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Re: Caribbean - Central America Weather

#21941 Postby cycloneye » Wed Sep 24, 2025 11:47 am

Area Forecast Discussion
National Weather Service San Juan PR
439 AM AST Wed Sep 24 2025

.KEY MESSAGES...

* A robust tropical wave (AL94) will cross the region today into
Thursday, bringing periods of squally weather with bands of
heavy showers, thunderstorms, and gusty winds.

* Elevated to significant flooding risks are anticipated from the
heavy rainfall, with potential for urban and small stream
flooding, flash flooding, rapid river rises, and landslides in
steep terrain.

* Hazardous marine conditions are expected as AL94 moves across
the region, with Small Craft Advisories in effect. Increasing
winds and seas will create dangerous conditions for mariners.

* An extended wet period will continue into the weekend, as deep
tropical moisture from AL94 and AL93, moving north of the area,
sustains rounds of showers and thunderstorms.

* For the U.S. Virgin Islands: Squally weather will persist
through Thursday with heavy showers, thunderstorms, gusty winds,
and hazardous marine conditions. Additional rounds of showers
are expected into the weekend, maintaining a risk of flooding in
vulnerable areas before gradual improvement by midweek of next
week.

&&

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

Tranquil conditions prevailed overnight across the region, with only
brief passing showers affecting eastern Puerto Rico and the US
Virgin Islands under light northeasterly winds that gradually
transitioned to more east to southeasterly. A few stronger showers
with isolated thunderstorms developed over the surrounding
waters, occasionally producing lightning south of Saint Croix and
northwest of Aguadilla, though no products were required.
Overnight lows ranged from the upper 70s to the low 80s in coastal
and urban areas, while interior valleys and higher terrain cooled
to the upper 60s to mids, slightly warmer than the previous
nights.

Unlike the last several days, heat will not be the main hazard
today. Instead, attention shifts to a flooding threat as a tropical
wave currently monitored by the National Hurricane Center steadily
approaches our region. Winds will gradually veer to the south,
favoring enhanced moisture transport and heavier rainfall along the
eastern and northern portions of Puerto Rico and the US Virgin
Islands. Model guidance shows above-normal precipitable water values
for this time of year, with mid-level temperatures near -7 degrees
C, both of which support deep convective development.

By late today into Thursday, interaction between the tropical wave
and an upper-level low will maximize instability and rainfall
potential. The most widespread and intense activity is expected
during this window, initially impacting the Virgin Islands before
spreading across Puerto Rico. Therefore, periods of squally weather,
heavy rainfall, and thunderstorms will bring the potential for
significant impacts, including rainfall totals of 2 to 6 inches,
along the northern and eastern half of PR and the US Virgin Islands.
The unsettled and unstable weather pattern will likely persist
through the end of the workweek. However, showers and thunderstorms
are expected to be less widespread after Thursday.

Given already saturated soils across the northern and western half
of Puerto Rico, as well as St. Thomas and western St. Croix, risks
include urban and small stream flooding, flash flooding, rapid river
rises, coastal water surges, and landslides in steep terrain.

Residents and visitors should remain alert for any changes in the
forecast, in order to make informed decisions. For further details,
refer to the hydrology section.

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

For this weekend, soils across the region will likely remain
saturated and streamflows elevated after several days of heavy
rainfall. These antecedent conditions increase the area’s
sensitivity to additional rainfall, meaning even moderate showers
could quickly trigger urban and small stream flooding, as well as
isolated landslides in steep terrain.

This weekend, little change is expected in the overall pattern
suggested by previous model cycles. A deep-layer southerly flow,
reinforced by the northward movement of Invest AL94 and AL93, will
continue transporting abundant tropical moisture into the region.
Precipitable water values will remain above normal, generally at
or above 2 inches, maintaining a moist and unstable environment.
In combination with daytime heating and sea breeze convergence,
this will favor frequent rounds of showers and thunderstorms,
particularly during the afternoon. Activity will tend to focus on
southern and eastern Puerto Rico and the smaller islands overnight
and during the morning, then shift toward the interior and
northwestern municipalities in the afternoon. The prevailing
southerly flow will also enhance rainfall potential along the
northern slopes of Puerto Rico.

The ECMWF Extreme Forecast Index now signals the potential for
extreme precipitation, especially across the southern and eastern
portions of the forecast area, although ensemble spread maintains
some uncertainty regarding the exact magnitude and focus.
Regardless, given antecedent soil conditions, the potential for
flooding impacts will remain elevated through the weekend and into
early next week.

Conditions are expected to gradually improve beginning Tuesday as
the moisture plumes shift north and precipitable water values drop
to near or slightly below seasonal levels, around 1.5 to 1.6 inches.
With this drying trend, shower and thunderstorm activity will become
more isolated, and the flood threat should begin to diminish
compared to the weekend. Still, isolated afternoon convection will
remain possible, especially across the western and interior portions
of Puerto Rico.

In addition to rainfall hazards, a persistent southerly flow will
maintain above-normal temperatures and oppressive heat indices
across coastal and urban areas. Extreme Heat Warnings or Advisories
are likely to be needed through much of the period, particularly
over the weekend when moisture levels and heat combine to create
dangerous conditions.


&&

.AVIATION...
(06Z TAFs)

All TAF sites should experience VFR conditions. However,
after 24/14Z, -SHRA/VCTS could affect TIST, TISX, and TJSJ. But
after 24/17Z, TSRA should prompt periods of MVFR conditions
across most TAF sites, with the heaviest TS activity as the
vigorous Tropical Wave being monitored by the National Hurricane
Center moves closer to the region. Winds will remain from the E-SE
and gradually become more S from 24/15-24/22Z at 8–15 kts and
higher gusts near the heaviest RA and TS associated to the
tropical wave.


&&

.MARINE...

Today, a vigorous tropical wave will move into the islands,
increasing the potential for thunderstorms and leading to localized
hazardous marine conditions. These storms may produce frequent
lightning over exposed waters. In addition, an increase in surface
winds is forecast through at least late tonight, particularly across
the offshore Atlantic waters, Anegada Passage and waters east of
Puerto Rico, around Vieques, Culebra, and St. Thomas, where Small
Craft Advisories are in effect. Seas up to 7 feet, particularly
across the offshore Atlantic waters and Anegada Passage.


&&

.BEACH FORECAST...

Increasing winds and choppy seas as AL94 crosses the region will
maintain hazardous conditions, particularly along the Atlantic-
facing beaches. As a result, a moderate rip current risk will
persist across the northern and eastern beaches of Puerto Rico,
Vieques, Culebra, and the U.S. Virgin Islands. Beachgoers are
urged to exercise caution and avoid swimming in high-risk areas.

In addition, thunderstorms associated with AL94 will pose
significant hazards at the coast. Frequent lightning strikes,
gusty winds, and heavy rainfall may lead to dangerous conditions,
including sudden reductions in visibility and localized flooding
near the shoreline. Remember: if thunder roars, go indoors.
Swimmers and boaters should immediately seek shelter when storms
approach.
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Re: Caribbean - Central America Weather

#21942 Postby cycloneye » Thu Sep 25, 2025 4:03 am

Area Forecast Discussion
National Weather Service San Juan PR
422 AM AST Thu Sep 25 2025

.KEY MESSAGES...

* The wet pattern will persist during the day as trailing
moisture from the tropical wave (Invest 94L) continues to
affect the local islands. The additional rainfall accumulations
will exacerbate flooding, especially across eastern sections of
Puerto Rico.

* For the U.S. Virgin Islands, additional shower activity is
expected for the rest of the morning, enhancing urban flooding
in already affected areas.

* Tropical moisture from the tropical wave (Invest 94L) is
expected to move out of the region by Saturday, resulting in a
more typical pattern with variable days: warm mornings and
showers in the afternoons.

* For the long term, a wet pattern is forecast from Monday into
Tuesday as moisture from the tail of tropical system Humberto
moves into the region.

* Seas will remain up to 6 feet today across the offshore
Atlantic waters and a moderate risk of rip current will remain
for the northern and western coastal areas.

