Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Mon Jun 28 2021

.SYNOPSIS...A drier air mass with Saharan dust will move across
the area through early Wednesday. A strong tropical wave is
forecast to move across the region on Thursday, increasing shower
and thunderstorm activity across all the islands. Hazardous seas
are expected with the wave passage.


&&

.SHORT TERM...Monday through Wednesday...

Weather conditions will become more stable as a mid-level ridge
builds over the northeast Caribbean, causing the mid-levels of the
atmosphere to dry out, especially Tuesday and early Wednesday. A
trade wind surge brought another pulse of moisture over the islands
producing scattered showers across the windward sections and
surrounding waters; these showers will persist throughout the
morning. During the afternoon hours, the shower and thunderstorm
activity will affect the northwest quadrant of Puerto Rico as the
moisture combines with daytime heating and local effects. Urban and
minor flooding will be a possibility with the heaviest and most
persistent rainfall activity.

A drier air mass with African Dust Particulate will arrive by
Tuesday afternoon, strengthening the trade wind cap and limiting
shower activity significantly, and hazy skies will also be possible.
Then, by Wednesday mid-morning into the afternoon hours, a robust
tropical wave will reach the Virgin Islands and eastern Puerto Rico,
increasing the potential to observe thunderstorm activity with heavy
rainfall.

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

A strong tropical wave is expected to bring squally weather
conditions across the region on Thursday. This tropical wave has
a low formation chance to develop during the next 5 days into a
tropical cyclone according to the National Hurricane Center.
Regardless, scattered to locally numerous showers and
thunderstorms are expected to affect the islands with the wave
passage, increasing the potential for urban and small stream
flooding, as well as localized flash flooding.

A strong ridge is forecast to build across the Atlantic basin
behind the wave, and another area of Saharan dust with drier air
is expected to move over the islands and promote fair weather
conditions on Friday into the weekend. However, another tropical
wave is forecast to move mainly south of the region early in the
weekend, increasing shower activity across the islands. Model
guidance is not in current agreement with the wave passage during
the weekend, as the ECMWF has a faster solution than the GFS,
which has a wave entering the eastern Caribbean by late Monday.


&&

.AVIATION...VFR conditions will persist through much of the forecast. -SHRA/SHRA
will reach the eastern terminals of PR/USVI during the morning from
time to time. SHRA/TSRA will form across the Cordillera Central and
NW-PR between 28/15-23z, and mountain obscuration will develop, and
some activity could reach JBQ. Winds will remain calm to light and
variable until 28/13z when they are forecast to return from E-ENE at
10-20 kt with higher gusts and sea breeze variations.


&&

.MARINE...Moderate winds up to 15 knots and seas up to 5 feet are
expected to prevail across the regional waters through at least
Tuesday. Winds and seas will gradually increase after Wednesday
due to an approaching strong tropical wave. Choppy to hazardous
seas are expected on Thursday. For beachgoers, there is a moderate
risk of rip currents for the northern and southern beaches of
Puerto Rico, Vieques and Culebra, and as well across the eastern
beaches of St. Croix.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 79 88 79 / 50 30 30 40
STT 89 78 88 78 / 50 30 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
437 AM AST Tue Jun 29 2021

.SYNOPSIS...

A typical pattern of shower activity is expected through midweek. On
Thursday, a vigorous tropical wave will make its way into the
region, bringing moisture and instability; unsettled weather is
expected, and significant rainfall is possible. Flash flooding will
be a concern, as well as the potential for mudslides. Drying is
likely for Friday.

For the local waters, increasing winds are expected with the
tropical wave, leading to building seas. Conditions could become
hazardous as soon as Wednesday night.

&&

.SHORT TERM...Tuesday through Thursday...

High pressure at mid-levels will promote dry air and subsidence
today and tomorrow. Meanwhile, at the surface, high pressure will
promote an easterly wind flow. Therefore, expect an advective
pattern, with pockets of moisture arriving embedded in the trade
winds from time to time. Then, afternoon convection will develop
over the western portions, due to the combination of diurnal
heating and sea breeze variations. Also, model guidance and
satellite imagery suggested suspended African dust particles,
which could create hazy skies. They will arrive between today and
tomorrow, before the arrival of a robust tropical wave by
Wednesday afternoon into Thursday.

The leading edge of the robust tropical wave is forecast to cross
the Lesser Antilles around early Wednesday, approaching the U.S.
Virgin Islands and eastern Puerto Rico by Wednesday afternoon. The
axis will move by PR/USVI late Wednesday night or early Thursday
morning. This wave will increase winds and the potential for
widespread showers and thunderstorms late Wednesday afternoon into
Thursday. An unstable weather pattern with a high risk of urban
flooding, flash flooding, and mudslides in steep terrain could be
possible through the passage of this wave.

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

On Friday, the tropical wave will be pulling away from the region,
replaced by a drier air mass, as ridging builds into the area.
Aloft, there is a mid- to upper-level ridge, as well, which will
also inhibit shower activity. There will, however, remain sufficient
low-level moisture to help sustain a typical pattern of shower
activity. Confidence in Friday`s forecast is relatively high.

Saturday is more of an enigma. Model guidance does not have great
agreement. The GFS is very bullish on a tropical wave that is set to
make its way into the Caribbean by the weekend. The CMC is the
closest it has to corroboration for this scenario, and that
corroboration is half-hearted, at best. It is likely that, whatever
becomes of this wave, some moisture will make its way into the
region, at least in southern portions, for Saturday. Ridging is
likely to remain in place aloft, maintaining conditions that are not
favorable for significant convective development. So, the big
questions for Saturday are with whether or not anything develops off
of this wave (which is not the most likely solution) and what
impacts any development (again, if it happens, which is not a
favored solution) would have on instability aloft, and how far
north does the moisture push. Presently, significant convective
development does not look likely. But, an increase in shower
activity is certainly possible. The forecast confidence for
Saturday into Sunday is low to maybe low-moderate.

For early next week, moisture is likely to decrease behind the wave
on Sunday, though patches of moisture are expected to affect the
region from time to time from Sunday night through the early part of
the week. Aloft, a mid- to upper-level trough will make its way
through the region from the east. However, the upper-level trough is
forecast to stall over or just east of the islands, which will
maintain less favorable conditions aloft, with convergence at the
upper-levels preventing good ventilation. As such, most moisture
will remain relegated to the lower levels. This will be enough to
maintain the typical pattern of showers, though. Confidence in the
forecast is moderate to high.

&&

.AVIATION...

VFR conditions with passing SHRA/-SHRA moving mainly across the
local waters, and some of them will make their way near terminals of
E-PR/USVI/Leeward Islands. Some Saharan dust will filter late this
afternoon/evening, but VIS will remain P6SM. Convection will develop
over the interior and western portions between 29/16-23z and may
affect JBQ. Winds will remain calm to light and variable until
29/13z when they are forecast to return from E-ENE at 10-20 kt with
higher gusts and sea breeze variations.

&&

.MARINE...

Winds remain generally light to moderate across the local waters
today. This will sustain choppy conditions for the local waters,
with seas of up to around 5 feet, especially for the offshore
waters. Increasing winds are expected tomorrow, and especially
overnight tomorrow night, with the approach of a tropical wave.
Building seas are expected, and hazardous conditions are likely by
Thursday morning, or as early as tomorrow night.

For the beachgoers, there is a moderate risk of rip currents for the
north coast of Puerto Rico, eastern Culebra, as well as for beaches
of eastern St. Croix. This risk will increase and spread with the
approach of the tropical wave.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 88 78 / 50 30 70 70
STT 88 79 90 79 / 30 30 50 70

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
448 AM AST Wed Jun 30 2021

.SYNOPSIS...

A tropical wave is expected to arrive by overnight tonight, and
unsettled weather conditions are expected tonight through tomorrow;
flooding will be a concern through this period. Drier air and
more settled conditions are expected for Friday. On Saturday, a
tropical system will approach the southern part of the region, and
unsettled conditions are expected. This system is being monitored
by the NHC for development; as of 2 am, it has a 70% chance of
forming a tropical depression within the next 5 days. Regardless
of development, there is the potential for a significant increase
in showers, and therefore an increase in flooding potential, for
the region on Saturday.

&&

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

Dry air and subsidence ahead of a tropical wave will limit shower
activity through at least this afternoon. An area with suspended
dust particles will also move over the northeast Caribbean, creating
hazy skies before the arrival of the tropical wave.

The leading edge of the tropical wave is moving into the eastern
Caribbean. It will increase the available moisture across the U.S.
Virgin Islands late this afternoon into the evening hours. The axis
of the tropical wave should be near PR/USVI late tonight into early
Thursday morning. As such, expect shower and thunderstorm
activity to slowly increase in frequency, intensity, and coverage
after this afternoon into Thursday. Eastern PR, the USVI, and
their surrounding waters can expect a peak in shower and
thunderstorm activity between late Wednesday night and early
Thursday. An unstable weather pattern with a high risk of urban
flooding, flash flooding, and mudslides in steep terrain could be
possible through this period.

The lingering moisture associated with this wave will remain across
the local islands through at least early Friday morning. Moisture is
forecast to erode around sunrise on Friday slowly and before the
approach of another tropical system on Saturday, monitored by the
National Hurricane Center.

