Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Thu May 2 2024

.SYNOPSIS...

Unstable conditions and increasing moisture levels will likely
persist during the rest of the workweek into the upcoming
weekend, as a mid to upper level trough lingers over the western
Atlantic and moisture from the Caribbean is steered by east to
southeast winds into the area. There is an elevated threat for
flooding across all the islands, particularly on Friday and
Saturday. The precipitable water content is forecast to remain at
normal to above normal levels through the long term period.


&&

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

Overnight, mostly calm weather conditions prevailed over land, with
a few showers developing along the eastern half of Puerto Rico and
the U.S. Virgin Islands. Nonetheless, showers and thunderstorms were
the dominant weather feature over the offshore Atlantic waters
through the night. The rainfall accumulations across the islands
were around half an inch. Minimum temperatures were in the low to
mid-70s across coastal areas and the mid-60s across the higher
terrains.

The inherited forecast remains unchanged as wet and unstable
conditions continue to evolve. This pattern, driven by an upper-
level trough approaching the area from the west, an induced surface
trough developing north of the region, and the introduction of
additional moisture from the Caribbean, will continue to enhance
shower and thunderstorm development across the local area. Later
today, expect more moisture to filter across the islands. At this
time, the forecast leans toward Friday into Saturday being the most
active days, with showers and thunderstorms being the dominating
features, particularly along the eastern half of Puerto Rico and the
U.S. Virgin Islands. By the end of the workweek, an upper-level
maxima will move across the islands with winds around 80 knots. On
Saturday, the yet maxima should remain to the north of the area.
Nonetheless, winds around 70 knots will still reach the region.
The Precipitable Water (PWAT) model guidance shows values above
normal climatological levels by the early part of the weekend. The
500 mb temperatures also suggest values around -8 degrees Celsius
on Saturday, meaning that there is an increase in the potential
for some isolated thunderstorm activity across Puerto Rico and the
U.S. Virgin Islands. As saturated soils prevail, any brief period
of heavy showers or persistent light rainfall could lead to urban
and small-stream flooding, localized flash flooding and
mudslides, particularly across the the interior, the eastern half
of Puerto Rico, and the U.S. Virgin Islands. We encourage
citizens and visitors to be aware of any additional updates in the
forecast.

Temperature-wise, they will stay in the upper 80s to low 90s along
the coastal/urban areas and in the upper 70s to low 80s along the
higher terrains.

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

Lingering moisture and the departing upper level-trough will continue
to promote shower and thunderstorm development on Sunday. At
lower-levels, a surface high pressure is expected to build over
the western Atlantic during the first part of the week. This will
promote moderate winds from the east to northeast through the long
term period. In addition, the remnants of the previous surface
trough to our north or just across the northeastern Caribbean are
expected to merge with a frontal boundary across the central
Atlantic and linger over the local area through at least Thursday.
Also, at upper levels, another trough will pass mainly to our
north from Tuesday onwards, maintaining unstable conditions in
general across the region. The highest precipitable water (PWAT)
values are expected during this period, with global guidance
suggesting between 2.10-2.25 inches of PWAT from Monday morning
through Thursday afternoon. Therefore, any period of moderate to
heavy showers across the islands would lead to quick urban and
river flooding, as well as mudslides in areas of steep terrain.
Residents and visitors are encourage to monitor the evolution of
the weather conditions during the next 5 to 7 days, and stay alert
for the issuance of any possible flood watch/warning products.


&&

.AVIATION...

(06z) TAFS

SHRA/TSRA were observed across the offshore Atlantic waters
overnight but dissipated around 02/07Z. VCTS could develop later
this afternoon near TJBQ/TJSJ/TIST/TISX, causing tempo MVFR to brief
IFR conds. ESE winds at 06-16 kt with stronger gusts near showers.


&&

.MARINE...

Light to moderate trades and a subsiding northerly swell will
promote seas up to 6 feet across the Atlantic waters, and portions
of the local passages today. Therefore, small craft operators
should exercise caution across these waters. Also, thunderstorm
development is likely across the Atlantic waters and the Mona
Passage. Lighter winds from the east to southeast and increasing
shower and thunderstorm activity is expected during the next
several days.


&&

.BEACH FORECAST...

A subsiding long period northerly swell will continue to promote a
high risk of rip currents along the north-facing beaches of Puerto
Rico, including Culebra today. A High Rip Current Risk (CFWSJU)
is in effect through late this afternoon.


&&

.HYDROLOGY...

An upper-level trough and an induced surface trough should promote
wet and unstable conditions throughout the weekend, particularly
on Friday and Saturday. There is an elevated flood threat due to
saturated soils across portions of the islands. Please refer to
the latest Hydrologic Outlook (ESFSJU) for more information.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
439 AM AST Fri May 3 2024

.SYNOPSIS...

A Flash Flood Watch is in effect for all Puerto Rico and the U.S.
Virgin Islands. Unstable conditions (due to an upper-level
trough approaching the area from the west and an induced surface
trough), increasing moisture, and lighter winds will promote
periods of showers and thunderstorms across the local islands,
particularly today through Saturday. The precipitable water
content is forecast to remain at normal to above normal levels
through the long term period, with a drying trend late next week.


&&

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

During the overnight hours, the eastern half of Puerto Rico
experienced some rainfall and thunderstorm activity. The highest
accumulations were observed in municipalities like Humacao, Naguabo,
and Yabucoa, with around 1 to 4 inches of rain. Fajardo, Luquillo,
and Ceiba also experienced rainfall rates of around 1 to 3 inches,
where Flood Advisories were issued. The island of St. Croix also
experienced some rainfall, but accumulations were not significant.
Overall, the eastern sections of Puerto Rico had an active night,
while the western sections experienced calm weather conditions.
Minimum temperatures were in the 70s to low 80s across coastal areas
and the upper 60s to low 70s across the mountainous areas.

The short-term forecast remains on track. An upper-level trough and
an induced surface trough will promote wet and unstable conditions
throughout the weekend, particularly today and Saturday. Tropical
moisture from the Caribbean will also move into the area, increasing
the chances for widespread rainfall and flooding through this
weekend. Showers and thunderstorms continue to be the dominating
weather features through at least Sunday, particularly along the
eastern half of Puerto Rico and the U.S. Virgin Islands. By the end
of the workweek into the weekend, an upper-level maxima will move
across the islands with winds around 70 knots. The Precipitable
Water (PWAT) model guidance shows values in the 75th percentile or
above normal climatological levels through the weekend. The 500 mb
temperatures also suggest values around -8 degrees Celsius, meaning
that there is an increase in the potential for some isolated
thunderstorm activity across Puerto Rico and the U.S. Virgin
Islands. As saturated soils prevail, any brief period of heavy
showers or persistent light rainfall could lead to urban and small-
stream flooding, localized flash flooding, and mudslides,
particularly across the interior, the eastern half of Puerto Rico,
and the U.S. Virgin Islands. A Flood Watch was issued through Sunday
afternoon. We encourage citizens and visitors to be aware of any
additional updates in the forecast.



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

Wet and unstable conditions should continue through midweek next
week. If the rainfall forecast materializes during the short-
term period, any additional shower activity over saturated soils
will further enhance the potential for flash flooding and
mudslides. Residents and visitors are encouraged to monitor the
evolution of the weather conditions over the long-term period.

A surface high pressure is expected to build over the western
Atlantic during the first part of the week. This will promote
moderate winds from the east to northeast through the end of the
workweek. In addition, the remnants of the previous surface trough
to our north or just across the northeastern Caribbean are
expected to merge with a frontal boundary across the central
Atlantic and linger over the local area through at least Thursday.
At upper levels, another trough will pass mainly to our north
from Tuesday through Thursday, maintaining unstable conditions
across the islands. The highest precipitable water (PWAT) values
are expected during this period, with global guidance suggesting
2.00-2.25 inches of PWAT. Daily rainfall amounts could range
between 1 and 3 inches, with the highest accumulations in diurnal
activity over portions of eastern, central, and western PR.

More stable conditions are forecast for Friday as a mid-to-upper
level ridge over the western Caribbean extends into the local
area, bringing drier air aloft and causing the PWAT to drop to
around 1.50 inches.


&&

.AVIATION...

(06z) TAFS

VRB weather conditions are fcst to persist throughout the period.
Expect VCTS to develop after 03/14Z at TJSJ/TIST/TISX and after
03/18Z at TJBQ/TJPS causing tempo MVFR to brief IFR conds. ESE winds
at 04-16 kt with higher gusts near heaviest showers.


&&

.MARINE...

A surface high pressure extending from the western to central
Atlantic will promote light to moderate trade winds across the
regional waters. Seas should remain between 2 and 5 feet during
the next few days, with the highest seas expected across the
offshore waters. An induced surface trough to our north will
yield lighter east to east- southeast winds and promote shower and
thunderstorm development across the area through early next week.


&&

.BEACH FORECAST...

Fading swell and lighter winds will promote mainly a low to
moderate risk of rip currents during the next several days.
However, flooding rains and thunderstorms are expected through
the weekend across the islands.


&&

.HYDROLOGY...

A Flash Flood Watch remains in effect for all of PR and the USVI
from this morning through Sunday afternoon. Rainfall totals
between 3 and 6 inches and locally higher are possible through the
weekend. Please refer to the latest Flash Flood Watch (FFASJU)
for more information.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
536 AM AST Sat May 4 2024

.SYNOPSIS...

A Flash Flood Watch remains in effect for all Puerto Rico and the
U.S. Virgin Islands. Unstable conditions are expected to continue
this afternoon influenced by an upper-level trough, an induced
surface trough, and above-normal tropical moisture. In addition,
lighter winds will continue to promote periods of heavy showers
and strong thunderstorms across the local islands. The precipitable
water content is forecast to remain above normal levels through
most of the forecast period, with a drying trend anticipated late
next week.

