evening, overnight and early morning hours. Occasional
bursts of squally conditions may also be possible over parts of the
regional waters mainly northeast and east of Puerto Rico,as well as
around U.S. Virgin Islands and the Anegada passage.

Wednesday, winds become more southerly and lighter a previously
mentioned as Phillipe is expected to continue its northwest track,
staying well northeast of the region. In doing so, expect winds to
become fairly light across the area with a more south to southwest
component. If this weather pattern unfolds, the expected scenario
along with local and diurnal effects and good moisture convergence,
afternoon showers development should be focused across the central
interior and north central to northeast sections of Puerto Rico
including parts of the San Juan metro. Shower development will also
remain possible as over the U.S. Virgin Islands particularly the
northern USVI St Thomas and St John based on the present forecast
track of Phillipe. Lesser shower activity is expected at St
Croix at this time. Stay tuned!

Indirect impacts for the period: Occasional outer bands will being
periods of moderate to locally heavy rains across the coastal waters
and north and east section of the islands, especially during the
overnight and early morning hours. Activity will later develop across
the interior and southwest quadrant of Puerto Rico and mainly
downwind of the USVI steered by the dominant northeast wind flow
through Tuesday. Ponding of water on roads and poor drainage areas as
well as minor urban and small stream flooding will be possible
through Tuesday. As winds more southerly by Wednesday, activity
should be focused over the east interior and southeast sections of
PR during the overnight hours, and the central interior as well as
the north and northeast sections during the afternoon hours as the
low level steering flow become more south to southwest based on the
latest guidance and expected track of Phillipe.

Swells generated by Philippe will affect portions of the U.S. Virgin
Islands and Puerto Rico waters and coastal areas during the next few
days. These swells will likely deteriorate marine conditions and may
cause life-threatening surf and rip current conditions. Please
continue to monitor the latest Coastal waters forecast (CWFSJU),
Marine weather messages(MWWSJU) and Surf zone forecast
(CFWSJU)issued by WFO San Juan Puerto Rico and for latest updates.

.LONG TERM...Thursday through Monday...

Despite its expected distance, Tropical Storm Philippe will
continue to influence the extended forecast period. With the
recently adjusted track, which now positions Philippe slightly
farther east, and aligned with the latest model guidance
consensus, variations in the prevailing wind patterns are likely
throughout the extended forecast period. These fluctuations will
be most noticeable in the steering flow direction within the
1000-850 mb layer. Nevertheless, despite these variations, the
average wind speeds at lower altitudes are expected to remain
within the 5-10 knot range, resulting in slow-moving showers.
Initially, anticipate south-southwesterly winds on Thursday,
gradually backing to the south on Friday, then further
transitioning to south-southeast on Saturday, southeast on Sunday,
and finally becoming more east-southeast by Monday.

Regarding moisture levels, Philippe's outer bands will
periodically bring a substantial amount of moisture, peaking at
approximately one standard deviation above the typical
climatological levels. Precipitable water values will likely range
around 1.9 and 2.1 inches on Thursday. As Philippe rapidly moves
northward and away from the local islands, its feeder band is
expected to extend across the region starting Friday, introducing
additional tropical moisture, with precipitable water values
exceeding typical climatological levels, around 2.1-2.3 inches.
The combinations of lingering moisture from Philippe's feeder band
and abundant moisture from an approaching tropical wave, trapped
over the northeastern Caribbean between a surface high pressure
system to the northwest under persistent east-southeasterly winds,
will maintain precipitable water values above the climatological
levels through the end of the cycle.

In summary, variable weather conditions will prevail, with showers
affecting southern and eastern sections of Puerto Rico and the
U.S. Virgin Islands during nighttime, followed by afternoon
convective development, with possible isolated thunderstorms,
clustering across the interior into northern areas between
Thursday and Saturday. From Sunday onwards, this activity should
spread northwestward to westward, steered by southeasterly winds.
In this scenario, expect increased flooding and possibly lightning
risk, particularly during high-moisture periods and peak heating
influence. There will also be ongoing concerns about excessive
heat hazards, with an increased risk as winds become more south-
southeasterly during the latter part of the workweek and into the
weekend. Some areas may experience relief from prolonged periods
of rain and increased cloud coverage.


&&

.AVIATION...Prevailing VFR, but wdly SCT SHRA/Isold TSRA en route
til 02/14z. SHRA will develop and steer southwestward across the
regional waters reaching the north and east coastal sections of PR
and the USVI. Brief MVFR and Mtn top obscr ovr E interior of PR,
with ocnl SHRA to affect TIST/TISX/TJSJ/TJBQ. Aftn convection over
the central and southwest PR with SCT SHRA/Isold TSRA psbl. VCTS at
TJMZ/TJPS and just S of TJBQ 02/17z-02/22Z. VCSH at the remaining
terminals. Winds fm the ENE btw 5-10 kts, bcmg fm NE 10-15 kts with
sea breeze variations and ocnly hir gusts with passing SHRA.


&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated subsiding seas between
2 and 5 feet, with the highest wave heights in bouys with
Atlantic waters exposure across northern Puerto Rico. Swells
generated by Philippe will maintain hazardous seas of up to 7
feet, extending through at least Wednesday morning, mainly across
the Atlantic waters, where a Small Craft Advisory remains in
effect. Small craft should exercise caution elsewhere,
particularly across the coastal waters and local passages with
northern and eastern exposure.

There is a moderate rip current risk for all local beaches with
northern and eastern exposure, where life-threatening rip currents
are possible. The risk will likely elevate to high by Tuesday
night.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
428 AM AST Wed Oct 4 2023

.SYNOPSIS...
Tropical Storm Philippe and its external circulation will
continue to dominate the weather pattern for the next few days,
causing unstable conditions with the potential for strong
thunderstorms and flooding. A wet pattern will continue through
the weekend until the arrival of drier air on Monday brings
comparably fairer conditions. Hazardous marine conditions will
continue to due to thunderstorm activity mainly across the eastern
half of the region.

&&

.SHORT TERM...Today through Friday...
The broad circulation around Tropical Storm Philippe now centered
some 120 miles or so north of San Juan Puerto Rico, will continue
to affect the steering wind flow across the region through the
end of the work week. This will result in a west to southwest
winds today through Thursday, and then a more southerly and
lighter wind flow by Friday, as Philippe tracks northwest then
more northwards and farther away from the region. In the meantime
expect the outer bands and a large plume of moisture trailing
Philippe to be lifted up across the region. This will help to
maintain a significantly moist and unstable airmass across the
forecast area through most of the period. The overall pattern will
therefore favor periods of moderate to locally heavy rains along
with brief wind gusts accompanying the shower and thunderstorm
activity, especially during the rest of the early morning hours.

Cloudiness and shower activity across Puerto Rico should slowly
diminish by late morning while considerable cloudiness and shower
and thunderstorm activity is so far expected to continue in and
around the U.S. Virgin Islands, at least into the early afternoon
hours. However, any breaks in cloud cover through-out the day will
support additional afternoon convection particularly across parts of
the central interior and eastern half of Puerto Rico including
around the San Juan Metro and over the U.S. Virgin Islands.

Due to the expected and ongoing conditions there will remain a
moderate to high change for urban and small stream flooding as well
as mudslides in areas as of steep terrain, as well as river flash
flooding today through at least Thursday. Squally weather conditions
will also remain possible over the regional waters especially during
the rest of the morning hours but mainly northeast of Puerto Rico,
around U.S. Virgin Islands waters and the Anegada passage.

Thursday into Friday, winds are forecast to become more southerly
then southeasterly as the region gradually breaks away from the
effects of Philippe. However recent model guidance suggest a fairly
moist airmass is expected to remain across the region, as a weak
tropical wave is forecast to approach the area from the east. This
along with the light southerly wind flow,good daytime heating and
local sea breeze variations will give way to afternoon convection
mainly across the northern half of Puerto Rico and over parts of the
U.S. Virgin Islands. Widespread rainfall is however not expected on
Friday at this time. Hot and humid conditions will also be likely
each day during the rest of the period and this may require possible
heat advisories for some of the coastal and urban areas.

