Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
516 AM AST Thu Dec 14 2023

.SYNOPSIS...
Mid to upper leve ridge will continue to erode today thru the
Friday as an upper level trough sweeps eastward across the west
Atlantic and approaches the region over the weekend. A surface
ridge across the west Atlantic and a strong low pressure system
lifting northwards across the north central Atlantic, will maintain
east northeast to easterly winds across the region through Friday.
This will promote moderate to strong low level winds and breezy
to locally windy conditions today. A wind advisory will remain in
effect at least until later this morning. Rough and hazardous seas
will continue as well as and dangerous surf and coastal conditions
for all north and east facing beaches. A high risk of rip currents
will also continue for these beaches.

&&

.SHORT TERM...Today through Saturday...
The western and southwestern parts of Puerto Rico experienced predominantly
clear skies, while other areas had varying cloud cover. Passing clouds
and occasional light to moderate showers affected most of the islands
periodically. Persistent east-northeast winds dragged patches of
trade wind moisture, bringing showers to coastal waters and reaching
inland areas mainly over the north and east sections of the islands.
Showery weather is anticipated to continue in these regions over
the next few hours, although they are expected to be brief. During
the morning hours, reduced visibility and slippery roads may be
observed in the affected area.

Throughout the night, pleasant temperatures persisted, ranging from
the mid to upper 70s in coastal areas to the low to mid-60s in higher
elevations and valleys. Breezy wind conditions persisted during the
night, with sustained winds ranging between 20-22 mph and gusts reaching
26-30 mph. Several weather stations in the northern and eastern coastal
sections of the islands reported these windy conditions early in the
night.

For the rest of the short-term forecast, variable weather conditions
will be observed, with increasing moisture expected by the weekend.
This afternoon and tonight, residual showers will persist, gradually
transitioning to slightly drier conditions by evening and late tonight.
The drop in relative humidities at 700-500mb and 850-700mb levels
to below-normal to near-normal levels will contribute to this change.
While some passing showers may occur, they are not expected to be
significant. Breezy conditions will persist, gradually diminishing
by tonight as the pressure gradient loosens over the local area.

By Friday, a surge in moisture is anticipated, remaining well above
normal through the weekend. Winds will shift from east-northeast to
more easterly as the surface pressure north of the area moves eastward.
Dynamically, a series of short-wave troughs and surface perturbations
will stream across the islands from Friday onwards. At low levels,
a broad and strong surface trough northeast of the Leeward Islands
will generate surface perturbations, carried by the easterly trades
toward the region. Some instability is indicated by 500mb temperatures
dropping to -5 to -6 Celsius and lower 250mb height fields, with 1000
mb-500 mb thickness also dropping to near normal levels. However,the
GFS Galvez Davison- Index suggests that most of the activity will
be shallow, with isolated thunderstorms occurring very sporadically.

The National Blend of Models predicts that northern and eastern
portions of Puerto Rico and smaller islands will experience the heaviest
rainfall during the short-term forecast, while the southern coastal
plains will observe less precipitation. There is approximately a
1-in-3 (33%) chance for rainfall accumulations to exceed one inch in
a 72-hour time frame through 17/06Z for northeastern portions of Puerto
Rico. Therefore, at most, this showery weather could lead to ponding
on roads and poorly drained areas, with possible urban and small stream
flooding, particularly over northeastern Puerto Rico.

&&

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

For the long term, model guidance have initialized well and remain
consistent, with only slight adjustments in forecast grids for the
timing and effect of the expected weather features. Above- normal
moisture levels are expected to persist through Saturday and still
forecast to gradually erode by Sunday and remaining at near-normal
levels by then. Ridging aloft will keep 500 mb temperatures relatively
warmer than the climatological normal with 250 mb height fields higher
than usual at least until Sunday but thereafter expect cooler mid to
upper level temperatures with the approach of a polar trough. Consequently,
by then conditions are to become more unstable and thus become more
favorable for isolated convective development. Breezy wind conditions
will continue, but they are anticipated to be considerably less pronounced
compared to recent days.

From Monday and through the remainder of the long- term forecast models
guidance continue to suggest the strengthening of an area of low pressure
over the south to southeast Gulf of Mexico and this feature is so far
expected to move across the southeast United States over the upcoming
weekend, then progress northward into the western Atlantic. As this
unfolds, an elongated frontal boundary associated with the low pressure
system is projected to approach and envelop the local area, with Tuesday
through Wednesday so far anticipated to be the wettest days.

This scenario is expected to will lead to east southeast winds which
will lift abundant columnar moisture, thus causing good moisture convergence
across the northeastern Caribbean and local islands. By then,conditions
aloft will become more conducive for deep convection. Again, it's crucial
to note that the timing and positioning of these features are subject
to change with varying models and each subsequent model cycle. Regardless,
there is an indication that the latter portion of the long- term forecast,
will again transition towards a more unsettled and wet weather pattern.

&&

.AVIATION...Mostly VFR conds durg prd. However, brief MVFR cigs are
possible at TJBQ/TJSJ/TIST thru at least 14/14z due to -SHRA/SHRA.
ENE winds at 20-25 kt at FL040...FL050. Sfc winds will vary between
15 and 20 kt with gusts up to 25 kt or higher after 14/12z.

&&

.MARINE...Fresh to locally strong east northeast to east winds
are expected to continue through the rest of today, with seas
remain rough between 8-12 feet and occasionally higher across
Atlantic offshore waters. East to east- northeast winds up to 20
knots with gusts up to 30 knots will remain possible. Therefore,
Small Craft Advisories are in effect through at least Sunday for
several areas. Please refer to the latest Marine Weather Message
(MWWSJU) for more information.

&&

.BEACH...Nearshore Atlantic buoys remain between 8-11 feet.
due to the continued strong winds and breezy to windy (15-25 mph)
with occasional gust up to 35 mph. Therefore, a Wind Advisory
will remain in effect at least until 9 am AST, a High Surf
Advisory has been extended until 12 pm AST, and several areas of
High Rip Current Risk will remain in effect. Please refer to the
latest Coastal Hazard Message (CFWSJU) for more information.

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
530 AM AST Fri Dec 15 2023


.SYNOPSIS...
Breezy conditions will persist across the region with sustained
winds between 15 to 20 mph, and higher wind gusts 30 mph possible
today. A mid to upper level ridge will continue to erode into the
weekend as an upper trough crosses the Atlantic just north of the
region. This will cause in a weakening of the trade wind cap inversion
resulting in a better chance for more frequent trade wind showers
across the area. The occasional patches of shallow moisture and
cloudiness will continue to spread across the islands carried by
the moderate to strong east northeast winds. Periods of isolated
to scattered showers is expected, especially over the windward and
northeastern section of Puerto Rico. Choppy to rough and hazardous
seas will continue into the weekend with dangerous surf
conditions expected to persist for the north and east facing
beaches.

&&

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

Fragmented high-level clouds with little to no rain prevailed across
the U.S. Virgin Islands and Puerto Rico overnight. Some passing showers
may be observed during the morning hours over windward coastal areas
with minimal rainfall accumulations for the rest of the morning hours.
Coastal temperatures dipped to the mid- and upper- 70s Fahrenheit,
while mountainous and valley areas experienced temperatures around
the low 60s. East-northeast surface winds ranged from 5 to 15 mph,
with occasional gusts reaching 20 mph in certain areas during the
early night.

The anticipated weather pattern remains consistent with previous
model runs. A significant surge in moisture is forecast, transitioning
from well below normal to two standard deviations above climatological
normal levels until Sunday. Precipitable water values could reach
2.25 inches by then, with the majority of the moisture confined
below the 500 mb layer increasing the potential for vertical mixing
and convection. In terms of dynamics aloft, weather conditions
appear to be very borderline for deep convection. A mid- to upper-
level short-wave trough, currently southwest of Hispaniola, is
expected to progress eastward over the region today through
Saturday, slightly flattening out upon reaching Puerto Rico. This
will momentarily lower the 250 mb height fields and 1000-500 mb
thicknesses through Saturday. Despite a decreasing trend, 500 mb
temperatures will remain warmer than usual. Sunday will see
slightly cooler 500 mb temperatures, with near-normal 700-500 mb
lapse rates. However, a building ridge from the west will elevate
height fields and thicknesses over the local islands once again.

Consequently, due to the presence of some stability aloft throughout
the period, thunderstorm activity was not been included in the
forecast. Nevertheless, due to the borderline conditions, there is
the possibility of very isolated and short-lived thunderstorms in
the area. This is backed by the GFS Galvez Davison-Index, which
suggests the potential for isolated thunderstorms but highlights
that any shower activity will be mostly shallow supporting showery
weather conditions. In terms of rainfall accumulations, Hi-Res
models suggest the wettest period occurring this evening through
tomorrow morning. The National Blend of Models indicates there is
approximately a 1-in-2 (50%) and 1-in-5 (20%) chance for rainfall
accumulations to exceed one inch and two inches, respectively, in a
72-hour time frame through 18/06Z, mostly for northeastern portions
of Puerto Rico. Therefore, there is only a limited flooding threat
for the eastern third of Puerto Rico.

&&

.LONG TERM...Monday through Friday...
Winds are forest to become more easterly on Monday and Tuesday,
as the high pressure ridge will shift farther east into the central
Atlantic and a cold front crosses the west Atlantic. Recent model
guidance continued to suggest a drier trend than recent days with
more seasonal precipitable water values ranging between 1.50 and
1.75 inches. An even drier pattern is forecast for the latter part
of the period, as low level moisture erodes in response to strong high
pressure building across the west and southwest Atlantic and winds
become northerly bringing more stable air and cooler temperatures.
However expect the trend of advective passing showers and shallow
trade wind moisture to continue each day, with the chance of late
evening and early morning showers especially across the the north
and east section of the islands. This will be followed by partly
cloudy to mostly sunny skies with afternoon showers limited to
parts of the central and east interior and west to southwest
sections of Puerto Rico, and mainly on the west-end and downwind
of the U.S. Virgin Islands.

Although no significant or widespread rainfall is expected during
the period, there will be times of quick passing moderate to locally
heavy downpours which may cause ponding of water on roads and hazardous
driving conditions. In addition, breezy conditions are forecast to
continue as the prevailing winds become more northeasterly then northerly
by the end of the period.

&&

.AVIATION...
Mostly VFR conditions will prevail today. However, SCT-SHRA will
cause VCSH during the day across all TAF sites. Clouds and mountain
obscuration could develop along interior PR this afternoon. The
frequency of SHRA will increase near TJSJ/TIST/TJBQ after 15/21z.
Winds will be from the ENE at 12-20 knots aft 15/13z with occasional
gusts reaching 25 knots.

&&

.MARINE...
The interaction of the surface high-pressure across the west
Atlantic and a strong low-pressure system slowly lifting northwards
across the central Atlantic will promote fresh to strong trade
winds with locally higher gusts over the regional waters into the
weekend. Expect seas to remain rough and hazardous during the period.

