Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
226 AM AST Mon Dec 15 2025

...New SHORT TERM, LONG TERM, AVIATION...

.KEY MESSAGES...
Issued at 214 AM AST Mon Dec 15 2025

* A surge in moisture associated with a pre-frontal trough moving
to the north of the area will promote more unstable and wet
conditions during the first half of the workweek across the U.S.
Virgin Islands and Puerto Rico.

* Choppy to rough seas are expected to continue across the
offshore Atlantic waters through at least today.

* A northwesterly swell is forecast to arrive by midweek,
deteriorating marine and coastal conditions through the upcoming
weekend.

&&

.Short Term(Today through Wednesday)...
Issued at 214 AM AST Mon Dec 15 2025

A surge in moisture associated with a pre-frontal trough moving to
the north is expected in the short-term period. The precipitable
water content (PWAT) is expected to increase to near 1.75 inches
late today, with no significant change in moisture levels through
the rest of the short-term period. Latest satellite imagery
indicates an area of cloudiness and showers moving over the Leeward
Islands into the Anegada Passage. This area will then reach the USVI
early this morning and spread across PR throughout the day. As the
local area lies between the front and a distant surface high
pressure, winds will generally persist from the east to southeast at
5 to 15 knots. For Tuesday and Wednesday, no significant variations
in moisture content are expected. However, the 500mb temperatures
are forecast to be the coldest on Tuesday afternoon, around -6.5C,
which should favor heavier showers and isolated thunderstorm
development. Ponding of water in roads and other poor drainage areas
can be expected each day across the islands, with a higher chance of
urban and small stream flooding on Tuesday in PR.

&&

.Long Term(Thursday through Monday)...
Issued at 214 AM AST Mon Dec 15 2025

The forecast remains on track with previous discussions. A
building surface high-pressure system over the western Atlantic
will continue to push lingering moisture from a frontal boundary
into the local area from Thursday into Friday. This will increase
the frequency of passing showers across Puerto Rico and the U.S.
Virgin Islands, particularly during the morning hours across the
windward portions. As the surface high continues to move over the
Atlantic Ocean, another frontal boundary will move east of the
eastern coast of the CONUS, promoting a northeasterly wind flow
across the area. Under this pattern, cooler temperatures will be
felt across the region during the upcoming weekend. By Sunday,
another surface high pressure behind the front is expected to
strengthen north of the local area, bringing slightly drier
conditions; nonetheless, patches of moisture will continue to move
into the islands, promoting showers from time to time.

&&

.AVIATION...
(06Z TAFS)
Issued at 214 AM AST Mon Dec 15 2025

Mainly VFR conditions are expected early in the fcst period.
However, SHRA en route from the Leeward Islands will reach the USVI
terminals btw 15/12-16z, this may lead to tempo MVFR conds,
particularly at TIST. Additional SHRA is expected to develop in and
around TJSJ and TJBQ btw 15/16-22z, which could lead to brief MVFR
cigs. Winds will increase 8-12 kt from the ESE, with sea breeze
variations at TJSJ/TJBQ aft 15/14z.

&&

.MARINE...
Issued at 214 AM AST Mon Dec 15 2025

A surface high-pressure system across the eastern into central
Atlantic will continue to promote moderate to locally fresh east to
southeast winds across the local waters today. Wind-driven seas
are promoting hazardous marine conditions for small craft
operators across the offshore Atlantic waters, where a Small Craft
Advisory remain in effect at least through Monday morning. A cold
front and another surface high-pressure system will move from the
western Atlantic into the central Atlantic over the next few
days, weakening the pressure gradient and allowing for gentle to
moderate winds from late today and Tuesday. By midweek,
increasing winds and a northwesterly swell will likely deteriorate
marine conditions once again.

&&

.BEACH FORECAST...
Issued at 214 AM AST Mon Dec 15 2025

A moderate risk of rip currents will continue along most beaches
of the islands through mid-week. This means that life-threatening
rip currents are possible in the surf zone, and beachgoers are
encouraged to exercise caution. The moderate risk of rip currents
is expected to prevail across north-facing beaches of Puerto
Rico, Culebra, and the U.S. Virgin Islands, with a low risk
elsewhere. Remember that even when the risk is low, life-
threatening rip currents can still occur, especially near groins,
jetties, reefs, and piers.