&&

.LONG TERM...Saturday through Wednesday...
As Tropical Storm Philippe continues to move northward into the
western Atlantic, a southerly wind flow will continue across the
surface to lower levels, becoming more southeasterly Sunday onward.
Precipitable water values remain elevated over the weekend as
tropical moisture continues to trail across the region, which will
continue a wet pattern with passing showers across southern Puerto
Rico and then afternoon convection focusing on the interior to
northern sections of PR. Flooding threats remain possible during the
afternoons for areas that became saturated over the previous days.

By Sunday, a surface ridge begins to establish east-northeast of
the northern Lesser Antilles. This will drive drier air into the
area and begin a slight backing of the lower level winds Monday
throughout the week. This will significantly reduce rain activity
compared to what was experience the days prior. However each
afternoon, thunderstorms are likely to form across the interior to
northwestern section of Puerto Rico. Then on Tuesday, the
possible arrival of a band of moisture may enhance the day's
rainfall amounts, followed by drier air on Wednesday. During this
long term period, southerly to southeasterly surface winds will
cause hot afternoon conditions across the islands, especially
northern coastal sections of Puerto Rico. Expect heat indices to
reach above 107F in some areas each afternoon.

&&

.AVIATION...Tropical storm Philippe centered near 20.2N 65.4W at
04/09z movg NW around 10 kt. Rainbands from Phillipe will bring SCT-
NMRS SHRA/Isold-SCT TSRA ovr regional waters and en route btw Puerto
Rico and the U.S.Virgin Islands with FQT LTG NE of PR. Prevailing
VFR but with -RA/VCTS at TJSJ/TISX/TIST and VCSH at TJBQ/TJPS. TEMPO
MVFR Psbl IFR with SHRA/TSRA at TJSJ and USVI terminals til 04/13Z.
Mtn top obscr ovr E interior of PR due to low clouds and -RA. SCT-
BKN lyrs nr FL022...FL050. BKN-OVC btw FL080-FL100. SFC wnd fm WSW 5-
10 kts, incr to 10-12 kts aft 04/14z. Ocnl hir gusts btw 25-33 kts
psbl with SHRA/TSRA accompanying the rainbands and TSRA.

&&

.MARINE...Activity associated with tropical Storm Philippe is
producing strong thunderstorms across the local waters, mainly for
the eastern half of the region. Gusty winds, frequent lightning,
and strong downpours capable of reducing visibilities are all
possible within the vicinity of these storms. Strong winds between
20 and 25 knots are possible for the offshore Atlantic and
Caribbean waters, the eastern coastal waters, and the Anegada
passage. Due to these winds a small craft advisory is in effect
until tonight for these areas.

Medium period northerly swells will continue across the northern
waters today, bringing surf heights to around 5 feet. There is a
moderate risk of rip currents for most beaches except the southern
coastline of Puerto Rico which has a low risk.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
447 AM AST Thu Oct 5 2023

.SYNOPSIS...
Tropical Storm Philippe will continue its track northward, while
lifting a plume of moisture over the region. Mid to high level
cloudiness will persist with mostly light to moderate showers
expected to affect the coastal waters, and portions of the islands
the rest of the morning. Rivers and streams across the eastern
third of Puerto Rico remain at high high levels although slowly
descending. Soils are already saturated, and any additional rains
during the day may result in mudslides/landslides in areas of
steep terrain. Although a gradual improvement is expected the rest
of the week, unstable weather conditions will last at least
through Friday, as a weak tropical wave may bring additional
moisture. Due to the anticipated conditions,an elevated risk for
urban and small stream flooding as well as isolated flash flooding
may continue into Friday. Improving conditions still expected for
the weekend.

&&

.SHORT TERM...Today thru Saturday...
As Tropical Storm Philippe continues to move away from the region,
the wind shifted from the south, bringing plenty of moisture into
the territories. Early in the evening hours, numerous showers
developed along the Caribbean Sea, moving over southeastern Puerto
Rico, Vieques, Culebra and over the Virgin Islands. The heaviest
activity was observed from Guayama to Maunabo, where several rivers
reached reacted, but none went into flood stage. In the Virgin
Islands, the highest amounts were reported over St. Thomas, with
almost one inch collected. It was very gusty too, with wind gusts of
15 to 25 knots observed on the Mesonet. Later in the evening, the
showers became stratified and weaker.

The only zone were rain never stopped was in St. Thomas and St.
John. Thus, in the morning hours, plenty of clouds will prevail, but
showers will be limited. However, the huge moisture field trailing
after Philippe is still covering most of the eastern Caribbean.
Since Philippe is expected to continue to move north, the winds will
stay from the south, meaning that new areas of showers and
thunderstorms may develop over the Caribbean waters, once again
reaching portions of Puerto Rico and the Virgin Islands. In fact,
the high resolution models show these showers becoming widespread by
this afternoon again. Hence, the risk for flooding will be elevated
today. Since soils are saturated, mudslides are also anticipated.
Additionally, the winds are enhanced due to low level convergence,
so gusty winds may be experienced at times.

Not many changes are anticipated for Friday, as moisture from a
tropical wave will convergence into the area. Although the wave
doesn't look particularly strong, additional showers can be
anticipated in this period. Then, once the wave departs, the wet
spell will be over, but gradually. A drier air mass is expected to
follow just after the wave, bringing a little of Saharan dust too,
with hazy skies in the picture.

In term of temperatures...the cloud shield from Philippe should
bring some protection from the intense heating that has been
punishing the islands. However, once skies begin to clear out, 925
mb temperatures will climb back up well above normal, so excessive
heat indices will become the norm once again.

&&

.LONG TERM...Sunday through Thursday...
As TS Philippe continues to move farther northward into the west
central Atlantic, the southerly flow from previous days will become
more southeasterly by Sunday then easterly during the latter part
of the period. Overall moisture content is expected to gradually
erode across the region as a surface ridge forecast to reestablish
east- northeast of the region, resulting in a much drier airmass
across the area. Consequently as this drier air filters in,passing
morning showers and daytime convection should be less frequent
with more seasonal conditions expected compared to the previous
days under the effects of Philippe and the aforementioned tropical
wave. However afternoon shower and isolated thunderstorm development
will still be likely but mainly across parts of the interior and
northwestern section of Puerto Rico, with activity mainly downwind
and just offshore of the U.S. Virgin Islands. By Tuesday into early
Wednesday however model guidance continued to suggest the arrival
of a band of tropical moisture across the region which may slightly
increase the chance to nearly morning showers and some enhanced afternoon
convection over parts of the islands. Thereafter, drier air will filter
in once again with a return of more seasonal conditions. For the period
a warm to hot spell is expected mainly along the north coastal and
urban areas of Puerto Rico and particularly the island of St Croix.
Therefore heat indices may range between 102-108 degrees F or slightly
higher in some areas each afternoon.

&&

.AVIATION...
Light SHRA from distant TS Philippe will continue to impact the
USVI terminals and surrounding waters this morning. Then, after
16-18Z, additional SHRA will develop near TJPS, the Cordillera
Central and reaching TJSJ and TJBQ. Periods of low ceilings and
reduced VIS can be expected with this activity. Winds will remain
from the S at 5 to 10 kts at the surface, but with gusts around 15
kts. Winds will be around 16-19 kts at FL050.

&&

.MARINE...
Trailing outer rainbands from distant Philippe will continue to affect
the local waters and passages bringing periods of showers and isolated
thunderstorms mainly across the Atlantic and local waters between eastern
Puerto Rico and the Anegada passage today. Moderate to locally fresh
south to southwest winds and small northerly swell will produce hazardous
and choppy conditions the rest of today. Marine conditions will gradually
improve over the next few days and into the upcoming weekend. Please
refer to the latest Coastal waters forecast (CWFSJU) for additional
info and updates.

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
511 AM AST Fri Oct 6 2023

.SYNOPSIS...Showers and isolated thunderstorms will continue mainly
across the local passages and south and east of the islands this morning
due to lingering moisture being lifted up across the region, along
with that accompanying tropical wave now crossing the eastern Caribbean.
Abundant moisture and good daytime heating will lead to the development
of afternoon showers and thunderstorms in and around the islands. This
will increase the risk of urban and river flooding and mudslides. Drier
conditions are forecast for the upcoming weekend into early next week.
A Saharan air layer with a low to moderate concentration of saharan
dust will spread across the region during the next several days. Hot
and humid conditions expected today has lead to the issuance of heat
advisories and excessive heat warnings across portions of the islands.