&&

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

Thunderstorms and rain showers affected the US Virgin Islands
overnight, where a Flood Advisory (St Thomas/St John) and a Flash
Flood Warning (St Croix) were in effect overnight, saturating the
soils. Additionally, yesterday's rain activity saturated Puerto Rico
soils even more, and most of the rivers' streamflows continued much
above normal. Minimum temperatures were between 70 and 75 F along
the coast and between 60 and 65 near mountains and valleys. Winds
were calm to light and variable, promoting the development of land
breeze.

The weather pattern remains unstable and moist today, influenced by
an upper-level trough with a jet stream, an induced surface trough,
and above-normal tropical moisture pooling over the Northeast
Caribbean. While we expect a brief respite in rain activity during
the morning hours, the afternoon could see the formation of intense
thunderstorms, particularly over and north of the Cordillera
Central. Additionally, due to the dangerous river and soil status,
these environmental and atmospheric conditions underscore the need
to keep the Flood Watch in effect. Thus, we encourage everyone to
stay updated and vigilant about the weather conditions. Be prepared
for any changes.

A surface high pressure will move into the Western Atlantic
promoting that above normal moisture pools over Puerto Rico and the
U.S. Virgin Islands Sunday and Monday. Regardless that we can
anticipate periods without rain, the pattern will continue favorable
for the formation of rain and afternoon thunderstorms. Given the
significant amount of rain that we has received during the past
week, any particular moderate to locally heavy rain will aggravate
the potential to observe flooding and landslides (along steep
terrains) across the islands.

&&

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

By the beginning of the long-term period, the latest models are
suggesting a surface high pressure dominating over the western to
central Atlantic. In our area, this will promote light to moderate
winds from the east to northeast through the end of the workweek.
At upper levels, another trough will pass mainly to our north from
Tuesday through Thursday, maintaining unstable conditions across
the islands. A moist airmass should linger over the local as
moisture from the tropics will be pulled and join the remnants of
the previous surface trough. The Precipitable Water (PWAT) model
guidance shows values above normal climatological levels through
at least next Thursday; values around 2.00-2.25 inches.
Consequently, the wet pattern is expected to continue with daily
showers and possible isolated thunderstorms development. Shower
activity should develop during the morning hours over portions of
eastern PR and USVI, followed by afternoon convection over central
and western PR resulting in greater accumulations. We encourage
residents and visitors to remain weather-aware because any additional
shower activity over saturated soils will further enhance the
potential for flash flooding and mudslides. On the bright side,
more stable conditions are forecast by the end of the week into
the weekend as a mid-level ridge over the western Caribbean
extends into the local area, bringing a drier air mass into the
region resulting in more seasonal PWAT values and decreasing the
potential for showers development.

&&

.AVIATION...
(06Z TAFS)

Expect an unstable weather pattern, promoting the formation of
SHRA/TSRA, especially in the afternoon and evening. VCTS/TSRA may
continue to promote tempo MVFR to brief IFR conditions btwn 04/16-
23z near JSJ/JBQ/IST. Expect SSE/SE winds at 5 to 15 kt with sea
breeze variations (aft 04/13z) and stronger gusts near heaviest
SHRA/TSRA activity.

&&

.MARINE...

An induced surface trough moving across our area will yield
lighter winds, while promoting shower and thunderstorm development
through early next week. A surface high pressure extending from
the western to central Atlantic will promote light to moderate
trade winds across the regional waters through the forecast
period.

&&

.BEACH FORECAST...

A fading northerly swell and light winds will promote low to
moderate risk of rip currents during the next several days.
However, flooding rains and thunderstorms are expected through the
weekend across the islands.

&&

.HYDROLOGY...

A Flash Flood Watch remains in effect for all of PR and the USVI
through Sunday afternoon. Estimated rainfall totals around 3 to 5
inches in portions of Puerto Rico and 2 to 4 inches in Saint
Croix, US Virgin Islands. Additional rainfall accumulations are
expected to range from 2 to 4 inches. Please refer to the latest
Flash Flood Watch (FFASJU) for more information.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
521 AM AST Sun May 5 2024

SYNOPSIS...

A Flood Watch remains in effect for all Puerto Rico and the U.S.
Virgin Islands until this afternoon, with saturated soils, any
brief period of heavy showers or persistent light rain could lead
to urban and small-stream flooding, localized flash flooding, and
debris flow. The precipitable water content is forecast to remain
above normal levels through at least next Thursday, with a drying
trend anticipated by the end of the week.

&&

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

Calm weather conditions prevailed overnight with little to no rain
and a few low-level clouds. GOES-E detected a cloud deck between the
mid and upper levels, with a more significant presence near St.
Croix. Shower activity began to increase offshore across the
Atlantic Waters early this morning. Minimum temperatures have been
in the mid and upper 70s across most coastal sites and in the mid
and upper 60s along mountains and valleys.

The wet pattern, fueled by near to above-normal moisture, will
persist throughout the beginning of this week. MIMIC-TPW2 has
indicated a wet air mass with values between 1.80 and 2.00 inches,
lending further support to the GFS guidance. Later today, the GFS
guidance suggests the possibility of additional moisture being drawn
from the Eastern Caribbean south of us over the islands. The
National Blend of Models (NBM) suggests calm weather conditions
during the day, followed by an active afternoon and evening weather
pattern with showers and thunderstorms developing along the
Cordillera Central and north of it and near La Sierra de Luquillo,
as well as downwind from St Croix. Environmental conditions remain
conducive to flash flooding, river flooding, mudslides, and
landslides, a potential risk due to last week's weather conditions.
Therefore, it's crucial to stay vigilant and prepared for any
additional. St Thomas and southern Puerto Rico, both, has the
potential to observe a mixture of sunshine and clouds with little to
no rain most of the day.

An upper-level trough will swing by Monday and Tuesday, which
combined with the lingering above-normal moisture content will
promote the continuation of the wet and unstable pattern. Although
we can anticipate periods of no rain, due to the much above normal
river streamflows, and saturated soils, any period of moderate to
locally heavy rain could result in dangerous flooding problems as
well as sudden mudslides/landslides. Currently, the most active
day, based on the latest model guidance could be expected between
late Monday into Tuesday.

&&

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

By Wednesday, the latest models agree that a surface high pressure
will remain dominating over the central Atlantic promoting light
to moderate northeasterly to easterly winds through the end of the
workweek. At upper levels, another trough should move through
Thursday, maintaining unstable conditions across the islands with
a moist airmass lingering over the local area. The Precipitable
Water (PWAT) models are suggesting above-normal climatological
levels through at least next Thursday; with values around 1.90-2.20
inches. Consequently, the wet pattern is expected to continue by
midweek with showers and possible isolated thunderstorms
development each afternoon. We encourage residents and visitors
to remain weather-aware because any additional shower activity
over saturated soils will further enhance the potential for flash
flooding and mudslides.

Thursday night into the weekend, a mid to upper-level ridge
extends into the local area from the western Caribbean, bringing a
drier airmass into the upper levels with PWAT values around normal
levels, decreasing the potential for shower development. By Saturday,
the high pressure over the north-central Atlantic will promote
southeasterly winds across our area. As a result, diurnal and
local effects can promote afternoon showers and thunderstorm
activity mainly across the interior to western Puerto Rico, but
not expecting significant accumulations since moisture levels
should be lower. In addition, a Saharan Air Layer should be near
the area, but the greater concentrations should stay over the
Caribbean waters.

In summary, expect unstable weather conditions to continue by the
middle of the week, then more stable conditions are anticipated
from Friday onwards.

&&

.AVIATION...
(06Z TAFS)

VFR conditions will prevail this morning, but the unstable
weather pattern will promote the formation of SHRA/TSRA,
especially in the afternoon and evening. VCTS/TSRA may continue to
promote tempo MVFR to brief IFR conditions btwn 05/16-23z near
JSJ/JBQ/ISX. Surface winds will shift from the ENE aft 05/12Z,
ranging between 10-15 kt, but locally higher due to sea breeze
variations and in/near TSRA.

&&

.MARINE...

A surface high pressure extending from the western to central
Atlantic will promote light to moderate easterly winds through the
forecast period. A northeasterly swell is expected to spread
across the local waters by Tuesday and gradually increase seas to
around 5 to 6 feet through the end of the week. Remnant moisture
from the induced surface trough located to our east will continue
to promote shower and isolated thunderstorms development across
the regional waters during the afternoon and evening for the next
several days.

&&

.BEACH FORECAST...

Low risk of rip currents should continue through Monday, then
becoming moderate from Tuesday onwards. However, life-threatening
rip currents often occur in the vicinity of jetties, and piers.

&&

.HYDROLOGY...

A Flood Watch remains in effect for all of PR and the USVI through
this afternoon. Please refer to the latest Flood Watch (FFASJU)
for more information.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
402 AM AST Mon May 6 2024

.SYNOPSIS...

A surface high-pressure building across the Western Atlantic will
promote the pooling of above-normal moisture content across the
Northeast Caribbean through at least mid-week. A trough between
the mid and upper levels will swing by late tonight through
Thursday, enhancing the dynamic aloft. Due to the soil saturation
across the islands and the much above-normal streamflows along
PR's principal rivers, afternoon and evening convection may result
in sudden urban and small stream flooding each day. Additionally,
due to the high moisture content, places without no rain may
experience above-normal heat indices (thus apparent temperatures)
surpassing 100 degrees Fahrenheit.

Pulses of northeasterly swells propagating across the Atlantic
Ocean will arrive from Tuesday night through the weekend, likely
causing life-threatening rip currents along the north—and east-
facing beaches in PR and the USVI.

&&

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

Last night, showers developed mostly in north-central Puerto Rico
resulting in several Flood Advisories for municipalities in that
area. Radar estimates recorded around 2 to 3 inches of rain in
municipalities such as Arecibo, Barceloneta, Manati, Vega Baja, and
Toa Alta, among others. Approximately, up to 5 inches of rain fell
on northern coastal waters. Later, additional showers developed over
the eastern sector of Puerto Rico leaving between 1 to 2 inches of
rain. During the overnight period, calmer weather conditions
dominated across most of the island and the USVI, while showers
continued over Atlantic waters and eastern PR. Minimum temperatures
have been in the mid and upper 70s across most coastal sites and in
the mid and upper 60s along mountains and valleys.

