Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
422 AM AST Thu Mar 4 2021

.SYNOPSIS...Fair weather conditions due to a drier than normal air
mass will prevail through early Friday. Moisture will increase in
southeasterly flow later Friday through Saturday, resulting in an
increase in shower activity. Drier conditions expected for Sunday
before low-level moisture gradually increases through most of
next week. Winds are expected to increase as well by early next
week as another surface high pressure moves across the western
Atlantic.

&&

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

Drier than normal conditions will prevail across the islands today
and early Friday morning, as indicated by the GOES-East water vapor
channels. At mid-levels, a high-pressure over the northeast
Caribbean is promoting subsidence and dry air at those levels. At
the surface, the interaction of a frontal boundary over the western
Atlantic and a surface-high pressure across the central Atlantic is
inducing a weak southerly wind flow across the northeast Caribbean.
Under these weather conditions, expect above-normal temperatures
north of the Cordillera Central of Puerto Rico, little or no rain
activity, and calm to light and variable winds across Puerto Rico
and the U.S. Virgin Islands.

The weather pattern will persist through at least late in the
morning or the afternoon of Friday when an easterly disturbance,
forecasted to propagate across the islands, enhance rain formation
across PR/USVI. Dynamic aloft could be reinforced by an eastward
propagating mid to upper-level trough forecast to reach the islands,
as both GFS and ECMWF suggest. The trailing moisture of this
disturbance will promote rainy conditions through at least Saturday.
If the timing is correct, urban and small stream flooding will be
likely Friday afternoon through Saturday evening.

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

Fair weather conditions are expected to return on Sunday as a
drier air mass moves across the area, limiting shower activity.
On Monday, a frontal boundary is expected to be situated northwest
of the area, with an increase in low-level moisture expected.
This will cause shower activity to increase somewhat with isolated
to scattered showers across eastern Puerto Rico and the USVI
during the morning hours followed by locally induced activity
across western Puerto Rico during the afternoon hours. The low-
level winds will then increase on Tuesday and Wednesday as a
surface high pressure builds across the western Atlantic. This
will favor a cool advective pattern with patches of moisture
moving across the area from time to time, resulting in trade wind
showers.

Then, by the end of the long term period, the weather pattern
begins to undergo changes aloft as a mid and upper-level trough
amplifies across the central and eastern Caribbean. If model
guidance is correct on this solution, then a more unstable
weather pattern is more likely by the latter half of next week
with more enhanced shower activity possible across portions of
the area.

&&

.AVIATION...VFR conditions will prevail today. Winds will persist
from the ESE- SE at 10 kt or less, with sea breeze variations
after 04/13z. VCSH will remain possible without any impact on
operations.

&&

.MARINE...A northerly swell is expected to impact the Atlantic
waters and local passages later today through Friday. This will
result in choppy seas of up to 6 feet, mainly across the offshore
Atlantic waters. Across the rest of the local waters, seas of up
to 5 feet are expected. Seas are expected to remain below 6 feet
through the upcoming weekend.

For beachgoers, there is a moderate risk of rip currents across
all the northern beaches of Puerto Rico and Culebra as well as the
easternmost beaches of Vieques and Saint Croix for today. The rip
current risk increases to high across the north-central beaches
of Puerto Rico for tonight due to the aformentioned northerly
swell.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 73 86 74 / 20 0 40 50
STT 85 73 85 73 / 20 20 50 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
419 AM AST Fri Mar 5 2021

.SYNOPSIS...Fair weather conditions will persist into this
afternoon, before low-level moisture increases later this
afternoon through Saturday with the passage of an easterly
disturbance, resulting in an increase in shower activity. Fair
weather conditions return on Sunday, before a transition to a
wetter pattern by much of next week as low-level moisture
increases.

&&

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

The upper-level ridge will slowly erode as a mid to upper-level
trough swings by from the west today. Winds will continue from
the southeast until the surface-high pressure builds stronger
across the western Atlantic by the weekend. GOES-East-derived
total precipitable water (TPW) images indicated additional
moisture approaching the islands from an easterly disturbance
located towards southeast. However, in the meantime, before the
arrival of this moist air mass, fair weather conditions with
mostly sunny skies and just a few isolated showers across the
windward sections of Puerto Rico and the U.S. Virgin Islands will
prevail during the morning hours. Then, as moisture moves closer,
shower activity will slowly increase across the local Caribbean
Waters, St Croix, and eastern/northern PR late this morning or
during the afternoon. Rain activity will spread over the interior
and western portions of Puerto Rico around the afternoon and this
evening. As this easterly disturbance moves away from the
islands, the trailing moisture, enhanced by low level-
convergence, could produce shower activity across the east, and
Caribbean coastal areas of Puerto Rico and St Croix, late tonight
into Saturday morning. The available tropical moisture will aid in
another round of afternoon convection across the San Juan metro
area and the northwestern quadrant of Puerto Rico on Saturday.
Today, the latest model guidance is not so aggressive in terms of
rainfall accumulations. Therefore, instead of urban and small
stream flooding, it is more likely to observe just ponding of
water in roads and poorly drained areas.

Little or no rain activity is forecast by Saturday evening and
Sunday morning as the tropical moisture pulls away. However, the
typical pocket of moisture advected by the winds will arrive at
times over the islands, bringing passing showers.

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

A frontal boundary will be located to our northwest on Monday.
This feature will drag some low-level moisture into the area with
an increase in showers expected. Isolated to scattered showers are
possible across portions of eastern Puerto Rico and the USVI
during the morning hours followed by afternoon activity across
western Puerto Rico. Low-level winds will then increase on Tuesday
into Wednesday as a surface high pressure moves across the
western Atlantic. This will result in a cool advective pattern,
with trade wind shower activity expected at times. Then, towards
the latter half of the week, the weather pattern will undergo
changes aloft. Global models continue to remain consistent in
showing a mid and upper-level trough developing and amplifying
west of the area, over near Hispanola. This would put the area
on the favorable side for upward vertical motion. If the global
models are correct in their current solution, then a more
unstable weather pattern can be expected towards the latter half
of the week with enhanced shower activity possible across portions
of the area.

&&

.AVIATION...VFR conditions will prevail this morning. SHRA/+SHRA
will develop across E-PR/USVI by 05/16z, spreading into the
interior/W-PR by 05/18z and onward. Winds will persist from the SE
at 10 kt or less, with sea breeze variations after 05/13z.

&&

.MARINE...A fading northerly swell will result in an improvement
in seas across the local waters for today with wave heights
expected to range between 3 and 5 feet. Fairly tranquil marine
conditions are expected to continue through the upcoming weekend
with east to southeast winds up to 15 knots. For beachgoers, there
is a high risk of rip currents for the north-central to San Juan
and vicinity beaches with a low to moderate risk expected
elsewhere.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 74 87 72 / 40 40 40 30
STT 84 75 84 74 / 30 30 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
433 AM AST Sat Mar 6 2021

.SYNOPSIS...

The moisture field associated with a tropical disturbance will
continue across the islands today. However, fair weather
conditions will prevail through the weekend. Showers will develop
across the interior and northwest quadrant of Puerto Rico during
the afternoon. A transition to a more unstable weather pattern is
forecast for the second part of next week.

&&

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

Latest GOES-16 Precipitable Water product is showing a surge of
moisture being advected into the area from a easterly disturbance
passing south of the local islands. However, despite this increase
in moisture, little to no shower activity is occurring due to a dry
layer in the low-levels around 850 mb. This dry layer will remain in
place through today, limiting shower activity across most of the
local area with mainly fair weather conditions expected. However,
across the northwestern quadrant of Puerto Rico, the low-level
moisture will be better and thus there is higher probability to
observe scattered showers this afternoon. Rainfall accumulations for
the most part should remain on the light side with only ponding of
water on roadways and in low-lying and poor-drainage areas expected.
As the moisture from the easterly disturbance moves westward away
from the area later this evening, a drier air mass will move in.
This will produce fair weather conditions overnight tonight.

Fair weather conditions are expected to prevail on Sunday as the
western periphery of a mid-level ridge situated across the central
Atlantic will build overhead and strengthen the trade wind cap.
Therefore, shower activity will be limited once again.

On Monday, an induced surface trough is expected to develop to the
east of the area. This will change the low-level winds to the east-
northeast. Some patches of low-level moisture will move across the
area to result in isolated to locally scattered showers across
portions of eastern Puerto Rico and the USVI during the morning
hours followed by some afternoon convection across the southwestern
quadrant of Puerto Rico. No significant rainfall accumulations are
expected.

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

At the surface, a frontal boundary will continue to approach the
islands from the west as a surface high pressure enters the
western Atlantic Ocean by Tuesday. This frontal boundary will
stall north of the region until it dissipates or moves away. Winds
will reinforce Tuesday and Wednesday as the high pressure builds
north of the region tightening the local pressure gradient. During
this period, the typical weather pattern will persist each day,
with cool advective-pattern overnight and early in the morning,
followed by afternoon convection across the interior and western
portions.

On the other hand, an amplifying mid to upper-level trough will
enter the western Caribbean by Tuesday. It will slowly amplify
over Cuba/Jamaica early next week until its axis position near
the Hispaniola by the second part of the next week. Exist some
discrepancies between GFS and ECMWF about the final location and
strength of this atmospheric feature. Therefore, we decide to wait
(until models agree about these aspect) to include thunderstorm
activity in the forecast package. However, an unstable-weather
pattern is possible Thursday and Friday, or even Saturday, if this
trough aloft lingers to the west of Puerto Rico and the U.S.
Virgin Islands (over the Hispaniola).

&&

.AVIATION...

Mainly VFR conditions expected across the area. Sct SHRA possible
across northwest PR between 06/17z and 06/22z, affecting the
vicinity of TJBQ with brief MVFR conditions possible. Winds will
remain light and variable through 06/12z, increasing to the E-ESE
between 10 and 15 kts with sea breeze variations after 06/14z.

&&

.MARINE...