&&

.SHORT TERM...Today through Sunday...
The most recent satellite imagery show some lingering moisture from
Tropical Storm Philippe just over the eastern tip of the Dominican
Republic, while additional cloudiness from a tropical wave reaches
the Virgin Islands. The local islands were in the middle of these
two areas of enhanced moisture, which resulted in tranquil
conditions earlier in the evening hours. However, still under the
indirect influence of Philippe, the winds remain from the south-
southeast, and that dragged late overnight showers across the
Caribbean waters, reaching St. Croix, St. Thomas, Vieques and
several municipalities along the southern coastline of Puerto Rico.

The tropical wave will continue to advance this morning into the
region, increasing the frequency of showers. However, the strongest
activity is expected again in the afternoon hours. The available
moisture will combine with local effects to result in widespread
showers across the area. So far, the greatest risk for flooding is
along the southern and eastern municipalities of Puerto Rico, and
also in the extreme northwest. Since soils are saturated and rivers
are running high, rapid rises in these streams and mudslides in
areas of steep terrain can be expected.

As the tropical wave departs later today or early tomorrow, high
pressure will dominate at all levels. A drier air mass will limit
columnar moisture only to the lowest levels of the atmosphere. The
aerosol models also show Saharan dust filtering in for the weekend,
so skies will turn hazy. A trade wind cap inversion will be present
at around 900 mb, limiting the vertical development of showers,
although with enough heating, isolated thunderstorms may still fire
up in the northwest each afternoon. Also, some lingering showers
will be moving over eastern Puerto Rico and across the U.S. Virgin
Islands. The Probability of Precipitation decreases further on
Sunday as the air mass becomes even drier, favoring fair weather.

In terms of temperatures, excessive heat indices will continue
today, surpassing the 108 degree mark in many urban and coastal
areas across the islands. Some places should see relief from the
heat when the rain from the wave arrives. For Saturday, a deep layer
of southerly winds, high pressure at all levels, and 925 mb
temperatures above the climatological values will translate in a
hot, hot day. On Sunday, surface high pressure over the central
Atlantic will finally allows for the trade wind to recover a more
easterly direction. This may bring some heat relief for some areas,
but the northern areas of Puerto Rico, Vieques, Culebra, and
possibly the Virgin Islands will still experience excessive heat
indices, mainly between the period of 10 AM to 5 PM AST.

&&

.LONG TERM...Monday through Friday...
A fairly light southeasterly wind flow will persist through at
least Tuesday, then become more easterly by Wednesday and through
the rest of the period, as a surface high pressure ridge is
forecast to build north of the region. This will result in a much
drier airmass for most of the period. The overall moisture content
is expected to steadily erode, as a mid to upper level ridge will
hold across the region. This will favor a much drier and more
seasonal conditions across the forecast area. Afternoon shower
and isolated thunderstorm development will still be likely each
day but mainly across parts of the interior, northwest and west
sections of Puerto Rico. Meanwhile over the U.s. Virgin islands,
shower activity should be mainly downwind and over the coastal
waters. By Tuesday into Wednesday however model guidance still
suggest a quick surge of moisture in the easterlies across the
region. This may slightly increase the chance for more early
morning showers followed by some enhanced afternoon convection
over parts of the islands. Thereafter, a drier air will again
filter in and return to more seasonal conditions with so far limited
rainfall accumulations expected. For the period a warm to hot spell
is expected mainly along the north coastal and urban areas of Puerto
Rico and The U.S. Virgin Islands, particularly the island of St Croix
with temperature to reach the low 90s each day.

&&

.AVIATION...
A weak tropical wave will increase SHRA and TSRA through the
period. Before 18Z, the USVI terminals should experience this
activity, spreading northward into the PR terminals at least into
22Z. Periods of reduced VIS and low ceilings are expected.
Mountain obscuration is also expected for the Cordillera Central
from 18-22Z. Winds are from the SSE at 10-14 kts, with stronger
gusts, especially along the thunderstorms.

.MARINE...
Trailing moisture being lifted across the region and accompanying
a tropical wave now crossing the eastern Caribbean today, will bring
periods of showers and isolated thunderstorms across the local waters
and passages. Seas will remain 5 feet or less, with winds from the
south to southeast between 10 to 15 knots.

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
444 AM AST Sat Oct 7 2023

.SYNOPSIS...

A drying trend is anticipated for the local islands. Saharan dust
will also filter in, causing hazy skies. Scorching hot
temperatures will prevail for the next several days. A long period
northeasterly swell will deteriorate marine conditions by the
middle of next week.

&&

.SHORT TERM...Tonight through Monday...

Drier air is moving into the U.S. Virgin Islands and Puerto Rico
from the southeast and should engulf most of the forecast area by
later today. Some moisture returns in the lower levels behind a weak
trough that is best seen at 700 mb over the Leeward Islands at the
moment. This trough is forecast to move into the U.S. Virgin Islands
this evening and beyond Puerto Rico by Sunday morning. This trough
appears to be a heat trough, as it has little moisture with it and
1000-850 mb thicknesses rise with its passage. At upper levels
heights are reaching near record highs with 1104 and 1254 dm at 250
and 200 mb respectively. This suggests that, high temperatures will
continue almost everywhere and, coupled with the southeast winds,
temperatures and heat indices will be punishing. It is likely that
San Juan will break its record high for the date of 92 degrees today
as the forecast calls for 94 degrees again. Temperatures are
expected to be in the warning/advisory categories during each
afternoon for Puerto Rico through Tuesday, with the highest
thickness values expected on Monday afternoon. The U.S. Virgin
Islands will, for the most part, be spared heat indices above 107
degrees, but will still exceed 90 degrees in many locations each
day. A few showers are still possible across the area where
streamers form, where winds converge in the northwest and over some
of the highest mountains and although conditions are still
relatively stable, some thunderstorms due to the strong heating are
also expected--mainly over the western portion of Puerto Rico and
the waters around the west side of the forecast area. Some rainfall
could still exceed one inch in very localized spots.

&&

.LONG TERM...Tuesday through Saturday...

High pressure at all levels will maintain fair conditions across the
northeastern Caribbean through the end of the week. During this
period, the surface high that will be centered just northeast of the
islands will drive the winds from the east-southeast at speed of 8
to 10 knots. The circulation of the high will also drag patches of
moisture from a low pressure system that it now over the central
Atlantic. Conditions aloft will not be supportive for strong
convection, but some showers may still be carried by the trade winds
over eastern Puerto Rico and the U.S. Virgin Islands early in the
day, while additional activity developing in the west each
afternoon. The risk for flooding will be limited for the afternoon
activity in the west, and it should be very localized. Additionally,
light amounts of Saharan dust will move on and off through the end
of the week.

The high pressure system will weaken by Friday and into the weekend
in response to a long wave trough over the United States and western
Atlantic ocean. This will cause the winds to die down in the
islands, with the GFS forecasting a low level steering flow of
around 4 knots on Friday, and 1 to 3 knots on Saturday and Sunday.
The global models are not showing any significant rain maker during
this period either, but since the winds will be that slow, any
showers that develop in the afternoon should last longer, increasing
the potential for some flooding...again, mainly for the interior and
western portions of Puerto Rico.

&&

.AVIATION...
Drier air will allow more heating drg the morning hours that will
bring some local sea breezes in SE flow at llvls and spawn strong
convection in the wrn portions of PR aft 07/16Z thru at least
07/21Z. Most SHRA/TSRA should dissipate ovr land by 07/22Z. Sfc
winds bcmg by 07/14Z SE 10-15 kts with lcl sea breeze influences. SE
flow to cont ovr USVI thru 08/08Z, but land breezes to redvlp ovr PR
by 08/02Z.

&&

.MARINE...