The wet pattern will persist during this period. Plenty of moisture
will remain present over the next couple of days with above than
normal values of precipitable water (around 2.0 to 2.4 inches).
Based on the latest weather models, a high pressure establishing
over the western Atlantic will maintain light to moderate winds
mainly from the east at the surface, while an upper-level trough
will move through mid-week keeping wet and unstable conditions
continuing across our region. For today, the National Blend of
Models (NBM) suggests some shower activity could begin earlier
across eastern sectors of Puerto Rico, and then concentrate over the
interior and west central areas later. During the afternoons from
today through midweek, showers and isolated thunderstorms are
possible across most of the area within mainland Puerto Rico, but
southern areas should receive minimal to no rain at all. Moisture
levels are expected to peak next Tuesday, which models guidance
suggests may be the most active day of the short-term period. Please
note that due to saturated soils and much above normal river
streamflows, any period of moderate to locally heavy rain could lead
to dangerous flooding problems, as well as sudden mudslides and
landslides in areas of steep terrain. For that reason, we encourage
residents and visitors to remain weather-aware and informed about
these potential hazards and to monitor the forecast for future
updates.

Temperature-wise, they will stay in the upper 80s to low 90s along
the coastal/urban areas and in the upper 70s to low 80s along the
higher terrains. Combined with above-than-normal moisture, heat
indices may reach 100ºF across coastal/urban areas of Puerto Rico
and the U.S. Virgin Islands through the period.

.LONG TERM...Thursday through Monday

The mid to upper-level trough will continue moving away from the
region on Thursday, leaving the islands in a less favorable
position for organized convection. A mid to upper-level ridge will
try to build over the Northeast Caribbean Friday into the
weekend, which may further decrease local instability, potentially
bringing relief from the current weather conditions.

At the surface, GFS Total Precipitable Water guidance suggests
values returning to the typical values for this time of year from
Thursday onward. However, patches of increased moisture may arrive
occasionally. Regardless of whether we observe a mixture of
sunshine and clouds each day, strong afternoon convection could
develop due to local effects and sea breeze variations each day.
Additionally, due to the atypical high sea surface temperature,
the advection of a cooler air mass across the warmer waters may
result in frequent nighttime showers, reaching the windward
sections each night.

Temperature-wise, combining high moisture content with the
typical upper 80s to low 90s maximum air temperatures will result
in heat indices between 100-107 Fahrenheit or even higher,
especially during the daily maximum heating, across the USVI and
PR's urban and coastal areas where no significant rain is
observed.


&&

.AVIATION...
(06Z TAFS)

Mostly VFR conditions expected for most TAF terminals this morning
but VCSH should continue near TJSJ. The potential for VCTS and
showers are expected to increase around 14Z across USVI and after 16-
18Z in PR sites. VCTS/TSRA may continue to promote tempo MVFR to
brief IFR conditions later today. E to NE surface winds at 10-15
kts, and then becoming lighter and more variable at night.

&&

.MARINE...

A surface high-pressure building across the Western Atlantic will
push a surface trough further east away from the Northeast
Caribbean, promoting light to moderate trade winds. From late
Tuesday night onward, pulses of northeasterly swell will spread
across the regional waters. Afternoon convection may result in
strong thunderstorms across the coastal sections of north and
western PR each day.

&&

.BEACH FORECAST...

Expect seas to be around 3 feet or less across most of the local
beaches in the Atlantic, mainly from the east at 6 to 7 seconds,
while across the Caribbean, seas will range up to 2 feet from the
east at 6 seconds. Therefore, we expect a slight risk of strong
rip currents through mid-week.

Pulses of northeast swells, with wave periods of 10 to 13 seconds,
will increase the risk of rip currents between moderate and high
from late Tuesday into next weekend across the north and east-
facing beaches of PR and the USVI.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
446 AM AST Tue May 7 2024

.SYNOPSIS...

A wet and unstable weather pattern will continue across the
islands through at least mid-week due to an approaching mid- to
upper-level trough and abundant tropical moisture. The risk of
flooding will be elevated to locally significant due to already
saturated soil and much above-normal river levels. Temperature-
wise, due to the high moisture content, places without rain
activity may experience above-normal heat indices (thus apparent
temperatures) that surpass 100 degrees Fahrenheit.

Pulses of northeasterly swells propagating across the Atlantic
Ocean will arrive later tonight through the weekend, likely
causing life-threatening rip currents along the north—and east-
facing beaches in PR and the USVI.

&&

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

During the overnight hours, calm conditions have persisted over
most of the islands, however, showers have continued over local
waters. Some of those showers moved inland, especially over
eastern PR, Vieques, and San Juan vicinity, leaving approximately
1.0 to 1.5 inches of additional rain. Flood warnings remain in
effect along the Rio Cibuco, Rio Grande de Manati, and Rio
Guanajibo. We urge citizens to stay informed and not cross flooded
roads.

The forecast remains on track during the short-term period. A
wetter and more unstable pattern will persist with an elevated to
significant risk of flooding through midweek. Plenty of moisture
will remain present today and Wednesday with above than normal
values of precipitable water (around 2.0 to 2.4 inches). Based on
the latest weather models, high pressure over the western Atlantic
will maintain light to moderate easterly to northeasterly winds at
the surface. On the other hand, an upper-level trough will continue
to swing by our region through mid-week, keeping favorable
conditions aloft for the wet and unstable pattern to prevail this
afternoon into Wednesday. In addition, mid-level temperatures will
drop to around -8 degrees Celsius tonight enhancing the potential
for thunderstorm development.

Please note that due to already saturated soils and much above
normal river streamflows, any brief period of moderate to locally
heavy rain or persistent light rainfall could lead to dangerous
flooding problems, as well as sudden mudslides and landslides in
areas of steep terrain. For that reason, we encourage residents and
visitors to remain weather-aware and informed about these potential
hazards. Be alert for any possible issuance of flood products.

During tonight's period, expect a similar scenario in comparison
with last night, where shower and isolated thunderstorm activity
shift to the local waters and coastal areas of northern and eastern
Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands. By
Thursday, improving weather conditions are expected to develop as
the mid to upper-level trough moves away and a mid-to-upper-level
ridge builds and dominates across the region. Moisture levels should
drop to near-normal levels, resulting in a more stable atmosphere
and hopefully a break from the current conditions. Any afternoon
convection that could develop will be due to local effects and sea
breeze variations.

Temperature-wise, hot and humid conditions will prevail throughout
the period. Daytime highs in the upper 80s to low 90s along the
coastal/urban areas and lows in the upper 70s to low 80s along the
higher terrains. Combined with above-than-normal moisture, heat
indices may reach 100ºF or higher across coastal areas of Puerto
Rico as well as the rest of the islands through the period.

.LONG TERM...Friday through Tuesday

Model guidance suggests a mid- to upper-level ridge is trying to
build over the Northeast Caribbean Friday into the weekend,
promoting stable conditions and potentially bringing relief from
the current weather conditions.

Once again, GFS Total Precipitable Water guidance suggests
returning the climatological values for this time of year, with
the advection of occasional patches of increased moisture.
Combining high moisture content with the typical upper 80s to low
90s maximum air temperatures will result in heat indices between
100-107 Fahrenheit or even higher, especially during the daily
maximum heating, across the USVI and PR's urban and coastal areas
where no significant rain is observed.

Although we expect variable weather conditions with a mixture of
sunshine/clear skies and clouds each day, local effects and sea
breeze fluctuations may promote strong afternoon convection each
day. Furthermore, the advection of a cooler air mass across the
above-normal warmer sea surface temperature may result in frequent
nighttime showers, affecting the windward sections and local
waters each night.

The NASA aerosol optical thickness (AOT) guidance suggests the
arrival of an air mass with possible African Dust Particles by the
upcoming weekend, which may extend into next week.

&&

.AVIATION...
(06Z TAFS)

Mostly VFR conditions expected this morning but VCSH should continue
near TJSJ and USVI sites. The potential for VCTS and showers are
expected to increase during the afternoon across all sites.
VCTS/TSRA may continue to promote tempo MVFR to brief IFR conditions
later today. Higher winds and reduced vis near thunderstorms. E
to NE surface winds at 10-15 kts, and then becoming lighter and
more variable at night.

&&

.MARINE...

The surface high-pressure building north of the islands from the
Western to Central Atlantic will maintain a shearline south of the
islands across the Northeast Caribbean, promoting light to
moderate trade winds. Pulses of northeasterly swell will spread
across the regional waters later tonight onward. Unsettled weather
conditions due to strong thunderstorms are likely (especially
during the afternoon and evening) today and tomorrow.

&&

.BEACH FORECAST...

Expect increasing seas of 3 to 4 feet across most of the local
beaches in the Atlantic, mainly from the northeast, at 6 to 8
seconds. Across the Caribbean, seas will range around 2 feet from
the east to southeast at 6 to 8 seconds. Therefore, we expect the
risk of rip currents to increase to moderate today.

Pulses of northeast swells, with wave periods of 10 to 13 seconds,
will increase the risk of rip currents to moderate from late
tonight into next weekend across the north and east-facing beaches
of PR and the USVI. There is still a possibility of a high risk of
rip currents during that period; it's crucial to monitor the beach
forecast for possible updates to the expected conditions as the
coastal hazards can change rapidly.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
439 AM AST Wed May 8 2024

.SYNOPSIS...

The continuation of a wet and unstable weather pattern will
maintain the risk of flooding between elevated and significant
across the islands through this evening and may extend into
Thursday evening. It's crucial to stay informed and take necessary
precautions during this time. Although a mid- to upper-level
ridge will slowly build across the Northeast Caribbean, afternoon
convection will develop daily from Friday onward, mainly across
the interior and western PR and downwind from the USVI. A drier
air mass with possible African dust particles will arrive by the
weekend and may extend into next week.

Pulses of northeasterly swells propagating across the Atlantic
Ocean will promote a moderate risk of observing strong rip
currents along the north and east-facing beaches of PR and the US
Virgin Islands throughout the week.

