Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
334 AM AST Wed Jun 28 2023


.SYNOPSIS...
An approaching tropical wave and a weak upper level trough will
increase instability across the islands, increasing the risk for
flooding and mudslides throughout the end of the week. Once the wave
departs late Friday and Saturday, skies will become hazy as Saharan
dust filters in. Hot summer temperatures will return on Friday and
will continue through the next workweek.

&&

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

Showers with isolated to scattered thunderstorm development will
lead to lightning and excessive rain hazard risk, with an increased
risk today and Thursday. Excessive heat hazard risks are likely
today and Friday.

The interaction between the leading edge of a robust tropical wave,
with its axis now located around 65W, and a weakening upper-level
trough induced showers with isolated thunderstorms over the local
waters. Some moved over eastern Puerto Rico and the U.S. Virgin
Islands, producing rainfall totals of up to a quarter of an inch.
Overnight low temperatures ranged from the upper 60s across higher
elevations to around 80 degrees across coastal areas of eastern
Puerto Rico and the US Virgin Islands. Winds were generally light
and variable.

The weak upper-level trough will continue to weaken to our
northeast. Yet, another weak upper-level trough will develop today
and settle west of the local islands until dissipating on Friday.
The field moisture from a vigorous tropical wave will continue to
spread across the local area today, maintaining above-normal
precipitable water values between one and two standard deviations
around 2.0-2.3 inches through most of the period. As a result,
abundant tropical moisture and sufficient dynamical forcing from the
wave's and trough's interaction will promote unsettled weather
conditions through at least late Thursday night. After that, drier
air and another pulse of Saharan Dust particulate will gradually
move over the area, promoting fair and hazy weather conditions with
limited shower activity from Friday onwards.

As the tropical wave propagates eastward, east-southeasterly winds
at 5-15 mph will gradually veer from the southeast and increase to
10-20 mph through the cycle, with breezy conditions likely over
southwestern Puerto Rico and the local islands. For today, and
following the steering flow, the showers with isolated to scattered
thunderstorm activity will distribute following the seasonal
pattern. That is, favoring eastern Puerto Rico and the U.S. Virgin
Islands through the rest of the morning hours and clustering along
the interior to northwestern Puerto Rico in the afternoon, where
there is a threat of lightning and excessive rainfall. The afternoon
activity could affect other areas, particularly portions of the San
Juan metropolitan area, eastern Puerto Rico, and the local islands,
but with lower lightning and excessive rainfall hazard risks. From
tonight and continuing through Friday morning, the focus of the
showers and thunderstorms will shift to eastern and southern Puerto
Rico and the local islands, in this case, moving inland from the
local waters with limited afternoon convective development over land
areas. Daily rainfall totals of 1-2 inches with locally higher
amounts, mainly over northwestern Puerto Rico today and eastern
Puerto Rico tonight into Friday morning, could result in flooding of
urban areas, roads, and small streams, with isolated flash floods
possible.

Increased cloud cover and rains should result in lower temperatures
today and Thursday, ranging from the upper 80s across lower
elevations in the daytime to the lower 70s across higher elevations
at nighttime. However, limited excessive heat hazard risks are
expected today across lower elevations and other urban areas of
western, northern, and eastern Puerto Rico and Culebra, where heat
indices of 102-107 degrees are likely. Once weather conditions
improve and become more seasonal on Friday, expect higher (lower)
maximum (minimum) temperatures with excessive heat hazard risks.

&&

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

Moisture from a departing tropical wave will continue to decrease on
Saturday. At the same time, Saharan dust will continue to filter in,
resulting in hazy skies. Additionally, the trade winds will be
enhanced due to a low-to-mid level high pressure system migrating
closer to the region. The steering flow will be from the southeast
at 14-18 kts. The high will also create a trade wind cap inversion,
so shower activity will be limited. On Monday, a weak tropical wave
will cross the region, increasing shower activity a little. Just
after the wave departs, an even denser cloud of Saharan dust will
reach the region, hence hazy skies will continue.

As we move into July, normal high temperatures are in the range of
86 to 92 degrees Fahrenheit, with warm nights too...mainly in the
upper 70s. Due to seasonal warmer temperatures and enhanced humidity
levels at the surface, elevated to significant heat indices will
persist throughout the period.

&&

.AVIATION...
TSRA/SHRA will result in brief MVFR conditions
across most terminals within 24 hours. For TJSJ and USVI terminals,
this scenario will prevail throughout the cycle. For TJPS and TJBQ,
this scenario is likely after 28/16Z and between 28/17Z and 29/02Z,
respectively. Calm to light and variable winds becoming more east-
southeasterly to southeasterly with sea breeze variations and
increasing to around 5-15 knots with higher gusts by 28/18Z. Winds
again become light and variable after 28/23Z. Higher winds and gusty
conditions are possible near the TSRA/SHRA.

&&

.MARINE...
Seas 1 to 3 feet are observed in the CariCOOS buoy network around
Puerto Rico and the U.S. Virgin Islands. However, seas 3 to 6 feet
are anticipated, with winds at 20 kts or locally higher as a
tropical wave moves in. This wave will also increase the frequency
of showers and thunderstorms throughout Friday. After that, rain
will decrease, but the trade winds will remain fresh, and choppy
seas are anticipated.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...ICP
LONG TERM....ERG

[cycloneye]

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

The night was active across the local islands and waters, with
thunderstorms developing along the northern Virgin Islands and
Culebra, eastern Puerto Rico and for southern Puerto Rico. Rainfall
accumulations were in the range of 1 to 3 inches, with several flood
advisories and special weather statements issued.

The combination of an upper level trough and a tropical wave will
maintain favorable conditions for additional shower and thunderstorm
production. The high resolution and National Blend Model have the
strongest activity developing along the southern and eastern half of
Puerto Rico and the northern Virgin Islands, but all the area will
experience rain, gusty winds and at least some lightning. Rainfall
accumulation should be in the range of 1 to 3 inches, with isolated
higher amounts. With the heaviest activity, urban and small stream
flooding, as well as water surges along rivers and mudslides can be
expected today. Flash flooding cannot be ruled out.

As the tropical wave departs toward Hispaniola, the air mass will be
substituted by dry air and Saharan dust. Friday should be a
transition day, with some lingering showers drove by the trade winds
along southeastern Puerto Rico and the Virgin Islands, while some
additional showers develop in the afternoon along the interior and
northwestern Puerto Rico. For the Virgin Islands, skies will become
hazy due to Saharan dust. These hazy conditions will quickly spread
across Puerto Rico on Saturday. The mid-levels will also dry out, so
rainfall activity should be limited. Additionally, the 925 mb
temperatures will-once again- warm up, resulting in highs climbing
into the low to mid 90s in the afternoon hours.

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

An extended and relatively drier air mass, accompanied by pulses
of Saharan dust particulate, will continue to spread across the
local area through most of the period, causing precipitable water
values to fall further from seasonal levels (around 1.6-1.8
inches) on Sunday and Monday to below seasonal levels (1.2-1.6
inches) from Tuesday through at least Thursday. A weak tropical
wave will cross the region on Monday, but the bulk of the moisture
should remain well south of the local islands. Expect the driest
period after the wave's passage, with precipitable water values
dropping as low as 1.2 inches between Tuesday and Wednesday.
Still, pockets of shallow moisture will stream across the area,
briefly causing precipitable water values to peak slightly higher
but not high enough to enhance significant shower development.
Despite these variations, shower development is possible even
during the driest period, following the seasonal distribution
pattern, with the heaviest rains of any intensity clustering
across Puerto Rico's western interior to western sections.
Elsewhere, little to no anticipated showers are expected,
particularly in fire-prone areas of southern Puerto Rico, Vieques,
Culebra, and the U.S. Virgin Islands.

Breezy conditions with generally east to east-southeast winds at
15-25 mph will persist through the period, generated by a low-to-
mid level high pressure spreading across the North Atlantic. The
strong mid-level zonal flow will bring an even denser cloud of
Saharan dust particulate across the region; hence, expect
persistent hazy conditions throughout the workweek.

Despite expected seasonal high temperatures, ranging between the
upper 80s and the lower 90s across lower elevations and other
urban areas, locally enhanced moisture levels across western,
northern, and eastern sections could yield elevated to significant
excessive heat hazard risks, with 102 degrees or higher heat
indices. In contrast, drier and breezy conditions could lead to
elevated fire weather hazard risks across southern Puerto Rico,
particularly around midweek.

&&


.AVIATION...Light to moderate rain continues across srn PR and
over TISX. Some MVFR conds there. TSRA expected to dvlp aft
29/17Z ovr land, but are already present S of PR and N of TIST.
Sfc winds less than 10 kt xcp nr TSRA. Max winds S 20-30 kt btwn
FL010-043 and SSW 20-25 kts btwn FL335-355.

&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated seas between 1 and 3
feet. However, seas up to 6 feet are likely with increasing east-
southeasterly wind speeds at 10-20 knots. This wave will also
generate a higher frequency of showers and thunderstorms today
into Friday morning, resulting in locally hazardous marine
conditions. Weather conditions will gradually improve tonight, but
marine conditions will remain choppy through Friday evening.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
414 AM AST Fri Jun 30 2023

.SYNOPSIS...An extended and relatively drier air mass accompanied
by Saharan dust particulate will reach the local islands today and
continue through the weekend into early next week, leading to
mainly fair weather, warm to hot, and hazy conditions. The
interaction between a tropical wave and an upper-level trough will
likely increase showers with thunderstorms on Tuesday, leading to
lightning and excessive hazard risks. Increasing winds associated
with the tropical wave will also yield hazardous marine and life-
threatening rip currents. Still, breezy conditions will persist
across coastal areas and the local islands.


&&

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

Showers and thunderstorms were observed along the southern coast of
Puerto Rico during the night, in the vicinity of St. Croix, over the
Caribbean waters and well offshore in the Atlantic. The rain was
heavy at times, mainly from Salinas to Penuelas. Cloudy skies
prevailed across the forecast area through the night.

Moisture from a departing tropical wave and a surface trough well
north of the region will gradually decrease during the day today.
However, there is still enough instability for additional showers
this morning across the southern coast of Puerto Rico. Based on
current observations, and data from the high resolution models,
about half to an inch of accumulation can be anticipated with this
activity. The cloudiness covering the region may delay local
effects, but some showers may still stream along the interior,
northwestern Puerto Rico, and offshore to the northwest of Puerto
Rico. Saharan dust will also filter in today, and skies will begin
to turn hazy.

This weekend, moisture levels will continue to drop to near normal
values, although some patches of clouds are forecast to still reach
the islands at times. It will also be hazy, as a moderate Saharan
Air Layer will linger. Under this pattern, the shower activity
should resume a more typical pattern, with some showers reaching the
Virgin Islands and eastern Puerto Rico at times, and convection
developing in the west-northwest in the afternoon. Since dynamics
are not that favorable for strong activity, rainfall accumulation
should remain light to moderate.

Seasonably hot temperatures will continue for the last day of June
and the first weekend of July. In fact, 925 temperatures will be
well below normal today, and a little lower (but still above normal)
for Saturday and Sunday. Therefore, expect surface temperatures in
the low to mid 90s at lower elevations, and heat indices above 108
degrees for coastal and urban areas around the islands.

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

Compared to previous model runs, the most recent model guidance
now suggests a slightly wetter pattern due to the interaction
between a tropical wave moving westward across the eastern
Caribbean and a developing upper-level low west of the local
islands. Despite discrepancies in the evolution of the upper-level
low (more robust in the GFS), timing variations (time delay in
the GFS), and wave's moisture field northern extent (further north
in the ECMWF) among both global model guidance, the overall
scenario suggests an increase in showers and thunderstorms
activity. With medium confidence, the long-term forecast scenario
will reflect a combination of both model guidance.