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

There remains significant uncertainty with respect to the forecast
for Saturday. The GFS remains very bullish with respect to potential
development with the tropical wave that is currently located around
40W. This system is also being monitored by the NHC, and has a 50%
chance of becoming a tropical depression in the next 2 days, and a
70% chance within the next 5 days. This tropical system, whatever
becomes of it, is forecast to be making its way across the eastern
Caribbean by Saturday morning. The details beyond that remain murky.
That being said, the GFS does appear to be capturing well what is
happening with this wave presently; it is currently showing some
organization, including hints of rotation. Additionally, other model
guidance, including the CMC and ECMWF is now suggesting the
potential for development with this system, though they remain less
aggressive than the GFS. Ensemble guidance is also in line with this
scenario. That being said, the additional confidence in the future
of this tropical wave does not necessarily mean an equal boost in
confidence to forecast conditions for the region. Right now, the
likely scenario includes an increase in moisture, likely a
significant one, across the area. This would bring a corresponding
increase in shower activity, especially for the local islands, but
also likely the Caribbean. That being said, the ECMWF maintains a
stronger mid-level and surface ridge over the region, as well as
an upper-level trough extending closer to the region from the
northeast; this would keep drier air over the area. This solution
cannot be entirely ruled out.

On the whole, the forecast for Saturday itself is fairly unstable -
a small change in the mid-level ridge or small alteration in the
development of the wave or its organization will likely have
substantial impacts on the conditions that we see for the local
area. Presently, however, leaning more towards the GFS solution,
considering it appears to be performing well with the systems at
play, and other models are gradually trending in its general
direction. Should this moisture materialize over the area instead
of remaining to our south, significant rainfall is possible, and
flooding would be a potential concern. Those with interests in
Puerto Rico or the USVI should monitor future forecasts and
products for any potential changes.

Moisture will linger over the area on Sunday, and possibly into
Monday. Given the aforementioned uncertainty, the forecast for both
of these days also retains a lower confidence level. A gradual
decrease in shower activity is likely. Conditions aloft are expected
to not be favorable for convective development, and organized
convection becomes decreasingly likely by the start of the work
week.

Late Tuesday into Wednesday, a tropical wave is forecast to pass by
the region to the south. Meanwhile, an upper-level trough and
induced mid-level trough are expected to move into the region from
the east. Some moisture from the wave will likely reach the local
islands, and the troughing will make conditions aloft less
unfavorable for convection by around midweek. An increase in shower
activity is expected, though not a very large increase.

Again, those with interests in and around the USVI and Puerto Rico
should monitor future forecasts, discussions, and products from
this office for any changes to the conditions expected for
Saturday.

&&

.AVIATION...

Calm weather and VFR conditions will prevail through this afternoon.
SHRA/TSRA may develop near the Leeward Islands by this afternoon.
The leading edge of a tropical wave will move closer to the USVI/E-
PR around 30/18z, which could bring VCSH/VCTS. SHRA/TSRA will
increase in frequency after 30/23z from the east. SHRA/TSRA will
develop near IST/ISX/JSJ/JBQ between 30/16-23z. Winds will remain
calm to light and variable until 30/13z, and then they will return
from E-ESE at 10-20 kt with higher gusts and sea breeze variations.

&&

.MARINE...

Increasing winds causing building seas are expected for today. Seas
of up to 6 feet are possible by later today, and overnight tonight,
conditions are expected to become hazardous. Small Craft Advisories
are in effect. On Saturday, with the approach of the aforementioned
tropical system, stronger winds are expected, especially for the
Caribbean waters, and hazardous conditions are likely to extend
through the weekend.

For the beachgoers, there is a moderate risk of rip currents for
northern, eastern, southeastern, and some southern beaches of Puerto
Rico, as well as most beaches of the USVI, Vieques, and Culebra.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 87 77 / 60 70 70 20
STT 89 79 86 79 / 50 70 50 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Thu Jul 1 2021

.SYNOPSIS...

Unsettle weather conditions will prevail today with the passage of
a Tropical Wave. Subsidence between this wave and Tropical Storm
Elsa will create brief calm weather conditions on Friday. However,
Elsa will increase, once again, the potential for flooding and
thunderstorm formation late Friday night through Saturday. Drier
and stable weather conditions will be possible for next week.

&&

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

Air remains moist behind the first leg of a tropical wave that
passed through the area on Wednesday. A knot of much better moisture
is passing south of the forecast area at this time. An upper level
jet is leaving the area to the north and those winds are subsiding
which will also remove some of the energy available for convection
today.

The National Hurricane center has declared the depression in
the tropical Atlantic about 1300 miles east southeast of San Juan to
be Tropical Storm Elsa. Elsa is moving very fast and is expected to
pass south of the forecast area Friday night and early Saturday
morning. Currently the intensity is more uncertain than the track,
but bands of rain are expected to impact Puerto Rico Friday night
and Saturday with flooding possible. The highest amounts are
expected over the southeastern slopes of our higher terrain and
across the southwest portion of the island. The U.S. Virgin Islands
should see beneficial rains from this system, but should bands form
in the area they could still bring local urban and gut flooding.
Models are showing considerable winds at lower levels with the
passage of this system with more than 50 knots forecast over Puerto
Rico and the U.S. Virgin Islands at 700 mb. Thus thunderstorms that
form in the area could easily carry winds gusts in excess of 50 mph
Friday night or Saturday.

Between the tropical wave now passing through the area and Tropical
Storm Elsa, subsidence dominates and a puff of Saharan dust
accompanies that dry air. Although precipitable water values are
above 2 inches now, they are expected to drop to 1.4 inches by
midday on Friday and then bounce right back to above 2.2 inches
during the passage of Tropical Storm Elsa to the south. Hence shower
and thunderstorm activity will be reduced greatly on Friday, but
thunderstorms due to intense heating and local circulations are
still expected to develop on Friday.

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

Dry air behind Elsa will filter in, limiting the potential to
observe rain activity. Model guidance also indicates the
possibility of having an African dust event, which could create
hazy skies Sunday through Monday. However, a high surface pressure
across the Atlantic Ocean will promote an advective pattern that
could bring patches of moisture from time to time over Puerto Rico
and the U.S. Virgin Islands.

Late Monday into Tuesday, a tropical wave is now forecast to pass
by the region, with its bulk of moisture south of the islands.
This wave will be coupled with an upper-level trough and induced
mid-level ridge moving westward with it.

For the second part of next week, a gradual decrease in shower
activity is likely, with conditions aloft forecast to be
unfavorable for convective development. Also, model guidance
propagates an extensive Saharan Air Layer into the region during
that period, which, if it materializes, will result in hazy skies
and above-average high temperatures.

&&

.AVIATION...

The last leg of a tropical wave will pass through the area today
with SHRA and sct TSRA dvlpg by 01/15Z and contg byd 01/22Z. Expect
areas of MVFR/IFR conds with mtn obscurations. ESE flow of 15-20 kt
will dvlp by 01/14Z and cont thru 01/21Z. Maximum winds ESE 25-35 kt
btwn FL026-180 increasing later today and tonight.

&&

.MARINE...

Hazardous marine conditions are expected over all the local waters
as a tropical wave moves into the region with strong winds up to
25 knots and seas up to 8 feet. This wave will increase shower and
thunderstorm activity over most of the local waters throughout
the day. Frequent lightning will occur with this activity. Small
Craft Advisories are in effect for most of the local waters
through at least Sunday.

Tropical Storm Elsa could move near the local Caribbean Waters
late Friday night into Saturday. Elsa will deteriorate even more
marine and weather conditions. Interest in Puerto Rico and the
U.S. Virgin Islands should monitor the evolution of this system.

Beachgoers, a high risk of rip currents is in effect for the south
and southeast coast of Puerto Rico, Vieques, Culebra and St Croix.
Elsewhere, there is a moderate risk of rip currents.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 88 79 / 90 40 40 80
STT 89 78 90 80 / 50 30 20 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
550 AM AST Fri Jul 2 2021

.SYNOPSIS...

A Tropical Storm Warning is in effect for the Caribbean Offshore
Waters and the Mona Passage from 8 PM AST through noon Saturday.

A dry air mass with suspended African Dust Particles will create
hazy skies across the local islands. In addition, subsidence ahead
of Tropical Storm Elsa will promote calm weather conditions
today. The fast-moving Elsa will pass well south of Puerto Rico
and the U.S. Virgin Islands late tonight through early Saturday
morning. Elsa will increase, once again, the potential for
flooding and thunderstorm formation late tonight through Saturday.
Drier and stable weather conditions will be possible through
early next week.

&&

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

An area of Saharan air with a significant amount of dust
particulates will leave the forecast area today as it moves
northwest being pushed ahead by Tropical Storm Elsa. Tropical Storm
Elsa is expected to pass just south of the forecast area tonight and
it is currently expected that tropical storm force winds will brush
the southwest corner of the forecast area south of the Mona Channel.
Outer rain bands will begin affecting Puerto Rico principally after
midnight tonight. The intensity and track of Elsa still have some
uncertainty and winds across the island will depend very much on how
close the system, however models have been fairly consistent and
bring 20 to 25 knots across exposed portions of the islands tonight
with gusts of over 30 mph possible. Elsa is moving very rapidly and
will move across the eastern Caribbean and be south of the Dominican
Republic by Saturday morning. This is when the best winds are
expected, but latest model guidance suggests that the envelope of
best moisture and rains will be west of the U.S. Virgin Islands by
Saturday and possibly even past eastern Puerto Rico. Therefore only
limited rains (for a tropical cyclone passage) are in the forecast.
After some drying Saturday night, an area of moisture will fragment
over the area on Sunday. East southeast flow should pull scattered
showers over southeast Puerto Rico during the morning and allow
showers or a few thunderstorms to form in northwest and interior
Puerto Rico during the afternoon. Only slight activity is expected
for the U.S. Virgin Islands Saturday and Sunday.