Expect reasonable quiet marine conditions through early next week,
with an east to southeast wind flow up to 15 knots and seas below
5 feet. However, local effects could increase winds between 15 and
20 knots, especially during the afternoon hours. Seas and winds
will increase early next week due to the combination of the
arrival of a northerly swell and stronger winds. These conditions
could result in hazardous marine conditions during the first part
of next week.

Beachgoers, a moderate risk of rip currents is in effect for the
north and east facing beaches of Puerto Rico and the U.S. Virgin
Islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 73 87 75 / 10 20 20 20
STT 85 74 85 73 / 10 20 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
423 AM AST Sun Mar 7 2021

.SYNOPSIS...

Expect another fair weather day, but with above-normal
temperatures due to an east-southeast wind flow. A transition to
an unstable weather pattern is forecast for the second part of
next week with the proximity of a mid to upper-level trough. A
northerly swell will deteriorate marine conditions Tuesday and
onward.

&&

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

The combination of a surface high pressure located across the
central Atlantic and a frontal boundary stalled well northwest of
the region will continue to result in an east-southeast flow for
today. Therefore, above normal temperatures are expected once again
across coastal locations with highs in the upper 80s to near 90
degrees. Another fair weather day is also expected, similar to
yesterday, as a trade wind cap will once again limit shower
activity. However, isolated to widely scattered showers cannot be
ruled out across portions of northwestern Puerto Rico this afternoon
due to local and diurnal effects.

On Monday, an induced surface trough will develop just east of the
area. This feature will cause the low-level winds to switch to the
east-northeast. Some patches of low-level moisture will also move
across to result in isolated to widely scattered brief showers
across portions of eastern Puerto Rico and the USVI during the
morning hours with shallow afternoon convection across southwestern
Puerto Rico. Rainfall accumulations for the most part will be light.

By Tuesday, the low-level winds are expected to increase to near 20
knots from the east-northeast as the local pressure gradient
tightens in response to a surface high pressure moving across the
western Atlantic. This will result in a cool advective pattern
across the region with trade wind shower activity expected, with the
highest concentration across the local waters as well as across
portions of eastern Puerto Rico and the USVI. Western Puerto Rico
may observe some activity during the afternoon hours. Given the fast
moving nature of these showers, rainfall accumulations will remain
limited.

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

An old cold front will linger north of the islands, promoting
moisture pooling over the region on Wednesday. The frontal
boundary will linger off to the north until it dissipated or
lifted away from the northeast Caribbean. Behind the front, a
surface high-pressure will move eastward across the western
Atlantic and will build across the central Atlantic throughout the
week. This high-pressure will increase local winds Wednesday and
Thursday, diminishing Friday into the weekend.

On the other hand, an amplifying mid to upper-level trough over
Cuba/Jamaica will approach PR/USVI weakening the ridge aloft. It
will cross the western Caribbean until its axis re-locate near the
Hispaniola by the second part of the week. They are some
discrepancy between the solutions of GFS and ECMWF. However,
they are consistently indicating an unstable weather pattern
Thursday through Sunday.

&&

.AVIATION...

VFR conditions to prevail throughout the period. Iso-Sct SHRA may
affect NW PR between 07/17z and 07/22z, however, no impacts to
area terminals expected at this time. Light and variable winds
through 07/12z, increasing to 10 to 15 knots from the E-ESE after
07/14z with sea breeze variations.

&&

.MARINE...

Tranquil to slightly choppy seas will prevail through early this
week. Mariners can expect seas up to 5 feet and winds around 15
knots. However, they should exercise caution across the Atlantic
Offshore waters and Anegada Passage due to seas up to 6 feet and
winds between 15 and 20 knots, respectively. Seas will become
hazardous across the Atlantic Waters and Caribbean Passages as a
northerly swell reach the local area. These conditions should last
through most of the work-week.

Beachgoers, a moderate risk of rip currents will continue for most
north and east-facing beaches in Puerto Rico and the U.S. Virgins
Islands through at least Monday. Then, the risk will become high
with the arrival of the northerly swell Tuesday and onward. Please
remain vigilant of the surf zone conditions to avoid a tragic
event.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 75 86 74 / 10 20 20 30
STT 86 74 85 72 / 10 40 40 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
429 AM AST Mon Mar 8 2021

.SYNOPSIS...

Relatively fair and stable weather conditions will prevail through
the middle of the week. An induced surface trough will end the
stable weather conditions and increase moisture content and shower
activity. A northerly swell will cause hazardous seas starting on
Tuesday. Late this week into the weekend looks unsettled as an
upper-level trough moves near the area and increases instability
and moisture content.

&&

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

A surface low pressure north of the local area is moving quickly to
the north as a surface high pressure enters the western Atlantic. As
the surface low moves north, its associated cold front will get a
little closer to the local islands, but will remain offshore and it
is not expected to directly impact the local islands in the short
term period, though it will cause slightly higher moisture than
normal over the local Atlantic and the waters west of PR. The
surface high pressure that will enter the western Atlantic over the
next few days, will gradually cause ENE winds by this afternoon and
then tighten the local pressure gradient, causing breezy conditions
for Tuesday in particular. In the mid to upper levels, there is a
broad trough that could cause an enhancement in shower activity over
PR this afternoon, but the mid to upper level trough will lift and
weaken over the local area by Tuesday and Wednesday, causing less
instability over the local area. As far as temperatures go, a return
to near normal temps are expected, with high temps in the mid 80s
across the lower elevations once again.

For today, overall near to slightly below normal moisture is expected
across the islands, with the exception of the western portions of
the local forecast area. This means that isolated to scattered brief
showers are to be expected over the local waters, USVI and eastern
PR in the morning, while central to western PR is forecast to have
locally induced showers, aided by slightly higher moisture and mid
to upper level trough. These showers are expected to produce more
rainfall accumulations and could cause minor ponding in poor
drainage areas.

For Tuesday, the sfc high pressure will tighten the pressure
gradient, causing breezy conditions with E to ENE winds up to
around 20 mph. This will result in brief trade wind showers once
again in the morning, affecting mainly the USVI and eastern PR.
That said, in the afternoon, especially past the middle afternoon
hours, locally induced showers could develop across western PR as
well, but the winds should be enough to cause the showers to move
quickly and therefore not expected to cause too much accumulation.

By Wednesday, the frontal boundary to our northwest could start
losing definition and will start fragmenting. This will cause higher
moisture to move into the local waters and western PR by Wednesday
afternoon and Wednesday night. This could then cause shower activity
across western PR in the afternoon, and widely scattered showers
over the local Atlantic waters during the night.

&&

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

Global models are in reasonably good agreement on the evolution
of the long-term period. An old frontal boundary washes out
northwest of Puerto Rico through the middle of the work week.
East to northeast winds will advect pockets of moisture from the
Atlantic waters over the local area periodically. The near-normal
moisture coupled with local and diurnal effects will induce
isolated to scattered showers during the afternoons over portions
of northwestern Puerto Rico. A surface-high pressure re-establishes
itself over the Atlantic waters and increases local winds through
Friday.

Late this week, the EURO and GFS model deepens an upper-level
trough north of Puerto Rico this weekend as several short-waves
and a mid-level low round the base of the trough. Guidance puts
Puerto Rico in the right entrance of the trough Sunday into
Monday. Relatively humidity in the mid to upper-level will range
from 30 to 60 percent, the highest values during the forecast
period, and 500 mb heights will range from -8 to -11 degrees
Celsius. The upper-level instability and meager mid to upper-level
moisture coupled with local effects will cause isolated to
scattered showers during the weekend. The instability and diurnal
heating could support isolated thunderstorms development across
the outer Atlantic Waters and portions of northwestern Puerto
late this week into the weekend. Weather conditions are forecast
to improve early next week when the trough lifts north of the
region.

&&

.AVIATION...

VFR conditions to prevail through the forecast period.
Brief VCSH could affect the IST/ISX and JSJ terminals this morning.
However, no significant hazards are expected across the local
terminals. Light and variable winds through 08/14Z, increasing to 10
to 15 knots from the E-ENE thereafter with sea breeze variations.

&&

.MARINE...

Choppy conditions are expected across the outer Atlantic waters
with seas up to 6 feet. Small craft operators should exercise
caution due to seas up to 6 feet. Relative tranquil marine
conditions are expected elsewhere with seas up to 5 feet. There
is a moderate risk of rip currents across northern sections of
Puerto Rico, all the eastern beaches of Vieques and Culebra, as
well eastern tip of St. Croix. Winds will be from the east ranging
from 10 to 15 knots with higher gusts.

A northerly swell will move into the outer Atlantic waters on
Tuesday and cause hazardous marine conditions with seas up to 8
feet. Small Craft Advisory goes in effect Tuesday morning due to
the hazardous seas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 74 84 73 / 20 20 20 40
STT 85 72 84 73 / 30 30 30 40

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
452 AM AST Tue Mar 9 2021

.SYNOPSIS...

Relatively fair and stable weather conditions with isolated
showers will prevail today. The proximity of a frontal boundary
will increase moisture content tomorrow through Thursday. Late
this week into the weekend looks unsettled as an upper-level
trough moves near the area and further increases instability and
moisture content. A northerly swell will cause hazardous seas
starting today.

&&

SHORT TERM...Today through Thursday...

A surface high pressure is entering the western Atlantic, and a cold
front just northwest of the local islands will remain offshore and
it is not expected to directly impact the local islands today.
However, the frontal boundary will get sheared off and will
fragment by Wednesday, which will cause moisture to increase on
Wednesday into Thursday. The surface high pressure that is
entering into the western Atlantic will cause ENE winds today as
it tightens the pressure gradient, causing stronger winds this
afternoon and tonight into Wednesday. In the mid to upper levels,
a trough will approach the local area for Thursday, which will
enhance the chances for isolated thunderstorms on Thursday
afternoon over western PR. As far as temperatures go, near normal
temps are expected, with high temps in the mid 80s across the
lower elevations.

