Caribbean - Central America Weather

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cycloneye
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Re: Caribbean - Central America Weather

#20301 Postby cycloneye » Mon Aug 31, 2020 4:48 am

Area Forecast Discussion
National Weather Service San Juan PR
525 AM AST Mon Aug 31 2020

.SYNOPSIS...

Moisture associated with a tropical wave, monitored by the
National Hurricane Center and moving off to the south of the
islands, across the eastern Caribbean Sea, will exit the region
today. Another tropical perturbation will reach the northeast
Caribbean later today, increasing shower activity and winds
locally. The axis of this perturbation will cross the islands of
Puerto Rico and the U.S. Virgin Islands on Tuesday. The chance for
shower/thunderstorm development will continue throughout the
work-week, with high uncertainty on the behavior of several
tropical waves across the Tropical Atlantic.

&&

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

The moisture associated with a strong tropical wave, monitored by
the National Hurricane Center, located well at our south over the
eastern Caribbean Sea, will continue to move out of the forecast
area today. Therefore, showers will continue to move across the
northern half portion of Puerto Rico, the U.S. Virgin Islands and
surrounding waters this morning. Then, moisture is expected to
increase as the leading edge of another tropical perturbation
move across the islands from the northeast.

Total Precipitable Water (TPW) associated with the aforementioned
tropical disturbance will increase between 1.8 and 2.5 inches late
this afternoon into the evening hours. This feature will bring
scattered to widespread shower and thunderstorm activity over
Puerto Rico and the US. Virgin Islands. The axis of the wave will
move across the islands on Tuesday. As a result, favorable weather
conditions for the development of showers and thunderstorms will
continue through the short term forecast. Urban and small stream
flooding will remain possible each afternoon with the strongest
activity.

Showers associated with the lingering tropical moisture will
continue to affect the islands on Wednesday. Easterly winds,
diurnal heating and local effects will aid in afternoon
convection over the western and interior sections of Puerto Rico.
A more drier air mass with Saharan dust is forecast to filter
into the region by the end of the short-term period. Maximum
temperature are expected between the upper 80s and low 90s across
the coastal and urban areas in Puerto Rico and the U.S. Virgin
Islands each day.

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

An upper-level trough will amplify over the Northeast-Caribbean
ramping-up local instability. This feature aloft will induce a set
of surface troughs lifting surface tropical moisture from the
southern Caribbean into Puerto Rico and the U.S. Virgin Islands.
There is a good agreement between meteorological guidance about
these features, as well as an increase in the available tropical
moisture, therefore, expect showery weather with afternoon
convection each day. As the trough moves westward over the
Hispaniola, ventilation aloft will promote better convection
across the region late Thursday night into Friday. The
aforementioned upper-level feature will move over the Windward
Passage, between Haiti/Cuba, by next weekend.

There is plenty of uncertainty about the possible weather
conditions across the tropical Atlantic for the weekend and early
next week. That said, islanders cannot rule out the typical
passing showers across the windward sections each night/morning,
followed by afternoon convection across the western sections. We
encourage people with interest in the Northeast Caribbean,
including PR and the USVI, to watch the weather evolution in the
Tropical Atlantic by following the products from the National
Hurricane Center and your Weather Forecast Office in San Juan.

&&

.AVIATION...

VFR conditions are expected to prevail through 31/15Z. Some
haziness associated with the remnants of a Saharan air mass is
expected today. However, VIS is expected to remain P6SM. Easterly
winds will persist today, and will increase at 10 to 20 knots
after 31/13z. SHRA/TSRA will develop along and to the west of the
Cordillera Central between 31/15-22z. Also, this wave will bring
SHRA/TSRA across the islands and could impact ISX/IST/JSJ.

&&

.MARINE...

Mariners can expect choppy seas during the next few days, with
wave-heights up to 6 feet. A tropical wave will exit the region to
our south today, and a second perturbation will move into the
northeast Caribbean, increasing showers and winds today and
tomorrow. Therefore, small craft operators should exercise caution
due to easterly winds between 15 and 20 knots across most of the
local waters.

There is plenty of uncertainty with a set of tropical waves, one
near the Cabo Verde Islands and another forecast to move away from
the African coast. Therefore, keep vigilant of the weather
conditions across the Tropical Atlantic by following the products
from the National Hurricane Center and your Weather Forecast
Office in San Juan.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 80 89 78 90 / 60 80 50 40
STT 82 88 79 90 / 70 70 40 40
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Re: Caribbean - Central America Weather

#20302 Postby cycloneye » Tue Sep 01, 2020 5:19 am

Area Forecast Discussion
National Weather Service San Juan PR
531 AM AST Tue Sep 1 2020

.SYNOPSIS...

A tropical wave will bring showers and thunderstorms across the
area today. Tropical moisture will continue across the region
through at least Wednesday. Then, an upper level trough will
increase instability once again Thursday and Friday. However, a
dry air mass with Saharan dust will filters from the east
Thursday and early Friday, but patches of moisture will reach the
islands at times.

&&

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

The axis of a tropical wave is moving over the region today.
Total precipitable water (TPW) derived from the satellite imagery
associated with the aforementioned disturbance range between 2.0
and 2.1 inches. This feature will enhanced the potential for
shower and thunderstorm activity over Puerto Rico and the US.
Virgin Islands today. According to the Radar Doppler shower
activity is expected to continue over local waters and move to
coastal sections of Puerto Rico an the U.S. Virgin Islands in the
morning hours. Then, shower and thunderstorm activity are forecast
to develop over northwestern, western and interior sections of
Puerto Rico during the afternoon. Urban and small stream flooding
across the islands is expected with the strongest activity.

The lingering moisture will continue to promote shower and
thunderstorm activity across the local waters through at least
Wednesday morning. A more drier air mass with Saharan Dust
particles are expected to filter into the region on Wednesday. At
the upper levels, a TUTT-Low will move westward across the
northeast Caribbean Wednesday through Friday. The islands of
Puerto Rico and the U.S. Virgin Islands will remain in the
subsidence side of it on Wednesday. However, as this upper level
feature moves westward, instability is forecast to increase over
Puerto Rico and the U.S. Virgin Islands after Thursday. Although
instability will increase, the limiting factor will be the
available moisture, which is forecast to be limited.

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

Model guidance is suggesting lingering dust particles across the
islands early Friday morning. However, the upper-level feature
will continue to migrate westward over Hispaniola, increasing
instability and inducing a surface trough which is forecast to
lift tropical moisture across the islands of Puerto Rico and some
over the U.S. Virgin Islands. Under this weather pattern, expect a
good chance to observe showers and thunderstorms, especially
overnight/early Friday morning and in the afternoon hours. The
limiting factor will be the timing of the moisture arrival and if
it coincides with the peak of instability.

As the upper-level trough moves westward over the Windward
Passage, between Haiti/Cuba, stable weather conditions will be
possible Saturday and Sunday. However, patches of moisture
embedded in the trades will increase the chance to observe
overnight/early morning showers across the windward sections of
PR/USVI followed by afternoon convection across the western
portions of the islands.

Model guidance is suggesting a tropical wave approaching the
islands Monday or Tuesday, and another one for Wednesday or
Thursday. At this time, the most robust wave between these two
tropical disturbances seems the one for mid-week. It`s too early
to determine the effects that would have these systems across the
islands. However, interests in Puerto Rico and the U.S. Virgin
Islands should monitor the behavior in the Tropical Atlantic.

&&

.AVIATION...

A tropical wave will bring SHRA/-SHRA across the islands today.
Isold-TSRA will remain possible across the local waters and some
of them could affect the vicinity of TIST/TJSJ/TISX through the
morning hours. TSRA/+SHRA will develop across the mountains and
over western PR btwn 1/16-23z and could impact JBQ/JSJ. Calm to
light and VRB winds will persist through 01/13z, then will prevail
mainly from the E-ENE between 10-15 kts with higher gusts and sea
breeze variation.

&&

.MARINE...
Mariners should exercise caution across the regional waters as a
tropical wave continues to produce showers and thunderstorms. In
addition, a wind surge will increase seas up to 7 feet across the
Atlantic Offshore waters and a Small Craft Advisory is in effect
from 8 am this morning through at least Wednesday evening.
Mariners can expect seas between 3 and 6 feet and winds between 15
and 20 knots, elsewhere. Seas will also increase across the
Anegada Passage and surrounding waters at up to 7 feet from this
evening through Wednesday morning. Seas will subside after mid-
week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 78 89 78 / 50 40 40 40
STT 88 79 90 79 / 50 50 40 50
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Re: Caribbean - Central America Weather

#20303 Postby cycloneye » Wed Sep 02, 2020 5:16 am

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
522 AM AST Wed Sep 2 2020

.SYNOPSIS...

Tropical moisture will continue to bring showers across the local
waters and windward sections in Puerto Rico and the U.S. Virgin
Islands through the morning hours. A drier air mass with Saharan
dust particles will move from the east later this morning into the
afternoon. Also, a TUTT-low will move westward across the islands,
keeping PR/USVI in the subsidence side today, but increasing
instability Thursday and Friday.

&&

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

Lingering moisture from the latest tropical wave will continue to
move over the region today. Satellite derived Total Precipitable
Water (TPW) ranged between 1.6 and 2 inches. The available
tropical moisture will aid in showers mainly across the local
waters through the morning hours, and some of them will reach the
east and southeast slopes sections of Puerto Rico and the U.S.
Virgin Islands from time to time. Later today, a somewhat drier
air mass (with TPW near normal values) is forecast to move across
the islands bringing Saharan dust particles over the region.
However, local effects may result in afternoon convection over
northwestern and western Puerto Rico.

At the upper-levels, a TUTT-low will move westward into the
region, keeping the islands of Puerto Rico and the U.S. Virgin
Islands in the subsidence side throughout the day. As the TUTT-low
moves westward into the Hispaniola instability will increase
according to model guidance on Thursday and Friday. Given the
presence of instability and the available surface moisture,
shower and thunderstorm activity will remain possible each
afternoon over the western portions of the islands. On Friday, a
surface induced trough will increase the potential to observe more
frequent and intense convection.