A relatively drier air mass will remain over the region on Monday,
with precipitable water values between 1.6-1.8 inches and within
seasonal moisture levels. Moisture levels will rapidly increase as
the wave's field moisture spreads across the forecast area from
Monday night into late Tuesday night, spiking around 1.9-2.1
inches and above seasonal levels by Tuesday evening. By Wednesday,
moisture should plunge below seasonal levels, around 1.2-1.5
inches. Moisture levels will again rise to seasonal moisture
levels on Thursday, followed by another significant spike on
Friday caused by another tropical wave.

A mid-to-upper level high will extend over the region early in the
period before being displaced eastward by a developing upper-level
trough settling between Hispaniola and Puerto Rico from Monday
night onwards. Shower development following the seasonal
distribution pattern is likely every day, even during the driest
periods. Although this pattern suggests the highest daily rainfall
from afternoon convective development, the showers and
thunderstorms expected between Monday evening and Tuesday night
should favor eastern and southern Puerto Rico and the U.S. Virgin
Islands, where lightning and excessive rainfall impacts are
likely. Breezy conditions with generally east-to-east-southeast
winds at 15-25 mph will persist through the period, generated by a
surface high pressure spreading across the North Atlantic. The
strong mid-level zonal flow will bring pulses of Saharan dust
particulate; hence, expect hazy conditions at times.

Despite expected seasonal high temperatures, ranging between the
upper 80s and the lower 90s across lower elevations and other
urban areas, locally enhanced moisture levels across western,
northern, and eastern sections could yield elevated to
significant excessive heat hazard risks, with 102 degrees or
higher heat indices.


&&

.AVIATION...SHRA will continue affecting the Caribbean waters
through at least 18Z. Then, additional isolated to scattered SHRA
may develop along the Cordillera Central and north of PR, and around
USVI. This activity could lead to mountain obscuration, reduced VIS
and low ceilings for the terminals. Improving weather is expected
after 22Z. HZ due to Saharan dust is also expected, but with VIS
generally at P6SM.


&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated seas between 1 and 4
feet. However, locally fresh southeasterly winds of 15-20 knots
will likely generate choppy seas of up to 6 feet, mainly across
the Mona Passage and coastal waters of southwestern Puerto Rico,
where small craft should exercise caution. A moderate rip current
risk continues for southeastern and southwestern Puerto Rico
beaches, where life-threatening rip currents are possible.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
434 AM AST Sat Jul 1 2023


.SYNOPSIS...

The presence of Saharan Air Layer across the Caribbean basin will
promote hazy skies through early next week. A robust tropical wave
is forecast to move across the region on Tuesday, increasing shower
and thunderstorm activity across the islands. Hazardous seas are
expected with the wave passage.

&&

.SHORT TERM...Tonight through Sunday...

Mainly partly cloudy skies prevailed this morning across much of the
islands with very limited shower activity. However, the remaining
moisture from the a departing tropical wave left few isolated
showers over the Caribbean Sea, but dissipated by mid morning. A
drier air mass and Saharan Dust filtered across the region this
afternoon, turning into hazy skies across the area. No precipitation
was observed by the local Doppler radar during the afternoon hours.
Maximum temperatures were observed in the low to mid 90s across the
coastal and urban areas of the islands, and in the mid to upper 80s
across the Central Cordillera. A Heat Advisory was in effect for the
northern coast of Puerto Rico, including Culebra, where the heat
indices fluctuated between 102 to 114 degrees Fahrenheit. The U.S.
Virgin Islands reported heat indices over 100 degrees.

For this weekend, mostly clear to partly cloudy skies are expected
to prevail. Skies will also be hazy due to moderate concentration of
Saharan Dust that is forecast to linger throughout the weekend. At
this moment, no significant rains are expected across the local
area. However, isolated shower activity could develop across the
western portions of Puerto Rico due to daytime heating and local
effects. Expect a hot and warm weekend as temperatures across the
local area could reach the low to mid 90s across the northern
portions of Puerto Rico and the U.S. Virgin Islands, once again.
Therefore, Heat Advisories and Warnings cannot be ruled out as
indices could reach 108 degrees Fahrenheit or higher across some
sectors.

On Sunday, a weak tropical wave is forecast to pass south of the
area. The bulk of this wave is forecast to stay over the offshore
Caribbean waters. However, associated moisture could reach the local
islands and slightly increasing the shower activity across the
southern and southeastern portions of Puerto Rico. Then, during
the afternoon hours typical convective activity is likely across
the western and northwestern portions of Puerto Rico. Sunday is
expected to be a transition into a wetter weather pattern.

&&

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

Model solutions persist on the passage of a robust tropical wave
with possible squally weather conditions across the region on
Tuesday. Model guidance also suggests the presence of a tropical
upper tropospheric trough (TUTT) in the vicinity, which may
interact with the tropical wave and promote unsettled weather
conditions. However, uncertainty exists regarding its positioning
with either a closer approach and settling northwest of Puerto
Rico (GFS) or remaining mostly north of the forecast area (ECMWF).
Additionally, a mid-level ridge east of the TUTT could somewhat
inhibit instability aloft. Nevertheless, scattered to locally
numerous showers and thunderstorms along with gusty wind
conditions can be expected to affect the islands with the wave
passage, increasing the potential for urban and small stream
flooding, as well as localized flash flooding. Forecast confidence
levels are low to moderate as it will depend on the positioning
of the TUTT with respect to the tropical wave.

As the wave crosses the local islands, the GEOS-5 model shows
another pulse of Saharan Air Layer (SAL) filtering in. With the
presence of Saharan dust particulate in the lower atmosphere,
enhancement of lightning activity within thunderstorms could be
possible. The concentration of the Saharan dust particulate from
Wednesday onwards will vary throughout the week but will remain
sufficiently high to cause hazy skies for most days through the
weekend.

The TUTT will remain in the vicinity for the rest of the forecast
period which could aid in deep convective development every
afternoon as enough low-level moisture, diurnal heating, and local
effects combine. However, the presence of Saharan dust particulates
could suppress convective activity of any sort.


&&

.AVIATION...VFR conds will prevail through the forecast period.
Isold SHRA ovr regional waters and en route btw islands. Hazy skies
will persist due to the extensive Saharan air layer spread across
the region. However expect VIS to remain P6SM at all terminals with
no restrictions to FLT VIS. SFC wnd calm to LGT/VRB, bcmg fm ESE 10-
15 kt with ocnly hir gusts and sea breeze variations aft 01/14Z. No
sig operational wx impacts attm.

&&

.MARINE...Moderate to locally fresh winds up to 20 knots and seas up
to 4 feet are expected to prevail across the regional waters through
at least Monday. Winds and seas will gradually increase on Tuesday
due to the approach of a robust tropical wave. Therefore, choppy
to hazardous seas are expected on Tuesday. For beachgoers, there
is a low risk of rip currents for all the local beaches for most
of the weekend.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
443 AM AST Sun Jul 2 2023

.SYNOPSIS...

Hot and hazy conditions are forecast to continue today across the
region. Another tropical wave will increase shower and thunderstorm
activity by Tuesday. Small craft operators should exercise caution
due to choppy marine conditions across some of the local waters.

&&

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

Skies were mostly clear to partly cloudy across the islands
overnight. Occasional patches of low level clouds and passing
showers were observed crossing the Caribbean waters and the Anegada
passage while affecting parts of southeastern Puerto Rico and
Vieques from time to time. No significant rains were noted so far. A
broad surface high pressure ridge across the north central Atlantic
and a tropical wave crossing the southeastern Caribbean, will
maintain light to moderare east southeast winds across the area
today into Monday. For the rest of the day, the slight increase in
moisture along with good daytime heating will favor isolated to
scattered afternoon showers with isolated thunderstorms mainly over
the west interior and northwest sections of Puerto Rico. Mostly
isolated showers can be expected elsewhere and downwind of the U.S
Virgin islands. A low to moderate concentration of Saharan dust will
persist across the region with hot and hazy conditions forecast to
continue.

A mid to upper leve ridge in place will continue to gradually erode
during the period and is to be replaced by an upper trough which is
forecast to sink southwards across the Mona passages by Monday and
Tuesday, while inducing a southerly wind flow and providing good
ventilation and unstable conditions aloft.

The tropical wave now crossing the southeastern Caribbean is
forecast to pass mainly south of the area today, with most of the
associated moisture expected to remain mainly over the offshore
Caribbean waters and south of the islands . However, still expect
peripheral moisture to reach the islands and coastal waters during
the rest of the overnight hours and throughout the day. This in turn
will bring a slight increase in moisture and thus support shower
development mainly across the south and southeastern portions of
Puerto Rico and around the islands of Saint Croix. Afternoon shower
development with isolated thunderstorms should be focused mainly
over the west interior and northwest sections of PR steered by the
east to south east wind flow. Improving conditions on Monday as this
wave exits the region and a brief slot of drier air filters in.
However this will be short lived as a more vigorous tropical wave is
expected to enter the eastern Caribbean late Monday night thorough
Tuesday. This will increase the chance for enhanced showers and
thunderstorm activity late Monday through Tuesday, when so far the
wettest conditions are expected. Therefore the potential for ponding
of water on roads and poor drainage areas as well as urban and small
stream flooding will be elevated by late Monday and through Tuesday
due to increasing instability aloft and the passage of the Tropical
wave.Another surge of Saharan Dust is also expected to accompany an
d trail the Tropical wave.

Hot and humid conditions will continue today and on Monday as
temperatures across the islands will reach the low 90s and slightly
above normal especially across the northern portions of Puerto Rico
and the U.S. Virgin Islands. A Heat Advisory will be in effect for
the west, northwest and north central coast of Puerto Rico,
including Culebra, where the maximum heat indices are expected to
again fluctuated between 107 and 112 degrees Fahrenheit.

&&

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

At the surface, a broad high pressure across the north-central
Atlantic will induce a generally east-to-southeast wind flow of
around 10-20 mph and locally higher through the cycle. Lingering
moisture on Wednesday from a departing robust tropical wave and
patchy weather scenario in the days after will maintain near-normal
to slightly above-normal moisture levels through Friday.

Despite variations in surface winds and moisture content, a
retrograding tropical upper tropospheric trough (TUTT) will sink
southward and meander northwest of the forecast area. Latest model
solutions leave the TUTT closer to the northeastern Caribbean than
in previous model cycles, even getting slightly stronger and closer
by the weekend. This will maintain somewhat favorable conditions for
deep convective development through most of the forecast period.
Aided by local and diurnal effects, this scenario will enhance
afternoon showers and isolated thunderstorm development mainly
across the interior to western sections of Puerto Rico, even during
the driest periods. Streamer-like showers could also affect portions
of eastern Puerto Rico and the San Juan metropolitan area each
afternoon. Although limited, overnight and early morning trade wind
showers will offer the chance for measurable rainfall amounts across
the U.S. Virgin Islands and eastern Puerto Rico. However, high
concentrations of Saharan dust particulates are also expected mostly
between Wednesday through Friday maintaining hazy conditions. The
presence of Saharan dust could potentially suppress some of the
shower activity across the area.

During the weekend, another robust tropical wave is expected to
cross the local islands with moisture content reaching 2.0 inches or
higher. This could increase shower and thunderstorm activity as it
interacts with the TUTT. However, forecast confidence is low as the
positioning of the TUTT continues to change with each model cycle.

&&

.AVIATION...
VFR conds durg prd. Isold SHRA ovr regional waters and en route btw
islands. Mstly SCT lyrs nr FL025...FL050. Sfc wnd mainly fm E 10 kts
or less. L/lvl wnds fm SE 15-20 kts BLO FL120...bcmg fm W ABV FL200.
Area of suspended Saharan dust particulates continued across the
flying area and will cause slght haze but with no restrictions to
FLT VIS. No sig operational wx impacts anticipated.