For today, the sfc high pressure will gradually tighten the pressure
gradient, causing ENE winds up to around 20 mph. This will result in
brief trade wind showers once again in the morning, affecting mainly
the USVI and eastern PR. That said, in the afternoon, the hi-res
model guidance suggests that showers will affect the eastern and
southern coastal municipalities, but past the mid-afternoon hours, a
few showers could also affect the eastern to western interior
sections of Puerto Rico, though accumulations are not expected to
cause significant hazards due to sfc-3km mean wind being nearly 20
knots according to the forecast soundings. That said, the global
models do not share this rainfall solution, but given the recent
model performance, we gave some consideration to the hi-res models,
though toned down the total amount of rain.

For Wednesday and Thursday, the frontal boundary to our northwest
could start getting sheared, losing definition and will become
fragmented. This will cause higher moisture to move into the local
waters and western PR by Wednesday afternoon and Thursday. This
could then cause shower activity across western PR in the afternoon
Wednesday , and widely scattered showers over the local Atlantic
waters during the night. By Thursday, a trough in the mid and upper
levels may cause some instability in the local area, and isolated
thunderstorms were added to the forecast for Thursday afternoon
across western PR.

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

According to model guidance weather conditions will become wetter by
the end of the workweek through the weekend. An old frontal boundary
and an easterly disturbance will continue maintaining a high
moisture content at lower levels over the forecast area on Friday.
GFS suggests precipitable water content increasing up to 1.5
inches through at least late Saturday night. In addition, weather
conditions aloft will become conducive for convective development
as the divergent side of a building polar trough settles over
Puerto Rico and U.S. Virgin Islands early Friday through at least
Sunday. In the meantime, a mid level short wave trough over the
central Atlantic will move southward and settle over the local
area on Friday before exiting the area late Sunday night. This
will set a colder air pattern aloft with 500 mb temperatures
cooling to -12 degrees celsius between Friday and late Saturday
night.

This combination will produce an increase in areal coverage of
shower activity. The instability and diurnal heating could
support isolated thunderstorm development across the outer
Atlantic Waters and, with an east southeasterly wind flow,
portions of northwestern Puerto Rico between Friday and late
Saturday night. However, latest GFS shows the presence of drier
air within the 850-700 mb layer that could suppress convection and
possibly limit shower activity. Nevertheless, even with the
presence of this layer of drier air, models are in agreement that
environmental conditions will be somewhat favorable to support
enhanced shower activity by the end of the workweek into the
upcoming weekend. Showers that develop could cause urban and small
stream flooding and ponding of water on roadways. By Sunday and
early next week, the mid short wave trough and polar trough are
expected to move eastward as a mid to upper level ridge is
forecast to move in from the west. This will re-establish the
trade wind cap with weather conditions improving through the long
term forecast.


&&

.AVIATION...VFR conditions to prevail through the forecast period.
Brief VCSH could affect the IST/ISX and JSJ terminals this morning.
However, no significant hazards are expected across the local
terminals. Light and variable winds through 09/14Z, increasing to 10
to 15 knots and gusty from the ENE thereafter with sea breeze
variations. VCSH possible at TJPS after 09/16Z.


&&

.MARINE...

A northerly swell will move across the Atlantic waters and spread
into the local waters and passages today. Therefore, choppy and
hazardous marine conditions will continue across most of the local
waters, with seas between 5 to 10 feet and winds up to 20 knots
from the E-NE. Small craft advisory is in effect starting today for
most of the local waters. A high risk of rip current will come
into effect today for all the northern coast of Puerto Rico,
Culebra and St. Thomas.

&&

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

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
Issued by National Weather Service Melbourne FL
615 AM AST Wed Mar 10 2021

.SYNOPSIS...Isolated to scattered shower activity across the area to
include the local coastal waters early this morning. Brief gusty
winds and downpours the main threats. The pressure gradient remains
tight with conditions breezy at times with easterly flow in the low-
levels. The proximity of a frontal boundary to the north combined
with some energy aloft and deep moisture will continue to provide a
focus for scattered showers through Friday. The pattern is expected
to remain unsettled into this weekend as an upper trough moves
across the area. A northerly swell will continue to cause hazardous
seas through at least Thursday afternoon.

SHORT TERM...Today through Friday...A weak east-west oriented
frontal boundary is depicted north of Puerto Rico on the most recent
surface analysis. Combined with some energy aloft and deep moisture,
isolated to scattered shower activity will remain in the forecast.
These will be the typical morning showers over the eastern coasts of
the islands and northern PR, reaching the western PR coast in the
afternoon. A fairly tight pressure gradient will keep continued
brisk easterly flow each afternoon with some lighter wind speeds
during the evening and overnight periods, especially away from the
coasts. Highs generally in the low to middle 80s across the lower
elevations and 70s across the higher terrain areas. Overnight lows
will range from the low 60s across the interior with upper 60s to
lower 70s near the coast.

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

The upper-level ridge over the eastern half of CONUS and into the
western Atlantic will continue to build. As the strong ridge and
associated surface high continue to build, it will push an upper-
level shortwave trough south and closer to Puerto Rico. As the
shortwave approaches the region, showers will increase in coverage,
especially during the afternoon hours with diurnal effects helping
increase the coverage of precipitation over the region. Scattered-to-
numerous showers and thunderstorms will develop on Saturday over
Puerto Rico with isolated showers possible over the Virgin Islands.
With little to no instability forecast, low lapse rates, and a lack
of forcing, thunderstorms are expected to be weak and isolated.

The upper-level trough will continue to meander around the islands
as it fills and weakens through the weekend. This means showers will
stick around, but the chance for precipitation will be slightly
lower on Sunday as the upper-level shortwave weakens. Temperatures
will continue to be relatively consistent and near normal with highs
in the low-to-mid 80s with cooler temperatures in higher elevations
where highs will only reach the mid 60s to mid 70s. Lows will drop
down into the upper 60s to low 70s with cooler temperatures in the
mountains with lows in the low-to-mid 60s.

As we head into the workweek, the chance for precipitation will
decrease as an upper-level ridge weakens and moves east over the
area with a more zonal upper air pattern setting up. Diurnally
driven showers will be possible through mid-week with east-
northeasterly flow. Temperatures will remain consistent with near
normal highs in the low-to-mid 80s with much cooler conditions at
higher elevations with temperatures in the upper 60s to low 70s.
Lows will be in the upper 60s to mid 70s with lower temperatures in
mountainous regions where temperatures will drop down into the low-
to-mid 60s.

&&

.AVIATION...Passing showers will continue early this morning into
the rest of today, though VFR conditions are expected to persist.
Coverage and intensity of showers is low at the moment, with any
passing shower leading to a brief reduction in visibility. Not
expecting to need TEMPO groups for stronger showers until perhaps
this afternoon when coverage of showers increase on parts of the
island.

&&

.MARINE...Current-Friday night...A weak frontal boundary remains
north of PR keeping conditions rather unsettled. Isolated to
scattered shower activity currently across the local waters with
this trend continuing through late work-week. A northerly swell
continues to move across the local waters and passages and will
produce choppy and hazardous marine conditions. A Small Craft
Advisory remains in effect through Thursday afternoon. A high risk
of life-threatening rip currents will be in effect for today and
tonight, possibly into Thursday for all the northern (NW/NE too)
coasts of Puerto Rico, Culebra and St. Thomas. Entering the
waters at the beach is not advised.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 84 72 / 40 30 30 20
STT 83 73 84 72 / 30 30 10 10

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
401 AM AST Thu Mar 11 2021

SYNOPSIS...

Isolated to scattered showers over interior and western Puerto
Rico during afternoon hours. Elsewhere, mainly fair weather
conditions will prevail today. The weather pattern is expected to
remain unsettled on Friday into this weekend as an upper trough
moves across the area. A northerly swell will continue to cause
hazardous seas through at least Saturday.


&&

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

A surface high pressure across the western Atlantic will continue to
generate easterly winds across the local area today. However, this
high pressure will weaken and move west on Friday and Saturday,
causing lighter and E-SE winds on Friday, and much lighter winds and
somewhat variable on Saturday. The expected wind flow, combined with
drier than normal airmass will result in fair weather in the
morning, but the local effects may cause locally induced shower
activity across western and the interior of PR in the afternoon.
Some of the showers could produce ponding of water in areas of
poor drainage. For Friday, a mid and upper level trough approaches
the area from the northwest. The proximity and location of the
mid and upper level troughs will increase instability. In
Addition, the 500mb temps will be cooler than normal, ranging from
-8C to -11C on Friday and Saturday, plus divergence is expected
in the upper levels due to stronger winds aloft. This combination
will result in better potential for more widespread shower
activity on Friday and Saturday with the potential of isolated
thunderstorms. One thing to note, is that the winds will be very
light on Saturday, which puts higher than normal uncertainty on
exactly where the afternoon convection will commence as well as if
and how the outflow boundaries of the showers that do develop
will aid in the development of additional showers as the afternoon
progresses.

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

By Sunday and early next week, the upper short wave trough is
expected to weaken as it moves eastward into central Atlantic while
a mid to upper level ridge is forecast to move in from the west and
persists through the long term forecast. At low levels, the
associated surface high pressure over Western Atlantic will move
eastward and settle north of the area through the long term forecast
period. This will re-establish the trade wind cap with improving
weather conditions.

However, as the weather pattern transitions on Sunday, lingering
moisture along with locally induced effects will produce shower
development over the area, especially during afternoon hours. The
surface high pressure to the northwest will continue promoting an
east northeast wind flow over the region focusing shower activity
over the southwestern quadrant of Puerto Rico. Weather conditions
aloft will be less conducive for thunderstorm development than
previous days according to both GFS and ECMWF models, therefore
expect morning isolated to scattered showers over USVI and eastern
Puerto Rico following with scattered to numerous showers over
southwestern Puerto Rico in the afternoon with some showers over
the local waters as evening approaches. Minor urban and small
stream flooding as well as ponding of waters on roadways and in
poor drainage areas will remain possible in isolated areas.