The offshore Atlantic bouy 41043 and the near shore San Juan buoy
continued to report seas of 8-10 feet with a period of around 11
seconds overnight. Given the actual and expected marine conditions,
the high surf advisory was extended until 6 PM today due to possible
breaking waves up to at least 10 feet. Please stay tuned for further
updates in the advisories and statements and refer to the latest
Marine Weather Message (MWWSJU) and Coastal Hazard message (CFWSJU)
for additional information.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Sat Dec 16 2023


.SYNOPSIS...
Issued at 505 AM AST Sat Dec 16 2023

Breezy wind conditions will persist over the local area throughout
the weekend. Hazardous marine and coastal conditions will
continue through at least next week. Variable weather conditions
are expected with alternating periods of sunny skies and showery
weather throughout the short- and long-term forecast.

&&

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

An area of convergence between the air flow around a high pressure
building into the western Atlantic and the trans-Atlantic flow south
of 20 north latitude kept showers streaming across the northern U.S.
Virgin Islands and the northeastern half of Puerto Rico. Amounts of
up to one half inch were seen in the interior and over one the inch
over the near shore waters north of Barceloneta. Winds became light
during the overnight hours, but then picked up after around 2 AM
AST. Some wind gusts were seen in the 20s--especially in the eastern
side of the forecast area and in the British Virgin Islands.

As a developing surface low in the Gulf of Mexico moves north
northeast into the southeastern United States it will cause a strong
high pressure moving southeast into the Atlantic from Canada to
build into the northeast Caribbean as well to strengthen winds
somewhat today. Winds will only abate when a front ahead of strong
high pressure approaches the area on Monday and begins to squeeze
the high pressure over us against a low developing to our east
northeast. At the same time the GFS shows the high pressure reaching
1048 mb in the central Atlantic north of 40 north. Tuesday will mark
the beginning of a period of cool air advection from the Atlantic
and also the beginning of a long decline in moisture.

&&

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

Specifics of the long-term forecast such as the timing and location
of key complex features continue to change. Tuesday starts with
what looks like a blocking weather pattern at upper levels called
an "Omega Block". This is composed of two strong low- pressure
systems located northwest over the Eastern Seaboard and northeast
over the central Atlantic of the local islands with a ridge axis
centered over the northeastern Caribbean. Initially, this ridge at
upper levels will inhibit deep convective activity over land
areas for the most part on Tuesday. Wind speeds will have
diminished with an east- northeast component. Surface-induced
perturbations from the low-pressure system over the central
Atlantic may be advected by the northeasterly trades from time to
time. Meanwhile, a frontal boundary associated with the strong
low- pressure system over the Eastern Seaboard will be approaching
from the northwest. This setup on Tuesday will not bring much
weather over the local islands other than showers and isolated
thunderstorms over the Atlantic waters and Mona Passage and
possible showery weather over windward coastal areas.

As the week progresses, all of these weather features will gradually
change. Moisture will range between the 50th and 95th percentile of
the climatological normal through Saturday as a strong surface high
pressure over the western Atlantic pushes the frontal boundary
towards the local CWA and fluctuates back and forth over us
throughout the week. This will induce a northerly wind flow while
wind speeds diminish further. The 925 mb winds are expected to range
within the 10th and slightly higher than the 25th percentile of the
climatological normal. Dynamics aloft will also fluctuate with
Wednesday having the highest instability of the long-term period
with 500 mb temperatures dropping to -7 and -8 degrees Celsius
promoting slightly steeper 700-500mb lapse rates. Therefore, at the
moment, the highest probability of observing some thunderstorms will
be Wednesday developing over the western local waters with some
approaching western coastal areas of Puerto Rico, and maybe in the
afternoon over the Cordillera Central. However, weather conditions
do not look too impressive for deep convection as the frontal
boundary seems to weaken once it crosses the northeastern Caribbean.
At most, a limited flooding threat could be observed on Wednesday,
with mostly showery weather expected for the rest of the long-term
forecast.

Much cooler temperatures are anticipated with this weather pattern,
with 925mb temperatures plummeting to two standard deviations below
normal levels. Therefore, to sum up, a very seasonal weather pattern
is expected for the long-term forecast with a mix of sun and cloudy
skies with showery weather affecting the local area at times,
particularly over northern and eastern sections of the local
islands. We can anticipate more enjoyable temperatures as we embrace
the tropical winter in the Caribbean.

&&

.AVIATION...
(06Z TAFS)
Issued at 505 AM AST Sat Dec 16 2023

Overall VFR conds will persist across most TAF sites,
with -RA to SHRA providing brief MVFR conds, including lwr cigs and
reduced VIS, particularly for TIST, TJSJ and TJBQ thru the prd. Mtn
obscurations will also prevail in PR. Winds from the ENE to E up to
20 kts with hir gusts are psbl bfr 16/14Z and will prevail-
-mainly along the coasts--thru at least 16/22Z. Maximum winds WSW
80kts arnd FL510, but winds are greater than 50 knots abv FL355. ENE-
ESE winds are seen blo FL140.

&&

.MARINE...
Issued at 505 AM AST Sat Dec 16 2023

Fresh to slightly strong northeasterly winds will persist promoting
moderate to rough seas across the local waters. Nearshore Atlantic
buoys continue to observe seas of 7 feet with wind speeds of 15 to
20 knots and higher gusts. This pattern is expected to persist
throughout the weekend with rough seas remaining up to 11 feet and
occasionally higher across the offshore Atlantic waters. Therefore,
Small Craft Advisories are in effect through at least Saturday.
Please refer to the latest Marine Weather Message (MWWSJU) for more
information.

&&

.SURF ZONE...
Issued at 505 AM AST Sat Dec 16 2023

The weak northerly swells have diminished somewhat but continue to
affect the northern regional waters. Life-threatening rip currents
due to moderate to rough surf and large breaking waves will
continue today. Nearshore buoys indicate that estimated breaking
waves are still ranging between 8 to 10 feet. Therefore, a High
Surf Advisory will remain in effect for all surf zones across
northern and eastern Puerto Rico. High Risk of Rip Currents are in
effect for all other beaches, except southern Puerto Rico.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
544 AM AST Sun Dec 17 2023


.SYNOPSIS...
Issued at 538 AM AST Sun Dec 17 2023

Frequent showers in the past 24-48 hours have caused well above
normal streamflows along rivers over northeastern Puerto Rico.
Therefore, there is a limited to elevated flooding threat across the
eastern third of Puerto Rico, particularly areas close to El Yunque.
Breezy wind conditions will persist over the local area today
promoting rough seas across the regional waters. Therefore,
hazardous marine and coastal conditions will continue today and
persist throughout the week. Variable weather conditions are
expected with alternating periods of sunny skies and showery
weather throughout the short- and long-term forecast.

&&

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

Showers have continued through the U.S. Virgin Islands and eastern
Puerto Rico all night, with three tenths of an inch since 6 PM AST
at San Juan and over one half inch in the Luquillo range. This has
brought Rio Blanco close to bankfull and a significant rise in the
Rio Grande river near El Verde. Overnight temperatures have been
close to normal for the season except in Saint Croix where
temperatures were up to 4 degrees above normal with a record high
maximum yesterday that tied the previous record of 89 degrees.
Conditions were breezy with gusts of 20 to 30 mph.

Low pressure moving out of the Gulf of Mexico has strengthened and
is moving along coastal Georgia while high pressure moves southeast
into the northwestern Atlantic with a ridge that reaches all the way
into the Caribbean. This has promoted and prolonged the breezy east
northeast flow and the band of moisture that is now centered across
the U.S. Virgin Islands and the northeastern half of Puerto Rico. A
strengthening jet of 110 plus knots near 25 north and 55 west is
wrapping around the southwestern side of a long wave trough and is
expected to generate a low pressure at lower levels by Monday east
of its position. Nevertheless the low will continue moving west
through Tuesday. Coupled with the ridge over the local area, winds
will turn briefly east southeast tonight with advancing bands of
lighter showers today, tonight and Monday. Then winds will become
east and east northeast with continued cool air advection coming off
the low pressure to the northeast. Moisture is expected to begin a
gentle decline this afternoon and level off at more moderate levels
Monday and Tuesday, but lower levels will remain moist through at
least Monday night even if that moisture is fairly limited in depth.
This will limit convection and shower intensity, but numerous
showers and perhaps some periods of sun should be expected until
then. On Tuesday the cold front associated with the deepening low
moving north through the New England states will be powered offshore
by a strong high of up to 1035 mb moving into Appalachia on Tuesday
and Tuesday night. This front should stall across Hispaniola as the
high pressure in the central Atlantic, forecast to reach a
surprising 1051 mb Tuesday night, opposes its progress. The result
of this will be improving conditions and subsiding winds.
&&

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

While there haven't been significant changes in the overall
anticipated long-term weather pattern, discrepancies persist among
models regarding specific details. All models agree on the
strengthening of a low-pressure system over the Gulf of Mexico,
lifting north with an associated surface frontal boundary and a
polar trough approaching the northern Caribbean from the northwest
throughout the week. Additionally, a robust deep-layered trough
northeast of the local islands will meander across the central
Atlantic.

On Wednesday, surface-induced perturbations from the northeast deep-
layered trough will stream across the region, driven by the easterly
trades. Above-normal moisture coupled with some instability aloft
could promote convective activity, but due to its marginal nature,
anticipate predominantly shallow convection. However, there is a
chance for isolated thunderstorm development, primarily occurring
over the local area, mostly concentrated over regional waters. Model
guidance suggests the highest rainfall amounts expected across
northwestern and north-central Puerto Rico.

After Wednesday, both ECMWF and GFS models differ in the location
and timing of the frontal boundary progression. ECMWF suggests a
slower advance while GFS suggests a faster one with huge
discrepancies in moisture content throughout the week. Some
instability will persist due to the proximity of the polar trough to
north of the Caribbean. A northerly wind flow will also persist
as the frontal boundary moves over the northeastern Caribbean.
Therefore, we can expect variable weather conditions with periods
of sunny to cloudy skies and shower activity.

The National Blend of Models indicates there is approximately a
1-in-5 (20%) chance for 24-hour rainfall accumulations to exceed
half an inch from Thursday onwards, mostly for north-central
municipalities of Puerto Rico. Therefore, at most, we could expect
ponding of water in roads and poorly drained areas. Urban and
small stream flooding is possible. Despite these conditions,
temperatures at 925 mb are anticipated to be two standard
deviations below the climatological normal, ensuring a very
pleasant end to the workweek.

&&

.AVIATION...
(06Z TAFS)
Issued at 538 AM AST Sun Dec 17 2023

Quick moving SHRA will persist through 18/14Z, affecting the USVI
and PR terminals at times. Brief periods of reduced VIS and MVFR
CIGS can be expected at times with this activity. Mtn obscurations.
Winds are enhanced, out of the E at 18-22 kts, with stronger gusts
at times, mostly before 17/22z. Max winds W 72-82 kts btwn
FL415-515.

&&

.MARINE...
Issued at 538 AM AST Sun Dec 17 2023

Fresh to strong east-northeast winds will persist promoting moderate
to rough seas across the local waters. Nearshore Atlantic buoys
continue to observe seas of 7 to 8 feet, dominant periods of 10-11
seconds, wind speeds of 15 to 20 knots, and higher gusts. This
pattern is expected to persist throughout the week with rough seas
remaining up to 11 feet and occasionally higher across the offshore
Atlantic waters. Therefore, Small Craft Advisories are in effect
through at least Saturday. Please refer to the latest Marine Weather
Message (MWWSJU) for more information.