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

As this week`s upper-level trough moves westward over the
Windward Passage, between Haiti/Cuba, a mid- level high pressure
will promote stable weather conditions on Saturday. A second mid-
to- upper-level low will move from the Atlantic Ocean into the
northeast Caribbean on Sunday. The islands will be on the
subsidence side of it, but patches of moisture embedded in the
trades will increase the chance to observe overnight/early morning
showers across the windward sections of PR/USVI followed by
afternoon convection across the western portions of the islands
each day. The aforementioned upper-level feature will drift
westward across the northeast Caribbean through at least mid-week.

Model guidance is now suggesting a set of an induced surface
trough affecting PR/USVI and the surrounding waters early next-
week. Then, a tropical disturbance will move close to the region
by mid-week.

Keep in mind that uncertainty increase as we move closer to the
end of the forecast period. Therefore, conditions may vary as we
move into the peak of the 2020-Hurricane Season, which is next
week. That said, it`s too early to determine which model is
correct or which one has the best solution. Regardless of this, we
encourage the people with interests in Puerto Rico and the U.S.
Virgin Islands to closely monitor the progress in the Tropical
Atlantic by following the products from the National Hurricane
Center and your Weather Forecast Office in San Juan.

&&

.AVIATION...
Mainly VFR conditions will prevail today. A Saharan Air Layer will
move from the east result in some haziness today, however, VIS
will remain P6SM. SHRA/TSRA will develop across the mountains and
western sections btwn 02/16-23z, this activity could impact JBQ.
Calm to light and VRB winds thru at least 02/13z, returning from
the E at 10 to 15 knots with sea breeze variation after 02/13z.

&&

.MARINE...
The available tropical moisture will induce shower activity across
the local waters today, and thunderstorms may be possible across
west PR and the Mona Passage during the afternoon hours. A wind
surge will maintain seas between 5 and 7 feet across the Atlantic
Offshore waters, where a Small Craft Advisory is in effect until
this morning. Mariners can expect seas between 3 and 6 feet and
easterly winds at 15 to 20 knots across most of the local waters
through at least tomorrow. Then, seas and winds will slowly
subside through the second part of this week. However, local
effects will result in locally higher winds and seas, especially
each afternoon.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 80 89 79 / 20 40 50 20
STT 91 79 90 80 / 30 40 50 30
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Re: Caribbean - Central America Weather

#20304 Postby cycloneye » Fri Sep 04, 2020 5:10 am

Area Forecast Discussion
National Weather Service San Juan PR
441 AM AST Fri Sep 4 2020

.SYNOPSIS...Upper-level low located north of Hispanola will result
in another round of enhanced afternoon convection across western
Puerto Rico. Improving weather conditions expected during the
weekend as mid to upper-level ridge builds overhead. Weather
conditions will turn unstable once again during the early to
middle portion of next week as another upper-level low moves
across the area from the northeast.

&&

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

TUTT/upper low located just north of the Hispanola will continue to
move west, reaching Cuba on Saturday. Meanwhile, the upper level low
is still providing good ventilation aloft to sustain unstable
conditions across the local islands today. In addition, an induced
surface trough will move over the Eastern Caribbean later this
morning adding low level moisture to fuel the afternoon convection.
However, one limiting factor for today`s convection will be some
drier air between 850mb-700mb. As a result, the shower coverage will
be less than yesterday due to the mid-level dry air intrusion and
the current position of upper level trough. However, the forecast
calls for another round of afternoon convection over the western
interior and northwest Puerto Rico as well as portions of the San
Juan metro area. Heavy rains will likely promote some urban and
small stream flooding especially over the northwest quadrant of
Puerto Rico in the afternoon.

Conditions will improve tonight into the weekend as a strong mid-
upper level ridge builds across the northeast Caribbean. This will
result in drier and more stable air spreading over Puerto Rico and
the U.S. Virgin Islands during the weekend. This drier air will
contain some Saharan Dust that may reduce somewhat the visibilities
and at the same time will help to limit the shower coverage across
the local region during the weekend.

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

Weather conditions will begin to turn more unsettled by Monday as
another upper-level low begins to approach from the northeast.
This will increase the instability aloft and as a result, more
enhanced afternoon convection can be expected, especially across
the western half of Puerto Rico. This upper-level low will
continue to remain near the area both on Tuesday and Wednesday as
well, continue to enhance the afternoon convection across the
western half of Puerto Rico. Overnight and early morning isolated
to scattered showers can be expected across portions of eastern
Puerto Rico and in and around the USVI.

Weather conditions by the end of the long-term period will be
dependent on a tropical disturbance currently located near the
Cabo Verde Islands. This disturbance is being monitored by the
National Hurricane Center for the potential for development as it
reaches the Central Tropical Atlantic by early next week. Given
the lack of a strong high pressure aloft, this disturbance
according to the latest model guidance looks to turn towards the
north before reaching the northern Lesser Antilles at this time.
Even though no direct impacts are expected if the solution
currently being depicted by model guidance verifies, some of the
peripheral moisture may reach the area by late next week to
deliver some rainfall activity across portions of the local area.

&&

.AVIATION...VFR conditions are expected over most of the TAF sites.
ISOLD TSRA are possible near TJMZ/TJBQ. This could lead to brief
MVFR conds between 18Z-22Z. At TJSJ, VCTS possible between 17Z-21Z.
E to ESE winds of 10-20 knots will prevail below FL100.

&&

.MARINE...Mainly tranquil seas between 3 and 5 feet can be
expected across most of the regional waters during the next
several days. However, locally higher winds on Saturday can result
in localized choppy seas, especially across the offshore waters
and local passages. Thunderstorms will be possible once again this
afternoon across the waters off the west coast of Puerto Rico.
There is a moderate risk of rip currents across the northern
and some southwestern beaches of Puerto Rico as well as across the
north and east-facing beaches of Culebra and Saint Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 79 88 79 / 30 30 50 50
STT 89 80 89 79 / 20 30 40 40
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Re: Caribbean - Central America Weather

#20305 Postby cycloneye » Sat Sep 05, 2020 5:17 am

Area Forecast Discussion
National Weather Service San Juan PR
419 AM AST Sat Sep 5 2020

.SYNOPSIS...

Drier than normal conditions are expected to prevail today, with
somewhat better moisture moving in for next week. However, no
major tropical waves or tropical systems are expected for the
foreseeable future. A weak tropical wave will arrive on
Monday, with moisture from an old tropical wave impacting us
thereafter. Seas will be choppy in the Caribbean today due to a
tropical wave passing to our south.

&&

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

Strong mid-upper level ridge over the Anegada Passage this morning
will move slowly to the west reaching Hispanola by Sunday. Under the
influence of this strong high pressure aloft, the shower activity
will be limited across the local islands through the weekend due to
the presence of a dry and stable air at mid-levels. Also the high
levels clouds over the region will delay the onset of the afternoon
convection. However, local effects such as sea breeze convergence
will likely trigger some late afternoon showers over northwest
Puerto Rico. However, accumulation will be in the low side, between
0.5 to 1.0 inch in some spots. On Sunday, fair weather conditions
will likely continue across Puerto Rico and the U.S. Virgin Islands.
The main change on Sunday is that the afternoon showers will likely
cluster over the Cordillera Central as steering flow weakens to 8-10
kt from surface to 700 mb. Little or no Saharan Dust is expected
during the weekend. Then, a tropical wave is forecast to reach the
eastern Caribbean between Monday and Tuesday bringing some moisture
and instability with it. However, no widespread shower activity is
expected as mid-level moisture remains low. The focus for the
afternoon convection on Monday returns to the west interior and
northwest Puerto Rico.

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

Fairly typical conditions are expected for most of the long-term
period. Moisture from an old tropical wave will move in between
Tuesday and Friday, thus bringing about periods of passing
showers. At this point it is difficult to determine which day will
have the most impactful showers, as forecast models are not clear
on which day has the most moisture. For Tuesday and Wednesday,
mid- to upper-level atmospheric conditions don`t appear favorable
for strong thunderstorms. A weak low pressure is expected to our
east at upper-levels with ridging to our west, putting us in the
subsidence side of this pattern. However, given the time of year
and abundance of warmth at low-levels, some lightning is possible
with the stronger showers. Conditions are expected to become more
conducive for thunderstorms on Thursday and Friday as a trough
develops to our west at upper levels. However, uncertainly is
large this far out. Uncertainty increases even more or the
weekend. A few long range models suggest a vigorous tropical wave
may approach the area for the weekend and pass well to our north.
Higher amounts of moisture and rainfall would be expected under
this scenario for our region. However, given the high
uncertainty, it is too early to determine what impacts, if any,
that this tropical disturbance may have on our region.

&&

.AVIATION...VFR conditions will continue at all the TAFs sites. No
operational impacts are anticipated today as fair weather conds are
forecast for the local region. VCSH possible near TJMZ around 19Z-
21Z. E winds of 15-20 knots will prevail below FL100.

&&

.MARINE...

A tropical wave is passing to our south today, so seas in the
Caribbean are expected to reach up to 6 feet. Elsewhere, more
tranquil conditions will prevail with seas below 5 feet. Winds
will be moderate to fresh at 10 to 20 knots. All seas are expected
to remain calm for much of this next week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 89 78 / 30 50 30 30
STT 90 80 89 79 / 20 40 40 40
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Re: Caribbean - Central America Weather

#20306 Postby cycloneye » Sun Sep 06, 2020 5:44 am

Area Forecast Discussion
National Weather Service San Juan PR
509 AM AST Sun Sep 6 2020

.SYNOPSIS...Mid and upper level ridge will dominate the local
weather pattern today and Monday, slightly drier air is expected
to move in today. Locally induced showers and possible
thunderstorms are expected in the afternoons across portions of
western Puerto Rico for the next few days, isolated to scattered
showers expected elsewhere in the forecast area.


