Caribbean - Central America Weather

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Re: Caribbean - Central America Weather

#20641 Postby cycloneye » Mon Oct 18, 2021 4:38 am

Area Forecast Discussion
National Weather Service San Juan PR
524 AM AST Mon Oct 18 2021

.SYNOPSIS...Light steering winds will promote slow moving storms
this afternoon, enhancing the risk for flooding. Winds are
expected to turn more from the east to northeast through midweek,
and moisture content is forecast to remain at normal to above
normal levels through at least Thursday. A building mid-level
ridge during the end of the week should promote a drying trend,
but diurnally induced afternoon showers are expected each day.


&&

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

Good moisture persists across the region. Based on Total
Precipitable Water imagery from GOES-16, moisture levels remain on
the high end of normal or above normal across and in the vicinity
of the CWA; PWATs are around 1.8 to 2.3 inches. Meanwhile, the
steering flow remains light. That said, it will increasingly become
more east-northeasterly today into tomorrow. Local effects and
daytime heating will continue to dominate the weather pattern.
Afternoon convection is likely to begin over the interior of Puerto
Rico, extending into southern portions of the island. Tomorrow, the
peak of activity will likely be over interior and southwestern
Puerto Rico.

Conditions aloft are not very favorable for convection, with mid- to
upper-level ridging. That being said, the moisture will combine with
available instability/daytime heating to cause widespread shower
activity with isolated thunderstorms. Showers will be slow-moving,
leading to locally high rainfall accumulations. Erosion of the ridge
is expected for tomorrow into Wednesday, providing an increase in
instability over the region. As moisture is expected to persist,
active weather is anticipated, remaining the theme through the short
term period. Additional moisture makes its way into the region late
on Wednesday, as a tropical wave approaches from the east. Also on
Wednesday, winds finally pick up. The frontal boundary, and its
trough, will pull away to the northeast, allowing the pressure
gradient to tighten somewhat, as a ridge builds into the western
central Atlantic. Streamers become more likely in the east with this
increase in wind speeds, and showers will not have the same tendency
to linger over an area for an extended period of time. That said, an
increase in activity means that the potential for high rainfall
totals in some areas continues.

There remains an enhanced risk for flooding for portions of the
region through the short term period, as rain falls on already
saturated soils.

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

A tropical wave is expected to cross the region on Thursday, with
good moisture content through 700 mb. At upper levels, a short wave
trough is expected to move over the area, and the 500 mb temperature
is forecast to remain between -6.5 to -7.0 degrees Celsius. The
wave should move across the USVI through the morning hours, and
across PR during the afternoon hours. This will enhance morning
convection across the USVI and later across mainland PR. Trailing
moisture during the evening hours will promote scattered shower
with posible thunderstorm activity across portions of the regional
waters and between the USVI/eastern sections of PR as well.
Therefore, the threat for flooding rains will remain high.

A mid-level ridge is then expected to build over the area from the
north and hold through the rest of the long term period. This will
promote drier air intrusion and warmer 500 mb temperatures. At
least on Fri-Sat, seasonable weather conditions are expected with
sunny to partly cloudy skies during the morning hours with an
occasional trade wind shower moving over portions of the USVI and
eastern PR, followed by diurnally induced afternoon showers with
isolated thunderstorms over the western interior of PR. On Sunday,
a tropical wave is forecast to move across the Caribbean waters,
increasing slightly moisture content and the chances of early
morning/afternoon convection in diurnal pattern across the
islands. Further warming of the 500 mb temps are expected early
next week, and precipitable water content is expected to decrease
between 1.50-1.75 inches. This should favor fair weather
conditions with shallow convection developing during the afternoon
over western PR.


&&

.AVIATION...Generally VFR conds expected next 24 hours across all terminals.
Local effects and daytime heating dominate activity - peak SHRA/TSRA
activity this afternoon expected to be interior into southern PR,
causing VCTS for TJSJ/TJPS. VCSH for most other terminals.
Relatively light winds are likely to be dominated by sea breeze,
with speeds to near 10 knots after sunrise.


