Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
507 AM AST Wed Dec 1 2021

.SYNOPSIS...An easterly wave will move over the area today,
increasing the moisture as well as shower activity. Then, through the
rest of the period, a seasonable weather pattern is expected to
prevail with overnight and early morning showers across the local
waters, with some of the activity affecting portions of eastern
Puerto Rico and the USVI followed by some afternoon convection
across western Puerto Rico. A mid and upper-level ridge is expected
to persist through the period, inhibiting the development of deep,
organized convective activity.

&&

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

The most prominent feature today has been the tropical wave moving
through the Caribbean. Although the strongest part of the wave went
through the Windward and ABC Islands overnight, some of the moisture
and showers have passed through the U.S. Virgin Islands since
01/04Z. Showers will increase during the day for Puerto Rico. The
axis of the trough has already entered Puerto Rico overnight and
will likely move into the Mona Channel later this morning, but the
best moisture is behind the axis. A lovely parabola of broken to
overcast low and mid level clouds is accompanying this wave, with a
few tops breaking out and streaking to the west in the upper level
winds. Overnight the GFS indicates that the moisture field at 850 mb
will become fragmented and shower activity will diminish, but still
expect scattered showers to continue moving into eastern Puerto Rico
while mostly side-stepping the U.S. Virgin Islands. On Thursday and
Friday winds will become a little more east northeasterly, but the
patchy moisture will continue to bring scattered showers to the
area. The GFS is forecasting 500 mb temperatures to drop from minus
5 to minus 6 during the period so have held a slight chance of
afternoon thunderstorm in the forecast for western Puerto Rico each
day.

As the upper level high over northern South America continues to
build, high pressure at upper levels will shift to the west of the
forecast area and cause winds aloft to become west northwest, but
this will not favor the convective activity expected. High pressure
at mid levels will continue over the forecast area through the
period and keep mid levels relatively dry.

.LONG TERM...Saturday through Thursday...

The mid and upper-level ridge will continue to persist into early
next week. This will inhibit the development of deep, organized
convective activity and thus the development of widespread,
significant rainfall activity. Meanwhile, at lower levels, a broad
surface high pressure is expected to build across the Atlantic
basin during the weekend and into next week. This will result an
east to east-northeast flow, resulting a cool advective pattern
with the low-level flow expected to increase between 15 and 20
knots. This overall pattern will feature overnight and early
morning passing showers across the local waters, with some of
this activity moving inland across northern and eastern portions
of Puerto Rico and the USVI, followed by locally induced afternoon
activity across western Puerto Rico.

By the middle of next week, there are indications that a mid and
upper-level trough will develop and amplify east of the area. If
model guidance is correct in this scenario, then the trough will
induce low-level perturbations, which will be driven westward by
the easterly wind flow and affect the local area with a more
showery weather pattern as we head towards the end of the period.

&&

.AVIATION...A trop wave movg thru PR from 01/04Z-01/14Z will usher in
addnl mstr today. Sct SHRA will cont over the USVI and spread
across PR fm 01/08Z with aftn SHRA and a slgt chc of TSRA over wrn
PR by 01/18Z. SHRA will bring lcl MVFR conds with mtn
obscurations. Winds will be east 10-15 kt with hir gusts nr +SHRA.
Conds imprvg slowly aft 01/22Z. Max winds W 35-47 kt btwn
FL400-500.

&&

.MARINE...A northeasterly swell will continue to persist today.
This will cause some choppy seas, mainly across the offshore
waters. A high risk of rip currents continues in effect for the
beaches from Aguada to Fajardo in mainland Puerto Rico as well as
for the beaches in Culebra, northern Vieques and Saint Thomas,
and northern and eastern Saint Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 86 75 / 50 40 30 50
STT 87 77 86 76 / 40 30 20 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
439 AM AST Thu Dec 2 2021

.SYNOPSIS...Moisture will diminish today through Saturday with
moderate east winds and near seasonal temperatures. Moisture
increases on Sunday, but returns to just below normal levels
Monday through Thursday. Persistent moisture in the lower levels,
however, will keep scattered showers over the local area for the
entire period, but as winds increase beginning on Sunday, showers
will become more frequent over eastern Puerto Rico. December is
here.

&&

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

The tropical wave responsible for the active evening yesterday
across northern Puerto Rico is moving away from the area, with a
more tranquil and seasonable weather pattern expected for today.
Surface high pressure located north of the area will result in an
easterly wind flow that will drag fragmented low-level clouds into
the area this morning, resulting in some passing showers across
the local waters, with some of the activity moving into portions
of eastern Puerto Rico. Then, during the afternoon hours, the
available low- level moisture will combine with daytime heating
and local effects to result in showers and a few thunderstorms
across western Puerto Rico, around Mayaguez and Vicinity, with
ponding of water on roadways being the main hazard. The USVI is
expected to observe mainly fair weather conditions.

Low-level winds will briefly weaken on Friday as a frontal
boundary, expected to move eastward well north of the area,
weakens the local pressure gradient. Winds will also become more
east-northeast and thus the afternoon convection that develops
will be concentrated more across the southwestern quadrant of
Puerto Rico, with brief overnight and early morning showers
across northeastern Puerto Rico as well as portions of the USVI.

On Saturday, low-level winds will strengthen once again from the
east-northeast as another surface high pressure moves over the
southwestern Atlantic. This will result in a cool advective pattern
with passing shower activity expected across the local waters, with
some of the activity moving into northern and eastern portions of
Puerto Rico as well as portions of the USVI. Afternoon showers due
to local and diurnal effects are also possible across the
southwestern quadrant of Puerto Rico.

A mid and upper-level ridge pattern is expected to prevail through
the period, resulting in dry and stable conditions aloft. This will
hinder the development of deep, organized convective activity so
that significant rainfall activity is not expected across the
area throughout the period.

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

High pressure will slide out of eastern Canada and
into the northern Atlantic Sunday through Tuesday, then this high
will elongate from east to west to both prolong and enhance the
easterly trade winds over the local area. Overall moisture will
be good on Sunday but will diminish early in the week and remain
at or below seasonal normals. Nevertheless lower levels will
remain moist and spawn scattered showers throughout the period
with the most persistent showers occurring along the eastern
coast of Puerto Rico. Mid levels will be particularly dry Monday
through Thursday even though some weakness in the ridge over the
local area is noted.

Winds at upper levels are mostly zonal Sunday and Monday, however
several shortwave troughs will pass through the area north of us
Tuesday and Wednesday and the sub-equatorial jet will approach
the area Tuesday night and Wednesday. The previous run of the GFS
brought a strong TUTT low over the local northern waters Thursday
through Saturday of next week as a more vigorous short-wave trough
moves southeast toward the area and cuts off, however confidence
in the strength of this feature is low at this time.

Moisture will diminish this coming Monday to between 1.2 to 1.5
inches which is normal to below normal for the date, but the
persistent wetness of the lowest 6000 feet will keep a chance of
showers in the forecast with brief passing showers over eastern
Puerto Rico likely for the most part.

&&

.AVIATION...Mainly VFR conditions expected to prevail through the
period across all area terminals. Winds will remain at less than 10
knots from E through 02/12z, increasing to up to 15 knots with sea
breeze variations after 02/14z. Sct SHRA and an isolated TS expected
across western PR between 02/18z and 02/22z. Maximum winds W 45-55
knots btwn FL390-470.

&&

.MARINE...Seas of 3 to 5 feet will continue in the local waters
until the winds begin to reassert themselves on Saturday. Then
seas will begin to rise over the weekend and into next week
spreading small craft advisory conditions over the local waters
from the northeast and a high risk of rip currents over the
exposed coasts. At this time we see only Friday night and
Saturday having any relief from a high risk of rip currents for
the area beaches with northern exposure.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 86 75 / 30 40 40 40
STT 86 76 86 76 / 20 30 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
451 AM AST Fri Dec 3 2021

.SYNOPSIS...Scattered showers will continue over the area today
and Saturday and increase on Sunday. Shallow moisture and
quickening trade wind flow will prolong the passing showers during
the next work week despite decreasing moisture Monday through
Wednesday. Showers will increase again toward the end of the week.
Strong convection does not appear to be indicated for the next 7
to 10 days.

&&

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

A mid and upper-level ridge will continue to remain well established
across the area, hindering the development of organized rainfall
activity. At low-levels, patchy moisture will move over the area
throughout the day. This will result in a few passing showers across
portions of eastern Puerto Rico and the USVI through the mid-morning
hours, followed by the development of showers and possibly an
isolated thunderstorm during the afternoon hours across interior and
southwestern portions of Puerto Rico as the low-level flow becomes
more east-northeast.

On Saturday, the low-level winds are expected to strengthen to
around 15-17 knots as a surface high pressure moves across the
western Atlantic, tighten the local pressure gradient. This will
result in a more advective pattern with some passing showers at
times across the local waters, with some of the activity affecting
portions of eastern Puerto Rico and the USVI, and some afternoon
convection due to local and diurnal effects across western Puerto
Rico.

On Sunday, the low-level winds are expected to increase even further
in excess of 20 knots as the aformentioned surface high pressure
strengthens across the western and central Atlantic. In addition, a
surge in low-level moisture is expected as well with precipitable
water values to increase to between 1.7-1.8 inches, which is above
normal climatologically speaking for this time of the year. This
will result in scattered to numerous passing trade wind showers,
with the highest concentration expected between the waters of the
USVI and eastern Puerto Rico, moving inland at times across the
eastern half of Puerto Rico.

.LONG TERM...Monday through Friday

High pressure in the northern Atlantic east of New York will move
southeast and elongate until it covers most of the Atlantic
waters between 30 and 35 north latitude. This will drive east
northeast to east tradewind flow during the entire period. At mid
levels high pressure will dominate the Caribbean and tropical
Atlantic with north to northeast winds. Some weakness in the ridge
is indicated over the local area. This will cause mid levels to
be predominantly dry and will contribute to some capping below 700
mb. A short wave trough at upper levels over Florida on Monday
will deepen over the local area on Tuesday night. The trough will
slowly shift eastward Wednesday through Friday.