&&

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

Overnight, the vigorous tropical wave (AL94) continued to promote
widespread heavy showers and thunderstorms across the regional
waters. By early night, a strong band of showers developed in a
southeast-to-northwest orientation over St. Thomas. By that time,
the wave was positioned just south to southwest of Puerto Rico,
inducing a southeasterly flow over the region. This advected lines
of strong showers into the southern coastal areas of Puerto Rico,
prompting the issuance of a Flood Advisory for the southern coastal
municipalities. Elevated streamflows persisted, with rivers across
the eastern third of Puerto Rico running at or near record highs. A
Flood Warning was issued for Rio Blanco due to overflowing banks,
which rendered some roads along the river impassable.

As the wave continues its west-northwestward movement, winds are
expected to gradually shift more southerly, advecting additional
deep tropical moisture over the region. Hi-Res model guidance
suggests Thursday will maintain variable weather conditions, with
morning convection mainly affecting the southern and interior
portions of Puerto Rico and the smaller islands. During the
afternoon, additional convection may develop across the northern
slopes of Puerto Rico; however, the extent of this activity will
depend heavily on cloud coverage during the day. Extensive cloud
cover, as suggested by the high-resolution guidance, could limit
instability and suppress afternoon thunderstorm development.
Nonetheless, tropical waves often behave erratically in terms of
shower and thunderstorm activity, and therefore, close monitoring is
warranted.

Looking ahead to Friday and Saturday, model guidance indicates
notable changes compared to previous cycles. Now that Tropical Storm
Humberto has developed northeast of the region, its forecasted track
has separated slightly from AL94. This shift allows drier air to
filter into the region much earlier than previously expected,
reducing the interaction between the two moisture plumes. Both the
GFS and ECMWF suggest a significant drop in mid-level relative
humidity (700-500 mb) from values above 90% to below 40%,
approaching below to near normal climatological levels. As a result,
widespread shower and thunderstorm activity will likely diminish
compared to earlier expectations. Still, localized afternoon
convection remains possible, especially where daytime heating
interacts with lingering moisture.

Despite this drier trend, uncertainty remains high regarding the
eventual evolution and interaction between AL94 and Tropical Storm
Humberto. Should the systems shift track or slow down, moisture
availability and convective potential could increase again.
Therefore, residents and local authorities should remain alert for
rapid changes in forecast conditions. With saturated soils and
elevated rivers, the threshold for flooding and landslide impacts
remains low, and even isolated strong thunderstorms could pose
significant hazards.

From Friday onward, the prevailing southerly flow combined with
ample low-level moisture will maintain above-normal temperatures and
elevated heat indices, especially across coastal and urban areas.
Periods of reduced cloud cover could further enhance daytime
heating, resulting in oppressive and potentially hazardous heat
conditions.

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

From Sunday (September 30) through early Tuesday, the local
weather pattern across Puerto Rico and the U.S. Virgin Islands
will be influenced by two tropical systems situated over the
Atlantic. The combination of these two systems will maintain a
southeasterly wind flow across the islands. On Sunday, both global
model guidance (GFS & ECMWF) show a less wet area moving into the
region, with precipitable water values dropping to around 1.70
inches (near the 25th percentile). This brief window of reduced
moisture presence will rapidly end as Hurricane Humberto
progresses farther into the western Atlantic, leading to an
increase in tropical moisture and the tail of the tropical system
over the islands by Tuesday and into early Wednesday. During this
period, mid-level lapse rates between 700 and 500 mb will support
stable conditions aloft due to an upper-level ridge. Thus,
although moisture levels increase, instability will be limited,
and afternoon convection on Tuesday will be driven primarily by
local effects. The bulk of the showers is forecast for the
interior and northwestern sections, as well as the San Juan Metro
area.

By Wednesday, weather conditions become more typical, with PWAT
values between 1.70 and 1.9 inches and relative humidity in the
700–500 mb layer climbing above 60%, allowing for variable weather
of warm mornings with heat indices rising up to 108 degrees and
active evenings with thunderstorms and gusty winds from 12 to 5 PM.
By Thursday, conditions will evolve again as an upper- level low
moves northwestward across the Caribbean, increasing instability
over the region. Despite slightly lower moisture, with PWAT values
still around the climatological median, the presence of
instability will be sufficient to support scattered convection,
particularly during the afternoon hours across the interior and
northwestern Puerto Rico. Meanwhile, the synoptic pattern at the
surface will favor a persistent east- southeasterly wind flow,
with breezy conditions as suggest by the 925 mb wind speeds in the
model guidance, largely driven by the interaction between a
tropical system moving over the central Atlantic. This will
sustain a warm trend in the morning with an increase in heat
indices followed by afternoon thunderstorm development as the week
progresses.

&&

.AVIATION...
(06Z TAFS)

A vigorous tropical wave (AL94) will continue to bring SHRA/TSRA
across through 24/15z, with TEMPO MVFR/IFR conds possible at times
due to low CIGS/VIS, especially at TJSJ/TJPS/TIST/TISX. TSRA
activity will gradually shift to the interior and northern PR by
aftn, potentially affecting TJSJ with PROB30 for reduced VIS/CIGS.
Elsewhere, VFR conds should prevail outside of convection. Sfc winds
SE 10-15 kt, bcmg more S aft 24/15Z, with sea breeze variations at
coastal terminals. Gusts up to 25-30 kt psbl in/near SHRA/TSRA.


&&

.MARINE...

A surface high pressure over the Western Atlantic and a tropical
wave moving across the region will enhance a moderate
southeasterly wind flow across the region. The actual moisture
from the tropical wave (Invest 94L) will continue to result in
localized hazardous marine conditions near the thunderstorm
activity along the local waters. As a result, mariners are urged
to exercise caution along the exposed local waters due to seas up
to 6 feet, especially across the offshore Atlantic waters.
Improving marine conditions are forecast for the upcoming weekend
with seas up to 5 feet.

&&

.BEACH FORECAST...

There is a moderate risk of rip current along the northern and
western coastal areas of Puerto Rico, including Culebra. For the
rest of the coastal areas, the risk will remain low. Similar
coastal conditions are expected to persist from Friday into
Saturday. Thunderstorms producing frequent cloud-to-ground or
water lightning will affect the local beaches. If you hear
thunder, please seek shelter by going indoors or moving to a safe
location.
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Re: Caribbean - Central America Weather

#21943 Postby cycloneye » Fri Sep 26, 2025 4:09 am

Area Forecast Discussion
National Weather Service San Juan PR
445 AM AST Fri Sep 26 2025

.KEY MESSAGES...

* Tropical moisture across the region from AL94, now located
north of Hispaniola, will contribute to a hot day with heat
indices reaching up to 144 degrees. As a result, a Heat
Advisory from 10 AM to 4 PM AST is in effect for the coastal
and urban areas of Puerto Rico, including Culebra & Vieques.

* For the U.S. Virgin Islands, a variable pattern will persist
through the first part of the morning, with considerable cloud
cover and limited shower activity, followed by a warm afternoon
with heat indices reaching up to 108 degrees. Therefore, there
is a heat advisory in effect from 10 AM to 4 PM AST.

* Another hot day is expected tomorrow, as surface winds from the
east- southeast promote periods of sunshine during the morning
and early afternoon.

* Tropical system Humberto moves over the Atlantic, at a safe
distance from PR and the USVI, conditions may become unstable
and moist by next Monday due to an increase in tropical
moisture across the CWA.

&&

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

A moist airmass associated with AL94 will linger over the region
today. Due to the proximity of this system, conditions will remain
somewhat unstable. With the expected break in clouds, the daytime
heating, combined with the available moisture and sea breeze
convergence, will trigger scattered afternoon convection over the
mountain ranges and west-northwest sections of PR. At the same time,
the potential remains high for observing showers and thunderstorms
over the local waters. Meanwhile, a col area is developing over the
northeastern Caribbean, and it is expected to meander close to the
USVI and offshore Atlantic waters as the slow-moving Humberto
continues to strengthen well northeast of the area. This pattern
will bring now better chances of rain across the USVI than
previously expected.

