Caribbean - Central America Weather

[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.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
436 AM AST Thu Jan 4 2024

.SYNOPSIS...

A stable weather pattern characteristic of the season will persist
across the islands as high surface pressure over the Central
Atlantic continues to dominate the local weather. An increase in
moisture is anticipated from today into Saturday, enhancing the
likelihood of more frequent showers over the windward sections of
the islands. In the long term, conditions are expected to stay
relatively consistent, characterized by surface high pressure and
low-level moisture originating from a frontal boundary just north
of the islands. Despite the favorable conditions for some showers,
there is no anticipated flood threat. Marine conditions are
expected to remain calm today, with seas reaching up to 5 feet
across all regional waters.

&&

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

Slightly warmer than normal temperatures today through Friday under
a light east southeast low level wind flow. However, the surface
winds although light will be more east northeast today as a surface
pressure ridge will continue to shift farther eastward over the
western Atlantic, then becoming more northeasterly and increasing by
Saturday as the surface ridge reestablishes north of the region. In
the mid to upper levels, expected weak ridging to remain in place
across the region while a broad upper trough and series of short
waves and associated cold fronts are forecast to cross the west and
central Atlantic north of the region while maintaining a moderate
zonal flow and prevailing westerlies aloft. All in all, other than
brief periods of mostly light passing showers across the north and
east coastal areas from time to time, and fewer afternoon showers
over parts of the central and west interior of PR, no significant or
widespread rains are forecast for the period in and around the
islands as mostly fair weather skies and stable weather condtions
will prevail.

On Saturday a slight increase in the frequency of the early morning
passing showers will be possible as the east northeasterly low level
winds increase in response to the tightening of the local pressure
gradient, thus allowing more fragments of moisture from old frontal
boundaries and shear-lines to move across the area form time to
time. However afternoon shower activity will be limited to mainly
parts of the east interior and west to southwest sections of Puerto
Rico steered by the prevailing wind flow. Again no significant
operational weather impacts are so far forecast for the period.

&&

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

The beginning of the long-term forecast promises a variable
weather pattern. At the surface, conditions will be dominated by
moisture trapped at lower levels under a predominantly eastward
wind flow generated by the interaction of a frontal band, its
induced trough, and a high-pressure system located in the central
Atlantic. These conditions will combine with a stable atmosphere
due to the presence of high pressure in the mid-levels, resulting
in a trade wind cap inversion that erodes most of the significant
humidity aloft. Under this pattern, the islands can expect
frequent arrivals of pockets of moisture from Sunday into Monday,
impacting the windward sections more significantly. Showers are
forecast to remain insignificant, with minimal rainfall
accumulations. Given the recent expected conditions, forecast
weather and QPF grids have been updated due to changes introduced
by the last runs.

By Tuesday, a broad-building surface high-pressure system
extending from the Northwest Atlantic into the central Atlantic
will dominate the surface pattern, pushing the shallow moisture
from a frontal boundary over the islands. As the surface high-
pressure system interacts in the Atlantic, fluctuations in the
winds will be introduced, with winds veering from Wednesday into
Thursday. Under these low-wind conditions, patches of trapped
moisture will continue to reach the islands, increasing the
potential for persistent showers over the southeastern sections.
Although surface-trapped moisture will be present for most of the
period, the lack of instability aloft will result in a variable
pattern with typical showers in the evening hours and early
morning each day.

&&

.AVIATION...
(06Z TAFS)
Issued at 422 AM AST Thu Jan 4 2024

VFR conditions at all terminals durg prd. SFC wnds calm to light and
variable bcmg mainly fm E between 5-10 kts with sea breeze
variations aft 04/14Z. Low level winds fm ESE BLO FL100. Few light
showers may affect mainly parts of the north and east coastal areas
of PR with VCSH at TJSJ and few -SHRA ovr regional waters and en
route between PR and the USVI til 04/12Z. Isold-SCT psbl ovr E and
ctrl to W interior of PR btw 14/16z-22Z but no sig operational wx
impacts anticipated.

&&

.MARINE...

The interaction of a cold front just northeast of the region and
a surface high pressure over the Central Atlantic will continue to
result in light to moderate easterly winds across the region.
Therefore, sea conditions will remain at 5 feet of less across all
the local waters. A small northwesterly swell is forecast to
arrive by late Thursday into Friday inducing seas up to 6 feet for
the last part of the upcoming weekend.


.BEACH FORECAST...

There is a moderate risk of rip current across all the north
exposed beaches of Puerto Rico, increasing tonight for Culebra and
St. Thomas, USVI. For the rest of the coastal areas, including
Vieques and St. Croix, the rip current risk will remain low. For
the last part of the upcoming weekend, the risk will turn high
for the northern coastal areas due to the arrival of a northerly
swell.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
439 AM AST Fri Jan 5 2024

.SYNOPSIS...
Issued at 439 AM AST Fri Jan 5 2024

Satellite Imagery shows a group of cloudiness and moisture just
east of the region. This increase in some cloudiness might result
in some brief cloudiness and some showers over windward sections
of the islands during the day. Although moisture will remain in
place for most of the forecast, stable conditions will persist
with minimal rainfall activity and no flood threat. For the
northern coastal areas, hazardous coastal conditions will prevail
today with a statement of a high risk of rip currents in effect.
Another pulse of northerly swell will move into the local waters
by Sunday, resulting in hazardous marine and coastal conditions.

&&

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

Overall fair and stable weather conditions will persist today and
through the upcoming weekend. A mid to upper level ridge will
continue to extend across the region from the Caribbean waters,
while a broad trough will slowly shift eastward across the Atlantic
and north of the region. This will maintain a high zonal/westerly
wind flow through Saturday then become more northwesterly by Sunday
as the ridge aloft builds across the region to maintain stable
conditions through the period. A cold front and associated surface
low will continue eastward across the west and central Atlantic
today into Saturday. This will aid in relaxing the local pressure
gradient resulting in fairly light and variable winds today, then
gradually increase and becoming more easterly by Saturday into
Sunday.

Shower activity across the region will be limited due to the lack of
significant moisture transport in an overall dry airmass. For now
and based on recent model guidance, the forecast calls for only
periods of shallow trade wind moisture shredded off from old frontal
boundaries with isolated to scattered passing showers to cross the
coastal waters and reach the coastal areas of the islands from time
to time. Afternoon showers if any will be locally induced by sea
breezes and limited to mainly part of the east and central to west
interior of Puerto Rico each day. Elsewhere a mostly seasonal
weather pattern of fair weather skies and pleasant temperatures can
be expected through the weekend with maximum precipitable water
values to be near normal and range between 1.20-1.50 inches. No
significant weather impacts are forecast for the period. &&

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

The long term remains on track. The main atmospheric feature will
be the mid to upper level, which will hold for most of the
period. This ridge will enhance stable weather conditions across
the region, providing drier air aloft and warmer temperatures at
the upper levels. At the low level, for the first part of the long
term, the interaction of a frontal boundary and a broad surface
pressure will result in easterly trade winds across the region.
Dragged by this wind flow, fragments of moisture with precipitable
water values around 1.5 inches, according to the global model
guidance, will dominate the local forecast pattern. Therefore,
residents can expect periods of clear skies and some brief passing
showers over the windward sections of the islands. Rainfall
activity is not forecast to be significant or widespread due to
the lack of support at the upper levels.

For the last part of the workweek, surface conditions will hold
under the influence of the broad surface high pressure. This
surface ridge will be pushing another cold front and the
associated low-pressure system, now located over the northwestern
Atlantic just east of the eastern coast of the United States, over
the waters. This surface change will bring the moisture from the
frontal boundary over the islands by Thursday, being the wettest
day of the period. After that, a significantly drier airmass will
filter into the region by Friday, with precipitable water values
of 1 inch, as suggested by the American global model guidance.

&&

.AVIATION...
(06Z TAFS)
Issued at 439 AM AST Fri Jan 5 2024

VFR conditions at all terminals durg prd. SFC wnds
lgt/vrb to calm bcmg fm E-NE between 8-12 kts with sea breeze
variations aft 05/14Z. L/lvl wnds fairly light fm SE 5-10 kts BLO
FL120,then incr and bcmg fm W while incr w/ht ABV. FEW-SCT lyrs nr
FL030 ovr regional waters and en route btw islands with Isold -SHRA.
No significant operational wx impacts durg prd.

&&

.MARINE...
Issued at 439 AM AST Fri Jan 5 2024

A cold front and the associated surface low progressing eastward
over in the Atlantic, causing light to locally moderate easterly
winds today. Meanwhile, another area of high pressure is expected
to move eastward from the Western to Central Atlantic, keeping the
remnants of a cold front present to the north of our region
throughout the weekend. A minor northerly swell will persist
across the Atlantic and Caribbean Passages until late Saturday
night, resulting in seas between 3-6 feet across the Atlantic
waters and up to 5 feet in the Caribbean water. A more energetic
pulse of long-dominant northeasterly swell will arrive on the
local waters on Sunday and continue into early next week.

&&

.BEACH FORECAST...
The present pulse of the northwesterly swell is resulting in
6-foot breaking waves across the northern sections of the islands.
Therefore, a high risk of rip current was issued for the northern
coastal area from Aguadilla to Carolina through 6 PM AST tonight.
Another more energetic pulse of moisture is forecast for Sunday
into the upcoming workweek.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
451 AM AST Sat Jan 6 2024


.SYNOPSIS...
A high pressure centered north of the area may bring fragments of
an old frontal boundary at times during the next few days, with a
mix of sun and clouds most of the time. Drier conditions are
anticipated later in the workweek. Several pulses from a northerly
swell will arrive this week, with beach conditions deteriorating
for the north-facing coast of the islands by late Sunday.