&&

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

During the overnight period, doppler radar indicated showers and
isolated thunderstorms affecting the local waters and eastern Puerto
Rico, where approximately 2 to 3 inches of additional rainfall fell.
A Flood Advisory was issued for municipalities such as Fajardo,
Loiza, Luquillo, and Rio Grande. The Flood Warnings for area rivers
(Rio Grande de Manati, Rio Grande de Arecibo, Rio Cibuco, and Rio De
La Plata en Toa Alta) continue in effect throughout this morning
because sensors reports indicated the rivers are receding but still
elevated.

The forecast remains on track. A high pressure moving eastward
across the central Atlantic will maintain light to moderate easterly
winds at the surface through Thursday, while an upper-level trough
swing across the area. Above-normal precipitable water values,
ranging from 2.0 to 2.2 inches, accompanied by an upper-level trough
moving from the west and below-normal mid-level temperatures (around
-8 degrees Celsius) will maintain instability across the area,
elevated risk of thunderstorms and an elevated to significant risk
of flooding today and Thursday. As a result, a wet and unstable
pattern is expected to persist through late tonight and may extend
into Thursday afternoon based on the latest guidance. At this time,
even though precipitable water values should start to return to near
normal, models are still showing and keeping some decent rain
accumulations for Thursday afternoon. Given the current situation of
saturated soils and significantly elevated river streamflows,
additional flooding and sudden mudslides cannot be ruled out of the
forecast tomorrow. Any additional moderate to locally heavy rain
poses a risk of dangerous flooding, including sudden mudslides and
landslides in steep terrain areas. Additionally, thunderstorms may
produce strong winds capable of causing tree falls, power line
disruptions, and movement of unsecured objects. Therefore, residents
and visitors are encouraged to stay weather-aware and informed about
these potential hazards and closely monitor the forecast for any
updates.

By Friday, the high pressure moves further east into the Atlantic,
changing our surface wind flow to a more southerly/southeasterly
one. Model guidance suggests a mid-to-upper-level ridge building
across the area, temperatures aloft warm up a bit, and precipitable
water values drop to near-normal levels potentially bringing relief
from the current weather conditions. Any strong afternoon convection
that develops across the interior and western sector of Puerto Rico
should be by local effects and sea breeze fluctuations. Under this
pattern, a warming trend will be likely with heat indices between
100-107 Fahrenheit or even higher, especially during the daily
maximum heating, across the USVI and PR's urban and coastal areas.
In summary, more stable conditions are anticipated by the end of the
week, but warmer temperatures and heat indices are very likely.

.LONG TERM...Saturday through Wednesday

Model guidance still suggests a mid- to upper-level ridge trying
to build over the Northeast Caribbean from Saturday onward,
promoting stable conditions and potentially bringing relief from
the current weather conditions.

Model guidance also suggests a return to the climatological
moisture values over the region, with the advection of occasional
patches of enhanced moisture. Additionally, we are more likely to
observe variable weather conditions with a mixture of
sunshine/clear skies and clouds daily. Also, the NASA aerosol
optical thickness (AOT) guidance one more time suggests the
arrival of an air mass with possible African dust particles by the
upcoming weekend, which may extend into next week. Meanwhile,
intense heating, local effects, and sea breeze fluctuations each
day will drive strong afternoon convection. Furthermore, the
above-normal warmer sea surface temperature will also enhance the
typical nighttime warm air convection. These frequent nighttime
showers could affect the windward sections and local waters of the
U.S. Virgin Islands and Puerto Rico.

Combining high moisture content with the typical upper 80s to low
90s maximum air temperatures will result in heat indices between
100-107 Fahrenheit or even higher, especially during the daily
maximum heating, across the USVI and PR's urban and coastal areas
where no significant rain is observed.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions expected the rest of the overnight period.
However, SHRA/TSRA developing across the local waters may cause
-RA/VCSH across the area terminals. The potential for VCTS and
showers are expected to increase around 16/18Z across all sites.
Tempo MVFR to brief IFR conds are possible btw 08/16z-22z at
TJPS/TJSJ.

&&

.MARINE...

The subtropical surface high-pressure north of the islands
extending from the Western to Central Atlantic promotes light to
moderate east to northeast winds through Friday. Winds will then
turn from the east to east-southeast from the weekend into early
next week. Pulses of northeasterly swell will spread across the
Atlantic waters and Caribbean Passages through the weekend.
Unstable weather conditions will promote strong thunderstorms,
especially during the afternoon and evening.

&&

.BEACH FORECAST...

Expect increasing seas of 4 to 5 feet across most of the local
beaches in the Atlantic, mainly from the northeast, at 6 to 11
seconds. Seas will then increase at 4 to 6 feet with a wave period
of 11-12 seconds, mainly from the northeast later this evening.
Therefore, we expect a moderate risk of strong rip currents from
today to Friday across the north and east-facing beaches in the
north and east-facing beaches in PR/USVI. Across the Caribbean,
seas will range around 2 feet from the east to southeast at 6 to 8
seconds.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
518 AM AST Thu May 9 2024

.SYNOPSIS...Elevated Rainfall Risk continues today across the
islands due to afternoon convection enhanced by unstable
conditions and saturated soils. Yesterday's flooding event
continues to affect areas near Rio Guanajibo and Rio Culebrinas,
where Flood Warnings are in effect. Patchy fog is present across
areas of the interior. Weather conditions are expected to improve
in the coming days as the upper-level trough moves away and the
amount of precipitable water decreases to more typical levels.
However, conditions will remain marginally conducive to deep
convective development and susceptible diurnal heating influence.
Winds are forecast to become more southerly into the weekend, this
can a promote limited to locally elevated heat risk during the
weekend.

&&

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

Overnight satellite and radar observations indicated clear skies
over most land areas, with only a line of showers affecting eastern
Puerto Rico after midnight, resulting in minimal rainfall
accumulation. Despite the rain-free conditions, excessive runoff
from previous heavy rainfall kept Rio Guanajibo and Rio Culebrinas
above flood stage, prompting continued Flood Warnings for Cabo Rojo,
Hormigueros, Mayaguez, Aguada, Aguadilla, Moca, and San Sebastian.
Coastal locations experienced low temperatures in the low-to-mid-
70s, while higher elevations recorded temperatures in the mid-to-
upper 60s. Winds were generally light and variable.

Weather conditions are expected to improve in the coming days as the
upper-level trough moves away and the amount of precipitable water
decreases to more typical levels, around 1.8 to 2.0 inches. However,
conditions will remain marginally conducive to deep convective
development and susceptible diurnal heating influence. Although
widespread rains are no longer expected, scattered to locally
numerous showers and isolated thunderstorms are likely during
afternoons. Winds at the 700 mbar layer will shift from the west
today to the southwest by Friday and Saturday, maintaining a
tendency for showers to spread eastward to northeastward. In
contrast, low-level winds will persist at light to moderate speeds
of 5-15 mph, with easterly winds veering to south-southeasterly by
Saturday. This southerly tendency will contribute to warmer
temperatures and, thus, fueling heightened convective development,
especially over the weekend. Given the weak steering flow, moderate
to locally heavy rains from slow-moving showers may lead to
additional flooding threats, exacerbate existing flood situations,
and disrupt ongoing recovery efforts. Coastal/Urban areas may
experience temperatures in the upper 80s to mid 90s, while higher
terrains will experience highs in the upper 70s to mid 80s. With
high moisture levels, heat indices could surpass 102 degrees
Fahrenheit each day, with the potential for 108-110 degrees in
localized areas during the weekend.

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

Model guidance continues to suggest a mid- to upper-level ridge
building over the region to start the long term forecast period.
This feature could potentially promote more typical weather.
Precipitable water (PWAT) values are forecast to generally stay at
normal values, 1.5 to 2.0 inches, through the period as patches of
moisture continue to advect into the region. Sunday appears to be
the wettest day, with high end normal values to possibly above
normal values under southerly steering flow. With veering flow
backing to become more easterly by Monday afternoon, PWAT values
should remain at normal values through the rest of the period. Some
exceptions could be during afternoon convection, were PWAT can
increase, and on Wednesday morning, when model guidance suggests a
patch of drier air reaching the islands. Most available moisture
will reach up to 700 mb on Sunday morning before gradually
decreasing and only reaching up to 850 mb by Wednesday. The NASA
aerosol optical thickness (AOT) guidance continues to suggests the
presence of an air mass with Saharan dust particles to start the
period, which may extend into next week. Diurnal heating, local
effects and sea breeze variations will continue to promote up to
strong afternoon convection, steered by southerly winds on Sunday
and by more easterly winds for the rest of the period, promoting
convective activity mainly over sectors of the interior to western
half of the Puerto Rico and downwind of the local islands. Above-
normal sea surface temperatures can also promote nighttime showers
across windward sectors of the islands. The Galvez-Davidson Index
(GDI) suggest that Sunday will be the day with stronger afternoon
convective activity. Limited Heat Risk (heat indices from 102 to 107
degrees Fahrenheit) or even higher, especially during the daily
maximum heating, will persists across several lower elevation
sectors of the islands where no significant rain is observed.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions expected the rest of the overnight period.
However, afternoon SHRA/TSRA developing may promote VCSH/VCTS and,
thus, MVFR conditions, across most PR terminals between 09/16-23Z.
The potential for VCTS and showers are expected to increase around
16/18Z across all sites. Light and variable low-level winds,
increasing to 10-15 knots and influenced by sea breeze variations
between 09/14-22Z. Light and variable winds will return after 09/22Z.

&&

.MARINE...

A surface high-pressure north of the islands will yield easterly
winds through tomorrow, becoming more east-southeast during the
weekend. Pulses of northeasterly swell will spread across the
Atlantic waters and Caribbean Passages. Weather conditions across the
local waters are expected to gradually improve towards the end of
the workweek.

&&

.BEACH FORECAST...