A transition to a drier, more stable, and warmer-than-average
weather pattern is expected across the islands in general through
the rest of the short-term period. Global model guidance suggests a
sharp decline in moisture content, with Precipitable Water (PWAT)
falling from wet conditions (above 75th percentile) today to near-
normal content (lower tier of the 50th percentile) through the
weekend, and a significant drop in mid-level (850-700 MB) relative
humidity, decreasing to near the 25th percentile by Sunday.
Regardless, afternoon convection is expected to develop over
portions of central and northern PR each day. This forecast is based
on the expected west/northwest movement of AL94 and TS Humberto, and
that weak ridging between the systems will bring briefly drier air
over the region. This synoptic pattern will bring light steering
winds with a southerly component over the islands, promoting 925 mb
temperatures near 24C (which is above two standard deviations).
Therefore, hot temperatures and heat indices reaching extreme
warning or heat advisory criteria can be expected each day across
the lower elevations of the islands.

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

The long-term forecast remains on track for the first part of the
upcoming workweek. On Monday, the surface weather pattern across
Puerto Rico and the U.S. Virgin Islands will be influenced by
Hurricane Humberto, a tropical system located over the western
Atlantic. At the upper levels, a mid- to upper-level ridge will
dominate, providing stability over the islands. Under this
pattern, southeasterly winds will transport patches of fragmented
moisture. According to global model guidance (GFS), precipitable
water values for Monday are expected to range between 1.9 and 2
inches, supporting a variable pattern with warm conditions during
the morning, followed by convection and thunderstorms across
northwestern Puerto Rico. By Tuesday, surface moisture is expected
to decrease to near the 25th percentile as the moisture plume
shifts into the western Atlantic, leaving the islands under a much
drier pattern. This reduction will favor a more stable day with
extended periods of morning sunshine, contributing to warmer
conditions as also suggested by the 925 mb temperatures. Weaker
winds will further support a dry pattern due to the lack of a
significant sea breeze effect, particularly across western Puerto
Rico. Although surface conditions will generally be unfavorable
for widespread weather activity, isolated showers with
thunderstorms cannot be completely ruled out.

From Wednesday through Friday, 250 mb heights are forecast to
decrease, resulting in slight instability due to an upper-level
trough near the region. However, compared to yesterday’s
solutions, today’s guidance suggests less instability for
Thursday. At the surface, fragmented moisture will be steered
mainly by the prevailing winds associated with a strengthening
surface high over the central Atlantic as Hurricane Humberto
continues moving into the northwestern Atlantic. As this high
pressure builds, a weak point in the pressure gradient is expected
to develop, diminishing the 0–3 km surface winds.

&&

.AVIATION...
(06Z TAFS)

SHRA/TSRA associated to a departing tropical wave (AL94) will
continue to produce areas of MVFR across the local terminals today.
However, mainly VFR conditions are expected early in the fcst
period. Weak land/sea breeze variations will dominate the local
winds, however, an ESE component up to 10 kt is expected to prevail
during the day.

&&

.MARINE...

Gentle to light will persist as the interaction of Invest 94L and
Tropical Humberto across the region. Therefore, mariners can
expect surface winds up to 10 knots with seas up to 5 feet. An
increase in seas is forecast for the upcoming weekend as a pulse
of a brief northerly swell from a tropical system moves into the
local offshore Atlantic waters, deteriorating marine conditions
across the Atlantic waters.

&&

.BEACH FORECAST...

There is a moderate risk of rip currents along the northern and
western coastal areas of Puerto Rico, including Culebra and St.
Croix. For the remaining coastal areas, the risk will stay low.
Similar conditions are expected to persist from Friday into
Saturday. By Sunday, however, the rip current risk will increase
to high as a northerly swell generated by Tropical System Humberto
moves northward.

In addition, thunderstorms producing frequent
cloud-to-ground and cloud-to-water lightning may impact local
beaches. If you hear thunder, seek shelter indoors or move to a
safe location immediately.
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Re: Caribbean - Central America Weather

#21944 Postby cycloneye » Sat Sep 27, 2025 4:37 am

Area Forecast Discussion
National Weather Service San Juan PR
426 AM AST Sat Sep 27 2025

.KEY MESSAGES...

* An Extreme Heat Warning is in effect for all coastal areas and
urban sectors of Puerto Rico, while a Heat Advisory is in
effect for Culebra, Vieques, and the U.S. Virgin Islands. Heat
indices are forecast to peak between 12 PM and 2 PM, reaching
up to 114°F.

* An increase in moisture is forecast from Monday
into Tuesday; however, Saharan dust will also move in,
resulting in hazy skies in some isolated areas.

* A long period northeasterly swell from Hurricane Humberto will
arrive across the northern local waters, increasing seas and
breaking waves, and resulting in a high risk of rip currents.
Additionally, there is a small craft advisory in effect from
this afternoon across the offshore Atlantic waters.

&&

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

For today, a meandering shallow band of moisture between Major
Hurricane Humberto to our northeast and PTC 9 near Cuba will support
an unstable and moist airmass over the local area. A weak mid-level
ridge will move over and southwest of the region by Sunday. Light to
calm winds with a southerly component will continue through the rest
of the weekend as TC Humberto moves north of the area. Therefore,
diurnally induced afternoon showers and thunderstorms, triggered by
daytime heating, weak sea breezes, and orographic lift, are expected
this afternoon. Due to the light steering winds, slow-moving
afternoon thunderstorms will increase flooding concerns, mainly
across PR. At the same time, the USVI should see an increase in
showers throughout the morning hours today, with a slight chance of
thunderstorms as they drift slowly between the Atlantic waters and
the Anegada Passage. Another surge in passing showers is expected by
late Monday.

Although a dip in PWAT is expected on Sunday, the 850-700mb lapse
rates will remain elevated; therefore, strong afternoon convection
is possible once again over portions of the Cordillera and western
PR. Elsewhere, the mid-level ridge and drop in PWAT are expected to
inhibit widespread shower development over the area. Winds will pick
up between 10-15 kt on Monday with an easterly component, and a weak
Saharan Air Layer will bring minor concentrations of Saharan dust.
However, as Humberto moves into the Southwestern Atlantic, it will
pull another shallow band of moisture over the islands, which will
enhance the diurnal convection cycle over the islands.

Temperatures and overall humidity will also remain well above
average, as the 925mb temperature and 850mb Theta-e values are
expected to continue at normal to above-normal levels, particularly
today and on Sunday. Therefore, despite the active afternoon
convection, high heat stress will be a primary concern. High
temperatures are expected to remain in the low to mid-90s across
most coastal areas, with Extreme Heat Warnings/Heat Advisories
anticipated each day.

Furthermore, swells generated by Humberto will increase the risk of
life-threatening rip currents along the north and east-facing
beaches of the islands from late today through Sunday night.

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

The long-term forecast remains on track. On Tuesday, the surface
pattern will continue under the influence of Hurricane Humberto
well north of the region and a strengthening surface high pressure
over the central Atlantic, resulting in a weak southeasterly wind
flow. Under this setup, the islands will experience brief
intrusions of Saharan dust with precipitable water values near 1.6
inches, close to the 25th percentile for the year. This pattern
will favor a generally stable day with calm conditions in the
morning and localized afternoon activity. Similar weather will
persist on Wednesday, while on Thursday precipitable water is
forecast to decrease further, with global model guidance
suggesting values nearly two standard deviations below normal.
Relative humidity between 700–500 mb also shows a drying trend,
supporting mostly stable mornings with only localized showers
across the interior regions.

A more unsettled pattern is expected from Friday into Saturday as
global model guidance indicates an increase in instability, with
700–500 mb lapse rates steepening and 500 mb temperatures slightly
decreasing to around –6 °C due to an upper-level trough extending
from the western Caribbean into the islands. At the surface, a
weakening of the pressure gradient is anticipated as a tropical
system moves into the northwestern Atlantic, reducing the
influence of the surface high pressure. This evolving pattern will
induce surface convergence, enhance instability, and result in
very weak steering flow. Consequently, a variable pattern is
forecast, with long-lasting afternoon showers primarily affecting
the interior, but drifting into different sections of the islands
due to weak winds.