&&

.SURF ZONE...
Issued at 538 AM AST Sun Dec 17 2023

Weak northerly swells coupled with fresh to strong winds continue to
produce rough to high surf conditions, mostly over northern exposed
beaches. Nearshore buoys indicate that estimated breaking waves are
ranging between 9 to 11 feet. Therefore, a High Surf Advisory is
once again in effect for all surf zones across northern and eastern
Puerto Rico. High Risk of Rip Currents are in effect for all other
beaches, except southern Puerto Rico. For more information and
details please refer to the latest Surf Zone Forecast (SRFSJU), and
the Coastal Hazard Message product (CFWSJU).

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
533 AM AST Mon Dec 18 2023

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

.SYNOPSIS...
Issued at 447 AM AST Mon Dec 18 2023

The passage of several long wave troughs to our north and the
approach of cold fronts generated by enhanced high and low pressure
systems will bring cooler weather with showery periods during the
up coming week.

&&

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

Fair and stable weather conditions prevailed across the forecast
area during the night and early morning hours. High clouds and no
rainfall activity were observed. Overnight temperatures were in the
lower to mid 70s across the coastal areas and in the low to mid 60s
across the mountains. The Luis Munoz Airport in San Juan reported a
minimum temperature of 73 degrees which is the coolest of the
month so far.

Surface high pressure over the central Atlantic and low pressure
with the associated frontal boundary located just off the east coast
of the United States over the Western Atlantic will continue to
promote easterly winds across the region during the day. This
easterly flow has provided good periods of moisture in the past
days; however, today, the islands can expect a slightly drier air
mass moving into the area, with Precipitable water values between
1.4 to 1.2 inches as suggested by the derived GOES imagery.
According to the latest model guidance, a low 850-700 MB lapse
rate presents good potential for a stable atmosphere.
Additionally, warmer temperatures at 500 MB will result in a
day of variable weather with occasional passing showers and
upper-level cloudiness driven by the winds over the eastern
sections.

By Tuesday, both models' guidance agreed on the progression of a
frontal boundary and the associated low-pressure more eastward
due to the influence of a broad surface high-pressure located
over the east coast of the United States. This movement will
induce a pre-frontal trough over the Hispanola, relaxing the
pressure gradient and decreasing the wind speed by Tuesday into
Wednesday. The same surface change will enhance backing winds,
becoming more east northeast. For Wednesday, weather conditions
become more conducive to shower activity. The 250 MB heights will
decrease, and colder temperatures are expected at 500 MB, reaching
minus 7 degrees. The above mentioned conditions, combined with an
increase in relative humidity from 700 to 500 MB, create more
favorable conditions for shower activity and some isolated
thunderstorms. In fact, according to The Gálvez-Davison Index
(GDI) (GFS ), there is a potential for isolated thunderstorms.

&&

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

The forecast of a cooling trend through Saturday morning has
remained, but the drying trend for the end of the work week has
proven to be evanescent. Westerly flow continues and strengthens a
little at upper levels with the passage of a long wave trough to
our north on Wednesday. This allows cooler air to invade the
forecast area from the northwest as a cold front settles in over
the area with showers. Low level winds will continue from the
northeast so that most of the rain will be focused over and north
of the Cordillera Central. The cold front will continue to be
nearby and it is too early to tell if it will move into the
Caribbean or stall over the local islands. Bands of moisture will
however continue to invade the area and reinforce the wetter
trend over the weekend.

The deepest moisture and the best dynamics will be on Friday,
owing to a second long wave trough passage to our north and the
front in the area, however shallow low level moisture will
persist beyond Sunday as cool air continues to filter in behind
the front and the low pressure to our northeast with the front
becomes more distant.

&&

.AVIATION...
(06Z TAFS)
Issued at 447 AM AST Mon Dec 18 2023

Aviation...VFR conditions will prevail across all the TAF sites
during the period. High clouds and light winds will remain until
18/14Z. East winds will increase up to 15 knots, and become gusty.
VCSH at 18/18Z-22Z might result in lower CIGS near the TIST and
TJSJ sites.

&&

.MARINE...
Issued at 447 AM AST Mon Dec 18 2023

An active Atlantic is keeping seas choppy in the south and
hazardous in the north of the forecast area. Small craft
advisories will begin dropping out everywhere except the local
outer Atlantic waters today and Tuesday, but seas in excess of 7
feet will begin to return on Wednesday.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Tue Dec 19 2023

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

.SYNOPSIS...
Issued at 351 AM AST Tue Dec 19 2023

Strong highs and lows across the eastern United States and the
central Atlantic will keep a number of decaying frontal boundaries
over or nearby the forecast area, with cool air advection and
passing showers in east or northeast flow across the surface.

&&

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

Stable weather conditions dominated the islands during the night and
early morning hours. Radar imagery showed no significant shower
activity, except for a few passing showers over the Caribbean
coastal waters. Overnight temperatures ranged from the mid-70s in
coastal areas to the low to mid-60s in the mountain areas.

Similar weather conditions are expected for most of the day,
characterized by below-normal precipitable water values (1.0 to 1.3)
as indicated by GOES-derived imagery. This surface pattern, coupled
with a lack of support at the mid to upper levels, will result in
mostly stable weather conditions during the day with minimal
rainfall activity.

Surface weather conditions will undergo significant changes late
today into tomorrow as a low-pressure system over the central
Atlantic interacts with a pre-frontal trough from the frontal
boundary, leading to backing winds in the islands. Light east-
northeast winds will initiate a wet pattern, pushing the remnants of
the frontal boundary into the region. Trapped moisture from the
surface to 700 MB will move into the area tonight, increasing the
potential for an showery pattern.

Wednesday's forecast indicates a more unstable outlook with lower
250 heights and colder temperatures at 500 MB. The current upper-
level conditions are expected to combine with available moisture
trapped in the mid to lower levels. While precipitable water values
will reach around 1.6 inches, resulting in shower activity over the
interior and southwestern areas, generalized isolated thunderstorm
activity is not included in the forecast. However, one or two
isolated thunderstorms cannot be ruled out on Wednesday. Shallow
moisture is anticipated on Thursday under a northeast wind flow. The
Winter Solstice will occur on Thursday, December 21st at 11:27 PM
Atlantic Standard Time.

&&

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

A ridge of high pressure extending southward out of a strong high
over Canada is sending northerly flow at lower level into the
forecast area this flow is also aided by a moderately strong low
in the west central Atlantic moving to the north. This is
reinforcing the convergence across the area and will sustain
upward vertical motion and shower activity across Puerto Rico and
the U.S. Virgin Islands from the moisture being advected in from
the Caribbean Sea. This high pressure moves quickly to the east
across the Atlantic and by Sunday is far enough along to allow
another low pressure to move across Maine and also into the
Atlantic. This low however drops southeast to a position of 38
north and 60 west to keep flow northeasterly with good cool air
advection. Current GFS 1000-850 mb thicknesses do not now recover
much over the weekend to maintain our cool and wintry weather.

At upper levels, a weak short wave trough will move through and
to the north of the area on Thursday, followed by an active sub
tropical jet on Friday and Saturday. The sub-equatorial jet will
also be in close proximity to the south to help keep showery
conditions in the area. Isolated afternoon thunderstorms cannot be
ruled out, but are not expected to be widespread.

&&

.AVIATION...
(06Z TAFS)
Issued at 351 AM AST Tue Dec 19 2023

VFR conditions will prevail across all the TAF sites for
the period. Winds will remain from the east at 10 knots, increasing
to 15 knots at 19/15Z. Due to increased cloudiness and showers, VCSH
will be present especially across TJSJ, TJBQ, and TIST at 19/22Z.

&&

.MARINE...
Issued at 351 AM AST Tue Dec 19 2023

Winds will abate somewhat today and tonight, but a new swell from
the northeast will invade the local area later tonight and
continue through Thursday. Yet another swell train will move in
from the north late Saturday into Sunday. Seas could exceed 9 feet
Friday and Saturday night.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
508 AM AST Wed Dec 20 2023

.SYNOPSIS...
Issued at 438 AM AST Wed Dec 20 2023

High pressure in the northeast United States and the northwestern
Atlantic will maintain northeasterly flow though much of the next
5 to 7 days. This will allow a cold front to strengthen near the
area that will bring scattered to isolated showers Friday, over
the weekend and into next week. Mostly fair weather is expected
today and Thursday before the front forms.

&&

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

Overnight, mostly clear skies and stable conditions prevailed across
Puerto Rico and the U.S. Virgin Islands. A little before midnight,
Aerosol Dust Models began to report light concentrations of Saharan
Dust particles as a patch of dry air and dust filtered across the
islands. At night, temperatures ranged from the low to mid-70s along
the coastal areas to the low to mid-60s in the mountain areas.

Despite the fair weather conditions that prevailed overnight, the
forecast for today leans into a day with variable weather conditions
as a frontal boundary continues to move north of the forecast area,
interacting with the surface low to the northeast of the Leeward
Islands. The interaction between these weather features will promote
a northeasterly wind flow from today through at least the end of the
workweek. The cold air advection will lead to passing showers
filtering across the local waters and windward sections of northern
PR, as well as the sections of the north of the U.S. Virgin Islands.
The interior sections of the islands could also experience some
shower activity if the wind pushes them far inland. The latest model
guidance does not suggest the development of significant rainfall
activity across the islands through Friday. Models now suggest
precipitable water values going from normal to slightly above normal
for this time of the year. It is worth noting that the moisture
content during the period stays below 700-500 mb, meaning that any
convection that does develop will not be strong enough to grow
vertically. Therefore, thunderstorm development is less likely, as
mid to upper-level conditions are not propitious.

Overall, we anticipate periods of clear skies followed by cloudiness
and passing showers during the short-term period. Temperature-wise,
they are forecast to range in the 80s along the coastal areas, while
over the mountainous regions, they will be in the 70s today.


&&

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

A stalled frontal system just north of or in the local Atlantic
waters will begin to move south again due to high pressure
emerging out of the New England states. The high pressure will
gain little strength over the weekend, leaving the front in
basically the same place with scattered to numerous showers over
the area and a slight chance of thunderstorms. The front is
expected to be oriented east to west on Saturday, but will become
more northwest to southeast by Tuesday, as from Saturday to
Tuesday the wind shifts from northeast to east.

At upper levels the long wave trough is expected to pass to the
north of the area today, but passing short waves will cause
troughiness to linger over the area prolonging the somewhat
unstable conditions. Hence, 500 mb will be relatively cool at
minus 8 to minus 9 degrees through the long term period.

&&

.AVIATION...
(06Z TAFS)
Issued at 438 AM AST Wed Dec 20 2023

VFR conditions will prevail across all terminals throughout the
forecast period. Winds will range primarily from the E-NE and then
NE at 10 to 15 knots with higher gusts; winds will become calm to
light and variable after 20/23z. As a frontal boundary moves near
the region, SHRA becomes possible.

&&

.MARINE...
Issued at 438 AM AST Wed Dec 20 2023

The model winds did not change for the period and the model waves
were much too low to use, therefore the forecast remains
unchanged and is in good agreement with the current conditions.

