Caribbean - Central America Weather

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cycloneye
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Re: Caribbean - Central America Weather

#20281 Postby cycloneye » Thu Aug 06, 2020 4:39 am

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Thu Aug 6 2020

.SYNOPSIS...

After some scattered showers throughout the day today, a tropical
wave will arrive tomorrow that will enhance shower activity across
the region. Thereafter, drier than normal conditions will prevail
for the next several days, with mild to moderate amounts of
Saharan dust. Another tropical wave is forecast to arrive next
Wednesday, though models disagree on the timing and intensity.

&&


.SHORT TERM...Today through Saturday

An upper-level low moving into the region is eroding the mid-level
ridge aloft. A surge of low-level moisture is promoting frequent
passing showers across the local waters, and some of them are moving
into the windward sections of PR/USVI. Later today, a slot of dry
air will filter into the region limiting shower activity. Winds are
forecast to continue from the east to east-southeast promoting
afternoon convection across the interior and northwest quadrant of
Puerto Rico, and downwind from the U.S. Virgin Islands and from El
Yunque. Periods of moderate to heavy showers in the form of
streamers are possible across the San Juan metro area and surrounding
municipalities. Thunderstorm activity will deteriorate weather
conditions, and urban and small stream flooding is possible across
the interior and western sections of Puerto Rico this afternoon.

A tropical wave across the tropical Atlantic, near the longitude
55W, will propagate into the region by Friday afternoon. Although
the bulk of moisture will move off to the south of the islands
across the Caribbean waters, the instability and the moisture field
associated with it will increase the potential for showers and
thunderstorms across Puerto Rico and the U.S. Virgin Islands. Late
Friday night into Saturday, a dry air mass with Saharan dust
particulate will be the dominant weather feature across the islands.
Therefore, expect limited showers activity, hazy skies and warm to
hot temperatures.

.LONG TERM...

Generally speaking, the long-term period is expected to be drier
than normal, with the exception of a tropical wave for the middle of
next week. To kick off the week, high pressure will dominate our
region at all levels, and this will promote mostly dry conditions.
Model soundings look particularly dry and warm at mid-levels, and
that will keep showers weak for the most part. Passing showers
are still possible for Monday and Tuesday. Though they are
expected to be weak, persistent showers over a given area can
still cause localized flooding. For both days, the best chance
for showers is over western Puerto Rico in the afternoon.

On Wednesday a tropical wave is expected to arrive sometime during
the daytime or evening. Models somewhat disagree on the timing and
intensity, with the European model forecasting a later and weaker
wave. If warming from the sun can occur before the wave arrives,
this could prime the atmosphere for strong showers. However, there
is still plenty of uncertainty regarding this feature.
Furthermore, the wave will have a lot of work to do to clear out
the very dry and warm air expected for earlier in the weak, and
this weakens the potential of this wave. Thereafter, more dry air
moves in for Thursday, with long-range models suggesting another
wave on Friday.

&&


.AVIATION...

VFR conditions are expected to prevail through 06/18Z. However, VCSH
will affect IST/ISX/JSJ at times. SHRA/TSRA will develop across the
mountains and western sections of PR btwn 06/16-23z, as well as
downwind from the USVI. The heaviest activity is expected near JBQ,
and could create MVFR or even brief IFR conds. Surface winds will
continue from the E-ESE at less than 10 knots, increasing around 15
kt with sea breeze variations and higher gust after 06/13z.

&&


.MARINE...

Tranquil seas are expected for the next few days, with seas below
5 feet. Winds will generally be around 10 to 15 knots, though
winds may reach 15 to 20 knots near the coast of the Atlantic and
Caribbean. Winds and seas increase behind a tropical wave moving
in tomorrow. A low risk of rip currents is forecasted for
everywhere except a moderate risk for the north central coast of
Puerto Rico.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 91 78 / 30 20 60 30
STT 89 79 90 79 / 40 30 50 30
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Re: Caribbean - Central America Weather

#20282 Postby cycloneye » Fri Aug 07, 2020 5:08 am

Area Forecast Discussion
National Weather Service San Juan PR
429 AM AST Fri Aug 7 2020

.SYNOPSIS...

A fairly weak and fast moving tropical wave will pass through
today, which will enhance showers across the region. Drier weather
moves in for the weekend with Saharan dust, though passing showers
are still possible. The next tropical wave is then expected to
arrive next Wednesday. Marine conditions are fairly calm today,
and will become more choppy tomorrow due to winds behind the
tropical wave.

&&

.SHORT TERM...Today through Sunday

Subsidence ahead of an approaching tropical wave will limit shower
activity across the islands this morning. Winds will shift from the
southeast resulting in above normal temperatures, and warm to hot
heat indices across the coastal and urban areas today. However, as
the tropical wave moves into the region, showers and thunderstorms
will spread over the islands. This wave will interact with an upper-
level low increasing instability and promoting convection.
Therefore, expect inclement weather today, and periods of moderate
to heavy rains could lead to urban and small stream flooding from
late this morning into the afternoon hours.

A dry air mass will spread across the islands this evening into the
weekend. This air mass will reach region with suspended African dust
particles. Also, a mid-to-upper level ridge will build aloft,
promoting a trade wind cap over the region. Under this weather
pattern, hazy skies, stable conditions, above normal temperatures,
and limited rain activity will persist across the islands during the
weekend. However, the typical passing trade wind showers during the
overnight and early morning hours, followed by some afternoon
convection will be possible each day.

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

To start the workweek, high pressure will dominate all levels of the
atmosphere in the central Atlantic, with a secondary high extending
into the western Atlantic. This will promote fairly benign
conditions across the region, with the usual easterly winds at 10
to 20 mph. Patches of low-level moisture are expected to pass
through Monday and Tuesday, yet very dry and warm air aloft will
make conditions hostile for shower activity. The moisture moving
through will likely drive some showers over western Puerto Rico
for both Monday and Tuesday, but these showers will likely be
unimpactful. Though the showers will not be very strong,
persistent showers over a given area can still produce ponding of
water.

The next tropical wave arrives Wednesday in the afternoon or
evening. Generally the models have been trending to a somewhat
weaker system, yet this wave will still very likely increase shower
and thunderstorm activity across the region. Forecast models suggest
the wave will last through Thursday morning, after which more dry
air will move in. During the wave, the biggest threat will be urban
and small stream flooding. Only passing showers are expected once
the wave moves out and through Friday. Models suggest another
tropical wave arrives for Saturday evening.

&&

.AVIATION...

VFR conds will prevail through at least 07/15Z. The leading edge of
an approaching tropical wave will bring SHRA/TSRA across the USVI/PR
after 07/15z. MVFR or even IFR conditions will be possible across
IST/ISX/JSJ/JPS btwn 07/15-20z, and in JBQ btwn 07/17-23z. Sfc winds
will continue from the E at less than 10 knots, then from the E-SE
at around 15 knots with higher gusts and sea breeze variations after
07/13z.

&&

.MARINE...

Seas up to 5 feet are expected across the region today with
easterly winds around 10 to 15 knots, and isolated areas up to 20
knots. However, the winds will pick up more tomorrow and
especially Saturday as the tropical wave moves through, and this
will result in seas up to 6 feet. For next week, seas calm down
through the middle of the week. Showers and isolated thunderstorms
are possible across the local waters today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 90 79 / 50 30 30 10
STT 90 80 90 80 / 50 20 20 20
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Re: Caribbean - Central America Weather

#20283 Postby cycloneye » Sat Aug 08, 2020 5:04 am

Area Forecast Discussion
National Weather Service San Juan PR
443 AM AST Sat Aug 8 2020

.SYNOPSIS...

A mid-to-upper level ridge will build and hold aloft through the
upcoming week. A dry air mass with African dust particles will
limit shower activity and produce hazy skies the next few days.
However, overnight and early morning showers across the windward
sections followed by afternoon convection across the western
sections will affect the islands each day. Warm to hot
temperatures will persist through the next few days. The next
tropical wave is forecast to arrive by the middle of next week.

&&

.SHORT TERM...Today through Monday

The weak and fast-moving tropical wave from yesterday is now moving
out of the region, and precipitable water values are now dropping.
Isolated showers will continue out over the local waters for the
next few hours. Winds behind the tropical wave are fairly breezy,
and regional buoys are currently seeing this increase in wind
speeds. Winds of 10 to 20 knots are expected today from the east.

High pressure currently extends from the lower to upper atmosphere
over the western to central Atlantic, and this feature will play a
primary role in our weather the next few days. Furthermore, forecast
model soundings show that this ridging will really dry out the mid-
levels of the atmosphere, thus creating hostile conditions for
shower development. The soundings also show warming temperatures at
low to mid levels, which also works against showers. Below average
precipitable water values are expected today through Monday,
generally ranging from 1.3 to 1.6 inches. Finally, mild to moderate
amounts of Saharan dust are moving in, and will be with us for the
next few days.

To sum up these conditions, the next few days looks quite calm
across the region with drier than normal conditions. Very little
shower activity is expected today over land, with the best chance
being over western Puerto Rico near Mayaguez in the afternoon. Only
fairly weak showers are expected. Tomorrow and Monday some low-level
moisture moves in from the west, yet given the effects of the
ridging, only minimal impacts are expected. Showers will continue to
favor western to northwestern Puerto Rico, and these showers will
likely be weak. Despite generally unfavorable conditions for strong
showers, persistent weak showers over a given area can lead to water
ponding. Isolated showers are possible over the local waters, and
may impact areas near the coast in eastern Puerto Rico in the
nighttime and morning hours.

.LONG TERM...Tuesday through Sunday

A mid level high pressure is forecast to be the dominant weather
feature through much of the work-week. This feature will promote a
dry air mass at mid level, and a persistent trade wind cap.
However, a weak tropical wave is now forecast to reach the islands
by Wednesday afternoon into the evening. This tropical system will
provide the best chance for shower and thunderstorm development
across the islands, but doesn`t look so impressive at this time.