&&

.SHORT TERM...Today through Monday...
Stable weather conditions prevailed across the islands during the
night and early morning hours. The satellite imagery detected a
few clouds over the local waters and some eastern sections of the
islands. A line of showers was observed by the Doppler Radar in
the late-night hours, resulting in moderate showers over the
north-central sections. No significant rainfall accumulations
were reported with this activity. Overnight temperatures ranged
from the low 60s over the mountains to the low to mid-70s across
the coastal areas of the islands.

For the rest of today, a variable weather pattern is expected, with
conditions influenced mainly by a northeast wind flow generated by
the interaction of the broad surface high pressure over the western
Atlantic, extending towards the central Atlantic, and a stationary
frontal boundary over the Central Atlantic. This wind flow will
continue to push patches of moisture with precipitable water values
ranging from 1.3 to 1.4 inches, as indicated by the derived GOES
satellite imagery. Although conditions are marginally conducive
for shower activity, the activity will be light and short-lived
due to stability and dry air at higher levels, due to a mid to
upper-level ridge.

Similar weather conditions will persist for the rest of the short-
term period, primarily dominated by the ridging aloft. However, by
Sunday and Monday, as the surface high pressure moves westward
into the central Atlantic, the pressure gradient will tighten and
winds will veer as speeds increase. Under this pattern, residents
can expect more frequent passing showers, especially over the
windward sections of the islands.

&&

.LONG TERM...Tuesday through Saturday...
High pressure at all levels will be the dominant feature through
the forecast period. From Tuesday onward, the pressure gradient
will tighten, with a steering flow around 15 to 20 knots anticipated
at the lower levels of the atmosphere. Also, a trade wind cap
inversion will be present at 850-700 mb, but it will be stronger
on Friday and Saturday. During these days, the enhanced trade
winds will be carrying a few fragments of old frontal boundaries
over the islands. Therefore, a pattern of passing showers is
expected, mainly for the Virgin Islands and northeastern Puerto
Rico. Conditions aloft are not favorable for strong showers, so
accumulations should not be significant.

&&

.AVIATION...
(06Z)

VFR conditions will persist across all the TAF sites during the
period. Light winds are expected through 06/15Z, increasing from
the E-NE up to 12 knots. Cloudiness and some showers near the
coastal areas might result in a lower ceiling, but not enough to
change the flight category. Winds will diminish again by 07/03Z,
becoming light and variable.

&&

.MARINE...
A surface high pressure will move eastward toward the central
Atlantic, maintaining the remnants of a frontal boundary north of
the region throughout early next week, and will maintain a
moderate easterly wind flow. A small northerly swell will continue
to move across the Atlantic and Caribbean Passages through late
today and then a stronger northerly swell, with a period around 13
seconds, is forecast to arrive Sunday into early next week.
Additionally, winds will pick up by the middle of the week as a
high pressure builds over the western Atlantic.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
424 AM AST Sun Jan 7 2024


.SYNOPSIS...
Winds will increase this week as a high pressure builds north of
the region. A frontal system moving north of the region may bring
a few showers later this week. An arriving northerly swell will
increase the rip current risk to high from tonight into much of
the workweek. Marine conditions will deteriorate too, becoming
hazardous to small crafts later in the week.

&&

.SHORT TERM...Today through Tuesday...
A broad surface high pressure over the central Atlantic and a
weak frontal boundary near 21N will maintain moderate trades
across the northeastern Caribbean through at least Monday. On
Tuesday, a stronger surface high pressure will build over the
western Atlantic, pushing another frontal boundary near 20N. This
will tighten the local pressure gradient and moderate to fresh
east to northeast trades are expected to prevail across the
region. Meanwhile, at the upper levels, a broad ridge will remain
as the dominant weather feature through the short term period.
This will continue to provide stable conditions aloft and drier
air above 800mb. Moisture content will remain trapped at the lower
levels of the atmosphere, as remnants of old frontal boundaries
move at times from the east.

Latest satellite and radar imagery shows a band of showers and
cloudiness stretching from the Anegada Passage into the coastal
waters of the USVI and the offshore Caribbean waters well south of
PR. This has promoted scattered showers in and around St. Croix with
minor rainfall accumulations, and is expected to produce similar
activity over PR throught the day. Further drier conditions are
expected on Monday and Tuesday, but a wind surge on Tuesday should
promote an advective weather pattern overnight, with showers moving
along the northern and eastern sections of PR as well across the
USVI at times.

&&

.LONG TERM...Wednesday through Sunday...
By the middle of the week, a cold front will be located just north
of the region, while a mid to upper level ridge dominate these
levels of the atmosphere. Moisture from the frontal system or a
perturbation associated with this feature could reach the islands
on Wednesday and Thursday. This could increase the frequency of
showers over the Virgin Islands and eastern Puerto Rico, but
conditions aloft are not favorable for significant rainfall
accumulation.

On Friday and Saturday, the trade wind cap inversion will
strengthen around 850 mb, so moisture will remain trapped in the
lower levels of the atmosphere. At the surface, the pressure
gradient will be a little tight with winds out of the east at
around 15 knots. So, even though conditions aloft will not be
favorable for shower production, east to northeast winds will
carry these areas of enhanced moisture over the region.
Significant rainfall amounts are not anticipated at this time.

&&

.AVIATION...
(06Z TAFS)

VFR conds are expected to prevail at all TAF sites with
occasional VCSH across the terminals. Winds generally out of the E,
with sea breeze variations and speeds of around 10 to 15 knots
through at least 07/22z. Winds will diminish after sunset, becoming
light again tonight.

&&

.MARINE...
A surface high pressure centered north of the region will maintain
moderate easterly winds across the region. By the middle of the
week these winds will increase in speed. A northerly swell will
arrive today, while a stronger pulse is anticipated by the middle and
latter part of the week. The increased winds and the swell will
deteriorate seas across the Atlantic, becoming hazardous by
Tuesday.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Mon Jan 8 2024


.SYNOPSIS...
Patches of moisture from old frontal boundaries will reach the
islands at times, increasing shower activity at times. Otherwise,
a mix of sun and clouds is expected through much of the week. A
northerly swell will maintain conditions dangerous for swimmers
along the north-facing beaches, as well as hazardous seas for the
Atlantic and passages.

&&

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

Multiple old cold front boundaries linger in the area, with two
evident in the total precipitable water product and showing up as
lines of scattered small showers that stretch east northeast to west
southwest: one stretching from just north of Aguadilla to outside
the forecast area north of the British Virgin Islands and the other,
a little broader, stretching from north of Saint Croix to south of
the forecast area south of Ponce. The showers in these lines were
moving west southwest at 15 knots. Few showers were noted overnight
across land areas and minimum temperatures so far were ranging from
the mid and upper 70 on the windward coasts to the lower 60s in the
higher elevations and mountain valleys.

The current synoptic pattern shows strong low pressure north of the
local area and east of New York moving east with a trailing cold
front. The cooler air behind the front will eventually fill most of
the western Atlantic with a moderate high pressure in the western
Atlantic by Tuesday morning. This will add one more cold front
expected to approach the local area from the north northeast and add
another layer of old boundaries that don't quite reach the local
area, but send shreds of moisture with brief but shallow showers
through the area.

At upper levels a ridge of high pressure will stretch from the west
or southwest Caribbean across the local area through at least
Wednesday, keeping mid and upper levels dry and stable.

The last sounding from San Juan at 07/12Z showed a relatively strong
inversion between 8000 and 8850 feet with extremely dry air just
above it. This will be an effective cap for the showers forming in
the modestly moist air below it.

Little change in this pattern is expected during the next 3 days
although winds will increase on Tuesday and shift a little toward
the east southeast on Tuesday night and Wednesday allowing for a
few degrees warming on the north coast and the Greater San Juan
Metropolitan area mid week.


&&

.LONG TERM...Thursday to Monday...
There has not been many changes in the long term forecast. A
ridge at the middle and upper levels will continue to be the
dominant feature, with a dry air mass at 700 mb and above. At the
surface, a high pressure north of the islands will maintain the
gradient tight on Thursday, with a low level steering flow out of
the east at around 18 knots. By this time, the surface high will
push the remnants of frontal system over the islands, so some
showers can be anticipated, mainly for eastern Puerto Rico and in
the surroundings of the Virgin Islands. After that, for Friday and
the weekend, the air mass will mostly dry out, with precipitable
water values falling below the climatological mean. The trade wind
cap inversion around 850 mb will be present all these days, but
it will be stronger on Monday. After Thursday, wind speeds will be
around 15-20 mph, and out of the east or northeast. Any shower
activity that may fall during this period should be brief, and
significant accumulations are not anticipated.

&&

.AVIATION...
(06Z TAFS) Mainly VFR conditions are expected to prevail across all
terminals through the fcst pd. However, brief MVFR cigs and mtn
obscurations are possible aft 08/16Z in SHRA across PR and adjacent
waters thru 09/04Z. Light and variable winds becoming east at 12-18
kt with higher gusts and sea breeze variations after 08/14z. Winds
will diminish and become land breezes aft 08/22Z.