Precipitable water values will decline from 1.6 inches Monday
morning to 1.2 inches Wednesday evening and recover most of that
decline to 1.5 inches on Thursday and Friday. But most of the the
moisture will lie below 800 mb or about 7000 feet. This layer will
be quite moist and the GFS time height section shows almost
continuous upward vertical motion from 1-3 microbars per second in
the layer during the period. This will favor shallow passing
showers enhanced by local terrain over eastern Puerto Rico for
much of the time with some showers activity due to local
circulation and heating over western Puerto Rico during the
afternoons. 500 mb temperatures generally decline through Thursday
night, but thunderstorms at this time appear unlikely. The U.S.
Virgin Islands will see minor showers from time to time during the
period, but amounts will be slight.

&&

.AVIATION...VFR conditions will prevail through much of the forecast
period. Passing clouds moving across the area through 03/12z, may
bring a few -SHRA across TJSJ/TIST/TISX, with no impacts to
operations expected. SHRA and an isolated TS expected across
interior and SW PR between 03/18z and 03/23z, resulting in VCSH at
TJPS. Winds will continue light and variable through 03/12z,
increasing to between 10 and 15 kts from the E-ENE with sea breeze
variations after 03/14z. Maximum winds W 45-55 knots btwn
FL360-460 and 45-50 knots at FL520.

&&

.MARINE...Wave heights will begin to increase with the wind flow,
Saturday through Monday, with small craft advisories to be issued in
the local outer Atlantic waters and the Anegada passage possibly
as early as Saturday night. The increasing seas will raise the
risk of rip currents over the weekend across the area`s northern
beaches significantly and this threat will remain through at least
Friday of next week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 75 87 75 / 40 40 40 50
STT 88 76 88 76 / 30 30 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
532 AM AST Sat Dec 4 2021

.SYNOPSIS...Increasing trade winds are expected through the rest
of the weekend into early next week, in response to a building
surface high over the western and central Atlantic. At upper
levels, a ridge over Caribbean Basin is forecast to hold during
the next few days. Moisture content is expected to gradually erode
during the workweek. Choppy seas and hazardous marine conditions
will continue through next week.


&&

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

At upper levels, a strong zonal westerly flow should remain mainly
north of the region. Meanwhile, a mid-level ridge over the Caribbean
Basin is expected to hold through the short term period. This mid to
upper level pattern is expected to promote drier air intrusion in a
northwest flow and marginally stable conditions aloft. At the lower
levels, increasing northeast trades between 15-20 kt are expected
during the day as a surface high pressure moves over the
southwestern Atlantic. This ridge is expected to strengthen and
build north of the region by Monday, in response winds are forecast
further increase across the regional waters. This will promote a
cool advective pattern during the night and early morning hours, to
promote showers across the northern and eastern sections of PR, and
as well as across the USVI. During the afternoon hours, diurnally
induced convection is expected to develop over portions of west and
southwest PR each day. Ponding of water in low-lying and poor
drainage areas can be expected with these showers.

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

A variably weather pattern is expected for the first part of the long
term period (Tuesday into Wednesday). In the mid levels, model
guidance continues to suggest a ridge located just over the
forecast area, promoting stable conditions aloft. Meanwhile, a high
surface pressure will move into the central Atlantic resulting in
a more east northeasterly wind flow. This wind flow will drag
some patches of moisture over the local region. As a result, an
increase in the potential for shower development is expected,
mainly over the windward sections and the San Juan metro area each
day, and with the typical afternoon convection over the interior
and southwestern Puerto Rico.

By early Thursday into Friday, at the surface, model guidances
are suggesting an increase in the low level moisture embedded in
the trade winds. This increase in moisture, with PWat above
climatological normals, are forecast to result in the typical
showery pattern for the rest of the long term period. However, in
the mid levels a strong ridge will result in a trade wind cap and
will bring some stable conditions aloft over the forecast area.
As a result, the shower activity is expected to be less in the
morning and evening hours, and turn more intense but localized in
the afternoon hours due to the local effects. Minor flooding and
ponding of water in roadways and poor drainage areas is possibles
with the heaviest activity each day.



&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, trade wind showers
could move at times across the USVI and north/east terminals of PR
through late in the forecast period. Also, SHRA with possible iso
TSRA may develop in and around TJPS btw 18z-22z. ENE winds are
expected to increase btw 10-15 kt aft 14z.

&&

.MARINE...
For today, light to moderate winds will continue for the local
waters for early morning and afternoon hours. As a result, for
today, seas will continue between 3 to 6 feet across all the
local waters. Therefore, small craft operators should exercise
caution over the offshore Atlantic waters. Winds are forecast to
increase late tonight, as a building strong high pressure move
over the central Atlantic and increase the pressure tide over the
area. On Sunday, seas are forecast to increase up to 7 feet across
some of the local waters, as a result, small craft criteria will
be in effect and small craft operators are urged to exercise
caution.

There is a high risk of rip current for all north exposed beaches
of the Islands. Given the expected hazardous conditions the risk
will remain for the rest of the weekend.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 76 87 75 / 40 50 50 30
STT 88 76 88 75 / 30 40 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
508 AM AST Sun Dec 5 2021

.SYNOPSIS...

Passing showers with gusty winds are expected to continue for the
rest of the morning hours mainly over windward sections of Puerto
Rico and the U.S. Virgin Islands. Then, afternoon activity with
isolated thunderstorms are forecast for western sections of Puerto
Rico. For the rest of the short term period, a more seasonal
pattern is expected and a moderate to locally fresh wind flow due
to a building high pressure moving near the area. Choppy to
hazardous marine conditions are expected to continue for all the
local waters.

&&

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

A surface to 700 mb ridge north of the region will tighten the
pressure gradient over the northeastern Caribbean during the short
term period. Increasing trade winds moving over warm waters will
cause showers to develop across portions of the coastal waters of
the islands during the night time and early morning hours each
day. During the afternoon hours, the available low-level moisture
in combination with daytime heating and the sea breeze convergence
over western PR will lead to the development of showers.
Precipitable water content is expected to remain above normal
values for the season, around 1.60-1.70 inches through at least
tonight, and then gradually decrease between 1.20-1.40 inches
through Tuesday. This drop in moisture content is in response to
drier air intrusion in a northerly flow aloft, from a building
mid-level ridge over the west- central Caribbean. Steering winds
are forecast to turn more from the northeast on Monday and
Tuesday, this will favor trade wind showers along the northeastern
coast of PR, and across the USVI during the overnight hours, and
shallow convection over the southwestern quadrant of PR each
afternoon.

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

A stable weather pattern is forecast for most of the long term
period. On Wednesday into Friday, mid level ridge are expected
hold in place. This will promote stable conditions aloft and a
trade wind cap over the forecast area, limiting the long-live shower
activity. Additionally, in the low levels, less patches of
moisture with precipitable water below normal are forecast to
filter into the area. As a result, minimal shower activity is
forecast for this period, with the typical pattern of passing
showers in the morning and evening hours and the afternoon
convection over the interior and western sections of Puerto Rico.
This activity could result in ponding of water over roadways and
poor drainage areas each afternoon. On Friday, winds will shift a
little more from the northeast, due to a surface high pressure
located well at our west over Cuba. As this high pressure move
northeastward into the central Atlantic, the wind flow will push
patches of moisture over the area increasing the potential for
shower activity.

On Saturday, both model guidances suggest a sinking upper level
trough moving just at north of the forecast area. According to GFS
model, the unstable side of the TUTT are expected to remain out
of the forecast area, however, some unstable conditions aloft
still possible over the U.S. Virgin Islands. Meanwhile, at the
surface, a building high pressure over the Atlantic will result in
a more east northeast wind flow over the local area. This wind
flow will drag patches of moisture over the area. The combination
of the water content and the local effects would result in
localized activity.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, trade wind showers may
cause tempo MVFR cigs at times across the USVI/eastern PR terminals.
Also, SHRA expected to develop over western PR btw 16z-22z this may
cause tempo MVFR conds at TJBQ. Low level winds will continue from
the east at 10-15 kt with higher gusts and sea breeze variations
after 14z.

&&

.MARINE...

A building surface high pressure across the Atlantic will continue
to result in a moderate to locally fresh east northeast wind flow
over the forecast area. Winds are expecting to increase more
tonight over the Caribbean local waters and local passages. Given
the expected conditions, a small craft advisory is in effect
starting this afternoon for the Atlantic offshore waters. For the
rest of the local waters, mariners should exercise caution.
Hazardous marine conditions are expected to prevail for the the
rest of the weekend and prevail for the first part of the upcoming
week. Across the exposed beaches, there is a high risk of rip
current for all the north coast of Puerto Rico, Culebra, Vieques
and some of the eastern beaches of St. Croix. This risk is
forecast to continue at least for the upcoming week.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 76 87 76 / 50 50 40 40
STT 85 75 88 76 / 40 30 40 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Mon Dec 6 2021

.SYNOPSIS...Building surface high pressure over the central
Atlantic will promote moderate to fresh trade winds during the
next several days. Winds are forecast to turn more from the east
to northeast, and prevail through late in the week. This will
promote a similar weather pattern each day, with trade wind
showers moving at times over the USVI and the east/north sections
of PR during the night, followed by afternoon shower development
over the southwestern quadrant of PR. Choppy wind-driven seas and
hazardous rip currents are expected to continue through the week.