By midweek, beach conditions are anticipated to deteriorate again
due to increasing winds and a northwesterly swell spreading across
the local Atlantic waters.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
524 AM AST Tue Dec 16 2025

...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...
Issued at 426 AM AST Tue Dec 16 2025

* Showers will move across the US Virgin Islands at times today,
producing moderate to locally heavy rainfall.

* Showers and isolated thunderstorms this afternoon may lead to a
slight chance of flooding and thunderstorm impacts, extending
from El Yunque into the San Juan metropolitan area and across
the northwest quadrant.

* A long-period northerly swell will arrive late tonight, creating
a high risk of rip currents along the exposed north-facing
beaches in PR, spreading to the rest of the north-facing beaches
from Aguadilla to Fajardo, Culebra, and the northern US Virgin
Islands on Wednesday.

&&

.Short Term(Today through Thursday)...
Issued at 426 AM AST Tue Dec 16 2025

We had calm weather with clear skies, which allowed for nighttime
cooling, resulting in pleasant low temperatures across Puerto
Rico and the US Virgin Islands overnight. Winds were calm to light
and variable, allowing the land breeze to form overnight.

Early this morning, a high likelihood of generally calm
conditions prevailed across the U.S. Virgin Islands; however, a
low-level perturbation embedded in the easterlies is expected to
introduce periods of cloudiness and passing showers,
intermittently affecting the local waters and islands. As this
feature progresses westward, the probability of showers is
expected to increase across the St Croix and the eastern third of
Puerto Rico by mid-morning, with precipitation chances rising
from low (10-20%) to moderate (30-40%) from late morning through
the afternoon across St. Croix and eastern Puerto Rico.

By early to mid-afternoon, model guidance suggests a moderate to
high likelihood (40-70%) of showers developing across the San
Juan metropolitan area and the northwest quadrant of Puerto Rico.
As a perturbation aloft approaches from the west, a slight chance
of isolated thunderstorms is anticipated, particularly during the
afternoon and early evening when instability peaks. Shower
activity is expected to gradually diminish after approximately 8
PM AST, as convection shifts offshore, allowing for a higher
probability of decreasing cloud cover and calmer conditions.
Nonetheless, another surge of moisture embedded in the easterlies
late tonight into early Wednesday morning may increase the
likelihood of showers, with locally moderate to heavy rainfall
possible.

On Wednesday, the weakening of the mid- to upper-level ridge
associated with an approaching upper-level trough, combined with a
jet streak maximum north of the region, will likely enhance
vertical development. At the surface, another low-level
perturbation is expected to increase moisture availability, and
when combined with diurnal sea-breeze convergence, will maintain a
moderate to high probability of showers, particularly across
western Puerto Rico during the afternoon. Consequently, the risk
of flooding rainfall ranges from slight across eastern Puerto Rico
to elevated across the interior and western sections. While a
flooding risk remains unlikely across the U.S. Virgin Islands,
brief periods of moderate to heavy rainfall cannot be ruled out.

By Thursday, model consensus indicates a strengthening ridge over
the Northeast Caribbean, promoting subsidence and drier air aloft.
Despite this, persistent easterly flow will likely sustain a
moderate chance (30–50%) of passing showers, especially across
windward areas of Puerto Rico and the U.S. Virgin Islands during
the afternoon and overnight periods.

&&

.Long Term(Friday through Tuesday)...
Issued at 426 AM AST Tue Dec 16 2025

Mid- to upper-level ridging will dominate the pattern at the
beginning of the long-term period, maintaining generally stable
conditions across the northeastern Caribbean. Subsidence associated
with the ridge will limit vertical development for the most part,
while mid-level relative humidity remains near climatological
values, occasionally dropping to very dry levels near or below 10
percent. This will tend to cap convection and keep shower activity
limited early on.

At the lower levels, precipitable water values will remain somewhat
near normal for most of the period. Patches of moisture will
continue to stream across the area from time to time, resulting in
passing showers, mainly across windward sections and during the
overnight and early morning hours. Rainfall amounts should remain
light and localized with minimal impacts.

Toward the latter portion of the long-term forecast, the mid-level
ridge begins to erode as a polar trough exiting the eastern U.S.
seaboard approaches from the northwest. This will introduce cooler
air aloft, with 500 mb temperatures falling into the -7 to -8 C
range. As a result, lapse rates will steepen, and the environment
will become increasingly unstable. At the surface, an associated
frontal boundary is expected to approach from the northwest late in
the forecast window. Columnar moisture will begin to increase, with
PWAT values trending upward with this setup. The combination of
cooling aloft, increasing moisture, and improved forcing suggests a
more unsettled pattern developing heading into the Christmas period.