&&

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

Passing showers have persisted all night across the region,
associated with decently high precipitable water values of around
1.80 to 2 inches. However, drier air is expected to move in for
today that will help to reduce the frequency of those showers, for
most places at least.

Currently high pressure exists over the region, producing above
average temperatures at mid-levels. With drier air moving in today,
drier weather is expected with only isolated showers possible for
most places. However, under east-southeasterly flow, showers and
isolated thunderstorms are expected to develop over western and
southwestern Puerto Rico this afternoon. Given the slightly less
favorable atmospheric conditions, the thunderstorms ought to be less
strong than yesterday, yet isolated areas of flooding and lightning
will still be a threat today. Higher amounts of moisture will move
in for tomorrow and Tuesday associated with an old tropical wave,
thus increasing the threat for showers. From tonight and into
tomorrow morning, passing showers are again likely, particularly for
eastern Puerto Rico and the USVI. During the day Monday, winds are
expected to shift from ENE to ESE, thus showers are likely in the
afternoon over northwest Puerto Rico. Upper-level conditions still
appear fairly uninspiring for producing strong thunderstorms, yet
still isolated thunderstorms are possible. Showers will also be
possible for the San Juan Metro area. Tuesday looks similar to
Monday, with again a chance for showers and isolated thunderstorms
over west to northwest Puerto Rico and San Juan in the afternoon.
However, models disagree on the amount of moisture over our area.

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

The long term forecast has a relative low confidence as the global
models are today somewhat in agreement, but that has not been the
case the past few days. We would like to see a bit more
consistency before putting more confidence in the long term
forecast, for that reason only small changes were introduced into
the long term forecast and climatology was heavily favored in the
forecast process. Having said that, the GFS model was used for the
wind forecast, and the rainfall pattern due to local effects were
derived from the general wind flow. However, there is some
agreement and consistency among the models in the forecast of a
patch of moisture that could reach the local area on Wednesday,
causing an increase in shower activity and possibly isolated
thunderstorms, the GFS being more aggressive than the ECMWF with
the amount of rain. Also, for the weekend, an upper low could
retrogress and move into the local area starting on Friday,
positioning itself over Hispaniola by Sunday. This upper low would
cause an increase in the instability and help with the development
of thunderstorms over the area. Other than locally induced showers
and thunderstorms over western PR in the afternoons, the best days
for significant rainfall are on Wednesday and Saturday, but the
latter will be highly dependent on the development and trajectory
of the systems the the National Hurricane Center are monitoring
with tropical cyclone development, both of which the global models
have moving well to the northeast of the local area.

&&

.AVIATION...VFR conditions will continue today, though SHRA/TSRA will develop
across the mountains and southwestern sections in Puerto Rico btwn
06/15-23z. Winds will blow from the E-NE at 10 to 15 knots after
06/13z, therefore, some SHRA/TSRA will move over the VCTY of JPS
during the afternoon. Isolated showers possible thereafter,
especially for the USVI.


&&

.MARINE...Relatively tranquil marine conditions expected for the
next several days. Seas less than 5 feet and winds less than 18
knots are forecast. There is a moderate risk of rip currents for
the beaches of northern Puerto Rico, low risk elsewhere.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 88 78 / 30 30 30 30
STT 90 80 88 79 / 30 30 30 30
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Re: Caribbean - Central America Weather

#20307 Postby cycloneye » Tue Sep 08, 2020 5:08 am

Area Forecast Discussion
National Weather Service San Juan PR
549 AM AST Tue Sep 8 2020

.SYNOPSIS...
Unstable weather conditions aloft will continue across the region
through Wednesday. This will result in showers and isolated
thunderstorms, mainly aross portions of interior and western
sections of the islands. A drying trend is expected for the rest
of the short term period. An upper-level low will promote a more
showery weather for the weekend. Tranquil marine conditions
continue with seas less than 5 feet across the regional waters for
the next few days.

&&


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

A mid to upper upper level trough will continue to move across the
region today through Wednesday to maintain unstable conditions
aloft. At the surface, moisture trailing a tropical wave with axis
now crossing the Mona passage, will continue to affect the region
today. The combination of the upper trough and the moist east
southeast wind flow will favor enhanced showers and thunderstorms
across the regional waters and parts of the islands during the rest
of the morning hours. During the afternoon, good moisture
availability along with unstable conditions aloft and local effects
will support afternoon convection over portions of the islands. Most
of this activity over Puerto Rico should be focused over parts of
the interior and west to northwest sections of the islands. The U.S.
Virgin islands should expect lesser activity with isolated to
scattered afternoon showers possible mainly on the west-end or just
downwind of the islands.

As a result, of the afternoon convection,Urban and small stream
flooding will be likely in some areas due to periods of enhanced
shower activity and heavy rainfall. For Wednesday and Thursday, a
gradual drying trend is forecast with an upper ridge expected to
build overhead resulting in more stable conditions aloft. This in
turn should limit early morning passing shower activity as well as
any widespread afternoon convection each day through Thursday.
However, lingering pockets of low level moisture in combination with
the local and diurnal effects may result in afternoon convection
over parts of western and interior sections of Puerto Rico with
mostly isolated shower activity elsewhere and a more seasonal
weather pattern.


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

An upper low is expected to move into the local area starting on
Friday, positioning itself over Hispaniola by Sunday. This will
cause the instability aloft and would aid in the development of
thunderstorms over the forecast area. Above normal moisture
content is expected mostly for Saturday and combined with the
upper trough approaching, showers and thunderstorms are to be
expected to be more widespread. A drying trend is expected to
start on Sunday and continue unto Tuesday. Therefore, expect
mostly fair weather across the islands. However, typical
afternoon convection is expected for these days across portions
of interior and western sections of the islands. Also, NHC is
currently monitoring two tropical storms over and near the central
tropical Atlantic. These systems are expected to remain far from
the local area.

&&


.AVIATION...

VFR conds will prevail at all terminals overnight and early in the
morning. Upr level trough movg ovr rgn will enhance SHRA/Isold TSRA ovr
regional waters and flying area especially btw Ern PR and USVI til
08/15Z. Few Tops btw FL250-FL300 w/TSRA. SCT-BKN lyrs nr FL022...
FL050...FL080 with SHRA/ Isold TSRA en route. VCSH at TISX/TIST/TJSJ
til 08/14Z w/MTN TOP obscr ovr Ern PR due to SHRA/low clds. Sfc wnds
calm to lgt/vrb bcmg E-SE 10-15 kt aft 08/14z with sea breeze
variations. SHRA/Isold TSRA also psbl VCTY of TJSJ/TJBQ/TJMZ
fm 08/16z-08/22z.

&&


.MARINE...

Tranquil marine conditions with seas of 5 feet or less across the
entirety of the local waters and passages. Winds will be out from
east southeast between 10 and 15 knots. There is a low risk of
rip currents for all of the local beaches. Passing showers and
isolated thunderstorms are possible in the morning hours.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 89 78 / 40 50 50 50
STT 89 80 89 78 / 20 50 40 40
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Re: Caribbean - Central America Weather

#20308 Postby cycloneye » Wed Sep 09, 2020 5:15 am

Area Forecast Discussion
National Weather Service San Juan PR
548 AM AST Wed Sep 9 2020

.SYNOPSIS...

Unstable weather conditions will continue through the rest of the
week as a upper level trough and an area of low pressure affects
the local islands. Drier conditions will arrive by next week
causing fair weather conditions across most of the area. Marine
conditions remain tranquil with seas up to 5 feet. However, a
small northeasterly swell will cause hazardous seas by Friday.

&&


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

A upper level trough and area of low pressure moving westward just
south of the local islands will help to maintain unstable conditions
across the region during the rest of today. As a result showers and
isolated thunderstorms will affect parts of the coastal waters and
portions of the islands during the rest of the morning hours. The
aforementioned feature along with the available moisture brought in
by the prevailing southeasterly wind flow will favor afternoon
convection over parts of the interior and northwestern quadrant of
Puerto Rico. Parts of the San Juan metro area may also experience
brief periods of afternoon showers but lesser activity is expected.
Urban and small stream flooding will be possible with the heavy
rains in areas of persistent rainfall.

By late Thursday, a upper level ridge will sink southwards across
the region from northwest resulting in more stable conditions aloft.
Meanwhile at the surface, the Atlantic high pressure ridge will
migrate farther westward into the west and southwest Atlantic,
Tropical Storm Paulette is forecast to lift northwestwards across
the tropical Atlantic and well north of the region late Thursday
through the end of the work week. This overall and expected
scenario should induce a light to moderate east to northeast wind
flow beginning late tonight and continuing through Friday.
Consequently, expect an overall drier weather pattern with
decreasing layered precipitable water values and a gradual erosion
of low level moisture across the region for Thursday and Friday.
Occasional patches of passing low clouds and early morning showers
steered by the prevailing northeast winds is however forecast to
persist although a drier air mass is so far expected during the rest
of the period. Locally and diurnally induced isolated to scattered
afternoon shower activity should to be focused over the central
interior and southwest quadrant of Puerto Rico each day with lesser
shower activity expected elsewhere, as mostly sunny and fair weather
skies will prevail based on latest model guidance.

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

An upper low will hold over the region through Sunday. This will
cause enough instability aloft to promote showers and isolated
thunderstorms over the islands during the rest of the weekend.
Above normal low level moisture will combine with the upper
trough on Saturday. Also, models suggest Saturday as the most
active weather day with widespread shower and thunderstorm
activity mainly in the afternoon hours. A drying trend is expected
to start on Sunday and continue for the rest of the long term
period. Therefore, expect mostly fair weather conditions across
the islands. However, typical afternoon convection is expected for
these days across portions of interior and western sections of
the islands.