For the end of the long-term period, which increase the amount of
uncertainty about this solution, a more robust tropical wave will
provide a better chance for inclement weather across the islands
late Friday night or Saturday.

Generally speaking, a seasonal weather pattern will persist
across the islands with overnight and early morning showers moving
across the local waters and windward sections, followed by
afternoon convection over the western portions of the islands.
Maximum temperatures will continue in the low 90s mainly over the
urban and coastal areas with heat indices from the upper 90s to
mid 100s.

&&

.AVIATION...

VFR conds are expected to prevail at all terminals for the next 24
hrs. Brief MVFR in SHRA/TSRA psbl btwn 08/17-21Z in wrn PR. Sfc
winds E less than 11 kts, bcmg 10-20 kt after 08/14Z, strongest near
the coast where sea breezes will influence.

&&

.MARINE...

Mariners can expect choppy seas across the Caribbean waters and
passages due to a wind surge. Small craft operators should
exercise caution across most of the local waters due to winds
between 15 and 20 knots. Seas will range between 2 and 5 feet.
Early next week, mariners can expect tranquil marine conditions,
but local effects will accelerate winds across the Caribbean and
Atlantic waters between 15 and 20 knots at times, especially
during the afternoon hours. A tropical wave will move across the
local waters by the middle of next week, increasing winds and
seas, and deteriorating weather conditions.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 90 79 / 50 30 20 10
STT 90 80 90 80 / 50 10 20 20
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Re: Caribbean - Central America Weather

#20284 Postby cycloneye » Sun Aug 09, 2020 4:52 am

Area Forecast Discussion
National Weather Service San Juan PR
402 AM AST Sun Aug 9 2020

.SYNOPSIS...

The influence of a mid-to-upper level ridge and a dry air mass
with African dust particles will continue to promote mostly
sunny/clear and hazy skies. Maximum temperatures will remain in
the low-90s with heat indices in upper 90s and mid 100s degrees
Fahrenheits. Overnight and early morning showers across the local
waters and windward sections followed by afternoon convection
across the western portion of the islands will happen each day.
The next tropical wave is forecast to arrive by the middle of this
week.

&&

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

Strong high pressure continues across the central Atlantic, which is
helping to produce drier than normal conditions across the region.
The effects of this ridging were evident in the sounding from
yesterday evening, with a strong inversion between 850 and 700 mb,
along with very dry air at mid to upper levels. Saharan dust has
also invaded the region, and mild to moderate amounts will continue
for the next few day. The aforementioned high pressure will also be
with us for the next few days, resulting in a continuation of drier
than normal conditions. Though no tropical waves are expected in the
short term, patches of moisture will move in from time to time,
resulting in periods of isolated to scattered showers.

Putting this all together, only isolated showers are expected for
the rest of the morning, primarily across the local waters and areas
near the coast of E. Puerto Rico and the USVI. For this afternoon,
east-northeasterly winds will favor showers over southwestern Puerto
Rico this afternoon. These showers will likely not be impactful,
though persistent showers may produce ponding of water in isolated
areas. Monday and Tuesday are essentially a repeat of today, except
the shower activity in the afternoon will center over western rather
than southwestern Puerto Rico. Again these showers will likely not
be very impactful.

.LONG TERM...Wednesday through Monday

The mid level high pressure is forecast to remain near the region
as one of the dominant weather features promoting dry air at mid
level, and a persistent trade wind cap. However, a weak tropical
wave is forecast to move across the islands by Wednesday afternoon
and should be out of the region by Thursday morning when a dry
air mass with African dust will filter from the east over the
islands. This tropical system will provide the best chance for
shower and thunderstorm development across the islands, but
doesn`t look so impressive at this time.

For the next weekend, a more robust tropical wave will provide a
better chance for inclement weather across the islands, now,
by Saturday afternoon into Sunday. Uncertainty still high because
this tropical system is too far in the long-term forecast,
therefore it`s too early to know its true nature and impacts
across the islands.

Generally speaking, you can expect a seasonal weather pattern with
overnight and early morning showers moving across the local waters
and windward sections, followed by afternoon convection over the
western sections of the islands each day. Maximum temperatures
will continue in the low 90s mainly over the urban and coastal
areas with heat indices from the upper 90s to mid 100s degrees
Fahrenheits.

&&

.AVIATION...

Primarily VFR conds expected at all terminals. Brief passing showers
possible for all terminals except TJPS/TJMZ/TJBQ through 16z with E
winds at 5 to 10 kts. Winds pick up to 10 to 15 kts with sea breeze
variations, and VCSH possible for TJMZ in the afternoon.

&&

.MARINE...

Mariners can expect tranquil marine conditions through much of the
forecast period. However, winds and seas will remain between 15
and 20 knots, and between 4 and 6 feet across the Caribbean
Offshore waters and the Mona Passage today. Also, local effects
could increase winds between 15 and 20 knots each day, especially
during the afternoon hours. Marine/weather conditions will
deteriorate due to a tropical wave between Wednesday afternoon and
early Friday morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 81 90 79 / 10 20 20 30
STT 91 81 91 79 / 20 30 30 30
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Re: Caribbean - Central America Weather

#20285 Postby cycloneye » Mon Aug 10, 2020 4:36 am

Area Forecast Discussion
National Weather Service San Juan PR
412 AM AST Mon Aug 10 2020

.SYNOPSIS...

A fairly typical weather pattern is expected to prevail across the
area for the first half of the workweek, though shower activity will
be somewhat inhibited due to relatively low moisture levels and
lack of favorable dynamics aloft. This is expected to change
around midweek, with a tropical wave forecast to push into the
area late on Wednesday. Increasing showers are expected for late
Wednesday afternoon, and increased passing shower activity
overnight into early Thursday morning.

&&

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

Mostly clear skies prevailed across the local islands during the
overnight and early morning hours with a few sprinkles noted over
the local waters and coastal areas. The overnight low temperatures
ranged from the upper 70s to around 80 degrees at lower elevations.
Winds were from the east northeast at 10 MPH.

A mid to upper level ridge will continue to hold across the local
islands through the forecast cycle. At lower levels, a surface high
pressure located across the central Atlantic will continue to
promote moderate east-northeast winds across the northeastern
Caribbean for much of the workweek. The next tropical wave
passage, and best moisture advection across Puerto Rico and the
US Virgin Islands, is expected late Wednesday into Thursday, with
precipitable water reaching about 2.0 inches. Nevertheless, the
ridge aloft holds, with upper level dynamics remaining marginal.

Therefore, continue to expect mainly fair weather conditions,
with locally-induced afternoon showers and isolated thunderstorms
across western Puerto Rico each afternoon. The intensity and
areal coverage of afternoon showers and thunderstorms are expected
to increase on Wednesday, as the tropical wave approaches the
forecast area. Under the east northeast wind flow, maximum
temperatures will continue to range from the low 90s in the lower
elevations to the upper 70s in the highest mountains.

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

On Thursday, a tropical wave is forecast to continue traversing the
area, with the bulk of the moisture being during the morning in the
west. Dry air will follow the wave, though patches of moisture will
stream across the area from time to time late Thursday into
Saturday. The strongest moisture during this time is forecast to
impact the area overnight Friday into early Saturday morning. Aloft,
conditions are not expected to be favorable for convective
development during this time. As such, the typical pattern of
showers is expected, with local effects dominating; passing showers
are possible during the nights and mornings in the east, and the
bulk of the afternoon showers will be in western and interior
portions of Puerto Rico. With winds shifting to be closer to east-
northeast on Friday, some of the showers may affect more of
southwestern Puerto Rico as well.

On Saturday, a relatively strong tropical wave is forecast to
approach the region, pressing into the area likely during the
afternoon. There remains substantial uncertainty with respect to the
forecast for this wave, especially in terms of its strength and
development. As such, it is difficult to ascertain for certain what
the exact impacts will be. But currently, the slightly more likely
scenario has enhanced moisture across the area through Sunday, with
some lingering moisture possible for Monday into Tuesday. Meanwhile,
some improvements are expected aloft, in terms of potential support
for convection. The mid-level ridge is forecast to have pulled away
by Saturday, and in the upper-levels, the ridge is expected to
weaken during the latter half of the weekend. As such, an increase
in showers and thunderstorms is expected starting late Saturday,
especially with the afternoon showers. The peak in afternoon
convection would likely be in northwestern and interior Puerto Rico,
with a secondary maximum in the east due to streamer development.
But again, with this being several days out and the uncertainty
being relatively high, this forecast is certainly subject to change.

With the drying trend for Monday into Tuesday, a decrease in showers
is anticipated. The typical pattern is expected to again dominate
across the area, with the highest potential for afternoon showers in
the northwest and interior, and passing showers in the east
overnight and into the morning.

&&

.AVIATION...

VFR conds are expected to prevail at all TAF sites through the
forecast period. Winds will continue from the east northeast at 10
knots, increasing at around 15 knots with higher gusts and sea
breeze variations aft 10/13z. VCSH are possible at JBQ aft 10/16z.


&&

.MARINE...

Seas of up to 5 feet are anticipated across the local waters,
accompanied by generally light to moderate trade winds. Locally
stronger winds are possible, most notably in the nearshore waters of
northern Puerto Rico, where winds to 20 knots are forecast.
Deteriorating marine conditions are anticipated for Wednesday into
Thursday, with the passage of a tropical wave over the region. There
is a moderate risk of rip currents at beaches of northwestern and
north central Puerto Rico, as well as eastern Culebra, Vieques, and
St. Croix.

&&

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

#20286 Postby cycloneye » Wed Aug 12, 2020 4:46 am

Area Forecast Discussion
National Weather Service San Juan PR
429 AM AST Wed Aug 12 2020

.SYNOPSIS...