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

A seasonal pattern is forecast for most of the short term period
across the forecast area. A mid level ridge will hold in place
promoting stable conditions aloft and a trade wind cap, limiting
the long lived shower activity over the area. At the surface, a
high pressure will increase the trade winds, and breezy conditions
will prevail. Under this moderate to fresh easterly wind flow,
some patches of moisture will filter into the area today.
According to GOES-16 Satellite, the available moisture will remain
below the climatological normals with precipitable water values
between 1.00 to 1.40 inches. This will result in cloudiness and
some passing showers across the windward sections in the morning
hours. In the afternoon hours, typical conditions are expected,
as showers will develop over the interior and western sections of
PR. This activity could represent a slight threat for flooding
due to the fast moving showers.

On Tuesday, temperatures at the 500 mb slightly decrease to -6.5
to -7 Celsius, this might help the formation of some isolated
thunderstorms. However, less available moisture with PWAT values
below normal content will reach the area. That being said, for
Tuesday afternoon, there is a chance for isolated to scattered
activity with a few isolated thunderstorms. For Wednesday, both
models(GFS & ECMWF) agree somewhat with a more unstable solution,
as a jet moves near the forecast area. This feature would
increase the instability, but given the lack of moisture over the
forecasts area, the activity associated will be limited and
localized. Daytime temperatures are forecast to remain in the low
to the upper 80s across the forecast area due to the east-northeast
wind flow.

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

Moisture content will continue to remain below normal values
through at least Friday. However, an upper level trough is
forecast to move over the area, with it`s axis crossing the
islands by early Friday morning. Later in the weekend, a weak
TUTT-low is forecast to develop just north of the area, further
decreasing the 500 mb temperature and creating favorable upper
level conditions for showers to develop each day. This upper
level-low is then expected to merge with a deep polar trough
Monday. As this weather pattern unfolds, the low-level moisture
content is expected to increase across the northeastern Caribbean.
In addition, a pre-frontal trough on Monday should turn the winds
briefly from the east to southeast and promote moisture pooling
across the region. Having said that, expect a similar weather
pattern each day, with quick passing showers streaming across the
islands during the overnight/early morning hours, followed by
locally induced showers over the southwest quadrant of PR. Then on
Monday, the activity shifts across the east/southeast sections of
PR during the night, and across the northern slopes and western
sections of PR.


&&

.AVIATION...VRF conditions are forecast to prevail for ALL the
TAF sites during the period. Winds will remain from the E with
land breeze variation at 15 knots or less, increasing around
06/14Z from the E-NE between 10-15 kts, gusty 20-25 kts. In term
of showers, mainly VCSH for TKPK,TNCM, TISX at least until
06/18Z, then afternoon convection will result in VCSH at TJBQ
around 06/18Z. Around 06/22Z winds will diminish and VCSH is
expected to return at TISX, TIST, TNCM & TKPK.


&&

.MARINE...Moderate to fresh trades will continue to promote choppy
seas across portions of the regional waters, with seas up to 7
feet expected across the offshore Atlantic waters. A Small Craft
Advisory is in effect for these waters. For the beachgoers, a
High Rip Current Risk remains in effect for most of the north and
southeast facing beaches of all the islands through at least
Tuesday afternoon. The threat of life-threatening rip currents is
expected to continue through the rest of the workweek.


&&

.FIRE WEATHER...A drier air mass is expected to further decrease
the fuel moisture content today across the southern plains of PR,
and winds between 15 and 20 mph with higher gusts should prevail
once again along the south coast of PR. Therefore, a Fire Danger
Statement (RFDSJU) was issued for the southern coastal plains of
PR.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 75 86 74 / 50 50 30 40
STT 88 75 87 75 / 40 30 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
506 AM AST Tue Dec 7 2021

.SYNOPSIS...Moisture content is forecast to remain below normal
values through the end of the workweek, and gradually increase
later in the weekend into early next week. Ridge pattern will
promote moderate to locally fresh trades today, and again during
the weekend. Upper level trough pattern is forecast to evolve
later in the week into next week.


&&

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

A dry pattern is expected for all the forecast area today. A
surface to mid level ridge will hold in place and will prevail as
the dominant feature for the short term period. This ridging
pattern will result in drier air and a trade wind cap over the
area. As a result, this will promote stable conditions aloft.
Meanwhile, at the surface, expect less patches of moisture with
precipitable water vales at 1.10 inches. Although temperatures at
500 MB will drop between -6.5 to -7.0 Celsius, the lack of
moisture content suggest a seasonal/dry pattern for today, with
the typical afternoon convection over the interior and
southwestern sections of Puerto Rico. Additionally, this activity
is expected to be fast moving due to the breezy conditions. On
Wednesday, similar conditions are expected across all levels.
However, winds are forecast to become more moderate from the east-
northeast.

The history changes on Thursday, when a band of moisture filters
in the low levels. According to the GFS model guidance,
precipitable water associated with the band remains slightly
above of the climatological normals. Additionally, at 500 mb
temperatures will remain between -7 to -8 Celsius. That being
said, a more active weather pattern is expected with afternoon
convection and possible isolated thunderstorms. This activity
could represent a slight threat for flooding.

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

An upper level trough is forecast to move over the region by
early Friday morning and meander just east of the area through the
weekend, while a strong low to mid-level ridge builds over the
western Caribbean and southwestern Atlantic. Northeast trade
winds are forecast to increase during this period, and a cool
advective pattern is expected, with showers increasing across the
local waters and moving at times across portions of the USVI and
northeastern PR during the night/early morning hours, followed by
afternoon shower development over western PR. Precipitable water
content is forecast to gradually increase across the forecast
area, from around 1.25 inches on Friday to 1.80 inches by early
next week. This surge in moisture content is in response to a
strong polar trough pressing against the ridge on Monday and
Tuesday, and as an induced surface trough moves across the
northeastern Caribbean. Currently, the GFS/ECMWF model guidance is
in agreement with this wetter solution by the end of the long
term period.


&&

.AVIATION...VRF conditions are forecast to prevail for ALL the
TAF sites during the period. Winds will remain from the NE between
5-10 knots until 07/13Z, increasing around 07/14Z from the E-NE
between 10-15 kts, gusty 20-25 kts. Mainly VCSH for TJBQ ,TNCM,
TISX & TISX until 07/16Z. Around 07/23Z winds will diminish and
VCSH is expected to return at TJSJ, TISX, TIST, TNCM & TKPK.


&&

.MARINE...Moderate to locally fresh trades will prevail today.
This will maintain choppy seas mainly across the offshore Atlantic
and Caribbean waters, as well as the local passages. However,
seas are forecast to remain below small craft advisory (SCA) criteria,
and the SCA was cancelled.

For the beachgoers, a high risk of rip currents continues for
the beaches along northwestern to northeastern, and southeastern
Puerto Rico, as well as most north, south and east-facing beaches
of Culebra, eastern Vieques, and St. Croix.


&&

.FIRE WEATHER...A drier air mass is expected to continue over the
region today, and favorable fire weather conditions will continue
across the southern coastal plains once again. Therefore, a Fire
Danger Statement (RFDSJU) was issued for these areas.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 74 85 74 / 20 20 40 30
STT 87 75 87 75 / 30 40 40 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
517 AM AST Wed Dec 8 2021

.SYNOPSIS...Northeast trades will prevail through next week across
the region. Showers embedded in the trades will move at times
across the islands. Pooling of moisture is expected by Sunday into
next week, as a mid-level ridge west of the area weakens under
pressure from a polar trof. Hazardous seas and coastal conditions
are expected during the weekend due to wind-driven seas.


&&

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

A seasonal/dry pattern is expected to prevail for today. At the
surface, a drier airmass with a few pockets of moisture will filter
into the area, while a mid level ridge promote stable conditions
aloft. This pattern is expected to result in some passing showers
in the morning hours over the north sections and local waters, as
well as the typical afternoon convection over the interior of Puerto
Rico. However, this activity is expected to remain light and
short lived due to the lack of moisture as suggested by the
latest data from the GOES-16 Total Precipitable Water product.
The weather pattern will begin to deteriorate on Thursday, as a
band of moisture with precipitable water values above
climatological normals reach the forecast area. Additionally, the
GFS model guidance continues to suggest colder temperatures at
500 MB. Even though the conditions are favorable for organized
convection, the shower activity is forecast to remain moderate,
due to the presence of the mid level ridge.

On Friday, an upper level trough is forecast to move over the
region, increasing the unstable conditions aloft. As a result,
cold temperatures in the upper levels could enhanced the chances
for thunderstorms over the forecast area. This, in combination
with moisture in the low to mid levels will intensify the coverage
and the duration of the shower activity. Therefore, a cool
advective pattern is forecast with morning and evening activity
over the local waters and some windward sections and scattered
activity with isolated thunderstorms over the interior of Puerto
Rico in the afternoon hours. This activity could represent a
moderate threat for flooding with the heaviest showers.

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

The upper level trough is forecast to move northeast of the
Leeward Islands by Saturday and induce a surface trough that is
expected to move across the eastern Caribbean by early in the
week. Meanwhile, a building mid-level ridge over the western
Caribbean and southwestern Atlantic will increase the trade wind
cap and promote fresh northeast winds during the weekend. Then, a
strong surface high pressure is forecast to exit the US east
coast on Tuesday. Therefore, the wind flow will remain from the
northeast through the long term period, and with increasing
moisture content the frequency of trade wind showers should
increase across the local area. Although the 500 mb temp increases
by a degree or two later in the period, unstable condtions aloft
are expected due to the proximity of the upper level troughs.
Therefore, showers will increase in areal coverage over land areas
in diurnal convection.


&&

.AVIATION...VRF conditions are expected to prevail for all the
TAF sites during the period. Winds will continue from the E-NE at
10 mph or less until 08/14Z, but around 08/16Z will increase
between 10-15 knots, and gusty to 20 knots with sea breeze
variations. VCSH expected around 08/22Z across TJSJ, TISX, TIST,
TNCM & TKPK.


