Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
339 AM AST Tue Sep 2 2025

.KEY MESSAGES...

* An increase in low-level moisture and warmer temperatures will
exacerbate heat indices in north-central areas and southern coastal
plains. Given the expected conditions, an extreme heat warning
is in effect from 10 AM to 5 PM AST today.

* For today, there is a elevated flood and lightning threat
along the northwestern Puerto Rico from 12 to 5 PM AST.

* For the upcoming weekend, a tropical wave, combined with an upper-
level trough, will increase the potential for showers and
thunderstorms, increasing the flood threat.

* For the U.S. Virgin Islands, variable weather conditions will
persist, with warm temperatures expected through the upcoming weekend.
The arrival of a tropical wave is anticipated to increase
shower frequency across the islands.

&&

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

Clear to partly cloudy skies prevailed across the islands during the
overnight hours. Scattered showers with isolated thunderstorms were
noted mainly over the northwestern waters of Puerto Rico, and the
Anegada Passage just before midnight. Showers are expected to move
over portions of the USVI and the eastern sections of PR through the
rest of the early morning hours. Minimum temperatures were from the
upper-70s to low 80s across the lower elevations of the islands to
the mid-60s and 70s across the higher elevations of Puerto Rico. The
wind was light with an easterly component.

A broad surface high pressure over the central Atlantic and front
across the northwestern Atlantic will continue to promote light to
moderate (10-15 kt) southerly steering winds through Wednesday.
These winds will bring a surge in low-level moisture from the
southeastern Caribbean today. Meanwhile, an upper-level low north of
the area will move southwest, just north of Hispaniola by Wednesday,
promoting colder 500 mb temperatures and increasing instability in
general, which will aid in the development of strong afternoon
thunderstorms each day. A tropical wave will cross the region late
on Thursday, bringing scattered showers and thunderstorms across the
regional waters and over portions of the islands late in the
forecast period.

At least through Wednesday, a similar weather pattern is expected,
with showers increasing in and around the U.S. Virgin Islands and
across the east/southeast sections of Puerto Rico during the morning
hours. This will then be followed by afternoon thunderstorm
development over portions of the interior and the northwestern
quadrant of PR, as well as downwind from el Yunque area and over
portions of the Cordillera. The main weather hazards will be urban
and small stream flooding, strong gusty winds, and lightning
strikes. In addition, the light southeasterly winds will continue to
promote hot temperatures across the lower elevations of the islands,
and heat advisory conditions are expected before the onset of
afternoon showers.

On Thursday, winds are expected to shift more from the east,
remaining around 15 kt as the weak tropical wave moves across the
region. The best moisture associated with the wave will arrive late
in the day. Therefore, fair weather conditions are expected during
the morning hours across the islands, with afternoon showers and
thunderstorm development over portions of the Cordillera and western
PR, and downwind of the islands.

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

The long-term forecast remains on track. According to the latest
global model guidance for Friday, the islands will be mostly
dominated by a broad surface high pressure over the central
Atlantic. Under this pattern, sufficient cloudiness and moisture
will support a typical weather regime, with variable conditions in
the morning followed by afternoon convection. An increase in
showers and thunderstorms is forecast from late Friday into the
weekend, as an upper-level trough near 250 mb enhances instability
across the region. This feature, combined with abundant tropical
moisture from a tropical wave, will favor stronger convection with
frequent lightning, gusty winds, and periods of heavy rainfall.
Based on the Gálvez-Davison Index (GDI), there is a high chance of
widespread showers and thunderstorm activity each afternoon
through the weekend. This activity is expected to range from
moderate to intense, leading to urban and low-lying flooding.
Additionally, the threat of lightning will increase, particularly
across the western interior and the San Juan metro area. From
Monday to Tuesday, moisture will diminish and an upper-level ridge
will erode the instability over the region. As a result, a more
typical weather pattern is expected, with afternoon convection
across the islands.

The presence of moisture and 0–3 km winds will enhance the heat
threat across all coastal and urban areas during the long-term
period. These warmer conditions could exacerbate heat-related
illness symptoms associated with heat exhaustion. Residents and
visitors are urged to follow the recommendations issued by the
health department.


&&

.AVIATION...

(06z TAFs)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hour. However, afternoon TSRA could develop near
TJBQ/TJSJ between 02/17-23Z, causing tempo MVFR to brief IFR
conditions. Elsewhere, mostly VCSH expected. Southeast winds
expected between 10-15 kt with sea breeze variations and higher
gusts aft 02/14z.