High rip currents and will continue for the rest of the week and
high surf for northern beaches will begin Wednesday night and is
expected to continue through Friday.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Thu Dec 21 2023

.SYNOPSIS...
Fragmented moisture will occasionally arrive across the islands
over the next few days. Cooler temperatures are forecast due to
northeasterly to northerly winds. A northeasterly swell continues
to bring hazardous marine and coastal conditions across the local
islands, lasting through the week into the weekend.

&&

.SHORT TERM...Today through Saturday...
During the overnight hours, mostly calm weather conditions prevailed
across Puerto Rico and the U.S. Virgin Islands. Nonetheless, some
showers filtered along the northeastern and eastern interior
municipalities of Puerto Rico throughout the night. This rainfall
activity left less than half an inch of rain. Once again, the
temperatures at night ranged in the 70s along the coastal areas and
the 60s in the mountain areas. The wind flow was from the north-
northeast, around 3-7 mph.

Today, mainly variable conditions will prevail across the islands.
This pattern will be accompanied by showery weather at times and
periods of no rainfall activity. At this time, Puerto Rico and the
U.S. Virgin Islands remain between a frontal boundary extending from
the Dominican Republic into the Atlantic and a surface low pressure
to the northeast of the Lesser Antilles. As the front approaches
from the north, expect winds to increase and become more northerly,
promoting convective instability and a better chance of
precipitation from tonight. Precipitable Water models suggest values
around normal climatological moisture through Friday.

Nonetheless, the latest model guidance suggests increasing moisture
content at all levels and mid-level temperatures around -9 degrees
Celsius by Friday into the weekend. This pattern usually leads us to
the potential for isolated thunderstorm development, particularly
with the strongest shower activity. Therefore, we anticipate
increased shower and thunderstorm activity with the weekend
entrance. Early into the weekend, a mid to upper-level high-pressure
system will position over the central Atlantic, while at the
surface, high pressure will position over the western Atlantic.
These weather features will introduce easterly winds across Puerto
Rico and the U.S. Virgin Islands by the end of the short-term period.

.LONG TERM...Sunday through Thursday...
Early in the forecast cycle, a lingering front just north of the
islands or in the local Atlantic waters will begin to slowly move
south again due to a building surface high pressure over the
western Atlantic. The high pressure will gain little strength over
the weekend, leaving the front in basically the same place with
scattered to numerous showers over the area and a slight chance of
thunderstorms. The front is expected to be oriented northwest to
southeast by Tuesday, as winds gradually shift from the northeast
to east by the end of the long term period.

At mid-to upper-levels, a series of short wave troughs will
promote unstable conditions aloft with 500 mb temperatures
dropping to minus 8/9 degrees Celsius until at least Tuesday.
Therefore, showers are expected in general across the islands
during the holidays, but flooding rains are not anticipated at
this moment. A drying trend is expected by midweek as an upper
level ridge builds from the central Caribbean.


&&

.AVIATION...
VFR conditions will prevail across all terminals. Winds will range
primarily from the N-NE at 5 to 12 knots with higher gusts; winds
will become calm to light and variable after 21/23z. As a frontal
boundary moves near the region, SHRA becomes possible.

&&

.MARINE...
A large northeasterly swell continues to build across the
Atlantic Waters and passages and is expected to max out in
strength through the morning hours today. Seas are forecast to
build between 8 and 12 feet, and Small Craft Advisories are in
effect for all Atlantic waters and exposed passages. This swell
will linger throughout the rest of the week, meanwhile a short to
mid-period northwesterly swell will also build over the next two
days. Promoting hazardous seas through the weekend. Winds will
generally be from the northeast around 10 to 15 knots during the
next several days.


&&

.BEACH FORECAST...
Latest coastal buoy readings indicated the swell at 7 to 9 feet
at 13 seconds, this translates to rough surf and life-threatening
rip currents along the entire northern coastlines of the islands.
A Coastal Flood Advisory was issued for the northern coast of
Puerto Rico today, as large breaking wave action could cause minor
coastal flooding along roads and low areas along the immediate
coast.

Beachgoers are encourage to avoid the northern and eastern
exposed beaches of the islands through the weekend. High Surf
Advisories and High Rip Current Risk are in effect for the next
couple of days. Please refer to the latest Coastal Hazards
Message (CFWSJU) for more details.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
401 AM AST Fri Dec 22 2023

.SYNOPSIS...
A wet pattern will evolve through Saturday morning as a front
lingers across the local area. This may lead to periods of
locally heavy rains at times. Pleasant tropical winter
temperatures will persist. Hazardous seas and life-threatening rip
currents will continue through the weekend due to northerly
swells.


&&

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

Tonight, showery weather prevailed across the northern, central
interior, and eastern half of Puerto Rico, while the U.S. Virgin
Islands experienced mostly calm and fair weather conditions. This
rainfall activity over Puerto Rico left around an inch and a half of
rain, particularly over northeastern PR and less than an inch
elsewhere. Overnight, the temperatures ranged in the 70s along the
coastal areas and the 60s in the mountain areas. The wind flow was
from the north-northeast, around 3-10 mph.

Today, expect similar weather conditions to dominate the forecast
area, meaning showery weather is anticipated again. Despite the
foreseen rainfall activity for today, the islands will sometimes
experience brief periods of no rainfall activity. As mentioned in
previous discussions, the wet pattern will continue to evolve today
through Saturday as the front lingers just north of the U.S. Virgin
Islands and Puerto Rico, sinking southward over the Northeast
Caribbean. Under this pattern, fragments of moisture will
occasionally arrive, bringing periods of showery weather. The latest
model guidance suggests increased intensity and vertical development
of showers as a mid to upper-level trough and associated jet maxima
provide better ventilation and dynamic aloft. At this time, models
continue to suggest temperatures at mid-levels below -8 degrees
Celsius. After further analysis, we decided to introduce
thunderstorms into the forecast for each afternoon through at least
Sunday.

Overall, due to the anticipated wet pattern, expect periods of
locally heavy rains that can cause water ponding on roads and
hazardous driving conditions. Temperature-wise, prepare yourself to
experience pleasant tropical winter temperatures throughout the
short-term period, and therefore the holiday weekend.

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

At upper levels, a jet segment of 80 kt winds is expected to pass
over the region on Monday and Tuesday, as the northeastern Caribbean
remains under the influence of a broad upper level trough over the
western Atlantic. This should continue to promote colder than normal
500 mb temperatures over the area around minus 8/9 degrees Celsius.
Therefore, convective development is possible each afternoon over
portions of central/southern PR. Low-level winds are expected to
prevail from the east to northeast as a broad surface high pressure
over the western Atlantic slowly meanders eastwards into the central
Atlantic. Embedded in this flow, moisture associated to the remnants
of an old frontal boundary and from weak surface lows over the
central Atlantic will reach the northeastern Caribbean from time to
time. Therefore, expect showers to continue to move during the
night/early morning hours across sections of northeastern PR and
across the USVI, followed by diurnal convection over portions of the
Cordillera Central during the afternoons. However, a drying trend is
expected during the second part of the week, as an upper level ridge
builds from the central Caribbean, bringing drier air and more
stable conditions aloft as 500 mb temperatures warm to around minus
4 degrees.


&&

.AVIATION...
(06Z TAFs) SCT/BKN layers btw FL030-FL090 due to FROPA, occasionally
OVC and lower CIGS possible at TJBQ/TJSJ with -SHRA through the
forecast period. +SHRA and VCTS possible after 22/18z at
TJSJ/TJPS. Winds will range from the N-NE at 5 to 12 knots and
occasional higher gusts.


&&

.MARINE...
As of 3 AM AST, buoy 41043 indicated a second large pulse of the
northeasterly swell, with swell heights peaking at 10-11.5 feet at
12 seconds. This will continue to promote hazardous seas up to at
least 10 feet across the Atlantic waters today. Seas are forecast
remain between 6 and 10 feet across the Atlantic waters and passages
through the weekend as another, but smaller northerly swell arrives
on Sunday. Therefore, Small Craft Advisories will remain in effect
for the next several days. Moderate northeast winds today are
forecast to weaken slightly and turn more easterly during the
weekend.

Coastal conditions remain hazardous with breaking waves up to 12
feet today, mainly along the northern coast of Puerto Rico. Breaking
wave heights will slowly decrease over the next few days however
expect life-threatening rip currents to continue across the north
and east facing beaches of the islands through the weekend. The
reinforcing pulse of northerly swell on Sunday will maintain similar
conditions along the northern beaches of the islands into next week.
Exercise caution due to these powerful waves and strong rip
currents.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
514 AM AST Sat Dec 23 2023

.SYNOPSIS...

The remnants of a weak frontal boundary will persist through the
weekend promoting shower activity at times throughout the
weekend. By mid- week next week the weather conditions will become
stable as a high pressure positions to the north of the area.
Northerly swells will persist, causing hazardous seas and life-
threatening rip currents throughout the weekend.

&&

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

A weak frontal boundary over the region promoted showers through
much of the overnight and early morning hours across the northern
and eastern half of Puerto Rico. The highest rainfall accumulations
after midnight were observed in Barceloneta and Manati with 1.50
inches. Accumulations near an inch of rain were also noted in Aguas
Buenas, Corozal, Bayamon, and Guaynabo. Minimum temperatures ranged
in the 70s along the coastal areas and in the 60s in the highest
mountains. The wind was from the east-northeast up to 10 mph in
general.

Latest model guidance suggest slightly less moisture content than
previously forecast through the rest of the short term period.
However, the linger frontal boundary across the northeastern
Caribbean and weak to moderate winds should continue to promote
moisture transport over the islands from time to time. An advective
pattern should favor showers across portions of northern and eastern
PR each day. However, locally induced afternoon showers with
possible isolated thunderstorms are expected each day over portions
of the interior, as the area remains under the influence of an upper
level trough and colder 500 mb temps. Across the USVI, less rainfall
is expected through the weekend but passing showers cannot be ruled
out at times.

&&

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

The inherited forecast remains on track. Latest model guidance
continues to suggest an upper-level jet segment of around 80 kt
winds crossing the region by Tuesday, as the northeastern Caribbean
remains under the influence of a broad upper-level trough over
the central Atlantic. This should continue promoting colder than
normal 500 mb temperatures over the area, ranging between minus
8/9 degrees Celsius through at least mid-week. Therefore,
convective development is possible each afternoon over
central/southern PR portions. Through the short-term period, the
low-level winds are foreseen to prevail from the east to northeast
as a broad surface high-pressure over the western Atlantic slowly
meanders eastwards into the central Atlantic. Embedded in this
flow, moisture associated with the remnants of an old frontal
boundary and from weak surface lows over the central Atlantic will
reach the northeastern Caribbean from time to time. Therefore,
expect showers to continue moving through the night and early
morning hours, particularly across the northeastern PR and USVI
sections. This rainfall activity is forecast to be followed by the
diurnal convection over portions of the Cordillera Central during
the afternoons.

We anticipate a drying trend by late Wednesday into Friday as an
upper-level ridge builds over the central Caribbean, bringing
drier air and more stable conditions aloft as 500 mb temperatures
warm to around -5 degrees Celsius.