&&

.MARINE...
A surface high pressure centered north of the region will maintain
moderate to locally fresh easterly winds. These winds will increase
tonight. A northerly swell will continue to reach the local waters
today. These increasing winds and swell will maintain hazardous seas
for small craft across the Atlantic Waters and Caribbean Passages,
lasting through the workweek.

.BEACH FORECAST...
A north-northeasterly swell will create dangerous conditions,
particularly along the northern coast of Puerto Rico, Culebra and
St. Thomas and St. John. Breaking waves around 10 feet are
anticipated for northern PR and Culebra. The risk of rip currents
will remain high for most of the workweek.

[cycloneye]

 https://twitter.com/TTWeatherCenter/status/1744424007481372817

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
454 AM AST Tue Jan 9 2024


.SYNOPSIS...
Winds will be picking up today, so it will feel breezy at times.
The remnants of old frontal boundaries may be pushed by the trade
winds at times, bringing occasional showers into the islands.
Marine and coastal conditions remain deteriorated due to a
combination of a small northerly swell and enhanced winds.

&&

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

Multiple old cold front boundaries still linger in the area, but
shower coverage is less widespread than yesterday. Again two bands
were seen, one stretching out of north central Puerto Rico to the
northeast, but not extending very far out to sea and another from
northwest of Saint Croix to south of the forecast area south of Cabo
Rojo. The showers in these lines were moving west southwest at 15
knots. Few showers were noted overnight across land areas and
minimum temperatures so far were ranging from the lower 60s in the
higher elevations and mountain valleys to the low to mid 70s in the
lower elevations. A few stations along the northern coasts saw 80
degrees as of 4:30 AM AST owing to enhanced breezes out of the east
northeast.

The current synoptic pattern shows strong low pressure in the
northwest central Atlantic with a trailing cold front. The cooler
air behind the front will eventually fill most of the western
Atlantic north of the local area with a moderate high pressure in
the western Atlantic by Tuesday morning. This will add one more cold
front expected to approach the local area from the north northeast
and add another layer of old boundaries that don't quite reach the
local area, but send shreds of moisture with brief but shallow
showers through the area. This next cold front should approach
Wednesday morning to about 220 miles northeast of San Juan and then
slide into the forecast area from the northeast with better moisture
and a good chance of showers across Puerto Rico and the U.S. Virgin
Islands on Thursday. The best showers will be over the eastern end
of Puerto Rico where up to one half inch could fall. Another front
will then traverse the western Atlantic, but a high pressure in the
central Atlantic ahead of it will then begin to retard its progress.

At upper levels a ridge of high pressure will stretch from the west
or southwest Caribbean across the middle of the Caribbean Sea,
keeping flow over us northwest and mid and upper levels dry and
stable.

The last sounding from San Juan at 08/12Z showed a relatively strong
inversion between 8000 and 8900 feet with extremely dry air just
above it. This will be an effective cap for the showers forming in
the modestly moist air below it.

Little change in this pattern is expected during the next 3 days
although winds will increase again today and shift a little toward
the east southeast on Tuesday night and Wednesday allowing for a few
degrees warming on the north coast and the Greater San Juan
Metropolitan area mid week. Then on Thursday winds will carry the
frontal boundary across the area west with more showers and slightly
cooler weather.

&&

.LONG TERM...Friday to Tuesday...
The pattern for the end of the week into early next week looks to
still be dominated by ridging at the mid and upper levels. On
Friday, the remnants of an old frontal boundary will begin to move
away from the islands, but some lingering moisture may still bring
a few showers into the region. This air mass will be replaced in
the weekend with drier air, and precipitable water values will
fall below the climatological value. At the surface, high pressure
to the north will maintain the pressure a little tight, with
speeds around 15 knots on Friday, a little more relaxed on
Saturday, but winds will pick up again on Sunday and Monday. A
patch of moisture a little deeper will also arrive by Monday, but
the trade wind cap at 750 mb should limit the vertical development
of any shower that forms. In general, no significant rain event is
anticipated through this period.


&&

.AVIATION...
(06Z TAFS)

VFR conditions are expected to prevail across all terminals thru the
fcst pd. Brief -SHRA alg the N coast PR til arnd 09/13Z should have
little impact on ops. SHRA over interior PR beginning arnd 09/17Z
will have MVFR conds and mtn obscurations til arnd 09/23Z. Light
winds from the ENE bcmg 12-18 kt with some hir gusts coastal
locations aft 09/14Z. Winds will become land breezes aft 10/00Z.
&&

.MARINE...
A surface high pressure centered northeast of the region will
maintain moderate to fresh easterly winds through tonight. The
combination of northerly swells and wind-driven seas will maintain
hazardous marine conditions for small craft across the offshore
Atlantic and Caribbean waters, and local passages. These conditions
will persist throughout the workweek.

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
540 AM AST Wed Jan 10 2024

.SYNOPSIS...
Warmer temperatures are expected today across the region, but
cooler air should return by Friday. A frontal system will approach
on Thursday, increasing the frequency of showers. Marine and
coastal conditions will remain deteriorated through much of the
workweek.

&&

.SHORT TERM...Today through Friday...
Widely scattered showers have been moving across the local area for
most of the night. Just before midnight a band of showers formed
just north of the north coast and moved over the Greater San Juan
Metropolitan area leaving five hundredths of an inch. This band
dissipated, but a few other minor showers have crossed through
eastern Puerto Rico. Local radar showed a few showers in the
vicinity of the U.S. Virgin Islands. Amounts are believed to be less
than measurable except in Cotton Valley where thirteen hundredths of
an inch fell.

Low pressure in the north central Atlantic moved north, but a cut-
off low formed along the front near 33 north 35 west and was
continuing to strengthen as it moves east. High pressure near 33
north 55 degrees west is moving southeast and is pushing the cold
front from the new low toward the local area. A band of showers and
better moisture has formed east of the area and is moving across the
area this morning. This is what caused the showers overnight.
Although the high pressure will weaken, the front will be driven
into the local area on Thursday and across Puerto Rico on Thursday
night. This will bring a better chance of showers. The showers will
remain capped by dry mid-levels even though vertical motion is
better in the lower levels. By Friday, both Puerto Rico and the U.S.
Virgin Islands will be seeing slightly cooler and drier air. In
fact, precipitable water values which are forecast to reach 1.9
inches Thursday evening, will drop below 1.2 inches by midday on
Friday as the front passes into the Caribbean.

The approach of the front will pull winds in from the east southeast
over the area and cause some warming on the north coast today. In
fact the record high temperatures for San Juan will be 88 degrees
today (set in 2003) and our forecast high could reach that or come
quite close. Thursday and Friday will see better chances of showers
and lower temperatures.

High pressure at upper levels extends from Honduras and Nicaragua
across the center latitude line of the Caribbean. This high will
shift to south of the Windward Passage with a weak ridge over the
local area by Friday. This will help drive subsidence over the area
on Friday and contribute to the drying of the lower layer of the
atmosphere above 6 kft.


&&

.LONG TERM...Saturday to Wednesday...
A ridging pattern is expected to continue this weekend, with dry
air at the mid levels of the atmosphere. At the surface, high
pressure northeast of the region will drive the trade winds from
the east, at 10 to 15 knots. On the weekend, precipitable water
values will remain below normal, with a trade wind cap inversion
at around 850 mb. Very little rain is expected this weekend,
except for isolated activity reaching the eastern municipalities
of Puerto Rico at times. As the workweek starts, some low level
patches of moisture may reach the local islands. Moisture levels
will be near normal, so a few more showers can be anticipated.
Aloft, conditions will remain stable, so no significant rains are
expected. By Wednesday, the global models show a more defined
low level feature reaching the area. Also, the pressure gradient
will be tight, hence wind speeds will increase. So far, a low
level steering flow at 20 to 25 mph. Late Tuesday into Wednesday
is the period with the best chance of showers, but the feature
will move quickly, followed by another mass of drier air.

&&

.AVIATION...
(06Z TAFS)

VFR conditions are expected to prevail across all terminals thru the
fcst pd. Brief -SHRA til arnd 10/15Z should have little impact on
ops. SHRA over interior PR beginning arnd 10/16Z will have lcl MVFR
conds and mtn obscurations til arnd 10/21Z. Drier air is expected to
invade from the southeast aft 10/22Z and clear most SHRA from PR and
the USVI. Light winds from the ENE bcmg 10-16 kt with some hir gusts
coastal locations aft 10/14Z. Winds will become land breezes aft
10/00Z.

&&

.MARINE...
A surface high pressure centered north of the region will maintain
moderate easterly winds today, and winds will increase tomorrow and
Friday. Another pulse of a northerly swell will arrive tomorrow. The
combination of northerly swells and wind-driven seas will maintain
hazardous marine conditions for small craft across the offshore
Atlantic waters, and the Anegada Passage. These conditions will
persist throughout the end of the workweek.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
521 AM AST Thu Jan 11 2024

.SYNOPSIS...
Issued at 520 AM AST Thu Jan 11 2024

Shallow moisture will continue to generate periods of light to
moderate showers in easterly flow as old frontal boundaries are
pushed through the area by high pressure to our north. Showers
will be most likely tonight and Friday, Monday and Wednesday.
Temperatures will continue to be slightly above normal.

