Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
445 AM AST Mon May 15 2023

.SYNOPSIS...

Mostly cloudy skies prevailed through the night across the islands.
Some showers were detected over waters and in the vicinity of the
US Virgin Islands. Temperatures dropped to the mid and upper 70s
near coastal areas under light and variable winds. Showers and
thunderstorms are expected to develop across western areas of
Puerto Rico as well as portions of the San Juan metro area this
afternoon. A similar weather pattern is expected to prevail much
of the upcoming workweek with Tuesday and Wednesday as the wettest
days. The risk for urban and small stream flooding, and heat
indices in the upper 90 degrees to the low 100s will continue as
well as a low to moderate risk of rip currents.

&&

.SHORT TERM...Today thru Wednesday...

Present satellite imagery, Doppler weather radar along with recent
model guidance and the previous TJSJ 15/00Z upper air sounding, all
suggest a light to moderate southeast low level wind flow, becoming
more southwesterly with an anticyclonic in the mid to upper levels.
Increasing upper level cloudiness across the region today as the
upper ridge will lift northwards across the region. This will
increase overall subsident conditions aloft. However still fair
amounts of low level moisture available to favor some isolated to
scattered afternoon convection across parts of the central and
northwest sections of Puerto Rico, with some streamers shower
activity possible on the west end and downwind of the U.S. Virgin
islands and over the coastal waters between eastern Puerto Rico and
adjacent islands. Showers may continue to brush parts of the USVI
the rest of the morning hours, with a afternoon streamer-like
convection possible over parts of the east interior and the San Juan
metro area.

For the rest of the short term period...a wetter pattern is likely
on Tuesday into Wednesday due to erosion of the upper level ridge
which will support increased instability aloft, as a short wave
trough and jet segment is forecast move just north of the region.
Meanwhile an induced low level trough will also favor an increase in
low level moisture convergence and pooling, thus favoring increasing
precipitable water values to around 2.0 inches as suggested by
recent model guidance. This expected pattern so far will increase
the chance for enhanced convection and isolated thunderstorm
activity especially during the overnight and afternoon hours. As a
result urban and small stream flooding as well as ponding of water
on roads and poor drainage areas will be likely on these days.

-Expected Impacts on Monday Isolated afternoon thunderstorms
possible, mainly northwest Puerto Rico with ponding of water on
roads and poorly drained areas with minor urban and small stream
flooding possible in isolated areas. On Tuesday and Wednesday...
elevated conditions expected with increased chance for urban and
flash flood flooding in isolated ares along the northern half of
Puerto Rico including the San Juan metro areas and isolated spots
over the U.s. Virgin islands.

&&

.LONG TERM...Thursday thru Tuesday...

Long term forecast is still on track. A mid to upper level ridge
pattern is still expected to prevail across the forecast area
Thursday and Friday. However, this pattern aloft will be short-
lived with the 250 hPa heights falling during the upcoming
weekend. At lower levels, a surface high pressure located across
the northeast Atlantic will continue to yield east to east
southeast winds. This will continue to promote moisture advection
and precipitable water values near or above seasonal levels much
of the week. Moisture advection is expected to peak Thursday and
Saturday with precipitable water values near 1.90 inches.

As a result, continue to expect locally induced afternoon showers
and thunderstorms across western areas of Puerto Rico each day.
These showers and thunderstorms are expected to be enhanced during
the upcoming weekend and into the next workweek due to the
proximity of an upper level trough.

&&

.AVIATION...

VFR conds at all terminals durg prd. SCT ocnl BKN lyrs nr
FL025...FL050 and BKN-OVC nr FL250. Wdly SCT SHRA ovr regional
waters and en route btw E PR and USVI with VCSH psbl at
TJSJ/TISX/TIST til 15/14Z . No sig operational wx impacts fcst.
SHRA/isold TSRA psbl ovr ctrl interior and northwest PR and VCTY
TJBQ/TJSJ fm 15/17z-15/22z. Brief MVFR conds possible, especially en
route to TJBQ with aftn convection. SFC wnd will be lgt/vrb less
than 5 kts bcmg fm ESE at 12-15 kt with ocnly hir gusts and sea
breeze variations aft 15/14Z.

&&

.MARINE...

Mariners should expect tranquil marine conditions, with seas between
2 to 4 feet, and occasional seas up to 5 feet. Showers with
isolated thunderstorms are expected each afternoon at the coastal
areas of western and northwestern Puerto Rico. Choppy seas could
be locally hazardous in and around thunderstorms. Winds will be
from the SE at 10 to 15 knots, with higher gusts near thunderstorms.
There is a moderate risk of rip currents along the north facing
beaches of Puerto Rico today.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...RAM
LONG TERM....OM
AVIATION...RAM

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
406 AM AST Tue May 16 2023

.SYNOPSIS...
Passing showers are expected across the U.S. Virgin Islands and
eastern portions of Puerto Rico in the morning hours.After that,
showers and isolated thunderstorms will develop across the
western and northwestern Puerto Rico due to the local effects.
The risks for the expected activity are urban and small-stream
flooding. For the upcoming weekend, expect an increase in the
frequency of the showers due to an upper-level trough.

&&

.SHORT TERM...Today thru Thursday...

Satellite imagery, Doppler weather radar along with recent model
guidance and the previous TJSJ 16/00Z upper air sounding, suggest
drier air with little or no shower activity across the region at
this time. Light to moderate east southeast low level winds prevail.
Mid to upper level winds continued from the southwest to west and
dominated by the anticyclonic flow. The mid to upper level cloud
shield has now shifted east of the islands, as an upper trough and
associated short wave continued to move eastward across the west and
southwest Atlantic. The short wave trough is expected to approach
the region and should cross just north of the area later today
through Wednesday. This will result in slow erosion of the upper
ridge and thus increase instability aloft. A surge of low level
moisture now crossing the northern Leeward islands is also expected
to approach the region from the east. This will lead to an increase
in low level moisture and instability across the region later this
afternoon and through Wednesday.

Still some pockets of low level moisture available to favor isolated
to scattered afternoon convection across parts of the central and
northwest sections of Puerto Rico, with streamer activity possible
on the west end and downwind of the U.S. Virgin islands, as well as
over the coastal waters between eastern Puerto Rico and adjacent
islands. Expect late afternoon enhanced convection today as the mid
to upper level cloudiness that aided in inhibited convection
yesterday, has moved out of the area thus allowing even better
daytime heating. Limited showers expected over the coastal waters
the rest of the overnight and early morning hours with partly cloudy
to mostly clear skies to prevail. Afternoon streamer-like convection
possible over parts of the east interior and the San Juan metro
area.

Models continued to suggest a fairly moist low level pattern and
instability aloft due to approach of the upper trough and weakening
of the upper ridge. This will support better chance for enhanced
afternoon and overnight convection later today and for the rest of
the period. The a short wave trough and jet segment will destabilize
the upper levels and low level moisture convergence and pooling will
increase with precipitable water values to be slightly above 2.0
inches by Thursday as suggested by recent model guidance. As a
result urban and small stream flooding as well as ponding of water
on roads and poor drainage areas will be likely each day.

Expected impacts are isolated to scattered afternoon
thunderstorms, mainly over west central and northwest Puerto Rico
with ponding of water on roads and poorly drained areas with minor
urban and small stream flooding possible in isolated areas. Late
this afternoon through Wednesday still looks like the best chance
for these elevated weather conditions with increased chance for
urban and flash flood flooding along the northern half and
sections of northwest Puerto Rico including the San Juan metro
area. The best change for periods of heavier rains for the U.S.
Virgin Islands which may lead to ponding of water on roads and
poor drainage areas still looks like later in the afternoon and
also on Wednesday. Guidance also suggest a low concentration of
saharan dust particulates to linger across the area through
Wednesday and this will support some hazy conditions.

For Thursday, early morning and afternoon shower activity is still
expected but as the mid to upper ridge reinforces aloft expect this
activity to be more diurnally driven and thus lesser chance for
significant rainfall accumulations. However, more streamer like
convection across the northern half of PR and on the west end and
downstream of the USVI as the southeast wind flow is forecast to
return once again.

&&

.LONG TERM...Friday trough Tuesday...
East to east-southeast winds will prevail for most of the long-
term forecast as the high surface pressure over the eastern
Atlantic absorbs a surface low over the central Atlantic. This
wind flow will feed the islands with advective moisture throughout
the period. Convective shower activity is anticipated on Friday
and Saturday, mostly due to the local effects and the diurnal
heating. Although some areas will observe showers, widespread
activity is not expected due to the mid-level ridge inducing the
trade wind cap inversion.

On Sunday into Tuesday, an increase in the instability is
forecast as an upper-level trough (TUTT) moves northwestward into
the region. The instability and moisture aloft will combine with
enough humidity at the surface, enhancing the potential for more
long-lived showers with t-storms. According to the model guidance,
the best day for widespread shower activity will be late Monday
into Tuesday, when the axis is over the Hispanola, leaving the
subsidence side across the area. Therefore, expect an advective
pattern in the morning, followed by moderate to strong shower
activity and some isolated thunderstorms over the northwestern
quadrant, interior, and the San Juan Metro Area due to the
southeasterly wind flow. As a result, there is a moderate flood
threat across those areas.

&&

.AVIATION...
VFR conds durg prd with mstly sct lyrs nr FL030...FL050 and SCT ocnl
BKN lyrs btw FL120...FL250 ovr offshore atl waters and btw USVI and
Nrn Leeward islands. SHRA dvlp ovr central interior and NW PR fm
16/17Z-23Z. LCL MVFR/ brief IFR likely ovr these areas with mtn
obscurations. Brief MVFR conds psbl at TJMZ/TJBQ with the aftn
convection. Sfc winds calm to lgt/vrb, bcmg fm E-SE 10-15 kts with
sea breeze influences and some hir gusts aft 16/14Z.

&&

.MARINE...