&&

.AVIATION...

(06Z TAFS)
Mainly VFR conds expected early in the period, however, SHRA/TSRA
over the local waters may cause tempo MVFR conds across the USVI
terminals through the morning hours. Thereafter, early afternoon
convection over the northern half of PR will trigger MVFR areas in
and around TJSJ/TJBQ thru 27/21z. Weak sea breezes will dominate
the local winds, however, the low-level winds will continue with a
southerly component.

&&

.MARINE...

A pulse of a long period northeasterly swell from Major Hurricane
Humberto will increase seas across the local waters from this
afternoon through the rest of the weekend. Seas are forecast to
build to around 7 feet across the offshore Atlantic waters by 2
PM, spreading into the coastal Atlantic waters and the Anegada
Passage during the weekend. As a result, a Small Craft Advisory
will be in effect starting at noon today and extend to the coastal
Atlantic water later toninght into Sunday. Seas are expected to
remain between 7 and 8 feet across the Atlantic waters and up to
5 feet across the Caribbean waters. Improving marine conditions
are forecast from Monday as the energy from the swell diminish
across the area.

&&

.BEACH FORECAST...

A long period northeasterly swell from Major Hurricane Humberto
will increase breaking waves starting at 12 PM this afternoon. As
a result, deteriorating coastal conditions are expected,
especially across the northern coastal areas of Puerto Rico,
including beaches along the northeast PR. For Culebra, Vieques,
the U.S. Virgin Islands, and northwestern Puerto Rico, the risk
will remain moderate. However, deteriorating conditions are
forecast to spread to more coastal areas, including St. Croix,
Culebra, and the northwestern coast of Puerto Rico, during the
weekend. Improving coastal conditions are expected beginning on
Monday.
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Re: Caribbean - Central America Weather

#21945 Postby cycloneye » Sun Sep 28, 2025 6:32 am

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Sun Sep 28 2025

.KEY MESSAGES...

* Another warm day is forecast today, with heat indices reaching
111 to 114. Therefore, an Extreme Heat Warning will be in
effect from 10 AM to 5 PM for the coastal and urban areas of
Puerto Rico, and a Heat Advisory will be in effect for Culebra,
Vieques, and the U.S. Virgin Islands for the same period.

* Localized afternoon convection is expected each afternoon from
today through Monday.

* An extended period of northeasterly swell from Hurricane Humberto
will continue to result in hazardous marine and coastal
conditions from today through late tonight.

&&

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

Scattered showers and isolated thunderstorms were noted across the
Mona Passage into the Caribbean waters and over the offshore
Atlantic waters during the early morning hours. Some of this
activity moved over the coastal areas of southwestern PR and St.
Croix. However, rainfall amounts were not significant. Minimum
temperatures ranged from the mid-60s across the higher elevations of
PR to the mid and upper 70s across the lower elevations. In the U.S.
Virgin Islands, temperatures were from the mid-70s to the low 80s.
Winds were light with a south to southwesterly component.

Another hot day is expected due to the combination of calm to light
winds with a southerly component, and as the 925mb temperature
remains well above normal, near 24C. Therefore, maximum temperatures
will again reach the low 90s across most coastal areas, and higher
dewpoints under weak sea breezes, particularly along the northern
coast of PR, will enhance the heat threat before the onset of
afternoon showers. Heat indices could increase up to 112°F in those
areas. Hi-res and global models suggest limited shower activity
today over the islands; however, satellite data indicate that the
shallow band of moisture that produced the overnight shower and
thunderstorm activity is merging with an external rainband from TC
Humberto. As this moisture is pulled over the islands during the
day, afternoon convection is expected mainly over the Cordillera.
Under a weak southwesterly steering flow, the showers are expected
to drift northeastward into nearby municipalities.

Minor concentrations of Saharan dust are expected to move over the
islands on Monday. Although the precipitable water content is
forecast to range from below normal to normal levels, the 850-700 mb
lapse rates are expected to remain in the 50th percentile throughout
the period. Therefore, a similar weather pattern is expected
throughout the short-term period. However, as winds pick up from 10
to 15 knots from the east to southeast, the focus of afternoon
convection will shift once again over west/northwest PR. In
addition, another band of moisture associated with distant Humberto
is still expected to increase shower activity across the USVI and
eastern PR between Monday night and Tuesday morning.

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

On Wednesday, at the surface, a high-pressure system will combine
with the extended influence of Hurricane Humberto, maintaining a
southeasterly wind flow across the region at least until early
Thursday. This surface pattern will favor a variable weather
regime with patches of fragmented moisture moving in and out of
the area. Precipitable water values on Wednesday are forecast to
range between 1.5 and 1.7, near the 25th percentile. From Thursday
into Friday, global model guidance continues to suggest an
interesting mix of patterns. At the surface, lapse rates between
850 and 700 mb indicate a stable pattern, with values dropping two
standard deviations below climatological normals. In contrast,
the mid-to-upper levels will exhibit increased lapse rates between
700 and 500 mb and colder 500 mb temperatures, ranging from -6 to
-7 degrees. Although this pattern supports afternoon convection,
models continue to show limited moisture with precipitable (PWAT)
of 1.50 inches. This pattern basically suggest a typical weather
pattern with localized showers, particularly across northwestern
Puerto Rico on Thursday.

On Friday into Sunday, veering surface winds are expected as the
tail of a tropical system moves eastward into the northeastern
Atlantic, weakening the surface high pressure diminish the
pressure gradient result in variable winds for the remainder of
the period. Therefore, on Friday, winds will become from the
north, inducing an advective pattern with sowers along northern
coastal areas in the morning and early evening hours. A rapidly
change will occur on Saturday, winds return from the east,
changing the weather pattern again. On Sunday, an increase in
tropical moisture with precipitable water values peaking up to 2
inches. So far today, Sunday looks like the wettest day of the
long term.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions are expected across all terminals during the
next 24 hours. However, iso TSRA/SHRA over central PR should cause
mostly VCTS across the PR terminals btw 28/17-21. Otherwise, VCSH
expected early in the fcst at TJPS/TISX/TIST. S-SW winds up to 13 kt
will continue mainly blo FL050.

&&

.MARINE...

Hazardous marine conditions continue due to a long-period
northeasterly swell generated by Major Hurricane Humberto, located
well to the north of the region. Seas will remain between 7 and 8
feet across the Atlantic waters and the Anegada Passage. A Small
Craft Advisory remains in effect through midnight. Improving
marine conditions are forecast from Monday into the workweek.
However, by midweek, model guidance suggests another northwesterly
swell will reach the local waters, deteriorating conditions once
again.

&&

.BEACH FORECAST...

Extremely hazardous coastal conditions are expected along the
northern and northeastern coasts, with breaking waves exceeding 10
feet. A High Surf Advisory is in effect until 6 PM AST for Culebra
and St. Croix. A High Risk of Rip Currents is also in effect.
Elsewhere, the rip current risk will remain moderate through
tomorrow. Improving coastal conditions are forecast from late
Monday into Tuesday. By midweek, another northwesterly swell is
expected to reach the region, worsening coastal conditions again.

&&
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Re: Caribbean - Central America Weather

#21946 Postby cycloneye » Mon Sep 29, 2025 4:42 am

Area Forecast Discussion
National Weather Service San Juan PR
518 AM AST Mon Sep 29 2025

.KEY MESSAGES...

* Another warm day is expected across the local islands, with heat
indexes exceeding 108 degrees Fahrenheit. Hence, a Heat Advisory
is in effect for the urban and coastal areas of Puerto Rico and
the U.S. Virgin Islands from 10 AM AST through 5 PM AST.

* For the U.S Virgin Islands, expect passing showers later tonight
across the islands.

* A large, long period northerly swell will promote hazardous
seas and life-threatening rip currents from late Thursday
through Sunday.