NHC is currently monitoring two tropical systems over and near
the central tropical Atlantic. These systems are expected to
remain far from the local area.NHC is also monitoring wave just
over Africa with a high potential for cyclonic development in the
next five days. As of now, latest model guidance shows high
uncertainty regarding posible intensification and track of this
system. However, as we are already into the peak of the Hurricane
season, it is highly recommended to continue monitoring the latest
official information issued by NHC.

&&


.AVIATION...

VFR at all terminals but with SCT ocnl BKn lyrs nr FL022...FL050
...FL080 and SHRA/Isold TSRA ovr the regional waters and btw E PR
and the U.S.VI. Few SHRA will move inland ovr coastal areas of
islands with VCSH at TISX/TIST/TJSJ TIL 09/14z. Brief Mtn Top obscr
psbl ovr Ern PR w/SHRA and SCT low cld lyrs. Aftn convection ovr the
interior and NW quadrant of PR fm 09/16Z-09/23z with VCSH/VCTS psbl
at TJMZ/TJBQ and slight chance of isold VCTS at TJSJ. Sfc wnd will
be calm to LGT/VRB bcmg fm SE 10-15 kts but with some sea breeze
variations aft 09/14z.

&&


.MARINE...

Tranquil marine conditions are expected to prevail for the next
couple days, with seas up to 5 feet and winds up 15 knots from
east- southeast. A northerly swell will increase seas across the
islands tomorrow and may become higher by Friday or Friday
night.For the beachgoers, there is a low risk of rip currents for
the beaches across the local islands.

&&


.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 89 78 / 30 40 30 40
STT 90 80 89 78 / 50 50 30 30
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Re: Caribbean - Central America Weather

#20309 Postby cycloneye » Sun Sep 13, 2020 5:29 am

Area Forecast Discussion
National Weather Service San Juan PR
435 AM AST Sun Sep 13 2020

.SYNOPSIS...

Generally unsettled weather conditions continue across the region
today and tomorrow. This is due to an upper-level low near the area,
which is enhancing instability, and therefore afternoon convection.
Drier conditions are possible as we move towards midweek. The local
Atlantic waters remain hazardous today, associated with a
northeasterly swell generated by Hurricane Paulette, located well to
our north-northeast.

&&

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

An upper level low almost 400 miles north of Arecibo will drift very
slowly to the west Sunday and Monday, and then begin to move to
the north. This will bring favorable conditions for convection
today, but more so on Monday. Moisture is now being swept up from
the southeast and will also peak late in the afternoon on Monday.
A band of drier air moves in from the east Monday night through
Tuesday.

At the surface, a weak ridge that has nosed into the northeastern
Caribbean between Paulette and Tropical Depression Twenty has
brought southeast flow and this pattern will persist through Monday
night. As Paulette recedes and a rapidly developing TD 20 approaches
the area, flow will become easterly Tuesday. Although Tropical
Depression 20 is forecast to become a hurricane by Tuesday midday,
it is still expected to turn northwest soon enough to present no
direct threat to the islands, aside from increased seas and easterly
swell.

The moisture today will remain high and peak above 2.2 inches of
precipitable water on Monday evening. This also represents more
moisture for today than was seen yesterday with similar stability.
Therefore, expect rain for most of Puerto Rico this afternoon and
Monday afternoon and heaviest in areas favored by the southeasterly
flow, namely the northwest and interior sections of the island.
Urban and small stream flooding is expected both today and tomorrow
in these areas with some thunderstorms. On Tuesday moisture
diminishes and flow shifts to the east, but some heavy rains are
still possible.

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

A relatively dry air mass is forecast to be over the region
Wednesday and Thursday. A mid- to upper-level ridge will also
contribute to relatively stable conditions; afternoon shower and
thunderstorm activity is likely to be inhibited. Fragments of
moisture are forecast to push into the region on Friday, what will
be left of what is currently Tropical Depression Rene. Meanwhile,
conditions aloft will be increasingly unstable, under the influence
of the troughing aloft that is expected to be associated with what
is currently Tropical Depression Twenty. By the end of the week,
that system is forecast to intensify into a hurricane, but its
current projected trajectory keeps the system well to the northeast
of the area. That being said, as noted above, indirect impacts are
likely to be felt across the local islands and waters. Increasing
shower and thunderstorm activity is anticipated, lasting into the
weekend. Late Saturday into Sunday, a dry slot will cross the area
ahead of a tropical wave, which is forecast to reach the area by
Monday, bringing another bout of unstable weather.

All of that being said, however, uncertainty remains quite high for
the long-term period. As alluded to above, impacts are possible from
tropical cyclones passing by the region to the north. Much of the
forecast hinges on the development and trajectory of Tropical
Depression Twenty. Given that the system is still a depression and
is expected to strengthen substantially, and we still have
significant lead time, confidence is generally low in the forecast.
Changes to the forecast - both for this system and its indirect
impacts on the local islands - are likely. Especially with this
being the peak of the hurricane season, it is very strongly
suggested that all those with interests in the area monitor products
from the National Hurricane Center, as well as future forecasts from
this office.

&&

.AVIATION...

SHRA over the local waters cont and will spread ovr ern
PR this morning. SHRA with areas of MVFR and mtn obscurations will
begin to dvlp btwn 13/15Z with TSRA beginning as early as 13/17Z.
TJMZ/TJBQ should expect periods of MVFR. Sfc winds SE at 8-12 kt
with sea breeze influences will begin arnd 13/13Z. Maximum winds WSW
40-50 knots btwn FL380-440 bcmg SW 30-40 kt btwn FL320-480 by 13/21Z.

&&

.MARINE...

Though seas are subsiding, northeast swell from the distant
Hurricane Paulette continues to cause hazardous marine conditions
for the local Atlantic waters today. Elsewhere, seas of up to 6 feet
are possible. There remains a high risk of rip currents for northern
beaches of Puerto Rico and eastern beaches of St. Croix today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 90 78 / 40 20 70 40
STT 88 80 88 80 / 40 20 20 40
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Re: Caribbean - Central America Weather

#20310 Postby cycloneye » Fri Sep 18, 2020 4:48 am

Area Forecast Discussion
National Weather Service San Juan PR
526 AM AST Fri Sep 18 2020

.SYNOPSIS...

A weak upper-level low will sink into the regional waters over the
next several days and create favorable upper-level conditions now
through the weekend. Modest low-level moisture, local and diurnal
effects will induce showers and isolated thunderstorms during the
afternoons. Light steering winds will cause convection to move
slowly, and could lead to urban and small stream flooding during
the weekend through next week. Hurricane Teddy will generate east
to northeast swells that will impact the regional waters through
Monday. Therefore, expect hazardous marine conditions today
through early next week.


&&

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

A weak upper level low over the Atlantic waters is forecast to sink
further south and into our region through the short term period.
Meanwhile, Major Hurricane Teddy currently located near 21N and 55W
will continue to track northwest and pull further away from
northeastern Caribbean. This will promote a light to moderate
northeasterly steering wind flow across the region. Therefore,
passing showers will continue to move from time to time today and
through at least tonight. During the afternoon hours, showers with
iso thunderstorms should develop over the Cordillera Central and
southern portions of PR.

As the upper low moves to our north/northwest and a light low-level
southerly wind flow establishes through the weekend, showers and
thunderstorms that develops during the afternoon hours are expected
to move slow over the same areas and this could cause urban and
small stream flooding. Including in and around the San Juan metro
area on Saturday. Max temps during the weekend could reach the low
90s across most of the lower elevations of the islands.

&&

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

The long-term period will be plagued with weak surface lows west of
Puerto Rico and TUTT lows to the east of the island that will move
near the island by mid-week. The global models have consistently
showed the above scenario over the last couple of days. The upper-
level conditions are expected to become relatively favorable due to
the proximity of the lows mentioned above. The ECMWF and GFS have
500 mb temperatures cooling to -6 to -7 degrees celsius through most
of the work week. The favorable upper-level conditions should aid in
the development of deep convection during afternoons; however, this
also depends on how much low-level moisture returns over the area,
when Hurricane Teddy`s tail lifts north of the region. Currently,
the GFS and EURO has near normal moisture across the region.
Additionally, light steering winds less than 10 kts will cause
showers and isolated thunderstorms that develop to move slowly, thus
leading to urban and small stream flooding and ponding of water on
roadways.

Friday and Saturday, guidance keeps relatively favorable upper-level
conditions, however, shows low-level moisture dropping below the
climatological average. Nevertheless, showers and isolated
thunderstorms are possible during the afternoons due


&&

.AVIATION...

Mainly VFR conditions are expected to prevail across all
terminals. Tempo MVFR possible at JPS btw 16z-22z. Northeasterly
winds around 10 kts with sea breeze variations are expected.

&&

.MARINE...

Hurricane Teddy will produce northerly swells over the regional
and local waters now through early next week. Marine conditions
will continue to deteriorate now through early next week. Seas up
to 10 feet across the the outer Atlantic waters and the Anegada
passage. A small craft advisory is in effect for the outer
Atlantic, Caribbean, and Anegada passage due to choppy and
hazardous seas. Elsewhere, small craft operators are urged to
exercise caution due to choppy marine condtions. There is a high
risk of rip currents for the northern and eastern beaches of
Puerto Rico. Also, for the beaches of the of Culebra, Saint
Thomas, and Cramer Park beach.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 89 78 / 30 30 20 20
STT 88 79 88 79 / 50 30 50 30
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Re: Caribbean - Central America Weather

#20311 Postby cycloneye » Sat Sep 19, 2020 4:55 am

Area Forecast Discussion
National Weather Service San Juan PR
502 AM AST Sat Sep 19 2020

.SYNOPSIS...An upper level-low north of the area will continue to
sink south and linger across the region through the short term
period. Light northeasterly trades will shift later tonight into
Sunday from the south as Major Hurricane Teddy moves further north
and close to Bermuda by early Monday. Low-level moisture gradually
increases through next week and normal to above normal PWAT
content is expected.