&&

.MARINE...Choppy seas up to 6 feet and easterly winds between 10
and 20 knots are expected to continue through the rest of the
workweek across the regional waters. Increasing winds are
expected during the weekend and hazardous seas will return once
again across the Atlantic waters. For the beachgoers, a High Rip
Current Risk continues in effect for the north and east facing
beaches of PR, Culebra and St. Croix through at least tonight.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 74 86 75 / 40 40 30 60
STT 87 76 86 76 / 40 30 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Thu Dec 9 2021

.SYNOPSIS...Increasing northeasterly trade winds, favorable
conditions aloft, and a surge in deep moisture will support an
increase in shower activity during the next few days. Expect a
higher frequency of evening-early morning showers moving inland
from the local waters, followed by afternoon convective
development across the interior and western sections of Puerto
Rico, as well as downwind from the local islands. Choppy to
hazardous marine and surf zone conditions will continue during the
next few days.


&&

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

Expect a showery weather pattern through the short-term period. A
short wave trough approaching from the west will break the trade
wind cap promoting a better chance for showers across the region and
maybe a few isolated thunderstorms. A surface high pressure across
the Atlantic will favor an advective pattern. Puerto Rico can expect
showers affecting the north, east and southeast coast, especially
during the evening and morning hours, followed by afternoon
convection across the interior and western sections. The U.S. Virgin
Islands can expect the arrival of quick passing showers from time to
time as the winds push them inland. This pattern will persist each
day.

The potential for thunderstorm formation will increase this
afternoon into Friday as a short wave trough swings across the
region. That upper-level trough will amplify near the Northeast
Caribbean (over the Atlantic), inducing a surface perturbation that
will bring a significant increase in moisture Saturday into early
next week.

Breezy to windy easterly winds will persist through the next few
days as a high pressure across the Eastern Atlantic tightens the
local pressure gradient today. This high will be replaced by another
surface high moving off the Eastern Seaboard eastward across the
western Atlantic, increasing even more local winds Friday into
Saturday.

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

The most recent model guidance suggests a wet pattern dominating
the local weather conditions during the long-term forecast period.
For starters, a set of strong surface high pressures moving across
the western Atlantic will promote a dominant fresh northeast flow
with winds remaining at 15-25 knots through the period. In the
meantime, another set of deepening upper-level troughs will swing
across the Northeastern Caribbean, enhancing convective
instability while sustaining the erosion of the trade winds
inversion across the forecast area. The resulting surface-induced
perturbations will promote low-level moisture convergence, and
with the weakening of the trade wind cap, precipitable water
values will fluctuate between 1.50 and 2.00 inches. This scenario
will support a higher frequency of evening-early morning showers
moving inland from the waters due to cooling advection processes
and the potential for afternoon convective development clustering
over the interior and southwestern quadrant of Puerto Rico and
downwind from the local islands as enhanced by the northeasterly
steering winds. Favorable conditions aloft may also support the
potential for isolated thunderstorm development, mainly as part of
the afternoon convection. Although both GFS and ECMWF model
solutions agree in this general scenario, there is still medium
confidence in this forecast since it is expected late in the
forecast period.


&&

.AVIATION...Expect mainly VFR conditions. Local winds will bring
clouds and SHRA/-SHRA at local terminals from time to time. This
activity will spread across the interior and southwest of PR
between 09/15-23z (isolated-TSRA cannot be ruled out). Expect calm
to light and variable winds through 04/12z, and from the ENE at
10 to 15 knots with gusty winds between 20-25 kt. Sea breeze
variations will also form


&&

.MARINE...Moderate easterly winds are expected through at least
Friday morning, maintaining choppy seas across the offshore
Atlantic waters. Elsewhere, seas up to 5 feet are expected. Increasing
trade winds up to 20 knots will result in choppy to hazardous
seas by Friday and continuing into the upcoming weekend. As a
result, a Small Craft Advisory has been issued for the offshore
Atlantic waters due to building seas up to 8 feet by Friday
afternoon. An increase in trade wind showers can be expected over
local waters during the next few days.

For beachgoers, there is a high risk of rip currents for beaches
of northwestern Puerto Rico and eastern-most beaches of Saint
Croix. The high risk will extend to most north- and east- facing
beaches by this evening into Friday morning.

&&

.FIRE WEATHER...Despite the shower activity that has been
observed in recent days, lack of wetting rains across the southern
coastal plains of Puerto Rico has promoted further drying of
soils and fuels, reflected in the most recent reports of KBDI and
10-hour fuel moisture. In fact, a KBDI value of 656 and a 10-Hour
fuel moisture of 8% were reported in Camp Santiago yesterday. Once
again, the forecast does not call for significant wetting rains
across these areas and relative humidity values are expected to
fall into the lower to mid 40s. The local wind flow should remain
at 10 to 15 mph with higher gusts, but variations due to sea
breeze may cause winds to peak higher between the late morning and
early afternoon hours. Therefore, elevated fire weather
conditions are expected across the southern coastal plains of
Puerto Rico, and a Fire Danger Discussion has been issued for
these areas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 76 85 76 / 50 60 60 50
STT 89 76 88 75 / 20 40 50 50

[cycloneye]

Area Forecast Discussion...UPDATED
National Weather Service San Juan PR
512 AM AST Fri Dec 10 2021

.SYNOPSIS...A patchy weather pattern will prevail through
Saturday, with increasing trade winds pushing patches of both
moist and relatively drier air across the forecast area. By Sunday
and continuing through at least midweek, an amplifying upper-level
trough and increase in moisture content will lead to favorable
conditions for enhanced shower and possible isolated thunderstorm
development. Windy to breezy conditions will prevail through the
weekend into early next week, resulting in choppy to hazardous
marine and surf zone conditions.


&&

.SHORT TERM...Friday through Sunday...

The northeasterly winds will push patches of moisture across the
islands, promoting showery conditions once again, especially across
the windward sections of the U.S. Virgin Islands and Puerto Rico
through the morning and evening, followed by afternoon convection
across the interior and southwest Puerto Rico.

A surface high pressure moving off the Eastern Seaboard eastward
across the western Atlantic will tighten the local pressure
gradient; thus, breezy to windy easterly winds will persist later
this afternoon into the weekend. A slot with dry air is now
forecast to arrive on Saturday, reducing the potential for passing
showers through the day and afternoon. However, an induced surface
trough should reach us by Saturday night into Sunday, increasing the
frequency and intensity of showers. The potential for thunderstorm
formation could also become marginally favorable by Sunday, as an
upper-level trough amplifies near the Northeast Caribbean, weakening
the mid-level ridge.


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

The most recent model guidance suggests that a wet pattern will
dominate the local weather conditions through the long-term
forecast period, but now with Thursday as transitioning day and
slightly drier conditions for Friday. At lower levels, a set of
strong surface high pressures across the western Atlantic will
promote a dominant moderate to fresh east to northeast flow with
winds holding at 15-20 knots through the period. The strongest
winds are expected by Wednesday onwards as the second surface high
pressure moves into the western Atlantic and closer to the
Caribbean region. In the meantime, an upper-level trough will
swing across the Northeastern Caribbean early next week, enhancing
convective instability while sustaining the erosion of the trade
winds inversion across the forecast area. The resulting surface-
induced perturbation will promote low-level moisture convergence,
and with the weakening of the trade wind cap, precipitable water
values will remain between 1.75 and 2.00 inches through at least
Thursday afternoon. This scenario will support enhanced shower and
possible isolated thunderstorm activity across the forecast area,
with the potential for ponding of water on roadways and poorly
drained areas to urban and small stream flooding.

Model guidance suggests a sharp decline in moisture content
beginning on Thursday evening, with precipitable water values
quickly falling to around 1.20 inches by Friday morning. This
transition will result from mid-level ridging extending into the
northeastern Caribbean, with trade wind cap inversion enveloping
the forecast area while supporting dry air intrusion. Although
both GFS and ECMWF model solutions agree in this general scenario,
there is still medium confidence in this forecast since it is
expected late in the forecast period.


&&

.AVIATION...Expect mainly VFR conditions. Local winds will bring
clouds and SHRA/-SHRA at local terminals from time to time, which
could result in BKN ceilings, especially between 10/15-22z. This
activity will spread across the interior and southwest of PR
between 10/15-23z. Winds will increase between 15 and 20 knots
with higher gusts and sea breeze variations.


&&

.MARINE...Increasing east to northeast trade winds will maintain
choppy to hazardous seas across most local waters during the next
few days. Small Craft Advisories (SCA) were issued due to
increasing seas up to 8 feet, starting with the offshore Atlantic
waters, the Anegada Passage, and Coastal Waters of Southern USVI,
Vieques, and eastern Puerto Rico this afternoon. Since conditions
will continue to deteriorate westward, additional SCAs will come
into effect for most remaining waters late tonight into Saturday
afternoon.

For beachgoers, a high risk of rip currents remains in place for
beaches across the north coast of Puerto Rico and some beaches of
Culebra, Vieques, and St. Croix. This evening into Saturday
morning, the high risk will expand to neighboring beaches,
including southeastern Puerto Rico and the northern USVI.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 76 85 75 / 60 60 50 70
STT 88 76 87 75 / 50 50 50 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
522 AM AST Sat Dec 11 2021

.SYNOPSIS...A patch of below-normal moisture will stream across
the forecast area today, limiting the potential for showers while
supporting fire danger threat conditions. A wetter weather
pattern is expected by late tonight and continuing through most of
the workweek as a plume of deeper tropical moisture moves into
the area. Thus, expect an increase in shower activity during the
next few days. Windy to breezy conditions will continue through
early next week, resulting in choppy to hazardous marine and surf
zone conditions.


.SHORT TERM...Saturday through Monday...