Increasing shower activity is expected today, with the arrival of
a tropical wave, which will linger over the area into tonight.
Widespread showers are likely for the afternoon, especially in
western and interior Puerto Rico, as well as isolated
thunderstorms. Behind the wave, drier air will move in place, with
some Saharan dust along with it. Some showers are still possible,
but generally fair weather is expected. Another tropical wave is
anticipated for this weekend, and we may also see some indirect
impacts from Tropical Depression Eleven, which is forecast to pass
by to the north.

&&

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

Fair weather is expected to prevail in the morning hours across the
local forecast area. A tropical wave will move in today, gradually
affecting the local waters and islands. The wave and its associated
moisture will cause showers and isolated thunderstorms across, in,
and around the U.S. Virgin Islands and eastern Puerto Rico
starting this morning. This activity will continue to spread
westward and affect the north, interior and western areas of
Puerto Rico during the afternoon. Therefore, numerous showers and
isolated thunderstorms are in the forecast for this afternoon
across many locations in the local forecast area. Some of the
showers and thunderstorms may be persistent enough to cause small
stream and urban flooding, especially in areas with poor drainage.
By this evening, most of the moisture and shower activity is
expected to have moved away, and the latest guidance is suggesting
drier air for tonight and much drier air with some Saharan dust
for Thursday. That said, isolated to scattered brief shower
activity will not be ruled out for Thursday, as the high res model
guidance still likes some shower activity, but the global models
favor a much drier solution on Thursday. Near normal moisture is
expected on Friday, and the mid to upper levels do not look
particularly favorable for deep convection, therefore the forecast
calls for scattered showers, mainly locally induced over Puerto
Rico and in the afternoon hours, while the USVI stays with mainly
fair weather and a slight chance of brief showers.

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

The forecast for Saturday, and, indeed, the rest of the weekend and
into Monday, is quite dependent on the development and trajectory of
Tropical Depression Eleven. Should the system strengthen, as is
presently expected, it would be likely to pull northward, away from
the rest of the tropical wave, as it neared the Caribbean. In this
scenario, a dry slot forms between the tropical cyclone and its
parent wave. That being said, there does remain some uncertainty, as
we are still several days out. A shift in the strength or trajectory
would shift the timing and location of any possible dry slot. A less
likely scenario involves the system not strengthening, or being
short-lived. This has the potential to lead to more moisture being
brought through the area. While this currently does not look likely,
it cannot be fully ruled out. Either way, it does look to be a
fairly rainy weekend, increasingly so as we move into Sunday.
Widespread showers are likely by Sunday, with isolated to locally
scattered thunderstorms. Conditions aloft are expected to be more
favorable for convective activity, but not very favorable. This will
still help contribute to the afternoon showers and thunderstorms,
though.

Moisture will remain in the area for Monday, when there will likely
be a continuation of Sunday, though slightly weaker in terms of
activity. Dynamic forcing aloft remains relatively weak, and its
influence will wane somewhat. Decreasing moisture is expected during
the evening and into the night. And by Tuesday, conditions aloft
will become decreasingly favorable for convection, with drying
forecast for the mid-levels. A large, but weak, developing
disturbance will help bring additional moisture into the area on
Tuesday into Wednesday; moisture levels will be near-normal levels,
climatologically speaking. A typical pattern of afternoon showers in
the west and passing showers overnight and into the morning in the
east will prevail through midweek. Further drying is expected
Wednesday night into Thursday, which will act to inhibit some of the
typical shower activity across the local islands.

&&

.AVIATION...

VFR conds expected across the local terminals expected
through the early morning hours. Approaching tropical wave will
start bringing SHRA/TSRA to the local area by 12/12Z. This will
cause VCSH/VCTS through much of the afternoon with brief periods of
SHRA/TSRA at the local terminals, except TJPS. Winds will be from
the east, but increase after 12/13Z to 10-15KT with occasional
gusts. Winds will be stronger near showers and thunderstorms.

&&

.MARINE...

Winds up to 20 knots are forecast for the majority of the local
waters over the next couple of days, associated with a tropical
wave passing through the area today. Building seas are also
anticipated, and heights of up to 6 feet are possible through the
end of the workweek. Conditions are expected to remain below Small
Craft Advisory criteria for now, though. That is likely to change
this weekend, as another tropical wave pushes through the area,
with the potential for a tropical cyclone passing by a couple
hundred miles to the north. There is a moderate risk of rip
currents at northern beaches of Puerto Rico, as well as some
south-central beaches and southeastern beaches, and also most
beaches of Vieques, Culebra, and St. Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 80 90 80 / 60 40 20 20
STT 90 81 90 80 / 60 40 20 20
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Re: Caribbean - Central America Weather

#20287 Postby cycloneye » Thu Aug 13, 2020 5:23 am

Area Forecast Discussion
National Weather Service San Juan PR
451 AM AST Thu Aug 13 2020

.SYNOPSIS...

Drier and more stable conditions are expected today, though there
is still the potential for showers due to local and diurnal
effects. This pattern will continue tomorrow, as well. Tropical
Depression Eleven is forecast to become a tropical storm today,
after which it will pass by the area to the north over the
weekend. No direct impacts are anticipated with this system,
though there is the potential for increased rainfall this weekend
into early next week.

&&

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

The tropical wave moved away during the evening, and drier air is
moving in. We now observe below normal moisture and it is expected
for the dry air to continue through the day. That said, some locally
induced showers and an isolated thunderstorm could occur across a
small section of western Puerto Rico this afternoon, with some
chance of measurable rainfall across the higher elevations of PR.
But, all other areas really have only a slight chance of showers,
expecting mainly fair weather today, and that is including the USVI.
For tonight into Friday, an area of higher moisture moves in, and
scattered showers could start moving in very early Friday across the
local waters, USVI, and eastern PR. Once again, locally induced
showers could occur on Friday afternoon across PR, but this time a
larger coverage area is possible, with portions of the interior and
Luquillo Mountain Range expected to see scattered showers. The
chances of thunderstorms appear to be slightly lower on Friday, as
the upper low moves further west and to the north of Cuba, which
will limit its influence in the local weather. The USVI will observe
mainly fair weather, with brief showers, on Friday. A similar
pattern to Friday is expected on Saturday, especially for the
morning hours, but the latest guidance is suggesting an area of much
deeper moisture moving in on Saturday afternoon, likely associated
with the current Tropical Depression Eleven. This makes the forecast
uncertain because the location of this plume of moisture will be
highly dependent on the overall organization and track of this
system, which has uncertainty as well. That said, it is likely that
moisture will increase and so will the shower activity late Saturday
into Sunday.

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

Conditions for the weekend and into early next week are highly
dependent on the fate of Tropical Depression Eleven. This system is
still expected to strengthen into a tropical storm, but there is
still uncertainty with regards to its strength. Furthermore, the
track of the system is fairly dependent on the strength, with a
stronger storm more likely to track further north. Either way, this
cyclone is not expected to have direct impacts on the area, but it
will certainly provide plenty of indirect ones. Model guidance,
especially the GFS, has become increasingly keen on the development
of a dry slot between the cyclone and its parent wave. This dry slot
has the potential to reverse expectations for Sunday, depending on
location and size. Some showers will be seen on Sunday regardless,
due to local effects and diurnal heating; a dry slot could inhibit
this activity, while any moisture associated with the cyclone or the
wave pushing over the area would enhance activity, as one might
generally expect. Given that the depression has struggled to become
more organized and stronger, the potential for a weaker system
slightly to the south still cannot be wholly discounted, in which
case a dry slot is not likely to be as prominent. All of this really
just to say that Sunday`s forecast is still up in the air a bit,
with substantial uncertainties. Monday is a similar story. The GFS
has been trending hard towards drier conditions over the local
islands again on Monday. But to really belabor the point, there are
uncertainties with respect to the Tropical Depression that could
lead to significant changes in expectations for Monday, in
effectively the same manner as for Sunday. Some moisture from the
wave is likely, at least, to make its way into the area Monday,
which is likely to bring increasing afternoon showers and
thunderstorms, and more widespread passing showers overnight, with
the potential for isolated thunderstorms.

Behind the wave, a large disorganized disturbance will bring patches
of moisture to the region, increasingly so by Tuesday night. This
will help to sustain a typical pattern across the local islands,
with afternoon showers and isolated thunderstorms, especially in
western Puerto Rico, and passing showers overnight and into the
morning, mostly in the east.

During midweek, the effects of another tropical wave are likely to
be seen over the area, as it passes by to the south. The bulk of the
moisture is forecast to stay generally south of the islands, but
increasing moisture is still likely. As such, showers are likely to
be more widespread and slightly more vigorous. A patch of dry air
will sweep into the region behind the wave for Thursday. There will
remain sufficient moisture to support some of the typical shower
activity, but it is likely to be somewhat inhibited.

And, for the end of the workweek, yet another tropical wave is
forecast to approach the region. Conditions aloft are forecast to
become a bit more favorable for convection, as well, with an upper-
level trough stretching over the area from the east, as well as a
weak trough in the mid-latitudes. Widespread and vigorous shower
activity is expected associated with this wave.

&&

.AVIATION...

Fair weather across the local area and prevailing VFR
are expected today. Saharan dust could cause some haze, but VIS is
expected to be P6SM. Winds will increase to around 15kt with higher
gusts from the east to ENE with sea breeze variations starting after
13/13Z.

&&

.MARINE...

Winds up to 20 knots are expected for the local waters, with seas up
to 6 feet possible, especially in the offshore waters. Tropical
Depression Eleven continues its march across the tropical Atlantic,
but remains well east of the area, by more than 1000 nautical miles.
This system is forecast to become a tropical storm today, and then
make its way past the area well to the north, by a couple hundred
miles north of the local islands. Its effects are likely to be felt
in portions of the local waters, however, most notably in the
offshore Atlantic waters, where there is the potential for hazardous
conditions over the weekend.

At the local beaches, there is a moderate risk of rip currents at
most beaches of Puerto Rico, Vieques, Culebra, and St. Croix
today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 80 88 79 / 10 20 30 40
STT 91 81 91 79 / 20 20 30 30
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Re: Caribbean - Central America Weather

#20288 Postby cycloneye » Fri Aug 14, 2020 4:54 am

Area Forecast Discussion
National Weather Service San Juan PR
407 AM AST Fri Aug 14 2020

.SYNOPSIS...