&&

.MARINE...Moderate to locally fresh winds up to 20 knots and seas up
to 4 feet are expected to prevail across the regional waters through
at least Monday. Winds and seas will gradually increase on Tuesday
due to a robust tropical wave. Choppy to hazardous seas are expected
on Tuesday. For beachgoers, there is a moderate risk of rip currents
for some east-facing beaches of Puerto Rico, Vieques, Culebra, and
St Croix USVI.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
430 AM AST Mon Jul 3 2023


.SYNOPSIS...

Hot summer temperatures will persist today. An approaching tropical
wave and a weak upper-level trough will increase instability across
the islands, particularly by late tonight through the 4th of July.
This will increase the risk of flooding across the local islands.
Once the wave departs by late Tuesday, skies will become hazy as
Saharan dust filters in.

&&

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

Skies were mostly clear to partly cloudy across the islands and
regional waters overnight as occasional patches of low level clouds
and passing showers crossed the local waters and passages between
the islands. Few showers continued to affect the windward side of
the islands steered by the trade winds...with isolated thunderstorms
noted moving westward over the Mona passage overnight. No
significant rains were noted so far over land areas.

Broad surface high pressure ridge north of the region now extending
southwestward into the west central Atlantic and a tropical wave
with axis now south of the Dominican south of the dominican can
republic will maintain light to moderare east southeast winds across
the area today Monday. The mid to upper leve ridge will continue to
erode today and will be replaced by a deepening upper trough still
forecast to sink southwards and linger across the Mona passage
through the period. This in turn will promote a southwesterly wind
flow while providing good ventilation and unstable conditions aloft.

Moisture trailing the aforementioned tropical wave which exited the
region Sunday evening, will continue to affect the regional waters
overnight, resulting in passing showers from time to time. Later in
the morning and the rest of the day a slot of drier air will spread
across the region resulting in mostly sunny skies with continued
hazy conditions although slightly less than recent days. Afternoon
locally and diurnally induced shower development will remain
possible today in and around the islands, with isolated
thunderstorms possible mainly over the west interior and northwest
sections of PR as well as in the interior sections of east PR.
Ponding of water on roads and in poor drainage areas will be
possible with the heaviest rains, with a chance for minor urban
flooding also possible in isolated spots in the west sections of PR.

Later this evening and through Tuesday a vigorous tropical wave just
east of the Lesser Antilles is forecast to enter the eastern
Caribbean, with the leading edge of the moisture field expected to
arrive across the local Caribbean waters and U.S. Virgin Islands by
then. This along with the deepening trough aloft will increase the
chance for enhanced showers and thunderstorm activity across the
region Tuesday and possibly into early Wednesday. So far model
guidance and local analyses continued to suggest the wettest
conditions are expected overnight into Tuesday 4th of July.
Therefore the potential for ponding of water on roads and poor
drainage areas, as well as urban and small stream flooding will be
elevated to significant at times overnight and through Tuesday, due
to the instability aloft and the passage of the aforementioned
Tropical wave.

Accompanying and trailing the tropical wave, another extensive area
of moderate to high concentration of Saharan dust is forecast on
Wednesday along with an erosion of tropical moisture as the mid to
upper level ridge build overhead, favoring improving weather
conditions and more typical summertime weather pattern.

Heat Advisory will be in effect for the west, northwest and north
central coast of Puerto Rico, including Culebra, where the maximum
heat indices are expected to again fluctuated between 108 and 111
degrees Fahrenheit.

&&

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

Suspended Saharan dust particulates with slight to moderate
concentrations will persist across the forecast area on Thursday,
gradually diminishing by Friday. Moisture content will remain
within the 50th percentile of the climatological normal through
Saturday. Latest model guidance is still indicating the tropical
upper tropospheric trough (TUTT) lingering in the vicinity through
at least the weekend. However, positioning continues to change
between each model cycle, with the latest placing it near or above
the forecast area by Thursday through at least the weekend. This
will provide unsettled weather conditions aloft, making it
conducive for deep convective activity, particularly every
afternoon as it combines with enough low-level moisture, diurnal
heating, and local effects. Therefore, expect shower and
thunderstorm activity across the interior and western portions of
Puerto Rico each afternoon. Streamer-like showers are also
possible downwind of the smaller islands and El Yunque mountain
range, with the latter affecting parts of the San Juan metro area.
Urban and small stream flooding is possible each afternoon. Some
passing showers can also be expected across windward coastal areas
during night and morning hours.

Another vigorous tropical wave will move across the northeastern
Caribbean by early Sunday morning. Both GFS and ECMWF are in pretty
good agreement in terms of timing and as well as positioning of this
wave exiting the forecast area by early Monday. The aforementioned
tropical wave is expected to bring precipitable water values of
around 2 inches or more. The TUTT will remain in the vicinity by the
time the tropical wave reaches the local islands, which could
enhance deep convective development. Therefore, cloudy skies and
periods of shower and isolated thunderstorm activity are expected
across portions of the local area. Urban and small stream flooding
and isolated flash flooding are possible. Pay attention to river
streamflow levels as weather conditions described above are
conducive for sudden water surges.

After the wave passage, slightly drier conditions will follow. A
pulse of 40-60kt jet at 700 mb will reach the islands. Usually,
these 700 mb jets are indicative of possible suspended Saharan Dust
particulates within the airmass. Therefore, fair weather conditions
along with hazy skies are possible by early next week.

&&

.AVIATION...

VFR cond will prevail at all terminals durg prd. Isold-SCT SHRA ovr
regional waters and en route btw islands with isold TSRA psbl ovr
the Mona passage early in the prd. Sfc wnds fm E-SE less than 5 kts
with land breezes,bcmg fm E-NE 15-18 kts and hir gust and sea breeze
variation aft 03/14Z. SHRA with psbl Isold TSRA mainly along and
west of the Cordillera Central btw 03/17-22z which may impact mainly
TJBQ. Incr cld cover and chc of SHRA/Isold TSRA across lcl flying area
aft 03/23Z as Tropical wave is fcst to enter the eastern Caribbean.

&&

.MARINE...
Seas 1 to 3 feet are observed in the CariCOOS buoy network around
Puerto Rico and the U.S. Virgin Islands. However, seas 4 to 7 feet
are anticipated, with winds at 20 kts or locally higher as a
tropical wave moves in late tonight through Tuesday. This wave will
also increase the frequency of showers and thunderstorms during this
period. After that, the rain will decrease, but the trade winds will
remain moderate to locally fresh, resulting in choppy seas across
the regional waters.

[cycloneye]

Area Forecast Discussion...DELAYED
National Weather Service San Juan PR
532 AM AST Tue Jul 4 2023

.SYNOPSIS...
A vigorous tropical wave with axis now entering the eastern Caribbean
will continue westward while bringing an increase in tropical moisture
across the region the rest of the morning and into the afternoon
hours. The interaction between the tropical wave and a deepening
upper level trough forecast to sink further southward across the
Mona passage, will increase instability aloft and favor enhanced
morning and afternoon showers and thunderstorms across the islands
and coastal waters. Moisture content is expected to rapidly erode
later in the evening and the rest of the workweek with the arrival
of another surge of the extensive Saharan air layer and a moderate
to high concentration of Saharan dust particulates.

The aformentioned conditions will increase the risk for urban flooding
in isolated spots as well as pounding of water on roads and in poor
drainage areas during the rest of today. Thereafter, a gradual improvement
is expected as drier air and hazy skies will return to the region. Hot
and humid conditions will result in heat advisory condition for parts
of the islands today.

&&

.SHORT TERM...Today through Thursday...
The interaction between the leading edge of the robust tropical
wave, with its axis now located around 61W, and a deepening
tropical upper tropospheric trough (TUTT) induced showers and
isolated to scattered thunderstorms over the local waters during
the overnight hours. The strongest thunderstorms were observed
across the coastal Atlantic waters and Mona Passage with GOES
Geostationary Lightning Mapper (GLM) indicating the presence of
frequent lightning associated with these storms. Some moved over
southern and eastern Puerto Rico, producing rainfall totals of up
to an inch.

The TUTT will continue to deepen while sinking southward, settling
over northwestern Puerto Rico for the rest of the short-term period.
This should provide favorable dynamics at upper levels for deep
convective development. The limiting factor will be the available
moisture across the forecast area. The tropical wave will provide
sufficient moisture for most of today. The Tropical Analysis &
Forecast Branch (TAFB) puts the axis of the tropical wave over
Puerto Rico by 04/12z and over Hispaniola by 05/00z. Behind the
tropical wave, a drier air mass with suspended Saharan dust
particulates will move in from the east. The relative humidity
within the 850-300 mb layer is expected to plummet, going down from
70% or more to less than 30% after the wave passes through. As this
drier airmass moves westward, shower and thunderstorm activity will
be suppressed, with hazy skies prevailing across the local islands.
There is some uncertainty about the timing of the aforementioned
weather scenario.

For now, model guidance suggests shower and thunderstorm activity
along with gusty wind conditions continuing during the morning
hours, with the southern and eastern municipalities of Puerto Rico
impacted the most. Vieques, Culebra, and U.S. Virgin Islands could
also observe some active weather as showers and thunderstorms over
the local waters pass near or over the islands. By late morning
through the afternoon hours, convective activity will affect the
western portions of Puerto Rico and Mona Passage. The eastern half
of the CWA may gradually transition to hazy skies and more stable
weather conditions during the evening hours. However, this will
depend on the timing of drier air and suspended Saharan dust
entering the forecast area.

Despite the presence of the TUTT northwest of Puerto Rico, moisture
content is expected to decrease below the 50th percentile on
Wednesday. Therefore, for most of the day, mainly stable weather
conditions and hazy skies will prevail. Some showers and a few, very
isolated and short-lived thunderstorms may develop out west in the
afternoon. Hazy skies will persist on Thursday, but moisture content
will jump back up to seasonal climatological levels. Therefore,
expect passing showers over windward coastal areas of the islands in
the morning hours. In the afternoon, enough low-level moisture,
diurnal heating, and local effects in combination with the effects
of the TUTT close by will promote shower and thunderstorm
development over interior and western sections of Puerto Rico.

Increased cloud cover and rains should result in lower temperatures
today, ranging from the upper 80s across lower elevations in the
daytime. However, high humidity will be enough to drive high index
values, mostly over northern coastal municipalities of Puerto Rico
and Culebra. Therefore, a Heat Advisory will be in effect for the
north-central coast of Puerto Rico, including Culebra, where the
maximum heat indices are expected to again fluctuate between 108 and
111 degrees Fahrenheit.&&

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

A drier airmass and more seasonal conditions are expected, with
the Saharan air layer and accompanying moderate concentration of
suspended dust particulates expected to linger across the region
at least until Friday. Near normal moisture content will persist
into the upcoming weekend. However, the lingering upper tropospheric
trough (TUTT) through the weekend will aid in providing sufficient
ventilation and instability aloft to combine with good daytime
heating and local effects for afternoon convection through Saturday.
Expect shower and thunderstorm activity mainly across the interior
and western portions of Puerto Rico each afternoon. Streamer-like
showers are also possible downwind of the smaller islands and El
Yunque mountain range, with the latter affecting parts of the San
Juan metro area. Ponding of water on roads and in poor drainage
areas as well as minor urban and small stream flooding will remain
possible each afternoon in isolated areas. Some passing showers
can also be expected across windward coastal areas during
overnight and early morning hours.