&&

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

Light northeasterly winds continued to pull moisture from the
eastern Atlantic across our nearshore waters and local islands
during the overnight hours; this activity will continue through the
remainder of the morning. A TUTT low north of Puerto Rico will
continue to meander north of the region through Sunday evening
before fizzling out. The GFS and EURO show 500 mb temperatures -4 to
-5 degrees celsius through most of the day; however, both models
show temperatures cooling to -6 or -7 degrees celsius on Sunday and
Monday. One exception to the forecast is low-level moisture; current
guidance keeps moisture below the climatological average through the
entire short-term period due to subsidence caused by Hurricane
Teddy. The lack of low-level moisture could inhibit the development
of deep convection during the short-term period.

Today, isolated to scattered showers will drift across the coastal
waters and northern areas of Puerto Rico through the remainder of
the morning hours, producing light rainfall accumulations. This
afternoon showers and isolated thunderstorms are expected to develop
over El Yunque and Cordillera Central due to sea breeze convergence.
Light steering winds of less than 10 kts will cause convection to
move slowly today, thus leading to urban and small stream flooding
and possibly landslides in higher terrain. Additionally, weak
troughiness aloft and the TUTT low north of the area will amplify
the convection that develops this afternoon.

Sunday, the upper-level low is expected to slowly fizz out,
however, troughiness aloft and light winds will remain which will
aid in the development of showers and thunderstorms mainly across
the northern areas of Puerto Rico during the afternoon. Winds are
expected to turn to the southeast due to the flow behind Hurricane
Teddy as it continues to move further away across the central
Atlantic.

Monday, upper-level conditions become more favorable as a Polar
trough deepens north of the forecast area. The global models has 500
mb temperatures cooling to -6 to -8 on Monday. However, at this time
modest moisture will limit the development of strong convection
across the forecast area.

.LONG TERM...Tuesday through Sunday...
At least through much of next week, upper level troughiness over
the western Atlantic should persist due to a series of polar
troughs exiting the northeastern coast of USA and moving north of
the area with associated TUTTs lingering to our northeast. This
is expected to keep 500 mb temperatures around -6C to -7C and
increase instability across the region. Meanwhile, a weak ridge
building from the eastern Caribbean will promote east to southeast
trades at lower levels. This weather pattern should promote an
increase in moisture and long range guidance suggest that
precipitable water content (PWAT) is expected to range between
1.75-2.00 inches through the long term period. This will result in
scattered afternoon showers with isolated thunderstorms developing
each day over portions of the interior and western PR.


&&

.AVIATION...VRF conditions will continue for all terminal sites through
19/16Z. ISO/SCT SHRA are possible across TJMZ, TJBQ, TJSJ, and
TIST through the entire TAF period. SHRA/TSRA are expected to
develop across the interior areas of Puerto Rico by 19/18Z and
linger through 20/02Z. sfc winds from the NE at 5 to 10 kts, then
veering from the SE by 20/09Z.


&&

.MARINE...Hazardous marine conditions will continue for the next
several days due to a large and long period east to northeast
swell from Major Hurricane Teddy, and from a lingering but smaller
northerly swell from Post-Tropical Cyclone Paulette. The swell is
expected to peak today and tonight between 8-12 feet, with
another second pulse and more northerly swell by midweek next
week. Small Craft Advisory conditions will be met for most marine
zones through the weekend and into Monday.

The swell will cause rough surf conditions and life threatening
rip currents along the northern and eastern exposed coasts of the
islands. A Coastal Flood Advisory is in effect for the north
coast of Puerto Rico due to possible isolated minor flooding along
coastal roads and in low-lying areas today. A High Rip Current
Risk continues in effect for the northern and eastern regional
beaches, and a High Surf Advisory is also in effect from the
northwest to northeast coast of PR and as well for the U.S. Virgin
Islands. Please refer to the latest Coastal Hazard Message
(CFWSJU) and Marine Weather Message (MWWSJU) for detailed
information.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 91 80 / 60 30 40 30
STT 88 79 89 80 / 30 30 30 40
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Re: Caribbean - Central America Weather

#20312 Postby cycloneye » Sun Sep 20, 2020 5:20 am

Area Forecast Discussion
National Weather Service San Juan PR
445 AM AST Sun Sep 20 2020

.SYNOPSIS...TUTT low north of the area will aid in the development
of afternoon showers and thunderstorms. Light southerly steering
winds today will cause showers to drift along the northern
sections of PR. Winds will continue from the east to southeast for
the next few days and diurnally induced afternoon convection
should shift more over the west/northwest portions of the islands.
Max temps should increase in general across the islands due to
the southerly winds.


&&

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

A TUTT low north of the area and an upper-level low will provide
modest instability over the region today. The upper-level low will
remain through Tuesday; however, the TUTT low is expected to peter
out later today. Hurricane Teddy will continue to move northwest
across the north central Atlantic today; winds are expected to shift
to the southeast as Hurricane Teddy relinquishes its hold on the
local and regional winds. The southerly winds will shift showers and
isolated thunderstorms to the northwestern and northern areas of
Puerto Rico this afternoon. Light steering winds will cause showers
that develop to move slowly, and cause urban and small stream
flooding and ponding of water on roadways.

Monday, upper-level conditions become more favorable as a Polar
trough deepens across the western Atlantic, downstream of the Polar
trough a mid to upper level low is expected to develop just north of
Puerto Rico. As a result, the global models has 500 mb temperatures
cooling to -6 to -8 Monday and Tuesday. Low-level moisture is
progged to increase each day during the short-term period. Tuesday,
low-level moisture return to near normal levels.

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

A short wave trough is forecast to move over the region from the
Atlantic waters on Wednesday, and increase instability. At lower
levels, moisture from a weakening front is expected to advect from
the northwest and a weak ridge over the northeastern Caribbean
will promote southerly steering winds. These features, will aid in
the development of scattered showers with possible heavy
thunderstorms along the northern slopes of PR during the afternoon
hours. Urban and small stream flooding is expected with the
heaviest showers.

A TUTT is expected to gradually build northeast of the area
through the rest of the long term period. Meanwhile, a surface
ridge building over the southwestern Atlantic will cause winds to
gradually turn from the east to southeast on Thursday and from the
east to northeast from Friday onwards, as it strengthens over the
western Atlantic. Normal to above normal precipitable water
content is expected and afternoon convection is expected each day
over mainland PR.


&&

.AVIATION...VFR conds expected to prevail at all TAF sites through at least
20/16Z. SHRA/ISO TSRA will develop over the interior PR by 20/17Z
and slowly move northward. These SHRA/TSRA could cause brief MVFR
conds over the interior PR. Brief MVFR conds possible for the
northern TAF sites of PR due to +SHRA/TSRA through 20/22Z. Sfc
winds lgt/vrbl til 20/14Z then bcmg sea breezes of generally less
than 12 kt til 20/22Z.


&&

.MARINE...Northeast swell generated by Hurricane Teddy will
continue to cause hazardous seas today and through early Monday.
Another second pulse of the swell is expected to increase seas
once again from Tuesday through much of the week and hazardous
seas will return once again across the Atlantic waters and local
passages. Offshore buoys were indicating a decreasing trend
in wave heights since yesterday, with buoy 41043 recently
reporting seas just near 7 feet. Regardless, due to the direction
of the swell, higher seas are still possible across portions of
the Atlantic waters. Therefore, Small Craft Advisories continue in
effect for most of the local waters today and through Monday
morning.

Across the Atlantic coastline of the islands, rough surf conditions
and life-threatening rip currents will continue for the next
several days. As the swell briefly drops on Monday, the High Surf
Advisory will be let to expire. However, the High Rip Current risk
will likely be extended through next week for the north facing
beaches of the islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 92 80 / 50 20 60 50
STT 89 80 88 81 / 30 30 50 40

&&
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Re: Caribbean - Central America Weather

#20313 Postby cycloneye » Mon Sep 21, 2020 5:55 am

Area Forecast Discussion
National Weather Service San Juan PR
450 AM AST Mon Sep 21 2020

.SYNOPSIS...

Though showers are expected over the interior of Puerto Rico and
possibly the San Juan Metro, greater activity is expected for
tomorrow and Wednesday as increased moisture moves in. The biggest
story is that though the most recent swell will weaken throughout
today, another swell associated with Hurricane Teddy will arrive
tomorrow, and likely keep seas hazardous through the workweek. In
the longterm, ridging aloft will limit the strength of
thunderstorms, though showers will still be expected.

&&

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

The islands will be under a light southerly wind flow as a result
of Teddy, which is located well off to the north of the local
islands over the Atlantic Ocean. Maximum temperatures should
remain in the low 90s across the coastal and urban areas with heat
indices in the low to mid 100s degrees Fahrenheit. At upper
levels, a TUTT-low lingering around the Northeast Caribbean will
keep a relatively unstable atmosphere through at least Tuesday.
However, a short wave trough will swing by the region by mid-week,
destabilizing the atmosphere once again.

Mostly clear skies with warm and hot temperatures will dominate
weather conditions this morning. Under a light southwesterly
steering wind-flow, afternoon convection will focus over St Croix
and across and to the northeast of the Cordillera Central,
including the San Juan Metro Area.

Moisture from the Caribbean will move over the islands on Tuesday,
increasing the potential for showers and thunderstorm development.
Then, moisture from an old frontal boundary will move from the
Atlantic Ocean over the islands, and it will interact with a short
wave trough, diurnal heating, and local effects to produce another
round of afternoon convection over the islands. Scattered showers
with possible heavy thunderstorms are possible Tuesday and
Wednesday. However, convection may change its focus on Wednesday,
as winds change more from the east-southeast.