.LONG TERM...Monday through Friday

Model guidance also indicates the possibility of having an
African dust event, which could create hazy skies Monday through
Tuesday. However, a high surface pressure across the Atlantic
Ocean will promote an advective pattern that could bring patches
of moisture from time to time over Puerto Rico and the U.S. Virgin
Islands.

Now, model guidance has the tropical wave arriving at the region
Tuesday or Wednesday, with its bulk of moisture south of the
islands. In addition, an upper-level trough could promote a better
dynamic if it locates near the Hispanola when the wave arrives.

Once again, a gradual decrease in shower activity is forecast for
the second part of the week. Due to unfavorable conditions for
convective development aloft. Model guidance also propagates an
extensive Saharan Air Layer into the region during that period,
which, if right, will result in hazy skies and above-average high
temperatures.

&&

.AVIATION...

VFR conds to prevail til aft 02/22Z all TAF sites xcp til aft 02/18Z
TNCM/TKPK for MVFR CIGs. A mass of drier air with Saharan dust is
passing through PR/USVI today and will cause visibilities to be less
than 15 miles. Sfc winds will begin to accelerate this morning ahead
of the passage of TS Elsa about 180 miles SSW of Cabo Rojo, PR arnd
03/06Z. Sfc winds are expected to be E 12-18G24 kt bcmg aft 02/22Z E
15-25g35kt. Minimal SHRA activity today, but SHRA incrg aft 03/04Z
ovr ern PR and the local Caribbean waters.

&&

.MARINE...

Hazardous marine conditions will continue across all the local
waters due to a moderate to strong easterly wind flow. Therefore,
mariners can expect seas up to 7 feet and winds between 20 and 25
knots. Small Craft Advisories are in effect for most of the local
waters through at least Sunday.

Tropical Storm Elsa will move near the local Caribbean Waters late
tonight through Saturday. Elsa will deteriorate even more marine
and weather conditions. Therefore, a Tropical Storm Warning is in
effect for the Caribbean Offshore Waters. A Tropical Storm
Warning means that tropical storm conditions are expected
somewhere within the warning area. Mariners can expect seas
between 10 and 15 feet and winds 25 to 40 knots with higher gusts.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 79 88 78 / 20 60 70 20
STT 90 80 89 81 / 20 30 50 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
522 AM AST Sat Jul 3 2021

.SYNOPSIS...
Hurricane Elsa continues to move rapidly westward across the
Caribbean sea, causing deteriorating weather conditions over the
forecast area. Light to moderate showers are expected to continue
in the morning hours as the outer rainbands are still expected to
affect the local islands. However, heavy showers are expected
across the local waters and southwestern PR this morning as well.
Rainfall accumulations with these rainbands are still expected to
range between 1 to 3 inches with isolated amounts of up to 5
inches. Gusty winds up to 40 mph are also expected with sustained
winds to range between 15 and 25 mph. On Saturday, weather
conditions are expected to improve as Elsa moves away.

&&

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

Hurricane Elsa`s rainbands is moving quickly to the west-northwest,
with its center over 150 miles to the south of the local islands.
The outer rain bands will affect the local islands today, especially
in the morning. The latest model guidance has most of the rainfall
just west of the USVI, and mainly affecting eastern and southern
Puerto Rico. The rainfall forecast has remained the same for Puerto
Rico, 1-3 inches and isolated up to 5, but again the higher amounts
are expected across south and eastern PR, with the rest of PR and
the USVI in the lower end of that range. The periods of moderate to
heavy rainfall may result in urban and small stream flooding, with
the potential of mudslides in areas of steep terrain. For more
information on Hurricane Elsa please visit the National Hurricane
Center at www.nhc.noaa.gov.

The weather is expected to improve starting tonight, and mainly fair
weather with isolated showers expected across the local waters,
USVI, and eastern PR. Much drier air with Saharan dust will be
moving in on Sunday, and remaining over the area through the short
term period. Hazy skies and low probability of significant rain is
forecast for Sunday and Monday.

The winds will be gusty today, up to around 35 mph, especially near
the showers. After the bands of the hurricane move away, starting
tonight, the winds will be mainly easterly, at around 15 mph, and
will be from the east to east southeast. The high temps across the
lower elevations are forecast to be in the upper 80s to low 90s for
the next few days.


.LONG TERM...Tuesday through Saturday

A drier and more stable weather pattern is expected in the long
term period. At the surface, high pressure will dominate the
region with an easterly wind flow pushing fragments of moisture
over the forecast area. At the upper levels, the subsident part
of an upper level low will promote stable conditions. This
combination will result in mostly clear skies and the typical
afternoon shower activity due to the local effects combining with
the available moisture and diurnal heating. As the upper level
low moves westward, unstable conditions aloft will promote an
increase in shower activity. These conditions in combination with
deep moisture from a tropical wave will increase the potential
for shower activity on Wednesday. According to the GFS model
guidance, temperatures at 500 MB will drop between -7 to -8
Celsius, increasing the potential for isolated thunderstorms on
Wednesday. A light concentration of Saharan Dust could limit the
shower activity.

In the latter part of next week, a stable weather pattern will
prevail over the forecast area. Both the GFS and ECMWF show a mid
to upper level ridge and a surface high pressure dominating the
forecast area. Additionally, Saharan dust is expected to affect
the local islands on Thursday and Friday causing hazy skies and
limiting the shower activity. Adding another limiting factor for
shower activity, the MJO forecast continues to suggest the
suppressed phase over the islands for the latter part of the long
term period.


&&

.AVIATION...
SHRA/TSRA expected this morning, causing VCTS/VCSH across the local
terminals. Winds will be sustained from the east at around 15-20KT
but gusting to 25-30 KT, especially near SHRA/TSRA. This activity
will move away by 03/21Z. Thereafter, winds will be around 15KT but
with fewer gusts and only a few SHRA left in the area. CIGs will be
at around FL040 this morning, then increasing to around FL080 after
03/16Z, but MVFR CIGs are possible near SHRA/TSRA.

&&

.MARINE...
Very hazardous marine conditions are expected to continue over all
the local waters with seas up to 14 feet in the Caribbean waters
and up to 10 feet over the Atlantic waters. Winds are expected to
range between 15 and 30 knots with higher gusts. However, across
the offshore Caribbean waters and Mona Passage, winds of up to 40
knots are possible with the showers and thunderstorms. A tropical
storm warning continues in effect for the Caribbean waters and
the Mona Passage until noon today. Across the rest of the local
waters, a Small Craft Advisory is in effect. A High Surf Advisory
and a high risk of rip currents are in effect for coastal
locations due to large breaking waves expected to range between 7
and 15 feet, with the largest breaking waves expected across the
south coast of Puerto Rico. Marine and coastal conditions will
gradually improve by Sunday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 91 78 / 70 30 20 30
STT 89 81 88 78 / 60 30 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
508 AM AST Mon Jul 5 2021

.SYNOPSIS...
Partly cloudy skies are expected to prevail in the morning hours
with isolated light showers over the eastern sections of Puerto
Rico. In the afternoon hours, an increase in cloudiness and shower
activity is expected across northwestern sections of Puerto Rico
due to a east-southeasterly wind flow. An increase in afternoon
shower activity is possible on Wednesday as a tropical wave
affects the area and combines with an Tropical Upper Tropospheric
Trough (TUTT).

&&

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

Patches of moisture will be moving through today, with the
available moisture ranging from near normal to below normal. This
means that isolated to scattered brief showers will affect the
local waters, USVI, and eastern PR in the morning. However, the
moisture combined with the diurnal heating and local effects could
cause showers and isolated thunderstorms across the western and
northwestern sections of PR this afternoon. A few showers could
also affect eastern PR in the afternoon, though the USVI could
remain with mainly fair weather or brief isolated showers. Then
on Tuesday, some Saharan dust could be moving in although not in
large concentrations. Also, a TUTT would be better positioned for
the development of thunderstorms over the local area, even though
the available moisture will be near or below normal. Therefore,
scattered showers are once again expected in the morning across
the local waters, eastern PR and the USVI, with afternoon isolated
thunderstorms occurring across western and northwestern PR. Then
on Wednesday, a tropical wave will pass well to the south of the
local islands, but the available moisture will increase briefly
over the local area. This increase in moisture will combine with
the TUTT, which will be much better positioned, to our west, for
the development of afternoon thunderstorms across western PR.
However, the Saharan dust is expected to be in larger
concentrations by then also, and it could have a relatively dry
layer at around 600-700mb, limiting the potential for widespread
showers and thunderstorms. This could be a reason why the local
guidance has modest coverage of shower activity as well as amount
of rain for Wednesday.

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

For the first part of the long term period, a stable weather
pattern will prevail over the forecast area. A drier air mass is
expected to move westward and filter into the region with Saharan
dust particles, turning the conditions unfavorable for shower
activity. Saharan dust is expected to affect the local islands
and will result in hazy skies until at least the late morning
hours of Friday. As a result, the GFS model guidance suggests
precipitable water values near 1.4 inches, which is below normal.
Regardless of the aforementioned conditions, afternoon convection
will not be ruled out for the western sections of Puerto Rico.

As a surface high pressure sinks into the Central Atlantic, a
more east southeasterly wind flow is expect to push low level
moisture into the forecast area. Starting on Sunday into Monday,
this aforementioned increase in low level moisture is expected to
result in shower activity in the afternoon hours, due to the
combination of diurnal heating, available moisture, and the local
effects. Daytime high temperatures are expected to fluctuate
between the low 80s to the low 90s each day.

&&

.AVIATION...VFR conds expected through the forecast period. Brief
-SHRA could affect the local terminals, but mainly causing VCSH.
Winds will be from the east at around 15KT with occasional gusts
during the day, decreasing after 05/22Z. VCTS possible at TJBQ
after 05/17Z.