&&

.MARINE...Relative tranquil seas will continue for the next
several days. Winds are expected to remain light today, slightly
increasing each day and turning more from the east. Choppy wind
driven seas up to 6 feet are forecast to return late in the
workweek. There is a low risk of rip currents across all the
islands today.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 88 78 / 40 40 30 40
STT 88 78 89 79 / 60 50 50 50
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Re: Caribbean - Central America Weather

#20642 Postby cycloneye » Tue Oct 19, 2021 5:05 am

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Tue Oct 19 2021

.SYNOPSIS...Slow moving showers and thunderstorms are expected
once again today in a light ENE steering wind flow. Winds will turn
more from the east and increase slightly each day till the end of
the week. Normal to above normal precipitable water (PWAT)
content will continue over the region through at least Thursday.
A mid/upper level ridge pattern is expected to promote drier air
and more stable conditions aloft late in the week into the weekend.


&&

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

Moisture persists over the region, much as it has for the last
several days, though there is a patch of slightly drier air over the
region this morning. Based on the 0Z sounding and satellite
estimates, PWAT values remain within seasonal normals, generally in
excess of 1.7 inches, a marked decrease compared to previous days.
And yet still more than sufficient to support shower activity. Winds
are increasing over the area; cloud layer mean winds are likely to
be above 5 knots for the first time since Friday. It`s a very
marginal improvement, but an improvement nonetheless. Showers are
still going to be slow-moving, leading to locally high rainfall
accumulations, much like has been seen in prior days, and has
contributed to flooding. The steering flow is east-northeasterly to
northeasterly today, and so rain is expected over the same general
areas again today. Showers will develop during the early to mid
afternoon over the interior of Puerto Rico/Cordillera, then lazily
drift into southern/southwestern Puerto Rico. As such, there remains
an enhanced risk for flooding, mostly urban and small stream
flooding, but flash flooding is possible, as are rapid river rises
and mudslides.

Tomorrow, moisture increases somewhat across the area. As the
frontal boundary to the north pulls away, replaced by a ridge
pushing off of the US east coast and building into the central
Atlantic, winds will continue to increase, moreso as we make our way
through midweek into the second half of the week. That said, showers
are still not going to be making any great haste tomorrow, either.
The increase in steering flow will also contribute to moisture
convergence expected over the area. Even with a "dry slot" ahead of
an approaching tropical wave, PWAT values will be at least within
the range of seasonal normals. Additionally, the ridging that has
been in place aloft will erode, making conditions more favorable for
convective activity. The steering flow will become more east-
southeasterly, however, and so the peak in showers and thunderstorms
tomorrow will be over the interior of Puerto Rico into the west and
northwest. The threat for flooding remains, especially for the
interior areas.

A tropical wave is expected to make its way across the region late
Wednesday into Thursday. Widespread shower activity is expected. It
is quickly followed by another, though weaker, tropical wave. There
is a small dry slot between the waves, which could lead to some of
the afternoon convection being inhibited, as it is forecast to be
over the islands in the afternoon. That being said, the dry slot is
likely to be squeezed between these two waves, to the point where it
effectively meets its demise if not over the CWA then not terribly
far to the west. So the impacts of the dry air will be brief, and
the decrease in moisture may not be particularly impressive. As
such, another wet, active day is expected for Thursday. And
therefore also the corresponding enhanced risk for flooding.


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

A drying trend is expected during the long term period, as drier
mid-level air filters from the east on Friday and lingers through
early next week. This is in response to a building mid to upper
level ridge over the northeastern Caribbean. A weak Saharan Air
Layer is expected to reach the area during this period. In
addition, more stable conditions are expected, due to warmer 500
mb temperatures. This should inhibit widespread convective
development across the islands, and decrease the potential for
thunderstorm development. At the surface, a broad ridge across the
central Atlantic should promote moderate to locally fresh trades,
with a tropical wave currently forecast to pass well south of the
area on Sunday, having little to no impact in moisture content
across the local area. Another tropical wave, with better moisture
content may reach the area on Tuesday.

Having said that, expect showers to develop in a diurnal pattern
over western PR each afternoon, and across the USVI and eastern
sections of PR during the overnight/early morning hours due to
passing trade wind showers with mostly light rainfall amounts.
Brief isolated thunderstorms could form in the afternoon hours as
the trade wind cap is not forecast to be strong enough at this
moment.