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

Heading into the latter-half of the workweek, strong high pressure
will persist to our west at mid to upper levels with a cut-off
area of low pressure to our southeast. Though there will not be
much in the way of upper-level forcing to encourage thunderstorm
development, 500mb temperatures will still be decent, around -6 to
-7 for the whole long-term period. Thus, isolated thunderstorms
will be in the forecast during this period, but they ought not to
be too strong. At low levels, high pressure will primarily
persist over the eastern Atlantic, with weaker pressure gradients
over our region. Thus, fairly light winds are expected over our
region during the long-term period, so slow moving showers and
high rainfall accumulation`s could be a threat. There are signs
of a strengthening high over the western to central Atlantic next
week.


Ample moisture from a weakening low will be with us for Wednesday
through Saturday. Precipitable water values will be above average of
around 1.8 to 2.0. With light winds, plenty of shower activity with
isolated thunderstorms can be expected, particularly over the
interior of Puerto Rico. The biggest threat is going to be areas of
isolated flooding under where the most persistent showers occur.
Thereafter, somewhat drier air is expected to move in, with low-
level wind speeds picking up a bit into the next week. Thus, the
next week is not expected to be as impactful given that the showers
should at least move along a bit more quickly.

&&

.AVIATION...
VFR conditions will prevail thru the forecast period. Expect
mostly clear skies with just a few passing clouds. Some
clouds/SHRA may develop during the afternoon and may impact JSJ
between 21/15-20z. Winds will remain calm to light/VRB. However,
gusty winds in/near showers, as well as sea breeze variations, are
possible.

&&

.MARINE...

The first swell associated with Hurricane Teddy will be
dissipating throughout the day. However, another swell will be
impacting the region tomorrow from the north, and this one is also
associated with Teddy. Small Craft Advisory criteria will once
again be met beginning tomorrow and this will last likely into
Friday. A High Surf Advisory may be needed as well.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 80 92 78 / 50 20 60 30
STT 89 81 87 80 / 20 50 30 20

&&
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Re: Caribbean - Central America Weather

#20314 Postby cycloneye » Wed Sep 23, 2020 5:18 am

Area Forecast Discussion
National Weather Service San Juan PR
445 AM AST Wed Sep 23 2020

.SYNOPSIS...

A northerly swell is impacting the region through Friday, and
dangerous marine conditions are occurring. Please be very
cautious if at any northern facing beaches! More active weather is
expected for the next several days due to a stalled trough and
its associated moisture. Areas of isolated flooding and frequent
lightning are the greatest weather threats for the next few days.
Winds will pick up a bit and weather will be more seasonal for
next week, with a possible tropical wave for mid-week.

&&

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

Hazardous coastal conditions will prevail across the Atlantic
Coastline from the northwest to northeast sections of Puerto Rico,
Culebra, Vieques, and the northern U.S. Virgin Islands. Residents
can expect life-threatening high surfs and isolated coastal
flooding due to the arrival of a long-period northerly swell.
Therefore, High Surf Advisory, Coastal Flood Advisory, and a High
Risk of Rip Currents are in effect for all the north and northeast
facing beaches in Puerto Rico and the U.S. Virgin Islands.

A frontal boundary north of the islands will stall until it
dissipates by the end of the work-week, promoting wet and unstable
weather conditions. A trough aloft will increase instability
furthermore during the afternoon hours today. Under the influence
of this frontal boundary, north of the islands, the steering flow
is forecast to become more south to southeast today. Therefore,
afternoon convection will form along and north of the Cordillera
Central, as well as downwind from the U.S. Virgin Islands. Urban
and small stream flooding is likely today, and cannot rule out
isolated flash flooding. Under the southeasterly wind component,
max temperatures in the low to mid-90s will persist today and
tomorrow, and the heat indices will surpass the 100s degrees
across urban and coastal areas in PR and the USVI each day.
However, winds will become more easterly by Thursday, inducing the
afternoon convection over the western sections. By Friday, winds
should return from the northeast as the boundary weakens in
response to a surface-high-pressure north of us, over the Atlantic
Ocean.

.LONG TERM...Saturday through Thursday

The long term forecast for this weekend looks somewhat more
favorable for active weather compared to what models have been
forecasting the past few days. Models have suggested mid to upper
level high pressure building to our west and this is still expected
over the weekend, yet the high pressure center appears to be far
enough west that it may not influence us much. Instead, both the GFS
and ECMWF models suggest weak low pressure over us that could help
enhance convection. Moisture values look fairly average for the
weekend, and definitely sufficient to produce plenty of shower
activity across the region with mildly favorable upper-level
conditions. At low levels, there is expected to be somewhat weak
high pressure over the central Atlantic, so pressure gradients and
associated low-level winds across the region are expected to be
somewhat light and generally easterly. Thus for Saturday, we will
likely see showers and thunderstorms over in the interior and
western Puerto Rico in the afternoon. Winds will turn more out of
the east-southeast for Sunday, so shower activity will then be
expected for northwestern Puerto Rico in the afternoon, as well as
a chance for showers over the San Juan Metro. Urban and small
stream flooding will definitely be a threat given the fairly slow
steering flow.

Heading into the workweek, the winds pick up a bit more at low
levels, which will help showers to move along a bit faster. High
surface pressure really strengthens over the central Atlantic next
week, which is the reason for the increased anticipates. Winds
will stay east southeasterly, so northwestern Puerto Rico and the
San Juan Metro have the best chance for showers. There will still
be plenty of moisture for the atmosphere to work with as well. Not
much change in upper level conditions are expected, so minimally
favorable conditions for thunderstorms remain in the forecast for
next week. Models still suggest a tropical wave moving in for next
Wednesday.

&&

.AVIATION...

SHRA/TSRA will continue across the coastal waters due to a frontal
boundary north of the islands. VCSH will affect USVI during the
morning, and some VCSH/VCTS could affect JBQ too. After 23/15z,
SHRA/TSRA will develop across the Cordillera Central and may
impact JSJ/JBQ. Line of SHRA/TSRA will form downwind from the USVI
and may impact IST/ISX btwn 23/15-19z. Winds will continue calm to
light and variable, but an S-SE, but sea breeze will develop after
23/13z.

&&

.MARINE...

A northerly swell is affecting the local waters and will continue
through Friday night, causing hazardous seas. Please refer to our
webpage and associated marine products for specific information. Light
to gentle southerly winds will prevail across the regional waters
today, with winds more from the east after today. Showers and
thunderstorms will be possible across the regional waters for the
next few days.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 92 79 92 79 / 50 40 40 40
STT 88 80 88 79 / 30 40 40 50
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Re: Caribbean - Central America Weather

#20315 Postby cycloneye » Thu Sep 24, 2020 5:25 am

Area Forecast Discussion
National Weather Service San Juan PR
519 AM AST Thu Sep 24 2020

.SYNOPSIS...

Hazardous coastal conditions will continue across the north facing
beaches of Puerto Rico and the U.S. Virgin Islands. Unsettled
weather conditions will persist as an old frontal boundary with
plenty of tropical moisture continues to produce periods of
showers and thunderstorms across the local islands.

&&

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

Long-period northerly swell is impacting the Atlantic Coastline of
Puerto Rico and the U.S. Virgin Islands. This event is producing
hazardous coastal conditions, and residents can expect life-
threatening rip-currents and high surfs, and isolated coastal
flooding. Therefore, High Surf Advisory, Coastal Flood Advisory,
and a High Risk of Rip Currents are in effect for all the north
and northeast facing beaches in Puerto Rico and the U.S. Virgin
Islands.

The municipalities along the Atlantic coastline will be
impacted by We have recently been under the influence of a trough
of low pressure with its associated surface front, and ample
shower activity with strong thunderstorms occured yesterday as a
result. This trough, coupled with high precipitable water values,
will produce more active weather for today. Winds will be more out
of the east, which is of course more normal for our region, yet
low level winds will remain light meaning slower showers and
higher rainfall amounts. High resolution model guidance suggests
interior and western Puerto Rico will be the focus of the
activity, but most of Puerto Rico has a decent chance of rainfall
tomorrow. Urban and small stream flooding will be the biggest
threat, and frequent lightning with gusty winds from thunderstorms
will also be a concern. Temperatures are not expected to be quite
as warm for the San Juan metro area as the past few days, given
the change in wind direction.

Heading into Friday and the weekend, one factors will cause our
weather pattern to shift to something a bit more normal. High
surface pressure will strengthen over the western Atlantic,
enhancing pressure gradients and the local low-level wind flow. Thus
a return to easterly winds of around 10 knots can be expected. The
weather will still be quite active though. Weak troughing will still
be over us for Friday and Saturday, and that will help to enhance
the chances for thunderstorms. Furthermore, there will still be
plenty of moisture available from the surface trough. Thus for
Friday, with winds pretty much easterly, showers and thunderstorms
will develop in the afternoon over western and interior Puerto Rico,
and there will be a good chance for isolated flooding. Saturday may
not be quite as active as precipitable water values drop a bit, yet
moderate to heavy showers with thunderstorms will still develop in
the afternoon over interior, western, and southwestern Puerto Rico.
Finally, with the help of troughing over the region, shower and
isolated thunderstorm activity will remain a threat over the local
waters for the next few days.

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

A surface high-pressure across the Atlantic Ocean will tight the
local pressure gradient and will be the dominant weather feature
in the first part of next week. Then, the leading edge of a
tropical wave will reach the islands around Tuesday, and its axis
will cross on Wednesday. After the passage of the wave, model
guidance is suggesting the arrival of a drier air mass with
African dust around late Wednesday night or early Thursday morning
into Friday. However, GFS dry-out faster than the ECMWF.

At upper levels, a trough low across the Atlantic Waters,
northeast of Puerto Rico and the U.S. Virgin Islands, will induce
surface perturbations Sunday and Monday. The aformentioned surface
high-pressure will push these perturbations across the islands
Sunday and Monday. A mid-level high pressure will slowly build
over the eastern Atlantic, moving into the northeast Caribbean
Tuesday through Thursday when a mid- to upper-level trough is
forecast to amplify from the northeast into the region of Puerto
Rico and the U.S. Virgin Islands by Friday.