By Sunday, another tropical wave is forecast to enter and move across
the northeastern Caribbean. Both GFS and ECMWF suggest the passage
of this wave and accompanying moisture field by Sunday and into Monday.
The aforementioned tropical wave is expected to bring precipitable
water values up to around 2 inches or so once again. As mentioned
the TUTT is expected to remain in the vicinity and will therefore
aid in enhancing convective development especially during the afternoon
and early morning hours. Urban and small stream flooding and isolated
flash flooding will remain possible.

By late Monday and the rest of the period, both models suggest slightly
drier conditions and once again seasonal weather pattern, with hot
and humid conditions as the trend of suspended Saharan Dust particulates
will continue. Therefore, mostly sunny skies but hazy weather conditions
are likely by early next week.

&&

.AVIATION...
TSRA/SHRA will result in brief MVFR conditions across most terminals
within 24 hours. For TJSJ, TJPS, and USVI terminals, this scenario
will prevail through at least 04/15z. For TJBQ, this scenario is
likely after 04/16Z. Calm to light and variable winds becoming more
southeasterly with sea breeze variations and increasing to around 10-
20 knots with higher gusts by 04/18Z. Winds again become light and
variable after 04/23Z. Higher winds and gusty conditions are possible
near the TSRA/SHRA.

&&

.MARINE...
Mariners can expect choppy wind driven seas between 15 and 20
knots with occasionally higher gust across most of the local
waters and passages today. A tropical wave crossing the eastern
Caribbean, will bring areas of enhanced showers with isolated to
scattered thunderstorms during the rest of the morning and early
afternoon hours. Small Craft Advisories are in effect for portions
of the Caribbean Waters and the Anegada Passage. Small craft
operators should exercise caution elsewhere. Please refer to the
latest Coastal Waters Forecast (CWFSJU) and the Marine weather
message (MWWSJU) issued by WFO San JUan PR for the most up to
date info.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
521 AM AST Thu Jul 6 2023

.SYNOPSIS...A typical summertime weather pattern is expected to
continue with significant levels of Saharan Dust, although gradually
diminishing, through Saturday. A tropical wave will increase
moisture, as well as shower and thunderstorm activity, from late
Saturday into Monday morning. High Heat indices are expected once
again today, particularly across north-central PR. Please stay
hydrated and take necessary precautions.

&&

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

At upper levels a tropical upper tropospheric trough extends
southwest from 30 north 50 west to across Haiti. At least three
centers are present, but the strongest is the farthest northeast.
At mid levels, high pressure extends into the area from Africa, but
there are reflections of the lows in the TUTT at both mid and lower
levels. Moderate high pressure at the surface will continue over the
east central Atlantic with easterly trade winds across most of the
tropical Atlantic and the Caribbean Sea during the period.

The worst of the Saharan dust has passed overnight according to the
latest models, but there will still be significant levels of dust in
the air through the period as the Saharan air layer diminishes. Some
haze will also be noted. Visibilities at all stations, however,
should remain above 6 miles. Moisture will increase on Friday with a
modest increment of shower activity both morning and afternoon, but
that will be followed a a fairly narrow dry slot Saturday just ahead
of a tropical wave which will enter the area late Saturday and into
Sunday.

&&

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

An increase in moisture is expected to start the long term forecast
period due to the approach of a tropical wave. Precipitable Water
(PWAT) values are expected to increase to above 2 inches, above
normal values for this time of the year, for Sunday into Monday.
Only pockets of moist air will continue moving across the area on
Tuesday, leaving overall PWAT at mostly below normal to normal
values. Hot and hazy conditions with Saharan dust particulates will
continue to linger during the period. At surface level, a high over
the central Atlantic will promote generally easterly, to east-
southeasterly, winds. These will see an increase later in the period
as the pressure gradient tightens. At the upper levels, a TUTT will
be east of the region to start the period. This will help increase
shower activity during the overnight and early Monday morning hours,
especially over the coastal waters between PR and the USVI. From
Sunday afternoon into Monday morning, urban and small stream
flooding along with isolated flash flooding will be likely, with the
addition of ponding of water over roadways and poor drainage areas.
Even after Monday, available moisture and high temperatures will
promote convective activity each afternoon mainly across interior to
western Puerto Rico, with possible streamer formation downwind from
El Yunque and the USVI. Current model guidance indicates another
area of moist air, related to another tropical wave, with above
normal PWAT reaching the islands. However there is some discrepancy
between the GFS and the ECMWF on the timing of this moisture, with
the GFS suggesting an arrival on Wednesday afternoon into Thursday
afternoon and the ECMWF suggesting an arrival on Thursday afternoon
into beyond the long term period.

&&

.AVIATION...VFR conds are expected through the fcst period altho
some haze will be present with vsbys greater than 6 SM. Isold light
SHRA in ern PR thru 06/18Z mainly downstream from El Yunque. Then
sct +SHRA/isold TSRA in wrn PR psbl from 06/17-21Z. Little to no
impacts at terminals expected. Sfc winds ENE less than 10 kt, bcmg
aft 06/14Z ENE 10-20 kt with gusts to 26 kt. Maximum winds WSW-W 30-
40 kt btwn FL390-470 and E 30-40 kts btwn FL070-100.

&&

.MARINE...Seas will remain at 5 feet or less through the weekend.
Winds of 10 to 20 knots and wind-driven seas, will result in
choppy marine conditions for small craft operators, particularly
across coastal waters of northern and southern Puerto Rico. There
is a moderate risk of rip currents for the northern beaches of
Puerto Rico from Aguadilla to westernmost Rio Grande, as well as
for easternmost beaches of Culebra and St. Croix. Low risk
elsewhere.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
546 AM AST Fri Jul 7 2023

.SYNOPSIS...A TUTT will weakly cross the area today with some
enhancement of shower activity, hazy conditions also continue
today as Saharan Dust lingers and gradually diminishes through
tomorrow. A tropical wave will move through the region this
weekend, increasing moisture mainly on Saturday into Sunday. From
Sunday night and into the workweek, another Saharan Air Layer will
filter into the area. High heat indices are expected once again,
particularly across north-central PR. Please stay hydrated and
take necessary precautions.

&&

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

At upper levels a tropical upper tropospheric trough (TUTT) extends
southwest from 24 north 60 west to across Haiti and Jamaica. It will
weakly cross through the area today with some enhancement of shower
activity. At mid levels, a ridge of high pressure just north of the
area extends across the Atlantic from a high just west of Africa and
will continue through the period. Moderate high pressure at the
surface will continue over the east central Atlantic with easterly
trade winds across most of the tropical Atlantic and the Caribbean
Sea during the period. A tropical wave in that flow will move into
the area late tonight from the east southeast, cross through on
Saturday and Saturday night with Saharan dust following directly on
Sunday night. This represents an earlier arrival of the wave than
originally forecast. There is a warming trend in the forecast
through Wednesday, but it will be interrupted during the wave
passage. Precipitable water values have been increasing slightly,
but there will be an abrupt rise tonight through Saturday morning,
and this will greatly favor an increase in showers and thunderstorms
across the area then. Saint Croix will likely be the first to feel
these effects Saturday morning and the best moisture will already be
over northwest Puerto Rico by 21Z on Saturday. After 00Z on Sunday
moisture will be decreasing. The lower levels will be the first to
see less moisture but mainly on the north coast, and additional
showers are expected to continue into the day on the southeast coast
of Puerto Rico through Sunday as residual moisture ascends over the
island. Afternoon thunderstorms cannot be ruled out in the northwest
quadrant of Puerto Rico on Sunday.

&&

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

Next workweek will start off with lingering moisture related to a
tropical wave that will be west of the islands by then. Current
model guidance suggest precipitable water (PWAT) of up to 1.9 inches
by early Monday morning. This will be quickly followed by drier air
with a Saharan Air Layer (SAL), promoting drier, hazy conditions
through the middle of the workweek. At surface level, high pressure
over the central Atlantic will promote generally up to breezy
easterly, to east-southeasterly, winds. At the upper levels, a TUTT
will be east of the region for most of the period. Passing shower
activity will reach windward sectors of the islands during the
overnight to morning hours. Available moisture and high
temperatures will promote shower and posible isolated thunderstorm
activity each afternoon mainly across interior to western Puerto
Rico, with possible streamer formation downwind from El Yunque and
the local islands. Recent model guidance shows discrepancies with
the timing of another area of moist air, related to a tropical
wave, with above normal PWAT reaching the region. Both the GFS and
ECMWF coincide on Thursday as the day of this moisture increase,
although the ECMWF suggest an early Thursday arrival than the GFS,
which suggest an increase in moisture later on Thursday. Moisture
would linger through Friday at above normal PWAT values. This
will increase shower and thunderstorm activity for the later part
of the workweek.

&&

.AVIATION...VFR conds are expected through the fcst period altho
some haze will be present with vsbys greater than 6 SM. Isold light
SHRA in ern PR thru 07/18Z mainly downstream from El Yunque and
Vieques. Then sct +SHRA/isold TSRA in wrn PR psbl from 07/17-21Z.
Little to no impacts at terminals expected. Sfc winds ENE less than
10 kt, bcmg aft 07/14Z ENE 10-20 kt with gusts to 26 kt. Maximum
winds WSW-W 30-40 kt btwn FL335-520 except btwn FL440-470. Maximum
winds E 30-35 kts btwn FL065-090.

&&

.MARINE...Seas will remain at 5 feet or less through the weekend.
Winds of 10 to 20 knots and wind-driven seas, will result in
choppy marine conditions for small craft operators, particularly
across coastal waters of northern Puerto Rico and the Mona
Passage. There is a moderate risk of rip currents for the
northwestern Puerto Rico and westernmost Sr. Croix.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
549 AM AST Sat Jul 8 2023

.SYNOPSIS...A tropical wave will cross the region later today
and tonight promoting variable and unstable weather with shower
and thunderstorm development across the region. As the day
progresses, the shower coverage will become more widespread.
Showers will continue into Saturday night and Sunday morning, but
amounts and intensities are expected to decrease after tonight.
Limited heat risk persists today over northern and western Puerto
Rico. Drier air with Saharan Dust arrives late Sunday and another
tropical wave is forecast to arrive next Thursday.

&&

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

A few thunderstorms have appeared south and southeast of Saint Croix
and east outside of the forecast area, but coverage has been
slight so far. Isolated light rain showers are also seen along the
coast of Puerto Rico from San Juan to north of Aguadilla. Rain
amounts over land have been slight. Low temperatures are ranging
from the mid 60s in the highest mountain valleys to the lower 80s
on the east and northeast coasts of Puerto Rico. Temperatures in
the lower elevations of the U.S. Virgin Islands have been in the
lower 80s.

A promising tropical wave crossing through the Leeward Islands at
the moment is raising precipitable water values from around 1.5
inches to more than 2.2 inches as it moves west northwest at about
20 mph. The boundary of the better moisture has already crossed into
Saint Croix and is expected in San Juan by 08/15Z and Aguadilla by
08/16Z. And, so it appears that the forecast for wetter weather is
on track for today and tonight for the U.S. Virgin Islands and for
Puerto Rico this afternoon and tonight. Amounts of 1 to 2 inches are
expected through 09/12Z with the highest amounts over and just
southeast of southeast Puerto Rico. After the peak moisture levels
occur this afternoon precipitable water values are expected to drop
to a minimum of around 1.8 inches on Monday afternoon. Showers will
continue into Saturday night and Sunday morning, but amounts and
intensities are expected to decrease after tonight.

The tropical upper tropospheric trough (TUTT) is pulling away from
Puerto Rico and the U.S. Virgin Islands today and a weak ridge will
build in over the area from the northwest at upper levels. Local
areas of divergence aloft will still enhance some activity today,
however, and mid level temperatures will decline slowly through the
period, allowing some shower activity to continue even with
declining moisture. Thunderstorms even if brief are therefore
expected each day during the warmest part of the day--mainly in
western Puerto Rico after today, with some thunderstorms possible
over the local waters during the overnight periods Sunday night--
mainly in the Mona Channel.