This evolving setup could support a higher potential for
thunderstorms and periods of locally heavy rainfall, increasing
the risk for flooding in prone areas. Confidence remains lower at
this time, given that these features occur late in the forecast
window, where uncertainty in timing and strength remains higher.
Subsequent forecasts will continue to refine the potential
impacts, if any.

&&

.AVIATION...
(06Z TAFS)
Issued at 426 AM AST Tue Dec 16 2025

Mainly VFR conditions across all TAF sites. Winds will continue
calm to light and VRB, becoming E-SE winds at 10 to 15 kts, with
higher gust and sea breeze variations aft 16/13Z. -SHRA/SHRA will
approach from the east, first near IST/ISX this morning, spreading
to PR (JSJ) by mid-morning and near JBQ around noon into the
evening. There is a slight risk of TSRA near JBQ/JSJ this
afternoon and evening.

&&

.MARINE...
Issued at 426 AM AST Tue Dec 16 2025

A cold front moving eastward across the Western Atlantic with a
prefrontal trough interacting with an Azores surface high will
promote a moderate to locally fresh easterly wind flow across the
islands today. The cold front will approach the northeast Caribbean
on Wednesday and Thursday and remain off to the northwest of the
islands, bringing trade wind perturbations across the islands,
resulting in showers and afternoon or early evening thunderstorms. A
long period northerly swell will arrive across the local waters late
tonight into Wednesday, deteriorating marine and coastal conditions.
Thus, Small Craft Advisories will be in effect for the middle of the
week.

&&

.BEACH FORECAST...
Issued at 426 AM AST Tue Dec 16 2025

The north and east-facing beaches of PR and the US Virgin Islands
can expect a moderate risk of rip currents through this evening.
The risk of rip currents is low along the west and south-facing
beaches. Then, the arrival of a long-period northerly swell will
increase the risk to high levels for the PR Atlantic Coastline. By
Wednesday, the risk will spread to high from Rincon to Fajardo,
Culebra, St Thomas, and St John. We encourage beachgoers to
monitor the beach forecast, as there is a moderate chance of High
Surf Conditions due to dangerous breaking waves, which could
promote life-threatening coastal conditions along these beaches,
especially on Wednesday.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
532 AM AST Wed Dec 17 2025

...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...
Issued at 429 AM AST Wed Dec 17 2025

* Life-threatening breaking waves and rip currents will impact the
north-facing beaches of PR from Rincon to Fajardo and Culebra.

* Life-threatening rip currents will form along the exposed north-
facing beaches in St Thomas and St John.

* Showers and isolated thunderstorms this afternoon may lead to a
slight chance of flooding and thunderstorm impacts, extending
from El Yunque into the San Juan metropolitan area and into the
interior, north- central, and northwest PR.

* Dangerous marine conditions for small craft operators will
prevail today across the local Atlantic Waters, and Caribbean
Passages.

&&

.Short Term(Today through Friday)...
Issued at 429 AM AST Wed Dec 17 2025

Although we observed calm weather with pleasant overnight low
temperatures, a pre- frontal trough brought passing showers across
the windward locations in PR and the US Virgin Islands overnight.
Additionally, a long- period north- northwesterly swell promoted
the formation of life- threatening rip currents along the north-
facing beaches in PR and the US Virgin Islands early this morning.
Winds were calm to light and variable, allowing the land breeze
to form overnight. However, the passing showers lead to occasional
gusty winds.

We have moderate/high confidence that a long-period northwesterly
swell will create life-threatening breaking waves and rip
currents, and minor coastal flooding at the most vulnerable
coastal locations from Rincon to Fajardo, especially this morning
around high tide. Also, life-threatening rip currents will form on
the north-facing beaches in Culebra, St. John, and St. Thomas.

There is a high confidence (60-80%) of mostly calm and stable
conditions across the interior, western, and southern plains of
Puerto Rico during the early morning hours, resulting in limited
weather impacts in those areas. In contrast, a pre-frontal trough
is expected to increase the likelihood of passing showers across
the U.S. Virgin Islands and the windward sections of Puerto Rico
this morning, with a moderate probability (30-50%) of brief
moderate to locally heavy rainfall.