&&

.AVIATION...

VFR conds have prevailed overnight, and will mostly continue today.
VCSH/VCTS will continue for the smaller islands TKPK/TNCM/TIST/TISX
through the morning. Winds light and VRB through the morning. Light
easterly winds thereafter with sea breeze variations. VCTS and
possibly TSRA possible this afternoon for TJSJ/TJMZ/TJPS/TJBQ.


&&

.MARINE...
Dangerous marine conditions continue due to a long-period
northerly swell. Mariners can expect seas between 8 and 12 feet
across the Atlantic Waters and Caribbean Passages through at least
tomorrow. Marine conditions are forecast to improve after
tomorrow when the northerly swell energy dissipates. A tropical
wave could increase the chance for showers and thunderstorms one
more time Tuesday into Wednesday next week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 93 77 89 79 / 50 40 40 30
STT 90 80 90 79 / 40 40 40 30
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Re: Caribbean - Central America Weather

#20316 Postby cycloneye » Fri Sep 25, 2020 4:52 am

Area Forecast Discussion
National Weather Service San Juan PR
357 AM AST Fri Sep 25 2020

.SYNOPSIS...

Coastal hazard conditions will persist throughout the day. The
Atlantic Coastline can expect hazardous surf and rip currents
today. Trofiness aloft will keep high the potential for the
development of showers and thunderstorms each afternoon through
the next few days. The next tropical wave will reach the local
islands Tuesday or Wednesday, followed by a dry air mass with
African dust.

&&

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

We have had very active weather the past few days, courtesy of a mid
to upper level trough with its associated surface front with ample
moisture. Though the moisture will be in place for the next few
days, precipitable water amounts will be just slightly lower at
around 1.8 to 2 inches. Furthermore, the aforementioned trough is
weakening and by this afternoon it will likely not have near the
influence that it has had over the past few days. Thunderstorms will
still be expected for today and the next few days, but they ought to
not be quite as intense as we observed yesterday. Finally of note,
high surface pressure has developed over the western Atlantic,
brining back the more typical easterly flow near the surface.
However, model soundings still suggest fairly light winds at 850 to
700 mb, meaning showers may still linger and cause high rainfall
amounts.

Heading into this afternoon, with light to moderate windflow from
the east, showers and thunderstorms will once again develop over
interior and western Puerto Rico. Though the storms will likely not
be quite as intense as yesterday, frequent lightning and areas of
isolated flooding will be the greatest threats. Activity over land
will calm down after the dinner hour, though isolated to scattered
showers will remain over the local waters overnight. For Saturday
afternoon, high pressure aloft will nudge closer towards our region
from the west, taking away the weak upper-level troughing. However,
lapse rates from model soundings do not really respond much. Thus
for Saturday, more showers and isolated thunderstorms can be
expected, though again the storms should be weaker than the day
before. The activity will again focus over western, interior, and
even southern Puerto Rico. For Sunday, more showers and
thunderstorms are expected for central, interior, and southwestern
Puerto Rico. Somewhat faster winds at steering levels should help
showers to move long a bit faster and be less impactful.

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

A mid- to upper-level trough near the Windward Islands will
induce a trade wind perturbation, increasing moisture and the
potential for showers and thunderstorms across the islands on
Monday. The leading edge of a tropical wave is forecast to reach
the islands between the afternoon or night of Tuesday. The axis of
the tropical wave will cross the islands of PR/USVI on Wednesday.
GFS precipitable water range between 1.9 and 2.25 inches Monday
through Wednesday, with the best moisture between late Tuesday
night and Wednesday. A dry air mass with African dust particulate
will follow the tropical wave creating hazy skies and limiting
shower and thunderstorm activity through at least Friday. However,
do not rule out the typical advective pattern overnight and early
in the morning, followed by the sea breeze convective pattern
across the western sections. Another trade wind perturbation
induced by an upper- level feature over the Atlantic Ocean will
make its way into the region late Friday night into Saturday.

&&

.AVIATION...

VFR conds have prevailed overnight, and will mostly continue today.
VCSH possible for TKPK/TNCM/TIST/TISX through the afternoon. Winds
light and VRB through the morning. Easterly winds around 10 kts
thereafter with sea breeze variations. VCTS possible this afternoon
for TJMZ and TJPS, and VCSH for TJBQ and TJSJ.

&&

.MARINE...

The northerly swell energy will slowly dissipate across the
Atlantic Waters and Caribbean Passages through the rest of today.
However, seas between 6 and 8 feet with occasional seas up to 10
feet will reach the regional waters. Mariners can expect lower
seas across the Caribbean Coastal areas, especially between Lajas
and Yabucoa, where seas between 3 and 5 feet are forecast. Seas
will rapidly improve over the weekend into next week. However, a
tropical wave could increase the chance for showers and
thunderstorms one more time Tuesday into Wednesday next week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 80 88 80 / 30 30 30 30
STT 89 79 90 79 / 30 30 30 30
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Re: Caribbean - Central America Weather

#20317 Postby cycloneye » Sat Sep 26, 2020 4:56 am

Area Forecast Discussion
National Weather Service San Juan PR
446 AM AST Sat Sep 26 2020

.SYNOPSIS...
Another active afternoon is expected over the interior and
southwestern Puerto Rico, and with saturated soils from previous
rainfall, urban and small stream flooding will be possible.
Moisture will remain high during the first half of the workweek
with more rain expected. Then, Saharan dust is expected to
filter in by the end of the week.

&&

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

A mid to upper-level trough will continue to weaken, but slight
troughiness will continue today. There is also above average
available moisture with precipitable water values at around 2
inches, but expected to decrease slightly as the day progresses.
Winds will be from the east to east northeast today. Because of the
available moisture, scattered showers will continue this morning
across the local waters, USVI and eastern PR. For the afternoon
hours, the diurnal heating and local effects will combine with
the weak trough in the mid and upper levels to help promote the
development of showers and thunderstorms over Puerto Rico,
especially across central to western and southwestern PR. The rest
of the local area is expected to observe isolated to scattered
showers. Because of the rainfall over the past few days, the
activity expected today could cause urban and small stream
flooding in some areas.

Even though the upper trough is expected to give way to an upper
ridge to our west and an upper low to our east by Sunday,
essentially causing subsidence, the available moisture will combine
with the diurnal heating and local effects to cause showers and
thunderstorms on Sunday and Monday afternoon across central to
western PR. The rest of PR and the USVI will observe scattered
showers over the next few days. That said, Sunday looks like it has
a better chance of showers and thunderstorms as a tropical wave is
expected to move late on Sunday, continuing into Monday.

.LONG TERM...Tuesday through Sunday
Another tropical wave is expected to approach the islands by late
Tuesday into Wednesday. Precipitable water values are expected to
climb between 1.9 to 2.1. At the upper levels, a trough to the
northeast of the Windward Islands will support cold temperatures
aloft. Hence, these ingredients will combine to create unsettled
weather conditions over the area, with an increase in shower and
thunderstorm activity. By Thursday, a drier air mass at the low to
mid levels is expected to filter in from the east. Saharan dust
will be embedded in this air mass, resulting in hazy skies over
the islands through the weekend. Even with the drier air,
fragmented groups of clouds will makes their way into Puerto Rico
and the U.S. Virgin islands, and in combination with diurnal
heating and local effects, should result in shower activity over
the interior and western Puerto Rico each afternoon.



&&

.AVIATION...VFR conds at terminals through 26/16Z. VCSH expected
across the local terminals through 26/13Z. VCTS psbl at TJPS after
26/16Z and at TJBQ after 26/18Z. Sfc winds at around 10 kts from the
east to northeast with sea breeze variations. BKN SKY possible at
around FL060...FL050 mainly with SHRA/ Isold TSRA activity.


&&

.MARINE...
As the northerly well continues to subside, seas are now at 6 feet
or less across the local waters. Isolated thunderstorms will be
possible each afternoon, especially across western Puerto Rico.
Choppy marine conditions are expected by the middle of the
workweek. For the beachgoers, a high rip current risk continues
for some of the north-facing beaches of Puerto Rico.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 79 88 79 / 30 50 50 50
STT 91 79 90 80 / 30 50 40 40
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Re: Caribbean - Central America Weather

#20318 Postby cycloneye » Sun Sep 27, 2020 5:46 am

Area Forecast Discussion
National Weather Service San Juan PR
435 AM AST Sun Sep 27 2020

.SYNOPSIS...
Above normal moisture is expected to continue over the area,
promoting the formation of showers and thunderstorms every
afternoon for the next several days. Urban and small stream
flooding will be possible. Another tropical wave is expected on
Wednesday with some Saharan dust expected for the end of the week.

&&

.SHORT TERM...Today through Tuesday...
For the next few days, a surface high pressure across the central
Atlantic will bring easterly trade winds to the local islands.
Above normal available moisture will persist over the local area
today, combined with a tropical wave that is expected to move
through the local area this afternoon, will cause the development
of showers and thunderstorms across the local area. For Puerto
Rico, the areas with the highest chance of thunderstorms are
across the western to eastern interior as well as portions of
southern Puerto Rico. These areas could observe urban and small
stream flooding. That said, scattered showers are expected
elsewhere in Puerto Rico and around the U.S. Virgin Islands, and
ponding of water on roadways and poor drainage areas can occur.
For Monday, the higher than normal moisture will linger across the
local area, which will cause scattered showers across the area
during the morning and overnight hours. However, Monday afternoon,
with the diurnal heating and local effects, we can once again
expect the development of showers and thunderstorms across Puerto
Rico. This time the convection is expected across central to
northwestern Puerto Rico, as the wind flow will be mainly from the
east to east southeast. Tuesday looks like it will have slightly
less shower activity since drier air will finally move in. That
said, there will still be enough moisture for good shower and
thunderstorm activity, but it will be limited compared to today
and Monday. The wind flow is expected to be more southeasterly on
Tuesday afternoon, so northwestern Puerto Rico has the best chance
of thunderstorms, with isolated to scattered showers elsewhere.