&&

.MARINE...

A surface high pressure over the central Atlantic will continue to
result in moderate to locally fresh east to southeasterly winds
across the local waters. Seas will remain up to 5 feet across the
Atlantic offshore waters and even lower across the coastal waters.
Localized hazardous marine conditions due to thunderstorms are
forecast from late Friday into Sunday as a tropical wave moves
into the local waters, resulting in an increase in cloudiness and
showers.

&&

.BEACH FORECAST...

There is a low risk of rip currents along all the coastal areas
of Puerto Rico, Culebra, Vieques and the U.S. Virgin Islands.
Therefore, coastal conditions are suitable for beachgoers and
visitors. Although conditions remain good stay alert to areas not
designated to beachgoers.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
358 AM AST Wed Sep 3 2025

.KEY MESSAGES...

* For today, another warm day is expected, with heat indices
reaching up to 111 degrees across coastal and urban areas, and
even higher in localized areas during the peak of the heat from
11 AM to 2 PM AST. Additionally, there is an elevated flooding
and lightning threat across western Puerto Rico due to the
afternoon convection.

* For the upcoming weekend, a tropical wave and an upper-level
trough will increase the potential for showers and
thunderstorms increasing the flood and lightning threat.

* For the U.S. Virgin Islands, variable weather conditions will
persist, with warm temperatures expected through the upcoming
weekend.

* There is a low risk of rip currents across the islands today.

&&

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

Partly cloudy skies were observed across the east/southern sections
of Puerto Rico and the U.S. Virgin Islands during the overnight
hours. Passing showers where increasing over the regional waters
under light steering southeasterly winds. These showers are expected
to move over portions of the USVI and eastern sections of PR through
the rest of the early morning hours. Minimum temperatures were from
the upper-70s to low 80s across the lower elevations of the islands
to the mid-60s and mid-70s across the higher elevations of Puerto
Rico.

A surge in moisture will continue over the area today, triggering
showers and thunderstorms once again over the islands and across the
local waters. These thunderstorms can produce heavy rainfall, strong
gusty winds, and frequent cloud-to-ground lightning as an upper-
level low meanders just west of the area. Light to moderate
southeast winds will prevail under the influence of a surface high
pressure centered just southwest of the Azores and a frontal system
across the western Atlantic. Therefore, another hot day is expected
before the onset of afternoon showers, and a Heat Advisory will be
in effect from 10 AM to at least 5 PM, for all coastal
municipalities of Puerto Rico and the U.S. Virgin Islands.

For Thursday and Friday, the surface high pressure will continue to
build over the central Atlantic, and easterly trades will return
across the eastern Caribbean. A drier air mass ahead of a tropical
wave will move over the local area on Thursday, causing the
precipitable water (PWAT) content to drop from near 2.00 inches
today to around 1.60 inches by Thursday morning. Therefore, mostly
fair weather conditions are expected to prevail across the islands
in general; however, intense daytime heating, combined with the
available moisture content and local effects, will trigger shower
activity over western PR in the afternoon hours, where the flood
threat will remain elevated. Temperatures will remain a few degrees
above normal under mostly sunny skies during the late morning hours,
and the heat threat will continue across most coastal and urban
areas of the lower elevations of the islands. By Friday, shower and
thunderstorm activity will increase across the islands as the PWAT
recovers to near 2 inches again with the passage of the tropical
wave. Also, a weak Saharan Air Layer with minor concentrations of
Saharan dust will arrive late Friday, promoting hazy skies.

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

The long-term forecast remains on track, with the island mostly
dominated by a broad surface high pressure over the central
Atlantic for the first part of the period.At the surface, sufficient
cloudiness and moisture from an induced surface trough from an
upper level trough moving westward into the region. This weather
configuration will lead a typical weather pattern along the
islands with afternoon convection across the northern Puerto
Rico. On Sunday, winds will veer more from the east- southeast as
the surface high pressure shifts into the northwestern Atlantic,
while instability increases further as 500 mb temperatures drop to
-8 C, favoring more widespread thunderstorms due to the approach
of the upper level low along the northeast of the region. Based on
the Galvez- Davison Index (GDI), there is a high chance of
widespread showers and thunderstorm activity each afternoon
through the weekend, ranging from moderate to intense, with
frequent lightning, gusty winds, and periods of heavy rainfall
that could lead to urban and low- lying flooding. The threat of
lightning will be particularly elevated across the western
interior and the San Juan metro area.