&&

.AVIATION...

(06Z TAFS) Mainly VFR conditions are expected to prevail across
all terminals through the forecast period. However, brief MVFR
conds are possible at TJBQ/TJSJ due to -SHRA through the day. Mtn
top obscd over eastern PR and BKN cigs btw FL030-FL080. ENE winds
up to 12 kt with higher gusts near showers.

&&

.MARINE...

The remnants of a cold front and associated moisture will linger
across the northeast Caribbean throughout the weekend. A surface
high- pressure building across the Western Atlantic will promote
moderate east-northeasterly winds across the regional waters today.
Northerly swells will promote hazardous marine and coastal
through the upcoming workweek.

The offshore Atlantic buoys continue to observe seas around 8-9
feet with dominant periods around 11 seconds. Pulses of
northeasterly swells will continue to persist throughout the
weekend with seas remaining between 7-8 feet and occasionally
higher. Therefore, Small Craft Advisories are in effect through at
least Monday. Please refer to the latest Marine Weather Message
(MWWSJU) for more information.

&&

.BEACH...

Coastal conditions remain hazardous with breaking waves up to 10
feet today, mainly along the northern coast of Puerto Rico.
Breaking wave heights will slowly decrease over the next few days
however expect life-threatening rip currents to continue across
the north, east, west facing beaches of the islands through the
weekend. The reinforcing pulse of northerly swell on Sunday will
maintain similar conditions along the northern beaches of the
islands into next week. Please refer to the latest Coastal Hazard
Message (CFWSJU) for more information.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
454 AM AST Sun Dec 24 2023


.SYNOPSIS...

The frontal boundary to the north of the region, a mid to upper-
level trough, and the northerly winds will advect some showers
across Puerto Rico and the U.S. Virgin Islands at times. This
could result in ponding of water across affected areas. Cooler
temperatures will persist. Hazardous marine and coastal conditions
continue as northerly swells continue to exist across the local
waters, mainly for the northern coastlines, Atlantic Waters and
passages.

&&

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

Light northerly winds promoted showers along the Atlantic waters and
across portions of northern Puerto Rico through the overnight hours.
However, no significant rainfall accumulations were observed over
land areas. Minimum temperatures were from the low 60s across the
higher elevations to the low and mid 70s across coastal areas.

A broad mid-to upper-level trough over the central Atlantic
extending just north of the northern Leewards with associated
frontal boundary and surface troughs north and east of the region
will continue to advect showers at times across the local waters
with some reaching portions of the islands during the next day or
so. In addition, a weak surface low pressure is expected to develop
just north of Anegada before merging with the frontal boundary later
today. This will promote light west to northwesterly steering winds
over the islands today. Therefore, diurnally induced afternoon
showers should develop over the Cordillera Central and drift over
the south/southeastern sections of PR, with possible rainfall
amounts up to an inch. On Monday, a drier air mass between 850-700mb
is expected to filter from the west, and the precipitable water
content could drop below normal levels around 1.2-1.3 inches.
Therefore, mostly light showers and fair weather conditions should
prevail on Monday. On Tuesday, another short-wave trough with a jet
max of 90 kt is expected to mover over the region, promoting
unstable conditions aloft with better divergence and colder 500 mb
temps than previous days. Therefore, isolated thunderstorms are
possible over the Atlantic waters and in diurnal activity over
mainland PR.

&&

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

No new changes were introduced to the long-term forecast. By
mid-week, an upper-level jet segment will continue to cross the
region with winds around 60 kt winds, as the northeastern
Caribbean transitions from the broad upper-level trough over the
central Atlantic to an upper-level ridge. From Wednesday onwards,
temperatures at 500 mb should go from normal to above-normal
climatological values, meaning that convective development is less
likely each afternoon over the interior and western sections of
PR. Easterly winds will dominate the low levels as a broad surface
high-pressure slowly moves eastwards into the central Atlantic.
At this time, we forecast seasonal weather conditions through the
period, meaning that trade wind showers will filter across Puerto
Rico and the U.S. Virgin Islands at times, particularly across
eastern PR and USVI, during the overnight and morning hours. As
remnants of an old frontal boundary linger near the forecast area
and a weak surface low pressure to the northeast of the islands,
we anticipate moisture embedded in the easterly wind flow to
filter inland occasionally.

Overall, we anticipate a drying trend by late Wednesday into the
weekend as an upper-level ridge builds over the central Caribbean,
bringing drier air and more stable conditions. Nonetheless, expect
some shower activity influenced by the trades moving across Puerto
Rico and the U.S. Virgin Islands.

&&

.AVIATION...

(06Z TAFS) Mainly VFR conditions are expected to prevail across all
terminals through the forecast period. However, tempo MVFR conds are
possible at TJPS btw 24/16z-22z. VCSH likely at TJSJ/TJBQ/TIST for
most of the period. Light and variable winds, with a NNW component
after 24/16z and a southerly sea breeze along the southern coasts.

&&

.MARINE...

The remnants of a cold front and associated moisture will linger
across the northeast Caribbean throughout the weekend. Gentle to
moderate east-northeasterly winds will prevail across the regional
waters for the next few days. Northerly swells will promote hazardous
marine conditions through at least Monday.

The offshore Atlantic buoys continue to observe seas around 8-10
feet with dominant periods around 13 seconds with the swell
direction from the NNE. Pulses of northeasterly swells will
continue to persist throughout the weekend with seas remaining
between 7-8 feet and occasionally higher. Therefore, Small Craft
Advisories are in effect through at least Monday. Please refer to
the latest Marine Weather Message (MWWSJU) for more information.

.BEACH...

Coastal conditions remain hazardous with breaking waves up to 11
feet today, mainly along the northern coastline of Puerto Rico.
The reinforcing pulse of northerly swell arriving today will
maintain similar conditions along the northern beaches of the
islands into next week. Please refer to the latest Coastal Hazard
Message (CFWSJU) for more information.

[cycloneye]

Area Forecast Discussion...UPDATED
National Weather Service San Juan PR
512 AM AST Mon Dec 25 2023

.SYNOPSIS...

Expect beautiful weather this morning followed by afternoon
convection along the Cordillera Central and southern slopes of
Puerto Rico for this Christmas Day. The northerly wind flow will
promote seasonable cool temperatures today. An increase of rain
is expected tonight into Tuesday. A fair weather pattern is
expected for Thursday onward as a mid to upper- level ridge
lingers across the western Atlantic. Breaking waves around 6 feet
are still possible today for northern coastlines of Puerto Rico.

&&

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

Puerto Rico and the U.S. Virgin Islands residents had a pleasant
Christmas Eve, with typical tropical winter low temperatures. The
lows in the coastal areas were in the low or mid-70s, while in the
mountains and valleys, the thermometer dropped into the 60s and mid-
50s. Skies were mostly clear, although the GOES-E infrared channel
detected a layer of cirrus clouds over St Croix, associated with a
jet stream moving across the Northeast Caribbean. Early this
morning, north-to-northwesterly winds pushed fragments of low-level
clouds and showers across the local Atlantic Waters, some moving
inland over northern Puerto Rico. But in general, we had beautiful
weather conditions this Christmas.

The most recent satellite-derived precipitable water imagery shows
an area with below-normal moisture moving from the north to the
local region. Regardless of this air mass, fragments of clouds and
showers will sometimes move across the northern and eastern half of
Puerto Rico, while the U.S. Virgin Islands will have a mixture of
sunshine and clouds. Additionally, a short wave trough with a jet
stream aloft will promote better dynamics, which, combined with the
local effects and sea breeze influence, will result in afternoon
convection along the Cordillera Central and southern slopes of
Puerto Rico during the afternoon. The northerly wind flow will
promote the seasonable cool temperatures today.

Winds will become northeasterly tonight as a surface high pressure
builds across the Western Atlantic, pooling moisture over the
islands and promoting cool air advection. Therefore, scattered to
numerous showers will develop across the surrounding waters, moving
over the windward sections of Puerto Rico and the U.S. Virgin
Islands late tonight into early Tuesday morning. A jet maximum will
also arrive by Tuesday afternoon, and thunderstorm activity may
develop, promoting the ponding of waters across poorly drained areas
in Puerto Rico. We cannot rule out urban and small stream flooding
with the heaviest rainfall activity.

A ridge pattern aloft will build over the U.S. Virgin Islands and
Puerto Rico on Wednesday. Although this weather pattern promotes
stable weather conditions, fragments of moisture pushed by the
easterly winds may produce periods of moderate to locally heavy
rains across portions of the islands, which may lead to ponding of
water over poorly drained areas.

&&

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

A mid to upper level ridge passing across the western Atlantic
will remain throughout the long term period, causing stable
conditions for the local islands and allowing a calm weather
pattern to prevail. Moisture across the region should remain
fairly consistent which will allow a diurnal pattern of clear
skies with light passing showers throughout the day mainly for
eastern PR and the USVI and then an increase of showers during the
afternoon for western sections of PR. A land breeze is likely to
form each morning, becoming more easterly by the afternoon for the
first few days of the period, then becoming more consistent from
the east over the weekend as a short-wave trough deepens near
Costa Rica/southern Central America and tightens the local lower-
level wind flow. Temperatures should be typical of seasonal values
during this time with higher elevation areas dropping into the
low 60s and coastal areas remaining in the 70s. Overall,
conditions are looking quite fair without any outstanding weather
features. Fog is possible to form across the valleys during the
early morning hours, however should dissipate once the sun is up
in the sky.

&&

.AVIATION...
(06Z TAFS)

VFR conditions will prevail across the islands. Occasional -SHRA
will arrive this morning across the windward sections, mainly near
JSJ. SHRA with possible isolated TSRA will develop across the
interior and southern PR and could impact JPS between 25/18-23z. The
northeasterly winds will bring more frequent SHRA near JSJ/IST/JBQ
after 25/23z. Winds will continue from NNW-N this morning between 5
and 10 kt, becoming more NNE after 25/22z.

&&

.MARINE...
A northerly swell continues to linger across the Atlantic waters
and local passages, resulting in hazardous seas. These conditions
should continue through at least early today, gradually improving
after that. Gentle to moderate northeast to east winds will
prevail for the days to follow.

.BEACH FORECAST...
Life threatening rip currents and large breaking waves are
expected to continue through tomorrow for the north and east-
facing beaches of Puerto Rico, Culebra and for the northern
Virgin Islands with mainland northern coastlines of Puerto Rico
having waves around 6 feet today.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Tue Dec 26 2023

.SYNOPSIS...

Favorable conditions to observe rainy conditions today as a
shortwave trough swings by the region. A drier pattern is
expected Wednesday into the weekend and then an increase of
showers is forecast next week as a frontal boundary approaches the
region. Marine conditions have improved significantly compared to
the previous days and will continue to improve.

&&

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

A fragment of moisture moved from the Atlantic into PR's northeast
and eastern interior sections overnight, producing ponding of waters
in poorly drained areas. Partly cloudy to mostly cloudy skies
prevailed, and winds were mainly from the north to north-northeast
at 5 to 10 mph but locally higher near showers. Most of the rain
activity remained across the surrounding waters of the US Virgin
Islands. The rest of the islands had calm weather conditions.
Overnight low temperatures dropped into the 70s across the coastal
areas and into the low 60s or mid-50s in mountains and valleys.