The most recent observations from Caricoos show seas 2 to 4 feet and
winds around 10 knots. These conditions will prevail for the next
several days. A long period northerly swell will arrive by the
middle of next week, deteriorating seas along the Atlantic waters
and local passages.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Sun Oct 8 2023


.SYNOPSIS...
Hot conditions are expected to prevail for the next several days.
It will be mostly dry too, with some haze due to Saharan dust.
Winds will become light by the middle of the workweek. A
northeasterly swell will deteriorate marine conditions by
midweek.

&&

.SHORT TERM...Today through Tuesday....

Drier air moved into Puerto Rico during the day on Saturday and was
still in place over most of Puerto Rico from San Juan west. A high
pressure centered just northeast of 20 north 60 west continues to
bring southeasterly flow over the area but is also bringing a band
of moisture out of the western tropical Atlantic and across the
Leeward Islands. Currently this moisture has reached the local
waters and islands east of Fajardo with precipitable water values
just under 1.6 inches. Only a few minor showers were seen in this
plume of moisture, however. Better moisture of up to 1.8 inches
remains upstream in this band and should move across the area on
Monday and Monday night. The atmosphere at mid levels over the
forecast area will be driest this morning. Some mild moisture
intrusion on Monday evening is expected followed by another 36-48
hours of mid level dryness. With 500 mb temperatures abnormally
warm, this will greatly limit the amount of rain or strong
convection that can form today through Tuesday. Some activity is
possible in northwest Puerto Rico and over the local mountains, but
amounts should remain below one inch. The GFS suggests that the
band of moisture will remain over the area through Tuesday. But more
importantly, temperatures will continue above normal. Overnight lows
have continued in the record range at San Juan, and southeast flow
is expected again today with only a brief intrusion of sea breezes
along the north coast that will lead to another day in the low to
mid 90s. This is typically the time of year when very warm
temperatures can occur, so there will be little chance of breaking
the record high maximum today as it has stood at 97 degrees since
1981. However, with warm ocean temperatures close to 86 degrees, dew
points will be quite high--up to 83 degrees in portions of the north
coastal plains--so heat indices during the period will be able to
reach or exceed 118 degrees and as high as 105 degrees in almost all
lower elevations. Therefore heat warnings and advisories will be in
effect from 10 AM to 5 PM AST.

&&

.LONG TERM...Wednesday through Sunday...

High pressure at all levels will be dominant feature across the
Caribbean on Wednesday and Thursday. The surface high will be
centered just north of the islands, maintaining winds from the east
at around 10 to 12 knots. A trade wind cap inversion at around 850
mb will maintain most of the moisture trapped to the lowest levels
as dry air should fill the column above these levels. Small
concentrations of Saharan dust will be present too, so skies will be
grayish. These atmospheric conditions favor fair weather, although a
shower or two may fire up in the afternoon across western Puerto
Rico due to strong diurnal heating.

By the end of the workweek and into the weekend, a deep-layer long
wave trough will weaken the pressure gradient, causing winds to die
down. The forecast low level steering flow will be below 5 knots at
times, and not much higher than 10 knots. The associated surface
trough or low pressure system will move west to east well north of
the local islands, but it will make the winds shift from the south.
Through this period, surface patches of moisture will converge near
the islands, and that could bring some passing showers at times.
However, the strongest activity should be the afternoon activity,
concentrating along the Cordillera Central, then drifting north.
During this period, if skies manage to remain free of clouds in the
morning and early afternoon hours, then temperatures will just not
cool down, and excessive heat indices, possibly exceeding 108F will
persist.


&&

.AVIATION...

Drier air will allow more heating drg the morning hours that will
bring some local sea breezes in ESE-SE flow at llvls. Aft 08/16Z
thru at least 08/21Z sct SHRA/isold -TSRA are psbl. If they form,
most SHRA/TSRA should dissipate ovr land by 08/22Z. Sfc winds bcmg
by 08/14Z ESE-SE 10-15 kts with lcl sea breeze influences. SE flow
to cont ovr USVI thru 09/08Z, but land breezes to redvlp ovr PR by
09/02Z.

&&

.MARINE...
Recent buoy observations show seas of 1 to 3 feet across the local
waters. Marine conditions will begin to deteriorate tomorrow as a
long period northeasterly swell arrives. These conditions will
spread into late in the workweek.

The risk of rip currents is low for today, but a high rip current
risk is expected Tuesday through Friday. Then, the risk of rip
currents could become low again by next weekend.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
535 AM AST Tue Oct 10 2023

.SYNOPSIS...
Issued at 453 AM AST Tue Oct 10 2023

Drier air is entering the forecast area and is now over the U.S.
Virgin Islands. It will continue westward over Puerto Rico and end
most shower activity by this evening. Moisture returns on
Thursday, and flow becomes more southeasterly again which will
prolong the heat well into next week. No major features are
noted, but the rip current risk will remain high through Thursday
from a northeasterly swell.


&&

.SHORT TERM...Today through Thursday...

Once again, it was another calm night with some passing showers
moving across eastern and southeastern Puerto Rico. Overnight
minimum temperatures along the PR and USVI coastal areas were in the
upper 70s to lower 80s, while in the mountains, they stayed in
the 70s. The wind flow across the local islands was mostly land
breezes. However, some southeasterly components were seen.

The latest guidance suggests the multi-level high pressure north of
the forecast area, is moving westwards. However, southeasterly
wind flow should prevail across Puerto Rico and the U.S. Virgin
Islands today as this high pressure continues to move away. With
the available moisture, local effects, and the southeasterly flow,
expect some afternoon convection and thunderstorm activity to
develop, particularly over the northwestern quadrant of Puerto
Rico. However, a patch of dry air will move across the U.S. Virgin
Islands today and Puerto Rico by early this evening cutting off
most of the shower activity. Moisture will begin to return late
Wednesday and into Thursday. That dry air will bring below-
normal climatological PW values, with the moisture content staying
below 850 mb on Wednesday. If any afternoon rainfall activity
develops on Wednesday, we should expect it along the interior and
western portions of Puerto Rico, as the prevailing wind flow is
from the east. Under this weather pattern, mainly isolated to
occasionally scattered showers are possible across the region. By
Thursday, the moisture returns around the 700 mb high north of
Puerto Rico. Most recent models show improved moisture extending
at least up to 500 mb. This will bring an increase in the
frequency of shower activity across the islands.

The daily maximum temperatures along the coastal areas today should
range in the 90s, while over the mountain they should stay in the
80s. Once again, expect another very warm day across the islands
as temperatures will continue above normal. Heat indices are
forecast to be above 112 degrees Fahrenheit along the low areas of
north-central, northwestern, and western Puerto Rico, including
Culebra. Therefore, an Excessive Heat Warning will be in effect
from 10 AM to 5 PM AST. Nonetheless, in the low/urban areas of the
southwestern, northeastern, eastern, and eastern interior PR and
Vieques, the heat indices are foreseen to be above 108 degrees.
Therefore, a Heat Advisory will also become effective beginning at
10 AM AST.

&&

.LONG TERM...Friday through Tuesday...

High pressure at upper levels will continue over and just north of the
Greater Antilles even as a TUTT develops in the western Tropical
Atlantic and drops south southwest through Sunday and then west
into the Caribbean Monday and Tuesday. High pressure at lower
levels is present over and just north of the area through Monday,
but redevelops northeast of the area on Tuesday. This will allow
some moisture to filter into the area from the east northeast, but
will also tend to block any strong features or the cooler air
mass to the north from reaching us. Flow will weaken somewhat and
turn more southeasterly Friday through Tuesday. This will allow
some showers and possibly a few thunderstorms to form in the
interior portions of Puerto Rico mainly due to converging winds
around the island.

With southeast flow returning Friday, heat indices and very warm
temperatures will continue over the area with the warmest
temperatures expected Friday and Tuesday.

&&

.AVIATION...
(06Z TAFS)
Issued at 453 AM AST Tue Oct 10 2023

VFR conditions across all terminals. Aft 10/18Z thru at least
10/23Z, afternoon convection will result in VCSH and psbl VCTS
and sct SHRA at TJBQ terminal. Sfc winds bcmg ESE-SE at 5-15 kts
with sea breeze influences by 10/14Z.