Monday, relatively fair weather conditions can be expected as the
surface high pressure moving eastward north of the region pushes
drier air across much of northeastern Caribbean. GFS suggests
precipitable water values to drop close to an inch or below
throughout the day. However, isolated showers cannot be ruled out.
Patches of moisture from the remnants of the upper short wave trough
well northeast of the region will be advected from time-to-time by
the easterly trades. A strong cap is forecast to remain in place,
thus, the pulses of moisture will be shallow in nature. All in all,
expect mainly fair weather conditions with shallow areas of moisture
embedded in the easterly wind flow reaching the islands from time-to-
time causing light passing showers across PR and USVI.

&&

.AVIATION...VFR conditions expected to prevail through the forecast
period. Light and variable or easterly winds expected through
11/13Z, with easterly winds increasing to 10-15KT with occasional
gusts thereafter. Skies should remain mainly FEW/SCT. VCSH is
possible in the late afternoon hours across TISX, TJPS and TJBQ


&&

.MARINE...A northerly swell and enhanced winds will continue to
result in hazardous marine conditions. Therefore, Small Craft
Advisories are in effect through at least early in the weekend,
due to seas 6 to 10 feet, especially across the Atlantic waters
and passages.

For the beaches, a high rip current risk is in effect for the
north facing beaches of Puerto Rico, Vieques, Culebra and for all
the U.S. Virgin Islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 72 84 72 / 20 30 30 10
STT 84 72 83 71 / 20 40 30 10

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
325 AM AST Fri Mar 12 2021

.SYNOPSIS...Conditions are expected to become more unstable today and
Saturday as a mid and upper-level trough sets up just north of the
area. This along with near normal moisture will result in shower and
isolated thunderstorm activity during the afternoon hours mainly
across interior and western portions of Puerto Rico. Weather
conditions improve late in the weekend into early next week as the
trough aloft pulls away and a ridge aloft builds in, resulting in
drier and more stable conditions.

&&

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

A surface high pressure across the western Atlantic is weakening as
it drifts west, which is weakening the local pressure gradient. This
will cause lighter and E-SE winds today, and much lighter winds and
somewhat variable on Saturday. For Sunday, the light winds will
continue, but will be more northerly as a surface high pressure
enters the western Atlantic once again. Mid level and upper level
troughs will be present just to our northwest today and Saturday,
with stronger winds aloft north and east of the local area. This mid
and upper level features will cause instability and divergence in
the upper levels. Also, the mid level temps will cool to about -11C
or so, which is cooler than normal. All this translates to an
enhanced chance of showers and thunderstorms, especially in the
afternoon hours over Puerto Rico when the instability combines with
the diurnal heating and local effects. For that reason, we have
thunderstorms in the forecast for this afternoon and Saturday
afternoon over portions of Puerto Rico. Given the very light winds,
the showers will not be moving much, and there may be persistent
rainfall over any one area, therefore there is a chance for urban
and small stream flooding this afternoon and Saturday afternoon.
That said, the rest of the local area should remain with mainly
isolated to scattered showers. The more significant rainfall is
expected over the interior sections of Puerto Rico and adjacent
areas, while the rest of the local area is expected to observe more
benign weather, though moderate scattered showers are expected.

For Sunday, drier air moves in, winds becomes northerly, and the mid-
upper level troughs will lift, leaving mainly zonal flow and less
instability. With that, mostly fair weather would be expected across
the local area. Since the northerly wind will still be relatively
light, the sea breeze convergence and diurnal heating over Puerto
Rico on Sunday afternoon can still cause brief convection over the
southern slopes into south central Puerto Rico, so scattered showers
are in the forecast, but mainly fair weather is expected elsewhere.

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

Monday starts dry with a weak mid level ridge over northwestern
Caribbean and the associated surface high pressure just east of
southern Florida. Throughout the forecast period the mid level ridge
will build and settle over the forecast area re-establishing the
trade wind inversion cap promoting stable conditions aloft. In the
mean time, at low levels, the surface high pressure will slowly move
eastward from western Atlantic while the pressure gradient tightens
promoting breezy conditions over the area. While doing so, the
induced northeast wind flow will push the remnants of an old frontal
boundary over Puerto Rico and USVI between late Monday into Tuesday.
According to GFS, precipitable water values will increase from less
than an inch up to 1.3 inches through early Tuesday. This surge of
moisture will increase cloudiness with passing showers during
overnight hours into Tuesday morning, especially over the local
waters, USVI and northeastern Puerto Rico. No significant rainfall
accumulations are expected with the passage of this old frontal
boundary since moisture will be confined below the 700 mb layer.

Tuesday afternoon could observe an increase in showers due to
locally induced effects over the Cordillera and southwestern
portions of Puerto Rico. However, stable weather aloft will limit
significant rainfall accumulations, though ponding of water in
isolated areas cannot be ruled out. For the rest of the workweek,
weather conditions look fairly stable with precipitable water
content further declining below to an inch through Friday. Although
mainly fair weather conditions are expected to hold for the
remainder of the forecast period, pulses of shallow moisture
embedded in the trades will slightly increase cloudiness with
possible isolated showers over the area, especially if combined
with local effects during afternoon hours.


&&

.AVIATION...VFR conditions expected to prevail through the morning
hours, but VCSH is expected at TJSJ and TIST in the morning. Light
and variable or easterly winds expected through 12/13Z, with
easterly winds increasing to 10-15KT thereafter. Skies should remain
mainly FEW/SCT over the local terminals, but SHRA/TSRA and OVC skies
expected in the interior of PR causing mountain obscurations. VCSH
or VCTS is possible in the afternoon hours for TJPS and TJSJ.


&&

.MARINE...A fading northerly swell will continue to result in
choppy to hazardous seas between 5 and 8 feet across the Atlantic
waters and local passages into Saturday. Across the rest of the
local waters, seas of less than 5 feet are expected. For
beachgoers, a high risk of rip currents continues for the north-
facing beaches of Puerto Rico and Culebra.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 72 85 72 / 50 10 30 30
STT 84 71 84 71 / 30 30 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Sat Mar 13 2021

.SYNOPSIS...
The combination of the local effects and the upper level trough
will maintain unstable weather for today. Therefore, scattered to
numerous showers will affect Puerto Rico and the U.S. Virgin
Islands, mainly in the early afternoon hours. Urban and small
stream flows are expected with the heaviest activity. Hazardous
marine conditions will continue across the offshore Atlantic
waters as a fading northerly swell continues to affect the local
waters with seas up to 7 feet. Therefore, a Small Craft Advisory
will remain in effect for that area until late this evening.

&&

.SHORT TERM...Today through Monday...
A mid to upper level trough will linger across the region today,
then gradually lift northwards Sunday through Monday while weakening.
An induced low level trough will persist across the area to maintain
good moisture convergence along with the unstable conditions aloft.
This in combination with the light low level winds and local effects
will favor another day of enhanced afternoon shower activity, mainly
over the interior and portions of southwest Puerto Rico. Due to the
light winds, any afternoon showers that do develop will be slow
moving. This may lead to minor urban and small stream flooding in
isolated areas, as well as ponding of water on roadways and in poor
drainage areas.

Overall, a fairly moist and unstable environment will persist into
early Sunday due to the proximity of the mid to upper-level trough
,as well as the induced low level trough. The low to mid level moisture
pooling along with favorable conditions aloft and local effects will
support the development of enhanced afternoon showers, with a good
chance for isolated thunderstorms, mainly over portions of the central
interior and southwest Puerto Rico. As previously mentioned, due
to the light winds, the afternoon convection should eventually spread
north and south of the central interior and affect some of the
surrounding municipalities including areas around the San Juan metro.
Some of this activity may lead to urban and small stream flooding
as well as ponding of waters on roadways and in poor drainage areas
due to periods of locally heavy rains. Fewer shower activity is forecast
for the U.S. Virgin Islands today and for the rest of the rest of
the weekend. However periods of isolated showers will remain possible
along the coastal areas during the morning hours, followed by lesser
activity during the afternoon.

Sunday through Monday an overall improvement is forecast as the
upper trough is to lift northwards while the associated low level
trough weakens along with the erosion of low level moisture. In the
meantime, a surface ridge will build across the west and southwest
Atlantic and further induce a light to moderate northeast wind
flow. The winds will continue to increase late Sunday through Monday
as the local pressure gradient tightens. Periods of passing trade
wind showers carried by the northeast trades should affect parts of
the north and and east coastal areas during the overnight and morning
hours, followed by isolated to scattered afternoon showers, mainly
focused over parts of the central interior and southwest sections
of Puerto Rico. Any shower activity over the U.S. Virgin islands
should be mainly downwind or on the west end of the islands during
the afternoon hours.

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

On Tuesday, a mid-level ridge located at the western Atlantic and
the associated surface high pressure will promote tightening in
the pressure gradient and a north-northeasterly wind flow over the
local area. This wind flow will push a fragment of moisture over
the region, increasing the potential for cloudiness and isolated
shower activity on Tuesday afternoon. On late Tuesday into
Wednesday, as the surface high pressure moves into the central
Atlantic, the wind flow will push the remnants of an old front in
the region. According to model guidance, precipitable water
values would fluctuate between 1.0 to 1.3 inches. This increase in
moisture combined with the breezy conditions will promote
cloudiness and passing isolated showers mainly due to the stable
conditions aloft. Therefore, ponding waters is possible with the
heaviest activity, specifically over southwestern sections of
Puerto Rico. Also, across the U.S. Virgin Islands, some passing
showers in the morning hours could be possibles, but mainly fair
weather conditions in the afternoon hours.

A slightly fair weather pattern will prevail on Thursday into
Friday as the surface ridge moves into the central Atlantic and
dominates the region. Given the expected wind flow and the clear
skies due to the lack of moisture, daytime temperatures may be
colder for the forecast area. On Saturday, as the elongated high
pressure located over the eastern tip of the Atlantic moves out,
lingering moisture from an old front will reach the local area
embedded in the trade wind increasing the potential for a shower
activity. However, at this moment, not significant rainfall
accumulations are expected.