&&

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

Skies were mostly clear to partly cloudy overnight as high level
clouds and passing low level clouds in the trade wind flow moved
in and out of the region from time to time. Some showers affected
the coastal waters especially between eastern Puerto Rico and the
U.S. Virgin Islands with a few reaching the north and east coastal
areas. Rainfall accumulations however were less than a tenth of
an inch. This pattern of passing showers is expected to continue
into the late morning hours, as another swath of trade wind
moisture from an old frontal boundary is forecast to cross the
islands during the rest of the day. Although significant and
widespread rains are not expected, there may be brief periods of
moderate to locally heavy rains at times. Early morning
temperatures were in the low to mid 70s along the coastal areas
and low to mid 60s in higher elevations and valleys.

A surface high pressure ridge spread across the central and west
Atlantic will shift slightly eastward today, with the moderate
east southeast winds forecast to become more east to northeast by
Friday and Saturday. This will aid in transporting fragments of
shallow moisture from the aforementioned frontal boundary across
the islands and regional waters. A mid to upper level high
pressure ridge will continue to build across the region and thus
maintain stable conditions aloft. This in turn will favor an
increase in the trade wind cap inversion and therefore limit
convection and vertical development especially by late Friday and
Saturday. Recent model guidance and the present weather pattern
both suggest Saturday as being the driest day for the period.
However, eastern Puerto Rico and the USVI may experience passing
late evening and early morning showers of short duration, followed
by locally and diurnally induced isolated to scattered afternoon
showers. This activity should be focused mainly across the
interior and west Puerto Rico and mainly downwind and on the west
end of the USVI. Later today into early Friday still a appears to
be the best chance for periods of mostly light to moderate rains
with brief winds gusts. This should mainly affect parts of eastern
Puerto Rico the U.S. Virgin Islands under the present and
expected advective pattern of the trade wind showers.

The forecast still calls for a gradual drying trend by late Friday
and into Saturday, with a slightly cooler and drier air, as winds
become northeasterly. By then precipitable water values which now
range between 1.30 and 1.75 inches are forecast to drop below 1.20
inches as the frontal boundary sinks farther southwards over the
Caribbean waters while eroding.

Overall, the period calls for no significant risk of heavy or
widespread rainfall with the expected shower activity. However
isolated areas of light ponding of water on roads and in poor
drainage areas will remain possible over portions of the interior
and urban areas with the heavier shower activity. Pleasant seasonal
temperatures can be expected along with occasionally breezy
conditions, especially along the coastal areas during the afternoon
and early evening hours.

&&

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

The heavy hand of the upper level high over the northern portion
of South America will be felt over the forecast area even beyond
the long term period. High pressure at mid levels will remain
closer to the local area keeping mid levels very dry.

High pressure at the surface north northeast of the area will be
crowded by a front over the western Atlantic from a low over
eastern Canada and another low pressure system 2100 miles
northeast of San Juan, Puerto Rico. High pressure will eventually
break out over the western Atlantic and reinforce the high already
there on Sunday. This will bring moist and cooler air at low
levels across the area on Monday. It will also cause a front from
the low northeast of the area to move through Puerto Rico and the
U.S. Virgin Islands on Wednesday. Between each of these features
drier air is seen. Hence the long term period will be punctuated
by persistent but shallow showers that will mostly effect eastern
Puerto Rico, and western Puerto Rico and the U.S. Virgin Islands
to a lesser degree followed by mostly sunny periods. Condtions
will be fairly breezy Sunday through Thursday, with winds around
15 to 25 mph in exposed areas and over the local waters.

&&

.AVIATION...
(06Z TAFS)
Issued at 444 AM AST Thu Jan 11 2024

VFR conds at all terminals durg fcst pd. SCT ocnl BKN lyrs nr
FL025...FL050 ovr regional waters and en route btw PR and the USVI
terminals with wdly SCT SHRA. Brief MVFR with and MTN Top Obscr ovr
E interior of PR due to low clds/-SHRA til 11/13Z. Low-level wnds
fm ESE winds 15-20 kts BLO FL180. SFC wnds calm to light and
variable, becoming mainly fm E 10-15 kts with hir gusts and sea
breeze variations aft 11/14Z.

&&

.MARINE...
Issued at 444 AM AST Thu Jan 11 2024

Another set of swell will enter the forecast area from the north
northeast and cause conditions to become more hazardous in the
Atlantic waters and the Anegada passage. These swell will begin
subsiding Thursday night and Friday, but still be working through
the Anegada passage Friday night. Although perhaps conditions in
the Anegada passage would not have been rough enough to need small
craft advisories, wind there will also be 15 to 20 knots so seas
are expected to reach 7 feet east of Saint Croix Friday night.
Seas should all be below 7 feet by Saturday mid morning.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Fri Jan 12 2024

.SYNOPSIS...
Issued at 428 AM AST Fri Jan 12 2024

Bands of moisture will bring shallow showers with limited
accumulations to eastern Puerto Rico and to a lesser extent, the
U.S. Virgin Islands and western and interior Puerto Rico. The
southwest and south portions of Puerto Rico will continue mostly
dry. Winds will relax only somewhat through the weekend, and then
increase again Monday and Tuesday. A high risk of rip currents
continue.

&&

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

Skies were partly cloudy to variably cloudy overnight as a band of
trade wind moisture from a frontal boundary continued to cross the
region bringing periods of passing showers. Some showers reached the
north and east sections of Puerto Rico as well as the adjacent
islands and the U.S. Virgin islands. Rainfall accumulations were
less than a tenth of an inch in most areas. This pattern is expected
to continue during the rest of the morning hours followed by a
gradual drier trend later in the afternoon and into the upcoming
weekend. No significant or widespread rains are forecast for the
period. There may be brief periods of moderate to locally heavy
rains at times but the activity will be of short duration. Early
morning temperatures were in the low to mid 70s along the coastal
areas and low 60s in higher elevations and valleys.

A surface high pressure ridge spread across the central and west
Atlantic will will maintain moderate east to northeast winds today
and through the weekend. This will aid in transporting occasional
fragments of shallow frontal boundary moisture across the region
from time to time. The mid to upper level high pressure ridge will
hold across the region to maintain stable conditions aloft. This
will favor an increase in the trade wind cap inversion and thus
limit/suppress convective development through the short term
period. Recent model guidance continued to suggest drier
conditions for both Saturday and Sunday, however portions of
eastern Puerto Rico and the USVI may experience periods of passing
late evening and early morning showers each day. Limited
afternoon shower activity is expected. This should be focused
across the east interior and west to southwest sections Puerto
Rico, and mainly downwind of the USVI.

The rest of the morning hours and early afternoon still appears to
be the best chance for periods of light to moderate rains today.
Thereafter a gradual diminishing of cloud cover and shower activity
is expected as a drier airmass is forecast to start filtering in.
This will result in a slightly cooler and drier air, as winds become
northeasterly and the layered precipitable water values drop to
below 1.20 inches as the frontal boundary sinks farther southwards
over the Caribbean waters while eroding. Consequently, pleasant
seasonal temperatures can be expected along with occasionally breezy
conditions, especially along the coastal areas during the afternoon
and early evening hours.

&&

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

The upper level high over the northern portion of South America
will continue with ridging over the local area. A TUTT will
develop in the tropical Atlantic and dig westward into the
Caribbean Wednesday through Friday. Mid and upper levels will
remain dry through beyond the long term period.

A patch of moisture associated with the flow out of the central
Atlantic high pressure at the surface will move through the local
area on Monday. A distant low pressure over the northeast
Atlantic near 31 N and 31 W will also carry a front that is
expected to pass through with good, but shallow, moisture on
Tuesday and Wednesday. Somewhat drier air then passes through
Thursday and Friday.

The result is that the moist bands and patches will all be shallow
and produce limited but persistent showers--most active over
eastern Puerto Rico but also affecting western Puerto Rico and the
U.S. Virgin Islands in the usual diurnal pattern of night and
early morning showers in the east and over the adjacent waters,
and some weak convection during the afternoon hours over western
and interior Puerto Rico and limited shower activity around the
U.S. Virgin Islands. The periods in between the aforementioned
features will feature a continuation of this pattern but with more
sun. Temperatures both minimum and maximum, will vary only a few
degrees from day to day depending on the wind direction with
temperature ranges of 8 to 12 degrees.

&&

.AVIATION...
(06Z TAFS)
Issued at 428 AM AST Fri Jan 12 2024

VFR conds for all the TAF sites durg prd. SFC wnd calm to lgt/vrb
but mainly fm E-SE 5 knots or less, then incrg and bcmg fm E-NE
12-15 kts aft 12/14Z. Hir wnd gust with passing SHRA. VCSH psbl at
TIST/TISX/TJSJ til 12/15Z and spreading to TJPS/TJBQ btw 12/17Z-
12/22Z. SCT ocnl BKN lyrs nr FL025...FL040...FL100 ovr regional
waters and en route btw PR with wdly SCT SHRA. Brief MVFR with MTN
Top Obscr ovr E interior of PR due to low clds/-SHRA til 12/14Z.
L/lvl wnds fm ESE 15-20 kts BLO FL120 then backing an incr w/ht
ABV.

&&

.MARINE...
Issued at 428 AM AST Fri Jan 12 2024

Seas are coming down very slowly, but the outer bouy, 41043, is
already reporting slightly less than 7 foot seas. Seas may
fluctuate a little with diurnal variations in the winds but will
generally relax somewhat through Sunday. Small craft advisories
are expected to come down this evening and are not expected to
return before Monday night.