&&

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

Isolated to scattered showers and brief isolated thunderstorms were
noted overnight across the Caribbean waters. Showers moved briefly
over the southern sections of the islands. Minimum temperatures
ranged from the upper-60s across the higher elevations to the upper
70s and low 80s across coastal areas. The wind was light from the
south to southeast.

Minor concentrations of Saharan dust will move over the islands
today. However, the precipitable water content will remain at normal
to above normal levels as Hurricane Humberto, well north of the
area, continues to pull tropical moisture in a deep southerly wind
flow over the eastern Caribbean. Shower activity is expected to peak
from late this afternoon through tonight across portions of the USVI
and east/southeast PR, with locally induced afternoon convection
expected over northwest PR. Trade winds will return by Tuesday, but
will turn once again from the south and become gentle to light on
Wednesday. Therefore, an elevated heat threat will persist across
the lower elevations of the islands. Maximum temperatures are
expected to reach the low to mid-90s each day across most coastal
counties. In terms of precipitation, a drier air mass is expected to
gradually fill from Tuesday into Wednesday, however, peaks on
moisture content are anticipated during the nighttime, favoring
showers across the windward areas of the islands. Also, locally
induced afternoon showers with isolated thunderstorms cannot be
ruled out over the NW quadrant of PR, particularly on Tuesday.

&&

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

Some changes were introduced to the long-term forecast. The wind
pattern will likely vary due to weather features inducing a col area
that should move over the CWA and promote lighter winds through at
least Sunday. A drier air mass filtering into the region and the
influence of a mid to upper level ridge will drop relative humidity
values and suppress deep convection activity, promoting stability
aloft. Based on the deterministic guidance of the GFS and ECMWF,
Precipitable Water (PWAT) values should stay between below-average
and seasonal values (1.5 - 1.7 inches, lower chance reaching 1.8
inches), but daytime heating combined with local effects could
lead to shower activity each day by midday into the afternoons.
Although deep convection activity may be limited, 500 mb
temperatures may cool and remain seasonal (-6 and -7 degrees
Celsius), increasing chances of isolated thunderstorms during the
afternoons. Due to winds becoming lighter, any shower activity
will likely remain stationary, increasing the flooding potential.
Hence, the flooding threat will remain limited to elevated over
the aforementioned areas. Moisture content will gradually increase
by Monday due to the approach of a vigorous tropical wave to the
CWA. Although there’s variability between ensemble members,
there’s a tendency for PWAT values to increase up to near above-
normal values (1.8 - 2.0 inches).

With well-above-normal 925 mb temperatures, slow SE-S winds, and
available moisture, heat indices are very likely to exceed 100
degrees Fahrenheit and reach Heat Advisory Criteria. Therefore, the
heat threat will remain elevated for the rest of the forecast
period.

&&

.AVIATION...

(06Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, tempo MVFR conds are possible at
TJBQ btw 29/18-22 due to -TSRA/SHRA over NW PR. Elsewhere, brief
periods of -RA/VCSH expected at times. HZ due to Saharan dust will
increase over the local area, but VSBY will remain P6SM. SSE winds
up to 12 kt with sea breeze variations expected after 29/13z.

&&

.MARINE...

The long-period northerly swell from Major Hurricane Humberto
continues to diminish across the region. Moderate southeasterly to
easterly winds will continue for the next few days, becoming
gentle by the end of the workweek. A large northwesterly swell
will promote hazardous marine conditions by late Thursday night
through the upcoming weekend.

&&

.BEACH FORECAST...

The long-period northeasterly swell from Major Hurricane Humberto
continues to diminish across the region. Although the rip current
risk downgraded to moderate across the northern beaches of Puerto
Rico, including Culebra, and St. Thomas and St. John in the U.S.
Virgin Islands, beachgoers are urge to exercise caution. A large
northerly swell will promote hazardous beach conditions by late
Thursday night through the upcoming weekend.
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Re: Caribbean - Central America Weather

#21947 Postby cycloneye » Tue Sep 30, 2025 4:55 am

Area Forecast Discussion
National Weather Service San Juan PR
507 AM AST Tue Sep 30 2025

.KEY MESSAGES...

* Warmer conditions will persist for the next few days. A Heat
Advisory is in effect for all urban and coastal areas from 10
AM AST through 5 PM AST. Stay hydrated and avoid prolonged sun
exposure.

* For the U.S. Virgin Islands, shower activity will increase later
tonight, with limited flooding threat.

* A large, long-period swell arriving by late Thursday night will
promote hazardous marine and beach conditions across the
islands, persisting through the weekend.

&&

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

Passing showers embedded in the trade winds moved over portions of
the U.S. Virgin Islands, and over the eastern third and south coast
of Puerto Rico overnight. The Doppler radar estimated up to half an
inch of rain between Las Piedras and Humacao. Minimum temperatures
ranged once again from the upper-60s across the higher elevations to
the upper 70s and low 80s across coastal areas. The wind was from
the southeast at 10 mph or less. Showers today will be enhanced by a
band of precipitable water content of around 2.00 inches. However, a
drier air mass of around 1.50 inches will gradually filter over the
region from the southeast through Wednesday. Meanwhile, a low-level
trough is expected to develop over the eastern Caribbean late in the
period, enhancing moisture transport into the local area by
Thursday. Moderate southeast winds will prevail today, and become
lighter and more southerly on Wednesday, by Thursday winds will
abate furthermore and acquire a north-northeasterly component due to
the influence of the trough and a col area developing just north of
the region.

An elevated heat threat will persist across the lower elevations of
the islands through the shor-term period, with heat advisories
likely issued each day, with a possible extreme heat warning on
Wednesday due to the expected deep layered southerly flow. Across
the lower elevations of the islands, maximum temperatures are
expected to reach the low to mid-90s through at least Wednesday,
while the northerly component on Thursday may bring temperatures
down by a degree or two. Regardless, heat concerns will continue.

Although a drier air mass will filter over the region early in the
period, the 850-700mb and 700-500mb RH layers are expected to
increase from the 25th percentile today to the 50th percentile on
Wed/Thu. Also, in terms of stability, conditions are forecast to
become gradually more unstable at the mid-levels, as warmer lapse
rates and colder 500mb temperatures are anticipated on both days.
This is supported by a series of short-wave troughs moving along the
base of weak ridge north of the region. Therefore, afternoon
thunderstorms and showers are expected to develop each day, mainly
along portions of the Cordillera Central and in areas favored by the
weak steering winds, with the combination of intense heating,
lighter winds, and increasing instability favoring stronger
thunderstorms and higher rainfall accumulations on Wednesday and
Thursday. Across the USVI, the frequency of passing showers will
increase early in the period, but as winds decrease, the locally
induced late morning/early afternoon showers over land areas could
linger longer than usual.

&&

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

Variable conditions are expected through the long-term forecast.
Winds will remain light and variable due to a col region
developing over the area, slightly increasing by Sunday, then
becoming lighter by the start of next workweek. As mentioned in
the previous discussion, a drier air mass is expected to filter
into the region due to the influence of a mid- level ridge that is
expected to linger northeast of the region. However, the latest
model guidance suggests that a mid-to- upper trough may move
south of the CWA by Friday and Saturday. The presence of this
feature is reflected in the projected 500 mb temperatures (between
-6.5 and -7.5 degrees Celsius), near below climatological
normals, enhancing the deep convection activity. As the
deterministic guidance of the GFS and ECMWF continues to suggest
low to seasonal PWAT values (1.6 - 1.8 inches), expect seasonal
weather conditions during the upcoming weekend, with isolated
showers moving over the local waters into windward sectors and
afternoon convection. Taking into consideration the wind speed,
there’s a high chance that any shower developing over the area
will stay stationary, meaning that the flood potential will be
more localized, particularly over the mountain ranges of Puerto
Rico. By early next week, a gradual increase in moisture content
and favorables conditions for deep convection are likely due to a
series of upper level troughs approaching the CWA. From the latest
model guidance, PWAT values should increase close to near above
normal values (1.8- 2.0 inches, low chance of reaching 2.2
inches). This could increase the frequency of showers and
thunderstorms moving across the local islands on Monday and
Tuesday, elevating flood potential. Given the expected conditions,
the flooding threat will remain from limited to elevated for the
rest of the forecast period.