&&

.MARINE...
Issued at 453 AM AST Tue Oct 10 2023

Seas will remain 6 feet or less in the Atlantic waters, but a
long period swell of up to 5 feet from the northeast will produce
a high risk of rip currents along the northern coasts and the
eastern tip of Saint Croix. High surf is no longer expected.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
533 AM AST Thu Oct 12 2023

...New SYNOPSIS, AVIATION, MARINE...

.SYNOPSIS...
Issued at 513 AM AST Thu Oct 12 2023

High pressure dominates the weather picture through the next 7
days. Moderate easterly winds are expected today, but winds will
generally become gentle and southerly with sea breeze influences
for the weekend. Morning sun will bring very warm temperatures
that will increase through Monday. Some shower and thunderstorm
activity will occur--with thunderstorms mainly in the west. After
Monday a more typical trade wind pattern will develop. Showers
will increase in the west and interior and easterly winds will
increase.

&&

.SHORT TERM...Today through Saturday...

A mid-to upper-level high pressure will continue to hold over the
western Caribbean with a ridge extending over the local area. The
ridge is forecast to slowly weaken through the period. At lower
levels today, a weak trough will move over the region bringing
moisture content to seasonal levels, and an increase in shower
activity compared to previous is expected. For Friday, although
lesser than today, some additional moisture will reach the area but
winds will turn more from the southeast and become lighter through
the weekend. Locally induced afternoon showers are expected to
develop each afternoon over the interior and western PR, with a
slight chance of isolated thunderstorms. Similar conditions are
expected on Saturday, but afternoon showers should develop mainly
along the northern and northwestern sections of Puerto Rico. Across
the U.S. Virgin Islands, today seems to be the best day to observe a
few showers, but an overall fair weather pattern should prevail.

Maximum temperatures will stay in the upper 80s along the Cordillera
Central and in the low 90s across the coastal and urban areas of the
islands. Heat indices and very warm to hot temperatures will
continue over the area through the weekend. An Excessive Heat
Warning and a Heat Advisory are in effect today for most coastal and
urban areas of Puerto Rico and St. Croix. Please refer to the latest
Heat Product (NPWSJU) for detailed information.

.LONG TERM...Sunday through Thursday...

High pressure at upper levels just north of Belize will have a
ridge that extends past the Atlantic waters north of Puerto Rico
and the U.S. Virgin Islands. The high will continue over and just
north of the Greater Antilles even as a TUTT develops in the
western Tropical Atlantic just off the northern coast of South
America. It will then turn west to ride along the northern coast
of South America-- passing south of the forecast area on Wednesday
while weakening. At mid levels, 500 mb temperatures cool
gradually by 3 to 4 degrees Celsius from Sunday through Wednesday
and this will bring a more favorable environment for at least
isolated thunderstorms. High pressure at lower levels is present
over and just north of the area through Monday keeping winds light
and generally southerly. Strong low pressures in the central
Atlantic will retreat and allow high pressure to ridge into the
central Atlantic which will bring back a typical tradewind pattern
with better moisture and showers Tuesday through Thursday.

With southeast flow returning Friday, heat indices and very warm
temperatures will continue over the area with the warmest
temperatures still expected on Monday and Tuesday, when records
may again be set in San Juan.

&&

.AVIATION...
(12Z TAFS)
Issued at 513 AM AST Thu Oct 12 2023

Mainly VFR conditions are expected to prevail across all
terminals through the forecast period. However, SHRA and -TSRA are
expected to develop in and around TJBQ btw 18z-22z, which may cause
tempo MVFR conds. Surface winds from the east at 10-15 kt with sea
breeze variations and higher gusts aft 12/14z.

&&

.MARINE...
Issued at 513 AM AST Thu Oct 12 2023

NOrtheast swell with periods of up to 15 seconds will slowly
subside across the Atlantic waters and passages through Friday.
This will reduce the rip current risk to moderate for the north
and north western coasts by tonight. Seas will continue to
diminish through Saturday. On Saturday night a northerly swell of
up to 2 feet will enter the area. Small craft advisories are not
expected during the next 10 days.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
501 AM AST Fri Oct 13 2023

.SYNOPSIS...A deep-layer high-pressure system will maintain
hostile atmospheric conditions for deep convective development,
maintaining generally fair weather conditions. However, intense
diurnal heating with near-normal moisture levels could trigger
showers with possible isolated thunderstorms each day, mainly from
afternoon convective development. Warm-to-hot conditions will
prevail, with some areas experiencing heat index values of 108
degrees or higher. Although life-threatening rip current
conditions are possible across most north- and east-facing
beaches, marine conditions should remain favorable for small
craft. As of 2 AM AST on October 13th, there is no tropical
cyclone threat to Puerto Rico and the U.S. Virgin Islands.


&&

.SHORT TERM...Today through Sunday...

A mid-to upper-level high pressure will continue to hold over the
western Caribbean with a ridge extending over the local area. The
ridge is forecast to slowly weaken through the period. At lower
levels, a weak high pressure just north of the area and a frontal
system moving across the western Atlantic will cause a col to
develop over the northeastern Caribbean. This will promote calm to
light southeasterly winds during the next few days. Therefore, warm
to hot temperatures will continue across the islands each day and an
Excessive Heat Warning and a Heat Advisory are in effect once again
for all the islands. Please refer to the latest Heat Product (NPWSJU)
for detailed information.

The precipitable water (PWAT) content is forecast to remain at near
normal levels through the weekend. Latest guidance suggest PWAT
ranging between 1.75-2.00 inches. This available moisture in
combination with daytime heating and a weak sea breeze convergence
should promote mainly shower and thunderstorm development over
portions of the Cordillera. Due to the ill define wind flow, these
showers could slowly drift over coastal areas of northern, southern
and western PR during the late afternoon/early evening hours. Across
the U.S. Virgin Islands, fair weather conditions should prevail
through the period.

.LONG TERM...Monday through Friday...

Based on the most recent model guidance, weather conditions should
remain favorable for outdoor workday activities. Generally, there
will be a predominance of drier air, except for the occasional
patch of shallow moisture carried by the trade winds and the
possibility of remnants from Hurricane Teddy impacting the area by
Thursday. Overall, moisture levels should remain below the typical
climatological thresholds, below 1.7 inches. The most significant
shift towards a brief period of wetter weather conditions,
transitioning from 1.3-1.4 inches to 2.0-2.2 inches, is expected
to occur between Wednesday evening and Thursday. Initially, the
winds are forecasted to be south-southeasterly at the start of the
workweek, primarily due to the influence of a surface high
pressure system positioned well to the east-northeast of the
local islands. However, as the week progresses, the winds should
shift to the east as the high-pressure system moves further into
the North Atlantic and away from the Caribbean region. This deep-
layer high-pressure system should maintain unfavorable conditions
for significant deep convective development in the area,
effectively sustaining a strong trade wind cap inversion, at
least through the initial portion of the week. Despite these
hostile conditions, there is still the possibility of convective
development, which can be initiated by intense daytime heating and
sea breeze convergence, ultimately breaking through the inversion
layer.

In summary, variable weather conditions will prevail, with passing
showers affecting southern and eastern sections of Puerto Rico and
the U.S. Virgin Islands during nighttime, followed by afternoon
showers with possible isolated thunderstorm development clustering
across central Puerto Rico. As winds gradually veer, this activity
should spread north-northwestern early in the week, ultimately
spreading towards more western sections later in the week. While
the risk of flooding or lightning will likely remain limited,
there may be an elevated risk on Thursday. Additionally, there
will be ongoing concerns about excessive heat hazards,
particularly with south-southeasterly winds in the early part of
the workweek, and this risk is likely to persist throughout the
week despite variations in wind direction.


&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals through the forecast period. However, SHRA and -TSRA are
expected to develop over central PR btw 18z-22z, which may cause BKN
cigs btw FL030-FL050 at TJPS and TJBQ. Surface winds from the east
at 6-12 kt with sea breeze variations aft 13/14z.