A surface high pressure interacting with a low pressure over the
Atlantic basin will continue to result in a east-southeast wind
flow pattern across the region. Seas up to 4 feet will remain across
the offshore Atlantic waters, and even less over the protected
coastal waters.These marine conditions are forecast to prevail
for the next several days. On Wednesday, a small pulse of a
northeasterly swell will invade the local waters, but seas will
remain up to 5 feet or less. There is a low risk of rip currents
for all the exposed beaches of Puerto Rico and the U.S. Virgin
Islands.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM & AVIATION...RAM
LONG TERM& MARINE ....LIS

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
413 AM AST Wed May 17 2023

.SYNOPSIS...
An increase in moisture and the southeasterly wind flow will
increase the heat indices values across the north-central coastal
sections. Therefore, there is a heat advisory in effect. In terms
of rainfall activity, the increase in moisture and the proximity
of a shortwave trough will enhance the potential for shower
activity across the region. The heaviest activity will be in the
afternoon. Unsettle weather conditions are forecast for the
upcoming weekend as an upper-level trough moves into the area.
Seas will remain up to 3 feet across all the local waters with a
low risk of rip currents.

&&

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

The present weather pattern and recent model guidance initialized
well, with both suggesting an increasing moist low level pattern and
instability aloft, as an upper trough quickly approaches the region
and the mid to upper level ridge aloft continued to erode. This will
support better chance for shower development over the coastal waters
during the rest of the morning hours followed by some enhanced
afternoon convection today. The combination of the short wave trough
and a upper level jet segment crossing the region, will destabilize
the upper levels while low level moisture convergence and pooling is
still expected to increase. Model guidance suggest layered PWAT
values to linger around d 2.0 inches or so through Thursday. As a
result urban and small stream flooding as well as ponding of water
on roads and poor drainage areas will be likely today with expected
impacts of numerous showers and isolated thunderstorms during the
afternoon, mainly over west central and northwest Puerto Rico and
isolated areas in the San Juan metro.

For Thursday and Friday, the mid to upper level ridge will
reestablish aloft once again. The low level winds will become more
easterly as a weakly induced surface low is forecast to briefly form
over the central Atlantic. This will aid in bringing occasional
patches of low level trade wind moisture with embedded showers
across the area from time to time especially during the overnight
and early morning hours. Locally and diurnally induced afternoon
convective shower activity is forecast each day with potential for
minor urban and small stream flooding mainly over the central and
west sections of Puerto Rico, where isolated thunderstorms will
remain possible. While the USVI may briefly experience locally heavy
rains in isolated spots each day, no significant accumulations are
anticipated. These rains may lead to minor ponding of water on roads
and in poor drainage areas but so far the activity will not be
widespread and should be of short duration.

&&

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

A transition to a more wet pattern is forecast for Saturday
afternoon lasting for most of the upcoming weekend into the next
workweek. An upper-level trough sinking southward will provide
subsidence aloft for vertical development. At the surface, an
extending high pressure from the Central into the eastern
Atlantic will maintain a southeasterly wind flow. This wind flow
will keep the islands under abundant Caribbean moisture, with PWAT
reaching 2 inches. According to the recent model guidance, the
upper-level trough will be present from Saturday into Monday,
eroding the mid-level ridge. Therefore, the best period for
widespread shower activity will be late Sunday into Monday, when
the trough axis reaches the Mona Passage, and conditions will be
favorable at all levels. Given the expected conditions, there is a
moderate flood threat each day across the northwestern quadrant
and over the San Juan Metro area.

For Tuesday into Wednesday, the upper-level trough will drift
eastward, inducing a surface trough just over the east of the
forecast area. This surface perturbation with the available
moisture and the local effects will cause pesky showers across
east Puerto Rico and the U.S. Virgin Islands in the morning.
Shower activity will not be widespread or long-lived due to
convergence at the upper levels. However, moderate to strong
showers are forecast over the western sections of Puerto Rico in
the afternoon hours. There is a limited flood threat with this
activity each day, resulting in ponding of water in roadways and
poor drainage areas.

&&

.AVIATION...
VFR conds durg the entire period, except for Sct-Nmrs SHRA and
isold TSRA mainly ovr NW and N central PR til 17/23Z. Aftn
convection may cause brief MVFR and Mtn top obscr. SCT ocnl BKN lyrs
nr FL025...FL050...FL090 en route. Calm to light and variable sfc
wnds will become fm ESE 10-15 kts aft 17/14Z. Incrg trade wind mstr
expected into early morning hours, with wdly SCT SHRA ovr regional
waters and btw PR and the USVI and mainly downwind of TISX/TIST.
&&

.MARINE...

A surface high pressure over the eastern Atlantic will maintain a
light to moderate wind southeast wind flow. Mariners can expect
seas of 3 feet or less across the local waters. The risk of rip
currents will remain low for all local beaches.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 11 AM this morning to 4 PM AST this afternoon
for PRZ005.

VI...None.
AM...None.
&&

$$

SHORT TERM & AVIATION...RAM
LONG TERM & MARINE....LIS

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
516 AM AST Thu May 18 2023

.SYNOPSIS...
Broad surface high pressure ridge across the north central Atlantic
will maintain light to moderate east southeast winds across the forecast
area. A mid to upper level ridge will continue to build and spread
northwards across the area, as a short wave trough shifts farther east.
Occasional patches of low level trade wind moisture will cross the region,
with showers expected to develop over the coastal waters and reach the
portions of the east and southeast coastal sections during the overnight
and early morning hours. Good moisture availability along with daytime
heating,local effects and sea breezes will favor showers and isolated
thunderstorm development each afternoon. Activity today should be
focused mainly across central and northwest Puerto Rico and on the
Leeside and just downwind of the the U.S. Virgin Islands. Above- normal
moisture under the southeasterly wind flow will promote slightly warmer
than normal temperatures again today. Overall tranquil marine conditions
are forecast for the next several days.

&&

.AVIATION...
VFR conditions will prevail for all the TAF sites during the period.
Winds will remain from the E-SE at 10 kt or less, increasing by 18/14Z
from the SE at 12 knots with sea breeze variation. VCSH and RA are forecast
for TJBQ at around 18/18Z, resulting in some brief MVFR conditions due
to the ceilings. Weather conditions will improve at 18/23Z. However,
VCSH will affect TIST, TISX & TJSJ at 19/03Z, lowering ceilings. Winds
will become light and VRB at 19/00Z.

&&

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

A variable weather pattern is forecast for the short-term period. At
the surface, a high pressure extending across most of the Atlantic
Basin will maintain an east-southeasterly wind flow during the
period. These wind patterns will keep dragging low-level Caribbean
moisture across the CWA. According to the latest satellite-derived
imagery, PWAT values around the islands are 2 inches above
climatological normals. Although humidity conditions will be
favorable, the 250 MB heights suggest ridging aloft from today into
Saturday.

Given the panorama, diurnal heating, and local effects, expect a
more typical convective pattern. Residents and visitors can expect
occasional showers in the morning and evenings across the windward
sections. Afternoon convection is forecast for each day, mainly
affecting the northwestern quadrant, the interior, and the San Juan
Metro area. Mudslides and urban flooding cannot be ruled over the
interior sections where the soils are already saturated. The major
concern for the U.S. Virgin Islands will be the advective pattern in
the morning and evening hours, promoting frequent passing showers.

Due to the east-southeasterly wind flow and the increase in moisture
across the region, heat indices will be a theme during the period.
According to the 925 MB temperature, the warmer day will be Friday,
when the heat indices can reach 108 F degrees across the northern
coastal sections of Puerto Rico. Stay hydrated and follow the
official recommendations.

&&

.LONG TERM...Sunday through Friday...
A fairly moist weather pattern is forecast Sunday through at least
the middle of the upcoming week. An upper-level trough is forecast
to sink southward across the region. This will support unstable
conditions and provide good ventilation aloft for convective development.
In the meantime the broad surface high pressure spread across the
Central and eastern Atlantic will maintain a southeasterly wind
flow. This in turn will aid in maintaining the flow of abundant
tropical moisture convergence across the local area. Recent model
guidance suggests layered PWAT values to be maintained around 2.0
inches. The aformentioned upper level trough will aid in eroding
the mid-level ridge thus providing the best chance for enhanced
and widespread shower activity Sunday through Monday, and possible
into Tuesday aided by the proximity of the upper long wave trough
and good moisture convergence. Given the expected conditions,
there will likely be an elevated threat for excessive rainfall and
potential for thunderstorm development through Monday, especially
across the northwestern quadrant of Puerto Rico and over the San
Juan Metro area where urban flooding of roads, small streams, rivers
and washes. The U.S. Virgin Islands will also experience periods
of locally heavy rains along with potential for minor urban and
gut flooding.

By late Tuesday and through Thursday, the upper-level trough will be
replaced by a building ridge as it is forecast to shift eastward while
inducing an elongated surface trough just northeast of the forecast
area. This low level troughiness along with the good moisture pooling
and the local effects will maintain periods of passing clouds and
showers across the coastal waters, eastern Puerto Rico and the U.S.
Virgin Islands during the overnight and morning hours. By then
passing showers and daytime convection is so far not expected to
be widespread as most of the activity should be locally and
diurnally driven. Periods of moderate to locally heavy rains will
however remain possible each day especially over the west sections
of Puerto Rico during the afternoon hours. As a result, there will
be limited flood threat with this activity, where ponding of water
in roadways and poor drainage areas will be possible.

&&

.MARINE...The marine conditions continue favorable for the small
crafts. Winds will continue out of the east southeast, with speeds
between 10 to 15 knots. Seas will be between 1 to 4 feet with a
short period across the local waters.

There is a low risk of rip currents for all beaches.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from noon today to 4 PM AST this afternoon for
PRZ001-005-008-010.

VI...None.
AM...None.
&&

$$

SHORT TERM...LIS
LONG TERM....RAM
AVIATION...LIS

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
409 AM AST Fri May 19 2023

.SYNOPSIS...
A broad surface high pressure over the northeast Atlantic Ocean
will maintain light to moderate east southeast winds into the
upcoming weekend. A mid to upper level ridge will extend
northwards across the area from the eastern Caribbean today but
will gradually erode over the weekend, as a deepening upper-level
trough will sweep across the region and destabilize the upper
levels. This along with a fairly moist east southeast wind flow
will increase the potential for enhanced showers and isolated
thunderstorm development each day. Low level winds are forecast to
become more southerly by late Sunday into early next week as an
elongated low pressure trough is forecast to develop and lift
northwards across the southwest Atlantic. Afternoon activity
should be focused across the central interior and west to
northwest Puerto Rico, and mainly on the Leeside and just downwind
of the the U.S. Virgin Islands. Limited to elevated excessive
heat hazard risks are likely each afternoon, with maximum heat
indices peaking between 102-108 degrees, primarily across northern
and western sections of Puerto Rico.