&&

.AVIATION...
SCT SHRA over the regional waters and local flying area
btw islands til 13/14Z. SCT-BKN lyrs NR FL025...FL050..FL080 til
13/4Z. FM 13/16Z-23Z Isold TSRA psbl mainly ovr ctrl MTN range and
SW quad of PR with VCSH at TJSJ/TJPS/TJMZ. Isold SHRA psbl
elsewhere. L/lvl wnds lgt but mainly fm NE 5-10 kts BLO FL120....
bcmg WSW and incr w/ht abv with 70-80 kts max wnd nr FL300. Sfc
winds calm to LGT/VRB bcmg fm NNE around 10 kts aft 13/14z.


&&

.MARINE...
Choppy and hazardous marine will continue over the local Atlantic
offshore waters, and local passages as a fading northerly swell
continue to affect the local waters. Winds will decrease and
fluctuate from light to gentle during the next several days.
Scattered to numerous showers with isolated thunderstorms may
affect the local waters today and possibly early Sunday, creating
hazardous marine conditions. Improving conditions are expected
thereafter, with seas up to 6 feet and wind up to 20 knots. Another
northerly swell is however expected to reach the local waters on
Wednesday, bringing choppy seas to the local waters and passages
once again.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 83 73 / 30 50 40 30
STT 83 72 83 72 / 20 30 30 10

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
449 AM AST Sun Mar 14 2021

.SYNOPSIS...

The combination of enough moisture and the influence of an upper
level trough will maintain unstable weather conditions once again
today. A building high pressure located over the western Atlantic
will promote a light to moderate north- northeasterly wind flow
over the local area. Therefore, afternoon convection should be
focused mainly over the interior and southwestern sections of Puerto
Rico and surrounding municipalities. Choppy marine conditions will
persist across the Atlantic offshore waters with seas up to 7 feet
until early this morning, followed by seas between 3-6 feet for the
local waters and passages during the rest of the day.

&&

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

A mid to upper level trough will continue to gradually lift
north and west of the region today through Monday while weakening.
An induced low level trough and weak area of low pressure northeast
of the region, along with a surface high pressure ridge building
across the southwest Atlantic, will induce a north northeast
windflow across the local area. This dominant flow will continue
to push moisture fragments from an old frontal boundary/shear line
across the region during the rest of the morning hours. For the
rest of the day, the available moisture along with the proximity
of the upper trough and local effects will aid in afternoon shower
development mainly over the central interior and the southwestern
quadrant of Puerto Rico. As a result, minor urban and small stream
flooding, as well as ponding of water on roadways and in poor drainage
areas will remain possible in these areas. Isolated showers of short
duration will be possible elsewhere including in and around the U.S.
Virgin Islands, but no significant rainfall accumulations are
anticipated.

By Monday and Tuesday an overall improvement is forecast as the
upper trough weakens and a mid level ridge builds across the
region. This will favor more stable condition aloft along with
the erosion of low level moisture. In the meantime, a surface
ridge will continue to build across the southwest Atlantic and
further induce a moderate north northeast wind flow which will
continue to increase through the period as the local pressure
gradient tightens.

Another band of trade wind moisture from an old shearline is
however forecast to sweep across the region late Monday through
Tuesday. This should bring brief intervals of morning showers
across portions off the coastal areas of the islands,followed by
isolated to scattered afternoon convection mostly over parts of
southwest Puerto Rico and downwind of the remaining islands mainly
due to local and diurnal effects. No significant rainfall accumulations
are expected at this time. Mostly fair weather skies should prevail
during the day with moderate northeasterly trades and breezy conditions
along the coastal areas.

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

The first half of the long term period starts with a dry pattern.
A mid to upper level ridge and the associated surface high
pressure will dominate the region, along with a drier air mass
moving over the area. According to model guidance, precipitable
water values will fluctuate between 0.90 to 1.2 inches on Wednesday
into Friday. As the ridge moves more eastward, a northeasterly
wind flow will dominate the region. This wind flow will push the
shower activity, if any, over the southwestern quadrant of Puerto
Rico each afternoon.

On Saturday into Sunday, as the high surface pressure moves more
to the eastern Atlantic, patches of moisture will filter the
area. This increase in humidity will slightly enhance the
potential for shower activity in the afternoon hours. Therefore,
mainly fair weather conditions are expected, with a few passing
showers over interior and northwestern sections of Puerto Rico in
the afternoon hours. At this moment, if model guidance is correct,
Sunday looks like the wettest day for the long term period.
Additionally, a southeasterly component in winds is forecast on
late Saturday through Sunday. This wind flow will promote warmer
temperatures over the region.

&&

.AVIATION...Wdly SCT SHRA over the regional waters and local
flying area til 14/14Z with SCT-BKN lyrs NR FL025...FL050...FL080.
FM 13/17Z-23Z Isold SHRA psbl mainly ovr ctrl MTN range and SW
quad of PR with VCSH at TJSJ/TJPS/TJMZ til 14/22Z. Isold SHRA
psbl elsewhere. L/lvl wnds lgt fm NNE 5-15 kts BLO FL100.... bcmg
SW and incr w/ht abv with 65-70 kts max wnd nr FL350. Sfc winds
LGT/VRB bcmg fm NNE 10 to 15 kts aft 14/14z.

&&

.MARINE...
Choppy marine conditions will prevail over the offshore Atlantic
waters with seas up to 7 feet the Atlantic offshore waters as a
fading northerly swell continues to invade the local waters.
Recent marine ship observations report 5 to 7 feet over the
offshore Atlantic Waters. Therefore, a small craft advisory is in
effect for these waters. Elsewhere, seas will range between 3 to
6 feet and wind up to 15 knots. That said, small craft operators
should exercise caution. Improving conditions will continue for
the rest of the day into tomorrow before another northerly swell
moves into the local waters. They were isolated to scattered
showers in the forecast for today as an unstable condition
prevailing over the region.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 74 85 72 / 40 30 30 30
STT 84 73 84 73 / 30 20 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
456 AM AST Mon Mar 15 2021

.SYNOPSIS... A light to moderate north northeast wind flow will
prevail as a strong surface high pressure ridge will build across
the southwest Atlantic and north of the region during the next few
days. A mid-level ridge will strengthen across the region resulting
in increasing stability aloft. Shallow moisture carried by the
prevailing northerly winds will move across the region and result
in periods of passing clouds and showers. This will affect portions
of the north and east coastal areas of the islands during the mornings,
followed by locally and diurnally induced afternoon showers. A gradual
drying trend is anticipated by mid week as a high pressure system
will establish and remain the dominant feature. Another surge of
moisture is however forecast by the latter part of the week, resulting
in more frequent passing showers. A northerly swell is also expected
to invade the local waters by late Tuesday night.

&&

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

A mid to upper level ridge and the associated surface high pressure
will dominate the region for the next several days as the ridge
moves eastward today, fragments of moisture embedded in the
northeasterly winds will maintain the potential for some passing
showers over the local region. According to GOES-16, precipitable
water values today are fluctuating between 0.90 to 1.1 inches over
the forecast area. Additionally, the surface ridge will also gradually
tighten the pressure gradient, causing winds to around 20 mph over
the local waters and cooler temperatures over the region for the
next several days. On Tuesday, mainly fair weather conditions will
prevail over the region as a drier airmass filter into the region.
In combination with stable conditions aloft, this will result in
clear to partly cloudy skies in the morning hours and mostly sunny
with a few passing showers in the afternoon hours, mainly over
western sections of Puerto Rico, due to the local effects. In
general, Tuesday will be the driest day of the short-term forecast.

On Wednesday, the pattern changes as the surface high pressure
enters the central Atlantic and pushes moisture remnants from an
old frontal boundary across the region. This additional moisture
will increase the potential for shower activity, mainly in the
afternoon hours due to the local effects. The expected shower
activity at this moment should not be significant due to the
stable conditions aloft. Therefore, only ponding of water in
roadways and poor drainage areas will be possible with the
heaviest activity.

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

The first half of the long term period starts with a drying trend
once again, as low level moisture will erode and the mid to upper
level ridge and associated surface high pressure will dominate
local weather pattern along with a drier air mass. So far model
guidance continued to suggest precipitable water values between
0.90 to 1.2 inches through Friday, as the surface ridge moves
further eastward and winds become more northeast to east. This
wind flow will however aid in bringing periods of passing showers
to the coastal areas during the overnight and early morning hours,
followed by some afternoon shower activity which should be focused
over the west and southwestern portions of Puerto Rico each afternoon.
Limited or no significant shower activity forecast elsewhere.

On Saturday and into Sunday, as the high surface pressure moves
into the east and central Atlantic, patches of moisture will
continue to filter the area but will be less frequent as the
local pressure gradient will loosen and winds will veer becoming
more east southeast while diminishing. Consequently, some weak
troughiness will establish across the area thereafter and bring a
gradual increase in low level moisture, as well as warmer daytime
temperatures. From Sunday onwards moisture convergence increases
once again, as a cold front will move into the west Atlantic and
stall northwest of the area. As a result, this would be the best
chance for early morning showers and enhanced afternoon convection
over portions of the islands but mainly the west and northwest
sections of Puerto Rico. The potential for urban and small stream
flooding will therefore increase Sunday through Monday as a somewhat
wetter pattern is expected so far.

&&

.AVIATION...Mainly VFR conditions thru period. Sfc winds fm NNE 10-15
kts with occasional gusts. Some vcsh could be possibles over TISX,
TIST and TJSJ mostly between 15/12Z to 15/18Z. Sfc Wnd will
diminish to 10 kts or VRB aft sunset 15/22Z. No significant
operational wx impacts attm.