&&

.BEACH FORECAST...

Seas have come down and wave periods have shortened sufficiently
that breaking waves will no longer reach 10 feet so the high surf
advisory was canceled. The high risk of rip currents, however,
will remain for exposed northern beaches until Saturday morning.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
406 AM AST Sat Jan 13 2024


.SYNOPSIS...
Issued at 401 AM AST Sat Jan 13 2024

With evening-early morning trade wind showers and limited afternoon
convective development, a seasonal weather pattern will prevail
through most of the forecast period. The driest period will be
expected by mid-week. High rip current risk and hazardous wind-
driven seas are anticipated by early next week.

&&

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

Variably cloudy skies were observed across the islands during the
overnight hours. Light rain showers were observed across portions of
the USVI and the north-central coast and eastern half of PR. The
doppler radar estimated near a quarter of an inch of rain over
coastal areas of Dorado and Toa Baja. Minimum temperatures were from
the low to mid 60s across the interior to the mid 70s across coastal
areas in general. Winds were from the east to northeast at 10 mph or
less.

A mid-to upper-level ridge will promote stable conditions and drier
air intrusion through the short-term period. However, shallow layer
moisture from an old frontal boundary will continue to move across
the northeastern Caribbean today. This will promote some cloudiness
with mostly light rainfall accumulations across the islands. Latest
guidance suggest less than a quarter of an inch of rain across the
USVI and eastern PR, and just over half an inch over western PR. A
drying trend is expected from this evening through Sunday as the
precipitable water content drops from near 1.50 inches today to near
1.00 inch by Sunday morning. A building surface high pressure over
the western and central Atlantic will promote moderate to locally
fresh east to northeast winds through the period, with breezy
conditions expected on Monday as the high pressure sinks further
southward near 25N. This wind surge should bring scattered showers
across the region, and mainly through the night/morning hours of
Monday.


&&

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

The most recent model guidance suggests a generally east-to-east-
southeast wind flow dominating the long-term forecast period,
supported by surface high pressure extending into the northeastern
Caribbean. Breezy conditions can be expected between Tuesday and
Wednesday as the pressure gradient tightens over the area due to the
surface high pressure in the Atlantic strengthening. As expected,
mid-level ridging will persist throughout the period. A slightly
drier pattern is also suggested, with low-level moisture convergence
driving patches of moisture across the area. Model-estimated precipitable
water vapor will range between 1.1 and 1.4 inches through early
Friday, with Wednesday and Thursday being the driest days of the
long-term period. Therefore, mostly fair weather conditions can be
expected with a few passing showers over windward coastal areas,
resulting in minimal rainfall accumulations.

Late into the week, a set of easterly disturbances will increase
available moisture, with precipitable water values peaking around
1.7 inches by Saturday. This should support isolated to scattered
showers over eastern portions of the islands during the morning
hours, followed by afternoon activity over western portions of
Puerto Rico. Despite this increase in moisture, rainfall accumulations
are not expected to be substantial, as most of this activity will
be shallow in nature.



&&

.AVIATION...
(06Z TAFS)
Issued at 401 AM AST Sat Jan 13 2024

Mainly VFR conditions are expected to prevail across all
terminals through the forecast period. BKN/OVC cigs btw FL040-FL060
and mtn tops obscd over eastern PR thru early Sat morning. Mostly
VCSH/-SHRA expected across the area terminals today as the remnants
of an old front moves across the CWA. East winds at 12-16 kt with
higher gusts and sea breeze variations after 13/14z.

&&

.MARINE...
Issued at 401 AM AST Sat Jan 13 2024

Gentle to moderate easterly winds will prevail. Seas of 4 to 6 feet
will persist over the Caribbean waters and local Passages.
Therefore, small craft operators should exercise caution over
these waters. Moderate to fresh easterly winds and hazardous wind-
driven seas will resume across the regional waters by early next
week into mid-week as a surface high pressure develops north of
the region.

&&

.BEACH FORECAST...
Issued at 401 AM AST Sat Jan 13 2024

Nearshore buoys indicate that the northerly swell affecting the
Atlantic waters has subsided, with estimated breaking waves mostly
below 6 feet. Consequently, the Rip Current Risk Statement has been
canceled. However, a moderate rip current risk will persist over
north- and east-facing beaches of the local islands this weekend. It
is important to note that life-threatening rip currents are still
possible in the surf zone of these beaches. The rip current risk is
expected to turn high once again by Monday. For more information and
details, please refer to the latest Surf Zone Forecast (SRFSJU).

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
354 AM AST Sun Jan 14 2024


.SYNOPSIS...
Issued at 348 AM AST Sun Jan 14 2024

Mostly fair weather conditions will prevail for the next few days,
with passing showers expected in windward coastal areas during the
morning hours and showers developing over western Puerto Rico each
afternoon. Breezy wind conditions are anticipated on Monday and
Tuesday. Wind-driven seas will promote hazardous marine and beach
conditions early this week.

&&

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

Variably cloudy skies were observed once again across portions of
the islands during the overnight hours. Light rain showers were
observed across portions of the northeastern to southeastern coast
of Puerto Rico. No significant rainfall amounts were observed over
land areas. Minimum temperatures were from the low to mid 60s across
the higher elevations to the mid and upper 70s across the lower
elevations. Winds were from the east at 10 mph or less.

A broad surface high pressure over the central Atlantic will promote
moderate to locally fresh trades through the period, with breezy
conditions expected on Monday and Tuesday. This wind surge will
bring shallow moisture in form of low-level clouds and scattered
showers from the Atlantic and eastern waters of the islands.
Meanwhile, a mid-to upper-level ridge over the northeastern
Caribbean will continue to hold through the short-term period,
promoting drier air and stable conditions aloft. Therefore, limiting
the vertical development of showers and rainfall accumulations in
general. Winds are expected to have an east to southeasterly
component during the workweek as the low-level high pressure
northeast of the region moves further into the central Atlantic by
Tuesday. Normal to above normal temperatures are expected to
continue across the islands.


&&

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

No major changes were observed in the latest model guidance. The
long-term forecast begins with dry conditions, as precipitable water
values are anticipated to fall within the 10th and 25th percentiles
of the climatological normal for the most part, which is below
normal for this time of year. This trend is expected to persist at
least through late in the week. Aloft, a mid-level ridge will
persist, promoting a weak inversion cap close to 850 mb, with the
bulk of low-level moisture trapped below it. Throughout this period,
anticipate mostly fair weather conditions with very few isolated
showers, if any. Breezy wind conditions will also be present as the
surface high pressure north of the region strengthens.

As the week progresses, a strong cold frontal system will exit the
Eastern Seaboard. As it approaches the area from the northwest,
winds will gradually shift from the east to more southeast with
decreasing wind speeds. This, in combination with mostly clear
skies, could lead to warmer-than-normal temperatures across the
islands during peak hours of the day. The 925 mb temperatures are
expected to rise above the 90th percentile of the climatological
normal, indicating temperatures well above normal. For the weekend,
ridging aloft will persist, inhibiting any deep convective activity.
However, as the frontal boundary approaches, moisture convergence
will increase. Precipitable water is expected to rise within the
range of 1.7 to 1.9 inches. Therefore, an increase in cloud cover
can be anticipated, along with isolated to scattered showers. At
times, these showers may become numerous, but they are expected to
be of short duration.


&&

.AVIATION...
(06Z TAFS)
Issued at 348 AM AST Sun Jan 14 2024

Mainly VFR conditions are expected to prevail across all terminals
through the forecast period. VCSH and brief -SHRA expected across
the area terminals. East winds at 12-16 kt with higher gusts and
sea breeze variations after 14/14z.

&&

.MARINE...
Issued at 348 AM AST Sun Jan 14 2024

A surface high pressure extending across the Atlantic Ocean north of
the region will promote moderate to fresh easterly winds through
midweek. A cold front will continue to move eastward across the
Western Atlantic over the next few days until it dissipates well
north of the region by Tuesday. By then increasing trade winds are
forecast to affect the regional waters.

&&

.BEACH FORECAST...
Issued at 348 AM AST Sun Jan 14 2024

A moderate risk of rip currents is expected across the coastal areas
of Puerto Rico from Aguadilla to Humacao, including Culebra and St.
Croix. The rip current risk will continue to improve through Monday.
However, by Tuesday, an increase in wind-driven seas is anticipated
to elevate breaking waves across the northern areas of Puerto Rico,
leading to hazardous beach conditions across the islands.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
508 AM AST Tue Jan 16 2024

.SYNOPSIS...
Breezy conditions are expected through at least Tuesday due to
tightening of the local pressure gradient. A drying trend is
expected for the rest of the workweek as a mid-to upper-level
ridge continues to dominate the local weather conditions.
Hazardous seas as well as life-threatening rip currents are
expected through at least Thursday.

&&

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

The mid-level ridge over the region will continue to hold, while the
strong surface high pressure across the western Atlantic will
persist during the next few days. This ongoing pattern will
reinforce a strong inversion cap near 850 mb, promoting subsidence
and stable conditions aloft. The forecasted total precipitable water
(TPW) content is anticipated to stay within the 10th to 25th
percentile, indicating values below the climatological normal for
the short-term forecast. Some TPW values may approach near-normal
levels, particularly over windward coastal sections.