&&

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

A variable and convective pattern will persist today. According to
the Satellite-derived imagery, low-level moisture across the islands
remains at 2 inches. This reservoir of Caribbean moisture will
continue for the rest of the period as the surface ridge provides
this east-southeast across the islands. This moisture plume will
enhance the advective pattern in the morning and evenings over the
local warm waters, resulting in pesky passing showers. Followed by
the deep convection across the interior and northwestern sections
due to the diurnal heating and the local effects of the islands.
Today's heaviest activity with isolated thunderstorms will develop
across the interior, drifting to the northwestern sections and
resulting in urban and small stream flooding. Showers and some
isolated t-storms are forecast for the San Juan Metro area.

On late Saturday, a deep upper-level trough over the western
Atlantic will sink southward near The Bahamas, partially eroding the
mid-level ridge. Conditions will deteriorate even more by Sunday
when the upper-level trough reflects at the surface, inducing a low-
pressure trough just over Haiti, inducing a prevailing southeasterly
flow. The winds will feed the islands with low-level moisture, and
unstable conditions will prevail at the upper levels. This change in
the predominant features will enhance the potential for more shower
activity across the islands increasing the flood threat to moderate
across the western and interior sections.

&&

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

A fairly moist and unstable weather pattern is forecast through at
least Tuesday of the upcoming week. The upper-level trough is forecast
to sink southward across the region and will support unstable conditions
while providing good ventilation aloft for convective development. In
the meantime the broad surface high pressure spread across the central
and eastern Atlantic will maintain a light southeast to south wind flow.
This in turn will aid in maintaining the flow of abundant tropical moisture
across the forecast area. Recent model guidance suggests layered PWAT
values to be maintained around 2.0 inches with this moist and unstable
pattern and therefore there will likely be an elevated threat for excessive
rainfall and potential for thunderstorm development through at Tuesday
or early Wednesday, especially across the central and northern half
of Puerto Rico including the San Juan Metro area where urban flooding
of roads, small streams, rivers and washes. The U.S. Virgin Islands
will also experience periods of locally heavy rains along with potential
for minor urban and gut flooding during the early part of the period.

By Wednesday and through the end of the period, the upper-level trough
will be replaced by a building ridge from the west, and it is forecast
to shift east of the local islands. By then the passing overnight
and early morning shower activity is expected to be less frequent,
and daytime convection is not expected to be widespread. Most of the
activity each afternoon will be locally and diurnally driven convection
due to good daytime heating and the available moisture convergence.
Periods of moderate to locally heavy rains will remain possible each
day especially over the west sections of Puerto Rico during the afternoon
hours. As a result, there will be limited flood threat with this activity,
where ponding of water in roadways and poor drainage areas will be
possible.

&&

.AVIATION...
VFR conditions will prevail for all the TAF sites. VCSH will
affect TIST, TISX & TJSJ thru 19/14z. Winds will remain from the
E-SE at 10 kts or less, increasing at 19/15Z up to 15 knots, with
sea breeze variations. Afternoon showers would decrease the ceiling
and will result in VCSH & -RA over TJBQ and TJPS around 19/18Z.
Another round of evening shower is forecast at 20/03Z affecting
TIST, TISX & TJSJ.

&&

.MARINE...
Mariners can expect seas of 1 to 4 feet and east to southeast
winds between 10 to 15 knots across the local waters today into
the weekend.

The risk of rip currents will remain low for all local beaches today
but increasing to a moderate risk of rip currents for some of the
north and east facing beach by Sunday.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM & AVIATION...LIS
LONG TERM & MARINE....RAM

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
512 AM AST Sat May 20 2023


.SYNOPSIS...
A humid and unstable weather pattern is forecast for the weekend
into the upcoming week as a plume of moisture and an upper-level
trough remains in the islands. Residents can expect showers each
day across the islands, resulting in urban and small-stream
flooding. There is a moderate risk of rip currents for the exposed
beaches at St. Croix and in San Juan Juan tonight.

&&

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

Unstable conditions will continue to today with cooler 500 mb
temperatures (slightly below minus 8 degrees) and copious moisture
(above 2 inches of precipitable water) will bring heavy showers
and scattered thunderstorms to Puerto Rico in the southeast flow
similar to yesterday. Moisture diminishes on Sunday, but only to a
small extent and then is forecast to be greater than today or
yesterday on Monday. This is all due to upper level troughing that
will slowly generate a low pressure system north of Hispaniola
that will prolong southerly flow and bring in additional moisture.
Scattered thunderstorms were seen on Friday--mainly in the
Atlantic waters, but are also likely in northern Puerto Rico.
Thunderstorms will see a diminishing trend Sunday and Monday as
mid level warm. But Monday and into the long period forecast
convergence over the area due to the low pressure will generate
heavier rainfall. Urban and small stream flooding is likely each
day and localized flash flooding is even more likely on Monday.


&&

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

On Tuesday, an upper-level trough will move eastward with the
axis over the Hispanola, creating unstable conditions while
providing good ventilation for convective development. At the
surface, the induced surface low pressure from this trough will
enhance light southeast to south wind flow. This wind flow will
inject into the islands abundant tropical moisture with PWAT
values above the climatological normal. Due to the moist and
unstable pattern, there is an elevated risk of excessive rainfall
and thunderstorm development from Tuesday through early Wednesday,
particularly in the central and northern half of Puerto Rico,
including the San Juan Metro area. This will cause urban flooding
of roads, small streams, and rivers.

For Wednesday into Thursday, the TUTT will move eastward out of
the region, and heights will increase for that period. Although
conditions at the upper level turn slightly less favorable, at the
surface, the surface low will induce a southerly flow dragging
plenty of Caribbean moisture across the CWA. This significant
amount of low-level moisture with a PWAT of 2 inches will enhance
a convective pattern.

For Friday into Saturday, model guidances suggest the influence
of an upper shortwave trough increasing the divergence aloft. The
favorable conditions, with enough low moisture, will enhance
shower activity across the windward sections of the islands and
northwestern Puerto Rico. However, a mid-level ridge will be in
place, reducing the potential for long-live showers.

&&

.AVIATION...SE flow over the area will bring sct SHRA across the
SE third of PR during the morning hours. Daytime heating will
bring increased +SHRA/TSRA activity spreading NW across PR and
downstream from the USVI. Mtn obscurations, local MVFR/IFR conds
expected genly aft 20/16Z. Winds SE 10-15 kt with a few hrs of sea
breezes on the north coast. Gust to 23kt in sea breezes and arnd
TSRA. Max winds WNW 60-70 kts btwn FL380-450, diminishing during
the period.


&&

.MARINE...

Surface high pressure over the northeast Atlantic will maintain
gentle to moderate east to southeast winds throughout the
weekend.Seas will remain up to 4 feet for most of the waters,
except for the offshore Atlantic waters where seas will reach the
5 feet, increasing up to 6 feet tonight. Locally choppy marine
conditions are possible near the shower and thunderstorm activity.
The risk of rip currents will remain low for all local beaches of
Puerto Rico. For St. Croix, there is a moderate risk of rip
currents.



&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM/AVIATION...WS
LONG TERM/MARINE....LIS

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Sun May 21 2023


.SYNOPSIS...

A deep-layer trough will continue to promote shower with isolated
thunderstorm activity for the next few days. Heavier rainfall
will cause areas of urban and small stream flooding and localized
flash flooding across Puerto Rico with lesser impacts across the
U.S. Virgin Islands. Saturated soils will enhance the potential
for landslides and rockfalls in steep terrain.

&&

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

A trough at upper levels is developing and contains a jet max that
will pass over Puerto Rico and the U.S. Virgin Islands this morning.
The trough will also generate a weak cut-off low at 250 mb this
afternoon north of Haiti that will drift south tonight and Monday
and then cross over Puerto Rico on Monday night creating a favorable
environment for thunderstorms. Low pressure forming north of
Hispaniola will develop today and tonight and move north
northeastward through the period. This will cause a line or even
several lines of broad convergence over the area in the moisture
laden flow. Rain activity will increase with increasing moisture
Monday and Tuesday and continue into the long term period. The
heaviest rains will tend to be on the southeast coast of Puerto Rico
during the early mornings, and the northwestern sections and along
the Cordillera central during the afternoons. Thunderstorm activity
will continue over the local waters well into the evenings. The
heaviest rainfall is expected on Monday and Tuesday with local
amounts able to reach 4 to 6 inches each day. The heavier rainfall
will cause areas of urban and small stream flooding and localized
flash flooding across Puerto Rico with lesser impacts across the
U.S. Virgin Islands. Wetter terrain may collapse in landslides.

&&

.LONG TERM...Wednesday through Monday...

The expected unstable and wet weather pattern that will prevail in
the short-term period may linger into the long-term, with perhaps
less intensity and fewer thunderstorms. Moisture availability at low
to mid-levels will remain well above normal, with 700-500 mb
relative humidities sometimes reaching beyond the 95% percentile.
The above-normal moisture could continue through the end of the
workweek. However, the reason why we may observe fewer thunderstorms
is that the deep-layered trough will have weakened while lifting
north of the area.

In the meantime, a weak mid-level ridge will build over the
northeastern Caribbean, which could inhibit, to some degree, deep
convective activity in some places. However, due to plenty of
available moisture that will persist over the eastern Caribbean
basin, isolated thunderstorm activity aided by sea breeze
convergence and surface heating are likely each afternoon. Friday
looks like the "driest" day as 700-500 mb moisture slightly
decreases, which could inhibit deep convective activity during peak
hours of the day. Flooding of urban areas, roads, and small streams
can be anticipated with possible isolated flash floods in localized
areas, particularly over the interior and western portions of Puerto
Rico each afternoon. Landslides and rockfalls are possible as
rainfall from previous days may promote saturated soils across steep
terrain. A decrease in shower activity during the night and early
morning hours can be expected each day, with some passing showers
affecting windward coastal areas.