&&

.MARINE...
Mariners can expect improving conditions over the Atlantic waters
for the day or so, however, small craft operators should exercise
caution due to seas between 4 and 6 feet and winds between 15 and
20 knots. Elsewhere, seas will continue at 5 feet or less and
winds between 10 and 15 knots. Another northerly swell and increasing
winds is forecast by late Tuesday night. Therefore deteriorating
marine and coastal conditions will again be likely.

Beachgoers, the risk of rip currents is moderate for the north-
facing beaches of Puerto Rico, St Thomas and Culebra today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 82 73 82 73 / 30 30 20 40
STT 84 72 83 73 / 40 20 10 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
504 AM AST Tue Mar 16 2021

.SYNOPSIS...
A strong surface high pressure will continue to build and spread
across the west and central Atlantic. This will continue to promote
a northerly wind flow across the region. as a result, shallow moisture
fragments from old frontal boundaries will move across the region
and bring periods of passing clouds and showers to the islands and
coastal waters through Wednesday. A somewhat drier pattern is expected
by the latter part of the workweek. Choppy and hazardous marine
conditions are expected once again later tonight and for the rest
of the week due to the increasing trade winds and the arrival of
a northerly swell .

&&

.SHORT TERM...Today through Thursday

A mid to upper level ridge will dominate the local pattern for the
short term period. As the surface high pressure moves more to the
central Atlantic will push a drier airmass into the region with
precipitable water values in less than one inch. The lack of
moisture combined with a trade wind cap and stable conditions aloft
will result in fair weather conditions Today over the forecast area.
Additionally, the surface ridge will gradually tighten the pressure
gradient, causing winds to around 20 mph over the local waters and
colder temperatures over the region. The weather conditions will
deteriorate on Wednesday as the ridge moves eastward, pushing the
remnants of a frontal boundary over the area. This will increase the
precipitable water content. According to model guidance, precipitable
water values will range between 1.1 to 1.30 inches. The increase
in moisture, combined with the local effects, will result in afternoon
shower activity over the interior and southwestern sections of Puerto
Rico. Although an increase in moisture is expected, shower activity
is not expected to be significant, due to the stable conditions
aloft. However, ponding of water in roadways and poor drainage
will remain possible in some areas.

On Thursday, the conditions will slightly improve as the frontal
boundary remnants move out of the region. However, fragments of low
level moisture embedded in trade winds will reach the forecast area.
Winds are expected to drift more to the east as the ridge moves to
the northeastern Atlantic.

.LONG TERM...Friday through Wednesday...

At least through Friday,a drying trend is expected, as low level
moisture will erode and the mid to upper level ridge and associated
surface high pressure will dominate local weather pattern along
with a drier air mass aloft. So far model guidance continued to
suggest precipitable water values between 0.75 to 1.2 inches through
Friday, as the surface ridge moves further eastward and winds become
more east northeast. This wind flow will aid in bringing periods
of passing showers to the coastal areas during the overnight and
early morning hours. Afternoon shower activity will be possible
but should be focused over the interior and west to southwest
portions of Puerto Rico each afternoon. Limited or no significant
shower activity forecast elsewhere.

On Saturday and into Sunday, as the high surface pressure moves
into the east and central Atlantic, patches of moisture will
continue to filter in across the the area but will be less
frequent, as the local pressure gradient will loosen and winds
will veer becoming more east southeast while diminishing.
Consequently, a weakly induced surface trough will establish across
the area and bring a gradual increase in low level moisture, as
well as warmer daytime temperatures. Afternoon shower activity on
Saturday will be locally induced and should again be focused over
the interior and west sections of Puerto Rico with some ponding of
water on roadways and in poor drainage areas expected with the
heaviest rains. From Sunday through the end of the period, moisture
convergence increases once again, as a cold front will move across
the west Atlantic and stall northwest and north of the area. As a
result, this would be the best chance for increased early morning
showers and enhanced afternoon convection over portions of the
islands but mainly the west and northwest sections of Puerto Rico.
The potential for urban and small stream flooding will also increase
Sunday through Monday and possible into Tuesday as a somewhat
wetter and unstable pattern is expected.

&&

.AVIATION...Mainly VFR conditions thru period. Sfc winds fm NNE 15-
20 kts with occasional gusts. Some vcsh could be possibles over TJPS
mostly between 16/16Z to 16/18Z. Sfc Wnd will diminish to 10 kts or
VRB aft sunset 15/22Z. No significant operational wx impacts attm.

&&

.MARINE...Small craft operators should exercise caution due to seas up
to 6 feet and winds between 15 and 20 knots. Winds will continue
to increase today and through the end of the work week. A northerly
swell will also arrive and spread across the Atlantic and local
passages later tonight. This will result in choppy and hazardous
seas and deteriorating coastal conditions. Stay tuned to local
marine and coastal products for additional details.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 73 81 72 / 10 50 50 20
STT 83 72 83 72 / 10 50 50 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Wed Mar 17 2021

.SYNOPSIS...
A frontal boundary and associated shearline just north of the islands,
will sink further southward steered by the dominant northeasterly winds,
as a surface high pressure ridge continues to build while shifting
eastwards into the central Atlantic. Shallow moisture associated with
this feature now over the local Atlantic waters will reach the islands
this morning and during the rest of the day bringing an increase in
cloud cover and thus a better chance for shower development. In the
meantime, the base of an upper level trough will shift east of the
region as a mid to upper ridge builds across the area. The present
pattern and recent guidance both suggest that additional shower
development will be possible across the region today. So far
significant and widespread rainfall accumulations are not anticipated
at this time. Increasing winds and deteriorating sea are expected
today through Thursday.

&&

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

A mid-upper level ridge and the associated building surface high
pressure located over the western Atlantic will dominate the local
weather pattern for the short term period. For Today, expect a
slight increase in the potential for shower activity as a weak
frontal boundary and the associated shearline sink more to the south
in the region. This boundary will bring shallow moisture trapped in
the low levels due to the stable conditions aloft generated by the
mid level ridge. According to GOES-16 derived data, Precipitable
water values will be around 1.2 inches over the region. Winds will
be breezy as the frontal boundary move over, so expect east-
northeast winds between 10 to 20 knots throughout the day. No matter
an increase in shallow moisture, shower activity will not be
significant due to the stable conditions aloft. However, ponding
water in roadways and poor drainage areas is possible mainly in the
morning hours over northern sections of Puerto Rico.

As the aforementioned weak boundary moves out, a drying trend is
expected, as the surface high pressure pushes a drier air mass into
the area. So far, model guidance suggests below average precipitable
water values in less than one inch for Thursday into Friday. As a
result, the lack of moisture combined with a trade wind cap and
stable conditions aloft will result in fair weather conditions over
the forecast area with mostly clear skies and some cloudiness.

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

Saturday and through the weekend, as the surface high surface
pressure moves further eastward into central Atlantic, patches of
moisture will filter in across the the area but will be less frequent,
as the local pressure gradient will loosen and winds will veer becoming
more east southeast while diminishing. Thereafter, a weakly induced
surface trough will establish across the area and bring a gradual
return of low level moisture to the region, as well as slightly
warmer daytime temperatures. Afternoon shower activity will be
mainly locally and diurnally induced and should again be focused
mainly over the interior and west sections of Puerto Rico, with
some ponding of water on roadways and in poor drainage areas
expected with the heaviest rains. From late Sunday through the
at least the middle of the following week, moisture convergence
is forecast to increases once again, as a cold front will move
across the west Atlantic and stall northwest and north of the
area. Therefore based on most recent model guidance, the best
chance for increased early morning showers and enhanced afternoon
convection would be late Sunday or Monday and continue at least
until Wednesday. Activity should be focused mainly over the interior
and west to northwest sections of Puerto Rico, however afternoon
showers will also be possible in and around the U.S Virgin islands
as well. The potential for urban and small stream flooding will
also increase Sunday through Tuesday as a somewhat wetter and
unstable pattern is expected. A gradual improvement and drier
conditions are forecast by Thursday.

&&

.AVIATION...An increase in cloudiness could cause BKN/OVC skies
around FL050, with VCSH expected through 17/20z or all TAF sites.
VCSH is possible over all the TAF sites until 17/22Z. Sfc Wnd
will continue to 10 kts or VRB until 17/10Z, increasing from ENE
up to 20kts with ocasional gust.

&&

.MARINE...Marine conditions are forecast to quickly become choppy
and hazardous today through Thursday due to increasing northeast
winds and the arrival of a northerly swell. As a result the Small
Craft Advisories are now in effect for the Atlantic waters and
local passages. There is also a High Surf Advisory, Coastal Flood
Advisory, and a High Risk of Rip Currents. Please closely monitor
the Coastal Waters Forecast (CWFSJU) Coastal Hazard and Marine
Weather Messages (CFWSJU/MWWSJU), as well as the Surf Zone
Forecast (SRFSJU) issued by WFO San Juan for additional details.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 82 72 82 71 / 50 20 20 20
STT 82 71 82 72 / 50 20 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
520 AM AST Thu Mar 18 2021

.SYNOPSIS...

A surface high pressure just north of the area will promote mainly
fair weather and breezy conditions through the short term period.
Limited afternoon shower is expected to yield in minimal rainfall
accumulations if any. Winds will shift more to the east southeast
while diminishing by the beginning of the workweek. Hazardous
marine and coastal conditions continue through the weekend.

&&


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

Drier air has moved into the area behind a cold front and dew points
have dropped into the lower 60s in the lower elevations and the
upper 50s in the mid and upper elevations. The cold front can be
seen past Guadalupe and some 275 miles south of San Juan. The Total
Precipitable Water Product shows another band of moisture
approaching the area from the northeast and it will generate mostly
isolated showers along the windward coasts and slopes of the
islands. Significant moisture does not otherwise return until next
week.

Mid and upper levels are generally unfavorable to significant rains
as well. High pressure at 500 mb over western and central Caribbean
sea will become a ridge over the local area on Saturday. At upper
levels high pressure will remain over the southwestern Caribbean
with mostly west northwest flow over the local area. A weak trough
is forecast to move through the area on Thursday night, but because
moisture is very shallow no effects will be seen.