Moisture will gradually increase today while the shortwave trough
and its jet stream maximum swing by the region, promoting favorable
conditions to observe rainy conditions today. Rain activity will
focus across the windward sections of Puerto Rico throughout the
day, although periods of no rain with passing clouds will occur,
too. The leeward sections can expect a mixture of sunshine and
clouds. In contrast, the US Virgin Islands may observe most of the
rain across their surrounding waters, and some may move inland at
times. By mid-morning into the afternoon, showers will spread into
the interior and southern sections of Puerto Rico, and as the jet
stream peaks aloft, stronger showers and possibly one or two
thunderstorms may develop. Ponding of water in poorly drained areas
is likely with moderate to locally heavy rains, without ruling out
isolated urban and small stream flooding.

A ridge pattern aloft will build over the US Virgin Islands and
Puerto Rico on Wednesday and Thursday, strengthening the trade wind
cap and, thus, reducing the potential for well-organized deep
convection. Although this weather pattern promotes stable weather
conditions, fragments of moisture pushed by the trade winds may
produce periods of moderate to locally heavy rains across portions
of the islands, which may lead to ponding of water over poorly
drained areas, particularly during the evening and early morning
hours. This rain pattern will be mainly due to cold air advection
over warmer nighttime waters.


&&

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

A mid to upper level ridge will dominate across the eastern
Caribbean through the weekend, which will provide stable conditions
for the local islands and allowing a calm weather pattern to
prevail. Friday through Sunday, rain activity should be minimal as
precipitable water values are below average in addition to the
stable conditions aloft. However, by Monday a deep upper-level
trough over the eastern United States associated with a frontal
boundary will begin to erode the stabilize effects of the ridge
across the region.

Currently Monday into Tuesday appears to be the
best day for passing showers as moist air begins to approach from
the south as the front passes into the western Atlantic. While it
strengthens throughout Tuesday into a low near the eastern
seaboard, southerly surface wind flow is possible beginning on
Tuesday. This may increase showers for southern Puerto Rico and
also cause warmer temperatures compared to the seasonal averages
especially for northern coastal areas. This scenario is dependent
on the evolution of the surface low that would form around Tuesday
in the upper-western Atlantic, and if this holds true it is
likely to also bring a strong northerly swell for the days to
follow.


&&

.AVIATION...
(06Z TAFS)

VFR conds will prevail across the islands. Occasional -SHRA/SHRA
will arrive across the windward sections this morning, mainly near
JSJ. SHRA with possible isolated TSRA may develop across interior
and S-PR and could impact JPS btwn 26/18-23z. The NE winds will
bring more SHRA near JSJ/IST/JBQ after 26/23z, and isolated TSRA may
develop across the regional waters; they may move inland near
terminals. Expect winds from NNE-NE btwn 5-10 kt with higher gusts
this morning, which will become calm-light/variable aft 26/22z.

&&

.MARINE...

A northerly swell continues weaken across the Atlantic waters and
local passages, generating seas up to 5 feet. Gentle to moderate
northeast to east winds will prevail for the days to follow. A
moderate risk of rip currents is present for northern and eastern
facing beaches.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
501 AM AST Wed Dec 27 2023


.SYNOPSIS...
Today, we expect calm weather across the islands and similar
conditions remain throughout the rest of the week. An increase of
rain is possibly by next week as a frontal boundary approaches the
region. Seas has subsided to up to 4 feet across the regional
waters. There is a moderate risk of rip currents for northern
facing beaches.

&&

.SHORT TERM...Today through Friday...
Calm weather conditions prevailed overnight with no rain activity
over the US Virgin Islands. The Doppler Radar detected some showers
over the local waters of north and east Puerto Rico, and some of
them moved inland, but in general, most of Puerto Rico did not
observe rain at all. Winds were calm to light and variable,
dominated by land breeze. Once again, overnight low temperatures
dropped into the 70s across the coastal areas and into the low 60s
or mid-50s in mountains and valleys.

Today, we expect calm weather across the islands under a light
northeast wind flow during the morning. The Total Precipitable Water
(TPW) will remain near or somewhat above the normal values for
December today. Orographic lifting and the influence of sea breeze
may play a better role during the afternoon, giving place to periods
of moderate to locally heavy rain over the mountains and southern
plains of Puerto Rico, spreading to the surrounding areas late
during the afternoon into the evening due to the weak steering
winds. Today may be the wettest day of the rest of this workweek.

A ridge at upper levels and a high pressure at mid-levels will
continue to build tomorrow into Friday, producing dry air intrusion
and subsidence aloft and strengthening the trade wind cap over the
northeast Caribbean. Additionally, moisture, in general, will slowly
erode across the region, leaving the islands under the fragments of
low-level moisture that the easterly winds may bring to the area.
Although we are not anticipating significant rainfall accumulations
under a mixture of clouds and mostly clear skies, these fragments
could result in moderate to locally heavy rains across portions of
the islands, which may lead to ponding water over poorly drained
areas, particularly during the evening and early morning hours. This
rain pattern will be mainly due to cold air advection over warmer
nighttime waters, typical for this time of the year.


&&

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

A post-frontal a band of moisture becomes replaces with drier air,
climatologically low precipitable water values, which will
significantly reduce the amount of showers across the area through
late Sunday. Upper to mid- level ridging will also contribute to
overall stable conditions. However beginning Monday morning a
frontal boundary starts to approach the region from the
northwestern corner of the CWA. The presence of the front will
also reduce the stabilizing effects of the ridge aloft and raise
local precipitable water values. As a result, an increase of
passing showers across northern and eastern Puerto Rico are to be
expected through Tuesday.

By Wednesday a strong surface low may form in the western Atlantic,
which would begin to cause a slight veering of the winds across the
western Caribbean, which will cause patchy air masses with greater
moisture content to advect across the region. This will further a
seasonal pattern of passing showers followed by afternoon
convection. Nothing hints at heavy rainfall, however this should be
a healthy increase of showers to keep soils wet across the islands.
Temperatures during this time will be around seasonally average to
slightly warmer once southeasterly winds possibly arrive on
Wednesday.

&&

.AVIATION...
(06Z TAFS)


VFR conditions will prevail across the islands. Some -SHRA/SHRA
cannot be ruled out to move near JSJ at times. SHRA/+SHRA may
develop across the interior and southern PR, spreading into JPS by
27/18-23z. Expect calm to light and variable winds through 27/13z,
and after that, return from the northeasterly at around 10 kt with
sea breeze variations.


&&

.MARINE...

CARICOOS nearshore buoy observations near San Juan are showing
heights of 4 feet while observations south of Ponce and St. John
show below 2 feet. A mid-period northerly swell continues to
will linger across Atlantic Waters, promoting seas and breaking
wave heights up to 4 feet. Gentle to moderate northeast to east
winds will prevail for the days to follow. The risk of rip
currents is moderate for northern facing beaches of Puerto Rico
and is low mostly elsewhere.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Thu Dec 28 2023

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

.SYNOPSIS...
Issued at 500 AM AST Thu Dec 28 2023

Under a weak northeasterly wind flow, we expect calm weather
conditions with typical December temperatures. A ridge at upper-
levels and a high pressure at mid-levels will promote a stable
weather pattern through Sunday. However, fragments of moisture and
local effects will result in occasional shower activity. A cold
front moving eastward across the Atlantic will approach the region
on Sunday, New Year's Eve. This front may produce favorable
weather conditions to observe a rainy pattern between Monday and
Wednesday.

&&

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

Mainly fair weather conditions prevailed overnight with the
exception of some cloud coverage and light showers across
northeastern PR. Temperatures have dropped into the low 60s for
higher elevations and in the low 70s for coastal areas. Winds were
light and variable as a land breeze developed early in the night.

Clear to partly cloudy skies and fair weather is expected for today
as a mid to upper-level ridge and a drier patch of air passes over
the islands. Precipitation chances are low yet are mainly for
northern and eastern PR during the morning hours and then due to
moisture convergence and diurnal heating they may be convection
across the interior to southern sections of PR during the afternoon.
Rainfall accumulations should be minimal from this. Showers may
linger across southwestern PR during the evening hours, however
should be light of any.

On Friday, a band of moisture associated with remnants of a
frontal boundary will approached the islands from the northeast.
It is not a strong band of moisture, however it may provide some
passing showers for the USVI and eastern PR throughout the day. By
now an easterly surface flow returned across the area as an area
of high pressure begins to exist north of the region between two
surface lows spread across the northern Atlantic. A drier weather
pattern is expected on Saturday as the ridge aloft strengthens and
precipitable water values remain quite low throughout the day.
Little to no rain is expected this day besides the chance of some
isolated showers across western PR.

&&

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

A mid-level high pressure lingering over the Northeast Caribbean
will limit organized convection across the islands. However,
fragments of moisture may result in the typical weather pattern,
consisting of passing showers across the windward areas.
Meanwhile, at the surface, a cold front will slowly approach
Puerto Rico from the west on Sunday.

The ridge aloft will erode Monday onward due to short waves
troughs moving near the region. The cold front previously
mentioned will approach the islands, leaving the area in an area
of convergence due to the interaction of the front and prevailing
easterly winds. This pattern may promote moisture pooling on
Monday, leading to favorable conditions for widespread rain
activity. As the shear line lingers north of the islands, it may
induce surface disturbance across the region, promoting periods of
moderate to locally heavy rain Tuesday through at least
Wednesday. GFS suggests above-normal Total Precipitable Water
(TPW) values early next week. Although it is too early to quantify
the possible impacts of this solution, if model guidance is
correct, we may begin 2024 under showery weather for the PR/USVI
region.

On Thursday, as the frontal boundary slowly dissipates near the
region, the above-normal TPW values may extend after mid-week,
resulting in occasional showers across PR/USVI windward sections
overnight and early in the morning and afternoon showers across
the leeward sections in PR. Regardless, we expect a mixture of
mostly clear skies and clouds across the region.

&&

.AVIATION...
(06Z TAFS)
Issued at 500 AM AST Thu Dec 28 2023

A gentle land breeze exist this morning, then 5-10kt winds out of
the NE will prevail after 14z. Mainly VFR conditions expected
through the period due to fair weather. An nearby jet aloft will
bring mid to upper-level clouds from time to time, however VFR
conditions will still prevail.

&&

.MARINE...
Issued at 500 AM AST Thu Dec 28 2023

The interaction between a high pressure north of the islands and a
surface trough northeast of the Caribbean will promote a light
northeasterly wind flow for the next few days. The seas will
remain around 4 feet, especially in the Atlantic Ocean and
Caribbean Passages. A small northeasterly swell due to a surface
low over the Central Atlantic will arrive late Saturday into early
next week.

In addition, a cold front will move into the Western Atlantic
late tonight into Friday, approaching the region early next week.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
422 AM AST Fri Dec 29 2023

.SYNOPSIS...
Issued at 422 AM AST Fri Dec 29 2023

We expect calm weather with a mixture of mostly clear skies and
clouds with pleasant December temperatures today. A ridge at
upper-levels and a high pressure at mid-levels will promote a
stable weather pattern through early next week. However, fragments
of moisture and local effects will result in occasional shower
activity. A cold front moving eastward across the Atlantic will
approach the region late Sunday night, New Year's Eve, lingering
off to the north near the islands Monday through Wednesday. This
front may interact with an easterly perturbation, converging over
the region by mid-next week.