Uncertainty increases during the weekend as both GFS and ECMWF
models differ on the timing of moisture content availability. A
strong frontal boundary will build across the western Atlantic
inducing strong moisture convergence across the eastern Caribbean
basin. GFS is forecasting precipitable water values of up to 2.3
inches! The GFS Galvez-Davison Index indicated the potential of
isolated to scattered thunderstorm activity east of the USVI moving
westward as time passes. Behind this surge of moisture, the easterly
trades will push a dry airmass over the islands. The ECMWF model is
much quicker transitioning to this drier, more stable weather
pattern. We will continue to analyze these features as we get closer
to the weekend.


&&

.AVIATION...Sct SHRA movg NW at arnd 20 kt will incrs durg thru
21/18Z. Isold TSRA psbl til 21/15Z bcmg sct-nmrs--mainly wrn and
central PR aft 21/15Z. Mtn obscurations, lcl MVFR/IFR conds in
SHRA/TSRA. Winds SE 6-12 knots with gusts to 20 kt incrg aft 21/14Z
to ESE-SE 10-16 kt. Maximum winds WNW 70-90 kt btwn FL435-470 incrg
thru 21/15Z.

&&

.MARINE...Moderate to locally fresh east southeast trades will
persist across the regional waters. Therefore, choppy marine
conditions with seas up to 6 feet and occasional higher seas will
persist for the next few days. Small Craft should exercise caution
over mostly the offshore Atlantic waters. A moderate risk of rip
currents exist for most north and east-facing beaches of Puerto
Rico, Culebra and St. Croix. Elsewhere, a low risk of rip
currents can be expected.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM/AVIATION...WS
LONG TERM/MARINE/PUBLIC....CVB

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Wed May 24 2023

.SYNOPSIS...

Southeasterly flow will continue, but a departing upper level low
will clear away most the cloud cover and bring warm temperatures
to the local area. A heat advisory is in effect for most of the
northern lower elevations. Increasing stability will limit the
number of thunderstorms and showers that grow over western and
interior Puerto Rico until Sunday when a band of moisture will
bring the best moisture of the next 6 to 8 days. Nevertheless
locally heavy showers will be able to produce spots of urban and
small stream flooding each day through Sunday. Drier weather is
indicated for the U.S. Virgin Islands.

&&

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

The mid/upper-level low continues above the forecast area and is
currently centered northeast of the U.S. Virgin Islands. Although
the trough has weakened somewhat, it continued fostering shower
and thunderstorm activity across the local waters close to USVI,
Vieques, and Culebra throughout the night. This is more or less
where the bulk of the moist plume induced by a surface low
northeast of the Bahamas is located. Convective activity will
continue to fluctuate through the morning hours, with some
affecting southeastern Puerto Rico as well but less intense than
the previous morning. Today will be the wettest day of the short-
term period. The mid/upper trough will continue to move eastward
throughout the day as a mid-level ridge with an axis over
Hispaniola moves in by Thursday. Although weather conditions aloft
will gradually improve as the day progresses, sufficient tropical
moisture and instability will be present during peak hours of the
day, with surface heating and sea breeze convergence further
enhancing deep convective activity. Fewer cloud during the
morning hours will prompt several regions to effortlessly reach
convective temperatures throughout the day. A south-southeasterly
wind flow will cluster activity across the interior, northwest,
and north-central Puerto Rico in the afternoon. A limited to
elevated flood risk will be present with the heaviest downpours.

Thursday and Friday will observe a more typical weather pattern with
overnight and morning showers affecting windward coastal areas at
times. Dynamics mentioned above will turn slightly more stable as
the weak mid-level ridge settles over the northeastern Caribbean
with 700-500 mb relative humidities dropping below 60%. The bulk
of the moist plume will remain mostly east of the forecast area,
but close enough to maintain moisture content within the 50% to
75% percentile of the climatological normal. Therefore, expect
showers and a few isolated thunderstorms to develop each afternoon
due to the combination of diurnal heating and local effects.
Activity should subside during evening hours as diurnal heating
declines.

Unfortunately, temperatures are expected to remain above normal for
this week. High temperatures in combination with high moisture
content will promote heat indices to reach 102 degrees or above in
low-lying areas every day through the workweek.

&&

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

Saturday will have only a modest high pressure at the surface over
the central Atlantic that will bring moderate trade winds from
the east over the area. A weak trough at the surface and in the
lower levels will demarcate a band of better moisture that will
move through the area from the northeast. This band will have the
best precipitable water that is expected to be seen until Friday
of next week. High pressure at mid levels centered over the area
on Saturday will move west of the area on Sunday, but this will
still impose a limiting factor in the shower and isolated
thunderstorm activity of the day. Dry air follows the band of
moisture immediately and, if the GFS is correct, Monday morning
will see the driest air of the next 10 days. Moisture then
improves during the week reaching even higher levels than the past
few days by the end of the long term period. This will be due to
a return of southeast flow in the lower levels by Tuesday as high
pressure sinks back into the eastern Atlantic near the Tropic of
Cancer. During this time, locally heavy afternoon showers will
develop along the Cordillera Central and in northwestern Puerto
Rico each day from local effects and strong heating. Urban and
small stream flooding, despite the limited instability cannot be
ruled out. Also, although some cooling will be seen Saturday
through Sunday night, Monday will mark the beginning of a warming
trend that will bring very warm temperatures on the north coast
by the end of the long term period.

&&

.AVIATION...
(06Z TAFS)
Issued at 406 AM AST Wed May 24 2023

Mostly VFR conds durg the entire period. SHRA/TSRA will
remain mostly E of TISX/TIST but may be close enough at times thru
24/14Z. Aftn convection in wrn and nrn PR may cause brief MVFR
and mtn top obscurations. Sct-Nmrs SHRA and isold TSRA are
possible mainly ovr NW and N central PR til 24/23Z. Calm to light
and variable sfc wnds will become SE 10-15 kts aft 24/14Z. Maximum
winds WNW 20-25 kt btwn FL430-480 incrg drg the day.

&&

.MARINE...

East or southeast flow during the next 7 to 10 days will not
generate much more than 5 foot seas during the next severals days
and the general trend for the rest of the period will be for
diminishing seas. No small craft advisories are foreseen during
the next 10 days.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 11 AM this morning to 4 PM AST this afternoon
for PRZ001-005-008-010.

VI...None.
AM...None.

&&

$$

SHORT TERM/AVIATION...CVB
LONG TERM/MARINE....WS

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
331 AM AST Thu May 25 2023

.SYNOPSIS...Today's main hazards are excessive heat, excessive
rainfall, and lightning. A variable weather pattern will persist,
dominated by local effects and diurnal heating in a high-moisture
environment. As a result, most showers with isolated thunderstorm
activity will occur in the afternoon, clustering along the
interior to northern sections steered by southeasterly winds.
Increased shower activity likely between Sunday and Monday. A
moderate risk of rip current will persist.

&&

.SHORT TERM...Tonight through Saturday...

GOES-16 Total Precipitable Water (TPW) imagery shows the moist plume
currently east of Puerto Rico, over the northern U.S. Virgin
Islands, being kept under a southeast wind flow. Today and Friday,
the moist plume will remain mostly east of the forecast area but its
proximity will maintain precipitable water values within 1.80 and
2.0 inches over the local islands with Friday looking like the
driest of the short-term forecast. At upper levels, although some
divergence and a 50-60 knot jet will be present at the 250 mb layer,
mid-levels will continue to stabilize as a mid-level ridge settles
over the eastern Caribbean basin. This will inhibit to some degree
deep convective activity. Nevertheless, enough low-level moisture
with surface heating and sea breeze convergence during afternoon
hours will be enough to induce showers and isolated thunderstorms
across the interior, northwestern and north-central municipalities
of Puerto Rico.

By late Saturday, the surface low east of the Eastern Seaboard will
continue north and stop influencing the low-level wind across the
northern Caribbean. This will allow the surface high pressure across
the North Atlantic waters to induce the more typical east
southeasterly trades across the area, pushing the moist plume across
the northeastern Caribbean. Therefore, as the typical afternoon
activity develops over interior and northwestern Puerto Rico,
eastern Puerto Rico, Vieques, Culebra, and U.S. Virgin Islands will
observe an increase in shower activity during the evening and
overnight hours. A few isolated thunderstorms may develop over the
local waters during this time frame. Urban and small stream flooding
is likely with the heaviest showers within the short-term period.

Highs will likely be reaching the lower 90s across lower elevation
areas with heat indices reaching above 102 degrees in localized
areas, particularly over the north-central municipalities of Puerto
Rico each day. In fact, a Heat Advisory has been issued for this
area today.

&&

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

Based on the most recent model guidance, the expected weather
conditions should remain variable, and showers will be driven
mainly by local effects and diurnal heating. A surface high
pressure across the North Atlantic will yield moderate easterly
winds at 10-15 mph, veering more from the southeast from Monday
onwards. At mid-levels, ridging will remain north of the region
but is expected to weaken by mid-week, steered by a mid-level low
moving over the western Atlantic. A plume of moisture, now to the
northeast of the northern Leeward Islands, with the highest
precipitable water values around 2.1-2.3 inches and above-normal
seasonal values in the cycle, will stream across the northeastern
Caribbean between Sunday and Monday. So far, the best chance for
showers with isolated thunderstorm development likely producing
flooding impacts is expected between Sunday and Monday. Despite
some drying during the workweek, afternoon convective development
is expected each day, clustering along the interior to
northwestern sections of the islands driven by the general
southeasterly steering flow. Seasonal temperatures will continue,
ranging from around 90 degrees during the day across lower
elevations and other urban areas to the lower to mid 60s at
nighttime across higher elevations.

&&

.AVIATION...VFR conditions will prevail for all the TAF sites
during the period. Winds will remain light and VRB, increasing by
25/14Z from the SE at 10 knots with sea breeze variation. VCSH and
-RA will persist for TIST thru 24/14z. VCTS are forecast for TJBQ
at around 25/18Z, resulting in some brief MVFR conditions due to
the ceilings. Weather conditions will improve at 25/23Z. However,
VCSH will affect TIST & TISX at 25/23Z, lowering ceilings.

&&

.MARINE...Light to moderate east to southeast winds at 5-15 knots
will generate seas at 5 feet or below for the next several days.
A moderate risk of rip currents will prevail for most north-
facing beaches of Puerto Rico and the easternmost beaches of Saint
Croix.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 11 AM this morning to 4 PM AST this afternoon
for PRZ005.