There is a Moderate Risk of Rip Currents today for the northern
coastline of Puerto Rico, from Rincon to Fajardo, as well as for
Culebra, northern and western St. Thomas and eastern St. Croix.
There is a low risk elsewhere. Areas with moderate risk of rip
currents are forecast to gradually diminish tomorrow and an
overall low risk of rip currents is forecast to start the weekend.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
452 AM AST Fri May 10 2024

.SYNOPSIS...Elevated to locally Significant Rainfall Risk today
across the region due to afternoon convection enhanced by
unstable conditions and saturated soils. Yesterday's flooding
event continues to affect areas near Rio Grande de Manati, Rio
Cibuco, Rio Guanajibo and Rio Culebrinas, where Flood Warnings
are in effect. Patchy fog continues to affect areas of the
interior and light to moderate showers are currently affecting
eastern municipalities. The upper-level trough will continue to
weaken as it moves away from the region. Simultaneously, an upper-
level jet streak will spread across the northeastern Caribbean,
further enabling the development of deep convection through at
least Saturday night. A shift towards southerly winds this weekend
will prompt a warmer trend, further boosting afternoon convective
development. This can also promote limited to locally elevated
heat risk as we head into the weekend. Lingering saharan dust will
persist through at least early next week.

&&

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

Overnight satellite and radar observations have indicated the
development of showers over the local waters, with some moving
across the local islands and eastern Puerto Rico. Rainfall totals
have peaked at approximately 2 inches between Naguabo and Ceiba,
and around a quarter of an inch in St Croix. Despite clearer
conditions elsewhere, excessive runoff from previous heavy
rainfall has caused Rio Guanajibo, Rio Culebrinas, Rio Grande de
Manati, and Rio Cibuco to remain above the action to flood stage,
leading to continued Flood Warnings for neighboring
municipalities. From around 8 PM AST, satellite-derived data has
also indicated persistent foggy conditions extending from Orocovis
east-southeastward to Cayey. Coastal areas have experienced
temperatures ranging from the mid-70s to around 80 degrees, while
higher elevations have recorded temperatures in the mid-to-upper
60s. Winds have generally been light and variable, influenced by
land breezes.

The upper-level trough will continue to weaken as it lifts out to
the northeast, away from the region. Simultaneously, an upper-level
jet streak (70-90 knots) will spread across the northeastern
Caribbean, further enabling the development of deep convection
through at least Saturday night, with 500 mbar temperatures falling
to around -7 degrees by Saturday evening. Consequently, there is a
potential for isolated to locally scattered thunderstorms, as
indicated by the Galvez-Davison Index. According to the latest model
guidance, the most active period is expected during peak diurnal
heating this afternoon and again on Saturday afternoon.
Nevertheless, anticipate prolonged stormy conditions over the local
waters tonight and again over Saturday night, with some activity
affecting Puerto Rico's eastern half, Vieques, Culebra, and the U.S.
Virgin Islands. Although conditions may become less favorable for
convective development on Sunday, afternoon showers with isolated
thunderstorm development are still likely.

Surface winds will persist at light to moderate speeds, ranging from
5 to 15 mph, with easterly winds gradually transitioning to south-
southeast by Saturday and Sunday. This shift towards southerly winds
will prompt a warmer trend, further boosting afternoon convective
development. As the prevailing steering flow influences the
distribution of showers, anticipate the highest rainfall totals to
transition from the interior today to the northern sections of
Puerto Rico during the weekend. Furthermore, a southwesterly
component at the 700 mbar level will likely drive some afternoon
activity towards the San Juan metropolitan area and northeastern
Puerto Rico. Given the persistently weak steering flow, moderate to
locally heavy rainfall from slow-moving showers over already
saturated soils will sustain an elevated flooding risk, exacerbating
existing flood situations, and disrupting ongoing recovery and
cleanup efforts.

Temperatures may soar into the upper 80s to mid-90s across coastal
and other urban areas, while higher elevations could see highs in
the upper 70s to mid-80s. With plenty of moisture across the region,
heat indices could exceed 102 degrees Fahrenheit, potentially
reaching around 108-110 degrees in localized coastal areas of
northern Puerto Rico over the weekend.

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

No major changes to the long term forecast. Model guidance to
suggest a mid- to upper-level ridge building over the region by the
start of the workweek, potentially promoting more typical weather
with afternoon convection due to diurnal and local effects.
Precipitable water (PWAT) values are forecast to generally stay
at normal values between 1.5 to near 2.0 inches, through the
workweek as patches of moisture advect into the region. ESE winds
to start the period will back to become more easterly by late
Monday through the rest of the period as a surface high moves into
the western Atlantic. Most available moisture should reach up to
850 to 800 mb for the period. The NASA aerosol optical thickness
(AOT) guidance continues to suggests the presence of an air mass
with Saharan dust particles lingering to start the period, this
could extend through the period. Limited Heat Risk (heat indices
from 102 to 107 degrees Fahrenheit) or even higher, especially
during the daily maximum heating, will persists across several
lower elevation sectors of the islands where no significant rain
is observed. This diurnal heating, local effects and sea breeze
variations will continue to promote up to strong afternoon
convection, steered by east-southeast winds on Monday, backing to
become more easterly winds for the rest of the workweek, promoting
convective activity mainly over sectors of the interior to
western half of the Puerto Rico and downwind of the local islands.
Above-normal sea surface temperatures can also promote nighttime
showers across windward sectors of the islands, patchy fog also
forecast for areas of the interior during the early morning hours.


&&

.AVIATION...
(06Z TAFS)

SHRA may result in reduced visibilities and lower ceilings across
the USVI terminals and TJSJ through 10/14Z. Afternoon SHRA/TSRA
development will prompt VCSH/VCTS and, thus, possible MVFR
conditions, mainly across PR terminals between 10/16-22Z. The
potential for VCTS and showers will likely increase after 10/22Z for
the USVI and TJSJ sites. Light and variable low-level winds,
increasing to 10-15 knots and influenced by sea breeze variations
between 10/14-22Z. Light and variable winds will return after 10/22Z.

&&

.MARINE...A surface high-pressure across the Atlantic will yield light
to moderate easterly winds through today, becoming more east to
southeast during the weekend. Pulses of northeasterly swell will
continue to spread across the Atlantic waters and Caribbean
Passages for the next few days. Weather conditions across the
local waters are expected to gradually improve towards the
weekend.

&&

.BEACH FORECAST...A High Rip Current risk is in effect for the
northern coastline of Puerto Rico, from Aguadilla to Fajardo,
through this afternoon. A Moderate Risk of Rip Currents is in
effect today for Aguada, Rincon, Culebra and most of the northern
USVI's coastlines and for the eastern half of St. Croix. Low risk
elsewhere. The risk of rip currents are forecast to gradually
diminish and an overall low risk of rip currents is forecast next
weekend.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
521 AM AST Sat May 11 2024

.SYNOPSIS...

Elevated to locally Significant Rainfall Risk today across the
region. A distant mid-to- upper level through will remain close
enough to keep marginally unstable conditions during the weekend.
In the meantime, an associated upper-level jet streak will
continue to spread across the northeastern Caribbean, further
enabling the development of deep convection through late tonight.
With southerly winds and available moisture, heat indices could
exceed 102 degrees Fahrenheit, potentially reaching around 108-110
degrees in localized coastal areas of northern Puerto Rico over
the weekend. Lingering saharan dust will persist through at least
early next week.

&&

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

Overnight observations from satellite and radar have indicated
showers and isolated thunderstorms development over the local
waters, with some moving across the local islands and reaching
southern and eastern Puerto Rico. Rainfall amounts have peaked at
approximately 2 to 3 inches in areas spanning from Yauco to Ponce in
the south, Patillas to Maunabo in the southeast, and Ceiba to
Fajardo in the east, prompting Flood Advisories in those regions.
Coastal areas have registered temperatures ranging from the mid-70s
to around 80 degrees Fahrenheit, while higher elevations have
registered temperatures in the mid-60s to around 70 degrees
Fahrenheit. Winds have generally remained light and variable,
influenced by land breezes.

A distant mid-to-upper level through will remain close enough to
keep marginally unstable conditions during the weekend. In the
meantime, an associated upper-level jet streak (70-90 knots) will
continue to spread across the northeastern Caribbean, further
enabling the development of deep convection through late tonight,
with 500 mbar temperatures falling to around -7 degrees.
Consequently, there is a potential for thunderstorm development, as
indicated by the Galvez-Davison Index. According to the latest model
guidance, the most active period is expected during peak diurnal
heating this afternoon. Stormy conditions will continue through late
tonight over the local waters, with some activity affecting Puerto
Rico's eastern half, Vieques, Culebra, and the U.S. Virgin Islands.

With precipitable water levels around normal to above-normal values
of approximately 1.9-2.1 inches across the region, this overall
scenario will likely heighten the risk of excessive rainfall today.
Surface south to southeast winds at 5 to 15 mph and a consistent
southwesterly component at the 700 mbar level suggest that afternoon
activity will likely spread northward, including portions of the San
Juan metropolitan area and northeastern Puerto Rico. Additionally,
southerly winds will contribute to a warmer trend today and Sunday,
further fostering afternoon convective development. Due to the
persistently weak steering flow, expect moderate to locally heavy
rainfall from slow-moving showers, mainly over already saturated
soils, posing an elevated to locally significant flooding risk. This
heightened risk could worsen flood situations and disrupt recovery
and cleanup efforts.

Despite conditions becoming less conducive to convective development
and a gradual decrease in moisture, afternoon showers with isolated
thunderstorms on Sunday and Monday are still likely. However, the
risk of excessive flooding will diminish over the next few days.
Wind speeds will persist at 5-15 mph, with a gradual shift in the
general steering flow to the east by Sunday night into Monday. This
shift will relocate the areas with the potential for the highest
rainfall totals from northern sections of Puerto Rico on Sunday to
western sections early next week.

Temperatures may soar along the coast and urban areas into the upper
80s to mid-90s, while higher elevations could see highs in the upper
70s to mid-80s. With abundant moisture across the region, heat
indices could exceed 102 degrees Fahrenheit, potentially reaching
around 108-110 degrees in localized coastal areas of northern Puerto
Rico over the weekend.