&&

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

Fair weather conditions prevailed overnight with clear skies
containing cirrus wisps at times. Temperatures have dropped into the
low 60s for higher elevations and in the low 70s for coastal areas.
Winds were light and variable as a land breeze developed early in
the night.

Stable weather conditions with clear to partly cloudy skies are
expected throughout today for most of the islands of PR and the
USVI. This is mainly due to the influence of a mid to upper-level
ridge anchored across the Eastern Caribbean and dry air/low
precipitable water values. No precipitation is expected for most
of the islands except for a chance of light afternoon convection
along the Cordillera Central during the afternoon hours and some
passing showers later in the evening as a patch of air with
slightly high precipitable water values starts to move across the
area. However, skies should clear by the evening. Pleasant
temperatures are expected throughout the day.

By tomorrow, drier air and stable conditions are forecast to exist.
It appears that this will be there driest day of the week with a
very low chance of rainfall for all of the local islands. Light
winds are expected in the morning followed by an afternoon
sea breeze. Cloud coverage will increase during the afternoon,
yet chances of rainfall are low to none.

On early Sunday morning a patch of moist air will advect into the
northeastern part of the region meanwhile an a surface high
pressure develops in the Gulf of Mexico. This will cause surface
winds to back, becoming more northeasterly, and the increase of
moisture will provide the chance of some northern coastal passing
showers and also enhance the potential for afternoon rain across
the interior to south western sections of PR. Overall a calm
weather pattern with cooler seasonal temperatures will prevail for
the next few days, perfect for spending time outdoors during the
finale of 2023.

&&

.LONG TERM...Monday through Friday

The ridge aloft will erode Monday onward due to short waves
troughs moving near the region, promoting a zonal flow aloft
through at least mid-week. On Wednesday, GFS suggested the passage
of a jet stream north or over the area, which may provide good
ventilation overhead. This jet could increase the mixing as long
as the mid-level high pressure weakens enough.

The cold front will move off to the northwest of Puerto Rico,
leaving the region in a convergence zone due to the interaction
of the front and prevailing trade winds. This pattern may promote
moisture pooling through mid-week, leading to favorable conditions
for widespread rain activity. Additionally, as the shear line
lingers north of the islands, it may induce surface disturbance
across the region, promoting periods of moderate to locally heavy
rain, especially late Monday night into early Tuesday morning.
Although pockets of dry air may sometimes limit rain activity, GFS
suggests near to above-normal Total Precipitable Water (TPW)
values through that period. If this weather trend is correct, we
may observe a wet and unstable beginning in 2024. This
meteorological pattern does not necessarily indicate continuous
rainfall; still, there may be occasional periods of moderate to
locally heavy rain (or downpours) leading to ponding water in
poorly drained areas and/or urban flooding.

On Thursday and Friday, a surface high-pressure building across
the Western Atlantic could maintain the frontal boundary near the
region til it slowly dissipates. This high pressure will tighten
the local pressure gradient, promoting the return of the wet
easterly winds across the islands, thus frequent passing showers,
especially across the windward areas during the night and early
morning hours. Regardless of it, we may experience a mixture of
mostly clear skies and clouds across the region.

&&

.AVIATION...
(06Z TAFS)
Issued at 422 AM AST Fri Dec 29 2023

Fair weather will prevail today with a chance of light showers
during the afternoon hours. A sea breeze between 7-10kts will
develop after 15z. Thus, VFR conds durg prd with no sig operational
wx impacts.

&&

.MARINE...
Issued at 422 AM AST Fri Dec 29 2023

The interaction between the surface low pressure across the
Central Atlantic and a surface high pressure to the north will
promote light northeasterly winds over Puerto Rico and the US
Virgin Islands through the weekend. A cold front moving eastward
across the Western Atlantic will approach and linger near the
region by early next week. Seas will remain favorable for small
crafts until at least early next week.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Sat Dec 30 2023

.SYNOPSIS...

Overall fair weather conditions with pleasant December temperatures
are expected today. Weather conditions should remain fair and
stable throughout the weekend into early next week with occasional
passing shower activity. An increase in passing showers is likely
on Monday. Patchy fog is also likely across areas of the interior
during morning hours. An overall increase in moisture is foreast
by the second half of next week.

&&

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

An analysis of overnight radar and satellite imagery indicated that
the night remained rain-free but not cloud-free as pockets of low-
level clouds streamed across the area. Overnight temperatures varied
across the region, ranging from around 60 degrees in higher
elevations to about 75 degrees across eastern Puerto Rico and the
local islands. Winds were generally light and variable.

Dominated by persistent drier air and mid-level ridging with a
strong trade wind cap inversion, weather conditions should remain
fair and stable throughout the weekend into early next week. There
is a chance of limited shower development across central Puerto Rico
during the afternoons, attributed to sea-breeze convergence.
Additionally, passing trade wind showers are likely early Sunday
morning accompanying a pocket of shallow moisture, primarily
impacting northeastern Puerto Rico and the US Virgin Islands.
However, these showers are not expected to result in significant
rainfall, remaining well below a quarter of an inch across the
wettest areas. The overall forecast focuses on mainly sunny to clear
skies, light winds, and pleasant temperatures, fluctuating between
the mid-80s and the mid-50s.

This weather pattern is expected to persist, with mostly clear
skies, Sunday evening into Monday as we welcome the new year.
However, gradually increasing northeast winds, yielded by a surface
high pressure moving over the western Atlantic, will likely increase
the frequency of passing showers on Monday.

&&

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

Current Precipitable Water (PWAT) model guidance indicates below
normal values by Tuesday morning and into Wednesday. A series of
surface high pressures and frontal lows will be moving across the
Atlantic during the period. Promoting the nearby approach of
frontal boundaries, or at least remnants of them, to the area from
the northwest. A more significant transition into higher PWAT
values occurs by the second half of the work week and into the
weekend due to an approaching boundary. Generally northeasterly
winds are expected to persist through the period becoming more
easterly by the end of the workweek. Although persisting, high
pressure aloft will be more eroded than during the short term
period. Passing shower activity across windward sectors of the
islands during the night to early morning hours will be limited to
start the period but will increase in frequency by the second
half of the work week and into the weekend. Patchy fog is likely
across areas of the interior and some convection is possible over
areas of the interior due to local effects. Temperature wise, 925
mb temperatures are forecast to be 1 standard deviation below
normal to normal for this time of the year, resulting near-
seasonal to seasonal temperatures.

&&

.AVIATION...
(06Z TAFS)
VFR conditions will prevail across all terminals. VCSH may affect
TJSJ and USVI terminals after 30/22Z without impacting operations.
Light to calm and variable winds, increasing to 5-10 knots while
dominated by sea breezes between 30/12-22Z.

&&

.MARINE...

Current CARICOOS nearshore buoy observations show seas up to 3 ft
across the northern coast and less than 2 ft across the southern
coast. The interaction between the surface low pressure across
the Central Atlantic and a surface high pressure to the north will
promote light northeasterly winds over Puerto Rico and the US
Virgin Islands through the weekend. A cold front moving eastward
across the Western Atlantic will approach and linger near the
region by early next week. Seas will remain favorable for small
crafts until at least early next week.

&&

.BEACH FORECAST...

There is a moderate risk of Rip Currents for most north oriented
beaches of Puerto Rico today, extending to beaches of Culebra and
St. Croix this evening. Low risk elsewhere. During the week up to
moderate rip current risk before a swell possibly promotes a high
rip current risk for northern and western Puerto Rico Thursday and
Friday.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
502 AM AST Mon Jan 1 2024

.SYNOPSIS...Ongoing hazard risks arise from the interaction of a
small northerly swell and locally fresh winds, impacting small
craft operations and rip current conditions. The passage of a
shallow patch of moisture may lead to an increase in passing
shower activity today. However, the overall weather pattern should
remain fair and stable through midweek, influenced by mid-level
ridging and lower-than-normal moisture. A gradual increase in
moisture is likely from Thursday into the weekend, potentially
contributing to increased passing shower activity and the
potential for afternoon convective development. Temperatures will
likely range from below-seasonal to seasonal levels in the next
few days. Nevertheless, above-seasonal temperatures are likely by
the end of the workweek.


&&

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

Happy New Year! The islands started off the year with fair weather
conditions and no shower activity during the overnight hours. Clouds
steered by generally light northeasterly winds continued reaching
the islands. Lows ranged in the low to mid 70s across coastal areas
of the islands and, as reported by stations, in the low 60s across
higher elevations of Puerto Rico. Localized lower minimums are
likely. Current satellite derived precipitable water (PWAT) values
indicate below normal values, 0.8 to 1.12 inches across the islands.
More humid air masses are located over the offshore Caribbean Waters
and filtering in from the east and northeast. These patches of more
humid air filtering in from the east and northeast will push PWAT
values up to seasonal values today. Current model guidance indicates
drier air, with below normal PWAT values, then filtering in and
persisting across the islands on Tuesday and Wednesday. A mid- to
upper- level ridge over the western Caribbean will continue to
promote drier air aloft and warmer mid-level temperatures, limiting
shower activity. A surface frontal boundary and associated moisture
will move into the western Atlantic will linger near the region.
Passing shower activity will affect mainly northeastern Puerto Rico
and the USVI today under northeasterly winds. Patchy fog is likely
across areas of the interior during the early morning hours.
Increased cloud cover and limited convective activity is also
possible during the afternoon over areas of the interior due to
local effects. High temperatures will be around the mid 80s across
coastal areas of the islands. A patch of moist air arriving this
evening will increase the chance of passing showers. Dry air
tomorrow, the driest day in the period, and Wednesday, along with
unfavorable conditions aloft, will serve to limit rain chances.

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

The most recent model guidance indicated that mid-level ridging
will linger across the Caribbean region. However, the associated
strong trade wind cap inversion will likely weaken as a polar
trough sinks southward across the western Atlantic by the end of
the period, allowing moisture to expand beyond the 800 mbar layer.
Despite fluctuations in moisture due to intermittent patches with
different compositions associated with an easterly perturbation
and an approaching frontal boundary, a transition into a period
with normal to above-normal moisture content is likely. Model
guidance estimates precipitable water vapor to range from around
1.3 inches during the lowest moisture periods (briefly early
Friday and Sunday morning) to slightly over 1.6 inches by Sunday
afternoon.

Between Thursday and Friday, low-level east-to-east-southeast
winds will become light and variable with the proximity of the
pre-frontal trough. Winds will then turn from the northeast on
Saturday before gradually veering to the east from Sunday onward,
yielded by a surface high pressure moving eastward across the
western into the central Atlantic. Changes in wind patterns will
likely result in temperature fluctuations, and there is a
possibility of experiencing warmer temperatures than usual early
in the period.