.LONG TERM...Wednesday through Monday...
A tropical wave is expected to move over the islands on
Wednesday, increasing moisture content once again with precipitable
water values around 1.9 to 2.2 inches. Additionally, a mid-level
trough in the area will cause instability to increase, with cold
temperatures and divergence aloft. As a result, showers and
thunderstorms are expected over the islands. Urban and small
stream flooding will be possible. For the rest of the workweek,
some Saharan dust will filter from the east, resulting in hazy
skies. However, fragmented groups of clouds embedded in the trade
winds will also move over the area. Therefore, the available
moisture in combination with local effects will result in
afternoon activity, especially over the interior and western
Puerto Rico. For the weekend, a mid to upper level high pressure
will begin to build north of the western Atlantic, decreasing
instability levels aloft. At the lower levels,a drier air mass is
expected to move in, with some Saharan dust lingering and
precipitable water values falling to near 1.6 inches. Hence, a
decrease in rainfall activity can be expected through Monday.



&&

.AVIATION...VFR conds at terminals through 27/16Z. VCSH expected
at the TJSJ, TIST, and TISX terminals today. VCTS psbl at TJPS after
27/16Z. Sfc winds at around 10 kts from the east to northeast with
sea breeze variations expected after 27/13Z. BKN SKY possible at
around FL050...FL070, especially after 27/16Z.

&&

.MARINE...
Seas are expected to remain at 3 to 5 feet with winds out of the
east northeast at 10 to 15 knots. This conditions should continue
for the early part of the workweek. There is a moderate rip
current risk for the north facing beaches of Puerto Rico, Vieques,
Culebra and St. Thomas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 80 90 79 / 40 50 50 30
STT 90 80 90 80 / 40 40 40 30

&&
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Re: Caribbean - Central America Weather

#20319 Postby cycloneye » Mon Sep 28, 2020 5:28 am

Area Forecast Discussion
National Weather Service San Juan PR
134 AM AST Mon Sep 28 2020

.SYNOPSIS...The tropical is moving across the local area,
bringing showers and thunderstorms to the general area.
The tropical wave will keep above normal moisture, which will
combine with a mid to upper-level trough (TUTT) that extends
northeast of the northern Leeward islands southwestward into the
eastern Caribbean. The tropical wave and TUTT combination will
continue to enhance the chances of showers and thunderstorms
today. On Wednesday, another tropical wave is expected to
approach the region, causing another increase in shower and
thunderstorm activity, followed by a slightly drier air mass by
the end of the week, perhaps with some Saharan dust.


&&

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

A tropical wave in combination with a mid-to-upper level trough will
cause unsettled weather conditions across the islands today. Data
from 28/00Z sounding, as well as satellite-derived precipitable
water indicate values near 2.1 inches over the area. Additionally,
Doppler radar and surface observations indicated an area of showers
and thunderstorms affecting the U.S. Virgin Islands and eastern
Puerto Rico. In fact, the high resolution models show that this
activity should continue through the morning hours, affecting the
same general areas. Since some of these soils are already saturated,
urban and small stream flooding will be possible. In the afternoon,
additional showers will continue to be affecting eastern Puerto Rico
and the U.S. Virgin Islands, but also, local effects and diurnal
heating will support activity developing over the interior, western,
and northern Puerto Rico, including the San Juan metro area. Some of
these showers could bring heavy rain at times.

A somewhat drier air mass is expected to filter in later in the
evening and early Tuesday. Additionally, as the mid-level trough
departs from the area, conditions are not going to be as favorable
for showers development. However, at the surface, groups of clouds
will make their way into the islands, resulting in another round of
showers early in the day for the eastern half of the forecast area,
followed by afternoon convection in western Puerto Rico.

Late Tuesday into Wednesday, another round of active weather is
anticipated. A favorable weather pattern for rain will be
established over the area, with a mid-to upper level trough causing
instability aloft, as well as cold temperatures in the mid-levels.
Additionally, a tropical wave will advance into the islands,
providing an increase in moisture. Therefore, widespread shower and
thunderstorm activity is expected for the local waters and the
islands. First, as is usual, the eastern half of PR/USVI should see
the bulk of the activity, but as the day progresses, the potential
will increase for the production of convection over the interior,
western, and northern PR, and in forms of streamers from Vieques,
Culebra, El Yunque and USVI.


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

Somewhat drier air is expected to move in on Thursday into Friday,
perhaps with some Saharan dust, which could limit the shower and
thunderstorm activity across the area, especially when compared to
what is forecast on Wednesday. That said, there is a tilted upper
level trough that could help in the development of isolated
thunderstorms. This upper trough is forecast by the global models
to remain near the local islands through the long term period,
though it could put PR and the USVI in the subsident side late in
the weekend. There is also a strong SFC high pressure in the
central Atlantic that will dominate the local wind flow, keeping
us observing east to east southeast winds. The available moisture
is expected to be near to slightly above normal for most of the
long term period. So given the current setup, we can expect
morning and overnight isolated to scattered showers with isolated
thunderstorms over the waters, near the USVI and eastern PR, while
each afternoon, showers and thunderstorms can be expected across
portions of central and western PR and areas of sea breeze
convergence.


&&

.AVIATION...A tropical wave will continue to cause TSRA across TISX/TIST at
least through 28/10Z, with some reduction in VIS and lower ceilings
expected. VCTS will also be affecting TJSJ and the Leeward terminals
through the day, and TJBQ after 28/17Z. Winds will be out of the ESE
at 10-15 knots with stronger gusts, especially near thunderstorms.

&&

.MARINE...Seas up to 5 feet and winds up to 20 knots are expected
today across most of the local waters. Showers and thunderstorms
causing locally higher seas and gusty winds are possible over the
waters as a tropical wave passes through. Seas will increase up
to 6 feet on Tuesday. Small craft operators are urged to exercise
caution. There is a moderate risk of rip currents across the north
beaches of PR and Culebra as well as eastern St Croix, low risk
elsewhere.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 90 79 / 60 50 50 40
STT 88 79 89 79 / 40 40 40 60
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Re: Caribbean - Central America Weather

#20320 Postby cycloneye » Tue Sep 29, 2020 5:26 am

Area Forecast Discussion
National Weather Service San Juan PR
402 AM AST Tue Sep 29 2020

.SYNOPSIS...Trailing edge of a tropical wave will continue to
produce showers and thunderstorms across the local area today.
Surface high pressure across the central Atlantic will bring
moderate easterly winds for the next several days. Weak upper
trough will strengthen by Thursday, causing an increase in
instability.

&&

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

Cloudiness associated with an exiting tropical wave continues to
linger across the skies. This wave generated moderate to heavy
showers over portions of eastern PR and USVI through the
overnight, as well as some thunderstorms with frequent lightning.
However, a drier air mass moved into the islands, tapering most of
the activity and limiting additional shower development. Although
the mid-levels are expected to remain drier than yesterday, at
the surface, additional pockets of moisture are expected to filter
in over the islands through the day. In facts, precipitable water
values are expected to remain around 1.9 to 2.0 inches.
Additionally, an upper level trough to the northeast of the
Caribbean is maintaining cold temperatures aloft. As a result,
some showers are expected to move in over eastern portions of the
forecast area early in the day, followed by afternoon convection
developing over the interior, northwestern Puerto Rico, from El
Yunque toward the San Juan metro area, and with stream-like
showers developing from the U.S. Virgin Islands, Vieques and
Culebra. Since some soils are saturated from previous rainfall,
urban and small stream flooding will be possible with the
strongest activity.

On Wednesday, a mid-level trough will be moving nearby or just to
the east of the islands, while another tropical wave approaches. In
general, the environment will remain favorable for rainfall
formation over the forecast area. However, there are some
discrepancies between the models on where the rain will be
concentrated. Nevertheless, expect another round of showers and
thunderstorms moving over the local waters and over land through the
day. For Thursday, conditions are expected to improve as a drier air
mass reaches the area. Saharan dust will be embedded in this
airmass, turning skies hazy. In terms of winds, a surface high
pressure over the western Caribbean will strengthen, thus tightening
the gradient over the area, causing stronger winds on Wednesday and
Thursday.

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

Somewhat drier air is expected to move in on Friday, perhaps with
some Saharan dust, which could limit the shower and thunderstorm
activity across the area. However, there is a tilted upper level
trough that could help in the development of thunderstorms over
the general area. This upper trough is forecast by the global
models to remain near the local islands through the long term
period, with the latest model run being more aggressive than the
model run from yesterday. There is also a strong SFC high
pressure in the central Atlantic that will dominate the local wind
flow, keeping us observing east to east southeast winds. That
said, the SFC high will move into the eastern Atlantic by early
next week, but the winds will remain from the east to east
southeast. The available moisture is expected to be near normal on
Friday and Saturday, but increasing to above normal from Sunday
onward. So given the current setup, we can expect morning and
overnight isolated to scattered showers with isolated
thunderstorms over the waters, near the USVI and eastern PR, while
each afternoon, showers and thunderstorms can be expected across
portions of central and western PR and areas of sea breeze
convergence.


&&

.AVIATION...VFR conditions will prevail for most of the period. A tropical wave
will cause VCSH for most terminals early in the day. Then, after
29/18Z VCTS are expected at TJSJ/TJBQ which could result in low
ceilings and VIS reduction. Winds are expected out of the east at 10
to 20 knots with stronger gusts.

&&

.MARINE...Winds will increase up to 20 knots with choppy seas up
to 6 feet. Therefore, small craft operators are urged to exercise
caution. Choppy seas and moderate to fresh winds will continue for
the next few days. There is a moderate risk of rip currents for
most of the local beaches today.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 90 79 / 60 50 60 40
STT 88 80 89 81 / 50 60 60 50
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