&&

.MARINE...
A surface high pressure across central Atlantic will
result in moderate easterly winds through the next few days. This
will result tranquil marine conditions with seas between 3-5 feet
across most of the local waters through Tuesday. Today, winds
will be moderate to fresh from the east causing choppy marine
conditions, especially across the offshore waters and local
passages, with seas up to 5 feet. Isolated to scattered passing
showers are expected. A slight increase in shower and thunderstorm
activity is forecast for mid week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 90 78 / 30 30 20 20
STT 88 80 89 79 / 30 30 40 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Tue Jul 6 2021

.SYNOPSIS...Strong surface High pressure across the central
Atlantic will promote moderate easterly winds across the local
area for the next few days. A TUTT is to the north of the local
area and is slowly moving west to southwest, and is expected to be
over Hispaniola by Thursday. A tropical wave will pass just to the
south of the local area from late tonight through Wednesday.
Saharan dust will be moving in today and linger through much of
the workweek, peaking in concentration on Wednesday and Thursday.

&&

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

During the short term period, a surface high pressure located across
the Central Atlantic will continue to result in a moderate to fresh
east-southeast wind flow over the forecast area. As the surface high
moves more to the north, a drier air mass with Saharan dust
particles is expected to filter into the region today. At this
time, GOES-16 satellite imagery showed precipitable water values
near 1.5 inches, which is below normal. Afternoon convection is
expected, causing mainly showers with a possible thunderstorm
over the western and northwestern sections of Puerto Rico.

On Wednesday into Thursday, a Tropical Upper Tropospheric Trough
(TUTT) will continue to sink more to the southwest, causing
unstable conditions. Meanwhile, a slight increase in moisture is
expected from a tropical wave moving to the south of the forecast
area, causing an increase of the precipitable water values to near
normal. However, the GFS model guidance is suggesting drier
conditions with a inversion cap, causing unfavorable conditions
for heavy and long lived shower activity. That said, this
increase in moisture can erode the inversion cap and result in
afternoon convection with isolated thunderstorms locally over
western and northwestern Puerto Rico each day. For the rest of the
day, hazy skies and relatively dry conditions will prevail due to
Saharan Dust moving over the forecast area.

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

A fairly typical weather pattern is expected in the long term
forecast. Isolated to scattered showers across the local waters,
USVI, and eastern PR are expected in the night time and early
morning hours, followed by afternoon showers and thunderstorms
across western PR depending on the sea breeze convergence and
overall wind flow. That said, a mainly easterly wind flow is
expected to prevail through the the rest of the week, then
southeast winds early next week. There is no particular mid or
upper level feature that would cause a significant increase in
instability and thunderstorm potential, except for an upper trough
that could cause a slight increase in instability on Sunday and
Monday. There is also a narrow tropical wave that is expected to
pass by quickly on Sunday, causing an increase in moisture, but it
will be over the course of just a few hours, and the increase in
moisture will be to that of what is normal for this time of year.
Small concentrations of Saharan dust could be moving in early next
week.


&&

.AVIATION...VFR conditions are expected across the local TAF
sites during the period. Winds will continue light until 06/12Z.
Then, winds will pickup at around 10 to 15 knots from the east,
with sea breeze variations and gusts. VCSH across TJBQ,TJSJ,
TISX, TIST, TNCM and TKPK from time to time during the period.
SHRA is possible over TJBQ after 06/17Z.

&&

.MARINE...Marine conditions will be choppy for the next several
days, as seas will be up to 5 or 6 feet and the local winds will
be up to 20 knots. Therefore, small craft operators are urged to
exercise caution. There is also a moderate risk of rip currents
across many of the local islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 88 78 / 20 30 40 20
STT 89 80 89 80 / 30 40 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
513 AM AST Wed Jul 7 2021

.SYNOPSIS...A tropical wave will pass to the south of the local
islands today, but the available moisture will increase across
the local area. Strong surface High pressure across the central
Atlantic will continue to promote moderate easterly winds across
the local area for the next few days. A TUTT is to the north of
the local area and is slowly moving west, and is expected to be
north of Hispaniola by Thursday. Saharan dust over the area will
limit shower activity today and cause hazy skies through at least
Thursday.

&&

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

A surface high pressure located across the Central Atlantic will
continue to cause a moderate to fresh east-southeast wind flow
over the forecast area during the short term period. An increase
in moisture is expected today, associated with a tropical wave
moving to the south of the region. GOES-16 satellite imagery
showed precipitable water values between 1.6 to 1.8 inches
associated with this tropical wave, which will move through the
local area and is near to slightly above normal. The GFS model
guidance is suggesting drier conditions in the mid levels and low
chances for thunderstorm activity, causing unfavorable conditions
for heavy and widespread shower activity. However, this increase
in moisture can result in afternoon convection with isolated
thunderstorms over western and northwestern Puerto Rico.

Later today into very early Thursday, the moisture associated
with the tropical wave will move out of the region. After that, a
drier air mass with lingering Saharan Dust is expected over the
forecast area, causing unfavorable the conditions for shower
activity, as well resulting in hazy skies. For Thursday into
Friday, at the upper levels, both GFS and ECMWF model guidances
continues to suggest a Tropical Upper Tropospheric Trough (TUTT)
moving westward. At this time, unstable conditions aloft are
expected mainly late Thursday into Friday were the axis of the
TUTT moves north of Hispanola. However, at the surface on
Thursday and Friday, a drier then normal air mass with Saharan
Dust will result in a trade wind cap. The combination of the
aforementioned conditions will result in limited shower activity
across the forecast area. Therefore, mainly fair weather
conditions with hazy skies in the morning hours with afternoon
localized shower activity is forecast for the latter part of the
short term forecast period.

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

A fairly typical weather pattern continue to be expected in the
long term forecast. Isolated to scattered showers across the local
waters, USVI, and eastern PR are expected in the night time and
early morning hours, followed by afternoon showers and
thunderstorms across western PR, depending on the location of the
sea breeze convergence and overall wind flow. A mainly easterly
wind flow is expected to prevail through the long term period, but
there may be stronger winds on Sunday into Monday as a tropical
wave passes through and the local pressure gradient tightens.
There is no particular mid or upper level feature that would cause
a significant increase in instability and thunderstorm potential,
as we will be mainly in between two upper level lows, one that
would move west and move over Cuba starting on Saturday, and
another to the northeast of the local islands. But some
troughiness in the upper levels could affect the local islands
early next week. A tropical wave is expected to pass by quickly
on Sunday into Sunday night, causing an increase in moisture and
possible causing stronger winds across the local area. Small
concentrations of Saharan dust could be moving in early next week.

&&

.AVIATION...VFR conditions are expected across the local TAF sites during the
period. Winds will continue from E with land breeze variation
until 07/12Z. Then, winds will pickup to around 10 to 15 knots
from the east, with sea breeze variations and gusts. VCSH across
TJBQ,TJSJ, TISX, TIST, TNCM and TKPK during the forecast period
due to moisture from a tropical wave moving to our south. After
07/18Z, SHRA and VCTS is possible over TJBQ.

&&

.MARINE...Marine conditions will be choppy for the next several
days, as seas will be up to 5 or 6 feet and the local winds will
be up to 20 knots. Therefore, small craft operators are urged to
exercise caution. There is also a moderate risk of rip currents
across many of the local islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 78 89 79 / 40 20 10 30
STT 89 80 90 79 / 20 20 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
504 AM AST Fri Jul 9 2021

.SYNOPSIS...
Dry weather conditions with hazy skies are expected to continue
for today. Above normal heat indices are expected mainly for
parts of the San Juan metro area. A week tropical wave will
quickly brush to the area on Sunday, increasing the chance for
showers and thunderstorms over the region. A second impulse of
high concentrations of Saharan dust will invade the area
thereafter. Choppy marine conditions will continue for the next
few days.

&&

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

TUTT low north of the area and associated trough will continue to
shift westward across the Mona passage today. This feature will
continue to weaken then lift just northwest of the region over
weekend, as high pressure ridge builds aloft. The strong and broad
surface ridge spread across the north central Atlantic will remain
in place into the weekend to maintain a fairly tight local pressure
gradient resulting in moderate to strong easterly winds and breezy
conditions at least through Saturday. For the rest of the morning
hours,the upper trough will aid in enhancing passing showers as
they cross the local waters, with some reaching the coastal areas
from time to time. Overall dry and stable conditions in the mid
level will continue to inhibit significant shower development during
the daytime.

For the rest of the day, local and diurnal effects will favor some
afternoon convection but mainly over the central interior and west
sections of Puerto Rico. Any shower activity over the U.S. Virgin
islands today will be of short duration and mainly on the west end
or just downwind of the islands as mostly fair weather and sunny
will prevail.

For the Saturday, a similar weather pattern is forecast with few
early morning passing clouds and showers, followed by a typical
summer time weather pattern during the day, as drier and more
stable conditions is expected. Afternoon showers should be focused
over the central and west interior sections of Puerto Rico with
limited or no shower activity forecast elsewhere including for the
U.S. Virgin Islands where mostly sunny skies should prevail.

By Sunday , the approach of a tropical wave will bring an increase
in moisture and instability across the region with better potential
for late evening and early morning showers, as well as increased
chance for enhanced afternoon convection along with isolated
thunderstorm activity and minor urban and small stream flooding
due to periods of locally heavy rains. So far model guidance all
suggest that this will be short lived as another surge of Saharan
dust of moderate to high concentration is forecast to accompany
and trail this tropical wave. Otherwise no other significant weather
feature is expected during the period.