Though conditions are generally drying behind yesterday`s
tropical wave, there is still sufficient moisture to maintain a
typical shower pattern for today. Locally heavy rainfall is
possible in southwestern and interior Puerto Rico this afternoon,
and there is a risk for urban and small stream flooding. Tropical
Storm Josephine is still expected to track well to the north of
the area over the weekend. The system could help to pull some
moisture across the area, though, bringing showers for Saturday.

&&

.SHORT TERM...Today through Sunday...
For today, a patch of moisture is forecast to move over the local
area and cause scattered showers in the morning. Then, isolated to
scattered showers are possible due to local effects mainly over
portions of eastern into the central interior of Puerto Rico.
However, some portions of the western interior into the
southwestern quadrant of Puerto Rico may observe numerous showers
and isolated thunderstorms this afternoon, some showers could be
heavy at times and could cause minor flooding. Another band of
moisture will move in tonight, and cause widely scattered showers
across the local area, especially the local waters, USVI, and eastern
PR. A small area of dry air will then move in on Saturday morning,
lingering into the early afternoon hours and causing mainly fair
weather. That said, a band of moisture associated with Tropical
Storm Josephine will move in on Saturday night, and affect the local
waters, northern PR, and northern USVI. But this forecast has a high
uncertainty since it is highly dependent on the overall organization
and general track of Josephine. However, it is expected for the
overall moisture to increase across portions of the local forecast
area, likely on the Atlantic side as Josephine passes to the NE of
the local islands. The latest model guidance suggests that a dry
slot will move in on Sunday, although there again will be some
uncertainty. But the GFS model suggests that a slot of dry air will
move in on Sunday along with southerly winds. This setup would cause
an increase in daytime temps across the northern half of PR,
possibly causing temps in the low to mid 90s. That said, if the
winds are as light as the models suggest, a strong sea breeze would
moderate these temps near the coast, and the higher than normal
temps would be more common a few miles inland on the northern side
of the island.

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

On Monday, moisture associated with Tropical Storm Josephine
combined with a relatively weak wave will stream across the area. As
such, an increase in shower activity is anticipated across the
region, with afternoon showers and thunderstorms, especially in
northwestern Puerto Rico. Behind the wave is a large area of
disorganized patches of moisture, which are anticipated to affect
the area of Tuesday. Moisture is likely to decrease late in the day,
however. A typical pattern is likely on the day, with shower
activity becoming more inhibited in the evening. This is due to a
small area of dry air ahead of another wave.

Late on Tuesday night, a vigorous tropical wave is forecast to make
its way into the area. Significantly higher moisture levels are
anticipated, and shower activity is likely to be fairly widespread.
The wave will linger over the area into Thursday. Once again, a
drier air mass is expected to move in ahead of the next wave mid-
morning on Thursday through the afternoon. The next wave is forecast
to arrive overnight on Thursday night into Friday, and this one is
also expected to be fairly vigorous. Another surge of moisture
across the area will lead to an increase in showers. Widespread
afternoon showers with isolated thunderstorms are anticipated for
Friday, with the peak in activity in western and interior Puerto
Rico. This will be followed by enhanced passing shower activity
during the night.

On Saturday, disorganized patches of moisture will help to sustain
shower activity across the area. Late in the day yet another
tropical wave is forecast to approach the area. So, on the whole,
next week is currently looking to be fairly repetitive.

&&

.AVIATION...

VFR conds expected through the forecast period across the
local terminals. VCSH is expected however, and a few brief SHRA may
affect the terminals, but it is not expected to significantly reduce
VIS or CIGs. TSRA is possible across SW-PR this afternoon, which may
cause VCTS at TJPS between 14/16 and 14/21. After 14/13Z, winds will
increase to around 15KT, from the east but with sea breeze
variations.

&&

.MARINE...

Winds of up to 20 knots persist across the bulk of the local waters,
contributing to continuing choppy conditions. Seas of up to 6 feet
are anticipated for portions of the Atlantic waters, with seas up to
5 feet elsewhere, through the weekend. Tropical Storm Josephine is
still forecast to pass by well to the north of the area over the
weekend. This has the potential to cause some deteriorating
conditions, mostly in the offshore Atlantic waters; though the
current forecast keeps waves to around 6 feet at maximum, locally
hazardous conditions cannot be ruled out.

There is a moderate risk of rip currents at most northern beaches of
Puerto Rico, as well as a handful of beaches in the southeast and
southwest, and eastern Culebra and St. Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 79 89 78 / 30 40 50 50
STT 91 80 88 80 / 30 40 30 40
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Re: Caribbean - Central America Weather

#20289 Postby cycloneye » Sun Aug 16, 2020 4:37 am

Area Forecast Discussion
National Weather Service San Juan PR
531 AM AST Sun Aug 16 2020

.SYNOPSIS...Tropical Storm Josephine is still forecast to pass
well north of the region today, but some impacts are still
expected with enhanced shower and thunderstorm activity and
choppy to rough marine conditions. Improved weather conditions
with the typical shower pattern are expected by early next week,
but a generally moist and unstable weather pattern will prevail
by midweek through the upcoming weekend due to the passage of
multiple tropical waves, interrupted by an induced surface
trough.


&&

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

The National Hurricane Center is issuing advisories on Tropical
Storm Josephine, located some 200 miles or more northeast of Puerto
Rico and the U.S.Virgin Islands. Maximum sustained winds were near
40 mph (65 km/h) with higher gusts based on the last discussion from
the National Hurricane center and TS Josephine is now in an area of
unfavorable upper-level wind shear. Therefore continued weakening is
expected during the next couple of days.

Locally, occasional bands of moisture fragments from distant
Josephine will continue to propagate west and south across the
region throughout the day. This moisture will aid in the development
of showers and possibly an isolated thunderstorm or two over the
regional waters during the rest of the morning hours. Some showers
will continue to reach parts of the north and east sections of the
islands, with periods of moderate to heavy rains possible in
isolated spots. Brief wind gusts with the passing showers and
isolated thunderstorms will also remain possible. For the rest of
today, a gradual increase in the low level moisture trailing
Josephine, along with better moisture convergence and local effects
will give way to afternoon convection over parts of the islands. The
heaviest rainfall should be over the west interior and northwest
sections of Puerto Rico. Period of locally heavy rains during the
afternoon may lead to minor urban and small stream flooding.

Lesser shower activity and a drier airmass is so far expected on
Monday. However, early morning and afternoon showers cannot be ruled
out in isolated areas on the windward side of the islands during the
early morning and over the west interior of Puerto Rico during the
afternoon. In addition, on Monday and into Tuesday expect a gradual
increase in the east to southeast trade winds as the northeast
Atlantic High pressure ridge builds across the forecast area. From
Tuesday onwards, expect afternoon convection to be in the form of
streamer-like showers in and around the islands, with the afternoon
rains focused mainly in the west interior and northwest sections of
Puerto Rico. Lesser shower activity is forecast during the afternoon
over the U.S. Virgin Islands, but a few showers will be possible on
the west-end or just downwind of the islands. Late Tuesday through
Wednesday, the next tropical wave is forecast to approach and move
mainly south of the region. Stay Tuned!

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

Recent model guidance continues to suggest that a wet and
unstable weather pattern will prevail across the region.
Significantly higher moisture levels with a chance for widespread
shower activity will enhance the potential for urban and small
stream flooding, as well as mudslides.

A fast-moving tropical wave, which is currently being monitored
by the National Hurricane Center and could potentially become a
tropical cyclone as is streams across the Caribbean Sea, is
forecast to stream south to southwest of the forecast area on
Wednesday. Lingering moisture from this wave is expected to affect
the area through at least Thursday, supporting diurnally induced
showers and isolated thunderstorms. Although an area of relative
drier air could briefly support improved weather conditions on
Thursday, locally induced activity is still expected. A surface
induced trough is forecast to quickly cross the forecast area on
Friday, followed by yet another and vigorous tropical wave during
the upcoming weekend. So far, both ECMWF and GFS model guidance
suggest that the latter, which also being monitored by the
National Hurricane Center, could potentially become a tropical
cyclone once it reaches the central tropical Atlantic with
closest approach to Puerto Rico and the US Virgin Islands by early
Saturday morning. A slight improvement in weather conditions is
expected by Sunday into early next week.

Even though it is too early to determine what impacts, if any,
these systems may bring to our area, residents and visitors in
Puerto Rico and the US Virgin Island should monitor the progress
of these systems as we move further into the peak of the
hurricane season.


&&

.AVIATION...VFR conds durg fcst pr. Passing SHRA w/chc of isold
TSRA ovr the local Atlantic waters and btw PR and the Northern
Leeward islands. VCSH at JSJ/IST/ISX/NCM/KPK with SHRA psbl
resulting in brief MVFR and MTN top obscr ovr ERN PR til 16/13z
.SCT-BKN lyrs nr FL025... FL050 with SHRA/Isold TSRA. SHRA/isold
TSRA psbl around the USVI, as well as along the ctrl MTN range and
W PR between 16/16-23z. Winds fm E-ESE at 10-20 knots after
16/13z with brief wnd gust psbl with passing SHRA. Please refer to
latest NHC ADVSY TS Josephine.


&&

.MARINE...Tropical Storm Josephine is generating choppy to rough
seas across portions of the offshore Atlantic waters and Anegada
Passage. As a result, a Small Craft Advisory continues in effect
through this afternoon. Elsewhere, seas up to 5 feet and winds up
to 15 knots are expected. There is a moderate risk of rip currents
for beaches along the north coast of Puerto Rico, most beaches in
Culebra, eastern beaches in Vieques and Saint Croix, western
beaches in Saint Thomas and southern beaches in Saint John.