Consequently, anticipate predominantly fair weather conditions, with
trade winds carrying occasional patches of moisture that could
result in light showers across the USVI and eastern sections of
Puerto Rico during the overnight/early morning hours. Subsequently,
limited shower development is anticipated over portions of western
Puerto Rico during the afternoon hours. Breezy east-to-east-
southeast trades are likely to contribute to slightly warmer-than-
normal temperatures throughout the week.

By late Thursday night, TPW is forecast to increase by around 1.50
inches. The mid-level ridge is expected to shift a little further
east, creating a weakness in the trade wind cap and enabling better
low-level moisture to temporarily increase from the east. Therefore,
anticipate an uptick in the frequency of showers by Thursday evening
and late-night hours, although no significant rainfall amounts are
anticipated at this moment.

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

The low to mid-level ridge is expected to move east-northeast of
the northern Leewards early in the cycle, allowing the trade wind
cap to relax during the weekend. At the same time, a frontal
system will move across the western Atlantic and press against the
ridge over the central Atlantic. In response, a pre-frontal trough
is expected to develop north of the region and winds will acquire
a southerly component. This will also allow for better pooling of
moisture content over the region, but precipitable water values
should increase to normal levels in general. Warmer than normal
temperatures are expected during this period. By early next week,
the 500 mb ridge is forecast to move over the islands and promote
drier air intrusion and stable conditions once again. At the
lower levels, a surface high extending from the southwestern
Atlantic and the overall ridge pattern will promote east to
northeasterly trades across the Atlantic waters, pushing the
frontal boundary closer to area between Tuesday and Wednesday.


&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. VCSH possible at times due to trade wind
showers across the USVI/eastern PR terminals, particularly around
16/10z. E/ESE winds will increase to 15-18 kt with higher gusts and
sea breeze variations after 16/14z.


&&

.MARINE...

Breezy conditions are expected to prevail across the regional
waters today due to winds peaking between 20-25 knots. A small
long period northeasterly swell is spreading across the Atlantic
waters and portions of the local passages. This will cause
hazardous seas up to 7 feet and choppy conditions due to the
strong wind-driven seas across portions of the offshore waters,
the eastern waters of PR and the USVI, and across both Anegada and
Mona Passage. Therefore, a Small Craft Advisory (MWWSJU) is in
effect through at least Wednesday afternoon.


&&

.BEACH FORECAST...

There is a high risk of rip currents across the north and east
facing beaches of Puerto Rico, Culebra and St. Croix. Therefore,
a Rip Current Statement (CFWSJU) is in effect. Life-threatening
rip currents should persist through at least Thursday due to the
combination of wind-driven seas and pulses of a small northeasterly
swell.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
437 AM AST Wed Jan 17 2024

.SYNOPSIS...

A drying trend is expected through much of the forecast period.
However, a trade wind perturbation should increase the frequency
of passing showers between Thursday night and Friday. Then, a
pre-frontal trough developing north of the region should increase
moisture content once again on Sunday. East to southeasterly winds
will prevail through the weekend, promoting above normal
temperatures across the islands. A cold front could reach the
local area by early next week. Hazardous seas as well as life-
threatening rip currents are expected through at least Thursday.


&&

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

Clear to partly cloudy skies prevailed across the local area. A few
isolated showers were noted across windward coastal sections, but
nothing significant. Overnight temperatures ranged from the middle
to upper 70s across lower elevations to the upper 60s to lower 70s
across higher elevations. Breezy wind conditions persisted
throughout the night, particularly across the eastern portions of
the islands.

Similar weather conditions will persist throughout the short-term
forecast, with a mid-level ridge pattern dominating the northeastern
Caribbean. This ridge will maintain an inversion cap in place.
According to the GFS Trade Wind Inversion (TWI) algorithm, this weak
trade wind inversion will be situated mostly between 850-800 mb
through Thursday, with below to near-normal moisture content
confined below this layer. This setup will promote predominantly
stable weather conditions across Puerto Rico and the U.S. Virgin
Islands. Therefore, mostly clear to partly cloudy skies and limited
rain activity will continue today and Thursday, with any showers
likely attributed to small pockets of moisture embedded in the
trades.

By late Thursday night and early Friday, a trade wind perturbation
will reach the local area, increasing moisture values close to the
75th percentile, which is above the climatological normal. The TWI
shows the mixing layer increasing to slightly above the 750 mb
layer. Therefore, expect shower activity to ramp up in some areas
with increased cloud coverage over eastern sections of Puerto Rico
and smaller islands by late Thursday night and early Friday morning.
Some shower development may occur during the afternoon hours over
western portions of Puerto Rico. However, significant rainfall is
unlikely due to stable weather conditions aloft and to the fast-
moving nature of these showers.

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

A ridge pattern across all levels will prevail through the long
term period. A broad surface high over the central Atlantic and a
700-500 mb ridge over the Tropical Atlantic extending into the
northeastern Caribbean will continue to promote drier air and
stable conditions in general. Winds are expected to shift from the
east to southeast during the weekend, and warmer than normal
temperatures are expected. At the same time, a frontal system
will move across the western Atlantic and press against the ridge
over the central Atlantic. In response, a pre-frontal trough is
expected to develop north of the region. This will allow for
better moisture content to pool over the region in general.

Later in the cycle, high pressure from the surface to 500 mb will
build from the southwestern Atlantic into the local area. This
will promote breezy northeasterly trades and bring closer or over
the islands the lingering frontal system between Tuesday and
Wednesday.


&&

.AVIATION...

(06Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. VCSH possible at times due to trade wind
showers across the USVI/eastern PR terminals. E/ESE winds increasing
to 15-20 kt with higher gusts and sea breeze variations after 17/14z.


&&

.MARINE...

A broad surface high pressure just north of the region will continue
to build over the central Atlantic and hold through Friday. Moderate
to fresh trades will prevail through at least Thursday. A long
period northeasterly swell has spread into the local waters and will
last for several days. Conditions will be hazardous to small craft
operators through at least Thursday across the offshore waters and
passages.


&&

.BEACH FORECAST...

The combination of a long period northeasterly swell and choppy
wind-driven seas will continue to cause rough surf conditions with
life-threatening rip currents along the north and east facing
beaches of Puerto Rico, Culebra and St. Croix. Therefore, a High
Rip Current Risk (CFWSJU) remains in effect through Thursday.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
509 AM AST Thu Jan 18 2024

.SYNOPSIS...

The brisk easterly winds will bring periods of passing clouds and
mostly light showers during the rest of the morning and later
tonight into early Friday, as patches of trade wind moisture will
cross the region. Winds are then forecast to become more southeasterly
and diminish by Friday afternoon and through the weekend bringing
warmer and unseasonal temperatures. Mostly dry conditions will however
persist dominated by fairly strong high pressure ridging for the
next few days. Marine conditions will remain hazardous to small
craft operators across exposed waters and passages at least until
early Friday. There is a high risk of rip currents for most northern
exposed beaches of Puerto Rico through Thursday and a moderate
risk elsewhere, except for a few protected beaches in the west and
south coast of Puerto Rico.

&&

.SHORT TERM...Today through Saturday

The short-term forecast will remain stable during this period.
Firstly, a mid to upper-level ridge will establish a stable
weather pattern across the region, resulting in drier conditions
aloft and a trade wind cap inversion, limiting vertical
development. Under this stable pattern, the weather will be
predominantly influenced by a broad surface high-pressure
extending across the Central and Eastern Atlantic. As the surface
high pressure interacts with a frontal boundary moving eastward
and builds even more over the central Atlantic, the islands can
expect veering winds. With this surface wind pattern, the islands
may experience slightly warmer temperatures, especially in sectors
of north-central Puerto Rico.

In terms of rainfall, for the rest of today, the islands will be
under a somewhat dry air mass, where satellite images show
precipitable water values of 1.0 to 1.3 inches. Due to the lack of
moisture, the islands may enjoy stable conditions in the early
morning hours, with sunny skies and some passing clouds through
the east of Puerto Rico. In the afternoon, as the day progresses,
a cloud cluster will move over the region, increasing the
potential for showers tonight into Friday morning, particularly in
sectors of northeast Puerto Rico. This patch of moisture is not
expected to persist for long, thanks to the moderate to strong
wind flow across the islands. For Saturday, the islands can expect
a stable day with slightly warmer temperatures due to the
southeasterly winds.

Forecast for Old San Juan: Today, visitors can expect mostly
stable conditions with windy conditions and temperatures around
the mid to upper 80s. An increase in moisture is forecasted for
tonight into early Friday, resulting in brief light to moderate
showers with no flooding threat. As far as today, the Saturday
forecast looks more stable, with sunny to partly cloudy skies and
minimal rainfall activity.

&&

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

Light southeasterly winds will persist through Sunday, becoming more
easterly and increasing by Monday through the rest of the period as
strong high pressure ridge will enter and spread across the west
Atlantic and a cold frontal boundary sinks southwards across the
region Wednesday through Thursday. This forecast pattern will then
favor a wetter weather pattern. Mid to upper level ridge is to
slightly erode late Sunday through Monday as a short wave trough
crosses north of the region, then build once again by Tuesday and
rest of the period. The chance of shower activity is therefore
limited Sunday at least through Tuesday with the driest period being
Monday through Tuesday, followed by a wetter and best chance for
increased cloudiness and showers and trade wind activity Wednesday
through Thursday associated with the aforementioned frontal boundary
and the increasing east to northeast trade wind. This will promote
breezy to windy conditions and cooler and more seasonal temperatures
once again by Monday and the rest of the period. Based on recent
model guidance, hazardous marine and dangerous coastal conditions
are so far expected from Monday onwards due to northerly swell
action and increasing trades. Stay tuned!!
&&

.AVIATION...
VFR conditions will prevail for most of the TA sites during the
period. Winds will continue from the E-SE, increasing up to 15
knots at 18/15Z, with gusty winds during the day and some
variation in the coastal areas. VCSH would increase for TIST and
TJSJ at 18/19 to 19/06Z.