The anticipated weather pattern will be characterized by a cooling
advecting pattern, leading to passing showers moving over areas
spanning east-northeastern Puerto Rico and the U.S. Virgin
Islands. These showers will be more prevalent at nighttime and
during the wettest periods, especially on Sunday. Additionally,
afternoon convective development is possible, and available
moisture and wind patterns will influence this activity's extent,
intensity, and location. Despite the expected shower activity, a
detailed analysis indicates that the resulting rainfall will not
likely pose a significant threat. Except for Thursday and
potentially Friday, which may be the warmest days, temperatures
will range from the mid-80s in lower elevations to the mid-50s in
higher elevations. Overall, the hazards throughout the long-term
forecast period should remain at the lowest risk levels.


&&

.AVIATION...

(06 TAFS) VFR conditions will prevail across the terminals. Light to
calm and variable winds, increasing to 5-10 knots, mainly from the
northeast, with sea breeze variations, after 01/12Z. VCSH at times
across TJSJ/TJBQ/TIST/TISX.

&&

.MARINE...

A surface high pressure over the western Atlantic will maintain
light to locally fresh east to northeasterly winds today. A cold
front moving eastward across the Western Atlantic will approach
and linger just northwest of the region. A small northerly swell
will continue to spread across the local waters today, generating
seas up to 6 feet across the Atlantic waters. The combination of
these conditions and increasing winds may impact small craft.
Another small north swell will reach the local waters by the end
of the workweek.

&&

.BEACH CONDITIONS...

A small northerly swell and moderate to locally fresh winds will
maintain a moderate risk of life-threatening rip currents across
the surf zone, particularly in beaches from Aguada and Rincon in
western Puerto Rico eastward across the north coast to Fajardo and
Ceiba in eastern Puerto Rico, Culebra, and the U.S. Virgin
Islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Tue Jan 2 2024

.SYNOPSIS...Ongoing hazard risks arise from the interaction of a
dissipating small northerly swell and locally fresh winds,
impacting small craft operations and possibly generating life-
threatening rip current conditions. The weather pattern should
remain fair and stable because of a persistent mid-level ridging.
However, intermittent patches of shallow moisture will bring rain,
especially across windward areas. A gradual increase in the
available moisture is likely from Thursday onward, potentially
contributing to increased shower activity. Temperatures will
likely range from below-seasonal to seasonal levels in the next
few days. Nevertheless, above-seasonal temperatures are likely by
the end of the workweek into the weekend.


&&

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

Passing shower activity steered by northeasterly winds that affected
north-central, northeastern, eastern, and southeastern Puerto Rico
gradually diminished during the overnight hours before leaving
minimal accumulations since midnight. Lows were in the low to mid
70s across coastal ares of the islands and, as reported by stations
in the low 60s across higher elevations of Puerto Rico. Localized
lower minimums are likely.

Satellite derived precipitable water (PWAT) values indicate a
patch of relatively drier air, with values of around an inch,
approaching the region from the northeast. The patch of moisture
that promoted the passing shower activity during the overnight
hours is mainly over the offshore Caribbean waters. Another humid
air mass is located to our northwest due to a pre frontal trough
and frontal remnants lingering near the region. Drier air from the
northeast will continue to filter into the islands today,
dropping PWAT values to below normal for most of the islands.
Current model guidance has this drier air persisting through
Wednesday evening. East-northeasterly surface winds will gradually
veer through the period to become east-southeast on Thursday, due
to the pre-frontal trough. Under this wind pattern, patches of
moist air with seasonal PWAT values will filter into the islands
from the southeast, particularly on Wednesday evening and
Thursday, promoting a wetter pattern. A mid- to upper- level
ridge over the western Caribbean will continue to promote drier
air aloft and warmer mid- level temperatures, limiting shower
activity. Brief passing shower activity will affect mainly
northeastern Puerto Rico this morning while patchy fog is likely
across areas of the interior. Increased cloud cover and limited
convective activity is also possible over areas of the interior to
western Puerto Rico due to local effects. Rain chances increase
as patches of moist air arrive Wednesday and Thursday. Highs
around the mid 80s across coastal areas of the islands.


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

The latest model guidance has integrated changes in the timing of
both peak and diminished moisture levels, as well as alterations
in wind patterns. Despite these changes, mid-level ridging will
remain across the Caribbean region, maintaining a trade wind cap
inversion and hostile conditions for deep convective development.
By Saturday night and Tuesday, the inversion will likely weaken as
polar troughs sink southward across the western Atlantic and steer
the ridge well over the western Caribbean, allowing moisture to
extend beyond the 800 mbar layer. While precipitable water (PWAT)
variations are likely due to fluctuations in airmass moisture
composition in the predicted patchy scenario, PWAT is expected to
remain within seasonal to above-seasonal moisture thresholds,
ranging from 1.2 to 1.7 inches. Tuesday is anticipated to
experience the most significant moisture change, encompassing the
driest and wettest period in the long-term forecast cycle.

Due to the proximity of a pre-frontal trough, low-level winds
should remain light and variable on Friday. By Friday night into
Saturday, winds will gradually back from the northeast before
veering to the east-southeast on Sunday and generally easterly
from Monday onwards, yielded by a surface high pressure moving
eastward across the western into the central Atlantic. An east-
to-southeast component in the general wind flow will likely result
in warmer temperatures than typical, especially early in the
period.

Typical for this season, the anticipated weather pattern will be
characterized by passing showers moving over areas spanning east-
northeastern Puerto Rico and the U.S. Virgin Islands. These
showers will be more prevalent at nighttime and during the wettest
periods, especially early Sunday and Tuesday. Additionally,
afternoon convective development is possible, and available
moisture and wind patterns will influence this activity's extent,
intensity, and location. Nonetheless, the resulting rainfall
should not pose a flooding threat. Temperatures should range from
the mid-80s in lower elevations to the mid-50s in higher
elevations. An increase of 2-5 degrees is possible during the
warmest period, especially on Sunday. Overall, the hazards
throughout the long-term forecast period should remain at the
lowest risk levels.


&&

.AVIATION...


&&

.MARINE...

A surface high pressure over the western Atlantic will maintain
moderate to locally fresh easterly winds today. A weak frontal
boundary and associated pre-frontal trough will approach and linger
just northwest and north of the region through Tuesday. A small
northerly swell spreading across the local waters and generating seas
up to 6 feet across the Atlantic waters will dissipate today. The
combination of these conditions and increasing winds may impact small
craft operations. Another small north swell will reach the local
waters by the end of the workweek.


&&

.SURF ZONE...

A dissipating small northerly swell and moderate to locally fresh
winds will maintain a moderate risk of life- threatening rip
currents across the surf zone, particularly in beaches from Aguada
and Rincon in western Puerto Rico eastward across the north coast
to Fajardo and Ceiba in eastern Puerto Rico, Culebra, and the
U.S. Virgin Islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
520 AM AST Wed Jan 3 2024

.SYNOPSIS...Ongoing hazard risks revolve around the possibility of
life-threatening rip current conditions across Atlantic beaches.
The weather pattern should remain fair and stable due to a
persistent mid-level ridging. However, patches of shallow moisture
will generate rain, especially across windward areas at nighttime.
A gradual increase in the available moisture is likely from
Thursday onward, potentially contributing to increased shower
activity. Temperatures will range from below-seasonal to seasonal
levels in the next few days. Nevertheless, above-seasonal
temperatures are likely during the weekend.


&&

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

Fair weather conditions with no shower activity observed across the
islands during the overnight hours. Light land breezes dominated and
minimum temperatures ranged between the low to mid 70s across most
lower elevations of the islands, with at least 1 station at lower
elevations of north-central Puerto Rico reporting a low of 69F.
Minimum temperatures were, as reported by stations, in the low to
mid 60s across higher elevations of Puerto Rico. Localized lower
minimums are likely.

Satellite derived precipitable water (PWAT) values indicate
relatively dry air across the islands, with PWAT at below normal to
normal values for this time of the year. Some patches of shallow
moisture will filter in today and then increase in frequency on
Thursday. Current model guidance indicate relatively dry air again
on Friday with patches of shallow moisture arriving at times. PWAT
should peak at normal values with these patches. The proximity of a
pre-frontal trough to our northwest will help promote winds to
diminish and become generally easterly today. Although winds should
remain generally easterly to ESE through the rest of the period,
they're forecast to veer later become more ENE to end the short term
period. However sea breeze and land breeze variations will be
present.A series of frontal lows and surface high pressures will
continue moving into and across the Atlantic north of the region,
relaxing and tightening the pressure gradient. A mid- to upper-
level ridge will continue to promote drier air aloft and warmer mid-
level temperatures, limiting shower activity.

Brief passing showers carried by shallow moisture can still affect
windward sectors of the islands this morning, but overall weather
conditions will be fair. Patchy fog over areas of the interior
likely this morning. Increased cloud cover and limited convective
activity is also possible over areas of interior to western Puerto
Rico during the afternoon due to local effects. As the frequency of
patches of moisture increases this evening, and tomorrow under more
ESE winds, rain chances will also increase. ESE winds tomorrow will
also promote slightly warmer temperatures across the region.


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

Similar to previous model guidance, changes in the timing of both
peak and diminished moisture levels and alterations in wind
patterns were introduced, given the nature of the expected patchy
weather pattern. While precipitable water (PWAT) variations are
likely, PWAT will remain within seasonal to above-seasonal
moisture thresholds, ranging from 1.2 to 1.7 inches. This new
guidance has delayed the highest and lowest PWAT to Wednesday and
Wednesday night, respectively. Despite these variations, mid-level
ridging and associated strong trade wind cap inversion will hold
across the Caribbean region. However, a slight weakening of the
inversion is likely as polar troughs sink southward across the
western Atlantic and steer the ridge well over the western
Caribbean, allowing moisture to extend beyond the 800 mbar layer.
The general wind flow at lower levels should remain around 5-15
mph from the east throughout the period, with a southeast
component during the weekend and a northeast component on Tuesday
and Wednesday, when wind speeds will likely increase to 10-20 mph,
yielded by a surface high pressure moving eastward across the
western into the central Atlantic.

The anticipated weather pattern will be characterized by passing
showers moving over areas spanning east-northeastern Puerto Rico
and the U.S. Virgin Islands. These showers will be more prevalent
at nighttime and during the wettest and breeziest periods,
especially on Tuesday and Wednesday. Limited afternoon shower
activity is possible across the interior to western Puerto Rico
during the wettest periods. Temperatures should range from the
mid-80s in lower elevations to the mid-50s in higher elevations,
but an increase of 2-5 degrees is possible on Saturday and
Sunday. Overall, the hazards throughout the long-term forecast
period should remain at the lowest risk levels.


&&

.AVIATION...

(06 TAFS) VFR conditions across the terminals. Mainly E to ENE
winds up to 15 knots with sea breeze variations higher gusts
through 03/22Z. Becoming light and variable, dominated by land
breezes after 03/22Z. Some VCSH possible across TJSJ/TIST/TISX,
increasing in frequency after 03/18Z.


&&

.MARINE...

A low pressure system along with its front, moving eastward across
the Western Atlantic, will approach the region and will linger
north of the forecast area today. At the same time, a migrating
high pressure will position over the Central Atlantic through the
end of the workweek. Therefore, expect light to moderate easterly
winds through much of the workweek. Another north swell will reach
the local waters by the end of the week.