&&

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

#20290 Postby cycloneye » Mon Aug 17, 2020 4:52 am

Area Forecast Discussion
National Weather Service San Juan PR
434 AM AST Mon Aug 17 2020

.SYNOPSIS...

Mid to upper level ridge will build across the region during
the next few days thus increasing the trade wind inversion and
resulting in stable conditions aloft. Surface high pressure ridge
will continue to build across the central and northeast Atlantic
to create a moderate easterly wind flow. An area of moderate to
high concentration of suspended Saharan dust particulates will
cross the region today through Tuesday. Increasing trade winds are
forecast through mid-week,as a fast moving tropical wave is forecast
to race aross the eastern Caribbean and pass mainly south of the
region Tuesday through Wednesday. This will be followed by an induced
surface trough on Friday and a vigorous tropical wave wave forecast
for the upcoming weekend.

&&

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

An area of cloudiness and showers, trailing to the remnants of
Josephine, will bring isolated to scattered showers over portions
of eastern Puerto Rico and the US Virgin Islands through the
morning hours. As the day progresses, the presence sufficient
lingering moisture, with GFS-model-estimated precipitable water up
to 1.85 inches by 18Z, will aid in the development of locally and
diurnally induced showers and isolated thunderstorms this
afternoon. This activity will cluster along the western interior
and northwestern sections of Puerto Rico, while some development
is possible from El Yunque and the local islands. Ridging aloft
may limit deep convective development and thus, significant
rainfall accumulations. Nevertheless, urban and small stream
flooding, as well as ponding of waters on roadways and low- lying
areas, remains likely with the strongest and more persistent
activity. Daytime high temperatures are forecast to peak into the
upper 80s to low 90s across coastal areas. East to southeasterly
winds at 10-15 mph with higher gusts and sea breeze variations are
expected today.

A mass of relatively drier air along with some Saharan Dust will
invade the northeastern Caribbean this evening and linger over the
region through midweek, resulting in generally fair weather
conditions and hazy skies. Peak dryness is expected on Wednesday
with model-estimated precipitable water falling to around 1.30
inches. Despite the expected dry condition and unfavorable
conditions aloft, overnight and early morning passing showers may
still move over portions of eastern Puerto Rico and the US Virgin
Islands from time-to-time, followed by the typical afternoon
convection over the far northwestern portion of Puerto Rico each
afternoon. In the meantime, a tropical wave will move into the
eastern Caribbean and stream westward and well south of the forecast
area on Tuesday and Wednesday. As a result, winds are expected to
increase, generating a strong steering flow and fast-moving showers
with limited impacts across the area.

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

Increasing tropical moisture by Thursday into the weekend with
approach of the induced trough on Friday followed by a vigorous
and potentially strong tropical wave based on latest model guidance.
Recent model guidance continued to suggest that a moist and unstable
weather pattern is to prevail across the region through most of the
long- term as we quickly approach the peak of the hurricane season.

Based on the model guidance, a surface induced trough is forecast
to quickly cross the forecast area Thursday through Friday,
followed by the aforementioned vigorous and potentially strong
tropical wave during the upcoming weekend. So far, both the
European (ECMWF) and American (GFS) model guidance suggest that
this wave also being monitored by the National Hurricane Center,
could potentially become a tropical cyclone once it reaches the
central tropical Atlantic with closest approach to Puerto Rico and
the US Virgin Islands as early as early as late Saturday through
Sunday based on which model you look as there is some
inconsistency in the models. Regardless both suggest wet and
deteriorating conditions for the weekend. A slight improvement in
the weather conditions is expected by the early part of the
following week and end of the period with the more typical passing
showers and and isolated afternoon thunderstorm activity
developing around the islands each day. Even though it is too
early to determine what impacts, if any, the previously mentioned
systems may bring to our area, residents and visitors in Puerto
Rico and the U.S. Virgin Island should continue to monitor the
progress of these systems as we quickly approach the peak of the
hurricane season.

&&

.AVIATION...Mainly VFR conditions expected. However, afternoon
convection may bring VCTS/VCSH to TJBQ and TJSJ between 17/14-23Z,
resulting in brief MVFR conditions with SCT-BKN between FL020-040
and locally higher winds. Light and variable winds for PR terminals
overnight, turning from the ESE after 14/12Z. ESE surface winds at
10-15 knots across USVI and Leeward terminals through the period.


&&

.MARINE...The trade winds will gradually increase today through
Wednesday to generate choppy to rough marine conditions.Small
craft operators should exercise caution across all local waters
and passages today. Moderate to fresh trade winds will continue
today, becoming fresh to locally strong Tuesday through Wednesday.
By that time Small Craft Advisories may be required. A surface
trough will cross the regional waters Thursday into Friday followed
by a vigorous tropical wave forecast for the upcoming weekend.
This will lead to hazardous and deteriorating marine conditions
along with increased potential for thunderstorm activity across
the regional waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 90 79 / 30 30 30 20
STT 91 82 90 80 / 20 20 20 30
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Re: Caribbean - Central America Weather

#20291 Postby cycloneye » Tue Aug 18, 2020 4:37 am

Area Forecast Discussion
National Weather Service San Juan PR
522 AM AST Tue Aug 18 2020

.SYNOPSIS...A dry air mass will continue as the suspended Saharan
dust particulates will linger across the region to maintain a mostly
fair weather pattern for much the forecast area today. Early morning
passing shower activity will be limited to the coastal waters and
in isolated areas on the windward side of the islands. Afternoon shower
development will be limited portions of western Puerto Rico and mainly
on the west- end or just downwind of the remaining islands, A tropical
wave will pass well south of the area today through Wednesday but
will cause an increase in winds as well as hazardous marine conditions.
A vigorous tropical wave with potential for further development is
still forecast to approach the Leeward islands by Friday then cross
the forecast area over the weekend. Stay tuned.

&&

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

The passage of a rapid-moving tropical wave across the Caribbean Sea
and well south of the area will generate fresh to strong winds
today. In the meantime, a mass of relatively drier air along with
some Saharan Dust will continue to invade the northeastern Caribbean,
resulting in generally fair weather conditions and hazy skies.
Despite the expected dry condition and unfavorable conditions due
to ridging aloft, overnight and early morning trade wind showers
may still move over portions of eastern Puerto Rico and the US
Virgin Islands from time-to-time, followed by limited afternoon
convection over the far northwestern portion of Puerto Rico in the
afternoon. Although the moisture associated to the wave will
remain well south of the local islands, a slight increase in
shower activity is possible for Saint Croix and portions of
eastern Puerto Rico tonight into Wednesday morning. Since the
passage of the wave will generate a strong steering flow, fast-
moving showers will prevent significant rainfall accumulations.

Further erosion of the available moisture is expected on Wednesday
and Thursday with model guidance now calling for peak dryness to
occur by midday Thursday with precipitable water plunging to 1.10-
1.20 inches. However, low-level moisture convergence and enhanced
shower and thunderstorm activity is expected as surface induced
trough and associated plume of moisture approaches the area by late
Thursday night.

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

Increasing tropical moisture is expected on Friday into the weekend
with the passage of a surface trough followed by a potentially
strong tropical wave for the weekend. Recent model guidance and
information from the National Hurricane Center continued to suggest
that this system has the potential for further development during
the next few days, as it approaches the Leeward Islands. There still
remain some inconsistencies in the model guidance but all suggest
a very moist and unstable weather pattern for the region through
much of the long- term, as we approach the peak of the hurricane
season. As previously mentioned there is still some uncertainties
between model guidance in the final forecast track and timing of
this feature but regardless, the potential for heavy rainfall
across the region over the upcoming weekend is high at this time
based on the present persistence in model guidance.

A slight improvement in the weather conditions is expected by Monday
though Tuesday as the strong Tropical system moves farther away from
the region and trailing moisture lingers across the forecast area.
A drier airmass and another surge of Saharan dust is so far forecast
by the middle of the upcoming workweek.

Even though it is too early to determine what or how much impacts the
previously mentioned systems may bring to our area, residents and
visitors in Puerto Rico and the U.S. Virgin Island should continue
to monitor the progress of these systems as we quickly approach the
peak of the hurricane season.

&&

.AVIATION...Mainly VFR conditions expected. VCSH possible at TJBQ
18/14-23Z, and at TISX after 18/22Z. Light and variable winds for PR
terminals overnight, turning from the ESE at 10-20g25 knots after
18/12Z. ESE surface winds at 10-20g29 knots across USVI and Leeward
terminals through the period.

&&

.MARINE...Marine conditions are expected to continue to deteriorate
today through Wednesday, as a wind surge accompanying a tropical
wave passing well south of the area, will create choppy and hazardous
seas of up to 8 feet across the offshore waters and local passages.
As a result, Small Craft Advisories are in effect for these waters
today through at least early Wednesday. Please refer to the latest
Coastal Waters Forecast (CWFSJU) and Marine Weather Message (MWWSJU)
issued by WFO san Juan PR..

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 91 79 / 20 30 30 30
STT 91 81 90 80 / 20 20 20 20
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Re: Caribbean - Central America Weather

#20292 Postby cycloneye » Wed Aug 19, 2020 4:24 am

Area Forecast Discussion
National Weather Service San Juan PR
448 AM AST Wed Aug 19 2020

.SYNOPSIS...
An overall dry and stable airmass will persist across the region
today at least until Thursday afternoon. The hazy conditions will
however improve as the suspended Saharan dust particulates across
the region will diminish causing mostly sunny and mainly fair
weather conditions over the area. A few passing clouds and showers
can be expected during the early morning followed by some locally
induced afternoon convection. A surface trough will quickly cross
the region late Thursday through Friday followed by the strong
and broad tropical wave(Invest 98l) which has a 90% chance of
developing into a tropical cyclone within the next 48 hours
According to the latest Tropical Weather Outlook from the National
Hurricane Center. This is being closely monitored as it may
approach the region this weekend. Please continue to monitor
future forecasts updates on invest 98l and its potential impacts
on the area.