The ridge in the Atlantic to our northeast will keep trade winds
active, but will also bring in another round of Saharan dust. Skies
will be the most hazy of the period on Monday.

&&

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

No major changes to the long term forecast. Drier conditions are
expected to start the period. Tuesday and Wednesday will have a
Saharan Air Layer (SAL) affecting the islands and promoting, drier,
hazy conditions. The GFS model seems to be a little more aggressive
in terms of moisture content over those days. At surface level, high
pressure over the central Atlantic will generally promote up to
breezy easterly, to east-southeasterly, winds. At the upper levels,
a low will be northeast of the region to start the period. Passing
shower activity will reach windward sectors of the islands during
the overnight to morning hours. Available moisture and high
temperatures will promote shower and possible isolated thunderstorm
activity each afternoon mainly across interior to western Puerto
Rico, with possible streamer formation downwind from El Yunque and
the local islands. Model guidance indicates that a tropical wave
will reach the islands on Thursday. This wave will increase moisture
to above normal levels of precipitable water (PWAT) with more than
2.0 inches. This wave will increase showers and thunderstorm
activity Thursday into Friday, where moisture should start gradually
decreasing again. This drying trend will continue to start the
weekend and end the long term forecast period.

&&

.AVIATION...SHRA and isold TSRA will increase from the SE across the
FA thru 09/00Z. Isold TSRA SE-S of TISX by 08/09Z and in PR by
08/17Z. Lcl MVFR conds with mtn obscurations. Sfc winds E less than
10 kts with land breeze influences bcmg aft 08/13Z ENE-E 10-15 kts
with hir gusts nr SHRA and alg the coasts. Winds veering to ESE-SE
10-18 kts from 08/16-20Z begg with SE stations first. Maximum winds
W 25-30 kt btwn FL365-380, but greatly decreasing during the
period.

&&

.MARINE...Squally weather is expected today due to a tropical
wave. Locally hazardous marine conditions are expected within and
near the strongest showers and thunderstorms. Another tropical
wave may reach the area by the end of the week, with hazardous
seas possible. Overall seas should be at 5 feet or less, with the
exception of near the strongest showers and t-storms. Moderate
to locally fresh winds will persist through early next week,
resulting in choppy seas. Small Craft Should Exercise Caution
particularly over waters east of Puerto Rico, the Anegada Passage
and the offshore Caribbean Waters. There will be a moderate risk
of Rip Currents for the easternmost beaches of St. Croix. Low risk
elsewhere.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
534 AM AST Sun Jul 9 2023

.SYNOPSIS...Thunderstorms followed by light to moderate rain due
to a tropical wave crossed through Puerto Rico overnight leaving
accumulations of up to around 4 inches, but generally less than 2
inches. Columnar moisture should remain above 2 inches and allow
showers and thunderstorms to continue developing over the area.
Conditions should gradually improve today and by tonight and into
the workweek another Saharan Air Layer will filter into the
region. Another tropical wave is expected by the second half of
the workweek. A limited heat risk is expected across most lower
elevation locations.

&&

.SHORT TERM...Tonight through Tuesday...

A band of thunderstorms followed by light to moderate rain crossed
through Puerto Rico overnight leaving up to 4 inches, but generally
less than 2 inches of accumulations. The thunderstorms were quite
active producing a light show as they traversed the area. Winds
became mostly less than 6 knots over Puerto Rico and the U.S. Virgin
Islands. Just before midnight showers and thunderstorms redeveloped
south of Saint Croix and moved northwest. These showers eventually
extended as far as 15 miles northwest of Culebra and began to
produce lightning. The resulting band decayed and moved inland
across eastern Puerto Rico leaving up to one third of an inch of
rain.

High pressure at lower levels over the western Atlantic and
northeast of Puerto Rico in the central Atlantic will maintain
moderate to fresh winds over the area that will slowly become more
easterly as the two highs merge north of the area. Satellite imagery
showers precipitable water (PWAT) values of better than 2 inches as
far upstream in the southeast flow as Guadeloupe and PWAT should
remain above 2 inches at least through 10/06Z. This will allow
showers and thunderstorms to continue developing over the area. The
tropical upper tropospheric trough (TUTT) low will slowly move
northeast through Monday and then stall. As it does so, high
pressure north of the Bahama Islands will ridge over the area at
upper levels creating northeast flow there. At the same time PWAT
will drop to around 1.8 inches. The drying at low to mid levels will
be enough to return shower and thunderstorm formation to seasonal
level but showers and isolated thunderstorms will continue in the
typical pattern. Some of the thunderstorms will have heavy rain
during the afternoon hours over west northwest Puerto Rico.
Temperatures are expected to warm a few degrees on Monday with a
return to heat advisory heat indices in the north central zone of
Puerto Rico and heat indices above 102 degrees in the lower
elevations of Puerto Rico and the U.S. Virgin Islands.

&&

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

The period will start of fairly dry with below normal precipitable
water (PWAT) and lingering Saharan dust particles. Model guidance
indicates that PWAT will increase to around 2.1 inches, above
normal values for this time of the year, Wednesday night as
moisture from a tropical wave approaches the islands. At lower
levels, high pressure over the central Atlantic will generally
promote up to breezy easterly, to east- southeasterly, winds.
Meanwhile at the upper levels, a tropical upper tropospheric
trough (TUTT) low will be northeast of the region to start the
period. The tropical wave should affect the islands mainly on
Thursday, maintaining PWAT values above normal. This wave will
increase showers and thunderstorm activity Thursday into early
Friday and promote urban and small stream flooding as well as
possible localized flash flooding. Current model guidance
indicates PWAT values decreasing to normal values by Friday
morning as dryer air with additional Saharan Dust moves in. This
drying trend should continue through the rest of the forecast
period. From Friday morning through Saturday a more typical
pattern should prevail with brief passing shower activity will
reach windward sectors of the islands during the overnight and
morning hours. Available moisture and high temperatures will also
promote shower and possible isolated thunderstorm activity each
afternoon.

&&

.AVIATION...Deep moisture behind a trop wave movg thru the Dominican
Republic will prolong SHRA and TSRA activity thru 09/22Z. Conds
impvg in wrn PR but areas MVFR with mtn obscurations will linger
thru 09/15Z in ern PR. Aft 09/16Z SHRA/TSRA will redvlp in wrn PR.
Sfc winds less than 6 kt bcmg aft 09/14Z ESE 10-15 kt with hir gusts
nr TSRA. Maximum winds E 25 kts at FL255.

&&

.MARINE...Seas of generally 5 feet or less are expected across
the waters. Showers and thunderstorms will continue to affect the
local waters, associated with the passage of a tropical wave.
Conditions will gradually improve today but locally higher waves
can be found near stronger showers and thunderstorms. Winds around
10 to 20 knots are expected for the region, resulting in some
choppy conditions. Another tropical wave is expected to approach
the islands during the second half of the workweek.

There is a moderate risk of rip currents tonight for beaches of St.
Croix, and eastern beaches of Vieques and Culebra. Low risk
elsewhere.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
441 AM AST Mon Jul 10 2023


.SYNOPSIS...

Today, expect a gradual drying trend as the Saharan Air Layer
brings hazy skies. However, some showers and thunderstorms are
likely, particularly in the afternoons across western and
interior Puerto Rico. The next tropical wave is expected to
arrive by midweek.

&&

.SHORT TERM...Tonight through Tuesday...

Today through Wednesday...

Quick passing showers were noted overnight between the USVI and
coastal sections of eastern and southern PR. Rainfall amounts were
just a few hundredths of an inch. As of 4 AM, minimum temperatures
were from the upper 70s to low 80s across the lower elevations of
the islands.

A similar weather pattern is expected through Tuesday, as a Saharan
Air Layer promotes hazy skies and limits the coverage of showers
over land areas during the day. However, locally induced afternoon
showers with possible isolated thunderstorms cannot be ruled out
each day over western Puerto Rico. Gusty winds between 25-30 mph are
possible along coastal areas. Max temps should range from the upper
80s to low 90s across the lower elevations of the islands, with heat
indices reaching 110-112 degrees at times along the urban and
coastal areas of north central and northwestern Puerto Rico.
Therefore, a Heat Advisory (NPWSJU) is in effect for these areas and
Culebra.

Weather conditions will gradually deteriorate once again from late
Tuesday night and through Wednesday night with the passage of a
tropical wave across the local area. Latest GFS guidance suggest
2.25-2.40 inches of precipitable water on Wednesday. Showers and
thunderstorms with periods of heavy rainfall and gusty winds can be
expected across PR and the USVI. Urban and small stream flooding,
isolated flash flooding, and mudslides in areas of steep terrain are
possible with this activity. The previous forecast was adjusted to
show a wetter trend for midweek.


&&

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

The inherited forecast remains unchanged. The latest model guidance
suggests that the residual moisture associated with the tropical
wave will range between 1.o and 2.35 inches across the islands on
Thursday. The combination of this tropical wave and a tropical
upper tropospheric trough (TUTT) northeast of the region will
maintain PWAT values above normal climatology. Therefore, expect
the shower and thunderstorm activity to remain. At this time,
urban and small stream flooding, as well as localized flash
flooding, cannot be ruled out. Nonetheless, models suggest late
Thursday into Friday as transition days. PWAT models suggest
precipitable water content decreasing to normal by Friday as dryer
air with additional Saharan Dust moves in. From Friday morning
through Saturday, a more typical weather pattern should prevail,
with some passing showers reaching the windward sectors of the
islands in the overnight and morning hours. Expect the available
moisture and high temperatures to promote showers and possible
isolated thunderstorms mainly across western Puerto Rico each
afternoon.

Another tropical wave is forecast to reach Puerto Rico and the US
Virgin Islands on Sunday. At this time, it is too early to talk
about the impacts and expected inches of rain across the islands.
Therefore, we encourage you to stay tuned for more updates.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, SHRA/TSRA expected to
develop over western PR btw 10/18z-22z, this may cause tempo MVFR
cigs at TJBQ. Sfc winds E at 12-18 kt with higher gusts and sea
breeze variations after 10/14z.

&&

.MARINE...Winds around 10-20 knots and occasionally higher are
expected to persist out of the east across the waters, maintaining
some choppy conditions.Thunderstorms are possible at times,
particularly each afternoon across the western coast of Puerto
Rico. Near these thunderstorms and stronger showers, locally
deteriorated conditions are possible. Overall, seas will remain
generally 5 feet or less.

There is a moderate risk of rip currents for beaches of St. Croix
and Culebra, which will spread to beaches of Vieques, Culebra, St.
Croix, northwestern as well as north central Puerto Rico.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
435 AM AST Tue Jul 11 2023

.SYNOPSIS...

Today, expect hazy skies across the islands as a Saharan Air Layer
continues to move over Puerto Rico and the US Virgin Islands.
However, locally induced showers cannot be ruled out in the
afternoon across the west.Late tonight into early Wednesday,
another tropical wave is forecast to approach the region. Active
weather with an increased risk of flooding, largely minor or urban
and small stream flooding, though with some flash flooding
possible, is expected for Wednesday. After that the typical
seasonal weather pattern should extend to the long term forecast.

&&

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

Breezy conditions were observed across coastal areas of the islands
during the overnight. Trade wind showers were noted mainly over
portions of northeastern PR. Minimum temperatures were from the
upper 70s to low 80s across the lower elevations of the islands.