GOES Satellite Total Precipitable Water as well as the CIRA layer
precipitable indicate a drier air mass upstream of the islands. This
air mass is expected to reach the islands later this morning
reducing the chances of rain through the afternoon hours. Then,
moisture levels will return to normal tonight into Sunday. This
increase in moisture combined with strong trade winds will favor
shallow convection across the north and east sections of Puerto Rico
especially at night and early in the morning. Afternoon showers are
also possible over southwest Puerto Rico on Sunday afternoon,
although no significant rainfall is anticipated as steering winds
remain strong. Weather conditions will become more unstable
onMonday as a short wave trough will approach Puerto Rico and the
U.S. Virgin Islands from the west. As a result, trade wind showers
will be enhanced by the instability and deeper moisture associated
with the upper-level trough. At this time, high resolutions models
suggest that the most active weather on Monday will occurover
northeast Puerto Rico including the San Juan Metro Area. The U.S.
Virgin Islands will also see various rounds of showers moving across
the islands Sunday and Monday. The fast movement of those showers
will limit the rainfall accumulations over the small islands like
Culebra, Vieques, and the Virgin Islands.

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

Although the reasoning behind the forecast and analysis has not
changed much since yesterday, the most recent model guidance now
suggests a delay in the occurrence of the strongest winds, a
southward shift of the bulk of the shower activity, and an
extended period under near- to above-normal moisture content.
Moderate to fresh east-northeast trade winds holding at 15-20
knots will dominate the lower levels of the atmosphere, with the
strongest winds now expected by Thursday.

A relatively wet pattern will persist through Thursday, followed
by a gradual transition into a more seasonal weather pattern
Friday into Saturday. An upper-level trough and surface-induced
perturbation will continue to draw a plume of deeper tropical
moisture into the forecast area through, but now with model-
estimated precipitable water of 1.50 to 1.75 inches persisting
through late Thursday night. This scenario will support an
increase in nighttime showers moving inland from time to time,
followed by afternoon showers and possible isolated thunderstorm
development clustering over the southwestern quadrant of Puerto
Rico. The moderate to fresh flow will also trigger streamers from
the local islands into eastern Puerto Rico and the San Juan
metropolitan area.

A mid-level ridge will approach the northeastern Caribbean from
the north, strengthening the trade wind cap inversion while
supporting dry air intrusion by Friday. This transition will
result in a gradual decline in moisture content, with model-
estimated precipitable water values falling to around 1.15 inches
by Saturday morning. Although global models coincide in this
general scenario, there is still medium confidence in this
forecast since the transition is expected late in the forecast
period.


&&

.AVIATION...VFR conditions continue to prevail across the local
TAF sites. NE winds will range between 20-25 kts below FL150.
Brief -SHRA is still possible at most of the terminals but no
operational impacts are anticipated with this activity. However,
mountain obscurations are likely across the Cordillera Central and
El Yunque. Higher chances of rain are forecast Sunday and Monday.


&&

.MARINE...Moderate to fresh east to northeast trade winds will
maintain choppy to hazardous seas across most local waters into
early next week. As a result, Small Craft Advisories (SCA) remain
in effect due to building seas up to 10 feet for most of the local
waters. Since conditions will continue to deteriorate, additional
SCAs will come into effect this afternoon for the coastal waters
of northern Puerto Rico and the Mona Passage.

For beachgoers, a high risk of rip currents remains in effect for
beaches of northern and southern Puerto Rico and most beaches of
Culebra, Vieques, and the U.S. Virgin Islands.


&&

.FIRE WEATHER...Drying soil and fuel conditions continue, with
the most recent KBDI and 10-Hour Fuel Moisture values as high as
678 and as low as 9% across portions of the southern coastal
plains of Puerto Rico.Unlike previous days, a patch with below-
normal moisture content streaming across the region under a
generally east to northeast steering flow will lead to somewhat
drier conditions today. The timing of the lowest moisture content
will be critical, with the potential for relative humidity values
to fall into the mid to upper 40s between the late morning and
early afternoon hours when local winds are forecast to peak at 15
mph or higher. This scenario will support elevated fire danger
threat conditions, and for that reason, a Fire Danger Statement is
in effect for the southern coastal plains of Puerto Rico.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 75 84 74 / 30 50 60 60
STT 87 76 87 76 / 40 60 60 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
451 AM AST Mon Dec 13 2021

SYNOPSIS...A wetter weather pattern continues to prevail over the
forecast area. Moisture associated to a weakening trough in the
upper levels is expected to develop showers from time to time.
Therefore, expect an increase in shower activity during the next
several days. This weather pattern will transition into drier
conditions at the end of the week.

SHORT TERM...Today through Wednesday...

Overall, a very similar pattern is expected each day in the short
term period. The available moisture will be near to slightly above
normal with precipitable water values between 1.50 and 1.65 inches.
It will be relatively breezy with a ENE winds that could be between
10 and 20 mph with occasional gusts, and the temperatures will be
near normal. As far as rainfall, this particular pattern favors
scattered to locally numerous showers across northern and eastern
Puerto Rico and around the USVI, generally through the day, but
perhaps slightly more significantly during the morning and overnight
hours. In the afternoon hours, the southwestern quadrant of PR would
have the higher chance of rain as the prevailing ENE wind will meet
the sea breeze across SW PR, which may cause convergence and the
development of showers across the area.

There is a weak trough in the upper levels over Hispaniola, which
caused isolated thunderstorms over the waters overnight, but it is
not expected to have a significant impact in the local islands later
today as the trough is weakening. That said, there is some
divergence in the upper levels over the local area, which could help
with the development of the showers that are expected to affect the
local islands, but with the expected wind speeds, these showers
should be brief over any one area.

LONG TERM...Thursday through Monday...

A relatively wetter pattern will prevail until at least late Friday.
An upper level trough will continue to bring bands of tropical
moisture into the forecast area for the beginning of the long term.
This pattern will support the development of nighttime and morning
showers in the windward side of Puerto Rico, and afternoon
convection in the central interior and western portions.

The GFS latest model guidance suggest a seasonal pattern, but much
drier weather conditions stating on Saturday. Then on Sunday, a
drier air mass pattern is expected to prevail across Puerto Rico and
the U.S. Virgin Islands through the end of the long term. At surface
levels the GFS model shows the presence of a dominating high
pressure prevailing over the Atlantic Waters. Moderate to fresh
east northeast trade winds ranging from 15 to 25 knots will
continue dominating the lower levels of the atmosphere.


&&

AVIATION...Prevailing VFR conds are expected across the local
terminals for the next 24 hours. However, VCSH and brief SHRA is
expected through the period across many of the local terminals
except TJPS. Winds today will be mainly from the ENE between 10
and 20 knots with gusts to around 25 knots. Sea breeze variations
will cause winds to be from the ESE at TJPS today through 13/20Z.


&&

MARINE...Moderate to fresh east to northeast trade winds will maintain
choppy to hazardous seas across most local waters into early next
week. Small Craft Advisories remain in effect due to building
seas up to 10 feet for most of the local waters. For beachgoers,
a high risk of rip currents remains in effect for beaches of
northern and southeastern Puerto Rico and most beaches of Culebra,
Vieques, and the U.S. Virgin Islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 75 83 74 / 60 60 50 40
STT 85 74 85 75 / 50 50 30 30

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
442 AM AST Tue Dec 14 2021

SYNOPSIS...A similar weather pattern is expected for the next
several days. Moderate to fresh winds out of the northeast will
prevail through at least the upcoming weekend. Showers across the
islands are expected though the day. Hazardous marine and coastal
conditions will continue for the next several days.

&&

SHORT TERM...Today through Thursday...

Very similar to yesterday`s discussion. Each day in the short term
period we are expecting essentially the same pattern, perhaps with
Wednesday into Thursday having a bit more moisture than the other
days. The available moisture will be near to slightly above normal
with precipitable water values between 1.50 and 1.65 inches, though
Wednesday night into Thursday morning could get up to 1.75 inches.
It will be relatively breezy with a ENE winds that could be between
10 and 20 mph with occasional gusts, and the temperatures will be
near normal. As far as rainfall, this particular pattern still
favors scattered to locally numerous showers across northern and
eastern Puerto Rico and around the USVI through the day, but perhaps
slightly more significantly during the morning and overnight hours.
In the afternoon hours, the southwestern quadrant of PR would have
the higher chance of rain as the prevailing ENE wind will meet the
sea breeze across SW PR, which may cause convergence and the
development of showers across the area. However, the winds on
Thursday might be a little stronger, which may limit the sea breeze
convergence over land to a very small area across southwestern PR.

Here is some divergence in the upper levels over the local area,
which could help with the development of the expected showers, and
perhaps even an isolated thunderstorm across southwestern Puerto
Rico this afternoon. As far as temperatures, they are expected to
be near normal today, but slightly below normal high temps on
Wednesday and Thursday due to the increase in moisture and
cloudiness.

LONG TERM...Friday through Tuesday...

An amplified upper level trough prevailing over the Atlantic waters
is expected to weaken by Friday into Saturday. However, associated
bands of moisture are expected to move inland, continuing with a
showery weather pattern across the islands. A shift to a more
easterly flow will favor slightly warmer temperatures by Friday into
the upcoming weekend. Development of morning showers can be seen
over portions of eastern Puerto Rico, followed by afternoon
convection over the southwestern and western Puerto Rico.

The GFS most recent guidance suggest the positioning of a mid
level ridge over the local area to prevail for most of the long
period, starting on Saturday through the end of the next week. A
mass of drier air will filter into the forecasted area limiting
formation of shower activity. Nonetheless, convection can still
happen over western Puerto Rico due to daytime heating and local
effects. This seasonal, but drier weather pattern will be
dominating the local weather conditions for the long term into
Christmas Day.


&&

AVIATION...Prevailing VFR conds are expected across the local
terminals for the next 24 hours. However, VCSH and brief SHRA is
expected through the period across many of the local terminals
except TJPS. Winds today will be mainly from the ENE between 10 and
20 knots with gusts to around 25 knots. Sea breeze variations will
cause winds to be from the ESE at TJPS today through 14/20Z.