&&

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

A mass of relatively drier air along with some Saharan Dust will
continue to invade the northeastern Caribbean, resulting in
generally fair weather conditions and hazy skies. In the meantime,
winds are expected to gradually diminish as a rapid-moving tropical
wave continues to move westward across the central Caribbean Sea and
away from the area today. Limited to no shower activity is expected
over the local islands through the morning hours. Despite the
expected dry condition and unfavorable conditions due to ridging
aloft, however, afternoon convection is likely over the far western
sections of Puerto Rico this afternoon. Further erosion of the
available moisture is expected to continue through early Thursday
afternoon, resulting in mainly fair weather conditions with limited
to no shower activity and mostly clear skies between this evening
and early Thursday afternoon. In fact, model guidance continues to
suggest that peak dryness will occur by late Thursday morning with
precipitable water plunging to 1.10-1.20 inches.

A quick shift to wetter conditions is expected by Thursday afternoon.
Increasing tropical moisture is expected as a surface induced trough
beings to move across the region from the east. As a result, enhanced
low-level moisture convergence and an increase in shower and
thunderstorm activity is expected, spreading westward across the
local islands through Friday. Moderate to heavy rains may enhance
the potential for urban and small stream flooding, particularly
with the thunderstorm activity.

Once the surface induced surface trough crosses the forecast area,
increasing tropical moisture associated to a tropical wave will
quickly move in. This system not only has the potential to bring
widespread shower and thunderstorms activity, but may support a
higher potential for urban and small stream flooding, as well as
mudslides, across the local islands. This tropical wave is being
closely monitored by the National Hurricane Center as it has
potential for Tropical Cyclone development during the next two days.
Interests in Puerto Rico and the US Virgin Islands should monitor
the evolution of this system, while reviewing their family emergency
plan.

.LONG Term...Saturday through Thursday...

Both model guidance continued to suggest deep layered tropical
moisture pooling across the region along with good low level
convergence by Saturday and continuing through the rest of the
weekend, as the vigorous Tropical Wave crosses the forecast area.
Recent information from the National Hurricane Center continued
to suggest that this system has potential For further development
during the next few days, as it approaches The Leeward Islands.
There still however remains inconsistencies in the model guidance,
although all suggest a very moist and unstable weather pattern
through the weekend and into at least Monday. As previously mentioned
there is still uncertainties as to the trajectory and intensity
of this system but regardless, the potential for periods of heavy
rainfall across the region over the upcoming weekend, remains high
at this time based on the persistence in all model guidance and
information from the National Hurricane Center. All suggest that
this feature which at this time remain very broad And elongated
will pass near to or over the forecast area, producing enhanced
convection with periods of heavy rainfall and thunderstorm Activity.
Therefore the potential for urban and small stream flooding will
continue over the weekend. We will continue to monitor this system
to see how it unfolds and update the forecast as needed.

A gradual improvement in the weather conditions is expected by Monday
through Tuesday, as the tropical system moves farther away from
the region, and trailing moisture lingers across the forecast area.
A drier airmass and another surge of Saharan dust is so far hinted
in the forecast by Wednesday into Thursday, but the typical early
morning clouds and trade winds showers can be expected, followed
by limited afternoon convection over the west end of the islands.

Although it is a still a bit to early to determine what or how
much impacts the aforementioned system (98L) may bring to our
area; residents and visitors in Puerto Rico and the U.S.Virgin
Islands should continue to monitor the progress of this and any
other additional systems as we quickly approach the peak of the
hurricane season.

&&

.AVIATION...Mainly VFR conditions expected. If any, VCSH possible at
TJBQ 19/16-22Z. Light and variable winds for PR terminals expected
overnight, turning from the ESE at 10-20 knots with higher gusts and
sea breeze variations after 19/14Z. ESE surface winds at 10-20 knots
will continue for USVI and Leeward terminals through the period.

&&

.MARINE...Small craft advisory in effect through Wednesday due to
strong winds and hazardous seas as a tropical wave passes south of
the local islands. There is a moderate risk of rip currents for
most of the local beaches tonight.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 89 79 / 20 20 60 60
STT 90 80 91 80 / 20 20 60 60
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Re: Caribbean - Central America Weather

#20293 Postby cycloneye » Sat Aug 22, 2020 5:48 am

Area Forecast Discussion
National Weather Service San Juan PR
540 AM AST Sat Aug 22 2020

.SYNOPSIS...Tropical Storm Laura is passing through the local
Caribbean waters today. Strong gusty winds and very heavy rains
will follow. Several tropical waves will pass through during the
upcoming week, but impacts will be fairly limited.

&&

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

Deteriorating weather conditions are expected for today as Tropical
Storm Laura approaches the local area. Rain bands will continue to
overspread the region from east to west throughout the day, becoming
more frequent and heavy. Total rainfall accumulations of 3 to 6
inches with maxima up to 8 inches can be expected. The highest
rainfall accumulations are expected across the southern and eastern
half of Puerto Rico. Rainfall of this magnitude will be capable of
producing areas of flash flooding, river flooding, and mudslides in
areas of steep terrain. As a result, a Flash Flood Watch is in
effect for the entire area. These rainbands will also be capable of
producing winds of up to 40 to 50 mph, mainly in gusts. Weather
conditions are expected to improve rather significantly for Sunday
as Tropical Storm Laura quickly moves away and the deep-layered
moisture content erodes. However, there will still be lingering
moisture to combine with local and diurnal effects to result in
some afternoon convection across northwestern Puerto Rico.

Weather conditions will once again turn unsettled on Monday. A
retrograding mid to upper-level trough is expected to induce a
surface trough, which is expected to move over the area. This
feature along with deeper moisture is expected to result in enhanced
shower and thunderstorm activity, with the heaviest expected across
western and southwestern portions of Puerto Rico. Given that the
soils are expected to be saturated from the heavy rainfall activity
left by Tropical Storm Laura, urban and small stream flooding may
materialize in areas that receive the heaviest rainfall activity.

.LONG TERM...Tuesday through Saturday...
A relatively weak tropical wave will pass through early on Tuesday
and bring southeast flow behind it. This will bring good showers
to the southeast quarter of Puerto Rico in the morning and some
showers to the U.S. Virgin Islands. Showers will shift to west
northwest sections of the island in the afternoon. Drier air will
follows with the driest air moving over the area on Wednesday
afternoon. This will not preclude shower activity in the west
northwest portion of Puerto Rico, but thunderstorms will be
isolated at best as the 500 mb temperatures reach the warmest
levels of the week of minus 4 degrees. After this dry slot, a
weak tropical wave moves through the area on Thursday morning with
a wind surge behind it. This drier period will last through
Friday. On Saturday moisture moves into the area, but only at the
lowest levels. This will lead to limited showers activity with
generally minor amounts of rainfall. Instability will be
increasing, however, and thundershowers will be more likely even
if not more frequent.

&&

.AVIATION...Deteriorating weather conditions expected as Tropical
Storm Laura approaches the area. Prevailing MVFR to possibly IFR
conditions expected at times with the associated rainbands.
Increasing winds are also expected with sustained winds 20-30 kts
with gusts as high as 40 kts from the ESE-SE.

&&

.MARINE...Winds have been weak across the forecast area so far
except near the core of Tropical Storm Laura. Seas of 12-16 feet
are still possible northeast of the system in the forecast area,
and buoy 41043 has registered almost 13 feet of wind waves from
the east southeast. Winds and seas will increase across the
forecast area as Laura moves through. The risk of rip currents
will be high for all coast, but at this time high surf of short
periods will be mainly confined to eastern and northward facing
beaches, although south facing beaches could see breaking waves of
more than 6 feet.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 77 89 79 / 100 90 20 50
STT 84 78 90 79 / 100 80 20 50
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Re: Caribbean - Central America Weather

#20294 Postby cycloneye » Sun Aug 23, 2020 5:32 am

Area Forecast Discussion
National Weather Service San Juan PR
451 AM AST Sun Aug 23 2020

.SYNOPSIS...Tropical Storm Laura has moved west and conditions
have improved considerably. An induced surface trough from an
upper level low will bring an increase in shower activity later on
Monday, then several tropical waves of a fairly weak nature will
move through on Thursday and next Sunday.

&&

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

Much more tranquil weather conditions are expected across the area
today as Tropical Storm Laura continues to move westward towards
Hispanola and Cuba. In addition, the deep layered moisture from
Laura will gradually erode. However, there will still be enough
moisture available to combine with local and diurnal effects to
generate afternoon convection across northwestern Puerto Rico.
Localized urban and small stream flooding is possible with the
heaviest activity. Elsewhere, very limited shower activity is
expected. Weather conditions on Monday will turn unsettled once
again. A mid to upper-level low located currently northeast of the
northern Leeward Islands is expected to retrogress towards the area
and be overhead just in time for max heating Monday afternoon. There
will also be a surface induced trough, which will result in
northeasterly winds. Deeper moisture will also pool in with
precipitable water values increasing to near 2.00 inches. The
combination of all of these factors is expected to enhance shower
and thunderstorm activity, with the heaviest activity expected
across interior and southwest Puerto Rico, where urban and small
stream flooding will be possible. Weather conditions are expected to
improve on Tuesday as the mid to upper-level low moves far enough
west and drier air filters in. However, some afternoon convection
across northwestern Puerto Rico will be possible as a result of
local and diurnal effects.

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

Precipitable water values decline from today through Wednesday
afternoon. A weak tropical wave will move through on Thursday and
a second wave will move through on Sunday. Each of these is
followed by a wind surge at 700 mb as high pressures migrate west
through the central Atlantic and these will bring some increases
in Saharan dust to the area. As the waves pass through winds will
become more southeasterly and this will result in increases in the
high temperatures across the northern coast of Puerto Rico. Also
from Thursday through Saturday 500 mb temperatures will fall, and
by Friday night reach a minimum of minus 8 degrees as cooler air
from the northeast struggles for influence over the area. This
will allow more active convection and thunderstorm activity. Since
lower levels, 850 mb and below, remain moist some scattered
showers will be expected across the area in the typical diurnal
pattern.