For today, a Saharan Air Layer will continue to promote hazy skies
and relatively drier conditions over land areas during the day.
However, locally induced afternoon showers with an isolated
thunderstorm cannot be ruled once again over western Puerto Rico.
Breezy conditions will continue with gusts around 25-30 mph along
coastal areas. Max temps should range from the upper 80s to low 90s
across the lower elevations of the islands, with heat indices
ranging between 108-111 degrees at times in the urban and coastal
areas of north central and northwestern Puerto Rico, and Culebra.
Therefore, a Heat Advisory (NPWSJU) is in effect for these areas.

A tropical wave just east of the Windward Islands will gradually
increase shower and thunderstorm activity from late tonight into
Wednesday across the local area. This wave will bring periods of
heavy rainfall across portions of the USVI and along the east and
southern sections of PR, where there is an elevated threat for
flooding. Rainy conditions will persist on Wednesday. Squally
weather can be expected across the local waters with the wave
passage. A drier air mass with another area of Saharan dust will
move quickly on Thursday behind the wave.

&&

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

By the later part of the workweek, expect a more typical weather
pattern as dryer air with additional Saharan Dust continues to
move across Puerto Rico and the U.S. Virgin Islands. Dust aerosol
guidances suggest optical depths greater than or equal to 0.20,
meaning the slight to moderate dust event will remain on Friday.
For that reason, haze has been added to the forecast for the whole
day. At this time, climatology models suggest precipitable water
values decreasing to normal and slightly below normal and
continuing like that through at least the weekend. Therefore,
typical weather conditions are anticipated through Sunday, with
some dry air still filtering across the area and some passing
showers reaching the windward sectors of the islands in the
overnight and morning hours. With these conditions and the
available moisture, expect high temperatures to prevail each day,
along with showers and possible isolated thunderstorms mainly
across western Puerto Rico each afternoon.

Besides that, the moisture content will gradually increase on Monday
as another tropical wave approaches the local islands. It is too
early to talk about the impacts and expected inches of rain across
the islands. Therefore, we encourage you to monitor our forecast
for more updates and changes.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals through much of the fcst period. However, SHRA/TSRA
expected to develop over western PR btw 11/18z-22z, this may cause
tempo MVFR cigs at TJBQ. Sfc winds ENE increasing 14-18 kt with
higher gusts and sea breeze variations after 11/14z. HZ due to
Saharan dust will continue today, but VSBY should remain P6SM. MVFR
conds possible late in the period across the USVI terminals due to
an approaching tropical wave.

&&

.MARINE...Winds remain generally out of the east across the
waters, with speeds of up to around 15 to 20 knots. Locally
stronger winds and gusts are possible, especially near the coasts.
This will maintain choppy conditions.

A tropical wave is forecast to begin to affect the waters late
today, resulting in an increase in shower activity. Additionally,
increasing winds are likely to occur behind the wave, resulting in
deteriorated conditions for Thursday.

There is a moderate risk of rip currents for nearly all local
beaches.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
418 AM AST Thu Jul 13 2023


.SYNOPSIS...

Showers remain possible especially in the morning hours as the
residual moisture continues to move out of the area. However, a
Saharan Air Layer will filter into the area today, bringing dust,
resulting in hazy conditions and more seasonal weather pattern
through the end of the week. This afternoon, the available
moisture, combined with diurnal and local effects, will aid in
developing afternoon showers with isolated thunderstorms across
the western sections of Puerto Rico,

&&

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

Showers with isolated thunderstorm development will lead to
lightning and excessive rain hazard risk today, with reduced risks
on Friday and Saturday. Excessive heat and wind hazard risks are
likely each day.

The tropical wave continued its westward path across the Caribbean
and away from the local islands, generating showers with isolated
thunderstorm activity through the overnight hours across the local
waters into portions of the U.S. Virgin Islands and northern and
eastern Puerto Rico. The entrance of a drier air mass, accompanied
by Saharan dust particles, will gradually cover the region. As this
occurs, the shower activity will slowly diminish throughout the
morning, yielding hazy skies and limited shower activity. Still,
showers will likely continue to affect windward sections throughout
the morning, with some moving further inland across eastern Puerto
Rico. Despite the drying scenario, precipitable water content (PWAT)
will likely remain at or above normal values throughout the day due
to lingering moisture from the wave. This available moisture,
combined with diurnal and local effects, will aid in developing
afternoon showers with isolated thunderstorms, mainly over the far
western sections of Puerto Rico, where limited flooding impacts are
possible.

A mid-level ridge north of the region will continue to promote drier
air intrusion on Friday and Saturday. Therefore, drier conditions
with hazy skies and limited shower activity will likely prevail
across the islands. Still, shower development is likely each
afternoon over western Puerto Rico, supported by diurnal heating and
local effects. East-to-southeast trades will keep maximum
temperatures in the high 80s to low 90s. Windy conditions, with wind
speeds peaking around 15-25 mph, are likely across coastal areas of
southern and northern Puerto Rico and the local islands.

&&

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

By Sunday, expect the typical weather pattern to prevail as
remnants of dry air with Saharan Dust particles continue to move
across Puerto Rico and the U.S. Virgin Islands. Dust aerosol
guidances suggest optical depths around 0.02 and 0.10. Again,
these values are below the threshold of 0.20 for dust events to be
considered slight to moderate. For that reason, we did not
include haze in the forecast. At this time, climatology models
suggest precipitable water values around normal through the
beginning of the workweek. By the end of the weekend and Monday,
some dry air will still filter across the area, as well as some
passing showers along the windward sectors of the islands,
especially in the overnight and morning hours. With these
conditions and the available moisture, expect high temperatures to
prevail each day, along with showers and possible isolated
thunderstorms, mainly across western Puerto Rico each afternoon.

The moisture content will gradually increase by late Monday as a weak
tropical wave approaches the local islands. Both models, the GFS
and ECMWF, agreed on this wave reaching and remaining through the
islands through Tuesday. Latest model guidance also suggests an
increase in moisture at all levels of the atmosphere. However, it
is too early to discuss the expected inches of rain across the
islands.

Besides that, the forecast for Wednesday leans into a more typical
weather pattern, with another mass of dry air filtering into the
area.

&&

.AVIATION...SHRA and isolated TSRA will persist across the Atlantic
waters and possibly Mona Passage. Cannot entirely rule out brief
MVFR or worse for TJSJ/TJBQ/TJPS, though the risk is decreasing. HZ
due to Saharan dust will increase, with VSBY dropping to 6SM at
times. Winds will be mainly from the east at 12-20KT with higher
gusts, but there will be sea breeze variations.

&&

.MARINE...Moderate to locally fresh easterly winds will
persist across the region, sustained by a surface ridge north of
the area. Widespread showers and thunderstorms associated to the
tropical wave that continues to move out of the area could result
in areas of stronger, gustier winds, which could deteriorate
conditions locally.

There is a moderate risk of rip currents for nearly all local
beaches.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
416 AM AST Sun Jul 16 2023

.SYNOPSIS...
Issued at 410 AM AST Sun Jul 16 2023

Expect another warm to hot day, especially across the urban and
coastal areas in Puerto Rico and the U.S. Virgin Islands. Pockets
of moisture will bring a few clouds and showers across the
windward sections, followed by afternoon convection across the
southwestern portions. The leading edge of a tropical wave will
bring showers and thunderstorms late tonight into Monday, and its
backside will produce a second round on Tuesday. A warm and dry
Saharan Air Layer (SAL) will promote above-normal low
temperatures, hazy skies, and limited rain activity Wednesday
through at least Friday. A summer-like pattern may evolve for the
following weekend.

&&

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

Passing showers moved across the islands overnight, leaving various
amounts of rain, mostly below half an inch as moist. Skies were
filled with cirrus clouds and the temperatures dropped into the low
70s for higher elevations and around 80F for coastal regions. Winds
were generally from the east-northeast between 10 and 15 mph.

For today, a typical pattern of passing showers and afternoon
convection is expected as patches of moist air moves across the
northern half of the region. Skies filled with cirrus clouds are
expected to linger through the early part of the day as upper-level
southwest flow pushes them over the islands. By the afternoon,
diurnal heating and local effects are likely to generate convection,
with the greatest rainfall anticipated across western Puerto Rico.
Eastern sections may receive a noticeable amount of rainfall as
well due to streamer development.

Overnight a tropical wave begins to enter the region with the axis
crossing during the morning hours. Increased precipitable water
values will bring a noticeable amount of showers and
thunderstorms and there will be a slight veering of the winds to
more of an east- southeast direction. Most of the activity will be
seen across the eastern half during the morning hours followed by
wide spread coverage including western Puerto Rico. There is a
possibly for isolated flooding for affected areas. The moisture
from the wave will linger throughout Tuesday, bringing more rounds
of showers and thunderstorms for the area until late Tuesday
night when the arrival of dry air with a Saharan Air Layer begins
a trend of hazy conditions.

&&

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

GFS indicated the presence of an African Easterly Wave
propagating into the Northeast Caribbean Wednesday through Friday.
In addition, NASA GEOS-5 Aerosol Optical Thickness (AOT)
suggested an extensive/dense Saharan Air Layer (SAL) through that
same period that may result in hazy skies across Puerto Rico and
the U.S. Virgin Islands, with the event's peak on Thursday.
Suspended Saharan Dust Particles may even last through Friday or
Saturday. Also, at the surface, a high pressure across the
Atlantic Ocean will tighten the local pressure gradient promoting
somewhat windy trades on Wednesday and possibly Thursday.
Regardless of the hot and dry air mass over the islands, the trade
winds may advect moisture pockets, producing passing showers
daily across the windward sections and local waters. Though near
to below-normal moisture will prevail through the long term,
extensive heating, local topography, and sea breezes may result in
periods of afternoon or evening thunderstorms across western P.R.
each day.

Several factors could play an active role in contributing to
above-normal high temperatures across the islands during the
second part of the work-week, among them a mid-level high pressure
promoting subsidence over the Northeast Caribbean, warmer-than-
normal low temperatures due to the SAL.

A summer weather pattern may hold for the next weekend, with the
typical trade wind showers followed by afternoon convection across
the western locations. &&

.AVIATION...
(06Z TAFS)
Issued at 410 AM AST Sun Jul 16 2023

Mainly VFR conditions will prevail across all terminals during
the next 24 hours. However, afternoon TSRA/SHRA could develop
across the interior and southwest portion of PR btwn 16/18-23z.
Winds will remain from the E-ENE, peaking around 14-20KT with
higher gusts and sea breeze variations. Lighter and variable winds
will return after 16/23Z. Starting around 17/04z, the arrival of
a tropical wave may bring TS to eastern terminals.

&&

.MARINE...
Issued at 410 AM AST Sun Jul 16 2023

Expect calm marine weather conditions with a pocket of moisture
resulting in passing showers across the local waters. Seas will
range at 3 to 5 feet across the offshore waters and less than 4
feet elsewhere. The winds will blow from the east to east-
northeast at 10 to 15 knots, but sea breeze may increase them
along the coastal areas.

The subtropical high pressure north of the region will promote
moderate to locally strong trade winds Monday through at least
Thursday, resulting in choppy seas across the islands. A tropical
wave will bring inclement weather Monday and Tuesday.

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Mon Jul 17 2023


.SYNOPSIS...
Issued at 500 AM AST Mon Jul 17 2023

A tropical wave will produce squally weather across the islands
today. Regardless of the expected weather heat index may exceed
100 degrees Fahrenheit during the peak of solar heating. The
unstable pattern will last through Tuesday afternoon when Saharan
Air Layer (SAL) will filter from the east around Tuesday evening.
The warm and dry SAL will promote above-normal low temperatures,
hazy skies, and limited rain activity from Wednesday through at
least Friday. A summer-like pattern may evolve for the following
weekend. A tropical wave/wind surge may approach the islands by
Monday next week.