The tendency of warmer conditions across the islands is expected
to continue due to above-normal temperatures, available moisture,
and light winds. Hence, the heat threat will remain limited to
elevated for the urban and coastal areas of Puerto Rico and the
U.S. Virgin Islands.

&&

.AVIATION...

(06Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, tempo MVFR conds are possible at
TJBQ btw 30/16-22 due to TSRA/SHRA developing over NW PR. Elsewhere,
passing SHRA should cause mostly VCSH at times. Winds will continue
from the SE up to 16 kt blo 1000 ft. Sea breeze variations expected
mainly at TJBQ aft 30/13z.

&&

.MARINE...

Moderate southeasterly to easterly winds will continue for the next
few days, becoming gentle by Thursday. A large northerly swell will
promote hazardous marine conditions for small craft by late Thursday
night through the upcoming weekend.

&&

.BEACH FORECAST...

Today, the risk of rip current is expected to remain moderate for
the north-facing beaches of Puerto Rico, including Culebra, and
St. Thomas and St. John in the U.S. Virgin Islands. Although the
risk is moderate, life-threatning rip currents are still possible
along the surf zone, beachgoers should exercise caution.
The risk is expected to decrease on Wednesday, but a large, long-
period northerly swell arriving by late Thursday night will
promote life- threatening rip currents through at least Sunday.
Hence, beachgoers are urged to exercise caution and heed the
advice of the flag warning system.
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Re: Caribbean - Central America Weather

#21948 Postby cycloneye » Wed Oct 01, 2025 4:30 am

Area Forecast Discussion
National Weather Service San Juan PR
509 AM AST Wed Oct 1 2025

.KEY MESSAGES...


* Hot temperatures today will promote hazardous heat conditions
across the islands. An Extreme Heat Warning is in effect for all
urban and coastal areas of the islands from 10 AM AST through 5
PM AST. Stay hydrated and avoid prolonged sun exposure.

* Showers and thunderstorms will increase the flooding and
lightning threat over interior and northern portions of Puerto
Rico this afternoon, while the U.S. Virgin Islands can expect
occasional passing showers throughout the day.

* A large, long-period northerly swell is expected by late
Thursday night, bringing hazardous marine and beach conditions
across the islands in the upcoming weekend.

&&

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

Calm weather conditions prevailed overnight with a few showers
moving across the local waters, and some making their way inland
across the US Virgin Islands and windward locations in PR. Winds
were mainly from the southeast, calm to light and variable. In
general, skies were mostly clear with some clouds moving through the
Virgin Islands. Low temperatures ranged from the mid- to upper 70s
along the coastal areas to the mid- to upper 60s across the
mountains.

An easterly perturbation will increase the available moisture across
the islands today, which, combined with a light southeasterly wind
flow and the above-normal maximum temperatures, will result in
extreme heating across the urban and coastal locations in the US
Virgin Islands and Puerto Rico. As a result, an Extreme Heat Warning
is in effect from 10 AM AST to 5 PM AST. The excessive heating will
then combine with the local effects, giving place to one or two
strong afternoon thunderstorms across the interior and northern
portions of PR. These thunderstorms will result in frequent cloud-to-
ground lightning, downpours, and gusty winds. The afternoon
convection is expected to dissipate by evening, leaving mostly clear
skies and calm weather conditions for the islanders. The weak
steering wind flow will allow the thunderstorms to remain almost
stationary, thus creating a slight risk of flooding rains,
especially if forming over areas with poorly drained conditions.

A similar weather pattern will prevail in the short term, consisting
of warm to hot indices during the maximum heating time of the day,
followed by afternoon convection across portions of PR, and a few
passing showers across the US Virgin Islands and windward locations
of PR overnight and early in the morning.

&&

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

The long-term forecast remains on track, with a transition to
wetter and unstable conditions for the first part of the
workweek. A tropical wave over Central Atlantic approaching the
Caribbean Basin is expected to arrive by Saturday, increasing
shower activity across the local islands but remaining limited due
drier air in the 700 - 300 mb layer. The latest model guidance
continues to suggest the approach of upper- level troughs over the
CWA by Saturday and lingering for the remainder of the period.
From the latest deterministic guidance of the GFS and ECMWF,
Precipitable Water (PWAT) values may increase to above normal
values (2.0 - 2.2 inches) by Monday through Wednesday.
Additionally, this could push relative humidities in the lower and
mid-levels to well above normal (around 80%). The presence of
these troughs should promote colder 500 mb temperatures (-7 and -8
degrees Celsius), favorable for deep convection activity. The
Galvez-Davison Index (GDI) also suggests the potential of isolated
to scattered thunderstorms on Monday and Tuesday, increasing the
lightning threat. Another factor that may influence the shower and
thunderstorm activity is that winds will once again drop by late
Monday night, meaning that any convection activity could remain
stationary and increase the flooding threat as well. At the
moment, expect an increase in shower and thunderstorm activity,
particularly over windward sections of the islands and deep
convection activity affecting mostly the mountain ranges of Puerto
Rico, gradually improving by Wednesday. Although the flooding and
lightning threat will remain limited to elevated during the long-
term forecast, confidence remains low due to variability between
ensemble members.

&&

.AVIATION...
(06z TAF)

VFR conditions will prevail today for all TAFs. However, a few TSRA
will develop during the afternoon (between 01/15-22z), which could
impact JSJ/IST/ISX or JBQ, creating brief MVFR conditions if those
TSRA move over them. Winds will prevail mainly from the SE-ESE at 5-
10 kt, with sea breeze variations after 01/13z, and gusty winds near
TSRA. Winds will turn calm to light and VRB aft 01/23z.

&&

.MARINE...

Light to gentle southeasterly winds will continue for the next few
days as a col area approaches the region. A tropical wave approaching
the Caribbean Basin should increase shower and thunderstorm activity
across the regional waters and local passages by Saturday. A large
long-period swell will promote hazardous marine conditions for small
craft by late Thursday night through the upcoming weekend.

&&

.BEACH FORECAST...

As anticipated, the risk of rip current became low for all beaches
of Puerto Rico and the U.S. Virgin Islands. Nevertheless,
a large, long-period swell is anticipated to arrive by late
Thursday night and persisting through at least Sunday. Life-
threatening rip currents are expected mainly along north-facing
beaches of Puerto Rico and the northern U.S. Virgin Islands. This
swell could also increase high surf potential as well, hence,
beachgoers should continue monitoring the beach forecast and heed
the advice of the flag warning system. Additionally, they should
stay weather alert due to the potential of showers and
thunderstorms moving over the western and northwestern coastal
areas of Puerto Rico in the afternoon.
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Re: Caribbean - Central America Weather

#21949 Postby cycloneye » Thu Oct 02, 2025 4:41 am

Area Forecast Discussion
National Weather Service San Juan PR
452 AM AST Thu Oct 2 2025

.KEY MESSAGES...

* Warmer conditions will continue today, particularly across the
urban and coastal areas of Puerto Rico and the U.S. Virgin
Islands. A Heat Advisory is in effect from 10 AM through 5 PM
AST. Stay hydrated and avoid prolonged sun exposure.

* Showers and thunderstorms along interior and northern portions
of Puerto Rico will increase flooding and lightning risk this
afternoon.

* Once again, occasional passing showers are expected across the
U.S. Virgin Islands throughout the day.

* A long-period swell will arriving late tonight will deteriorate
marine and coastal conditions through early next week. Small
Craft Advisories are in effect from midnight tonight for the
Atlantic offshore waters and from noon Friday for the Atlantic
coastal waters and the Mona Passage.