&&

.AVIATION...Generally VFR conditions expected across all terminals
next 24 hours. Afternoon convection likely over interior into
southern/southwestern PR. VCSH for TJBQ, and VCTS for TJPS. Cannot
rule out tempo MVFR or worse, mostly for TJPS between 19/18Z and
19/22Z. Passing showers overnight causing VCSH, with SHRA possible,
for TJSJ/TIST/TISX. Winds generally out of the E to near 10 knots
after sunrise, subsiding after sunset.


&&

.MARINE...A small northerly swell will move across the Atlantic
waters later today. However, seas are forecast to remain at 3
feet or less, and the risk of rip currents will continue low
across the islands today. Light winds will prevail once again from
the east-northeast. Winds and seas are forecast to gradually
increase during the second part of the workweek, and another long
period northerly swell is forecast to move across the Atlantic
waters and passages by late Friday into Saturday. The combination
of wind driven seas and the swell will cause choppy seas up to 6
feet and a high risk of rip currents along the northern beaches of
the islands through the weekend.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 88 77 / 20 40 60 60
STT 89 78 88 78 / 50 50 50 50
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Re: Caribbean - Central America Weather

#20643 Postby cycloneye » Wed Oct 20, 2021 5:04 am

Area Forecast Discussion
National Weather Service San Juan PR
515 AM AST Wed Oct 20 2021

.SYNOPSIS...A tropical wave will continue to promote good moisture
content through Thursday. A weak Saharan Air Layer, with drier
air and hazy skies is expected to move by Friday and continue
through the weekend. Another wet weather pattern is expected by
midweek next week.


&&

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

Moisture continues across the region. Aloft, the ridging is being
eroded, as a tropical wave and weak low- to mid-level trough
approach from the east. Ahead of the tropical wave is a "dry slot,"
which will affect the region during the early part of the day today.
Even so, precipitable water values are forecast to be within
seasonal normals. This combination of sufficient moisture with
conditions becoming more conducive for convection aloft is expected
to result in another afternoon of wet, active weather. Winds are
veering somewhat, becoming more easterly to east-southeasterly. As
such, the peak in shower activity is expected to be for the interior
and western/northwestern parts of Puerto Rico. Winds are increasing
today, and showers will move slightly more quickly; the cloud layer
mean winds will be near 10 knots. This will mitigate some of what
has been seen over previous days in terms of locally high rainfall
amounts from showers developing and lingering over an area, slowly
drifting. That being said, periods of heavy rain are possible with
these showers and thunderstorms, and the enhanced potential for
flooding persists, as well as rapid river rises and mudslides in
affected areas.

The tropical wave is forecast to cross the region tonight into
tomorrow, and hot on its heels is another wave for tomorrow into
Friday. Active weather is expected again tomorrow. The timing of the
waves and dry slot, however, leaves somewhat drier air over the
west during midday/afternoon tomorrow, which could inhibit some of
the convective development earlier in the afternoon. Again, there
will be an enhanced risk for flooding.

Friday looks to be a little drier. Moisture will gradually decrease
across the area, and conditions aloft will become somewhat more
stable. Still, showers and isolated thunderstorms are likely during
the afternoon, as the typical diurnal pattern prevails across the
region.

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

A drying trend will continue on Saturday and Sunday in response
to a building upper level ridge and a weak Saharan Air Layer over
the region. In general, hazy skies with limited shower activity
across the islands is expected. However, a shallow layer of
moisture will be enough to trigger diurnal rainfall activity over
portions of western PR each day. Across the USVI and eastern
sections of PR, brief passing showers are possible at times. A
low-level trough is expected to move briefly from the east on
Monday, increasing slightly moisture content across the area.

Then by midweek, a wet pattern seems to unfold in response to a
TUTT induced surface low developing briefly just east of the
Bahamas and opening into a trough over the western Atlantic by
Wednesday. Winds are expected to shift from the south, and this
will pull moisture from the ITCZ across the eastern Caribbean.

&&

.AVIATION...Generally VFR conditions are expected next 24 hours.
Winds increase after sunrise, generally out of the east to east-
southeast around 10 knots. Afternoon convection is expected over
the interior into northwest, with streamers in the east. VCTS
expected for TJSJ/TJBQ, and tempo MVFR or worse cannot be ruled
out. VCSH elsewhere are expected to have limited operational
impacts at terminals. VCSH for TIST/TISX overnight. Winds subside
after sunset.