VI...None.
AM...None.
&&

$$

SHORT TERM...CVB
LONG TERM....ICP
AVIATION...CVB
PUBLIC...ICP/CVB

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
430 AM AST Fri May 26 2023

.SYNOPSIS...Today's main hazards are excessive heat, excessive
rainfall, and lightning. A seasonal weather pattern will persist,
with showers and isolated thunderstorm development driven by local
effects and diurnal heating each afternoon along the interior to
northern sections steered by southeasterly winds. Increased
rainfall totals and excessive rainfall risk with increased
moisture levels are likely by the end of the weekend into early
next week. A moderate risk of rip current will persist.

&&

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

A surface low pressure is expected to develop from a frontal
boundary and a trough over the southwestern Atlantic later tonight,
while slowly drifting northwards through the weekend along the US
Southeast coast. This will continue to promote a southerly component
in the steering winds today. There is enough moisture content across
the area for diurnally induced afternoon showers and thunderstorms
to develop once again over portions of the interior, western and
northern Puerto Rico. Meanwhile, a building high pressure over the
central Atlantic will promote a more easterly flow during the
weekend, shifting westward the afternoon convection. Another surface
low is expected to develop from the frontal boundary on Sunday, well
north of the area while moving to the northeast over the surface
high. In response, a moist plume of moisture is expected to move
over the eastern Caribbean, with precipitable water content
increasing above 2 inches across the local area. Therefore, an
increase in nighttime/early morning convection between the USVI and
eastern PR, and later in the afternoon across PR is expected on
Sunday. The 500 mb temps are expected to remain relatively warm
through the period as mid to upper level ridge builds across the
Caribbean, regardless, isolated thunderstorms can be expected each
afternoon. Urban and small stream flooding will remain as the main
hazards for the next couple of days. However, southerly winds will
promote once again hot temperatures along the northern
municipalities of PR, and a Heat Advisory was issued for the north
central areas of PR due to heat indices possibly reaching 108-111
degrees Fahrenheit.

&&

.LONG TERM...Monday through Saturday...

Following the most recent model guidance, expect gradual drying
from Monday through Thursday morning, with precipitable water
values falling as low as 1.3-1.4 inches and below seasonal
moisture levels around Tuesday afternoon. Then, a gradual increase
in moisture is suggested from Thursday afternoon onwards, holding
above-normal seasonal moisture levels of 2.1-2.3 inches between
Friday and Saturday. A meandering surface high pressure across the
North Atlantic will generally yield east to southeast winds at
10-15 mph through most of the cycle, with slightly more southerly
winds by the end of the workweek into the weekend. Aloft, mid-to-
upper level ridging will hold over the region, maintaining a trade
wind cap inversion and somewhat hostile conditions for deep
convective development.

Despite these conditions, local effects and diurnal heating
should trigger showers with isolated thunderstorm development each
afternoon, favoring the interior and northern sections of Puerto
Rico and downwind from the El Yunque into northeastern Puerto Rico
and the local islands into adjacent islands. Moderate to locally
heavy rains could lead to excessive rainfall impacts, causing
ponding water on roadways and poorly drained areas. Urban and
small stream flooding are possible. An increase in moisture
content could lead to increased shower development and, thus,
flooding potential by the end of the workweek into the weekend.
Seasonal temperatures will continue, ranging from the lower 90s
during the day across lower elevations and other urban areas to
the mid 60s at nighttime across higher elevations. During periods
of high moisture

&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, SHRA/TSRA expected to
develop in and around TJBQ btw 17z-23z, this may cause tempo MVFR
conditions. Sfc winds ESE at 8-12 kt with sea breeze variations aft
14z, mainly along the north/west coasts.

&&

.MARINE...Light to moderate east to southeast winds at 5-15 knots
will maintain seas at 5 feet or below for several days. A
moderate risk of rip currents will persist for the beaches of
northern Puerto Rico and eastern Saint Croix.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 11 AM this morning to 4 PM AST this afternoon
for PRZ005.

VI...None.
AM...None.
&&

$$

SHORT TERM...DSR
LONG-TERM...ICP
AVIATION...DSR
PUBLIC...ICP/DSR

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
348 AM AST Sat May 27 2023

.SYNOPSIS...Feature of interest is a moist plume extending across
the Lesser Antilles, which is expected to move over the islands
later today and through Sunday. Precipitable water content is
expected to peak around 2.20 inches, increasing shower activity in
general across the USVI and PR. Hot temperatures and increasing
dew points may cause heat indices to range between 108-111 degrees
Fahrenheit today between Arecibo and Toa Baja, where a Heat Advisory
(NPWSJU) is in effect. Drier, but seasonal weather conditions are
expected next week.


&&

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

Showers with isolated thunderstorms could lead to lightning and
excessive rain hazard risk. Limited to elevated excessive heat
hazard risk levels are likely each afternoon.

A moist weather pattern will prevail on Saturday and Sunday. This
pattern will result from a moist plume, now moving over the northern
Leeward Islands and with satellite-estimated precipitable water
values as high as 2.2 inches, moving westward into the northeastern
Caribbean by east-to-southeasterly winds. Despite a mid-level
ridging meandering across the region, maintaining a trade wind cap
inversion and drier air entrainment, this feature will remain weak
enough to not fully inhibit deep convective development,
particularly in the afternoon, when local and diurnal effects are
more robust. Showers will continue to move over eastern Puerto Rico
this morning, with increasing frequency as the day progresses. Late
this morning and continuing in the afternoon, expect showers with
isolated thunderstorm development, clustering along the interior to
western sections of the island, where limited to elevated excessive
rainfall is likely. Showers are possible elsewhere, mainly downwind
from El Yunque into the San Juan metropolitan area and from the
local islands into adjacent islands and eastern Puerto Rico,
possibly causing ponding of water on roadways and poorly drained
areas. Shower activity will again favor windward areas tonight.

Today's temperature will range from the lower 90 degrees across
lower elevations and other urban areas in the daytime to mid 60s
across higher elevations at nighttime. A southeasterly component in
the winds in a high moisture environment could yield 108 degrees or
higher heat indices, mainly across northern Puerto Rico, where a
Heat Advisory is in effect.

A similar weather pattern is likely on Sunday, but model guidance
suggests drier conditions on Memorial Day (Monday). Still, limited
afternoon convective development is expected on Monday, clustering
over northwestern Puerto Rico steered by more southeasterly winds.
Limited excessive heat risk levels are likely on both days.

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

A weak mid-to upper-level ridge pattern is expected to prevail
over the islands through the long term period. This will keep the
500 mb temperature relatively warm, around minus 5 degrees
Celsius and promote drier air aloft, limiting the vertical
development of showers. However, isolated thunderstorms are
expected to develop each afternoon over portions of western PR due
to the combination of the available low level moisture, daytime
heating, and the sea breeze convergence. Heat indices should
increase between 108-111 degrees Fahrenheit, triggering Heat
Advisory criteria once again across portions of the lower
elevations of northern and western PR, as winds acquire a
southeasterly wind component from Tuesday onwards.

In terms of moisture content, PWAT values are expected to remain
between 1.50-1.75 inches through at least Thursday, increasing
near 2.00 inches from Friday into the weekend. Therefore,
seasonal weather conditions should prevail across the islands in
general, with passing showers moving across windward areas during
the night and early morning hours, followed by diurnally induced
afternoon showers with isolated thunderstorms over western PR each
day, and increasing in coverage late in the forecast cycle.


&&

.AVIATION...Mainly VFR conditions will prevail across most
terminals. However, afternoon TSRA/SHRA could result in brief MVFR
conditions across all TJSJ and TJBQ terminals between 27/16-23Z.
Calm to light and variable winds becoming more east-southeasterly
with sea breeze variations and increasing to around 5-15 mph by
27/18Z. Winds again become light and variable after 27/23Z.


&&

.MARINE...Relative tranquil seas will continue through the
weekend. Light to moderate southeasterly trades will prevail
today, turning more easterly by this evening into early next week.
Shower activity with isolated thunderstorms are expected to
increase from the Anegada Passage later today, and continue
through Sunday across the rest of the local waters.

The risk of rip currents is low for most of the beaches of PR and
the USVI, with the exception of north central PR, where a moderate
risk of rip currents persists.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 11 AM this morning to 5 PM AST this afternoon
for PRZ001-005.

VI...None.
AM...None.
&&

$$

SHORT TERM...ICP
LONG TERM...DSR
AVIATION...ICP
MARINE...DSR

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
319 AM AST Sun May 28 2023

.SYNOPSIS...A surge in moisture will continue to produce shower
and isolated thunderstorms across the area today. Drier air and
more stable conditions are expected during the workweek. Diurnally
induced afternoon convection is expected across western PR each
day. Passing showers will continue across windward areas during
the night and early morning hours. Southeasterly winds return from
Tuesday onwards and the heat indices will increase once again to
around 108-112 degrees Fahrenheit.


&&

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

Similar to previous days, showers with isolated thunderstorms,
particularly in the afternoon, could lead to lightning and excessive
rain hazard risk. Limited to elevated excessive heat hazard risk
levels are likely each afternoon.

A moist weather pattern will prevail today, although some drying is
likely later this evening. This pattern results from a moist plume,
now crossing the area from the east, with satellite-estimated
precipitable water values as high as 2.2 inches. Despite a mid-level
ridging holding across the region, this feature will remain weak
enough to not fully inhibit deep convective development,
particularly in the afternoon, when local and diurnal effects are
more robust. Showers with isolated thunderstorms will continue to
move over eastern and southern Puerto Rico from the waters this
morning. Late this morning and continuing in the afternoon, expect
showers with isolated thunderstorm development, clustering along the
interior and western to northwestern sections of the island, where
limited to elevated excessive rainfall risk is likely. Showers are
possible elsewhere, mainly downwind from El Yunque into the San Juan
metropolitan area and from the local islands into adjacent islands
and eastern Puerto Rico. The expected moderate to locally heavy
rains could result in ponding water on roadways and poorly drained
areas. Urban and small stream flooding to localized flash floods is
likely with the heaviest downpours. Shower activity will again favor
windward sections tonight but with lesser frequency and intensity
due to the entrance of a drier air patch.

Today's temperature will range from the lower 90 degrees across
lower elevations and other urban areas in the daytime to mid 60s
across higher elevations at nighttime. East to east-southeast trade
winds at 10-15 mph will prevail. A southeasterly component in the
winds in a high moisture environment could yield 102 degrees or
higher heat indices, mainly across western and northern Puerto Rico.