.LONG TERM...Sunday through Saturday...

A surface high surface pressure moves further eastward into
central Atlantic. This will result in windy conditions and mostly
fair weather skies. However, patches of moisture will filter in
across the the area from time-to-time. The local pressure
gradient will loosen and winds will shift more to the east
southeast while diminishing by the early part of the workweek.
Then, a weakly induced surface trough will establish across the
area. This will bring a gradual increase of low level moisture to
the region, as well as somewhat warmer high temperatures.
Diurnally induced afternoon showers will focused mainly over the
interior and west sections of Puerto Rico. This activity may
result in some ponding of water on roadways and in poor drainage
areas with the heaviest rains. From late Sunday through the at
least the middle of the following week, a cold front will move
across the west Atlantic and stall northwest and north of the
area. Therefore, based on most recent model guidance, moisture
convergence is forecast to increase once again. This will promote
a the best chance for increased early morning showers and
enhanced afternoon convection for Monday and continue at least
until Wednesday. Activity should be focused mainly over the
interior and west to northwest sections of Puerto Rico. However
afternoon showers will also be possible in and around the U.S
Virgin islands as well. A gradual improvement and drier
conditions are forecast by the end of the long term period.

&&


.AVIATION...

VFR will prevail today. There is a slight chc of SHRA
forming over WSW PR aft 18/20Z, but they will not last thru 18/23Z.
NE sfc winds 10-20 kt with gusts to 30 kt psbl alg the coast nr TJBQ
aft 18/14Z. Winds will bcm less than 12 kt over land by 19/00Z.
Maximum winds W 55-65 kt btwn FL365-470.

&&


.MARINE...

Hazardous marine conditions will continue today across the
Atlantic waters and passages with seas between 8 to 10 feet. Seas
will gradually subside to around 7 feet by Friday morning. Large
breaking waves are expected to create rough surf conditions, life
threatening rip currents, localized beach erosion and possible
minor coastal flooding across the Atlantic coastline and beaches
with northern exposure to the swell. For detailed information
please refer to the latest Coastal Waters Forecast (CWFSJU),
Coastal Hazard and Marine Weather Messages (CFWSJU/MWWSJU), as
well as the Surf Zone Forecast (SRFSJU).

&&


.PRELIMINARY POINT TEMPS/POPS...
SJU 83 70 85 72 / 20 30 30 20
STT 85 75 85 73 / 20 20 20 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Fri Mar 19 2021

.SYNOPSIS...
A surface high pressure will continue to promote mostly fair
weather across the islands through the weekend. Winds will be from
the east northeast, shifting to the east southeast by Monday. This
will result in somewhat warmer daytime temperatures. An induced
surface trough will increase moisture across the area to enhance
shower activity over the islands by mid-week. Seas are slowly
subsiding, but remain hazardous today.


&&

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

At upper levels, a weak trough passage last night will cause winds
to become more northwest with a weak jet branch splitting out of the
sub-tropical jet to the northwest and joining a trans Atlantic jet
around 20 degrees north over the tropical Atlantic waters.

At mid levels high pressure will extend northeast of of the central
Caribbean Sea and shift east across the local area on Saturday and
by Sunday flow up to 15 knots will be south to southwest.

A weak area of moisture moving in from the central Atlantic will
affect the local area during the period. This area shows patchy
clouds generated by instability underneath a strong cap of very dry
air that extends down as low as 6000 feet. As winds become more
easterly Saturday and Sunday and weak troughs pass through, the
marine layer will deepen and showers will gain some strength. This
additional moisture will allow better chances for rain in western
Puerto Rico also.

Mid and upper levels therefore will maintain a mostly dry pattern,
but patchy shallow moisture out of the central Atlantic will still
be able to generate brief passing showers. Showers will follow the
typical diurnal pattern with most showers in the late nights and
morning hours over the northeast third of Puerto Rico with lesser
amounts and chances over the U.S. Virgin Islands.

Thicknesses indicate a warming trend that gradually flattens out by
mid week next week.


.LONG TERM...Monday through Sunday...

Winds will shift more to the east southeast while diminishing as
the local pressure gradient loosens by the early part of the
workweek. Unstable weather conditions are expected thereafter, as
a weak induced surface trough establishes across the area. This
will bring a gradual increase of low level moisture coverage over
the region. Local effects will combine with the aforementioned
moisture to produce afternoon showers mainly over the interior and
west sections of Puerto Rico. This activity may result in ponding
of water on roadways and in poor drainage areas with the heaviest
rains. Due to the southeasterly wind flow, slightly warmer high
temperatures are also forecast.

A cold front will move across the western Atlantic and stall
northwest of the area. Recent model guidance suggests an increase
in moisture convergence once again. This will promote early
morning showers and enhanced afternoon convection through at least
least Wednesday. Activity should be focused mainly over the
interior and west to northwest sections of Puerto Rico. However
afternoon showers will also be possible in and around the U.S.
Virgin Islands. Drier conditions are forecast by the end of the
long term period.

&&

.AVIATION...VFR will prevail today altho brief MVFR CIGs psbl at
TNCM/TKPK. There is a chc of SHRA forming over wrn PR aft 19/19Z,
but they will not last thru 19/23Z. NE sfc winds 10-20 kt with gusts
to 26 kt psbl alg the coast nr TJBQ/TJSJ aft 19/14Z. Winds will bcm
less than 12 kt over land by 20/00Z. Maximum winds W 45-60 kt btwn
FL345-445.

&&

.MARINE...
Seas are slowly subsiding, but are still hazardous across the
Atlantic waters and passages with seas around 7 feet. These
conditions will remain until at least late tonight. Winds up to
20 knots will continue for the next couple of days. There is still
a high risk of rip currents for the northern beaches of Puerto
Rico, Vieques, Culebra and the USVI. For detailed information
please refer to the latest Coastal Waters Forecast (CWFSJU),
Coastal Hazard and Marine Weather Messages (CFWSJU/MWWSJU), as
well as the Surf Zone Forecast (SRFSJU).

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 72 86 72 / 20 30 20 30
STT 85 73 84 73 / 20 20 10 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
507 AM AST Sat Mar 20 2021

.SYNOPSIS...High pressure at the surface will continue over the
central Atlantic ocean. At upper levels high pressure continues
over South America and the Caribbean sea, interrupted only by the
passage of a weak trough on Tuesday night and Wednesday. Moderate
to fresh easterly trade winds continue over the area for at least
the next 7 days.

&&

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

Relatively stable weather is expected to prevail through most of the
short-term period as a result of ridging from the mid to upper
levels. The surface high pressure over the western Atlantic will
move eastward north of the region relaxing the pressure gradient and
slightly decreasing the wind flow pattern. Moisture is confined
between 1000 to 700 MB, local, and diurnal effects could produce a
few showers during Saturday Afternoon. Showers that do develop
during the weekend will be short-lived and produce light rainfall
amounts.

Model guidance suggest Sunday as the most active day of the short-
term period, as weak surface perturbation reaches the forecast area.
This feature will advect showers inland, mainly over portions of
northeastern Puerto Rico during the morning. Diurnally induced
showers are expected for portions of interior and western Puerto
Rico. By Monday, winds will become more from the east southeast.
Thus, low level moisture will combine with local effects to generate
showers over the northwestern third of Puerto Rico.

.LONG TERM...Tuesday through Friday...
Moisture deepens in the area just as a short wave trough
approaches from the northwest at upper levels. This will generate
better showers in western Puerto rico during the afternoon with
some showers in eastern Puerto Rico Tuesday and Wednesday
mornings. 500 mb temperatures will fall to almost minus 10 degrees
Celsius Tuesday and also generate isolated thunderstorms over
western Puerto Rico during the afternoon. Flow around the high
pressure moving northeast in the western Atlantic at mid and low
levels pushes the moisture back toward the south, leaving a
pattern Thursday through Saturday consisting of scattered showers
in shallow patches of moisture riding in the easterly trade winds
over Puerto Rico and the U.S. Virgin Islands. Hence we can expect
isolated to scattered showers in the overnight and morning hours
in eastern Puerto Rico and over the waters around the U.S. Virgin
Islands, and scattered showers in the afternoons in western and
interior Puerto Rico for the remainder of the period.

&&

.AVIATION...Mainly VFR conditions will prevail across all terminals
during the next 24 hours. However afternoon SHRA are expected at
TJMZ/TJBQ, but no significant impacts to operations are
anticipated. East to northeast low-level winds will continue
through 22z at 15-25 kts, decreasing 10-15 kt overnight.

&&

.MARINE...Seas are diminishing and winds are forecast to be a few
knots less over the local waters today. Small craft advisory
conditions are not expected through Friday, but mariners will need
to exercise caution for the next few days. Winds will also
diminish some more after Sunday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 73 86 73 / 30 30 30 30
STT 84 73 84 74 / 10 20 20 40

[cycloneye]

/issued 533 AM AST Sun Mar 21 2021/

SYNOPSIS...Moisture-rich air in the Caribbean is spreading west
and a little north and causing showers to linger across the area.
Drier air will press in later today. High pressure at the surface
remains north and east of the area driving moderate to fresh
easterly trade winds. Areas of moisture will ride across Puerto
Rico and the U.S. Virgin Islands and bring intervals of isolated
to scattered showers through the period.

SHORT TERM...Today through Tuesday...
Recent Total Precipitable Water from GOES-16 and infrared satellite
imagery confirms the presence of an area of clouds and enhanced
moisture located over the Caribbean Sea affecting portions of
Puerto Rico and the U.S. Virgin Islands. However, drier air
follows, as indicated by both the GFS and ECMWF global models.
Therefore, shower activity is expected to diminish during the
morning hours, with only isolated showers lingering.