&&

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

Calm weather conditions prevailed overnight with little to no rain
for the US Virgin Islands and windward locations in PR. Winds were
calm to light and variable, influenced by a land breeze. In general,
skies were mostly clear with some clouds moving through the Virgin
Islands. Nighttime cooling allowed the low temperatures to drop from
the mid- to upper 70s in coastal areas to the mid- to upper 60s
across the mountains.

A col area near the region will continue to promote light
southeasterly winds today and tomorrow. Moisture content is expected
to remain near or below normal through Friday. However, the
available moisture, combined with above-normal expected maximum
temperatures, will result in warm to hot heat indices during the
peak of daily heating this afternoon. Thus, a Heat Advisory is once
again in effect for coastal and urban locations in the US Virgin
Islands and Puerto Rico. Excessive heating, enhanced by local
effects and variations in sea breezes, will result in strong
thunderstorms across the interior and northern regions of PR. This
activity is expected to result in cloud-to-ground lightning, heavy
rain, and strong winds. Due to weak steering winds, expect some
thunderstorms to remain almost stationary, leading to a heightened
risk of flooding in poorly drained areas. Be prepared. These storms
will likely clear by evening, resulting in calm weather. A similar
weather pattern is expected to repeat on Friday.

A long-period north-northwesterly swell will impact the Atlantic
coastline, producing dangerous breaking waves and life-threatening
rip currents starting late Thursday night or early Friday morning.
It's essential to acknowledge the significant threat this poses to
beachgoers who go to the north-facing beaches in Puerto Rico and the
northern US Virgin Islands. Avoid becoming just another statistic.

For Saturday, a weak tropical wave moving across the Caribbean Sea
and a frontal boundary lingering north of the islands over the
Atlantic Ocean will increase the moisture content somewhat, as well
as the potential for more frequent passing showers followed by
isolated to scattered thunderstorms during the afternoon.

&&

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

No major changes were introduced to the long-term forecast. A
transition to an unstable and wetter pattern is still anticipated by
the beginning of the workweek, with gradual improvement by
Wednesday. Global models continue to suggest the approach of an
upper-level trough into the CWA by Sunday night. From the
deterministic guidance of the GFS and ECMWF, the tendency towards
wetter conditions is increasing, as Precipitable Water (PWAT) values
may range between 2.0 and 2.2 inches, above the climatological
normal. The latest model solutions also suggest a rise in relative
humidity content in the low and mid levels as well (> 60 %, up to 80
- 90%) during Monday and Tuesday. In terms of instability, the
presence of this upper feature should bring colder than normal 500
mb temperatures (down to -8 degrees Celsius), favorable for the
development of strong thunderstorms. The latest Galvez-Davison Index
(GDI) tool keeps suggesting the potential of isolated to scattered
thunderstorms across the CWA, higher on Monday and Tuesday. As
mentioned in the previous discussion, winds will become lighter late
Monday night and Tuesday, meaning that there’s a high chance of
stationary showers and thunderstorms. Given the expected conditions,
the potential of flooding and lightning will increase, particularly
over mountain ranges and eastern Puerto Rico, including Vieques and
Culebra, and the U.S. Virgin Islands.

Conditions should gradually improve by Wednesday, as a drier air
mass may filter into the region. Although PWAT may drop to seasonal
values (1.5 - 1.7 inches), the available moisture combined with
diurnal heating and local effects could trigger convection activity
in the afternoon, affecting mainly portions of interior and western
Puerto Rico, including the San Juan Metropolitan Area. Nevertheless,
the likeliest scenario could be mostly ponding of water over
roadways, urban, and poorly drained areas.

The National Hurricane Center is monitoring a tropical wave expected
to move off the coast of Africa in the next few days, with a 20%
chance of cyclonic formation in the next 7 days. The latest model
solutions suggest an increase in moisture content due to this
tropical wave approaching the Caribbean Basin by late Thursday
night, but the variability between them is high, introducing
uncertainty to the forecast. Hence, we’ll keep monitoring the
development of this system.

&&

.AVIATION...

(TAFs 06z)

VFR conditions will prevail today for all TAFs. However, a few TSRA
will develop during the afternoon, between 02/15-22z, which could
impact JSJ or JBQ, creating brief MVFR conditions if those TSRA move
over them. Winds will prevail mainly from the S-SE at 5-10 kt, with
sea breeze variations after 02/13z, and gusty winds near TSRA. Winds
will turn calm to light and VRB aft 02/23z.

&&

.MARINE...

A col near the region will promote a light to gentle southerly wind
flow across the islands through Friday. A long-period north to
northwesterly swell will begin to spread across the local Atlantic
waters late tonight and into Friday, deteriorating marine and coastal
conditions through early next week. Additionally, a weak tropical
wave is expected to move over the Lesser Antilles by Friday, moving
near the islands by Saturday. At the same time, a frontal boundary
will remain positioned to the north over the Atlantic.

&&

.BEACH FORECAST...

No major changes were introduced to the beach forecast. As
anticipated, the rip current risk increased to moderate mainly for
the northern beaches of Puerto Rico, including Culebra. As
mentioned in previous discussions, a long-period swell will arrive
late tonight, bringing hazardous beach conditions through at
least early next week. Life-threatening rip currents are expected
along the north- facing beaches of Puerto Rico, including Vieques
and Culebra, and the northern U.S. Virgin Islands, spreading over
west-facing beaches of Puerto Rico and St. Croix in the U.S.
Virgin Islands during the weekend. Additionally, the potential of
High Surf conditions is increasing due to high chance of breaking
waves above 10 feet. Therefore, citizens and visitors are
encouraged to continue monitoring the beach forecast and heed the
advice of the flag warning system. Regarding the weather forecast,
beachgoers should stay weather alert due to the potential of
showers and thunderstorms near and/or approaching the beach zone,
particularly over the western and northeastern coastal areas of
Puerto Rico.
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Re: Caribbean - Central America Weather

#21950 Postby cycloneye » Fri Oct 03, 2025 4:36 am

Area Forecast Discussion
National Weather Service San Juan PR
502 AM AST Fri Oct 3 2025

.KEY MESSAGES...

* A strong, long-period northerly swell will create hazardous
marine and beach conditions across the islands through at least
early next week.

* Showers and thunderstorms in the afternoon over will enhance the
flooding and lightning threat for the next few days. If thunder
roars, stay indoors.

* Occasional passing showers are expected across the U.S. Virgin
Islands tonight through early Saturday.

&&

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

Tranquil conditions prevailed during the night hours across Puerto
Rico and the Virgin Islands. Some showers managed to form in the
local waters, but otherwise, skies were mostly clear.

A series of deep-layered longwave troughs are maintaining very weak
winds across the islands. In fact, the steering flow is expected to
be from the northeast at 4 to 8 kts today, from the southeast at 4
to 10 knots on Saturday, and also from the southeast on Sunday, but
a little stronger, with speeds around 10 kts. There is also a weak
low to mid level ridge centered west of Puerto Rico. This feature
will keep moisture below normal for today. Even though the
atmosphere is not prime for widespread significant rainfall, diurnal
heating will still trigger showers and isolated thunderstorms across
the Cordillera Central in Puerto Rico. Since winds are light, some
localized urban flood could develop, while isolated lightning
strikes cannot be ruled out. In the vicinity of the Virgin Islands,
some showers are expected to develop too, although mostly staying
over the local waters.

On Saturday, an upper level low will move over Hispaniola, then
advancing toward the local islands by Sunday. This feature will
induce some showers over the local waters, potentially reaching the
Virgin Islands and portions of eastern Puerto Rico. It is worth
mentioning that moisture at the mid levels will remain below normal,
although it will increase a little at the surface. Nevertheless,
these conditions should still support afternoon showers and isolated
thunderstorms each afternoon. On Saturday, the focus of the rain
should be along the Cordillera Central. On Sunday, the western
interior and northwestern portions of Puerto Rico are favored. These
areas will likely experience localized urban and small stream flood.
Thunderstorms are not expected to be too widespread, but some
lightning strikes are still anticipated each afternoon.