&&

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

The arrival of a tropical wave brought scattered showers and
thunderstorms across the region with varied amounts of rainfall
across eastern and northern Puerto Rico. A stronger band with
thunderstorms is currently over northern central PR, with up to 2
inches fallen by around 4am AST. Cloudy skies prevailed through
the night and the temperatures dropped into the low 70s for higher
elevations and around 80F for coastal regions. Winds were
generally from the east around 10 mph.

For Today, a tropical wave that entered the region early this
morning will keep precipitable water values around 2 inches.
Dynamics of the wave will also cause an increase of instability,
combining with the available moisture to provide scattered to
numerous showers with isolated thunderstorms to form. Most of the
activity is expected across the wind exposed coastal regions until
mid-day when convection starts to bring showers across the interior
to western sections of Puerto Rico. Strong thunderstorms are
possible across northwestern Puerto Rico as the tropical wave brings
a veering of the lower-level winds to a east-southeasterly flow.
Streamer development off of the smaller islands and the mountains
may bring heavier rain for eastern Puerto Rico and the metro areas.
This activity may produce flooding, lightning, and strong winds.

The tropical wave will continue to pass through the region until
Tuesday afternoon when a thick Saharan Air Layer (SAL) approaches,
beginning a dry trend for the rest of the week. However, visibility
will be reduced and it will be hazy out. This appears to be the
stronger Saharan Dust event of the year so far with an aerosol
optical depth of over 0.2. Rainfall will be very limited during this
time with western Puerto Rico having the best chance each afternoon.

&&

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

GFS indicated, once again, suggested the propagation of the
African Easterly Wave across the Northeast Caribbean through
Friday. The peak of the SAL will be possible on Thursday, as the
maximum NASA GEOS-5 aerosol optical thickness (AOT) suggested. If
the solution is correct, Puerto Rico and the U.S. Virgin Islands
may observe hazy skies and reduced visibilities on Thursday.
Suspended Saharan Dust Particles will possibly last through Friday
or Saturday. Regardless of the hot and dry air mass over the
islands, the trade winds may advect moisture pockets, producing
passing showers daily across the windward sections and local
waters. Though near to below-normal moisture will prevail through
the long term, extensive heating, local topography, and sea
breezes may result in periods of afternoon or evening
thunderstorms across western P.R. each day.

Warmer-than-normal temperatures will be possible due to several
atmospheric factors across the islands during the second part of
the work week. Some of them are the mid-level high pressure
promoting subsidence over the Northeast Caribbean and warmer-than-
normal low temperatures that may be observed due to the SAL.

A summer weather pattern may hold for the next weekend, with the
typical trade wind showers followed by afternoon convection across
the western locations. A tropical wave or a wind surge could
approach the islands the following Monday, creating an unstable
weather pattern.

&&

.AVIATION...
(06Z TAFS)
Issued at 500 AM AST Mon Jul 17 2023

Mainly VFR conditions will prevail across all terminals. However,
a tropical wave will bring squally weather with TSRA/SHRA
affecting the local flying area, which could result in brief MVFR
conditions throughout the day, especially for TJSJ/TJBQ between
17/16z and 17/23z. Winds will be mainly from the ESE, peaking
around 15-20KT with higher gusts and sea breeze variations.
Lighter and variable winds will return after 17/22Z.

&&

.MARINE...
Issued at 500 AM AST Mon Jul 17 2023

Locally breezy conditions, with 10-20 knots winds and higher
gusts, will promote locally choppy marine conditions for small
craft. Small Craft operators should exercise caution over most
local waters.

A tropical wave will promote squally weather with strong showers
and thunderstorms throughout the day. Locally higher seas can be
found near stronger showers and thunderstorms. This wave will
maintain an unstable weather pattern through Tuesday. A
subtropical high pressure will promote fresh to locally strong
winds Wednesday and Thursday.

There is a moderate risk of rip currents the north and east-facing
beaches in Puerto Rico, as well as for Vieques, Culebra and the
U.S. Virgin Islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
502 AM AST Tue Jul 18 2023

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

.SYNOPSIS...
Issued at 442 AM AST Tue Jul 18 2023

The trailing moisture of the tropical wave will continue across
the region through this afternoon. Then an African Easterly Jet
will promote the advection of a Saharan Air Layer (SAL) into the
Northeast Caribbean as early as this afternoon into the weekend.
The warm and dry SAL will bring above-normal low temperatures,
hazy skies, and limited rain activity from Wednesday through at
least Saturday morning. A slight increase in tropical moisture may
result in a typical summer-like pattern during the weekend, with
strong thunderstorms developing during the afternoon. A tropical
wave/wind surge may approach the islands by Monday and Tuesday
next week.

&&

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

Light showers passed over the eastern half of the region with Aguas
Buenas, Humacao, Las Piedras, and Vieques receiving the highest
amounts of rain, about a quarter of an inch. Cloudy skies prevailed
through the night and the temperatures dropped into the low 70s for
higher elevations and around 80F for coastal regions. Winds were
generally from the east around 10 mph.

For today, a tropical wave continues to move across the region,
promoting an enhancement of showers with the best chance during the
early morning and late afternoon hours. However, an African Easterly
Jet enhanced by a mid-level high pressure north of the region is
causing the advection of a dry Saharan Air Layer (SAL) across the
tropical Atlantic and the western boundary of this airmass will
arrive to the islands this afternoon. A rapid drying trend is
forecast to occur as the increase of dust particulates will stunt
the development of showers. However, afternoon convection is still
likely to bring rain across western Puerto Rico and downwind of
the smaller islands in the east.

This SAL will persist across the region throughout the rest of the
week with Aerosol Optical Thickness values ranging between 0.2
and 0.4. This will result in hazy skies that will reduce
visibility. Limited rainfall is forecast on Wednesday and Thursday
due to this, with western Puerto Rico having the best chance
during the afternoon hours. Hot days are to be expected,
especially for urban coastal areas. However, breezy to locally
windy easterlies may bring occasional showers across the windward
sections.

&&

.LONG TERM...Friday through Tuesday.

NASA GEOS-5 aerosol optical thickness (AOT) suggested the
presence of enough suspended particles for hazy skies across the
region on Friday, with some traces remaining on Saturday and maybe
Sunday. These suspended particles will promote warmer-than-normal
low temperatures overnight by limiting nighttime cooling.
Therefore, observing above-normal max temperatures across the
islands (especially in the urban and coastal areas) from Friday
through Sunday will be possible, with heat index values between
100-112 degrees Fahrenheit.

Regardless of the near to below-normal moisture content, the trade
winds will bring pockets of moisture with clouds and rains across
the local waters and windward sections of PR and the USVI each
day. In addition, the trade wind cap could weaken during the
weekend, allowing the formation of isolated strong thunderstorms
due to the combination of sea breezes, local effects, diurnal
heating, and traces of Saharan Dust across the windward sections
of Puerto Rico.

A tropical wave could arrive the following Monday and Tuesday
across the U.S. Virgin Islands and Puerto Rico. This wave seems
disorganized due to a wind surge moving with it, which may result
in occasional squally weather.

&&

.AVIATION...
(06Z TAFS)
Issued at 442 AM AST Tue Jul 18 2023

Mainly VFR conditions will prevail for all terminals. Periods of
MVFR conditions are possible due to SH as a tropical wave
continues to pass. VCTS/VCSH are possible for JBQ between 18/16z
and 18/22z. ESE winds around 10 kt until 18/13z when 12 to 20 kt
possible with higher gusts and sea breeze variations. After
18/18z, Saharan Dust begins to arrive, reducing visibility due to
haze.

&&

.MARINE...
Issued at 442 AM AST Tue Jul 18 2023

Expect up to 6 feet over the offshore and coastal Atlantic
waters, up to 5 feet elsewhere. Fresh winds, with 10-20 knots
winds and higher gusts, will promote locally choppy marine
conditions for small craft. Small Craft operators should exercise
caution over most local waters.

Winds will become fresh to locally strong Wednesday through
Thursday. Suspended Saharan dust particles will increase from this
afternoon through Friday.

There is a moderate risk of rip currents the north and east-facing
beaches in Puerto Rico, as well as for Vieques, Culebra and the
U.S. Virgin Islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
445 AM AST Wed Jul 19 2023

.SYNOPSIS...Relatively drier air with suspended Saharan dust
particles will continue to dominate the region, supporting mainly
fair weather, warm-to-hot, and hazy conditions with limited shower
activity throughout the workweek. An increase in shower activity
is likely during the weekend into early next week with the
proximity of a mid-level trough and passage of a tropical wave.
Rains from the latter could result in elevated excessive rainfall
risks. Increasing winds will yield choppy to hazardous marine
conditions during the next few days.


&&

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

Light passing showers moved over eastern Puerto Rico overnight, with
the USVI remaining dry. Party cloudy to clear skies prevailed
through the night and the temperatures dropped into the low 70s for
higher elevations and around 80F for coastal regions. Winds were
generally from the east ranging from 10 to 15 mph with higher gusts.

A dense Saharan Air Layer (SAL) will continue to fill the region
with Saharan dust, causing hazy skies and poor visibility. Aerosol
Optical Depth values are estimated to be around 0.4 this morning,
with values remaining above 0.2 for the rest of the week. These
dusty conditions are being paired with strong easterly winds as high
pressure dominates north of the region from the surface to the
mid tropospheric levels. Wind speeds are expected to sustain above
15 mph for most of the region, with sea breeze enhancements
across western Puerto Rico possibly bringing sustained 20 mph for
the northwestern and southwestern coastlines, with stronger gusts.
The USVI is also likely to experience sustained strong winds.
Precipitable water values are dropping to values that are not
conducive for shower development. These clear, hazy skies will
allow afternoon temperature indices to rise into the 100s, even
above 110F at times. Due to this, there will be an Heat Advisory
for Puerto Rico's coastal sections of western, northwestern, and
north central, and also for Vieques and Culebra between 10 AM and
5 PM AST. An isolated thunderstorm is possible for western Puerto
Rico during the afternoon, yet nothing impressive is expected.

A similar pattern will continue through Friday as the robust SAL
moves across the Atlantic Basin. There may be a slight increase of
passing showers on Friday for eastern sections from the arrival of
patches of moisture, yet overall hot and hazy conditions are
forecast for the next few days.


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

Model guidance suggests a slightly wetter pattern during the
weekend into early next week, with the proximity of a mid-level
trough during the weekend and the passage of a tropical wave
between Monday and Tuesday. Increasing moisture levels between 1.6
and 1.8 inches are likely on Saturday into Sunday, but even
higher and above-normal moisture levels (2.0 inches or higher) are
possible between Monday afternoon and Tuesday morning. Although
both features will increase the chance of precipitation, the
resulting showers during the weekend will follow the seasonal
shower, characterized by the heaviest rains over western Puerto
Rico. In contrast, the wave's passage timing will lead to showers
with isolated thunderstorms favoring eastern Puerto Rico and the
local islands, where rainfall totals of 1-2 inches and possible
isolated higher amounts will likely result in urban and small
stream flooding. After that, the entrance of relatively drier air
will again lead to mainly fair weather conditions with limited
shower activity from Tuesday afternoon into Wednesday. Model
guidance also suggests that another tropical wave may stream
across the eastern Caribbean between Wednesday and Wednesday
night, but the bulk of the moisture should remain well south of
the local islands. Although previous model runs have suggested
tropical cyclone development from the latter, a typical model
guidance scenario during the peak of the hurricane season, the
National Hurricane Center has indicated that tropical cyclone
development is not expected during the next seven days.

At the surface, a high pressure system spreading across the
central Atlantic will maintain generally easterly winds at 10-20
mph, with some variations with the passage of tropical waves.
Daytime high temperatures, peaking at the upper 80s and the lower
90s across lower elevations and other urban areas, and near-normal
to above-normal moisture levels could yield elevated to
significant excessive heat hazard risks each day, with 102 degrees
or higher heat indices.