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

The NASA aerosol optical thickness (AOT) guidance continues
to suggest lingering Saharan dust particles to start the period.
Model guidance to suggest a mid- to upper-level ridge affecting
the region by the start of the period, promoting more typical
weather with afternoon convection due to diurnal and local
effects. However, model guidance suggests an upper trough closing
in on the islands from the northwest by Friday and moving across
through Saturday. Precipitable water (PWAT) values are forecast to
generally stay at normal values, between 1.5 to near 2.0 inches,
through the workweek as patches of moisture advect into the
region, Friday and Saturday look to be the wettest days with high
end normal values to possibly above normal values. Light to
moderate easterlies are forecast through the period as a surface
high moves into the western Atlantic. Most available moisture
should reach up to 850 to 800 mb for the period, with model
guidance suggesting additional available moisture through the mid
levels by Friday and Saturday. Limited Heat Risk (heat indices
from 102 to 107 degrees Fahrenheit) or even higher, especially
during the daily maximum heating, will persist across several
lower elevation sectors of the islands where no significant rain
is observed. This diurnal heating, local effects and sea breeze
variations will continue to promote up to strong afternoon
convection, steered by easterly winds and possibly enhanced by the
upper through on Friday and Saturday. This will promote
convective activity mainly over sectors of the interior to western
half of the Puerto Rico and downwind of the local islands. Above-
normal sea surface temperatures can also promote nighttime
showers across windward sectors of the islands, patchy fog is also
forecast for areas of the interior during the early morning
hours.

&&

.AVIATION...
(06Z TAFS)

SHRA/TSRA will result in lower ceilings and reduced visibilities
at TJBQ, where TEMPO MVFR conditions conditions through 11/06Z.
Afternoon SHRA/TSRA will likely bring brief MVFR conditions across
northern PR and USVI terminals from 11/16Z onward. Light and
variable surface winds becoming southerly with sea breeze
variations at 5-10 knots after 11/14Z.


&&

.MARINE...

A surface high pressure across the central Atlantic and a building
low in the western Atlantic will allow southeasterly winds through
the weekend. Weak pulses of northeasterly swell will begin to fade
across the Atlantic waters and Caribbean Passages over the next
few days. Strong showers and thunderstorms over the waters can
result in locally higher seas and gusty winds.


&&

.BEACH FORECAST...

Weak pulses of northeasterly swell will begin to fade across the
Atlantic waters and Caribbean Passages over the next few days. Low
Risk of Rip Currents today and possibly through the weekend.
However, they occur most often at low spots or breaks in the
sandbar and in the vicinity of structures such as groins, jetties
and piers.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
501 AM AST Sun May 12 2024

.SYNOPSIS...

A more seasonal weather pattern is forecast through the period.
A limited to elevated excessive rainfall risk is present today
for mainly the NW quadrant of Puerto Rico during the afternoon
under south to southeast winds. As winds become more easterly, the
focus of the afternoon activity during the workweek will shift to
portions of the western interior to western Puerto Rico.
Temperatures along the coast and in urban areas today can reach
the upper 80s to mid 90s today, with heat indices that may exceed
102 degrees Fahrenheit (localized areas possibly experiencing
108-110 degrees).

&&

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

Overnight observations from satellite and radar have indicated
isolated showers and an isolated thunderstorm over the local waters.
Some moved across southern Puerto Rico and Saint Croix, leaving
minimal rainfall accumulations. Most showers dissipated after 2 AM
AST, with skies clearing afterward. However, from around 11 PM AST,
satellite-derived data has also indicated persistent foggy
conditions along the Cordillera Central eastward to Sierra de Cayey.
Overnight low temperatures ranged from the upper 60s across higher
elevations to the lower 80s across eastern Puerto Rico and the local
islands. Winds were generally light and variable, influenced by land
breezes.

During the short-term forecast period, expect a typical seasonal
weather pattern characterized by significant rainfall accumulation
resulting from afternoon convective activity. With an upper-level
jet streak (70-90 knots) situated to the north, today's conditions
will remain marginally favorable, with diurnal heating being the
primary triggering factor. Moisture levels are expected to remain
high, with precipitable water values ranging from 1.7 to 1.9 inches,
leading to scattered showers and isolated thunderstorm development,
particularly after the peak diurnal heating around 2 PM AST. Surface
south-to-southeast winds at 5 to 15 mph and south-southwesterly
winds at the 700 mbar level suggest that today's activity will
spread northward again, affecting municipalities of the northern
half of Puerto Rico, including portions of the San Juan metropolitan
area and northeastern Puerto Rico. Due to the persistent weak
steering flow, the expected moderate to locally heavy rainfall from
slow-moving showers will likely pose a limited to elevated excessive
rainfall hazard risk today, with the highest risk likely across the
northwestern quadrant of Puerto Rico.

As the jet streak gradually moves northward early next week, a mid-
level high pressure will extend into the northeastern Caribbean,
establishing a trade wind cap inversion and bringing drier
conditions aloft. Consequently, precipitable water values will
decrease, eventually falling to the lower end of typical thresholds
as moisture becomes confined below the 700 mb layers. Despite
conditions becoming less conducive to convective development and a
gradual decrease in moisture, afternoon showers with possible
isolated thunderstorms on Monday and Tuesday are still likely, with
less area coverage and intensity each passing day, possibly
generating limited flooding risk. As winds become more from the
easterly and increase to 10-15 mph early next week, the focus of the
afternoon activity will shift to portions of the western interior to
western Puerto Rico.

Due to consistent southerly winds, temperatures along the coast and
in urban areas today may rise to the upper 80s to mid-90s, while
higher elevations could experience highs in the upper 70s to mid-
80s. With abundant moisture throughout the region, heat indices may
exceed 102 degrees Fahrenheit, with localized areas possibly
experiencing 108-110 degrees. Although slightly cooler temperatures
are likely early next week, warmer conditions will persist.
Lingering saharan dust is present in the area.

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

Precipitable water (PWAT) values should remain at normal values for
this time of the year, between 1.5 to near 2.0 inches, during the
period, as patches of moisture advect into the region. Model
guidance seems to have backed off on moisture significantly
increasing by the end of the workweek, now showing only patches of
high end seasonal PWAT reaching the islands. For at least the start
of the period, NASA aerosol optical thickness (AOT) suggests
lingering Saharan dust particles to start the period. A mid-level
ridge will exert its influence over the region to start the
period, promoting more typical weather with afternoon convection
due to diurnal and local effects. Model guidance now suggests an
upper trough moving north of the islands from the northwest by
Friday and Saturday. Most available moisture should reach up to
850 to 800 mb for the period. Light to moderate easterlies are
forecast through the period as a surface high moves into the
western to central Atlantic. Limited to possibly elevated Heat
Risk, especially during the daily maximum heating, will persist
across several lower elevation sectors of the islands where no
significant rain is observed. This diurnal heating, along with
local effects and sea breeze convergence will continue to promote
up to strong afternoon convection, steered by easterly winds. This
will promote convective activity mainly over sectors of the
interior to western half of the Puerto Rico and downwind of the
local islands. Early morning and overnight passing showers are
also forecast across windward sectors of the islands along with
patchy fog over areas of the interior.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions across most local terminals during the next 24
hours. Afternoon SHRA/TSRA may result in brief MVFR conditions,
with periods of reduced visibility and lower ceilings, across
TJSJ/TJBQ between 12/16-23Z. VCSH may also affect TJSJ and USVI
terminals after 12/23Z, with minimal impacts to operations. Light to
calm and variable winds increasing to 8-12 knots and turning more
from the east with sea breeze variations between 12/13-23Z.

&&

.MARINE...

Seas will be favorable for small craft through at least Thursday. A
surface high pressure across the central Atlantic and a low in the
western Atlantic will allow southeasterly winds to prevail today. As
another high moves into the western Atlantic winds will be light to
moderate easterlies through the rest of the period. A weak northerly
swell will continue to fade across the Atlantic waters and passages.
Afternoon convective activity could move from the islands towards
nearby waters.

&&

.BEACH FORECAST...

Weak pulses of northeasterly swell will continue to fade across
the Atlantic waters and Caribbean Passages. Low Risk of Rip
Currents today and tonight. However, they occur most often at low
spots or breaks in the sandbar and in the vicinity of structures
such as groins, jetties and piers.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
441 AM AST Mon May 13 2024

.SYNOPSIS...
Stable conditions during the morning hours and a southeasterly
component in the wind flow will promote warmer conditions across
the northern coastal areas of Puerto Rico. Warmer conditions are
forecast to begin around 10 AM, which will be more significant for
the coastal areas. Given that, a heat advisory was issued for the
northern coastal municipalities. Residents are urged to stay
hydrated and follow the local law enforcement recommendations.
Typical weather is forecast for the short term, with mostly stable
weather conditions in the morning, followed by afternoon showers
across mountain sections. An upper-level trough is forecast to
increase shower activity late in the upcoming weekend.

&&

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

Overnight observations from satellite and radar have indicated
mainly clear to partly cloudy skies, with a few isolated showers
remaining over the local waters. From around 11 PM AST and
continuing through the night, satellite-derived data indicated
persistent foggy conditions along the Sierra Cayey and Sierra
Luquillo. Overnight low temperatures ranged from the upper 60s
across higher elevations to the lower 80s across northeastern Puerto
Rico and the local islands. Winds were generally light and variable,
influenced by land breezes.

Expect drier-than-normal weather conditions during the short-term
forecast period, with heightened rains favoring a typical seasonal
pattern each afternoon. As the jet streak moves northward and away
from the area, a mid-level high pressure system will start extending
into the northeastern Caribbean, gradually establishing a trade wind
cap inversion and enhancing drier air entrainment. Consequently,
anticipate a reduction in moisture levels, with precipitable water
values dropping from typical to below typical thresholds or from
approximately 1.8 inches to around 1.5 inches through Tuesday
evening, as moisture becomes confined below the 700 bar layers. From
Tuesday night onward, precipitable water values will rise again to
typical moisture levels of around 1.6-1.8 inches. Light
concentrations of Saharan dust will persist throughout the forecast
period.