Satellite-derived precipitable water vapor data and model guidance
suggest drier conditions on Memorial Day (Monday) and Tuesday. After
the moist plume, intermittent patches of drier and relatively moist
air will stream across the region. Despite moisture variations,
afternoon convective development is likely each afternoon,
clustering over northwestern Puerto Rico steered by more east-
southeasterly winds.


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

A mid-to upper-level ridge pattern is expected to prevail over
the islands through the long term period. This will promote drier
air intrusion and a relative warm 500 mb temperature, around
minus 5 degrees Celsius. This should limiting the vertical
development of showers in general. However, isolated thunderstorms
are expected to develop each afternoon over portions of western
PR due to the combination of the available low level moisture,
daytime heating, and the sea breeze convergence. Heat indices
should increase between 108-112 degrees Fahrenheit, triggering
Heat Advisory criteria once again across portions of the lower
elevations of northern and western PR, as winds acquire a
southeasterly wind component by midweek.

In terms of moisture content, the precipitable water content is
expected to remain between 1.50-1.75 inches through at least
Thursday, increasing near 2.00 inches from Friday into the
weekend as deep layer trough approaches the area from the west.
Therefore, seasonal weather conditions should prevail across the
islands in general, with passing showers moving across windward
areas during the night and early morning hours, followed by
diurnally induced afternoon showers with isolated thunderstorms
over western PR each day, and increasing in coverage late in the
forecast cycle due to the proximity of the trough.


&&

.AVIATION...SHRA/TSRA will result in brief MVFR conditions
during the next 24 hours. For TJSJ, TJPS, and USVI terminals,
VCTS/VCSH through 28/14Z. For TJSJ and TJBQ, VCTS/VCSH between 28/16-
23Z. For USVI terminals, VCSH after 28/23Z. Calm to light and
variable winds becoming more east-southeasterly with sea breeze
variations and increasing to around 5-15 mph with higher gusts by
28/18Z. Winds again become light and variable after 28/23Z.


&&

.MARINE...Seas will prevail at 5 feet or less, with the highest
seas expected today across the offshore Atlantic waters. Light to
moderate easterly trades are expected through Monday, turning
east-southeast for the remainder of the week. There is a moderate
risk of rip currents across most beaches along the north coast of
Puerto Rico, Culebra, and the eastern beaches of St. Croix.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...ICP
LONG TERM...DSR
AVIATION...ICP
MARINE...DSR

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
439 AM AST Mon May 29 2023


.SYNOPSIS...
A building ridge in the mid and upper-levels will provide
relatively stable conditions. Afternoon convection is forecast
along and to the west and north of the Cordillera Central. Warm
conditions will continue, especially for urban coastal areas. A
wet pattern is expected to begin on Thursday as moist tropical air
moves into the region. Seas remain generally calm with heights 5
feet or below. The risk of rip currents is generally low with a
moderate risk for north/northwestern Puerto Rico.

&&


SHORT TERM...Today through Wednesday...

Throughout the day, the U.S. Virgin Islands and Puerto Rico will
experience a consistent east-southeasterly wind flow due to a
surface high pressure situated off to the northeast in the Atlantic
Ocean. As a result of this wind flow, there will be intermittent
surges of moisture, leading to passing clouds and showers across the
windward sections of Puerto Rico and the Virgin Islands. Despite the
potential for moderate to locally heavy rains with the passing
showers, the atmosphere will remain relatively stable thanks to a
building ridge at the mid and upper levels. The maximum temperatures
will reach the upper 80s and low 90s along the coastal and urban
areas, and the mid-80s and upper 70s along the higher elevations.

The available moisture, the east-southeasterly wind flow, and the
air temperatures due to the diurnal heating will result in heat
index values between 100 and 107 across the urban and coastal areas,
especially in Puerto Rico's west and north coast, Culebra, and St
Croix. Moreover, the combination of orographic effects, sea breeze
influence, and diurnal heating will likely lead to afternoon
convection along and to the west and north of Cordillera Central.
There is a moderate chance of showers developing downwind from the
Virgin Islands, which may affect the western regions. Additionally,
there is a better chance for shower development from La Sierra de
Luquillo towards the San Juan Metropolitan area.

Winds will become more southeasterly Tuesday and Wednesday as a
surface low pressure moves eastward across the North Atlantic Ocean.
Under this wind flow and relatively high moisture, the warm spell
will likely extend throughout the short term, with a mixture of
sunshine and clouds during the morning. The winds will persistently
bring occasional passing showers across the windward sections, and
the diurnal heating, local effects, and sea breezes will promote
afternoon convection each day.

&&

.LONG TERM...Thursday to Monday....

By the end of the week an upper-level low begins to reflect down to
the surface in the Atlantic Basin, weakening the usual easterly
trade regime. Low pressure off the east coast of Florida then
begins to redirect the surface flow across the region, becoming
more southerly by Friday afternoon and remaining southerly
throughout the rest of the long term. With southerly flow across
the Caribbean Basin, moisture sourced from the ITCZ begins to
advect northward, causing a moist airmass with precipitable water
values around 2 inches to move over the local islands for the
following several days.

During this time, a ridge in the upper-levels will help tame the
quantity of showers however with diurnal heating and local effects,
numerous showers can be expected during afternoon hours. With this
southerly flow, various sections of northern Puerto Rico will
experience the greatest amounts of rainfall. Flooding is possible
with the heaviest activity and thunderstorms are likely as well.
Also, maximum temperatures and heat indices will rise greatly for
the northern coastlines with very hot heat indices possible due to
the high humidity values. In summary, a hot and wet second half of
the week is forecast.

&&

.AVIATION...VFR conditions will prevail throughout most of the
period. SHRA/TSRA activity may develop this afternoon along, and
north and west of the Cordillera Central, it will possibly affect
JBQ/JSJ (btwn 29/16- 22z). Mountain obscuration, gusty winds and
lightning activity will be possible near the activity. Winds will
prevail from the ESE at 6 kt or less, increasing to around 10-13
kt with sea breeze variations after 29/13z.

&&

.MARINE...Favorable conditions prevail across the local waters with
seas between 3 to 5 feet for the Atlantic Waters and lower
everywhere else. East winds 10 to 15 knots are to be expected. The
risk of rip currents is diminishing with just
northern/northwestern Puerto Rico having a moderate risk today and
everywhere else having a low risk.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.

&&

$$

SHORT TERM...CAM
LONG TERM...RC

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
458 AM AST Tue May 30 2023

.SYNOPSIS...
An increase of moisture will bring an enhancement of showers
across the local islands today with the best rain falling over
northwestern Puerto Rico and downwind of El Yunque during the hot
afternoon hours. This pattern will continue until late in the
week when the formation of an area of low pressure north of the
region causes moist, tropical air to arrive which will begin a
wetter pattern for the weekend. The risk of rip currents is low
for the rest of the week as wave heights continue to lower for
the entire region.


&&

.SHORT TERM...TODAY THROUGH THURSDAY...

A surge of moisture brought passing clouds and showers across the
local waters, and some moved inland across the U.S. Virgin
Islands and the windward sections of Puerto Rico. St Croix
observed some beneficial rains overnight. Skies were variably
cloudy, and low temperatures were in the mid-70s along the coast
to the upper 60s in the mountains.

Maximum temperatures today will climb into the low 90s across urban
and coastal areas by mid-morning into the afternoon. Winds will
continue from the east-southeast and will push additional moisture
across the islands today, which, combined with the expected air
temperature, will result in heat index values between 100 and 107
degrees Fahrenheit during the maximum heating, especially across the
urban and coastal areas. Nevertheless, showers will move from the
east-southeast across the islands throughout the morning, resulting
in showery weather, which may alleviate the high temperatures. Winds
will slowly become more southeasterly in response to a surface low
pressure moving across the Atlantic Ocean. Therefore, we expect
afternoon convection to develop across the northern half of Puerto
Rico and downwind from the U.S. Virgin Islands. Even though a ridge
is forming in the mid and upper levels over the Northeast Caribbean,
which makes it difficult for thunderstorms to develop, we cannot
entirely dismiss the possibility of their occurrence, as factors
such as orographic effects, intense heating, and sea breeze
collisions in the afternoons may still contribute to their
formation. Therefore, we have chosen to include them in the
forecast. Ponding of water in roads and poorly drained areas is
possible with periods of moderate to locally heavy rains across
portions of Puerto Rico.

Winds will prevail from the southeast on Wednesday as the surface
low pressure moves eastward across the North Atlantic Ocean but may
return more from the east-southeast by Thursday as the surface high-
pressure reinforce again across the Central Atlantic. Under this
wind flow and relatively high moisture, the warm spell will likely
extend throughout the short term, with a mixture of sunshine and
clouds during the morning. The ridge at the upper levels and the mid-
level high pressure will limit the vertical development of the
showers, thus, the formation of thunderstorms. However, each day,
the advective pattern will result in occasional passing showers
across the windward sections, followed by afternoon convection due
to the excessive heating, local effects, and sea breeze.


&&

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

A surface low beings to develop around 30N and 70W, north of the
region on Friday. This will further veer the surface to mid-level
flow to a southerly direction, with south-southeasterly winds at
the surface. Moist tropical air will advect into the region
resulting in a significant increase of showers both throughout
the day, during the afternoons, and overnight. Over the weekend,
the eastward migration of this low into the Atlantic will cause
the surface southerly flow to be variable, with south-
southwesterly winds possible at times. This pattern will continue
through late Monday until an area of high pressure develops to the
east of the region causing the advection of relatively drier air
over the islands on Tuesday.

During these days, the rate of passing showers will increase
significantly with southern to eastern Puerto Rico and the USVI
receiving the bulk during the morning hours. Each afternoon, hot
and steamy conditions will allow convection to form which is
forecast to effect the northern sections of Puerto Rico including
the San Juan metro area. Thunderstorms may occur, however a ridge
in the mid to upper-levels will help stabilize conditions
somewhat. High humidity values and southerly flow will allow heat
indices to reach high values around 110s across northern coastal
areas, therefore it will be very hot especially for the northern
central urban areas of Puerto Rico.