&&

.AVIATION...Mainly VFR conds will prevail at all terminals. SFC
wnds fm E btw 15- 18 kts with ocnly hir gusts btw 20-28 kts with
sea breeze variations...bcmg E around 12 kts aft 19/23Z. Extensive
area of Suspended dust particulates from a Saharan Air Layer will
continue to spread across the region bringing HZ across the
flying area. However no restrictions to flight VSBY and at local
terminals at this time. Possible iso TS near TJMZ after 19/16z.


&&

.MARINE...Recent CariCOOS buoy network observations around Puerto
Rico and the U.S. Virgin Islands indicated seas between 2 and 4
feet. Moderate to fresh easterly winds generated by a surface high
pressure across the central Atlantic will yield choppy seas up to
6 feet across most local waters, and small craft should exercise
caution. However, slightly higher winds of 20-25 knots will likely
generate locally hazardous marine conditions throughout the day,
mainly across the nearshore waters of southern, northern, and
southwestern Puerto Rico, offshore Atlantic and Caribbean waters,
and the Mona Passage, where Small Craft Advisories are in place.
For details, please refer to the Marine Weather Message (MWWSJU)
issued by the National Weather Service, San Juan office.

A moderate rip current risk continues for most northern, eastern,
and southern beaches of Puerto Rico, Vieques, Culebra, and the
U.S. Virgin Islands, where life-threatening rip currents are
possible.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
437 AM AST Thu Jul 20 2023

.SYNOPSIS...An extended drier air mass and Saharan Air Layer (SAL)
will dominate the local weather conditions through early Sunday.
These will limit serve to limit shower activity. A tropical wave
will bring increased moisture and shower activity during the early
part of the next workweek. Heat indexes equal to or greater than
108 degrees are possible today across northern and western Puerto
Rico, Vieques and Culebra, where Heat Advisories and an Excessive
Heat Warning (for north-central PR) will be in effect from 10 AM
to 5 PM AST.

&&

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

Fair weather with hazy skies and limited to no shower activity
prevailed during the overnight hours. A layer of upper-level cirrus
clouds and pockets of low-level cumulus clouds moved across the
local islands, generating partly to variable cloudy skies, though
mostly clear skies prevailed. Overnight low temperatures fell into
the upper 60s across higher elevations and lower 80s across lower
elevations. Winds were generally light and variable.

Today's hazard risks are excessive heat and wind hazard risks at
limited to elevated levels. Excessive heat hazard risks are likely
each day.

An extended drier air mass and Saharan Air Layer (SAL) will dominate
the local weather conditions through the short-term forecast period.
As this air mass moves further across the region, expect a decline
in precipitable water content (PWAT) into below-normal seasonal
levels (below 1.6 inches), with as low as 1.2 inches and nearly two
standard deviations below seasonal values expected by Friday. A
slight increase in PWAT is likely after that, reaching the lower end
of seasonal levels around 1.6 inches by Saturday afternoon into
Sunday night. Overall, fair weather conditions with hazy skies
should persist through Saturday.

Despite this dry scenario, showers with possible isolated
thunderstorm development are likely each day, mainly in the
afternoon across the far western sections of Puerto Rico, aided by
local effects and diurnal heating. Elsewhere, passing shower
activity is possible. As a mid-level trough, approaching the region
from the north-northeast, replaces a mid-level ridge, expect a
weakening of the trade wind cap inversion and a boost in moisture
levels, causing a slight increase in shower activity late Saturday
into Saturday night. Still, daily rainfall totals should be minimal,
remaining around a quarter of an inch as much.

A southward-migrating weak surface high pressure over the western
Atlantic will yield 10-20 mph east trades today, weakening to 10-15
mph and backing from the east-northeast and veering from the east-
southeast on Friday and Saturday, respectively. Breezy conditions,
with wind speeds peaking around 15-25 mph, are likely across coastal
areas of southern and northern Puerto Rico and the local islands
today. Daily maximum temperatures are forecast to peak in the upper
80s to the mid 90s across lower elevations and urban areas, where
heat indices of 102 degrees or higher are likely. Heat indexes equal
to or greater than 108 degrees are possible across northern and
western Puerto Rico, Vieques and Culebra, where Heat Advisories
and Excessive Heat Warnings are in effect today. Additional heat-
related advisories and warnings may be required each day.

&&

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

Model guidance suggests lingering Saharan Dust layer with an
aerosol optical depth of over 0.2 through early Sunday. Before
gradually diminishing into the workweek. Patches of moisture of
around 1.5 to 1.8 inches, in terms of Precipitable Water (PWAT)
should continue to reach the islands Sunday and Monday. A mid to
upper level trough will also be north-northeast of the islands to
start the period. The frequency of these patches of moisture will
increase as a moisture field related to a tropical wave approaches
the region, and ultimately increases PWAT to 2.0 inches or higher
by Monday evening through Tuesday morning to midday. Shower and
t-storm activity will increase at this time, particularly over
eastern Puerto Rico and the local islands. Urban and small stream
flooding are likely. Surface high pressure will promote generally
easterly winds at 10 to 20 mph, with sea breeze variations and
variations due to the tropical wave. High temperatures will reach
the upper 80s to lower 90s across lower elevations of the island.
High heat indices of 102 degrees Fahrenheit or higher are expected
each day.

Drier air will filter in for the rest of Tuesday and Wednesday.
Uncertainty in the forecast increases by this time as moisture and
overall weather conditions depend on a tropical wave with a low
chance of cyclonic development that is currently in the eastern
tropical Atlantic. As of now the GFS model is more aggressive in
a moisture increase across the region due to this system. Please
continue to monitor the latest products issued by the WFO in San
Juan and by the National Hurricane Center (NHC) for future
updates.

&&

.AVIATION...HZ from a persistent dense cloud of Saharan Dust
particles could result in brief MVFR conditions across all local
terminals, with reduced visibility equal to or below 6 SM. SHRA will
be limited, if any, with no impact on operations. Winds will be
mainly from the east at 5-15 knots with land breeze variations, but
light and variable at TJBQ and TJPS. Winds will then increase to 10-
20 knots with higher gusts and sea breeze variations after 20/13Z.

&&

.MARINE...Seas up to 5 feet with occasional seas up to 6 feet are
expected. However, a strong subtropical high pressure will
continue to promote fresh to locally strong easterly winds across
the region. Winds will gradually become moderate to locally fresh
by late tonight through the rest of the workweek. This will
result in choppy wind driven seas. Small Craft Should Exercise
Caution over sectors of the nearshore northern waters, Caribbean
waters, and the Mona Passage.

An overall dry airmass with an extensive area of Saharan dust
will linger across the region through early Sunday and therefore
aid in limiting shower development across the region waters.

There is a moderate risk of rip currents for the northern waters
of Puerto Rico from Aguadilla to around Las Croabas, Fajardo, as
well as for the eastern beaches of St. Croix and beaches of
Culebra. Low risk elsewhere.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Fri Jul 21 2023

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

.SYNOPSIS...
Issued at 403 AM AST Fri Jul 21 2023

Saharan dust that has suppressed most shower activity will begin
to diminish tonight and moisture will increase somewhat through
the weekend. A tropical wave with a weak low near 48 west will
slowly gain strength and resume its movement toward the west
northwest on Sunday. Some development is possible but it is too
early to know if it will develop into a tropical cyclone that
passes just south of the local area. Drier air is expected behind
the wave on Thursday and Friday.

&&

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

Fair weather conditions with hazy skies and limited shower activity
prevailed overnight. A few light showers moved over eastern Puerto
Rico, leaving minimal rainfall accumulations. Pockets of low-level
clouds briefly generated partly cloudy skies, though clear skies
prevailed across most land areas. Overnight low temperatures fell
into the upper 60s across higher elevations and lower 80s across
lower elevations. Winds were generally light and variable.

An extended drier air mass and Saharan Air Layer (SAL) will continue
to dominate the region, with a further decline of precipitable water
content (PWAT) to nearly two standard deviations below
climatological moisture levels (CMLs) and aerosol optical depth
(AOD) concentrations at 0.3-0.4 today into Saturday, respectively. A
slight increase in PWAT and decrease in SAL is likely from late
Saturday into Sunday, reaching CLMs around 1.6-1.8 inches and AOD
below 0.2 by Sunday morning onwards. A mid-level high pressure will
position over the region today, adding to the already hostile
environment for deep convective development with a strong trade wind
cap inversion. However, its influence will be brief, and the
trade wind cap will likely weaken as a weak mid-level trough moves
southwestward and north-northeast of the region, steering the
ridge further west during the weekend.

In this scenario, expect fair weather conditions with hazy skies
today into early Saturday. Still, overnight and early morning
passing showers may move over eastern Puerto Rico and the U.S.
Virgin Islands, and afternoon convection, if any, will be limited
and localized, producing minimal rainfall accumulations. After that,
reduced haziness is likely, and a slight increase in showers with
isolated thunderstorms is possible, mainly from afternoon convective
development. By Sunday afternoon, the resulting rainfall totals may
lead to limited flooding impacts, particularly across the
northwestern quadrant of Puerto Rico. Elsewhere, rainfall totals
should be minimal, with no significant outcomes.

A southward-migrating weak surface high pressure over the western
Atlantic will yield east to east-southeast winds at 10-15 mph, but
locally higher wind speeds are possible. An east-northeast mid-level
wind component will veer more from the east-southeast on Sunday,
causing a more northwestward distribution of the expected shower
activity. Daily maximum temperatures are forecast to peak in the
upper 80s to the mid 90s across lower elevations and urban areas,
where heat indices of 102 degrees or higher are likely. Heat indices
equal to or greater than 108 degrees are expected across northern
Puerto Rico and Culebra, where Heat Advisories are in effect today.
Additional heat-related advisories may be required on Saturday and
Sunday.

&&

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

The TUTT low to the northeast and the upper low in the central
Caribbean Sea will be forced apart by high pressure intruding from
the northwest over Puerto Rico and the U.S. Virgin Islands Monday
and Tuesday. However on Tuesday night and Wednesday the TUTT
reasserts itself from the northeast and travels across the area
from the east.

At the surface, weak low pressure near 13 north 49 west will
begin to strengthen. THe ECMWF carries it across the southern
Caribbean, but the GFS develops it into a tropical cyclone that
passes between Martinique and Dominica Tuesday night and just
south of the local area Wednesday and Wednesday night. This pulls
up considerable moisture from the southeast out of the
Intertropical Convergence Zone and into the area. The GFS has not
been particularly consistent with the track of this system which
has yet to develop, so the forecast for Wednesday and Thursday
is much more uncertain. Nevertheless, by Friday, moisture is
expected to diminish along with shower activity. Warmer
temperatures will also return to the north coast in east southeast
flow. Please continue to monitor the latest products issued by
the Weather Forecast Office in San Juan and by the National
Hurricane Center (NHC) for future updates.

&&

.AVIATION...
(06Z TAFS)
Issued at 403 AM AST Fri Jul 21 2023

HZ from a persistent dense cloud of Saharan Dust could result in
brief MVFR conds across all local terminals, with reduced
visibility around 6 SM. SHRA will be limited, if any, with no
significant impact on operations. Winds will remain light and
variable, increasing to 10-15 knots with higher gusts and sea
breeze variations after 21/13Z. Winds will become light and
variable after 21/22Z.

&&

.MARINE...
Issued at 403 AM AST Fri Jul 21 2023

At least through Tuesday winds will remain easterly 15 knots or
less except where winds close to Puerto Rico go around the
island. This will keep seas below 5 feet through Tuesday night.
Mariners should watch the forecast after Tuesday for the
possibility of tropical weather that could affect the area.