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

A typical seasonal weather pattern is expected as mainly easterly
wind flow is expected to prevail through the long term period. A
second pulse of high concentrations of Saharan dust particles are
expected to reach the area on Monday. Thus, expect relatively fair
weather conditions with hazy skies during the first half of the
workweek. Patches of moisture will reach the islands from time to
time during the second half of the workweek, promoting passing
showers each morning over parts of eastern PR and USVI. Then
afternoon convection will spawn showers mainly over parts of
interior and western PR. However, this showers are expected to be
short-lived and produce light rainfall amounts. Troughiness in
the upper levels will dominate the region for the rest of the
long- term period.

&&

.AVIATION...

VFR conds to prevail through the fcst prd. Few-SCT passing clds
nr FL025...FL050 with mostly Isold SHRA en route btw islands
SFc wnds fm E at 10 kts or less ...bcmg fm E-NE 15-20 kts with sea
breeze variations aft 09/14Z. Some locally and diurnally induced
aftn convection mainly ovr central and w sections of PR fm
09/17Z-09/22Z.

.MARINE...

A surface high pressure across the central Atlantic will continue to
cause moderate to fresh easterly winds across the local waters
at least through Monday. Thus, choppy marine conditions are
expected to prevail for the next few days, with seas up to 6 feet
and winds up to 20 knots. Small craft operators should exercise
caution. There is a moderate risk of rip currents for most of the
local beaches.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 90 79 / 50 40 40 20
STT 89 78 90 78 / 20 40 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
514 AM AST Sat Jul 10 2021

.SYNOPSIS...
Mid to upper level ridge will build and hold across the region
through the weekend. A broad surface ridge will remain anchored
over the north central Atlantic to maintain moderate to strong
easterly winds across the region. A tropical wave is forecast to
enter the eastern Caribbean later tonight then cross the region on
Sunday. This will bring an increase in tropical moisture as well
as better potential for enhanced showers and thunderstorms across
the area Sunday into early Monday. Another surge of Saharan air layer
with suspended dust particulates of moderate to high concentration
will quickly trail this wave bringing a drier airmass but hazy and
breezy conditions.

&&

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

Passing showers embedded in the trade winds will continue to move
from time to time across parts of eastern and northern sectors of
Puerto Rico and the U. S. Virgin Islands during the morning hours.
However, most of these showers will remain over the waters and
coastal sectors.

A tropical wave makes its way into the region late tonight, promoting
more instability and moisture to generate more widespread shower
activity across the forecast area. The 500mb temperatures and mid-
level lapse rate suggest enough instability for not ruling out the
possibility of isolated thunderstorms over the municipalities
across northwestern Puerto Rico. Also, expect at least ponding of
water with the heaviest and most persistent rains. The wave will
move west of the region by Monday. Aerosol forecast models suggest
a second surge of Saharan dust particles over the region, and
with it a drier air mass. However, lingering moisture associated
with the wave is expected to combine with diurnal and local
effects to produce shower activity during Monday afternoon.

.LONG TERM...Tuesday through Sunday...

A dry airmass and typical summertime weather pattern is expected
Tuesday into Wednesday under the influence of the dominant surface
high pressure and moderate to fairly strong easterly trade winds.
Patches of moisture will however continue to move across the
region from time to time and will aid in the developing locally
and diurnally induced afternoon convection each day, with a slight
chance of an isolated thunderstorm mainly in the interior and west
sections of Puerto Rico. Mostly sunny skies will prevail in and
around the USVI. Most of the shower activity should be short-lived
with no significant rainfall accumulations anticipated.

By late Wednesday through Thursday an upper trough will move across
the region along with an induced low level trough. These features
will increase the chance and frequency of early morning showers as
well as enhanced afternoon convection over the central interior
and west sections of Puerto Rico, and on the west-end of the U.S.
Virgin islands. So far no widespread rainfall is expected with
this activity. However, by Friday into early Saturday model
guidance continued to suggest that a tropical wave will enter the
eastern Caribbean, then move across the region. This along with
the proximity of the upper trough will favor unstable weather
condition with increased potential for shower and isolated
thunderstorm development across the islands and over the coastal
waters. As a result , urban and small stream flooding will be
possible in isolated areas. For the remainder of the period a
gradual drying trend is expected with improving weather conditions
and increasing easterly tradewinds once again.

&&

.AVIATION...
Mainly VFR conditions are expected across all the terminals
during the next 24 hours. VCSH expected at times for TJSJ/TJBQ til
10/14Z. Then afternoon convection will result in VCSH for TJBQ.
Low-level winds will continue around 10 kt from the ENE, increasing
at 15-25 kts with sea breeze variations aft 10/14Z.

&&

.MARINE...
Choppy seas continues across the local waters due to easterly
winds between 15 and 20 knots and seas up to 6 feet. A slight
increase in winds and seas is expected late Sunday into Monday due
to the passage of the aforementioned Tropical Wave which will
maintain choppy wind driven seas. A small craft advisory for seas
up to 7 feet may be required by then. Stay tuned.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 86 78 / 60 50 70 50
STT 89 79 87 79 / 40 50 50 20

[cycloneye]

Area Forecast Discussion...DELAYED
National Weather Service San Juan PR
540 AM AST Sun Jul 11 2021

.SYNOPSIS...
Mid to upper level ridge will build and spread across the region
through Monday to maintain an overall anticyclonic flow aloft.
In the meantime a tropical wave with axis now entering the eastern
Caribbean will cross the region to bring an increase in moisture
and instability across the forecast area during the rest of today
and into early Monday. This in turn will increase the potential
for enhanced showers with isolated thunderstorm development
across the islands and coastal waters. Quickly trailing the wave
is another area of moderate to high concentration of Saharan dust
which will will filter ni and bring a drier airmass with hazy and
breezy conditions to the region as the trade winds increase once
again.

&&

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

The tropical wave is expected to continue affecting the local
islands today , promoting more instability and provided moisture
that will combine with a strong TUTT to generate more widespread
shower activity across the forecast area, mainly in the afternoon
hours. Isolated thunderstorms over the municipalities across
northern and northwestern Puerto Rico cannot be ruled out across
these areas. The main threat for these areas will be urban and small
stream flooding with the heaviest and most persistent rains. Shower
activity downwind from El Yunque cannot be ruled out and therefore
the San Juan metro area is expected to continue observing active
weather during the afternoon hours. There is good potential for
isolated thunderstorm activity during the afternoon mainly due to
daytime heating and local forcing. Moisture embedded in the easterly
windflow will continue to bring passing showers in and around the
islands during the overnight hours.

The wave will move west of the region later tonight into Monday.
However, lingering moisture associated with this feature is expected
to combine with diurnal and local effects to produce shower activity
and isolated thunderstorms during the afternoon. Drier, more stable
conditions are likely for Monday; a Saharan Air Layer is forecast to
filter into the area, providing a significantly dry layer at the mid-
levels. Thus, expect a summertime weather pattern through Tuesday.

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

The dominant surface high pressure across the central Atlantic will
maintain moderate to strong easterly trade winds across the region.
Patches of moisture will move across the region from time to time
and will aid in developing passing showers across the regional waters.
Locally and diurnally induced convection over portions of the islands
can be expected each afternoon but in isolated areas. By late Wednesday
through Thursday an upper trough will move across the region along with
an induced low level trough. These features will increase the chance
and frequency of early morning showers as well as enhanced afternoon
convection over the central interior and west sections of Puerto Rico,
and also on the west-end of the U.S. Virgin islands. So far widespread
rainfall is not expected with this activity.

By Friday into early Saturday model guidance continued to suggest that
a tropical wave will enter the eastern Caribbean, then move across
the region. This along with the proximity of the upper trough will
favor unstable weather condition with increased potential for shower
and isolated thunderstorm development across the islands and over
the coastal waters. As a result , urban and small stream flooding
will be possible in isolated areas. Thereafter a gradual drying
trend is expected with improving weather conditions and increasing
easterly tradewinds once again at least until Sunday. Another
tropical wave is forecast to approach the region lat Sunday into
Monday.

&&

.AVIATION...
Mainly VFR conds expected across the local terminals during the
forecast period. However, SHRA/Isold VCTS to incr across the local
flying area from the east due to an approaching tropical wave. SCT
ocnl BKN lyrs nr FL025...FL040...FL080 with SHRA/Isold TSRA en
route btw islands. Aftn convection ovr the central mountain range
of PR btw 11/17Z-11/23Z will lead to brief MVFR and VCSH at most
terminals with VCTS psbl at TJMZ/TJBQ. Wnds will be fm the E 10
kts or less bcmg E-NE 15-20 kts with higher gust and seas breeze
variations aft 11/14Z.

&&

.MARINE...Surface high pressure anchored across the Central Atlantic
will continue to promote moderate to fresh easterly winds over the
regional waters through Monday. This along with a tropical wave moving
across the regional waters, will maintain choppy and hazardous seas.
Therefore, small craft advisories will be in effect later today through
Monday for portions of the local waters. Small craft operators should
exercise caution elsewhere. Showers and isolated thunderstorm
development will be likely across the local waters today as the
tropical wave moves across the local waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 79 89 79 / 60 50 50 20
STT 89 80 90 79 / 50 30 30 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 PM AST Sun Jul 11 2021

.SYNOPSIS...
Weather conditions will continue to improve as the tropical wave
moves westward and out of the region. However, for the rest of
today, cloudiness and isolated to scattered shower activity will
prevail over local waters. For tomorrow, a drier air mass with
Saharan Dust is expected to filter into the region and will limit
the shower activity over the forecast area.