&&

.MARINE...Winds and seas are forecast to gradually increase during
the next few days, but conditions should remain below Small Craft
Advisory criteria through at least Friday. Then, a long period
northerly swell is forecast to move across the Atlantic waters and
local passages by late Friday night into Saturday. The combination
of wind driven seas and the swell should cause choppy seas around
6 feet and a high risk of rip currents along the northern beaches
of the islands through the weekend.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 78 89 76 / 60 60 50 50
STT 88 77 89 77 / 50 50 50 40
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Re: Caribbean - Central America Weather

#20644 Postby cycloneye » Thu Oct 21, 2021 4:37 am

Area Forecast Discussion
National Weather Service San Juan PR
441 AM AST Thu Oct 21 2021

.SYNOPSIS...

Active weather is expected today, as a tropical wave traverses the
region. This will result in a continuing enhanced risk for flooding.
Conditions are expected to gradually dry into the end of the week,
with a relatively dry pattern expected through the early part of
next week. Even so, a typical diurnal pattern of shower development
is likely each day. More active weather is expected by late next
week.

&&

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

Numerous showers and isolated thunderstorms were observed across
most of the local waters and over the eastern third of Puerto Rico
through the overnight hours. The doppler radar estimated between 1-2
inches of rain with this activity in general, and flood advisories
are in effect through the early morning hours for eastern PR. The
area remains between lingering moisture from a departing tropical
wave and another weaker tropical wave moving across the eastern
Caribbean. A drier air mass with increasing trades is currently
moving between these two areas of moisture, and it should continue
to move during the morning hours across the U.S. Virgin Islands and
eastern PR. This should put an end to the overnight rainy conditions
over the eastern municipalities of PR. Later during the day, the
available moisture in combination with daytime heating and local
effects will promote shower and thunderstorm development once again
across mainland PR. The risk for urban and small stream flooding will
continue elevated through this afternoon.

Moisture content is expected to gradually decrease tonight into
Friday, as a Saharan Air Layer moves from the east and an upper
level ridge builds aloft. However, quick passing showers could move
at times across the USVI and eastern sections of PR during the
night/early morning hours, followed by diurnally induced afternoon
showers over western PR. Further drying will continue into Saturday,
and mostly fair weather conditions are expected to prevail.

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

At the start of next week, patchy moisture is expected to make its
way through the region. The moisture will generally be sequestered
to the lower levels, with dry air aloft, associated with a Saharan
Air Layer. Additionally, ridging in the mid- to upper-levels will
result in conditions that are less favorable for convective
development. A typical pattern of showers is expected over the
region, though development is likely to be somewhat inhibited. There
may be a small increase in showers on Monday, with a somewhat more
substantial patch of moisture makes its way into the region. This
relatively dry pattern will continue through the early part of the
week.

Around midweek, the ridging aloft will begin to erode, as a deep-
layer trough associated with a low over the US Northeast and
Canadian Maritimes intensifies and digs southward. Conditions aloft
will become more favorable for convective development because of the
influence of this trough as it approaches from the west/northwest.
Additionally, a secondary low may form in the tail of this trough
and linger near the region, promoting additional and prolonged
instability. Meanwhile, moisture is expected to be pulled up over
the region from off of the ITCZ. Though it is likely that model
guidance is being a little overly zealous with these features, it is
likely that there will be another stretch late next week with a
prolonged active, wet pattern over the region.

&&

.AVIATION...

Mainly VFR conditions are expected to prevail across all terminals
through the forecast period. However, SHRA/TSRA may cause tempo
MVFR conds across the eastern terminals of PR thru 21/11z, and
once again from 21/16z-22z, including TJBQ. East winds at 10-15 kt
should prevail, with sea breeze variations aft 21/14z.

&&

.MARINE...

Winds are increasing across the region, and are generally out of the
east at up to 15 knots. Seas of generally 5 feet or less are
expected across the local waters today. A northerly swell is
forecast to affect the region, with choppy conditions approaching
hazardous criteria, though likely remaining just under said
criteria, by this weekend for the offshore Atlantic waters.