&&

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

The long-term forecast remains on track, with a wet and unstable
pattern for the beginning of the workweek. Recent model guidance
indicates an upper-level cutoff low over the region, which is
expected to gradually move south and migrate westward by the end of
the period. As mentioned in previous discussions, the deterministic
guidance from the GFS and ECMWF keeps suggesting an increase in
moisture content, with PWAT values likely to range between 2.0 - 2.2
inches (up to or above climatological values). Additionally,
ensemble members continue to suggest a wetter and unstable pattern
across the CWA on Monday and Tuesday, with Monday through early
Tuesday being the wettest period. A difference between the previous
solution runs is related to instability, as 500 mb temperatures look
slightly warmer (between -6.5 to -7.0 degrees Celsius).
Nevertheless, the latest Galvez-Davison Index (GDI) solution keeps
suggesting the potential of isolated to scattered thunderstorms
across the CWA, but not a widespread scenario. Another factor that
may influence the weather pattern is the low-level wind speed,
expected to increase and remain E-SE during that period. The most
likely scenario remains the same, with an increase in shower and
thunderstorm activity across the windward sections of Puerto Rico
and the U.S. Virgin Islands throughout Monday and early Tuesday. The
deeper convection should be expected in the afternoon, particularly
over the mountain ranges and western/northwestern Puerto Rico. Given
the expected conditions, the flood threat will remain limited to
elevated, and a limited lightning threat is also expected across the
aforementioned areas. The gradual improvement of weather conditions
is still anticipated by Wednesday, as a drier air mass filtering
into the region will promote stability aloft. Nevertheless, this
pattern may increase the heat threat, becoming elevated to
significant on Wednesday and Thursday.

The National Hurricane Center is monitoring a tropical wave expected
to move off the coast of Africa in the next few days, with a 20%
chance of cyclonic formation for the next 7 days. The latest model
solutions continue to suggest an increase in moisture content by the
end of the forecast period due to this tropical wave approaching the
Caribbean Basin, but the variability between them continues high in
terms of trajectory and intensity. Hence, the uncertainty remains
high for Friday’s forecast.

&&

.AVIATION...

(06Z TAFS)

Mainly VFR conditions are expected to
prevail. SHRA is expected after 17Z along the Cordillera Central,
causing mountain obscuration. VCTS are also expected for TJPS
after 17Z, with brief periods of reduced VIS and low ceilings.
SHRA in the vicinity of the USVI should cause little to no impact
to operations. Winds are light, coming from the NE and below 10
knots.

&&

.MARINE...

A col near the region will promote a light to gentle variable wind
flow across the islands for the next few days. A long- period north
to northwesterly swell arriving into the region will spread across
the local Atlantic waters and passages today into the weekend,
deteriorating marine and coastal conditions through early next week.
Small Craft Advisories are in effect for the Atlantic offshore and
coastal waters, including the Mona and Anegada Passages.

&&

.BEACH FORECAST...

A strong, long-period northerly swell arriving into the region
will create hazardous beach conditions through at least early next
week. Hence, the high rip current risk is in effect for exposed
coasts to the Atlantic, including western to northeastern Puerto
Rico, Culebra, Vieques, St. Thomas and St. John through at least
Monday night. As mentioned in previous discussions, the potential
of breaking waves exceeding High Surf Criteria is very high,
resulting in localized beach/dune erosion and dangerous swimming
conditions. Therefore, a High Surf Advisory is in effect for the
exposed beaches to the Atlantic as well, from northwestern to
northeastern Puerto Rico, Culebra, and St. Thomas and St. John
through Monday morning. Citizens and visitors are encouraged to
continue monitoring the beach forecast and heed the advice of the
flag warning system. Beachgoers, do not risk your life, is better
to stay out of the water!
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cycloneye
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Location: San Juan, Puerto Rico

Re: Caribbean - Central America Weather

#21951 Postby cycloneye » Sat Oct 04, 2025 4:36 am

Area Forecast Discussion
National Weather Service San Juan PR
306 AM AST Sat Oct 4 2025

.KEY MESSAGES...

* A strong, long-period northerly swell will continue to produce
hazardous marine and beach conditions across the islands through
at least early next week. A Coastal Flood Advisory, Small Craft
Advisories, Rip Current Statements, and High Surf Advisories
remain in effect.

* Showers and thunderstorm activity is expected this afternoon
over portions of central and northwestern Puerto Rico, enhancing
the flooding and lightning threat across the area. If thunder
roars, stay indoors.

* Across the U.S. Virgin Islands, passing showers will move
occasionally over the region through the afternoon hours.

&&

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

Conditions were mostly tranquil during the night hours. Some showers
manage to form in the vicinity of the Virgin Islands and eastern
Puerto Rico, but accumulation over land was very little. Skies were
mostly clear.

The trade winds are still weak, with a steering flow now shifting
from the southeast and at 4 to 8 kts. The winds will increase just a
bit on Sunday and Monday, but still around 8 to 11 kts. At the upper
levels, an upper level low will maintain some instability in the
area, and this feature will linger into early in the workweek.
Moisture is a little below normal today, but it is expected to
increase toward more normal values on Sunday, and even a little more
on Monday due to an approaching tropical wave. In general, the
pattern will favor afternoon showers along the Cordillera Central
and western Puerto Rico today and Monday. Showers could also stream
from El Yunque toward the San Juan metro area. The risk of flooding
will be elevated with a medium chance of these areas experiencing
urban and small stream flooding. Some lightning strikes will be
possible too. In the Virgin Islands, as well as some sections of
eastern Puerto Rico, passing showers will be on the increase by late
Sunday and Monday. While flooding is not really anticipated, ponding
of water and wet roads can still be expected.

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

The forecast period starts with a wet and unstable pattern due to
the influence of an upper-level low over the region. By Tuesday, the
convergence of this low with an approaching weak tropical wave is
expected to enhance the potential of convective activity,
specifically showers and thunderstorms, across the U.S. Virgin
Islands and Puerto Rico. High atmospheric moisture will sustain the
showers and thunderstorm activity through Tuesday evening, with
PWAT content near-to-above-normal (2.00 to 2.25 inches). A
noticeable change is anticipated for Wednesday, as a departing
upper-level low allows drier air to move in, causing PWAT values
to fall to the 1.50 to 1.75 inch range. Looking ahead to Thursday,
local conditions will become dependent on the evolution of a
tropical wave currently near the coast of Africa.

Regarding the potential system, the National Hurricane Center (NHC)
has given this wave a medium formation chance (50%) over the next 7
days. Although the latest model guidance indicate increasing
moisture by the weekend, the system's eventual trajectory and
intensity remain highly uncertain. All residents and visitors must
continue to track the progress of this system as it moves westwards
over the Atlantic Ocean.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions expected to prevail through the forecast
period. After 17-19Z, SHRA and TSRA are expected to develop along
the Cordillera Central. These showers should reach the PR terminals,
causing periods of reduced VIS and low ceilings. VCSH are expected
for VI terminals, but impacts to operations are expected to be
minimal. Winds are light, out of the E to ESE at 2-8 kts.

&&

.MARINE...

A col near the region will promote a light to gentle variable wind
flow across the islands for the next few days. A long-period north
to northwesterly swell will spread across the local Atlantic waters
and passages through early next week, deteriorating marine and
coastal conditions through early next week. A tropical wave will
approach the region by Monday, increasing the frequency of
showers.

&&

.BEACH FORECAST...

A strong, long-period northerly swell will continue to produce
hazardous beach conditions through at least Monday night along the
Atlantic exposed beaches, including from western to northeastern
Puerto Rico, Culebra, Vieques, and the U.S. Virgin Islands. As a
result, there is a high risk of life-threatening rip currents in
the aforementioned areas.

A Coastal Flood Advisory is in effect for all the Atlantic exposed
beaches of the islands through Saturday evening. In addition, a
High Surf Advisory is in effect for these areas through Monday
morning. Please refer to our Coastal Hazard Message (CFWSJU) for
additional details. Residents and visitors are urged to monitor
the beach forecast and follow the beach flag warning system.
Beachgoers, do not risk your life, it's better to stay out of the
water throughout the upcoming weekend!
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