At the surface, a high pressure system over the central Atlantic
will maintain an east to east-southeast wind flow through at least
early Tuesday, with a mid-level high pressure holding to the north
of the islands through the rest of the weekend. As a result,
moisture content is expected to be confined to the lower levels,
with precipitable water values around 1.2 inches. Since moisture is
expected to be less when compared with yesterday, afternoon
convection should be limited to the northwestern quadrant of Puerto
Rico, although stream-like showers may affect the San Juan metro area
as well. Ponding of water on roadways and low-lying areas will be
possible.

For the beginning of the workweek, as the mid-level high pressure
flattens out, moisture is expected to gradually penetrate a little
deeper into the mid-levels of the atmosphere. For Monday, the
weather pattern suggests another round of afternoon convection over
northwestern Puerto Rico. Then, on Tuesday, as a mid to upper level
trough to the northwest of the region escort a short-wave across the
region, conditions aloft are expected to become more favorable for
shower activity. Additionally, the latest guidance are indicating
precipitable water values around 1.4 to 1.6 inches, and 500 mb
temperatures cooling down to around -9 degree Celsius. These
factors, aided by local effects, should increase the potential for a
wider coverage area and intensity of the afternoon activity,
including possible isolated thunderstorms, mainly over the interior,
northern and western Puerto Rico.

LONG TERM...Wednesday through Sunday...
High pressure continues over the northeast central Atlantic water
and east winds will continue at the surface. The mid level trough
will have passed the area by Wednesday and high pressure will
slowly build back. At upper levels the trough will deepen to the
east, leaving the area on the convergent side and flow turning
from west to north from Thursday to Saturday. Areas of shallow
passing moisture, however will continue through the period
enabling isolated to scattered showers in the typical diurnal
pattern, that is night and morning showers for eastern Puerto
Rico and afternoon showers in western Puerto Rico with light
passing showers for the U.S. Virgin Islands.

AVIATION...Mainly VFR conditions expected to prevail across the local
terminals. VCSH for TJSJ/TISX through 21/14Z could result in
brief periods of MVFR conditions. Also, VCSH are expected for TJBQ
after 14/17Z, with brief periods of reduced VIS and low CIGs
possible. SFC winds through FL050 are expected out of the east to
east southeast at 10 to 15 knots. Maximum winds W 50-60 knots btwn
FL350-420.

MARINE...Seas diminish for the next 18 hours, but a northerly
swell returns briefly on Monday and conditions become hazardous in
the local Atlantic outer waters.

FIRE WEATHER...Conditions yesterday hovered just above critical
fire weather levels with relative humidity dipping below critical
levels when winds were lighter. With drier air moving in from the
northeast relative humidity levels are expected to continue when
winds are able to ramp up to 15 mph or more. Conditions will also
be somewhat gusty. Therefore elevated fire danger should be
expected for the south coast of Puerto Rico today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 73 87 74 / 20 30 30 30
STT 83 74 84 73 / 10 40 40 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
441 AM AST Mon Mar 22 2021

.SYNOPSIS...

Mostly tranquil conditions are expected for today as drier air
moves into the region. However, this dry air coupled with breezy
winds will lead to elevated fire danger for the Southern Coastal
Plains. Tomorrow will have a better chance for showers as an
upper level trough moves in from the west along with increased
moisture. A weak swell is currently impacting the Atlantic waters
today, with a Small Craft Advisory in effect till 2 PM this
afternoon.

&&

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

A shallow area of moisture from a weak low-level trough will move
from the east today across the islands. However, as the upper level
ridge continues to hold over the eastern Caribbean; this should only
cause typical light morning showers over portions of the U.S. Virgin
Islands and eastern sections of Puerto Rico. Due to the presence of
drier air and stable conditions at upper levels, only locally
induced afternoon showers are expected to develop downwind from el
Yunque into San Juan and vicinity and over portions of central and
western Puerto Rico. Ponding of water in roads and in other poor
drainage areas is expected with this activity.

For Tuesday, an upper level jet and short wave trough at 500 mb
moving from the west will further weaken the upper level ridge and
promote unstable conditions over the region. Precipitable water
content is expected to increase from around 1.00 inch today to near
1.40 inches by Tuesday afternoon. The 500 mb temps will also drop
from around -6.5 degrees Celsius to -9.5C by Tuesday evening, these
two factors should promote isolated thunderstorm development during
the afternoon/evening hours over the interior and western sections
of PR. Therefore, the potential for urban and small stream flooding
will increase. For Wednesday, another ridge is expected to build
from the west as the upper trough moves further east. Weather
conditions should improve, however, lingering low-level moisture
will combine with daytime heating, the sea breeze convergence and
other local effects to cause shower development along portions of
the Cordillera Central and western PR during the afternoon.

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

Generally seasonal weather is expected for the long-term period,
with patches of moisture moving in from the east. Thursday looks
fairly dry and uneventful. A high pressure ridge aloft will exist
to our west, with troughing to our east. The atmosphere will
generally be dry, and under the influence of the ridging, with
below average precipitable water expected. High pressure at the
surface to our north will encourage breezy winds and lead to
fairly quick moving isolated showers, and these showers will
likely be unimpactful. Conditions will be more conducive for
showers on Friday. A weak patch of moisture is expected to arrive
during the day on Friday which will encourage shower development.
Furthermore, these showers may be enhanced by a trough of low
pressure aloft that will dig down over our region. One limiting
factor to the showers that will develop is that winds will remain
breezy at low-levels, leading to fast moving and less impactful
showers. However, any persistent showers over a given area may
lead to ponding of water over roadways and low-lying areas.

The weekend looks mostly dry. The aforementioned trough pushes
further south and east and a ridge will once again influence our
region with drier and more stable conditions. A few patches of
moisture will pass through during this period and into Monday as
well, but their impact is forecast to be minimal. Winds will
increase from Friday and into the weekend, and this will keep
showers moving quickly, and also may negatively impact marine
conditions.

&&

.AVIATION...

Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, SHRA is expected to
develop in and around TJSJ/TJBQ from 16z-22z, and may cause tempo
MVFR conds. East-southeast winds increasing to 10-15 kt with sea
breeze variations and higher gusts after 14z.

&&

.MARINE...

A weak northerly swell is producing hazardous seas for the outer
Atlantic waters today. There is a Small Craft Advisory out for
these waters through 2pm today, with choppy seas into Tuesday.
However, seas under 5 feet are expected for the next few days
thereafter. Approaching the weekend, winds are expected to pick up
which may once again result in Small Craft Advisory conditions.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 73 86 73 / 20 20 30 20
STT 84 73 84 72 / 40 20 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
408 AM AST Tue Mar 23 2021

.SYNOPSIS...

Fairly active weather is expected today due to an incoming trough
of low pressure from the west. Showers and isolated thunderstorms
are possible for western Puerto Rico this afternoon. Another
trough moves through on Friday, which again could lead to some
active weather. Seas are calming down after a weak swell impacted
the region yesterday.

&&

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

A mid to upper level trough will move just north of the region
today. This will promote unstable conditions aloft as 500 MB
temperatures are forecast to drop to around -9.5 degrees Celsius
later today. Precipitable water content is expected to gradually
increase from 1.20 to 1.40 inches by this afternoon. Light east to
southeast steering winds are expected to prevail, as the pressure
gradient decrease over the region. Therefore, slow moving showers
with possible thunderstorm development is expected this afternoon,
mainly over the interior and western sections of Puerto Rico. Urban
and small stream flooding can be expected with this activity. Shower
development is also expected over the eastern portions of the island
and across San Juan and vicinity. For the U.S. Virgin Islands, the
best chance for showers are during the morning and overnight hours
through the short term period. Especially on Wednesday.

On Wednesday and Thursday, an upper level ridge is expected to build
west of the region, while the upper level trough moves just east of
the Leeward Islands. This will promote a more east to northeast
steering wind flow and unfavorable conditions aloft for widespread
rainfall activity. Regardless, diurnally induced afternoon showers
are still expected to develop each day over portions of the interior
and west/southwest PR.

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

Friday looks more active in the latest forecast models due to a
more prominent trough of low pressure to our northeast at mid to
upper levels. The axis of the trough is forecasted to pass through
sometime late Friday or Saturday, moving from northwest to
southeast. This trough will help to amplify any shower activity
for Friday and possibly Saturday as well. There are some
mitigating factors however. First, there will only be below
average moisture to work with. Second, winds will be breezy, so
showers will be fairly fast moving and thus less impactful. These
winds will be out of the east-northeast, so showers can be
expected for eastern and northern Puerto Rico Friday morning, then
for southwest Puerto Rico in the afternoon. There could be some
isolated thunderstorms in the afternoon, but they will likely be
quite weak given the expected very dry air aloft. Similarly for
Friday night and Saturday morning, showers for northwest PR are
likely. By Saturday afternoon, with the trough then likely to our
southeast, weaker shower activity can be expected again over
western to southwestern PR.

Greater moisture moves in for Sunday, but we will lose that shower
enhancement that comes from the trough, as it should move away to
the east during the day. The increased moisture should still lead
to some decent shower activity for western Puerto Rico in the
afternoon. In fact, low-level winds are expected to switch to be
more out the east-southeast during the day. This would also favor
showers for northwest PR in the afternoon. Monday and Tuesday
will continue to see above average moisture, but atmospheric
conditions that are not favorable for thunderstorms or strong
showers. However, showers will likely form again on both of these
days for northwestern PR on Monday and western PR on Tuesday.

&&

.AVIATION...

Mainly VFR conditions are expected across all terminals.
However, SHRA/TSRA expected to develop in and around TJSJ/TJBQ from
17z-23z, causing tempo MVFR conds. East winds 10-15 kt with sea
breeze variations after 14z.

&&

.MARINE...

Seas are continuing to calm down as the weak northerly swell
continues to diminish. Seas will be choppy today for many
locations, but below 5 feet for tomorrow and the next few days
thereafter. During the weekend, seas are expected to become
hazardous again as winds pick up across the region.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 73 85 74 / 40 20 30 40
STT 84 74 84 74 / 30 30 30 30