&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated steady seas between 2
and 4 feet, with the highest wave heights observed in bouys with
Atlantic waters exposure. Marine conditions should remain
favorable for small craft, with seas within the 2-4 feet range
during the next few days. For beachgoers, life-threatening rip
currents are possible across beaches with northern and eastern
exposure across Puerto Rico, Vieques, Culebra, and Saint Croix.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
444 AM AST Sun Oct 15 2023

.SYNOPSIS...A weak surface ridge east of the region and a couple
of frontal system moving from the western Atlantic into the
central Atlantic will promote light southerly winds through early
in the week. Therefore, warmer than normal temperatures will
persist for the next few days. Overall fair weather conditions
should prevail across the islands through at least Tuesday, but
diurnally induced afternoon convection is expected to develop over
central and northern PR each day. An upper level low is forecast
to move over the eastern Caribbean Sea by midweek increasing
instability and favorable conditions for thunderstorm development.


&&

.SHORT TERM...Today through Monday...

Mainly fair weather conditions prevailed during the overnight hours
under clear to partly cloudy skies. Since midnight, Doppler Radar
estimated only minimal accumulations over sectors of eastern to
southeastern to south-central Puerto Rico, as passing showers
affected those areas. Minimum temperatures ranged in the upper 70s
to low 80s across lower elevations of the islands, and in the mid to
upper 60s across higher elevations of Puerto Rico.

A mid-to upper-level ridge will continue to affect the island
through most of the period. A southerly wind component will
continue with surface wind flow being southeast to south, mainly
due to a frontal system moving across the western Atlantic and a
weak surface high over the western and central Atlantic. More
easterly winds are forecast by Tuesday due to a building surface
high over the central Atlantic. Current satellite derived
precipitable water (PWAT) values show most of the region with
between 1.7 to 2.10 inches, within normal values for this time of
the year. Current model guidances suggest normal PWAT values to
continue before drier air filters in early tomorrow, patches of
moisture will still reach the area from time to time, ahead of
moisture from the current T.C. Sean which should reach the area
during the long term period.

Warm to hot temperatures are expected each day with 925mb
temperatures being forecast to be more than 2 standard deviations
above normal. Highs will range from the upper 80s to around the
low 90s across lower elevations of the islands.Excessive Heat
Risk will continue as several urban and low elevation areas will
reach heat indices above 108 degrees; particularly each late
morning to each late afternoon. For today's heat related warnings
and advisories please refer to the latest NPWSJU/NPWSPN. Sea
breeze convergence, diurnal heating, available moisture and local
effects, will promote afternoon shower and thunderstorm activity,
particularly over interior to western and northern PR, although
under light winds, activity can drift to neighboring areas.
Afternoon activity will be concentrate more over western/nw PR on
Tuesday due to more easterly winds. Evening to early morning
passing shower activity can affect windward areas of the islands
throughout the period.


.LONG TERM...Tuesday through Sunday...

A building surface high pressure over the central Atlantic will
increase trade winds from Tuesday onwards across the northeastern
Caribbean. Embedded in this flow, moisture associated to the
remnants of TC Sean will reach the area by midweek. Also, an upper
level low is forecast to enter the southeastern Caribbean on
Wednesday and the 500 mb temperatures are expected to drop to
minus 8 degrees Celsius by Thursday. This weather pattern will be
favorable for shower and thunderstorm development across the
islands and surrounding waters. Thereafter, an upper level ridge
is expected to build from the north which will slowly warm the 500
mb temperatures. However, the proximity of the upper level low and
near normal precipitable water content(1.75-2.00 inches) are
expected to aid in the development of afternoon convection each
day, mainly across western PR. Heat advisories may be required
each day for portions of north central Puerto Rico, Vieques and
Culebra as heat indices may reach 108 degrees Fahrenheit or
higher.


&&

.AVIATION...Mainly VFR conditions across all terminals. Afternoon
SHRA/TSRA development over interior to W/N PR could result in brief
MVFR conditions at TJBQ between 15/17-22Z. After 15/13Z, generally
SE winds up to 10 kts with locally higher seabreeze variations and
gusts before decreasing after 15/22Z. Higher gusts possible near
TSRA/SHRA.


&&

.MARINE...Coastal buoys indicated seas at less than 2 feet and
winds at less than 8 knots. Tranquil seas and light winds from
the south-southeast are expected to continue into Monday, with
locally higher sea breeze variations across the southwestern and
northeastern coast of Puerto Rico. There is a low risk of rip
currents across all the beaches of PR and the USVI. However,
life-threatening rip currents often occur in the vicinity of
groins, jetties, reefs, and piers.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Mon Oct 23 2023

.SYNOPSIS...Despite Tammy's continued movement away from the local
islands, Tammy will maintain an inflow of tropical moisture under
west-southwesterly winds, favoring afternoon convective
development towards northeastern sections. Hazardous seas for
small craft will continue across the Atlantic Waters and the
Anegada Passage until this evening. As we approach the latter part
of the workweek and head into the weekend, expect deteriorating
marine and surf zone conditions due to northerly swells generated
by Tammy. Simultaneously, a frontal boundary, expected to approach
the area, may bring cooler temperatures, which, combined with a
set of surface and upper-level troughs, will likely increase the
likelihood of showers and thunderstorms through the upcoming
weekend.


&&

.SHORT TERM...Today through Wednesday...

Mainly fair weather prevailed overnight with the movement of some
light showers across northwestern Puerto Rico. Winds were light and
variable with a bit of westerly compenent in them. Temperatures were
in the low 80s to high 60s across coastal regions and the mountains,
respectively.

Hurricane Tammy is roughly 300 miles northeast of our islands now as
it moves further north into the western Atlantic. A moist airmass
asscoiated with this storm will remain over the region through
tomorrow until drier air starts to move in from the north as a
frontal boundary pushes into the western Atlantic. For today,
westerly wind will prevail, which will bring passing showers for
multiple coastal sections of Puerto Rico. Following afternoon
convection is expected across the interior to eastern sections of
Puerto Rico, with the greatest concentration of thunderstorms over
the eastern interior. There will be a risk of isolated flash and
urban flooding, rapid river rises, and isolated mudslides in areas
of steep terrain. Conditions should improve into the evening hours
as convective activity subsides.

The advection of drier, cooler air on Wednesday from a frontal
boundary passing into the area will bring northerly winds and a
reduction in rainfall. Cooler temperatures are also forecast during
this time. Afternoon convection is still possible especially across
southwestern Puerto Rico. By the end of Wednesday, Tammy will no
longer have an influence over the local weather conditions due to
it's distance.


.LONG TERM...Thursday through Monday...

The current forecast follows a consensus between primary global
models, and even though this scenario has persisted in recent
model runs, there are still high uncertainties regarding the
timing and influence of each key feature.

Several distinct atmospheric features should contribute to the
persistence of wet and unstable weather conditions likely through
the latter part of the workweek into the upcoming weekend. First,
a frontal boundary that should have reached the local islands by
Tuesday-Wednesday will linger over the region. Simultaneously, an
elongated surface trough, which model guidance suggests will
remain stationary well to the east of the Lesser Antilles by
midweek, will slowly migrate westward by Thursday as the same
frontal boundary that held it anchored weakens. Moisture from both
features will likely merge over the northeastern Caribbean,
trapped between a surface high pressure over the Florida-Bahamas
region and persistent easterly winds generated by the North
Atlantic high. As this abundant moisture gradually builds up, a
mid-to-upper-level cut- off trough will sink southward, with a
positively tilted axis extending over Hispaniola and the
associated divergence side expanding over the local islands from
Friday onward.

If this scenario materializes, with each atmospheric component
exerting equal influence, expect a persistent pattern of showers
coupled with thunderstorms. This heightened activity could amplify
the risk of flooding and lightning-related hazards, such as flash
floods and mudslides. The most intense weather activity is
currently anticipated to affect eastern Puerto Rico and the U.S.
Virgin Islands. However, any departure from the outlined scenario
may alter the expected activity's focus, intensity, and
frequency.


&&

.AVIATION...SHRA/TSRA, mainly from afternoon convection, could
result in brief MVFR conditions across TJSJ, TJPS, and USVI
terminals throughout the period. Impacts are most likely for TJSJ
and USVI terminals. Higher gusts are likely near the SHRA/TSRA. Calm
westerly to northwesterly winds are expected with seabreeze
variations. Weather conditons should improve after 23/22Z.