&&


.AVIATION...Generally VFR conds expected next 24 hrs for most
aerodromes. Occasional passing SHRAs will affect the local TAFs
throughout the day. SHRA and maybe isolated TSRA will develop over
PR's interior and northern locations by 30/17-22z. Thus, cannot
rule out brief MVFR or IFR at JBQ. Streamers will possibly affect
TJSJ and will mostly move away from ISX/IST. Winds will continue
calm to light and VRB thru 30/13z, when will return from the ESE
at 9-13 kt with higher gusts and sea breeze variations.


&&

.MARINE...The calmest marine conditions in a while arrived with
sea around 4 feet for the Atlantic waters and generally lower for
the Caribbean waters. Southeast winds between 10 to 15 knots will
prevail, with locally fresh gust during the afternoon hours. The
rip current risk is low for all of the islands as breaking waves
are 3 feet or below.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.

&&

$$

SHORT TERM...CAM
LONG TERM...RC

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
449 AM AST Thu Jun 1 2023

.SYNOPSIS...
Hot conditions are expected for the local islands today, with
heat indice temperatures reaching between 105 and 115 degrees
Fahrenheit across coastal and urban areas. Due to this, a Heat
Warning is in effect for the northern coastal and urban areas of
Puerto Rico from Arecibo to Carolina and also Culebra. A Heat
Advisory is in effect for various other regions mentioned below.
This weekend moist tropical air will arrive causing a significant
increase of rain, with Saturday through Monday looking the
wettest. For the local beaches, the rip current risk is low for
the next several days.

&&

.SHORT TERM...TODAY THROUGH SATURDAY...

Last night, some beneficial rains moved across St Thomas and St John
around midnight, and an isolated thunderstorm developed west of the
islands. Regardless of a few showers moving inland across the
windward sections of Puerto Rico and St Croix, the islands observed
a fair weather pattern, with a layer of cirrus clouds moving
eastward aloft. Low temperatures remain in the upper 70s or low 80s
along the coastal areas and around the low 70s in many mountain
locations. Winds were from the east-southeast at 10 mph or less.

Today, the weather will remain stable due to a strong mid to upper-
level high pressure system over the Northeast Caribbean. These
weather features are causing air to sink, which prevents vertical
development and widespread heavy rains from forming. At the same
time, a set of surface low pressures moving across the Atlantic
Ocean (north of the islands) is inducing winds from the south and
gathering moisture over Puerto Rico and the U.S. Virgin Islands. As
a result, maximum air temperatures will reach the low and mid-90s
along the lower elevations, and the apparent temperatures will feel
extremely hot, with heat index values between 105 and 115 degrees
Fahrenheit during mid-morning and afternoon in urban and coastal
regions of Puerto Rico and the U.S. Virgin Islands. Therefore, we
issued a Heat Advisory for most coastal areas in the west and
northwest from San German, northward to Aguadilla and Hatillo, in
the south from Yauco to Santa Isabel, and the eastern interior for
Caguas, Gurabo, Juncos, San Lorenzo, and Las Piedras. Meanwhile, an
Excessive Heat Warning is in effect from Arecibo to Carolina and
Culebra. The remaining urban and coastal areas of Puerto Rico and
the U.S. Virgin Islands will also experience excessive heat.

Local effects, sea breeze variations, and excessive heat will result
in some showers across PR's northwest quadrant during the afternoon
and downwind from St Croix and Vieques that may impact eastern
Puerto Rico. Ponding of water in roads and poorly drained areas will
be possible.

On Friday and Saturday, a lot of tropical moisture will come from
the south, which will cause rainy weather in the windward sections
of the islands. In the afternoons, there will likely be scattered
showers with some thunderstorms due to the possible increase in
instability combined with local effects. Model guidance consistently
indicates temperatures higher than usual, which may result in
excessive heating, especially in urban and coastal areas. However,
if widespread showers develop throughout the day, the temperatures
may cool down more than the guidance suggests.

&&

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

Low pressure across the western Atlantic continues to drive moist,
tropical air over the region due to breezy southerly flow from
the surface to 250 MB. Due to this, an increase of passing showers
across southern Puerto Rico and the local islands is expected
throughout the day. There will also be convection each afternoon
forming on the northern side of the Cordillera Central, effecting
the northern sections of Puerto Rico, including the San Juan metro
area. A robust ridge in the mid to upper-levels over the eastern
Caribbean will help to stabilize conditions, also it will help
each day become very hot as it provides sinking air. Urban and
coastal areas are expected to experience heat indices in the 110s
which can be hazardous.

This pattern will continue until Monday night when a surface high
builds to the east of the region causing a backing of the winds which
will bring drier air into the region. Shower activity during this
time will be limited due to the persistent ridging aloft and low
precipitable water values, however afternoon convection can still
produce noticeable rainfall each afternoon. Thursday in
particular looks very dry, the driest day possible for the
beginning of summer. Each day around noon time, coastal and urban
areas will experience hot temperatures, therefore stay diligent
in checking if excessive heat advisories or warnings are in
effect.

&&

.AVIATION...Expect mainly VFR conditions across all terminals
during the next 24 hours. Afternoon SHRA may form btwn 01/18-23z
with possible isolated TSRA across PR's northwest quadrant, near
JBQ. Surface winds will continue from the southeast at less than 6
knots, and will increase to around 11-13 kt aft 01/13z with sea
breeze variations.

&&

.MARINE...Moderate to locally fresh southeasterly winds and seas
4 feet and below continue across the regional water today.
Passing showers are expected at times and heavier storms are
possible near the northwestern coastal waters of Puerto Rico each
afternoon. On Saturday the wind becomes southerly, with a
significant increase of showers. The rip current risk remains low
for the next several days.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Warning from 10 AM this morning to 5 PM AST this
afternoon for PRZ001-005-012.

Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
for PRZ004-007-008-010.

VI...None.
AM...None.

&&

$$

SHORT TERM...CAM
LONG TERM....RC

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
502 AM AST Fri Jun 2 2023

.SYNOPSIS...
Today expect rainy conditions across the southern and eastern
sections of Puerto Rico and less activity but with some passing
showers across the US Virgin Islands. There is an Excessive Heat
Advisory for west and northwest Puerto Rico and Culebra and an
Excessive Heat Warning from Arecibo to Carolina due to hot
conditions from late morning through the afternoon. Rainy
conditions will continue throughout the weekend due to plenty of
tropical moisture. Drier air with Saharan Dust particles will
begin to move into the region on Tuesday, with Thursday as the
current driest day. The risk of rip currents is low today.

&&

.SHORT TERM...TODAY THROUGH SUNDAY...

Puerto Rico experienced scattered to widespread rain showers in its
southern region. Radar estimates showed rainfall between 0.10 to
0.50 inches, with a local peak of 1 to 2 inches in Yauco,
Guayanilla, and Penuelas. The U.S. Virgin Islands had a few passing
showers, leaving behind a small amount of rainfall. Overnight
temperatures were higher than normal in Northern Puerto Rico and the
Virgin Islands, and the skies were somewhat hazy due to African dust
particles. The winds were blowing from the south at a speed of 10
mph or less and varied with the land breeze. The coastal areas had
low temperatures in the upper 70s or low 80s, while mountainous
regions had temperatures around the low 70s.

Winds will continue from the south today due to a surface low
pressure north of the region and will persist throughout the weekend
as it moves eastward across the Atlantic Ocean. Although mid to
upper-level high pressure will continue creating subsidence and
limiting vertical development, the above normal tropical moisture
over the area due to the southerly winds will promote rainy
conditions across the south and eastern sections of Puerto Rico and
less activity but with some passing showers across the Virgin
Islands. In addition, as the mid-level ridge moves eastward,
instability may increase across the islands, and we cannot rule out
the formation of thunderstorms due to excessive heating and local
effects.

Under the southerly winds and plenty of moisture, the maximum heat
indices will range between 105 and 115 degrees Fahrenheit along the
urban and coastal areas on the west and north coast of Puerto Rico.
Therefore, we have a Heat Advisory for west and northwest Puerto
Rico and Culebra and an Excessive Heat Warning from Arecibo to
Carolina. Elsewhere (urban and coastal regions), we cannot rule out
excessive heat with a heat index between 102 and 107 if rain
activity does not form during the maximum heating hours.

During the weekend, above-average tropical moisture will filter from
the south, which will cause rainy weather in the windward sections
of the islands and across the local waters. In the afternoons, there
will likely be scattered to numerous showers with some thunderstorms
due to the possible increase in instability as the mid-level high
pressure moves eastward away from the Northeast Caribbean combined
with local effects. Model guidance consistently indicates
temperatures more elevated than usual (especially along the PR's
northern coast and St Croix), which may result in excessive heating,
especially in urban and coastal areas. However, if widespread
showers develop throughout the day, the temperatures may cool down
more than the guidance suggests.

&&

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

Moist, southerly flow continues on Monday continuing a pattern of
passing showers across southern regions. However by the evening
hours, drier air with Saharan dust particulates will begin to
enter the region as the development of a ridge to the east returns
more of an southeasterly flow. A significant reduction of showers
is expected from this as precipitable water values drop. A robust
mid to upper- level ridge continues to sits over the eastern
Caribbean during this time which will also help to stabilize
conditions, reducing shower activity. It will also help each day
become very hot by noon time with possible heat indices in the
110s for coastal and urban areas.

During Tuesday and Thursday the best chance for rain will be
during the afternoon hours due to convection. The driest part of
the airmass will reach the region by Thursday, resulting in a day
when little to no rain is expected. Friday also looks dry, however
during the evening hours moist air starts to move in to bring an
increase of rainfall for the weekend. Visibility may be slightly
reduced during this time due to the Saharan Dust.

&&

.AVIATION...Expect mainly VFR conditions across all terminals
during the next 24 hours, with showers spreading from the south
across the islands. Afternoon SHRA may form btwn 02/18-23z with
possible isolated TSRA near JSJ/IST/JPS. Surface winds will
prevail from the S-SE at less than 6 knots, and will increase to
around 11-13 kt aft 02/13z with sea breeze variations.

&&

.MARINE...Seas are 4 feet or below for the regional waters.
Moderate to locally fresh southeast winds will prevail today and
tonight until turning southerly by tomorrow. An increase of
showers is forecast for the next few days as moist air moves into
the region. Isolated thunderstorms are possible across the coastal
waters during the afternoons. The rip current risk is low today.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Warning from 10 AM this morning to 5 PM AST this
afternoon for PRZ001-005.

Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
for PRZ008-010-012.

VI...None.
AM...None.

&&

$$

SHORT TERM...CAM
LONG TERM....RC

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
448 AM AST Sat Jun 3 2023

.SYNOPSIS...The main concern today is once again heat. High heat
indices will continue, particularly over lower elevations of the
islands and reaching up to 108 to 117 over mainly north-central PR
and sectors of the metro area. Plenty of moisture is being
steered into the region under southerly winds, this will increase
showers and posible isolated t-storms over southern PR with
additional activity possible over the interior to NE PR. A drier
pattern will start late Monday as more Saharan Dust filters in.

&&

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

Showers have been moving across the southern and eastern sections of
Puerto Rico throughout the night, but rainfall accumulations have
not been to significant. Some showers were also observed around St.
Croix and St. Thomas, but with the bulk of the activity remaining
over waters. It has been gusty at the San Juan LMM Airport, with
some Saharan dust present too.

Not many changes in the overall pattern are being observed in the
short term forecast period. Near or at record high temperatures are
expected for the islands today, especially for the urban and coastal
areas of the region. A deep layer high pressure over the eastern
Atlantic and a deep layer trough centered over Cuba are promoting
southerly winds over the eastern Caribbean. This southerly flow also
brings a lot of moisture into the region, with precipitable water
values hovering around the 2.0 inches mark. Under this pattern,
temperatures at 925 mb are expected to be way above normal, causing
this dangerously hot pattern to prevail. For the weekend, heat
indices are expected to reach values of 108 to 117 for north-central
Puerto Rico and sections of the San Juan metro area; values of 108
to 111 across northwestern Puerto Rico, the urban valleys of the
eastern interior and for Culebra. It won't be much cooler elsewhere.
Heat indices of 102 to 107 are anticipated, including for St. Croix
in the Virgin Islands.

Today, aside from the heat, the southerly flow will bring some
showers across southern Puerto Rico throughout the day. Then,
diurnal heating may fire up additional activity across the
Cordillera Central and northeastern Puerto Rico. Ponding of water on
roadways and low lying areas is expected.

On Sunday and Monday, as the ridge holds stronger over the area,
conditions will become unfavorable for shower development, but the
extreme heat will continue. Additionally, Saharan dust will
gradually increase in concentration, with hazy skies and a drier air
mass anticipated for late Monday and Monday night.

&&

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

The long term forecast period begins with a Saharan Air Layer (SAL)
over the islands. A surface high pressure northeast of the islands,
will promote more southeasterly winds, which will steer this SAL
over the islands. For now, aerosol models indicate higher
concentrations on Tuesday, but Saharan dust will continue to linger
for a great part of next week, promoting hazy skies. With this SAL
comes generally drier air over our region, current model guidance
indicates Precipitable Water (PWAT) values gradually dropping to
normal/below normal values for this time of the year. The driest day
appears to be Thursday, as PWAT values plummet to around and below
an inch. In the mid to upper levels, a ridge will dominate our
region, limiting vertical convective development, leaving way for
mostly dry air above 850 mb and promoting more stable conditions
over the islands. There is some discrepancy on moisture content for
the end of the workweek with the ECMWF suggesting that the dry
pattern will continue and the GFS suggesting that frontal moisture
remnants that moved around the surface high pressure will be steered
towards the islands on Friday promoting and increase in moisture
before gradually drying again on Saturday. Depending on moisture
content, the seasonal weather pattern will vary in intensity but
will include passing showers across windward sectors of the islands
and convective activity due to diurnal heating and local effects,
mainly across western/northwestern Puerto Rico. High heat indices
will continue, reaching the 110s, especially across lower elevations
and coastal sectors. Please refer to our NPWSJU product for
precautionary and preparedness actions.

&&

.AVIATION...Mainly VFR conditions are anticipated. SHRA will be
moving across the Caribbean waters today, reaching TJPS at times.
Additional activity is expected to develop across the Cordillera
Central after 17Z, with mountain obscuration possible. HZ due to
Saharan dust is expected, but with VIS remaining at P6SM. Winds
will be from the S at 8-14 kts, and stronger gusts.

&&

.MARINE...Seas at 4 feet or below are forecast for most of the
local waters, with only the offshore Atlantic waters having up to
5 feet. Moderate to locally fresh southeast winds will prevail.
Small Craft Should Exercise Caution due to winds over the Atlantic
Waters and Mona Passage today. An increase in shower activity is
forecast for the next few days as moist air moves into the region.
Isolated thunderstorms are possible across the coastal waters
during the afternoons. There is currently a low risk of rip
currents for all of the local beaches.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Watch until 10 AM AST this morning for PRZ001-004-
005-008-010-012.

Excessive Heat Watch from this afternoon through Sunday
afternoon for PRZ001-004-005-008-010-012.

Excessive Heat Warning from 10 AM this morning to 5 PM AST this
afternoon for PRZ001-005.

Excessive Heat Watch through Sunday afternoon for PRZ002-003-006-
007-009-011-013.

Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
for PRZ004-008-010-012.

VI...Excessive Heat Watch through Sunday afternoon for VIZ001-002.

AM...None.

&&

$$

SHORT TERM...ERG
LONG TERM....MRR

[NDG]

Incredible heat in PR.
I was in the beautiful island in late April, I was expecting a nice strong easterly sea breezes to cool us off like I encountered in late June last year but the sea breeze was absent this time, in the mornings it was dead calm right on the beach near Rio Grande.

[cycloneye]

:uarrow: Incredible heat in PR.
I was in the beautiful island in late April, I was expecting a nice strong easterly sea breezes to cool us off like I encountered in late June last year but the sea breeze was absent this time, in the mornings it was dead calm right on the beach near Rio Grande.

Look what we have.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
423 AM AST Sun Jun 4 2023

.SYNOPSIS...Above normal moisture will continue to be steered
into the island by breezy southern winds. Due to the combination
of high temperatures and moisture, high heat indices are expected
once again from late morning to the afternoon hours. A drier
pattern is expected to start late tomorrow into Tuesday as winds
become more southeasterly and more Saharan Dust filters in.

&&

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

The Doppler radar summary since midnight indicates slight rainfall
accumulation across the southern half of Puerto Rico, and also for
Vieques and Culebra. No rain was detected over the Virgin Islands.
This rain was the result of passing showers reaching the coastal
areas from the Caribbean Sea.

No significant changes were introduced to the near term forecast,
except to reduce the probability of precipitation late Monday and on
Tuesday. The general pattern is still dominated by a deep layer high
pressure over the eastern Atlantic and a deep layer trough centered
near Cuba. These features are driving the low and mid level winds
from the south today and tomorrow. Under this pattern, temperatures
will continue to warm up, reaching the mid 90s along the coastal and
urban areas of Puerto Rico, and the upper 80s to low 90s along the
Virgin Islands. The wind flow will also maintain the moisture levels
above normal, with precipitable water values around 2.0 inches. With
the combination of hot temperatures and high humidities, heat
indices are again expected to surpass 111 degrees along north-
central Puerto Rico...above 108 for Culebra, the northeast,
northwest, around Mayaguez, and in the urban and valleys of the
eastern interior...and from 102 to 107 for the southern coast of PR,
Vieques, and all of the U.S. Virgin Islands. The heat will not give
way, and above normal temperatures will persist throughout the end
of the forecast period.

On Tuesday, the upper level trough will lift and the high pressure
will make the winds to back a little, becoming out of the southeast.
Winds will remain enhanced too, with the low level wind steering
flow at 20 knots today, and around 15-18 kts on Monday and
Tuesday. Additionally, the aerosol models indicate that Saharan
dust will increase in concentration, resulting in hazy skies, with
higher concentrations on Monday and Tuesday. Finally, discussing
rainfall probabilities, the mid to upper level high will result in
unfavorable conditions for strong showers to develop. However,
passing showers will continue to move across the southern
municipalities of Puerto Rico, resulting in wet roads and ponding
of waters in areas of low elevation.

&&

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

No major changes to the long term forecast. A surface high pressure
northeast of the region will promote more southeasterly winds and
steer a Saharan Air Layer (SAL) over the islands. Model guidance
indicates higher concentrations on Thursday, where Aerosol Optical
depth could reach more than 0.20 over the islands, above the 75th
percentile. Saharan dust will continue to linger for most of the
period, promoting hazy skies. A mid- to upper- level ridge will
dominate the region and mostly dry air will be present above 850 mb.
This will limit convective development and promote stability over
the islands. In terms of Precipitable Water (PWAT) values, these
should remain at normal to below normal for this time of the year
with the driest day being Thursday, with PWAT values around or below
an inch. Model guidance now seems in more agreement with an increase
in moisture for Friday. Frontal moisture remnants that moved around
the surface high pressure will be steered towards the region on
Friday promoting an increase in PWAT values. Patches of both drier
and humid air will reach the region during the weekend but an
overall drying pattern will be observed. The seasonal weather
pattern will vary in intensity depending on moisture content; on
days with more moisture, passing showers across windward sectors of
the islands and afternoon convective activity due to diurnal heating
and local effects will be more likely. High heat indices are
expected each day, reaching 105 degrees to the 110s, especially
across lower elevations of northern and western Puerto Rico.

&&

.AVIATION...Mainly VFR conditions expected to prevail. Passing
SHRA expected to move at TJPS through the period, with brief
periods of reduced VIS and low ceilings possible. HZ due to
Saharan dust is expected, but with VIS remaining at P6SM. Winds
will be from the south at 13-20 kts, and stronger gusts.&&

&&

.MARINE...Moderate to locally fresh south to southeasterly winds
will continue across the region. Small Craft Should Exercise
Caution mainly over the offshore Atlantic, eastern waters, western
waters and the Mona Passage due to these winds. Expect seas 4
feet or less over the local waters. There is a low risk of rip
currents for all of the local beaches.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Watch until 10 AM AST this morning for PRZ001-005-
008.

Excessive Heat Watch from this afternoon through Tuesday
afternoon for PRZ001-005-008.

Excessive Heat Warning from 10 AM this morning to 5 PM AST this
afternoon for PRZ001-005.

Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
for PRZ002-004-008-010-012.

VI...None.
AM...None.
&&

$$

SHORT TERM...ERG
LONG TERM....MRR