&&

.AVIATION...Mainly VFR conditions expected. SHRA and isold TSRA
possible across northwestern Puerto Rico between 23/16z and
23/22z, affecting the vicinity of TJBQ/TJMZ. Low-level winds will
be from the ESE-E up to around 15 knots with sea breeze
variations developing after 23/14z. Max winds ESE 25-30 kt btwn
FL060-135 and NW-NNW 30-40 kt btwn FL390-490.

&&

.MARINE...Seas will be gradually subsiding after tropical storm
Laura and are expected to be less than 7 feet in all areas by 2 AM
AST Monday. Small craft advisories are not expected for the
remainder of the week.

&&


.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 88 76 / 20 50 50 40
STT 90 78 89 81 / 20 50 50 40
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Re: Caribbean - Central America Weather

#20295 Postby cycloneye » Tue Aug 25, 2020 5:38 am

Area Forecast Discussion
National Weather Service San Juan PR
412 AM AST Tue Aug 25 2020

.SYNOPSIS...
Winds will be from the east-southeast today, hence shower activity
in the afternoon is expected to be over northwestern PR and the
San Juan metro area. A tropical wave will move on Thursday,
bringing additional showers. A drier air mass along with Saharan
dust is anticipated afterward, lasting through the weekend.

&&

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

A TUTT induced surface trough is currently moving across the region
and it is expected to continue to move west and away of the area
during the day. This has caused winds to shift from the east to
southeast and afternoon convection today is expected mainly over the
northwestern quadrant of PR and from el Yunque area into San Juan
and vicinity. Occasional showers could move over the USVI and
streamers are expected to develop around noon off the islands. A mid
level ridge is expected to build just north of the area on Wednesday
and this will promote more stable and fair weather conditions across
the islands. However, diurnally induced afternoon showers are still
expected to develop over the northwestern sections of PR. A weak
tropical wave is forecast to move quickly on Thursday, increasing
the potential for scattered showers across the local waters and
increasing the areal coverage of afternoon convection over land
areas across mainland PR.

.LONG TERM...Friday through Tuesday...
A ridge at the low and mid-levels will continue to dominate the
local weather through Saturday. While the ridge migrated toward the
west, a wind surge will continue to carry a dry air mass along with
Saharan dust over the area. This will result in mainly fair weather
for the islands, although, as is usual, afternoon convection might
develop over western Puerto Rico due to local effects. In the
meantime, an upper level just to the northeast of the Leeward
Islands will help to sustain 500 mb temperatures around -7 to -8
degree Celsius. Therefore, there will be a slight chance of
thunderstorms during the afternoon hours with the activity. Not much
changes are anticipated for Sunday as the dry air mass remains in
place, although fragmented groups of clouds embedded in the trade
winds may reach the islands from time to time.

By Monday, the dry air mass begins to erode, as a tropical wave
escort moisture into the area. There is still great uncertainty in
this part of the forecast, as the guidance diverge in timing,
strength and position of the wave. Regardless, the first half of the
next workweek looks to be unstable, with an increased potential for
showers and thunderstorms over the area.

&&

.AVIATION...Mainly VFR conditions expected across all terminals
during the next 24 hours. However, brief SHRA may cause tempo MVFR
conditions across the USVI/Eastern PR terminals through the early
morning hours. Then, diurnally induced afternoon SHRA/TSRA ovr NW PR
and over the eastern interior could also cause tempo MVFR conds at
TJSJ/TJBQ from 16z-22z. ESE winds at 10-15 kts are expected today.


&&

.MARINE...
Seas generally at 5 feet or less are expected to prevail through
the next few days. A small northeasterly swell will reach the
waters tomorrow and will continue through the workweek. A tropical
wave will bring additional showers on Thursday. A moderate rip
current continues for the northern coast of Puerto Rico and St.
Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 91 79 / 40 10 10 20
STT 88 80 90 81 / 20 20 20 30
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Re: Caribbean - Central America Weather

#20296 Postby cycloneye » Wed Aug 26, 2020 5:28 am

Area Forecast Discussion
National Weather Service San Juan PR
334 AM AST Wed Aug 26 2020

.SYNOPSIS...
Mainly fair weather conditions should prevail today, before a weak
tropical wave approaches the islands by tomorrow. Saharan dust is
expected to result in hazy skies through the weekend. A strong
tropical wave is anticipated for early next week.

&&

.SHORT TERM...Today through Friday...
A weak mid-level ridge is forecast to build north of the area
today, this should promote more stable conditions and a fair
weather pattern with the entrance of drier air and minor Saharan
dust accumulations. However, diurnally induced afternoon showers
are still expected to develop over the western sections of PR, as
well as downwind from the U.S. Virgin Islands and el Yunque
mountain. Then, a weak tropical wave is forecast to move stream
quickly on Thursday, increasing the potential for shower and
thunderstorm activity over mainland PR. Localized urban and small
stream flooding is possible with the wave passage. For Friday,
drier air and more stable conditions are expected as a 700 mb
ridge moves over the region with a Saharan Air Layer. Hazy skies
and limited shower activity will prevail across the islands into
the weekend.

.LONG TERM...Saturday through Wednesday...
For the weekend, at the upper levels, a low pressure system will aid
in maintaining 500 mb temperatures around -7 to -8 degrees. On
Saturday, the low to mid level ridge will continue to migrate toward
the west. Therefore, a mainly fair weather weekend is anticipated as
the dry air mass, along with Saharan dust continue to linger over
the islands. This ridge will cause a wind surge over the area and
maintain a trade wind cap at around 800 mb, which should limit
rainfall accumulation. Nevertheless, any available moisture, may
combine with local effects to result in afternoon convection over
western Puerto Rico with isolated thunderstorms possible.

The generally tranquil weather continues into the first day of the
next workweek. Afterward, conditions are expected to change. A
strong tropical wave should move into the eastern Caribbean late
Monday into Wednesday. Although there is still uncertainty on track
and intensity of this system, for the moment the wave should result
in an unsettled weather pattern over Puerto Rico and the U.S.
Virgin Islands with an increased potential for showers and
thunderstorms.



&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, SHRA is expected to
develop over western PR btw 16z-22z, which may cause tempo MVFR cigs
at JBQ. East winds will prevail at 10-15 mph with higher gusts and
sea breeze variations after 14z.

&&

.MARINE...
A small northeasterly swell will reach the waters today, but seas
will generally remain at 5 feet or less. Limited shower activity
is expected today, but a tropical wave should increase showers on
Thursday. A moderate rip current risk continues for most of the
beaches of the northern coast of the islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 90 79 / 20 20 50 50
STT 90 81 91 81 / 10 30 50 20
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Re: Caribbean - Central America Weather

#20297 Postby cycloneye » Thu Aug 27, 2020 5:11 am

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Thu Aug 27 2020

.SYNOPSIS...A weak tropical wave will increase shower activity
today across the region. Saharan dust and drier air will persist
through the weekend. A strong tropical wave is forecast to move
across the eastern Caribbean by early next week.

&&

.SHORT TERM...Today through Saturday...
Recent satellite imagery shows an area of enhanced humidity
approaching the islands, in association with a tropical wave. This
feature will result in some passing showers across eastern PR and
USVI through the morning hours. The wave will provide low level
convergence, and along with local effects, will result in showers
and isolated thunderstorms across the interior and western Puerto
Rico, as well as for some municipalities of the eastern interior of
Puerto Rico, and streaming westward from the U.S. Virgin Islands.

Conditions are expected to improve tonight as the wave moves away
from the area. A drier air mass, along with Saharan dust is expected
to be in place for the rest of the short-term period, resulting in
hazy skies. Precipitable water values are expected to fall below
climatology, ranging between 1.4 to 1.6 inches. On the other hand,
an upper level low will move over the islands through the weekend,
which will help in maintaining 500 mb temperatures between -7 to -9
degrees. As a result, only limited afternoon activity is expected
each afternoon over western Puerto Rico, while isolated thunderstorm
activity cannot be ruled out.

Along with the drier air and the Saharan dust, a wind surge also
moves in, resulting in breezy conditions for some of the areas
around the islands. In terms of temperatures, for today, increasing
moisture will combine with near normal or just above normal
temperatures to result in heat indices ranging between 100 to 107
degrees across the lower elevations of the islands. These heat
indices will ease a bit for tomorrow and Saturday over Puerto Rico
with the drier air, but will remain above 102 degrees for the U.S.
Virgin Islands through at least Saturday.

.LONG TERM...Sunday through Thursday...
Drier air and Saharan dust will persist through late Sunday night
across the region. However, typical afternoon shower activity is
expected over western PR. Unsettled weather conditions are
possible across the islands from Monday through early Wednesday
morning, as a strong tropical wave is forecast to move across the
eastern Caribbean and into the region. This wave is currently
being monitored by the National Hurricane Center and it has a 20
percent chance of development during the next 5 days. Although
there is some uncertainty on the possible development and impacts
of this system, residents across the U.S. Virgin Islands and
Puerto Rico should monitor the latest forecast from the National
Hurricane Center and from the San Juan Weather Forecast Office.


&&

.AVIATION...A tropical wave moving through will cause some showers over the
terminals today. However, VFR conditions are expected to prevail
through most of the day. VCTS may trigger TEMPO groups due to
reduced VIS and low ceilings at TJBQ after 17Z, with conditions
improving after 22Z. Winds will be out of the E at 10 to 20 knots.


&&

.MARINE...Fading northeasterly swell and tropical wave passage
today will cause choppy seas around 5 feet across most of the
regional waters, with easterly winds between 15-20 knots. There is
a high risk of rip currents for the northwestern beaches of Puerto
Rico today, and a moderate risk across the rest of the islands
beaches.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 79 90 80 / 30 30 20 10
STT 92 82 90 80 / 50 20 20 20
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Re: Caribbean - Central America Weather

#20298 Postby cycloneye » Fri Aug 28, 2020 4:57 am

Area Forecast Discussion
National Weather Service San Juan PR
446 AM AST Fri Aug 28 2020

.SYNOPSIS...Saharan dust and drier air will move across the region
through the weekend. Hazy skies are expected through at least
Sunday. A strong tropical wave is forecast to move into the
eastern Caribbean and across the local area between late Monday
and Tuesday.