&&

.SHORT TERM...Rest of Today through Tuesday...

A surface high pressure located across the Central Atlantic will
continue to result in a moderate to fresh east-southeast wind flow
over the forecast area during the short term period. As the axis of
the tropical wave continues to move westward, the moisture
associated with it is expected to move out of the region tonight.
On Monday, a drier air mass with Saharan dust particles is
expected to filter into the region. At this time, GOES-16
satellite imagery showed precipitable water values near 1.3
inches, which is below climatological normals. Additionally, the
GFS model guidance is suggesting drier conditions in the mid
levels with low chances for thunderstorm activity, causing
unfavorable conditions for heavy and widespread shower activity.
However, a slight increase in moisture can erode the inversion cap
and result in afternoon convection over western Puerto Rico. That
said, hazy skies and relatively dry conditions are expected to
prevail elsewhere due to Saharan Dust moving over the forecast
area. As the high pressure at surface sinks, a slight increase in
moisture will move over the region embedded in the trade winds.
The aforementioned moisture could result in passing shower
activity over eastern sections of Puerto Rico and the U.S. Virgin
Islands starting on Tuesday evening.

.LONG TERM...Wednesday through Monday...From Prev Discussion...

The dominant surface high pressure across the central Atlantic will
maintain moderate to strong easterly trade winds across the region.
Patches of moisture will move across the region from time to time
and will aid in developing passing showers across the regional
waters.
Locally and diurnally induced convection over portions of the
islands can be expected each afternoon but in isolated areas. By
late Wednesday through Thursday an upper trough will move across the
region along with an induced low level trough. These features will
increase the chance and frequency of early morning showers as well
as enhanced afternoon convection over the central interior and west
sections of Puerto Rico, and also on the west-end of the U.S. Virgin
islands. So far widespread rainfall is not expected with this
activity.

By Friday into early Saturday model guidance continued to suggest
that a tropical wave will enter the eastern Caribbean, then move
across the region. This along with the proximity of the upper trough
will favor unstable weather condition with increased potential for
shower and isolated thunderstorm development across the islands and
over the coastal waters. As a result , urban and small stream
flooding will be possible in isolated areas. Thereafter a gradual
drying trend is expected with improving weather conditions and
increasing easterly tradewinds once again at least until Sunday.
Another tropical wave is forecast to approach the region lat Sunday
into Monday.

&&

.AVIATION...
Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. Low level winds will continue from the
east at 15-20 kt, decreasing 10-15 kt tonight.

&&

.MARINE...

A surface high pressure across the central Atlantic will continue to
promote moderate to fresh easterly wind over the regional waters
through Monday. This will maintain choppy and hazardous seas for
most of the local waters. Therefore, small craft advisories will be
in effect through Monday. Small craft operators should exercise
caution over nearshore waters. There is a high risk of rip current
over eastern tip of st. croix and some eastern beaches at Culebra.
Showers and isolated thunderstorm development will be likely across
the local waters tonight as the tropical wave moves out of the
region.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 79 89 79 90 / 40 30 20 30
STT 80 90 79 88 / 10 20 20 30

[cycloneye]

Area Forecast Discussion...DELAYED
National Weather Service San Juan PR
542 AM AST Mon Jul 12 2021

.SYNOPSIS...
A drier air mass with Saharan Dust is expected to filter into the
region and will limit shower activity over the forecast area. East
southeast trade winds and high relative humidities will result in
heat indices above 102 across the north central and southeast coastal
plains among others. Hazardous marine conditions will prevail
through at least late tonight.

&&

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

A TUTT low will drive southwest toward the island today and spread
some cooler mid level air over the local area. It will make a slight
loop on Tuesday and then move west to 26 north, north latitude north
of Cabo san Juan by late Wednesday. High pressure will spread west
across the central Atlantic during the period but weaken allowing
our tradewinds to relax.

The axis of the tropical wave has advanced into the Windward
passage, while active thunderstorms follow behind mainly south of
the Dominican Republic. Moisture drops off dramatically today over
our local forecast area but models continue to keep the atmosphere
at 850 mb very moist through at least 14/00Z. Also the GFS sounding
shows minus 9 500 mb temperatures as well as a lifted index of minus
9. Ordinarily for a mid July day this would result in widespread
showers and thunderstorms, but a strong inversion with a top at
around 8 kft and a dry profile above it due to another invasion of
Saharan air loaded with dust, should limit showers today to shallow
low level activity over eastern Puerto Rico this morning and tonight
and some heavier, showers over western Puerto Rico this afternoon.
Isolated thunderstorms are possible in such an unstable atmosphere
in the west only if better moisture can be found in an isolated
pocket or protected local circulation. Also 25 to 30 kt winds from 3-
16 kft will move much of the activity into the Mona Channel if it
can overcome the inversion cap. The dust has already peaked
according to the model, but a second weaker lobe will pass through
on Tuesday afternoon.

Also on Tuesday, stability increases considerably, but the inversion
is also expected to diminish. This will likely produce another round
of showers. On Wednesday with stabilities very modest, Puerto Rico
and and the U.S. Virgin Islands will find themselves of the
divergent side of the TUTT low now migrating west. This and a weak
trough at 700 mb should create a more favorable environment for
showers and for western Puerto Rico, afternoon thunderstorms.

.LONG TERM...Thursday through Tuesday...

The surface high pressure over central Atlantic is expected to
promote a gentle to moderate easterly southeasterly wind flow across
the region throughout the long-term period. Lingering effects from a
retrogressing TUTT and its associated low-level induced trough
northwest of Puerto Rico along with moisture content at normal
levels will continue to produce scattered showers and isolated
thunderstorms over the local area on Thursday. This activity is
expected to stream across the northern regional waters into coastal
areas during morning hours. In the afternoon, shower and
thunderstorm activity will be concentrated over the Cordillera and
northwestern sections of Puerto Rico caused by the combination of
sea breeze convergence, surface heating and local effects. This
activity might be short-lived as the TUTT weakens while moving
northward and drier air filters in during evening hours.

Some discrepancies exist on Friday through early Saturday as GFS
increases moisture content due to the arrival of a weak tropical
wave whereas ECMWF has the tropical wave passing south of the
forecast area. Thus, weather conditions will vary from fairly
stable to increased cloudiness and shower activity depending on
which model solution plays out. A brief fairly dry area is
expected to move in of what remains of Saturday with both global
models showing well below normal moisture. This will precede the
arrival of another tropical wave early Sunday through the end of
the forecast period which will increase cloud cover and promote
shower activity across Puerto Rico and U.S. Virgin Islands.


&&

.AVIATION...Small fast moving SHRA will cont across the local waters
and ern PR. Aft 12/17Z SHRA psbl across wrn PR. VSBYs limited to 7-
15 SM due to Saharan dust. Sfc winds incrg to 12-18 kt with gusts to
26 kt aft 12/14Z. Max winds E-ESE 25-32 kt btwn FL007-165
diminishing somewhat aft 12/18Z.


&&

.MARINE...Moderate to fresh winds maintain choppy to hazardous
marine conditions today. Seas up to 7 feet are expected.
Therefore, small craft advisories will be in effect through
evening hours. Small craft operators should exercise caution over
nearshore waters. Winds gradually subside during the day tomorrow,
leading to improvements in marine conditions.

There is a high risk of rip currents for eastern St. Croix and
Playa Jobos in northwestern Puerto Rico. There is a moderate risk
for nearly all other beaches.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 79 90 78 / 30 20 40 40
STT 90 79 88 78 / 20 20 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
501 AM AST Tue Jul 13 2021

.SYNOPSIS...Hazy skies will continue today due Saharan Dust across
the area with improvements starting tonight. Weather conditions
are expected to deteriorate tomorrow, as conditions at upper
levels turn more favorable for shower activity due to the
proximity of a TUTT low to the forecast area.

&&

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

A TUTT low will drift west and dig southwest over Hispaniola
southwest today and Wednesday. Moisture (precipitable water) will
increase thru 15/09Z but will be interrupted for a short period of
time by a dry slot passing through Thursday ahead of a band of
moisture that will move through on Friday.

Today, stability increases considerably, but the inversion is also
expected to diminish. This will likely produce another round of
showers. On Wednesday with stabilities very modest, Puerto Rico and
and the U.S. Virgin Islands will find themselves of the divergent
side of the TUTT low now migrating west. This and a weak trough at
700 mb should create a more favorable environment for showers and
for western Puerto Rico, afternoon thunderstorms. Expect normal to
just above normal temperatures during the period.

Significant improvement in the concentrations of Saharan dust should
be seen tonight and Wednesday as the puff that plagued the island
moves westward.

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

Both GFS and ECMWF continue to show discrepancies for Friday
regarding the evolution of a retrogressing tropical upper-
tropospheric trough (TUTT) low. By early Friday, GFS has the TUTT
and induced perturbation in the easterly trades northwest of the
forecast area dragging moisture to its southeast across Puerto
Rico and U.S. Virgin Islands as the induced trough moves
northwestward through Friday night. Conversely, the 12/12z ECMWF
has the TUTT and induced inverted trough pulling away more rapidly
with a much drier environment for the same day. However, latest
13/00z ECMWF has begun to caught up with GFS regarding moisture
availability on Friday. Dynamically speaking, both models pretty
much agree with 500 mb temperatures around -6.5 C which puts it at
normal levels for this time of year. Therefore, the major
differences in the past few model cycles have been on moisture
availability by Friday. GFS suggests precipitable water values up
to 1.8 inches which, with marginal instability aloft, would be
sufficient for shower activity and isolated thunderstorms to
develop. This activity would especially affect interior and
western portions of Puerto Rico during afternoon hours. Streamers
and rainfall activity could also be triggered downwind of the
Luquillo Mountain Range and the local islands.