&&

.MARINE...Moderate to fresh trade winds continue to result in choppy to
hazardous marine conditions. Seas from 8 to 10 feet are expected.
These conditions will linger through at least early in the
weekend. Small craft advisories remain in effect for most of the
local waters, except for western and southern Puerto Rico.

For beachgoers, there is a high risk of rip current for most of
the northern, eastern and southeastern coast of Puerto Rico,
Vieques, Culebra and the U.S. Virgin Islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 75 81 73 / 50 40 50 50
STT 86 74 84 74 / 30 30 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Wed Dec 15 2021

.SYNOPSIS...A wetter weather pattern with a chance of isolated
thunderstorms is forecasted for today. Fresh to strong winds will
continue to result in hazardous marine and coastal conditions at
least through this upcoming weekend. Passing showers will increase
in frequency later tonight and on Wednesday. Shower activity may
finally decrease by the weekend and early next week.

&&

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

Similar pattern to the last few days is expected today and on
Thursday, but there is an approaching pre frontal shearline that may
cause locally numerous showers especially late this afternoon into
Thursday. There is also a slight chance of thunderstorms late this
afternoon and evening and through tonight. There may be a shallow
front moving in on Friday, which will cause a more significant
increase in moisture. The available moisture today and Thursday will
be near to slightly above normal with precipitable water values
between 1.50 and 1.65 inches, though Friday could get upwards of
1.75 to 1.8 inches, which is about the 75th percentile comparing to
climatology. It will be relatively breezy with a ENE winds that
could be between 10 and 20 mph with occasional gusts, becoming even
windier on Thursday into Friday. The temperatures will be near
normal, though the latest guidance has the max temps about 2 degrees
below normal for today. As far as rainfall, this particular pattern
still favors scattered to locally numerous showers across northern
and eastern Puerto Rico and around the USVI through the day, but
there is also a chance of thunderstorms across the aforementioned
areas late this afternoon into tonight into Thursday. In the
afternoon hours, the southwestern quadrant of PR has the a good
chance of rain with isolated thunderstorms. Since the winds on
Thursday and Friday are expected to be a bit stronger, they may
limit the sea breeze convergence over land to a very small area
across southwestern PR, and the shower activity in the afternoons
those days may be limited to scattered showers.

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

An upper level trough prevailing over the Atlantic waters, will move
out of the forecast area by late Saturday. However, patches of
moisture will promote the development of morning showers over
portions of eastern Puerto Rico from time to time. The latest
guidance shows an acceleration of the trade winds in response to
the building surface ridge over the north Atlantic. East to
northeasterly trade winds are forecast to persist over the local
area for the long period.

The GFS model continues to suggest the positioning of a mid level
ridge over Puerto Rico and the U.S. Virgin Islands as it has been
mentioned in the previous discussions. This will be the
predominant feature for the long period. A mass of dry air will
linger across the islands until at least Wednesday afternoon,
limiting the formation of shower activity. Nonetheless, convection
can still happen over western Puerto Rico due to daytime heating
and local effects. A more seasonal weather pattern is expected
late on Wednesday. A pre-frontal band is expected to arrive,
increasing the moisture content and enhancing the shower activity
for the holidays coming up.

&&

.AVIATION...Prevailing VFR conds are expected across the local
terminals today. However, VCSH and brief SHRA is expected through
the period across many of the local terminals except TJPS. Winds
today will be mainly from the ENE between 10 and 20 knots with gusts
to around 25 knots. Sea breeze variations will cause winds to be
from the ESE at TJPS today through 15/20Z. An increase in shower
activity after 15/19Z with a slight chance of thunderstorms, may
cause brief MVFR conds at TJSJ with VCTS into the evening hours.

&&

.MARINE..Fresh to strong winds will continue at least through the
weekend, with building seas 5 to 10 feet across most of the local
waters, and up to 12 feet for the offshore Atlantic by Thursday and
Friday. Small craft advisories continue in effect for all the local
waters, except the southern and western coast of Puerto Rico.

For the beachgoers, there is a high rip current risk for the
north, east, and southeastern coast of Puerto Rico, as well as for
all beaches across Vieques, Culebra and the U.S. Virgin Islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 82 74 83 74 / 60 60 40 50
STT 84 73 84 75 / 50 60 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
512 AM AST Thu Dec 16 2021

.SYNOPSIS...An approaching pre-frontal shearline may cause
locally to numerous showers today across the local islands. Expect
a a mix of sun and clouds during morning hours, and then in the
afternoon shower activity is forecasted. A building surface high
pressure will be the dominant feature for the upcoming weekend.
Hazardous marine conditions will continue across the local waters
until at least Sunday afternoon.

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

There is an approaching pre frontal shearline that may cause locally
numerous showers today, especially this afternoon, then a shallow
front is moving in on Friday, which will cause an increase in
moisture. The available moisture today will be near to slightly
above normal with precipitable water values between 1.50 and 1.65
inches, then on Friday could get upwards of 1.75 to 1.8 inches,
which is about the 75th percentile comparing to climatology. On
Saturday, the available moisture will gradually diminish as drier
air starts to move in, and precipitable water will go down to around
1.25 inches. It will be breezy today and Friday with an E to ENE
wind flow that could be between 10 and 20 mph with occasional gusts,
though closer to 15-20 mph with gusts in the windward side of the
local islands. The temperatures will be near normal, though the
latest guidance has the max temps about 2 degrees below normal in
the short term period.

As far as rainfall, a mix of sun and clouds with brief periods of
rain is forecast. Scattered to locally numerous showers across
northern and eastern Puerto Rico and around the USVI is expected,
but the high resolution guidance favors the numerous showers across
the eastern half of PR, as well as portions of western PR to occur
in the afternoon; the global models are much more modest with the
rainfall totals which have proven to be underestimating the rainfall
amounts over the past few days for many areas over Puerto Rico.
Since the winds on today and Friday are expected to be a bit
stronger that what they have been over the past few day , the shower
activity may make it a bit further inland over PR, while causing the
showers to be mainly brief though persistent. The shower activity on
Saturday may be limited mainly for eastern PR and the USVI in the
morning, then drier air will be moving in for the afternoon, which
may cause some shower activity across western PR but limited since
the drier air will move in quickly by the mid afternoon hours.

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

A surface high pressure dominating over the Atlantic waters, will
continue to accelerate trade winds over the Caribbean Basin. A
mass of dry air is expected to filter across the area on Sunday,
promoting fair weather conditions. Therefore, limited shower
activity across the islands are expected through the day. East to
northeasterly trade winds are forecast to persist over the local
area until at least Thursday.

The latest model guidance continues to forecast a seasonal, but
slightly drier weather pattern over Puerto Rico and the U.S.
Virgin Islands. As it has been mentioned in the previous
discussions, a surface high pressure will prevail until Tuesday.
Moisture pulled from the Caribbean will place over the islands,
enhancing unstable conditions aloft and shower formation. This
pattern will linger through the end of the long period, by then a
pre-frontal band is expected to arrive before Christmas Eve.


&&

.AVIATION...Prevailing VFR conds are expected across the local
terminals today. However, VCSH and brief SHRA is expected this
afternoon across many of the local terminals except TJPS. Winds
today will be mainly from the E-ENE between 10 and 20 knots with
gusts to around 25 knots. Sea breeze variations will cause winds to
be from the ESE at TJPS today through 16/20Z.


&&

.MARINE...Hazardous marine conditions are expected to continue
across the local waters for at least Sunday. Seas will build up
to 12 feet across the offshore Atlantic Waters and between 6 to 10
feet for the rest of the local waters. Also, life-threatening rip
currents will continue to the upcoming weekend across all the
islands. For the beachgoers, there is a high risk of rip currents
for most local beaches.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 74 83 73 / 50 50 40 40
STT 83 73 84 74 / 60 50 40 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
435 AM AST Fri Dec 17 2021

.SYNOPSIS...Slightly drier than normal moisture is present over
the local area today. A shallow front is moving in this afternoon
into early Saturday, increase in moisture content across the
islands. Isolated to scattered showers are expected across
northern and eastern Puerto Rico and around the USVI. Hazardous
marine conditions continue over the local waters. High risk of rip
current remains in effect.

&&

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

Slightly drier than normal moisture is present over the local area,
and there is also an ENE wind flow of 15-25 mph, causing the
scattered shower activity over the local waters to be particularly
brief, and if any of the showers reach land areas, it would have
minimal to no accumulations. A shallow front is moving in this
afternoon into early Saturday, which will cause an increase in
moisture. The available moisture will increase to near normal this
afternoon, with precipitable water values near 1.5 inches, but
increasing gradually to around 1.65 inches by Saturday morning. This
will support isolated to scattered showers during this time period,
but the shower activity will continue to be mainly brief. By
Saturday afternoon onward, the available moisture will decrease as
drier air starts to move in. The precipitable water will go down to
around 1.35 inches across the USVI, but under 1.2 inches over PR.
The breezy conditions will continue through Saturday, but winds will
decrease slightly on Sunday. Therefore, we are expecting winds up to
around 20 mph with occasional gusts, but closer to 15 mph with gusts
on Sunday over land areas. The temperatures will be near normal,
though the latest guidance has the max temps about 2 degrees below
normal today and Saturday, increasing about a degree on Sunday.

As far as rainfall, the expected mix of sun and clouds with brief
periods of rain is forecast. Isolated to scattered showers are
expected across northern and eastern Puerto Rico and around the USVI
through today, and during the overnight and morning hours on
Saturday and Sunday. Western PR could observe scattered showers in
the afternoon hours. Overall, the rainfall amounts are not expected
to be too significant, and any impact would be expected to be
minimal, causing at most ponding of water on roadways over poor
drainage areas, given that both hi-res and global model guidance is
very modest with the rainfall accumulation forecast.