From Monday to Tuesday, a deep layer of tropical moisture between
700 and 300 mb will place the islands under a wetter pattern,
increasing the frequency of showers. Combined with some
instability aloft and temperatures around -5 to -6 C at 500 mb,
this will favor rounds of showers across the islands. The pattern
would include frequent passing showers during the morning hours
along windward sections and a deep layer of cloudiness from late
morning into the afternoon, enhancing convective activity.
Additionally, the presence of deep moisture and southeasterly low-
level winds will continue to enhance the heat threat across
coastal and urban areas, potentially exacerbating heat-related
illness symptoms associated with heat exhaustion. For Wednesday,
discrepancies in global model solutions (GFS & ECMWF) remain due
to the uncertainty of the next tropical system, which currently
has a high chance of formation in the next seven days according to
the NHC. The GFS favors surface winds from the east-southeast,
while the European model (ECMWF) indicates a more easterly flow.
This pattern should become clearer as we approach the weekend;
however, for now, the forecast calls for active afternoon
convection along western Puerto Rico.

&&

.AVIATION...
(06z TAFs)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hour. However, afternoon +SHRA/TSRA expected to
develop in and around TJBQ/TJSJ between 03/16-22Z, causing tempo
MVFR to brief IFR conditions. Elsewhere, mostly VCSH expected,
however, VCTS is expected at TJPS through the afternoon hours. East
to southeast winds will increase between 10 and 15 knots with sea
breeze variations and higher gusts after 03/13z.

&&

.MARINE...

A surface high pressure across the central Atlantic will continue
to promote moderate to locally fresh east to southeasterly winds
across the local waters today, with seas generally up to 4 feet,
calmer near the coast, and occasionally higher in and around
thunderstorms. Strong convection developing through this evening
will result in moderate chop, gusty winds, and localized hazardous
seas, reducing visibility in heavy rainfall. Conditions are
expected to deteriorate by late Friday night into the weekend as a
tropical wave increases the frequency of showers and
thunderstorms, leading to periods of locally hazardous marine
conditions, with small craft operators advised to exercise
caution.

&&

.BEACH FORECAST...

There is a low risk of rip currents along all coastal areas today
through the upcoming weekend. Coastal conditions will be generally
favorable for beachgoers and visitors. However, despite the good
conditions, caution is advised as other coastal hazards such as
lightning, especially during the afternoon hours, may pose a
threat.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
430 AM AST Thu Sep 4 2025

.KEY MESSAGES...

* Another warm day is expected today, with heat indices up to 111
degrees across coastal and urban areas, and potentially even
higher in localized areas during peak heating from 11 AM to 2
PM AST.

* Afternoon convection with thunderstorms will trigger an
elevated threat of flooding and a limited lightning threat
across northwestern Puerto Rico.

* An increase in moisture and instability will induce a wet and unstable
pattern from Friday into Monday, increasing the flood threat
and the lightning threat along the islands.

* For the U.S. Virgin Islands, variable weather conditions will
persist, with warm temperatures expected through the upcoming
weekend.

* There is a low risk of rip currents across the islands today
and into the upcoming weekend.

&&

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

Mostly clear to partly cloudy skies were observed across the islands
overnight. Passing showers where noted mainly over the regional
waters under light steering easterly winds, with a few reaching
portions of eastern PR, where the Doppler radar estimated around a
quarter of an inch of rain in Humacao and vicinity. Minimum
temperatures were from the mid-70s to low 80s across the lower
elevations of the islands to the low-60s and mid-70s across the
higher elevations of Puerto Rico.

A broad surface high pressure will continue to build over the
central Atlantic during the next few days, promoting moderate trade
winds through the forecast period. Embedded in this flow today is a
drier air mass with precipitable water (PWAT) values below
climatology, which will move across the region. However, shallow
moisture content trapped below 850mb will be sufficient to aid in
the development of afternoon showers and thunderstorms over western
PR. Across the USVI, passing showers could move at times,
particularly tonight through Friday morning, as shower activity is
expected to increase ahead of a tropical wave currently located east
of the Leeward Islands. Temperatures will remain similar to
yesterday, with daytime highs ranging from the upper 80s to low 90s
across most coastal areas. Heat indices will peak around 108°F,
mainly across western and northern PR. Regardless, due to plenty of
sunshine expected elsewhere, a Heat Advisory was issued for all
coastal municipalities in PR and the USVI.