&&

.MARINE...
A broad surface high pressure north of the region will continue
to build over the central Atlantic and hold through Friday. This
will promote moderate to fresh trade winds through at least later
tonight or early Friday morning. A weak long period northeasterly
swell will linger, but will weaken over the next few days. Conditions
will be hazardous to small craft operators through at least early
Friday morning across exposed waters and local passages.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
425 AM AST Fri Jan 19 2024

.SYNOPSIS...
Issued at 412 AM AST Fri Jan 19 2024

For today, variable weather conditions will persist with the
arrival of a patch of humidity across the region. This will result
in shower activity across the eastern sectors of the islands
during the morning and afternoon. Similar conditions are expected
for the rest of the weekend, with a southeast wind flow resulting
in slightly warmer temperatures than usual. For the next week, an
increase in humidity is expected from Wednesday to Thursday due to
the arrival of moisture associated with a frontal band. Maritime
conditions are expected to remain hazardous today across the
exposed waters of the Atlantic, where a small craft advisory
remains in effect until 6 PM AST this evening.

&&

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

Generally, fair and stable weather conditions will prevail as the
mid-to upper-level high pressure ridge will aid in suppressing and
limiting convective development. This will also support a moderate
to strong 2-3 degree cap inversion which will hold at least until
Saturday, when the upper ridge is forecast to slightly erode in
response to a short wave trough crossing the Atlantic just north of
the region. Local east southeast winds will become more
southeasterly today through the upcoming weekend while gradually
diminishing as the Atlantic surface ridge lifts farther northward
over the northeast Atlantic and the local pressure gradient relaxes
and in response to a low level prefrontal trough developing just
west and north of the region.

In the meantime for the rest of today and on Saturday, occasional
patches of shallow trade wind moisture will continue to cross the
region bringing periods of mostly light to moderate passing shower
across parts of the east and southeast sections of the islands
during the morning hours. This will be followed by limited afternoon
showers mainly over parts of the east and central interior with
lesser activity expected over western Puerto Rico and the USVI.
Recent model guidance continued to suggest layered precipitable
water values to remain between 1.00 and 1.50 inches typical for this
time of the year. Rainfall accumulations are therefore forecast to
be less than a quarter of an inch with the heaviest rains through
Saturday. By Sunday however a slight increase in showers is so far
forecast across the region, as a patch of low level moisture will
cross and converge across the region. This along with good daytime
heating and the prevailing southeasterly wind flow should aid in
afternoon shower development across part of the central and north to
northwest Puerto Rico and mainly downwind of the adjacent islands.
Lesser activity is forecast for the U.S. Virgin Islands at this time
although period of passing showers cannot be ruled out from time to
time. Daytime high temperature will be slightly higher than normal
due to the prevailing southeasterly wind flow and should range
between the mid to upper 80s especially along the north coastal
areas. Cool seasonal overnight temperatures can be expected under
mostly clear to partly cloudy skies. Other than brief periods of
passing morning showers and late afternoon and early evening
showers, overall fair and dominantly stable weather conditions are
forecast for the period with no significant impacts anticipated at
this time.

&&

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

Minor changes were introduced to the long-term forecast. Model
guidance continues to show a variable pattern during the upcoming
workweek. A mid to upper level will remain in place for the whole
period, resulting in drier conditions aloft and a lack of vertical
support. In the lower level, at the beginning of the week, the
islands will be dominated by an eastward flow of winds resulting
from the interaction of surface high pressure and a frontal band
moving towards the center of the Atlantic. By Tuesday, as the high
pressure continues to develop over the western Atlantic,
extending to the central Atlantic, it will move moisture from a
frontal band north of the region under a prevailing east-northeast
wind flow, persisting for the rest of the period.

According to global guidance (ECMWF & GFS), fragments of moisture
from the frontal band with precipitable water between 1.4 to 1.6
inches will move into the region, increasing the potential for
showers. Due to the northeast wind flow, shower activity will
predominate through the northeastern and northern sectors of the
island and through the mountainous interior and southwestern
sectors of the island in the afternoon. Despite an expected
increase in rainfall, since an increase in wind speed is
forecasted due to a pressure gradient generated by the high
surface pressure, significant rainfall accumulations are not
expected on Wednesday and Thursday.

By Friday, surface conditions will change as surface high
pressure builds and expands over the Atlantic, resulting in more
easterly winds across the region. Under this pattern, the islands
can expect the frequent entry of shallow patches of fragmented
moisture, inducing a showery pattern for the windward sections of
the islands.

&&

.AVIATION...
(06Z TAFS)
VFR conds at all terminals durg prd. SCT-BKN lyrs near
FL025...FL040...FL080 with Isold-Wdly SCT SHRA ovr regional waters
and en route btw PR and the USVI.Brief Mtn Top psbl ovr E PR due to
passing SHRA low cld lyrs til 19/13Z. SFC wnd calm to lgt but hir w
passing trade winds SHRA. WND bcmg fm E to ESE 12-15 kts, with
higher gusts and sea breeze variations aft 19/14Z. VCSH at mainly
TJSJ/TISX/TIST durg prd.
&&

.MARINE...

For today, hazardous marine conditions will prevail across the
offshore Atlantic waters, as moderate to locally fresh winds
remain during the first part of the day. Therefore, the small
craft advisory remains in place for the offshore Atlantic waters
until 6 PM AST this evening. For the rest of the local waters,
seas will remain up to 6 feet, and windy conditions might result
in choppiness, especially in the exposed waters. Winds are
forecast to diminish later today; however, a surface high pressure
will enhance moderate to locally fresh northeasterly winds by the
upcoming week. The wind-driven seas will combine with the arrival
of a northeasterly swell on the island by midweek. This
combination will enhance building seas for most of the coal
waters.

.BEACH FORECAST...

There is a moderate risk of rip currents across most of the
locally exposed coastal areas in the islands. The risk will remain
moderate for the rest of the upcoming weekend. For the upcoming
workweek, the arrival of pulses of a long period northeasterly
swell will result in large breaking waves across the northern
coastal areas of Puerto Rico and the U.S Virgin Islands,
increasing the risk to high.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
425 AM AST Sat Jan 20 2024


.SYNOPSIS...

Expect, variable weather conditions across Puerto Rico and the
U.S. Virgin Islands as shallow patches of moisture and dry air
will filter across the islands at times. During the weekend,
southeasterly winds will result in slightly warmer than usual
temperatures. Next week, an increase in rainfall is foreseen from
Wednesday to Thursday due to the arrival of moisture associated
with a frontal band. Improving maritime conditions will lasting
through the weekend. By early next week, expect a northeasterly
swell to arrive and deteriorate the marine and coastal conditions.

&&

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

Fair weather and mostly clear skies prevailed across Puerto Rico and
smaller islands during the overnight hours as drier air moved in.
The overnight low temperatures were in the mid to upper 70s across
the lower elevations, while the higher elevations observed
temperatures from around 60 degrees to the mid-60s.

The mid-level ridge, consistently responsible for stable weather
conditions in the northeastern Caribbean throughout this month, is
expected to persist during the short-term forecast. This persistence
will lead to subsidence aloft, maintaining 500 mb temperatures at or
below -4.5 degrees Celsius overall and hindering any deep convective
activity across the area. Despite these weather conditions, some
unusual deviations are anticipated in the next few days, influenced
by the surface high pressure over the central Atlantic and the
frontal boundary currently over Florida.

This setup will maintain a southeasterly flow today, turning mostly
south-southeast by 18Z, promoting higher temperatures across the
islands. The 925 mb temperatures could reach 22 degrees Celsius,
exceeding the 90th percentile which is well above the climatological
normal for this time of year. Consequently, some urban and coastal
areas may still experience a limited excessive heat threat, with
heat index values reaching 102-107 degrees Fahrenheit. Therefore,
there is the possibility of heat exhaustion occurring with prolonged
exposure in urban and coastal regions of the local islands. Below-
normal to near-normal moisture content will prevail, with the
majority of it trapped below the 850 mb layer. As a result, limited
shower activity is expected throughout the day.

As the frontal boundary moves southeasterly and approaches from the
northwest, moisture convergence over the local islands is likely.
Sunday appears to be the wettest day in the short-term forecast,
with precipitable water content exceeding the 90th percentile of the
climatological normal. As a result, scattered to numerous showers
can be anticipated over the southeastern and eastern portions of
Puerto Rico during the morning hours, with similar activity possibly
developing across the northwestern quadrant. This could lead to
ponding of water in roads and poorly drained areas across these
sections. The smaller islands may experience mainly isolated to
scattered showers late tonight and early tomorrow morning. Model
guidance suggests moisture content plummeting to below 1.0 inches by
Monday with the frontal boundary remaining northwest of the area.
Therefore, mostly clear skies with limited shower activity will
dominate the forecast area.