Saturday still looks dry with moisture well below normal levels,
although isolated showers are still possible, especially when
induced by local effects and sea breeze convergence across western
Puerto Rico in the afternoon. This activity will be shallow in
nature due to the expected presence of a strong inversion cap close
to 800 mb and dry air aloft. A surge of moisture increasing
precipitable water to above normal values owed to the arrival of a
tropical wave between Sunday through Monday will erode the trade
wind inversion cap. This will cause an increase of clouds and shower
activity. Dynamics aloft will not be impressive, but enough to
trigger deep convection when combined with orographic effects and
moisture convergence in localized areas. Lingering moisture can be
expected late Monday night, but will transition once again to
establish an easterly trade wind inversion through the long term
period. Patches of moisture embedded in the trades will bring
occasional passing showers across the area.


&&

.AVIATION...SHRA incrg btwn PR and TIST. Ely sfc 5-15 kt winds movg
some onshore with mtn obscurations arnd El Yunque. Aft 12/14Z winds
to increase to 12-18g26kt. SHRA will increase ovr land especially
wrn PR aft 13/17Z with lcl MVFR conds.Otherwise VFR conds to prevail
thru 14/02Z. Max winds E 25-30 kts btwn FL125-170 diminishing
slowly.


&&

.MARINE...Moderate to fresh winds will maintain choppy marine
conditions today. Seas up to 6 feet are expected, mostly for the
offshore Atlantic and Caribbean waters and local passages.
Therefore, small craft should exercise caution over those waters.
Marine conditions will continue to improve throughout the day. There
is a moderate risk for nearly all beaches.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 87 78 / 40 40 40 30
STT 89 78 89 77 / 30 40 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
508 AM AST Wed Jul 14 2021

.SYNOPSIS...

Conditions at upper levels have become more conducive for
convective development. This has caused shower activity to develop
throughout the overnight hours mainly across the local waters and
is expected to continue and move inland throughout the day. Drier
conditions are expected tomorrow.

&&

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

A TUTT low will drift west while elongating NE/SW over Hispaniola
today and Thursday. Moisture (precipitable water) will increase thru
15/07Z but will be interrupted for a short period of time by a dry
slot passing through Thursday ahead of a tropical wave that will
bring much better moisture on Friday.

Today, with stabilities very modest, Puerto Rico and and the U.S.
Virgin Islands will find themselves on the divergent side of the
TUTT low now migrating west. This and a weak trough at 700 mb should
create a more favorable environment for showers and for western
Puerto Rico, afternoon thunderstorms. Expect normal to just above
normal temperatures during the period.

Significant improvement in the concentrations of Saharan dust should
be in place today with improvement into Friday.

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

Model guidance suggests a mix of relatively dry conditions with
patches of moisture embedded in the easterly trades, the passage of
a weak tropical wave, and Saharan Dust Particulates for the long
term period. The weekend starts with some lingering moisture in
morning hours that could produce passing showers on Saturday. By
the afternoon, things will clear up as a drier airmass moves in
accompanied by a gradual increase of Saharan Dust Particulates
that will affect the area but with surface heating and local
effects in combination with east-southeast wind flow spawning
scattered showers and isolated thunderstorms across interior and
northwestern portions of Puerto Rico.

A weak tropical wave is expected to move into the forecast area by
Sunday morning. The wave moisture will aid in the development of
showers and isolated thunderstorms across eastern Puerto Rico and
the U.S. Virgin islands during the morning hours, followed by
showers and isolated thunderstorms during the afternoon over the
interior and western areas of Puerto Rico. The bulk of the tropical
wave and its associated moisture are expected to be west of Puerto
Rico by Monday morning. Lingering moisture will be present on Monday
through Tuesday and 500 mb temperatures cooling close to -9
degrees Celsius could enhance shower and thunderstorm
development, especially in the afternoon over western sections of
Puerto Rico. However, guidance shows that a dry Saharan air mass
will still be present during that period. This will limit the
development of convective activity, however, locally and diurnally
induced activity are possible, but restricted by the amount of
dust in the air.

The rest of the forecast period looks relatively dry and hazy as
Saharan dust will continue to affect the area and an airmass with
below normal moisture content filters in. However, locally and
diurnally induced showers are expected to develop each day.


&&

.AVIATION...A weak trop wave is movg thru the FA with SHRA--mainly
over the local waters in ENE sfc flow of 10-15 knots. SHRA will
increasingly spread ovr PR and the USVI drg the day, with isold TSRA
psbl in wrn PR aft 14/17Z containing MVFR conds and mtn
obscurations. Max winds NW 28 kt at FL440. Conds greatly imprv
aft 15/00Z but ern PR will cont to have passing SHRA.


&&

.MARINE...

Winds are generally out of the east at up to 15 knots. This will
sustain somewhat choppy conditions across the local waters,
especially for the offshore waters. Seas remain less than 6 feet,
however, into the end of the week. Locally stronger winds with
increased shower activity expected today could lead to locally
degraded marine conditions.

For the beachgoers, there is a moderate risk of rip currents for
northern and eastern exposed local beaches.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 78 88 78 / 40 40 30 20
STT 89 77 89 79 / 40 40 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
425 AM AST Thu Jul 15 2021

.SYNOPSIS...Drier airmass will move over the local islands today
limiting rainfall amounts. However, a tropical wave will move
through the local area on Friday increasing shower activity once
again. Surface high pressure across the north central Atlantic is
causing an easterly wind flow across the local area, and is
expected to continue through the rest of the week.


&&

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

The upper level low that is located northwest of the local region
will continue to slowly move westward over the next day or so. This
will allow a mid-upper level ridge to build in from the east later
today. As a result, conditions will become less favorable for
showers and thunderstorms over the local islands through Saturday.
For today, satellite precipitable water analysis suggests a dry slot
upstream of the U.S. Virgin Islands. This drier airmass will move
over the local islands limiting the showers activity to the extreme
northwest portions of Puerto Rico this afternoon. Then, the passage
of a tropical wave on Friday will likely bring a few rounds of
scattered showers across portions of the islands from time to time.
However, weak upper level dynamics should maintain the rainfall
accumulations in the low side. On Saturday, the moisture associated
with the wave moves away giving way to a dryer and more stable air
mass. Low concentrations of Saharan Dust also arrive on Saturday,
resulting in hazy skies with limited shower activity.

East to southeast flow will keep the temperatures slightly higher
than normal especially in the northern half of the islands today.

.LONG TERM...Sunday through Friday...

Another episode of Saharan Dust particulates with concentrations in
the low side will move into the forecast area during the weekend.
Latest model guidance is still indicating the passage of another
tropical wave at a fairly quick pase that will move across the
eastern Caribbean and near the vicinity of the forecast area by
early Sunday morning. Both GFS and ECMWF are in pretty good
agreement in terms of timing and as well as positioning of this wave
exiting the forecast area by late Monday. The aforementioned
tropical wave is expected to bring precipitable water values of
around 2 inches. Therefore, cloudy skies and periods of shower and
isolated thunderstorm activity are expected across portions of the
local area. Things get uncertain when we take into consideration the
presence of Saharan Dust particulates with concentrations increasing
drastically by Monday. This will limit the development of convective
activity, however, locally and diurnally induced activity are
possible, but restricted by the amount of dust in the air.

After the wave passage, drier conditions as well as the continued
effect of suspended Saharan Dust particulates will follow for most
of the workweek. Therefore, fair weather conditions along with hazy
skies can be expected. Afternoon convection will be possible across
western Puerto Rico due to local and diurnal effects. Another
tropical wave could affect the area by Friday, bringing additional
rainfall activity.


&&

.AVIATION...SHRA will move west across the regional waters
without affecting the TAF sites. Therefore, VFR conds will likely
prevail through the forecast period. Some SHRA may develop in the
afternoon over the northwest portions of Puerto Rico, however
conds should remain VFR. East to southeast winds of 10-15 kt
expected below FL150.


&&

.MARINE...Choppy conditions with seas to 5 feet and winds to 15
knots, occasionally higher. These conditions will persist at
least into the weekend. Moderate risk of rip currents for northern
beaches of Puerto Rico, and eastern beaches of St. Croix,
Vieques, and Culebra.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 78 87 77 / 20 20 30 40
STT 88 79 88 78 / 20 40 40 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
348 AM AST Fri Jul 16 2021

.SYNOPSIS...
Two approaching tropical waves are expected to increase moisture
over the forecast area today and Sunday. However, another episode
of African Dust particles is expected to filter in the area by
Saturday, thus promoting more stable weather conditions. Fair
weather conditions along with hazy skies can be expected for most
of the long term cycle. Marine conditions remain choppy for the
next several days.

&&

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

A tropical wave moving over the Caribbean Waters will enhance the
moisture convergence and instability across the local islands
throughout the day. Although the bulk of the moisture will remain
south of the forecast area, moisture levels will increase just above
normal over Puerto Rico later today. This moisture combined with
local effects will induce the development of showers with heavy
rainfall across portions of Puerto Rico and the U.S. Virgin Islands,
especially over northwestern PR. Locally heavy Downwind of El
rainfall is also possible downwind of El Yunque affecting portions
of the San Juan Metro Area during the afternoon hours. Some of these
areas may experience urban and small stream flooding with this
shower activity.