The tropical wave is expected to cross the local area on Friday,
resulting in an increase in shower and thunderstorm activity through
the region. The PWAT is likely to recover at normal levels, around
2.00 inches, which is the high end of the 50th percentile. The main
hazards will be urban and small stream flooding, as well as gusty
winds and lightning strikes with the thunderstorms. Although hot
temperatures are still expected on Friday, the cloud cover and
showers could limit the heat threat in certain areas. A weak Saharan
Air Layer with minor concentrations of Saharan dust will arrive with
the wave passage, bringing hazy skies and affecting people sensitive
to these particles.

On Saturday, unstable conditions will continue across the region as
an upper-level low north of the area and associated trough combine
with lingering low-level moisture from the departing wave. The flood
threat will remain elevated, with possible isolated flash floods and
mudslides in areas of steep terrain, particularly across western PR.

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

The forecast for the first part of the long-term remains on track.
An upper-level low, just north of the region, will continue to
increase the instability aloft and induce colder temperatures at
500 Mb, ranging from -6 to -7°F. Meanwhile, at the surface, plenty
of tropical moisture will move with Precipitable water (PWAT)
ranging between 1.8 to 2.0 inches will move into the area,
increasing the potential for shower activity. As a result, the
islands will experience a showery pattern from morning hours
across the windward section of the islands, and widespread
activity across western Puerto Rico in the afternoon hours.
Especially across northwestern Puerto Rico, where there is a
potential for scattered thunderstorms as the Galvez-Davison Index
(GDI suggests. Instability will remain in place from Monday into
Wednesday as the upper-level low/trough extends from another area
over the Western Caribbean. This upper-level feature will induce a
surface trough, resulting in plenty of cloudiness and moisture
along the islands. At the surface, winds will predominate from the
east-southeast as a surface high-pressure system over the central
Atlantic dominates the area. This wind flow will push the sower
activity along the San Juan metro area and northwestern sections
of Puerto Rico.

For Thursday, the forecast remain with a lot of uncertainty due
to two different solutions from the global model guidances (GFS &
ECMWF). According to the latest data, there are some discrepancies
in the weather patterns along the islands and the surface winds
due to the approach of the next tropical system monitored by the
National Hurricane Center, with a high chance of formation in the
next seven days. According to the GFS and with consistency, the
tropical system will move northeast of the region, resulting in
mostly east-southeast winds across the islands. On the other hand,
the ECMWF, with different solutions from yesterday, located the
system slightly closer to the islands for the weekend. Although
the long-term forecast only includes the Thursday forecast,
residents and visitors are urged to check the tropical emergency
plans and stay tuned for further official information regarding
this tropical wave.

&&

.AVIATION...
(06z TAFs)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hour. However, locally induced TSRA is expected
to develop in and around TJBQ between 04/16-22Z, causing tempo MVFR
to brief IFR conditions. Elsewhere, mostly VCSH expected. East winds
will increase between 10 and 15 knots with sea breeze variations and
higher gusts after 04/13z.


&&

.MARINE...

A surface high pressure across the central Atlantic and an induced
surface trough just northeast of the islands over the Atlantic
will continue to promote moderate to locally fresh east to
southeasterly winds across the local waters today, with seas
generally up to 5 feet. Afternoon showers will result in choppy
seas, gusty winds, and localized hazardous seas, reducing
visibility in heavy rainfall.

Weather conditions are expected to deteriorate by late Friday
night into the weekend as a wet and unstable weather pattern
increases the frequency of showers and thunderstorms, leading to
periods of locally hazardous marine conditions

&&

.BEACH FORECAST...

There is a low risk of rip currents along all coastal areas today
through the upcoming weekend. Coastal conditions will be generally
favorable for beachgoers and visitors. However, despite the good
conditions, caution is advised as other coastal hazards like
lightning, especially during the afternoon hours.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
424 AM AST Fri Sep 5 2025

.KEY MESSAGES...

* Another warm day is expected today, with heat indices climbing
up to 111 degrees across coastal and urban areas, and
potentially even higher in localized areas during peak heating.

* A tropical moisture with an induced surface trough will
increase the potential for shower activity along the islands
from Friday into the weekend.

* For the U.S. Virgin Islands, variable weather conditions will
persist, with warm temperatures expected through the upcoming weekend.
From Saturday into Sunday, a showery pattern is expected
mostly for the morning and evening hours across the islands;
however, no flooding threat is forecast.