Despite conditions becoming less conducive to convective development
and fluctuations in moisture levels, afternoon showers with possible
isolated thunderstorms are still probable, even during the driest
periods on Tuesday. As a result of diminishing area coverage and
intensity, the risk level for excessive rainfall hazards will
decrease from elevated today, with urban and small stream flooding
likely, to limited on Tuesday. While there is a limited risk on
Wednesday, the potential for flooding could increase with future
forecast updates as moisture levels return to normal thresholds. As
light winds shift from east-southeasterly today, afternoon activity
will concentrate on central to western sections of Puerto Rico.
However, as winds become more easterly and speeds increase to 10-15
mph on Tuesday and Wednesday, activity will likely focus on far
western sections of the island.

Due to a southeasterly component in the prevailing wind pattern,
temperatures along the coast and in urban areas today could reach
the upper 80s to mid-90s. Conversely, higher elevations might see
highs ranging from the upper 70s to mid-80s. With plenty of moisture
throughout the region, heat indices could surpass 102 degrees
Fahrenheit in most coastal and urban areas, with some sections
likely experiencing extended periods of 108 degrees or higher across
western, northern, and eastern Puerto Rico and Saint Croix.
Consequently, a Heat Advisory has been issued, effective from 10 AM
to 5 PM AST this afternoon. Although model guidance indicates
slightly cooler 925 mb temperatures in the following days, warmer
conditions will persist.


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

A typical weather pattern will be present for most of the long
term. On Thursday, at the surface, east-southeast winds promoted
from a surface ridge extending across all the central Atlantic
will continue to inject the islands with tropical moisture.
According to the late model guidance, PWAT values from Thursday to
Friday will remain near the climatological normals. Both model
guidances (GFS and ECMWF) at the upper levels agreed on an upper-
level trough just in the region. Although the present moisture
will keep high chances for general shower activity, the stability
aloft provided for the convergent side of the TUTT will permit
only localized showers resulting from the local and diurnal effect
across the interior sections, the San Juan metro area, and the
northwestern quadrant of Puerto Rico.

As the upper feature moves out, moisture availability will increase
even more by Saturday into Sunday when surface winds turn again
from the southeast in response to a building high pressure just
over the northwestern Atlantic. This influx of moisture and the
warm temperatures over the land areas in the afternoon hours will
enhance periods of moderate to heavy showers with isolated
thunderstorms. Given the moderate southeasterly wind pattern, the
showers will be mostly over the interior and northwestern
sections; according to the Galvez-Davison Index (GDI-GFS), the
shower activity is forecast to remain very localized.

Unfavorable weather conditions are forecast for the upcoming week
as upper-level conditions change. By late Sunday into Monday, an
upper-level trough will move just over the region, leading to
divergence aloft and colder temperatures at 500 MB, enhancing
vertical development for shower activity. Uncertainty remains
present due to the forecast period. However, the islands can
expect increased episodes of widespread shower activity in the
afternoon.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions across most local terminals during the next 24
hours. Afternoon SHRA/TSRA may result in brief MVFR conditions,
with periods of reduced visibility and lower ceilings, across
TJSJ/TJBQ between 13/16-23Z. Light to calm and variable winds
increasing to 8-12 knots and turning more from the east with sea
breeze variations between 13/13-23Z.


&&

.MARINE...
Surface high pressure extending over the northeastern Atlantic
into the Central Atlantic will continue to promote east-
southeasterly winds today. Therefore, winds will remain at 15
knots or less, with some gusty winds near the afternoon showers
across some coastal sections. Seas are forecast to remain up to 4
feet across most local waters and even lower across the coastal
areas. From late Tuesday night onward, pulses of northeasterly
swell will spread across the regional waters.Afternoon convection
may result in thunderstorms across the coastal sections of north
and western PR each day.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Tue May 14 2024

.SYNOPSIS...

Stable weather patterns will prevail for the next several days in
the morning hours, followed by afternoon convection each day
across the interior sections of the island. Clear to partly cloudy
skies in the morning will allow warmer temperatures, increasing
the heat indices across the northern sections. Although slightly
warmer, heat indices will fluctuate between 102 and 107 degrees
Fahrenheit. Therefore, residents should stay hydrated and tune for
further updates. A similar pattern is forecasted until Thursday
when surface winds will increase from the southeast. Instability
will be a defining factor for the upcoming workweek, increasing
the potential for shower development.

&&

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

Skies were mostly clear to partly cloudy overnight with isolated to
scattered passing showers noted over the offshore coastal waters,
and limited to no shower activity noted over land areas. Overnight
low temperatures were in the upper 70s to low 80s along the coastal
areas and near mid 60s to low 70s in higher elevations and valleys.
Surface winds were calm to light and variable.

Overall warm and mostly fair weather conditions are expected today
for much of Puerto Rico and the adjacent islands including the U.S.
Virgin Islands. Under a fairly light east southeast wind flow and
mostly sunny skies, daytime highs will reach the upper 80s to low
90s along the coastal areas with maximum heat indices to range
between 100 and 107 degrees particularly along the northwest to
north coastal areas and in urban areas of Puerto Rico including
Vieques, Culebra and portions of the U.S. Virgin Islands. Afternoon
showers and possibly an isolated thunderstorm or two cannot be ruled
out over portions of the central and west sections of Puerto Rico
with the chance of locally heavy rains, which may lead to ponding of
water on roads and in poorly drained areas and with the possibility
of minor urban and small stream flooding in isolated spots. Fewer
afternoon shower activity is expected elsewhere and only on the west-
end and downwind of the U.S. Virgin Islands.

For the rest of the short-term period, a somewhat drier trend and
more seasonal weather pattern is forecast as winds slightly increase
and become more east to northeast by Wednesday and Thursday. A mid-
to upper level high-pressure system will continue spread eastwards
across the region from the west and southwest Atlantic, while a
surface high pressure will build across the west Atlantic.
Consequently this will increase the trade wind cap inversion while
eroding low level moisture. Recent analysis and NASA aerosol optical
thickness continued to suggest only light concentrations of Saharan
dust to persist at least through Wednesday. Latest model guidance as
well as satellite derived analyses all suggest overall PWAT values
to continue to diminish and range between 1.4 and 1.7 inches for
today, then slightly increase to between 1.5-1.8 inches for the rest
of the period as winds become more easterly and slightly increase.

That said, although the overall synoptic conditions are forecast to
be less conducive for significant convective development, shower
development and possibly an isolated thunderstorm will remain
possible each afternoon especially over parts of the central
interior and west sections of Puerto Rico locally steered by the
east to northeast low level wind flow. Warm conditions and slightly
above normal temperatures are expected to continue for the next few
days with daytime temperatures peaking in the upper 80s to low 90s
along the coastal and urban areas. Residents and visitors to the
islands are urged to stay hydrated and limit direct sun exposure
when possible.

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

The long-term forecast remains on track. A broad surface high-
pressure extending from the north-central Atlantic into the
Caribbean will maintain the east-southeasterly wind flow across
the region. During the first section of the period, tropical
moisture dragged by the surface winds and some instability (lower
250 MB height) will trigger afternoon convection each day. An
induced surface trough will weaken the pressure gradient at the
north, resulting in southeasterly light to moderate winds. Surface
winds from the southeast will drive most of the showers across
Puerto Rico's interior and northwestern quadrant. The most
vigorous shower activity and the light steering flow would result
in enough rainfall accumulation to cause a minor flooding threat.
By Monday into Tuesday, mid to upper-level conditions change, as a
trough results in instability aloft and colder temperatures at the
500 MB level. According to the Galvez-Davison Index (GFS output),
there is a high probability of experiment-isolated thunderstorms,
especially in the afternoon hours each day. Given the expected
conditions, the flood threat is forecast for the last part of the
long-term.

&&

.AVIATION...(06Z TAFS)

VFR conds through the fcst prd. Isold-SCT SHRA mainly over the
regional waters and en route to the islands. Mstly SCT lyrs nr
FL028...FL050...FL250. Aftn SHRA/Psbl isold TSRA ovr ctrl and west
interior sections of PR fm 14/18-22Z with VCSH psbl at TJBQ/TJSJ til
23Z. Calm to lgt/vrb wnds will become mainly fm E around 10-13 kts
with ocnly hir gusts and sea breeze variations aft 14/14Z.

&&

.MARINE...

A surface high-pressure system over the western Atlantic will
continue to promote light to moderate easterly winds across the
region. These conditions will lead to tranquil marine conditions
for all the local waters, with seas up to 5 feet in the offshore
waters and up to 4 feet in the coastal waters. Winds will continue
from the east at 15 knots or less for the next several days,
becoming more from the southeast due to a surface high pressure in
the central Atlantic.Recent forecasts show tranquil marine
conditions with seas up to 4 feet and periods of 8 seconds.
Therefore, there is a low rip current risk for the next several
days across all the exposed coastal areas.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
519 AM AST Thu May 16 2024

.SYNOPSIS...
Surface high pressure ridge spread across the west central Atlantic
and weakly induced trough northeast of the region will maintain a
light east to northeast wind flow today. Passing showers steered by
this flow will reach the local waters and portions of the north and
east coastal areas from time to time during the early morning hours.
Afternoon shower development will be possible mainly across the
interior and western sections of Puerto Rico. Mostly fair weather
and sunny skies are forecast elsewhere. An increase in early
morning and afternoon shower activity is expected by Friday and
into the upcoming weekend due to better moisture transport and
instability aloft due to the proximity of a mid to upper-level
trough. Warm and humid conditions will continue for the next
several days especially with winds forecast to become more
southeasterly.

&&

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

Stable weather conditions prevailed during the night and early
morning hours. Around midnight, Radar Doppler showed a few passing
showers affecting the northeastern sections of Puerto Rico,
resulting in minimal rainfall accumulations. The rest of the area
and the U.S. Virgin Islands mainly observed clear skies and no
rainfall activity. Overnight temperatures were a little warmer,
especially across the coastal areas, ranging in the upper 70s to
lower 80s and mid-70s across the mountains.