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

A dominant surface high pressure over the Atlantic waters is the
main feature, at least for the first half of the long period. The
tightening of the pressure gradient leads to the acceleration of
the trade winds over the Caribbean Basin. Dry weather conditions
will prevail from Monday through Wednesday. Limited shower
activity across the islands are expected. However, some patches of
moisture will filter into the area on Wednesday, enhancing the
potential for morning showers over portions of eastern Puerto Rico
from time to time. East to northeasterly trade winds are forecast
to persist over the local area.

The latest GFS model guidance is forecasting patches of moisture
pulled from the Caribbean. Those patches will place over the
islands, enhancing unstable conditions aloft and shower
formation. This pattern will linger through the end of the long
period. A pre- frontal band is expected to arrive before Christmas
Eve, bringing more instability before a cold front reaches the
local area.

&&

.AVIATION...Prevailing VFR conds are expected across the local
terminals today. However, VCSH is expected in the morning across
TJSJ, TIST, and TISX. Winds today will be mainly from the E-ENE
between 10 and 20 knots with gusts to around 25 knots. Sea breeze
variations will cause winds to be from the ESE at TJPS today through
17/20Z.

&&

.MARINE...
Fresh to strong winds will continue for the next several days.
Winds will increase by today, mainly out of the east-northeast.
Hazardous conditions are expected across most of the local
waters and Small Craft Advisories remains in effect. Seas of up
to 10 feet are expected today, with seas of up to 12 feet for the
offshore Atlantic waters by tonight.

For the beachgoers, there is a high risk of rip currents for most
of local beaches. Breaking waves of up to 10 feet are expected.
Caution should be exercised by anyone participating in activities
in and around the water.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 73 83 73 / 40 40 50 30
STT 84 73 85 74 / 40 40 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
445 AM AST Sat Dec 18 2021

.SYNOPSIS...
Strong winds will continue through at least tomorrow, resulting in
passing showers, as well as hazardous marine and coastal
conditions. Patches of moisture in the trade winds will increase
the chance of rainfall by the latter part of the next workweek.

&&

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

Showers are increasing across the local Atlantic and eastern waters
of the islands, as a strong surface high pressure over the
southwestern Atlantic is pushing the remnants of an old frontal
boundary across the region. Breezy conditions will continue through
the day, and wind gusts between 25-35 mph could be observed with the
passing showers. Northeast steering winds will prevail today, and
shallow afternoon convection is expected to develop over portions of
the southwestern quadrant of the island. However, rainfall amounts
should remain at less than half an inch of rain due to the fast
moving nature of the showers.

A mid-level ridge will promote drier air and more stable conditions
aloft through the short term period. However, as the low to mid-
level ridge moves east of the region during the next couple of days,
winds will turn more easterly on Sunday and a weak perturbation in
the trades is expected to increase slightly the columnar moisture to
around 700 mb by late Sunday and early Monday. This should continue
to promote mostly trade wind shower activity across the local
waters, and portions of the USVI and eastern sections of PR. Shallow
convection is possible over western PR each afternoon, but no
significant rainfall amounts are expected.

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

A surface high pressure over the Central Atlantic will drag an
induced surface trough over the local islands. Although this
disturbance does not look particularly strong, it will increase
the moisture content from the surface up to 700 mb. By Wednesday,
an upper level trough will exit the eastern coast of the United
Stated with an associated cold front also moving toward the
western Caribbean. In response, the surface wind flow will shift more
from the east-southeast. At the same time, another, more
significant, surface trough will reach the islands. These
features will result in moisture convergence over the area through
Saturday, increasing the chance of rainfall. For Thursday and
Friday, as the upper level trough approaches, divergence aloft
will increase, hence resulting in an enhanced potential for
isolated thunderstorm development over the region. Since this this
scenario is still a few days away, the confidence on the timing
and amount of rainfall expected is still low, and the forecast
will be updated during the next cycles of the area forecast
discussion.

&&

.AVIATION...
Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, trade wind showers may
cause tempo MVFR cigs at times across the USVI/eastern PR terminals.
Low level winds will continue from the east-northeast at 15-25 kt
with higher gusts and sea breeze variations after 14z.

&&

.MARINE...
Hazardous marine conditions continue due to fresh to strong winds.
Seas up to 12 feet have been observed across the offshore Atlantic
waters and up to 10 feet in the nearshore buoys. These conditions
are expected to continue at least through tomorrow. Small craft
advisories are in effect. For the beaches, there is a High Surf
Advisory for the northern coast of Puerto Rico, Culebra and St.
Thomas, and a high rip current risk for much of the local area.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 85 73 / 50 50 50 40
STT 86 76 87 76 / 50 40 40 40

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
413 AM AST Sun Dec 19 2021

.SYNOPSIS...
Frequent passing showers are expected today as a weak disturbance
crosses the area. Hazardous marine and coastal conditions will
continue today, but they will gradually improve by Monday. Showers
will increase once again by the latter part of the workweek into
the weekend.

&&

.SHORT TERM...Today through Tuesday...
Recent satellite imagery, the derived blended total precipitable
water as well as the NWS doppler weather radar, all suggest a
gradual increase in low level moisture advection, as a weak
disturbance continued to cross the northern Leeward islands and
approach the region this morning. This along the the moderate east
northeast trade winds, will help to sustain frequent passing showers
in and around the islands during the rest of the morning hours. Some
of the showers will continue to affect parts of the north and east
coastal areas, while producing periods of moderate to locally heavy
downpours with brief wind gusts. This activity may also lead to
minor ponding of water on roads and in poor drainage areas. A
gradual clearing and diminishing shower activity is forecast by late
morning, followed by some afternoon convection. This activity should
then be mainly focused in the western and interior parts of Puerto
Rico and downwind and on the west end of the U.S. Virgin Islands.
However, the overall development of the shower activity should be
limited as a mid to upper level ridge will build across the region
today. This should aid in suppressing and the shearing off of any
afternoon convection.

By Monday and into Tuesday, a drier airmass in expected as the ridge
will continue to build aloft and aid in eroding low level moisture
advection. This along with the weakening of the local pressure
gradient will also promote a decrease in the tradewinds which are
expected to become more east southeast by Tuesday. Overall drier air
is expected behind the aforementioned low level disturbance.
Lingering moisture across the region will be sufficient to aid the
the development of less frequent passing showers with afternoon
convection limited to parts of the central interior and west to
northwest sections of Puerto Rico and mainly downwind of the U.S.
Virgin Islands. For the most part, overall seasonal and fairer
weather condtions are expected for the islands on Monday and most of
Tuesday. However, recent model guidance does suggest that this
pattern will again change by late Tuesday, as another surge of
moisture is to be lifted up across the region from the east
southeast. This in turn will increase the chance for more frequent
late afternoon and evening showers especially around parts U.S.
Virgin Islands particularly St Croix, as well as over parts of the
eastern and southern Puerto Rico. Will however continue to monitor
and see how this unfolds.

.LONG TERM...Wednesday through Sunday...
The long-term portion of the forecast appears to be on the wet
side. First, the wind flow will shift from the southeast in
response of a trough exiting the eastern coast of the United
States and a high pressure migrating toward the eastern Atlantic.
This wind flow will caught a surface trough and move it over the
islands on Wednesday, deepening the moisture content into the 200
mb-levels of the atmosphere. By Thursday, the GFS forecast
soundings show that the southeasterly wind flow will extend into
the mid-levels of the atmosphere. This will pull additional
moisture from the south over the region, with precipitable water
values rising to just above 2.0 inches. Then, on Friday, a cold
front approaching from the west will be added to the mix, further
increasing low-level convergence over the area. So far, both the
GFS and ECMWF models agree on this feature stalling or just moving
across the local islands by Christmas`s Eve and early on
Christmas Day. As a result, from Wednesday onward, there will be
an enhanced potential for shower development over the area.
Although thunderstorms were left out of this forecast cycle due
to lacking upper level support, isolated thunderstorm activity
cannot be ruled out, especially by late Thursday and Friday.
Finally, late Saturday and on Sunday, drier air behind the cold
front moves through the area, resulting in improving weather
conditions.


&&

.AVIATION...VFR conds at all terminals durg prd with ENE SFC winds
at 10 knots or less overnight then increasing to between 12-20 knots
with occasional gusts to around 25 knots aft 19/14Z. SCT ocnl BKN
cld lyrs nr FL025... FL050...FL080 en route btw the local islands.
Low level cld cover and SHRA will incr en route btw PR the U.S.V.I
through 19/14Z. Mtn Top Obscr psbl ovr E interior and El Yunque with
brief MVFR due to low clds/SHRA. Brief prds of -SHRA/SHRA at
TJSJ/TIST/TISX/TIST and the Northern Leeward Islands til at least
19/14z. Low level winds mainly FM E-NE 18-25 kt BLO FL180 bcmg fm W
and incr w/ht ABV.


&&

.MARINE...
Hazardous marine conditions continue across the local waters. The
offshore buoy (41043) shows seas around 9 feet, and the inner buoy
has seas at 6 to 7 feet. These conditions will persist through at
least early tomorrow. Then, seas and winds are expected to
gradually subside. Small craft advisory conditions continue today
for most of the local waters, expect southern and southwestern
Puerto Rico.

Across the local beaches, there is a high rip current risk for the
western, northern, eastern and southeastern coast of Puerto Rico,
Vieques, Culebra and much of the U.S. Virgin Islands. There is a
High Surf Advisory for northern Puerto Rico, Culebra and St.
Thomas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 84 73 / 50 40 40 40
STT 85 74 85 73 / 40 30 20 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Mon Dec 20 2021

.SYNOPSIS...
Surface high pressure ridge will shift eastward and spread across
the central Atlantic, while weakening and relaxing the local
pressure gradient. This will promote diminishing tradewinds and a
more east southeast wind flow through Tuesday. The mid to upper
level ridge will erode as a short wave trough moves across the
west Atlantic. The upper ridge will build overhead once again on
Tuesday then linger across the area through Thursday. A weak surface
trough will set up across the region by Friday as a cold front enters
and moves across the west and southwest Atlantic. Increasing moisture
convergence and instability is therefore expected by the end of the
work-week. In the meantime a seasonal weather pattern is expected
with diminishing trade winds.