* The National Hurricane Center is monitoring a tropical wave
(Invest 91L) with a high chance of formation in the next seven days.
For now, there is a lot of uncertainty in the outcome of the
forecast related to this tropical system; however, residents
and visitors should stay tuned for further updates from the
official sources.

&&

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

A tropical wave located across the Anegada Passage and Caribbean
waters will increase shower and thunderstorm activity today across
the islands. These showers could lead to minor flooding across
portions of the U.S. Virgin Islands during the later morning/early
afternoon hours. The flood threat across Puerto Rico will be
elevated, particularly across the eastern interior and western
sections of Puerto Rico during the afternoon hours. These
thunderstorms can produce brief gusty winds and cloud-to-ground
lightning strikes. A weak Saharan Air Layer with minor
concentrations of Saharan dust will arrive with the wave passage,
bringing hazy skies and reducing the air quality somewhat through at
least Saturday.

For the rest of the weekend, unstable conditions will persist across
the region as an upper-level low, located north of the area, and its
associated trough combine with lingering low-level moisture from the
departing wave. The flood threat will remain elevated, with possible
isolated flash floods and mudslides in areas of steep terrain,
particularly across western Puerto Rico. For the USVI, passing
showers will continue to move at times, with isolated thunderstorms
mainly developing over the regional waters.

Although cloudiness will increase during the day due to the expected
showers, the heat threat will remain elevated in general for all
lower elevations of the islands through the forecast period.
Particularly between the late morning and early afternoon hours, and
before the onset of afternoon showers. Heat advisories could be
issued each day.

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

The forecast for the first part of the long-term remains on track.
An upper-level low just north of the region will continue to
increase instability aloft and induce colder temperatures at 500
Mb, ranging from -6 to -7°C. Meanwhile, at the surface, plenty of
tropical moisture with Precipitable Water (PWAT) values ranging
between 1.8 to 2.0 inches will move into the area, increasing the
potential for shower activity. As a result, the islands will
experience a showery pattern from morning hours across the
windward section of the islands, and widespread activity across
western Puerto Rico in the afternoon hours, especially across
northwestern Puerto Rico, where there is a potential for scattered
thunderstorms as the Galvez-Davison Index (GDI) suggests. From
Wednesday into Thursday, instability will increase again as
another upper-level trough moves south of the region, favoring
colder temperatures near -7°C at 500 Mb. This feature, combined
with PWAT values near the 75th percentile, will support enhanced
cloudiness and frequent showers and thunderstorms across the
islands. At the surface, east-southeast winds driven by high
pressure over the central Atlantic will prevail, steering
additional convection toward the San Juan metro area and the
northwestern sections of Puerto Rico.

From late Thursday into Friday, the forecast becomes more
uncertain due to the approach of a tropical system track by the
National Hurricane Center, and with a high chance of formation
(90%) in the area. Differences remain in the global model guidance
(GFS and ECMWF), particularly in the position and the intensity
of the system. The latest GFS run suggests a more southerly track,
aligning with the ECMWF, which continues to place the system
closer to the islands and therefore capable of altering local
weather conditions. Given the length of the forecast period,
additional changes are still possible. For now, the most certain
course of action is for residents and visitors to review their
tropical emergency plans and remain tuned to official updates from
the National Hurricane Center.

&&

.AVIATION...

(06z TAFs)

A tropical wave will increase SHRA/TSRA across the local area today.
Tempo MVFR to brief IFR conditions are possible at TISX/TIST btw
05/12z-18z, and across the PR terminals btw 05/16z-06/00z. HZ due to
minor concentrations of Saharan dust expected after the wave
passage, but VSBY should remain P6SM. East winds will increase
between 12 and 16 knots with sea breeze variations and higher gusts
after 05/13z.

&&

.MARINE...

A surface high pressure across the central Atlantic, a tropical
wave, and an induced surface trough just northeast of the islands
over the Atlantic will continue to promote moderate to locally
fresh east-southeasterly winds across the local waters today, with
seas generally up to 5 feet. Conditions are expected to
deteriorate by late Friday night into the weekend as a wet and
unstable weather pattern increases the frequency of showers and
thunderstorms, leading to periods of locally hazardous marine
conditions, with small craft operators advised to exercise
caution.

&&

.BEACH FORECAST...

There is a low risk of rip currents along all coastal areas today
through the upcoming weekend. Coastal conditions will be generally
favorable for beachgoers and visitors. However, despite the good
conditions, caution is advised as other coastal hazards like
lightning, especially during the afternoon hours.