The short-term forecast is still on track. A mid to upper-level
ridge will continue to result in drier air aloft and stability. At
the surface, a building high pressure over the central to
northeastern Atlantic will result in an east-southeasterly wind.
Embedded in this wind pattern, as shown by the GOES Satellite-
derived products, patches of moisture with PWAT near normals will
drive a convective pattern in the afternoon across the islands
today. Due to the more southerly surface wind change, shower
activity will concentrate across the interior and northwestern
quadrant of Puerto Rico. Elevated moisture levels and southeasterly
winds will enhance heat indices around 102-107 degrees Fahrenheit
across the northern coastal sections, resulting in a limited heat
threat for most coastal areas and some isolated areas with higher
heat indices near 108 degrees Fahrenheit.

Recent model guidelines and the Hi-res model show increased shower
activity from Friday to Saturday. This pattern will be mainly driven
by the favorable side of an upper-level trough sinking into the region,
positioning a regional zonal flow over the region. This instability
and the available moisture will enhance periods of strong showers
during the afternoon hours from Friday into Saturday. The bulk of
the showers should remain localized across the northwestern quadrant
and the San Juan metro area. A weakness in the pressure gradient
will result in lighter to moderate winds, affecting the movement
of afternoon showers. That said, for Friday into Saturday, the islands
can expect deteriorating weather in the afternoon.

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

A surface high pressure system extending from the central and
northeast Atlantic will maintain southeasterly winds across the
region during the initial phase of the period. These winds will
aid in transporting patches of tropical moisture to the region,
and therefore increase the likelihood of shower development each
day,but particularly in the afternoon. Most showers should be
focused across the interior and northwestern quadrant of PR and
and in isolated areas around the San Juan metro area. There will
be plenty of sunshine and hot and humid conditions through the
weekend and into early next week. These conditions will yield
increasing heat indices, posing a limited to elevated heat threat
for the northern coastal and urban areas of Puerto Rico and the
adjacent islands including the U.S. Virgin Islands.

Moisture convergence and instability is expected to gradually
increase by late Sunday and throughout the forecast period
as a deep layered trough is forecast to move across the western
Atlantic and become amplified west of the region while moving
eastward. Recent model guidance continued to suggest, the
strongest divergence and most favorable side of the deepening TUTT
(Tropical Upper Tropospheric Trough) and its associated jet
stream will reach the forecast area from Monday and continue to
affect the region through Thursday. With increasing instability
aloft along with colder temperatures and abundant tropical
moisture convergence,precipitable water (PWAT) values are forecast
to exceed the climatological normals by over 2 inches. Consequently,
a wet period is still forecast for the islands and coastal waters,
with the increasing probability of showers and thunderstorm development
with areas of widespread rains likely especially during the late morning
and afternoon hours. This so far anticipated periods of heavy rainfall
will increase the risk of urban and river flooding from Tuesday through
the rest of the period. Stay tuned as we will continue to monitor how
this unfolds and and make adjustments to the long term forecast if
needed.

&&

.AVIATION...
(06Z TAFS)

VFR conditions will prevail for all TAF sites during the period.
Winds will increase by 16/15Z from the east at 15 knots or less,
with sea breeze variation. SHRA and VCST are forecasted for the
mountain sections, resulting in lower ceilings, and VCTS and SHRA
across TJPS and TJBQ. Winds will decrease by 16/23Z, becoming
variable with land breeze variation.

&&

.MARINE...
A surface high pressure extending from the western Atlantic into
the Central Atlantic will continue to promote light to moderate
easterly winds across the region. With this pattern, seas will
remain up to 4 feet across all the local waters and passages.
These conditions will prevail across the local waters during the
period. Similar tranquil marine conditions are expected for the
coastal areas, where the risk for rip currents will remain low
for the next five days or so.

&&

.BEACH FORECAST...
There is a low rip current risk today across all area beaches of
Puerto Rico and the U.S. Virgin Islands. The risk will likely remain
low for the next several days. However, life-threatening rip currents
can often occur in the vicinity of groins, jetties and piers. In addition,
with possible heat indices between 102-107 degrees, along the local
beaches, heat exhaustion will be possible with prolonged exposure.
Stay hydrated!

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
454 AM AST Fri May 17 2024

.SYNOPSIS...
Surface high pressure spread across the central and northeast Atlantic
will maintain a light easterly wind flow becoming more southeasterly
later today an over the weekend. Passing showers will continue across
the local waters and reach portions of the north and east coastal
areas during the rest of the morning hours. Afternoon showers will
likely develop across the central interior and northwestern quadrant
of Puerto Rico. Mostly sunny and fair weather skies are forecast
elsewhere but few showers cannot be ruled out around the U.S. Virgin
Islands. Hot and humid conditions will continue through the weekend
but with another round of Saharan dust forecast to spread across the
region. The potential for afternoon shower development will however
continue in isolated areas each day.

&&

.SHORT TERM...Today through Sunday

Calm weather conditions prevailed during the night and early morning
hours. Doppler radar showed a few passing showers affecting the
local waters and streaming across the southeastern sections of
Puerto Rico, with most showers occurring from Patillas to Maunabo.
Since the shower activity was relatively shallow, rainfall
accumulations remained insignificant. Overnight temperatures were a
little warmer, especially across the coastal areas, ranging in the
upper 70s to lower 80s, and mid-70s across the mountains.

The short-term forecast remains on track. The interaction between
two surface high pressures, one in the central Atlantic and the
other over the western Atlantic, will continue to maintain a
southeasterly wind flow across the islands. As a result, patches of
tropical moisture will reach the islands daily. Although instability
will slightly increase as an upper-level trough moves eastward into
the area, the islands can expect an increase in afternoon shower
coverage today. According to high-resolution models and the NMB
model, the bulk of the showers today should be across the
northwestern sections of Puerto Rico and some interior areas.
Additionally, the southeasterly wind flow, combined with clear skies
and high water content, will increase heat index values, especially
across the northern-central coastal areas and most urban and coastal
regions. Residents and visitors can expect warm conditions with high
chances of precipitation.

According to recent model guidelines, the high-resolution model
continues to show increased shower activity for Saturday into
Sunday. As suggested yesterday, this pattern will mainly be driven
by the favorable side of an upper-level trough moving into the
region, positioning a zonal flow over the area. This instability and
the available moisture will enhance periods of strong showers during
the afternoon each day. Additionally, according to the NASA Goddard
Earth Observing System Model V5, a significant pulse of Saharan Air
Layer will filter into the region, resulting in hazy skies across
the islands. Given the expected conditions, the bulk of the showers
should remain localized across the northwestern quadrant and the San
Juan metro area, slightly limited by the presence of Saharan Dust on
Sunday. A weakness in the pressure gradient will result in lighter
to moderate winds, affecting the movement of afternoon showers.
Therefore, the island can experience minor flooding in urban areas,
including small streams and arroyos.

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

Surface high pressure system extending from the central and northeast
Atlantic will maintain southeasterly winds across the region during
the initial phase of the period. These winds will aid in transporting
patches of tropical moisture to the region, and therefore increase
the likelihood of shower development over land areas particularly
during the afternoon hours. Shower development should be focused
across portions of the interior and west to northwest sections of
Puerto Rico as well as in isolated areas in the San Juan metro.
Mostly sunny skies and hot an humid conditions will persist through
Monday. As a result these conditions will increasing maximum heat
indices, posing a limited to elevated heat threat especially for
the northern coastal and urban areas of Puerto Rico and the adjacent
islands including the U.S. Virgin Islands.

Recent model guidance although there is some discrepancy between
the them both point toward an increasing moist and unstable
weather pattern with increased low level moisture convergence and
instability aloft for most of the period. The GFS model guidance
continued to be the most aggressive and suggests a wetter pattern
during the period. It has so far initialized well with the
present and ongoing pattern and continued to suggest the formation
of a deep layered trough forecast to deepen and move across the
western Atlantic while becoming amplified west of the region while
moving eastward. So far the strongest divergence and most favorable
side of the trough and its associated jet max should reach the forecast
area by Tuesday and continue to affect the region through Thursday
and Friday. With increasing instability along with cooler advective
temperatures aloft and abundant tropical moisture convergence, the
forecast layered precipitable water (PWAT) values are still expected
to exceed 2 inches during the latter part of the period. Consequently,
this wet and unstable period is forecast for the region, with the
moderate to high probability of showers and thunderstorm development
with areas of widespread rains likely, especially during the overnight
and afternoon hours. The anticipated period of excessive and heavy
rainfall will therefore increase the risk of urban and river flooding
especially from Tuesday onwards with the most favorable impacts being
Wednesday through Thursday but activity could continue thorough the
end of the work week. Stay tuned and be prepared, as we will continue
to monitor how this pattern unfolds and make the necessary adjustments
to the long term forecast.

&&

.AVIATION...
(06Z TAFS)

VFR conditions will prevail at all TAF sites during the period.
Winds will increase by 16/15Z from the E-SE at 15 knots, with sea
breeze variations. SHRA and VCTS are forecasted for the mountain
areas, resulting in lower ceilings and VCTS and SHRA across TJPS and
TJBQ. Winds will decrease by 17/23Z, becoming variable with land
breeze variations.

&&

.MARINE...
A surface high pressure across the central and northeast Atlantic
will result in light to moderate east to southeast through the
weekend. Overall, tranquil marine conditions are forecast throughout
the forecast period. Afternoon showers and isolated thunderstorms
could develop and move from western Puerto Rico into the coastal
waters each day.

&&

.BEACH FORECAST...
There is a low rip current risk today across all area beaches of
Puerto Rico and the U.S. Virgin Islands. The risk will likely
remain low through the weekend. However, life-threatening rip
currents can often occur in the vicinity of groins, jetties and
piers. In addition, with possible maximum heat indices between
102-107 degrees or higher, along the local beaches, heat
exhaustion will be likely with prolonged exposure. Stay hydrated!