A mid-level ridge will then dominate the conditions on Saturday. The
stable air mass will be accompanied with low concentrations of
Saharan Dust. This will likely result in hazy skies and limited
shower activity. Wetter conditions will return on Sunday when the
next tropical wave reaches the northeast Caribbean region. This wave
will bring additional showers as well as an increase in the trade
winds. Squally weather is possible with the wave on Sunday as winds
between 1-2 km above ground will peak around 25 knots.

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

Moisture from the tropical wave will linger on Monday, but drier air
is expected to move in by late afternoon to evening hours. The
latest guidance shows the precipitable water going from over 2
inches on Sunday to just over 1.5 inches by Monday evening.
Although models still suggest sufficient moisture from the
tropical wave present during the day prior the entrance of much
drier air, high concentrations of Saharan Dust particulates will
filter in starting late morning hours. This will suppress
development of shower activity. Some activity could be present but
it will be less widespread with no significant rainfall
accumulations.

It remains fairly dry and stable with hazy skies due to Saharan
Dust particulates through Thursday. However, patches of moisture
will move through the area from time to time yielding the typical
summer pattern of night and morning passing showers in eastern
Puerto Rico and heavier showers in the afternoons. Although this
pattern will not be quite as generous for the U.S. Virgin Islands,
some light showers are expected and streamer are likely to form
downstream. Another tropical wave could reach the local area
between late Thursday night to Friday morning, causing an increase
in low-level moisture and shower activity once again.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across
most of the TAF sites except TJBQ where SHRA/TSRA could develop
between 16/17-23z. Mountain obscurations are also possible over the
western interior sections of PR in the afternoon. Winds will persist
from the E-ESE at 10 to 15 knots with higher gusts and sea breeze
variations.


&&

.MARINE...
Choppy marine conditions will continue today due to winds up to 20
kts and a weak tropical wave that will cause squally weather over
the local waters. Seas will range from 3 to 5 feet across the
Caribbean and Atlantic waters today, and then seas are forecast to
increase to 4 to 6 feet across the Anegada Passage by the evening
hours and extend to the local waters throughout the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 87 78 / 30 30 20 60
STT 89 79 90 78 / 40 30 50 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
439 AM AST Sun Jul 18 2021

.SYNOPSIS...

Showers have increased across the region overnight tonight, as a
tropical wave makes its way over the area, and passing showers will
continue through the morning. Afternoon convection is expected, with
scattered to numerous showers and isolated thunderstorms, especially
for northwestern and interior Puerto Rico, as well as downwind of
orographic features, including El Yunque and the eastern islands.
Drying is anticipated for the early part of the workweek.

&&

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

A tropical wave is expected to stream quickly west across the region
today. Shower and thunderstorm activity was observed through the
overnight hours across the local waters and over portions of the
U.S. Virgins Islands, and the northern and eastern sections of
Puerto Rico. This activity could continue through the morning hours
and further inland across Puerto Rico, as the wave axis moves
further west and away of the local area. Precipitable water content
(PWAT) is expected to remain at or above normal values through the
rest of the day, due to lingering moisture from the wave. This
moisture in combination with diurnal and local effects will aid in
the development of afternoon convection over the eastern, north
central and northwestern sections of PR. Urban and small stream
flooding is possible with the heaviest showers.

For Monday and Tuesday, a mid-level ridge northeast of the region is
expected to promote drier air intrusion and a Saharan Air Layer
across the local area. Therefore, drier conditions with hazy skies
should prevail in general across the islands. However, shower
development is expected each afternoon over western PR due to
diurnal effects. East to southeast trades will keep maximum
temperatures in the high 80s to low 90s.

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

Drier, more stable conditions continue over the region on Wednesday.
Ridging aloft will also maintain stability over the area. Even so,
some showers are likely due to local effects, mostly in western and
interior Puerto Rico. On Thursday, more patches of near-normal
moisture will track across the area, which will increase shower
activity. With continuing stability, however, organized convection
is unlikely, and rainfall amounts will remain low. Confidence in
this trend is relatively high.

On Friday, a weak tropical wave is forecast to pass by the region,
mostly to the south. Some moisture is likely to make it to the
region, however, resulting in more showers. There is some
uncertainty in the extent to which the moisture will affect the
region; model guidance has backed off on the strength and size of
this feature in the last 24 hours. Confidence is low to moderate.

Drying is expected overnight on Friday into Saturday. However,
moisture levels will not drop as substantially as in the early part
of the week. Still, precipitable water is likely to be generally
below seasonal normals, or maybe on the low end of normal. Following
this is increasing moisture, associated with an approaching tropical
wave. Meanwhile, aloft, a mid-level trough is forecast to move over
the region, with an upper-level trough following it from the east on
Saturday. The upper-level trough is forecast to be west and north of
the region by Slate Saturday into Sunday, which will help to provide
instability over the area. Above normal moisture is expected for
Sunday; combined with the improved instability, increases in shower
activity are anticipated, both in intensity and coverage. Confidence
in the forecast for the weekend is moderate.

Lingering moisture will help to sustain showers on Monday.
Increasing stability is expected aloft, with ridging in the mid- to
upper-levels. A typical shower pattern is expected, though with
decreased activity. Confidence is moderate.

&&

.AVIATION...

SHRA/TSRA expected today due to a tropical wave passage. This may
cause tempo MVFR conds at times across the USVI/PR terminals
through at least this afternoon. Mtn tops obscd and SCT/BKN cigs
btw FL030-FL100 possible. Low-level winds ESE at 15-25 kts. VFR
conditions and HZ due to Saharan dust expected tonight into
Monday.

&&

.MARINE...

Easterly winds up to around 22 knots are expected to continue across
the local waters, associated with a wind surge due to a passing
tropical wave. This will sustain choppy conditions, with seas of up
to 6 feet. Winds will diminish somewhat Monday into Tuesday, and
seas will subside slightly as well, likely to 5 feet or less by
midweek.

There is a moderate risk of rip currents for nearly all local
beaches; beaches of western Puerto Rico and some beaches of south
central Puerto Rico have a low risk.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 89 78 / 60 40 20 20
STT 89 80 89 80 / 40 30 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
420 AM AST Mon Jul 19 2021

.SYNOPSIS...

Drier air is moving into the region from the east, in the wake of
the wave yesterday. More stable weather conditions are likely during
the day today, though there will remain sufficient moisture to
sustain some shower activity. Additionally, there is a Saharan
Air Layer that is part of this drier air mass, and hazy skies are
likely. Increasing patches of near-normal moisture are expected
for midweek into the end of the week, and increasing shower
activity is anticipated.

&&

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

A mid-level ridge and a Saharan Air Layer will promote drier
conditions and hazy skies across the region through most of the
short term period. At lower levels, east to southeast trade winds
are expected to continue through Tuesday. Patches of moisture
embedded in this wind flow will move at times across the region.
Therefore, a few passing showers can be expected across the U.S.
Virgin Islands and the eastern sections of Puerto Rico during the
night and early morning hours, followed by diurnally induced
streamers off the islands and shallow shower development over the
western sections of PR each afternoon. However, no significant
rainfall accumulations are anticipated at this time.

For Wednesday, a TUTT-induced low-level trough is expected to
move from the east, increasing moisture content and causing winds
to shift from the east to northeast. This will promote an increase
in night time and early morning showers across the northeastern
sections of PR and over the USVI. Showers with better vertical
development than previous days are expected to form over the
southwestern quadrant of PR.

.LONG TERM...Thursday through Tuesday...

On Thursday, there will be patches of near-normal moisture streaming
across the area from time to time. This will support a typical
pattern of showers through the day, though rainfall amounts will
likely be relatively low. Forecast confidence for Thursday is
moderate to high.

To the east, a tropical wave is expected to break Thursday into
Friday, then make its way into the region on Friday into Saturday.
Model guidance shows a further decrease in how well this feature
holds together, and with how much moisture makes its way to the
local islands, continuing the trend from yesterday. As such, the
forecast continues to back off on expected shower activity. However,
moisture is still likely to increase Friday into early Saturday,
which will have a correlated increase in shower activity. Troughing
in the mid- to upper-levels will also decrease stability over the
region, which will also act to increase somewhat the potential for
showers. During the day on Saturday, the wave is forecast to have
moved out of the region, and moisture will decrease in its wake.
Precipitable water values are forecast to be on the low end of
seasonal normals, or slightly below. Very dry mid-levels will also
act to inhibit shower activity. Still, some showers are expected.
Forecast confidence for the end of the week is low to moderate.

Another wave is forecast to approach the region during the beginning
of next week. As with previous forecasts, how far north this wave
tracks remains uncertain, though model guidance has continued to
push it further north. This does seem reasonable, considering
weakness in the ridge to the north, which is forecast to be pulling
away to the northeast at the time. On the whole, the trend is
towards increasing showers for Sunday into Monday. Dry air makes its
way into the region for late Monday into Tuesday behind the wave,
and more stable conditions are expected. Confidence in the general
trend of the forecast for next week is moderate to high, but
confidence in the details is low.

&&

.AVIATION...

Mainly VFR conditions expected across all terminals
during the next 24 hours. HZ due to Saharan dust expected to
continue, but VSBY should remain P6SM. East to southeast winds will
increase around 15 kt with sea breeze variations and higher gusts
aft 14z.

&&

.MARINE...

Choppy conditions continue today into tomorrow, associated with
moderate to fresh, and locally strong easterly winds behind the
tropical wave that has exited the region. Sustained winds of up to
22 knots are expected, and seas up to 6 feet. Winds will gradually
diminish into midweek this week, and seas will subside.

There is a moderate risk of rip current for nearly all local
beaches, with some exceptions along the southern west coast and the
south central coast of Puerto Rico.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 77 89 78 / 20 10 20 20
STT 91 80 88 78 / 20 20 20 30