&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated steady seas between 2
and 5 feet at 7-10 second periods, with the highest wave heights
observed in bouys with Atlantic waters exposure. Marine conditions
should remain favorable for small craft, except for the offshore
Atlantic waters, where a Small Craft Advisory remains in effect
for seas up to 8 feet, and coastal waters of northern Puerto Rico,
where small craft should exercise caution.

For beachgoers, life-threatening rip currents are likely across
beaches of north-central Puerto Rico, where a high risk is in
place for today. Life-threatening rip currents are possible across
the remaining north- and east-facing beaches.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Tue Oct 24 2023

.SYNOPSIS...Despite Tammy's distance from the local islands,
residual moisture will favor convective development, favoring
eastern sections and the local islands, driven by westerly winds.
A southward-propagating front, may bring a relief to the
persistent warm-to-hot conditions by the end of the workweek. The
assocaited pre-frontral trough and residual moisture, combined
with a set of surface and upper-level troughs, will likely
increase the likelihood of showers and thunderstorms, and thus, an
increased risk of flooding, by the end of the workweek into the
weekend. By Wednesday and continuing into the weekend, expect
deteriorating marine and surf zone conditions as northerly swells
generated by Tammy spread across the local Atlantic waters and
Caribbean passages.


&&

.SHORT TERM...Today through Thursday...

Northerly winds across the local waters brought light passing
showers across northern Puerto Rico and the USVI. St. Thomas
recieved the best rainfall with over a quarter of an inch in some
spots according to radar estimates. A land breeze set up across the
island of Puerto Rico with calm speeds. Temperatures were in the low
80s to high 60s across coastal regions and the mountains,
respectively.

The interaction of drier, cooler airmass from a frontal boundary and
the moist air from Hurrcane Tammy, that is about 400 miles northeast
of the islands, will result in a regime of passing showers across
northern areas of PR and the USVI. Showers should be light yet
consistent at times. This norhterly wind flow throughout the day
should bring slighly cooler temperatures and a better chance of
afternoon convection across southern Puerto Rico, where
thunderstorms are possible. Conditions should calm by the evening
hours back to light passing showers across northern exposed sections.

Wind speeds are expected to increase on Wednesday as the drier air
from the frontal boundary moves closer to the islands. Precipitable
water values will also drop to levels below average, which will
reduce the amount of passing showers and afternoon convection. Might
be a slightly warmer afternoon due to more diurnal heating as
clearer skies will prevail. Similar conditions will prevail for
Thursday morning until later in the afternoon when a tropical wave
begins to enter the eastern Caribbean and a Tropical Upper
Tropospheric Trough deepens across the northern Caribbean. An
increase of shower and thunderstorm activity is forecast for
Thursday afternoon onward into the weekend due to these features
with a concentration of convection across western PR for Thursday
afternoon due to northeasterly winds. During the evening hours
eastern PR and the USVI will experience the most rainfall.

.LONG TERM...Friday through Tuesday...

Model guidance still suggests a wet and unstable weather pattern
by the end of the week and early next week; the latest forecast
follows this direction. Even though this scenario has persisted in
recent model runs, there are still high uncertainties regarding
the timing and influence of each key feature.

Several distinct atmospheric features should contribute to this
persistent wet and unstable scenario. To begin with, pre-frontal
trough and residual mouisture are expected to linger over the area
on Friday. Simultaneosly, an elongated surface trough will
gradually move westward. Moisture from both of these systems will
converge over the northeastern Caribbean, trapped between a
surface high-pressure system in the Florida-Bahamas region and the
consistent easterly winds generated by the North Atlantic high-
pressure system. As large amounts of moisture build up over the
region, a deep upper-level trough, with a positively tilted axis
extending over Hispaniola and the associated divergence side over
the local islands, will yield favorable conditions for deep
convective development. Even as this trough gradually moves away
from Sunday onwards, driven by a mid-to-upper level ridge,
conditions are expected to remain marginal for the development
thunderstorm development, considering steady above-normal
precipitable water across the region.

If this scenario unfolds, with all atmospheric components
aligning as expected, anticipate an persistent pattern of showers
and thunderstorms. These heightened conditions may increase the
risk of flooding and lightning-related hazards, including the
potential of flash floods and mudslides in areas of steep terrain.
While earlier guidance focused on the eastern sectons of Puerto
Rico and the U.S. Virgin Islands for the most frequent activity,
the latest model guidance suggests that heavy rainfall is equally
possible across all land areas, including the U.S. Virgin Islands.
However, it is importante to state that any deviation from this
outlined scenario has the potential to alter the expected rainfall
patterns.



&&

.AVIATION...SCT SHRA over regional waters and across all terminals
throughout the day besides TJPS. However, VCTS possible at TJPS
after 17z. Variable land breeze during the morning hours followed by
calm to moderate W to N winds across all terminals with increasing
sea breeze variations aft 24/13z.


&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated steady seas between 2
and 5 feet, with the highest wave heights observed in bouys with
Atlantic waters exposure. Marine conditions should remain
favorable for small craft, except for the offshore Atlantic
waters, where a small craft should exercise cautions. For
beachgoers, life-threatening rip currents are possible across
beaches with Altantic exposure of Puerto Rico, Culebra, and the
northern U.S. Virgin Islands.

Northerly swells generated by Hurricane Tammy are anticipated to
reach and spread across the local Atlantic waters and Caribbean
passages by Wednesday into Thursday. This is likely to result in
dangerous marine conditions for small craft and life-threatening
rip currents for beachgoers throughout the upcoming weekend.
Currently, Small Craft Advisories have been issued for the
offshore Atlantic waters, starting from Wednesday morning.

[cycloneye]

[Div][Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Wed Oct 25 2023

.SYNOPSIS...Northerly swells generated by Tammy, located well to
the north of the area, will spread across the local Atlantic
waters and Caribbean passages today into the weekend, resulting in
hazardous marine and life-threatening surf zone conditions. In
the meantime, expect variable weather conditions, influenced by an
approaching frontal boundary and associated pre- frontal trough.
This feature will likely bring pleasant temperatures during the
next few days, primarily due to the influence of the resulting
northerly winds. A set of surface- induced and mid-to-upper level
troughs will likely increase the likelihood of showers and
thunderstorms and, thus, an increased risk of flooding by the end
of the workweek into the weekend.


&&

.SHORT TERM...Today through Friday...

Light passing showers continued through the night across northern
Puerto Rico and the USVI, however rainfall accumulations were very
minimal. North wind between 5 and 10 miles per hour prevail across
the region. Temperatures were in the low 80s to high 60s across
coastal regions and the mountains, respectively.

The interaction of a frontal boundary northwest of the island and
Hurricane Tammy to the northeast will cause northerly flow to
continue across the lower-levels. A vertically shallow moisture
column with the prevailing N wind flow will allow light passing
showers to frequently pass across northern Puerto Rico and the USVI
throughout the day, then during the afternoon hours diurnal heating
and local effects will allow convection to form across southern
Puerto Rico. Thunderstorms are possible during this time and rain
may be heavy across isolated spots causing ponding of water across
roads and poorly drained areas.

A similar pattern of passing showers is expected overnight and
Thursday morning until late Thursday when conditions start to
deteriorate due to a tropical wave moving into the eastern
Caribbean and a Tropical Upper Tropospheric Trough (TUTT)
positioning over the region. By this time, the surface to lower-
level wind flow will have veered to a northeasterly direction,
which would concentrate Thursday's afternoon convection across the
interior to southwestern sections of Puerto Rico. Thursday night
onward numerous passing showers are expected across eastern Puerto
Rico and the USVI. Conditions worsen into Friday as the axis of
the tropical wave passes through the islands and the TUTT
positions right in a sweet spot that would increase lower-level
vertical motion.

This is the beginning of a wet pattern that will continue throughout
the weekend, possible into next week. During this time flooding and
thunderstorms remain the greatest threat over land with the chance
of isolated flash and urban flooding, rapid river rises, and
isolated mudslides in areas of steep terrain. Overall temperature
should be slightly cooler over the next few days due to northerly
wind flow and abundant cloud coverage from all of this weather.

.LONG TERM...Saturday through Wednesday...