&&

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

The inherited forecast remains unchanged. Model guidance continues
to show a mid to upper-level ridge through the long-term period,
meaning that mostly dry conditions aloft and a lack of vertical
support will prevail across Puerto Rico and the U.S. Virgin
Islands. On Tuesday, a surface high-pressure system over the
western Atlantic will develop and extend over the central
Atlantic, pushing away the surface low pressure attached to a
frontal boundary to the north of the region. The interaction
between these weather features will promote east-northeasterly
wind flow for the rest of the period. With this northeasterly wind
flow, expect an increase in shower activity as frequent patches
of moisture begin to filter over the area, particularly over the
northern, northeastern, and interior sections of Puerto Rico.
Despite the anticipated increase in rainfall, we are not
forecasting significant rainfall accumulations across the islands,
as winds will also increase by midweek due to the tightening of
the pressure gradient generated by the surface high.

As the surface-high pressure continues to build and expand over
the Atlantic and the mid-upper level ridge holds, expect mostly
seasonal stable and calm weather conditions to prevail across the
islands from Friday into the weekend. Nonetheless, trade wind
passing showers cannot be ruled out.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions expected across the local terminals. Winds
will continue from the ESE below 10 kts through 20/13z, increasing
to up to 15 kts and turning more SE after 20/14z, with sea breeze
variations. Passing SHRA could affect TJPS/TISX/TIST after 21/00z,
resulting in VCSH. Brief MVFR conditions cannot be ruled with these
passing SHRA.

&&

.MARINE...

A broad surface high pressure across the central Atlantic will
continue to allow moderate to locally fresh trades to prevail through
tonight. Conditions will improve over the weekend as an area of low
pressure in the western Atlantic weakens the local wind gradient.
Conditions will then deteriorate once again next week due to
increasing winds and a northerly swell. A weak cold front passage is
expected on Wednesday when the winds are strongest.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
503 AM AST Sun Jan 21 2024

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

.SYNOPSIS...
Issued at 437 AM AST Sun Jan 21 2024

A patch of moisture will bring showery weather today, but its
passage will bring drier conditions on Monday. Winds will increase
on Tuesday and Wednesday as a cold front approaches and then
passes the area with numerous showers. Showery weather will
continue in a shallow layer, gradually abating through the next
weekend.

&&

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

Overnight, mostly calm weather conditions prevailed across Puerto
Rico and the U.S. Virgin Islands. Nonetheless, some showers filtered
over the eastern and southeastern municipalities of Puerto Rico, as
well as the island of Saint Croix. Like previous nights, the
southeasterly wind flow prevailed over the region. Tonight, the
temperatures ranged in the low to upper 70s along the coastal areas,
while across the mountains, they remained in the 60s.

The latest model guidance continues to suggest an area of enhanced
moisture, with values ranging from the 50th to 75th percentile
reaching the forecast area today. First, the frequency of shower
activity will increase across eastern Puerto Rico and the U.S.
Virgin Islands. Then, in the afternoon, showers will develop along
the western sections of Puerto Rico. The trade winds will recover
as winds shift from the southeast to the east during the evening
hours. Overall, today, expect a combination of sunny and cloudy
skies at times, accompanied by periods of frequent passing
showers, as well as periods with no rain. Despite the moisture
many temperatures today will be above normal for the month.

On Monday, a patch of dry air will move over the islands, with
precipitable water values dropping below the 25th percentile or
below normal climatological levels. Therefore, we anticipate
minimal/no significant rain by the beginning of the workweek.

On Tuesday, a surface high-pressure system over the western Atlantic
will develop and extend over the central Atlantic, pushing away the
surface low pressure and place the moisture behind the frontal band
to the north of the region. The interaction between these weather
features will promote breezy east-northeasterly wind flow for the
rest of the period, and expect the return of frequent passing
showers.

&&

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

At lower levels high pressure over the western Atlantic will
maintain a good north-south pressure gradient. A cold front will
push into the area from the north northeast on Wednesday
accompanied by strong breezes and fast moving showers. The front
will move south of the area on Wednesday night with showers
continuing in the cooler air behind. On Friday another, weaker,
band of moisture will move into the area with continued showery
weather, but amounts will be less. Showers will begin to taper off
as the high pressure in the mid latitudes moves east of the area,
but bands of showers will continue to move through--only more and
more infrequently. Showers will favor the north and east side of
the islands and some showers will also be seen in the U.S. Virgin
Islands. Cooler temperatures from the air behind the front and
breezy conditions will be quite noticeable by Thursday.

Mid and upper levels will still remain dry however, and upper
levels will be dominated by high pressure. It will recede south by
the weekend but still remain the dominant influence.

&&

.AVIATION...
(06Z TAFS)
Issued at 437 AM AST Sun Jan 21 2024

Mainly VFR conditions will prevail across the local terminals.
Winds will continue from the SE below 10 kts through 21/13z,
increasing to up to 15 kts after 21/14z, with sea breeze
variations. Passing SHRA could affect TJSJ/TJBQ after 21/17z.
Brief MVFR conditions cannot be ruled with these passing SHRA. The
mstr producing lwr CIGs and VSBYS should have cleared the area by
21/14Z. Maximum winds WNW 35-40 kts btwn FL455-485.

&&

.MARINE...
Issued at 437 AM AST Sun Jan 21 2024

Seas will subside a little today but there will be a general
increase in seas as winds increase through Wednesday. A swell from
a vigorous storm in the northern Atlantic will add to the
expectation of hazardous seas by Monday night and continuing into
the following weekend.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
329 AM AST Mon Jan 22 2024


.SYNOPSIS...

Expect the weather conditions across the islands to remain stable
through Tuesday. Winds will increase by Tuesday, and they will
remain fairly enhanced through at least the upcoming weekend. A
cold front will approach the islands by midweek, increasing the
frequency of showers. Marine conditions will be deteriorated all
week.

&&

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

An analysis of overnight radar and satellite imagery indicated that
most of the region mainly remained rain- and cloud-free, except for
windward areas of eastern and northern Puerto Rico and the US Virgin
Islands, where pockets of low-level moisture generated partly to
variably cloudy skies and passing showers after midnight. Overnight
temperatures from official reporting sites ranged from around 60
degrees in higher elevations to about 75 degrees across eastern
Puerto Rico and the local islands. Winds were generally light from
the east to east-northeast across windward areas but calm and
variable elsewhere.

With an entrance of an airmass exhibiting lower-than-average
moisture levels as low as 0.8 inches, as indicated by satellite-
derived precipitable water, and a strong trade wind cap inversion
supported by a persistent mid-level ridge, the weather will likely
remain stable today and Tuesday. Despite hostile conditions for deep
convective development, there is a chance for increased cloud cover
and shower development on Wednesday due to increased moisture levels
associated with the remnants of an old frontal boundary reaching the
area. Although most of the activity should focus across the eastern
half of Puerto Rico and the local islands, other areas could
experience some shower activity. Nonetheless, this activity is
unlikely to result in significant rainfall, staying well below a
quarter of an inch with the most frequent activity.

The overall forecast features decreasing 925 mbar temperatures and
increasing wind speeds through the period. For today and Tuesday,
expect sunny to clear skies, daytime high temperatures in the mid
80s, and winds at 10-20 mph with higher gusts. Then, with increased
cloud cover and showery weather, expect more pleasant temperatures
and breezy conditions, with wind speeds at around 15-25 mph for
Wednesday.

&&

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

The inherited forecast remains unchanged. Models suggest residual
moisture associated with the past cold front across Puerto Rico
and the U.S. Virgin Islands by Thursday. The precipitable water
content is forecast to remain in the 50th percentile/around normal
climatological values. Another surface high pressure will build
over the western Atlantic on Thursday. This surface high pressure
will push additional patches of moisture from an old frontal band
across the region by the end of the workweek, allowing some
showery weather at times. Despite the anticipated entrance of
these patches, we forecast minimal rainfall activity over the
islands through Friday, as the mid to upper levels remain dry and
ridging dominates the area. However, on Saturday, model guidances
suggest a weakening on the mid to upper-level ridge. This
weakening is foreseen to allow surface moisture to reach the mid-
levels, enhancing the vertical development of rainfall activity
along with some unstable conditions across the islands.
Precipitable water models show PW values around 1.70 inches,
meaning that it will be above normal climatological values.
Overall, from Saturday into Sunday, expect an increase in rainfall
activity across Puerto Rico and the U.S. Virgin Islands. The
east-northeasterly wind flow will prevail through the weekend, and
we anticipate an improvement in weather conditions by the
beginning of the workweek when some dry air reaches the forecast
area.

&&

.AVIATION...

(06Z TAFS)
VFR conditions will prevail across all terminals. Light to calm
and variable winds, increasing to 14-18 knots with gusts up to
25-30 knots and sea-breeze variations between 22/14-23Z. Wind
speeds will fall back to 8-12 knots after 22/23Z.

&&

.MARINE...

A broad surface high pressure ridge across the central Atlantic will
continue to lift northeastward as a cold front moves across the
western Atlantic while weakening. This will promote light to moderate
east winds today. Seas are expected to gradually deteriorate from
late Monday onwards due to increasing winds and the arrival of a
northerly swell. The weak frontal boundary is forecast to sink
southwards across the regional waters by Wednesday as a surface high
pressure builds once again across the west Atlantic and the easterly
winds increase promoting hazardous marine conditions.