&&

.SHORT TERM...Today through Sunday...
A low to mid-level high pressure is escorting Saharan dust over the
skies of Puerto Rico and the U.S. Virgin islands, resulting in hazy
conditions that should linger through the weekend. This dry air
mass, with precipitable water values around 1.4 to 1.5 inches should
limit shower formation over the area. As a result, a mainly fair
weather pattern is anticipated to continue through the day. In the
afternoon, however, local effects may aid in the development of
afternoon showers over western Puerto Rico. Although, unfavorable
conditions aloft should limit rainfall accumulation from this
activity.

For the weekend, the high pressure will begin to migrate toward the
east, while an upper level low will moves across the islands. This
low will help maintain 500 mb temperatures between -9 to -8 degrees.
At the surface, however, Saharan dust linger, but moisture trapped
in the lower 850 mb of the atmosphere should result in another round
of afternoon convection over the interior and western Puerto Rico
with isolated thunderstorms possible. In terms of temperatures,
highs will remain at or above the 90 degree mark at lower
elevations, but heat indices are once again expected to climb
between 100 to 106 degrees through the weekend.

.LONG TERM...Monday through Friday...
A strong tropical wave is forecast to move across the local area
between Monday and Tuesday, increasing the potential for urban and
small stream flooding across the islands. This wave is currently
being monitored by the National Hurricane Center and has a 30%
chance of development during the next 5 days. Lingering moisture
on Wednesday will aid in the development of seasonable afternoon
convection over the islands. An upper-level low is forecast to
develop to the northeast of the Leeward Islands by midweek and
retrogress over the local area through Friday. This should
increase instability over the area and aid in the development of
diurnally induced afternoon showers and isolated thunderstorms
over mainland PR.


&&

.AVIATION...VFR conditions are expected to persist through the forecast period.
Saharan dust will continue to filter in from the east, resulting in
hazy skies. However, visibility is expected to remain at P6SM. Winds
will be out of the east at 10 to 15 knots.


&&

.MARINE...Small crafts should exercise caution today across the
Caribbean waters and the Mona Passage due to easterly winds up to
20 knots. Elsewhere, winds up to 15 knots are expected. Seas
should continue to range between 3-5 feet through the weekend.
Seas and winds could increase early next week when a strong
tropical wave is forecast to move close to the region. A moderate
risk of rip currents will prevail across most of the eastern and
northern beaches of the islands through the weekend.


&&


.PRELIMINARY POINT TEMPS/POPS...
SJU 90 80 88 81 / 20 20 20 10
STT 91 80 91 81 / 10 20 20 20
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Re: Caribbean - Central America Weather

#20299 Postby cycloneye » Sat Aug 29, 2020 5:01 am

U

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Sat Aug 29 2020

.SYNOPSIS...
A dry air mass with Saharan dust particulate will continue to
limit shower activity and produce hazy skies across the islands
through the weekend. This weather pattern will persist until the
arrival of a tropical wave early next week, which NHC is
monitoring and has a moderate chance of becoming a tropical
cyclone. A TUTT-low will bring unstable weather conditions for the
second part of the work-week next week.

&&

.SHORT TERM...Today through Monday...
A high pressure ridge is dominating the local pattern along with a
pulse of Saharan dust over Puerto Rico and the U.S. Virgin islands.
Therefore, dry conditions and hazy skies are expected to continue
for the rest of the weekend. However, for this afternoon, isolated
to scattered showers are possibles over southwestern Puerto Rico.
The proximity of an upper-level low, low temp temperatures at
500mb (between -9 and -9.5 degrees C, according to the GFS) will
increase the possibility of thunderstorm formation. The limiting
factor for today`s activity is the lack of moisture in the
atmosphere. At this time, not significant rainfall accumulation
is expected. Maximum temperatures will range between upper 80s to
the low 90s with heat indices in the low and mid 100s. A similar
weather pattern is forecast on Sunday.

For Monday, a strong tropical wave is expected to cross the Lesser
Antilles and its leading moisture will reach the islands. Ahead of
the wave, a wind surge is forecast to bring low-level moisture and
increasing winds across the regional waters and coastal areas.
This moisture will increase the potential for locally induced
afternoon convection across PR/USVI with a better chance to
have urban and small stream flooding across the islands.

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

The axis of a tropical wave is forecast to move across the islands
on Tuesday. Both global models are depicting this vigorous
tropical wave, GFS/ECMWF. The National Hurricane Center (NHC) is
currently monitoring this wave and has a medium chance of
formation (40%) through the next five days. The weather picture
for that day looks wet and unstable, and if the guidance is
correct, expect an increasing potential for urban and small stream
flooding across the islands.

An upper-level trough moving westward, from the Central Atlantic
into the Eastern Caribbean, will follow the aforementioned
tropical wave by mid-week. This upper-level feature will swing
aloft until position over the Hispaniola by Friday afternoon. The
following unstable scenario is suggested by ECMWF/GFS increasing
confidence in this solution. This instability with the available
moisture, diurnal heating, and local effects could result in
inclement weather, especially on Friday afternoon.

The weather pattern for Wednesday and Saturday seems similar,
where the lingering moisture will aid in the development of the
typical September weather conditions with overnight/early morning
passing showers across the windward sections in PR/USVI. Then,
afternoon convection will develop across interior and west PR, as
well as downwind from the U.S. Virgin Islands and El Yunque.
However, a mid-to upper-level ridge will build from the east over
the region by the end of the long-term period, next weekend.

&&

.AVIATION...
Mostly VFR conditions are expected to prevail through the forecast
period. Although Saharan dust will continue to move into the region
and result in hazy skies the visibility is expected to remain at
P6SM. Winds will be out of the east-northeast between 10 to 15
knots.

&&

.MARINE...
Mariners can expect seas to remain below 5 feet through much of
the forecast period. Surface high pressure will build across the
Atlantic Ocean, promoting a moderate to locally fresh easterly
wind flow. A tropical wave is forecast to cross the Lesser
Antilles on Monday, moving across PR/USVI on Tuesday, and
increasing the chance for showers and thunderstorms those days.
Please, remain vigilant to the development of this tropical wave,
because it could deteriorate even more the marine conditions.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 81 90 80 / 20 20 20 30
STT 91 81 90 79 / 20 20 20 40
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Re: Caribbean - Central America Weather

#20300 Postby cycloneye » Sun Aug 30, 2020 5:01 am

Area Forecast Discussion
National Weather Service San Juan PR
517 AM AST Sun Aug 30 2020

.SYNOPSIS...

Stable weather conditions will prevail today. Although Saharan
dust concentrations will slowly diminish as the day progress,
skies will remain somewhat hazy. A tropical wave, monitored by the
National Hurricane Center, will cross the Windward Islands today,
moving off to the south of the local islands across the Caribbean
Sea late tonight into Monday. Another tropical perturbation will
bring an increase in winds and showers Monday into Tuesday.

&&

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

A surface high pressure located over the north-central Atlantic
will continue to generate a moderate east-northeast wind flow
over the region. Saharan dust particles will continue to move away
of the region, but will limit shower activity. However, locally
induced showers will remain possible over western and interior
sections of Puerto Rico during the afternoon.

A tropical wave, monitored by the National Hurricane Center, will
cross the Windward Islands today and will move well to the south
across the Caribbean Sea late tonight into Monday. Although the
bulk of moisture will remain to the south of PR/USVI, low-level
moisture will range between 1.5 and 1.8 inches over the area.
Also, a wind surge will bring a surge of moisture on Monday,
increasing the potential for shower development. As a result,
expect afternoon convection over the local waters, the U.S. Virgin
Islands, and the interior and western sections of Puerto Rico.

On Tuesday, GFS suggests the axis of another tropical wave
reaching the local area. So far, the forecast indicate an
increase in the potential for widespread showers and thunderstorm
activity over the area. This will increase the potential to
observe urban and small stream flooding across the islands with
the strongest activity. Maximum temperatures in Puerto Rico and
the U.S. Virgin Islands will remain from the upper 80s to the
low 90s in coastal/urban areas.

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

At the surface, the easterly winds will push enough tropical
moisture across the islands on Wednesday. At upper levels, an
upper-level trough moving westward from the Central Atlantic into
the Eastern Caribbean will increase somewhat local instability
through at least Friday. Both guidance, ECMWF/GFS, continues to
agree in this scenario. Instability will ramp-up little by little
after mid-week as this upper-level feature reach the Hispaniola by
Friday. Also, the Total Precipitable Water (TPW) is forecast to
increase Friday afternoon. Therefore, the available moisture
combined with diurnal heating, and local effects could result in
unsettled weather each afternoon, especially on Friday afternoon.

As the upper-level trough digs more into the Windward Passage,
between Haiti/Cuba, a mid-to-upper-level ridge will build from the
east over the region by next weekend. Although we cannot rule out
the typical passing showers across the windward sections each
night/morning, a stable weather pattern is probable by next
weekend.

&&

.AVIATION...

Mostly VFR conditions are expected to prevail through 30/06Z to
31/06Z. Although Saharan dust will continue to filter into the
region and result in hazy skies the visibility is expected to remain
at P6SM. Winds will be out of the east-northeast between 10 to 15
knots.

&&

.MARINE...

Mariners can expect seas to remain at 6 feet or less early this
week. A tropical wave is forecast to move across the Windward
Islands today and south of PR/USVI tonight and early Monday
morning. Another trade wind perturbation will increase winds/seas
and showers Monday and Tuesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 89 78 / 20 10 50 70
STT 92 80 90 79 / 20 40 40 70
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