Model guidance suggests a continuous and unstable weather pattern
throughout the weekend, and the most recent forecast aligns with
these projections. Despite the model consensus of this scenario,
there remains significant uncertainty, primarily due to
discrepancies regarding the duration of this weather pattern.
While the ECMWF (European model) predicts improved weather
conditions beginning Monday, the GFS (American model) anticipates
a prolonged wet pattern.

This scenario will result from a surface trough induced by
distant Tammy, extending over the northeastern Caribbean, enhanced
by a deepening mid-to-upper level trough, with a positively
tilted axis extending over Hispaniola and the associated
divergence side over the local islands. Trapped between a surface
high-pressure system over the Florida-Bahamas region and the
consistent easterly winds generated by the North Atlantic high-
pressure system, expect the surface- induced through to linger
over the area while advecting large amounts of tropical moisture
(precipitable water values around 2.2-2.6 inches) through the
weekend and possibly early next week. Even though the upper-level
trough will likely begin to move westward and away from the
northeastern Caribbean, steered by a weak upper-level ridge,
conditions should remain marginal (500 mb temperatures around -5
and -3 degrees Celsius) for thunderstorm development, mainly
driven by steady, low-level moisture convergence.

If this scenario unfolds, with all atmospheric components aligning
as expected, anticipate a persistent pattern of showers and
thunderstorms on Saturday and Sunday, as suggested by the Galvez-
Davison Index. These heightened conditions may increase the risk
of flooding and lightning-related hazards across all local
islands, including the potential of flash floods and mudslides in
areas of steep terrain. However, it is essential to state that any
deviation from this outlined scenario has the potential to alter
the expected rainfall patterns and potential risks, particularly
early next week.


&&

.AVIATION...SCT SHRA over regional waters and across N exposed
terminals throughout the day. VCTS possible at TJPS and along the
Cordillera Central after 25/16z. Light to moderate N to NE winds
across all terminals with sea breeze variations.


&&

.MARINE...Recent observations from the CariCOOS buoy network in
the vicinity of Puerto Rico and the U.S. Virgin Islands have
shown consistent marine conditions with wave heights ranging from
2 to 5 feet and dominant periods of 8-11 seconds.

Marine conditions will deteriorate as swells generated by the
distant Hurricane Tammy propagate through the local Atlantic
waters and Caribbean passages from today through the weekend. As a
result, Small Craft Advisories are currently in place through
Sunday morning due to the anticipated increase in wave heights,
which may reach up to 10 feet. The initial advisory comes into
effect this morning for offshore Atlantic waters, with subsequent
advisories for the Mona Passage and the coastal waters of
northern and northwestern Puerto Rico, Culebra, and the northern
U.S. Virgin Islands this evening.

These swells are likely to cause life-threatening rip current
conditions. Additionally, these swells have the potential to
generate high surf conditions over the weekend, leading to
localized coastal flooding and beach erosion. Consequently, a Rip
Current Statement is in effect, starting with the beaches of the
north-central and northwestern shores of Puerto Rico this morning.
This statement will subsequently encompass all north-facing
beaches in Puerto Rico, Culebra, and the northern U.S. Virgin
Islands this evening, extending to the shores of Saint Croix on
Friday.
/Div]

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
535 AM AST Thu Oct 26 2023

.SYNOPSIS...Moisture from a frontal shear line, the proximity of
a mid- to upper- level trough (TUTT), and a surface trough, will
maintain a very moist and unstable weather pattern across the
islands and coastal waters through at least the upcoming weekend.
Northerly swells from the distant Hurricane Tammy, and from the
frontal boundary, will continue to promote hazardous marine and
coastal conditions for Atlantic waters and passages, as well as
hazardous coastal conditions for north oriented beaches, at least
until Sunday.

&&

.SHORT TERM...Today through Saturday...

The combination of moisture from a frontal shear line along with
the proximity of a mid to upper level trough (TUTT) and a broad
surface trough forecast to shift westward across the region today
through the upcoming weekend, will maintain a very moist and
unstable weather pattern across the islands and coastal waters.

Light passing showers steered by the north northeast low level winds
will bring brief periods of light to moderate showers to the north
and east coastal areas during the rest early morning hours. Isolated
thunderstorms will be also possible but mainly over the offshore
coastal waters of the Caribbean during the rest of the morning.
Thereafter, afternoon showers and thunderstorm development will
again be likely over the central interior, southern slopes and east
sections of Puerto Rico, as well as around the USVI. Overall light
northerly winds will prevail between 8 to 12 mph during the day with
sea breeze variations. Near normal high temperatures can be expected
today, in the mid to upper 80s along the coastal areas and mid 70 to
low 80s in higher elevation.

By Friday and through Saturday tropical moisture is still forecast
to increase with the approach of a tropical wave and the presence of
both the surface trough and upper trough which will remain in place
across the region through the period. As a result this wet weather
pattern is expected especially late Friday into Saturday as the axis
of the aforementioned tropical wave is expected to cross the eastern
Caribbean and local islands. Enhanced early morning and afternoon
convection across the islands will lead to urban and small stream
flooding as well as flooding in some areas across the southwest,
central and east sections of Puerto Rico and possibly in isolated
spots ovr the USVI on these days.

Although there is much disagreement and uncertainty in the model
guidance in both the short and long term, the present weather
pattern and overall synoptic flow all suggest the continued wet
pattern will remain in place through the period. During this time
flooding and enhanced afternoon convection with strong thunderstorms
will remain the greatest threat, with isolated flash and urban
flooding, rapid river rises, and mudslides in areas of steep terrain
likely due to loose and unstable soil.


.LONG TERM...Sunday through Thursday...

Model guidance continues to suggest a wet and unstable weather
pattern to start the long term period with precipitable water (PWAT)
values persisting at around and above 2.5 inches across the region.
The GFS model continues to suggest that this weather pattern will
persist through the long term period while the ECMWF model once
again suggest improved weather conditions by Tuesday. Because of
this, significant uncertainty remains in the forecast. Several
weather features will be in play as we enter the long term forecast
period. A surface trough will persist over the area and additional
tropical waves arriving from the east. Southerly flow will be
maintained during most of the period helping to lift tropical
moisture into the area from the ITCZ. A mid to upper level ridge
also builds overhead by Sunday while upper level trough lifts
northward and away from the region. Although the environment will
remain moist, the driving force for the afternoon convection will
be diurnally induced as conditions become more stable aloft with
additional instability from the lingering surface trough. Model
guidance suggest another upper trough approaching the area by the
end of the period, bringing unstable conditions aloft once again.
Overall, a wet and unstable pattern is forecast with urban and
small stream flooding likely and, with saturated terrain, the
potential for flash flooding and mudslides in areas of steep
terrain, uncertainty in the forecast increases by Tuesday onwards,
please continue to monitor future updates.

&&

.AVIATION...Prevailing VFR conds at all terminals durg prd. SCT-
bkn lyrs nr FL025...FL040...FL090. Wdly SCT SHRA/ psbl Isold TSRA
ovr regional waters and en route btw islands. Low level northerly
winds BLO FL180 will bring prds of SHRA/-SHRA vcty TJSJ/TIST/TISX
til 26/14Z. SFC wnd...calm to lgt/vrb bcmg fm N-NE btw 5-12kts
with sea breeze variations aft 26/14Z. Proximity of upper trof and
the presence of a surface trough will maintain unsettled weather
conds durg prd especially btw 26/16Z-23Z with SHRA/Isold TSRA
dvlpmnt ovr ctrl and E interior of PR.VCTS psbl at TJSJ/TJPS/TJMZ
and VCSH at all other terminals til 26/23Z.

&&

.MARINE...CARICOOS buoys detect wave heights 7-8 feet with
periods of 10.5-11s across the San Juan, Arecibo, and Fajardo
buoys. Northerly swells generated by the combination of Hurricane
Tammy and a frontal boundary moving south into the area will
continue to spread across the local Atlantic waters and Caribbean
passages. This will promote dangerous marine conditions for small
craft and life- threatening rip currents throughout the upcoming
weekend. Small Craft Advisories are in effect for the offshore and
nearshore Atlantic waters and the Mona Passage. A Rip Current
Statement is in effect into the upcoming weekend. High surf
conditions, generating localized coastal flooding and beach
erosion, are possible by late Friday and into the weekend.