&&

.SHORT TERM...Today through Wednesday...
A surface high pressure will continue to move into the central
Atlantic, finally weakening the pressure gradient over the islands.
As a result, lighter winds are expected to prevail across the area,
but still moderate with the low-level steering flow forecast to be
at around 13 knots. In the meantime, the forecast area is currently
located between a pocket of drier air to the north and an area of
enhanced moisture moving over the Caribbean waters. Recent infrared
and Doppler radar data show scattered shower activity moving around
St. Croix and brushing the southern coast of Puerto Rico. At the
upper levels, there is a short-wave trough advancing into the area.
This feature, in combination with the low level moisture, should
fuel showers over western Puerto Rico this afternoon, with the high
resolution models and the National Blend Model showing moderate to
locally high rainfall accumulation. Ponding of water on roadways and
low-lying areas will be expected, and urban and small stream
flooding will be possible. Although thunderstorms cannot be ruled
out completely due to instability aloft, for now they were left out
of the forecast due to the lack of mid-level moisture. Once the low-
level patch of clouds departs the area by this evening, precipitable
water values will be falling to 1.0 inch or even less. Therefore,
mainly fair weather conditions are expected tonight and early on
Tuesday.

By mid-day Tuesday, the wind flow is expected to gain a
southeasterly component in response of a cold front exiting the
eastern coast of the United States and the surface high pressure
being displaced into the eastern Atlantic. The trade winds will
bring a surface trough into the area by the end of the day and
through the night hours, which should result in another increase in
shower activity. This should be followed by another slot of drier
air by early Wednesday, but another area of enhanced moisture should
reach the islands by the end of the day and into the evening hours.

.LONG TERM...Thursday through Tuesday
By Thursday, the GFS model guidance which has so far initialized well,
continue to suggest winds becoming more east southeast then
southeasterly, as the surface ridge moves into the central Atlantic.
An induced surface trough is forecast to then develop across the region
through Friday as a cold front will move across the west Atlantic.
Meanwhile , the upper ridge is to erode in response to a polar trough
becoming amplified over the west and southwest Atlantic as it move
eastwards. This pattern suggests increasing instability aloft along
with additional moisture convergence over the region, with precipitable
water values rising to just around 2.0 inches by Friday and into the
weekend.

So far both the GFS and ECMWF models are in agreement and maintain
the stalled frontal boundary north and west of the area or sinking
just north of the area by Christmas`s Eve and on Christmas Day.This
suggests a continued trend for a wetter pattern with increasing
instability aloft and moisture convergence at least through Saturday
with good potential for enhanced shower development over the islands
as well as the possibility of some isolated thunderstorms over the
local Atlantic waters or near the north and east coastal areas of
the islands. This will result in increased potential for minor
urban and small stream flooding and/or ponding of water on roads
and in poor drainage areas mainly in isolated areas as so far the
heavy rainfall activity is not expected to be widespread.

A gradual improvement in the overall weather pattern is expected
by Sunday and into Monday of the following week as a drier and
stable airmass will enter and spread across the region with
winds gradually increasing while becoming more northeasterly as
the Surface high pressure ridge builds across the west Atlantic
and north of the region. That said, expect a return of more seasonal
weather pattern during the latter part of the period. However, as
the northeast winds increase on Monday and Tuesday expect a cool
advective pattern to return, thus promoting the occasional passage
of late evening and early morning tradewind showers from time to
time along the north and east coastal areas. This should be followed
by limited afternoon convection mainly over parts of the interior
and southwest sections of Puerto Rico with lesser activity forecast
in and around the U.S. Virgin islands.

&&

.AVIATION...
Mainly VFR conditions expected to prevail through the forecast period.
Winds will increase to 10 to 15 knots after 12-14Z, out of the ESE,
with stronger gusts and sea breeze variations. VCSH are expected for
TJBQ after 17Z, which could result in brief periods of MVFR conditions
due to reduced VIS and low ceilings.

&&

.MARINE...Winds and seas will continue to gradually subside
during the next 72 hours. At this time some Small Craft Advisories
will be taken down by 8 AM AST this morning, but will remain for
the offshore Atlantic waters until later this afternoon.
Thereafter, Small craft operators should continue to exercise
caution due to choppy seas. Rip current risk will remain high for
most beaches today then becoming moderate to high by Tuesday and
for the rest of the work- week. Please refer to the latest Coastal
Waters Forecast (CWFSJU), Marine Weather Messages (MWWSJU), as
well as Coastal Hazard Message (CFWSJU) issued by the WFO San Juan
PR, for the most up to date marine and surf zone information.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 85 73 / 40 40 50 50
STT 84 73 84 73 / 20 40 60 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
431 AM AST Tue Dec 21 2021

.SYNOPSIS...
A train of easterly pertubations and accompanying surges of low
to mid level moisture will continue to affect the area for the
next few days, driven by the dominant surface high pressure ridge
and a moderate steering wind flow. Intervals of dry and stable air
will cross the region on occasions resulting in a mixture of sunshine
and clouds. Showers are is expected to be of short duration but some
may cause minor ponding of water on roads and in poor drainage areas.
An upper ridge will build and hold across the area through Thursday.
An induced surface trough is forecast to set up across the area by
Friday, as a cold front stalls across the west Atlantic and north
of the area. Increasing instability aloft and moisture convergence
is forecast by Friday. In the meantime, a seasonal weather pattern
is expected with the prevailing east southeast tradewinds.

&&

.SHORT TERM...Today through Thursday...
Recent infrared satellite imagery, as well as Total Precipitable
Water from GOES-16 show a weak surface trough over the eastern
Caribbean. This feature is expected to cross the islands through the
day, with moisture content increasing all the way to 500 mb, and
thus bringing another round of showers through the day. At sunrise,
it should be mainly tranquil, but by mid-morning into early in the
afternoon, the moisture field will begin to envelope the U.S. Virgin
Islands, then gradually advancing into eastern Puerto Rico. The high
resolution models, as well as the National Blend Model, indicate
moderate rainfall amounts, especially over the eastern half of
Puerto Rico. Additionally, since the trough will be moving over the
area through the day, the combination of low level convergence,
available moisture and diurnal heating should trigger additional
showers over the area, including western Puerto Rico. Ponding of
water on roadways and low-lying areas is anticipated, and isolated
urban and small stream flooding cannot be ruled out.

By Wednesday, as a frontal system exits the eastern coast of the
United States and the surface high pressure migrates toward the
eastern Atlantic, the low to mid level steering flow will shift from
the east-southeast. Then, a similar weather pattern repeats, with a
slot of dry air moving across the area early on the day, followed by
another area of enhanced moisture by the afternoon and evening
hours. This feature, however, looks weaker and with the bulk of the
activity remaining over the Atlantic waters. Then on Thursday, the
front will pull a plume of moisture into the eastern and central
Caribbean. So far, the bulk of the moisture appears to stay west of
the local islands, but close enough to interact with local effects
and result in another round of afternoon showers across western
Puerto Rico.

.LONG TERM...Friday through Wednesday...
An induced surface trough is forecast to develop across the region
through Friday, as a cold front will move and eventually stall across
the west Atlantic and north of the region. An upper level ridge will
erode in response to a polar trough becoming amplified over the west
and southwest Atlantic as it moves eastwards. This in turn is so far
expected to increase instability aloft along with low level moisture
convergence over the region. Model guidance still suggest that the
layered precipitable water values are forecast to increase to around
2.0 inches on Friday and into the weekend.

Latest model guidance continued to be in agreement and maintain the
stalled frontal boundary north and west of the area but with moisture
sinking just north of the islands by Christmas`s Eve and on Christmas
Day. This scenario suggests a continued trend for a wetter pattern
with increasing instability aloft and moisture convergence through
at least Saturday with good potential for enhanced shower development
over the islands as well as the possibility of isolated thunderstorms
over the local Atlantic waters or near the north and east coastal
areas of the islands. This overall scenario will result in increased
potential for minor urban and small stream flooding and or ponding
of water on roads and in poor drainage areas, but mainly in isolated
areas as so far the heavy rainfall and shower activity is not expected
to be widespread.

A gradual improvement in the weather pattern is forecast by Sunday
and through Monday of the following week, as a drier and stable
airmass will enter and spread across the region. Winds will gradually
increase while becoming more northerly as a strong surface high
pressure ridge builds across the west Atlantic and north of the
region. Expect a return of a seasonal weather pattern through Monday
and into Tuesday with a cool advective pattern expected to return.
This will promote the occasional passage of late evening and early
morning tradewind showers along the north and east coastal areas,
followed by limited afternoon convection mainly over parts of the
interior and southwest sections of Puerto Rico. Lesser activity
forecast in and around the U.S. Virgin islands. By Wednesday the
pattern is forecast to change again with approach of a remnant
frontal boundary shearline as the high pressure ridge builds north
of the region and moisture returns to the region from the northeast.

&&

.AVIATION...
Mainly VFR conditions expected through the forecast period. Passing
showers could result in SHRA across most of the terminals with brief
periods of MVFR conditions due to reduction of VIS and low ceilings.
Winds will be out of the east at 10 to 12 knots, with stronger
gusts and sea breeze variations.

&&

.MARINE...Choppy seas up to 6 feet are forecast across the offshore
Atlantic and Caribbean waters as well as the local passages today.
Small craft operators should therefore exercise caution. Seas between
3 to 5 feet can be expected elsewhere. For the rest of today there
is a moderate risk of rip currents for most beaches, however some
beaches of Culebra and east beaches of St Croix may return to a
high risk of rip currents by early Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 87 73 / 60 50 20 40
STT 83 73 85 74 / 60 60 40 60