As the day progresses, east to east-southeast winds associated
with the pre-frontal trough will likely favor the development of
El Yunque Streamer, extending into the San Juan Metropolitan
Area, and afternoon convection over portions of the interior,
north-central, and northwest Puerto Rico. In these areas, there
is a moderate to high chance (40–70%) of periods of moderate to
locally heavy rainfall, which could lead to localized ponding of
water in poor drainage areas and brief reductions in visibility,
especially during the afternoon commute, as well as isolated urban
and small stream flooding.

The proximity of an upper-level trough and a jet streak will
introduce marginal instability, resulting in a slight chance of
isolated thunderstorms during the afternoon and evening hours
across parts of Puerto Rico and the surrounding U.S. Virgin
Islands waters. However, most model guidance indicates that the
strongest dynamical support will remain north of the region,
limiting thunderstorm coverage and keeping the overall flooding
risk low, with only a localized and brief flooding threat in areas
experiencing repeated heavy showers.

Looking ahead to Thursday and Friday, confidence is high that a
mid- to upper-level ridge will build over the Northeast Caribbean,
promoting subsidence and drier air aloft. Despite this,
strengthening easterly trade winds will maintain a moderate to
high chance (30–60%) of passing showers across windward locations
of Puerto Rico and the U.S. Virgin Islands. These showers will be
most frequent during the overnight and early morning hours, with
some activity likely spreading into the interior and western
Puerto Rico during the afternoon, resulting in generally minor but
recurrent wet-weather impacts.

&&

.Long Term(Saturday through Wednesday)...
Issued at 429 AM AST Wed Dec 17 2025

Saturday through Wednesday...

A mid-to-upper-level ridge will dominate local weather for the first
half of the period, maintaining stable conditions aloft. During this
time, precipitable water (PWAT) values will remain below the
seasonal climatological values, ranging from 1.2 to 1.5 inches. At
the surface, patches of low-level moisture will continue to drift
into the area, bringing passing showers to windward sections of the
islands. Rainfall accumulations will stay limited, though localized
afternoon showers are possible across western Puerto Rico. Overall
impacts are expected to remain minimal.

Transitioning into the second half of the period and through
Christmas Eve, a wetter pattern will evolve. The mid-level ridge
will erode as a polar trough, exiting the eastern U.S. coast,
approaches from the northwest. This will increase instability, with
500mb temperatures dropping to between -6 and -8°C. At the surface,
an associated frontal boundary is forecast to approach late Tuesday
into Wednesday. During this period moisture will increase, with PWAT
values reaching 1.5 to 1.75 inches. This combination of cooling
aloft and increased moisture suggests an unsettled pattern for the
Christmas holiday, potentially bringing isolated thunderstorms and
locally heavy rainfall that could increase the risk of flooding in
prone areas starting late Tuesday or Wednesday.

&&

.AVIATION...
(06Z TAFS)
Issued at 429 AM AST Wed Dec 17 2025

Passing SHRA/+SHRA will impact JSJ/IST and ISX throughout the day.
Then, between 17/16-23z, we have a moderate confidence that TSRA
will form near JSJ and JBQ, when MVFR conditions could develop.
Winds will prevail calm to light and VRB thru 17/13z, then we
expect E-ESE winds at 10 to 15 kt with higher gusts and sea breeze
variations. Calm to light/VRB winds will return aft 17/23z. There
is a slight chance that TSRA could develop during the evening
along the PR's Atlantic Coastline.

&&

.MARINE...
Issued at 429 AM AST Wed Dec 17 2025

A cold front extending from around Turks and Caicos to the
northeastern Atlantic and a pre-frontal trough will promote moderate
to locally fresh east to east-southeast winds across the islands
today. Meanwhile, a long-period north-northwesterly swell will create
hazardous marine conditions for small craft throughout the day. Thus,
a Small Craft Advisory is in effect for the Atlantic and Caribbean
Passages. The frontal boundary will linger off to the northwest as an
occluded low form over the Central Atlantic, far to the northeast of
the region, Thursday and Friday.

&&

.BEACH FORECAST...
Issued at 429 AM AST Wed Dec 17 2025

A long period north to northwesterly swell will create life-
threatening breaking waves and rip currents along the north-facing
beaches in Puerto Rico from Rincon to Fajardo, and Culebra.
Meanwhile, the north- facing beaches in the US Virgin Islands can
expect life- threatening rip currents throughout the day. By this
evening the risk will spread to the southwest of Puerto Rico and
Vieques. We encourage beachgoers to avoid visiting these beaches.