There is a moderate risk of rip currents for beaches of northern
Puerto Rico and Culebra, as well as eastern St. Croix and
northwestern St. Thomas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 77 90 76 / 60 40 20 20
STT 87 77 88 77 / 40 50 40 40
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Re: Caribbean - Central America Weather

#20645 Postby cycloneye » Fri Oct 22, 2021 5:16 am

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
455 AM AST Fri Oct 22 2021

.SYNOPSIS...A drier and more stable weather pattern is expected
to prevail today into early the next week. Hazy. A wetter pattern
is expected by midweek next week. The combination of moderate to
fresh easterly winds and a northerly swell will result in choppy
seas through the weekend.

&&

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

A drying trend is expected today and into the weekend, as a drier
air mass with Saharan dust moves from the east and a mid-level ridge
builds across the northeastern Caribbean. Warming of the 500 mb temp
is expected, and more stable conditions are expected in general to
prevail aloft. At lower levels, a surface high pressure building
across the central Atlantic will promote an east to southeast trade
wind flow and a wind surge is expected to continue across the local
area, with 15-20 kt trades prevailing through at least Saturday. Max
temps should reach the low 90s across the lower elevations and heat
indices up to 106 degrees are expected along the north-central and
western sections of PR through the short term period.

Under this expected pattern, hazy skies and mostly fair weather
conditions are expected to prevail across the islands each day.
However, diurnally induced showers are expected to develop over
northwest PR each afternoon, producing light to moderate rainfall
amounts. Although PWAT plummets through the short term period,
shallow moisture embedded in the trade winds will bring the
occasional passing shower across the regional waters and portions of
the USVI and east/southeast PR during the nighttime. On Sunday, a
slight decrease in the trades is expected and somewhat better
moisture content pools briefly over the region. This should increase
the aereal coverage of showers during the day over land areas.
However, flooding rains are not anticipated.

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

Ridge pattern aloft is expected to erode by midweek as an upper
trough develops across the west and central Atlantic into the
northeast Caribbean. At lower levels, a surface high will yield
moderate early winds early in the cycle, becoming light and from
the southeast on Wednesday and onwards. Shallow patches of
moisture embedded in the trade winds will move from time to time
Mon-Wed, however, moisture is expected to pool across the eastern
Caribbean by the end of the workweek as a result of the
aforementioned trough. Latest guidance continues to suggest a low
forming south of the area, promoting additional moisture and
prolonged instability by the end of the forecast cycle.

Under this evolving pattern, continue to expect mostly fair weather
conditions with diurnally induced convection over Mayaguez and
vicinity Mon-Wed. However, by the end of the cycle with a sharp
increase in moisture, expect a wetter pattern with frequent
passing showers during the night and early morning hours across
the USVI and portions of east/southeast PR, followed organized
convection across Puerto Rico in the afternoon.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. Tempo MVFR possible at TJBQ fm
16z-21z due to SHRA/TSRA. HZ due to Saharan dust will continue
across the region but VSBY should remain P6SM. Surface winds will
continue ESE at 12-16 kt with sea breeze variations and higher gusts
after 14z.

&&

.MARINE...Winds and seas are expected to increase today and into
the weekend due to the arrival of a northeasterly swell along with
the tightening of the local pressure gradient. This will result
in moderate to locally fresh trade winds and choppy seas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 77 90 78 / 20 40 20 10
STT 88 78 88 79 / 20 20 20 20
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Re: Caribbean - Central America Weather

#20646 Postby cycloneye » Sat Oct 23, 2021 5:17 am

Area Forecast Discussion
National Weather Service San Juan PR
455 AM AST Sat Oct 23 2021

SYNOPSIS...A ridge aloft along with generally below normal moisture
content will promote mainly fair weather conditions through early
next week. However, intermittent patches of low-level moisture
moving over the area from time to time will result in trade wind
shower activity with no significant rainfall accumulations
expected. Choppy marine conditions will continue throughout the
weekend.


&&

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

A mid to upper-level ridge pattern will promote stable weather
conditions across the region through the short-term period. In
addition, lingering suspended dust particles will continue to result
in hazy skies today, diminishing the concentrations on Sunday but
increasing once again on Monday with the arrival of another African
dust event. Nevertheless, the rain activity across the U.S. Virgin
Islands and Puerto Rico`s windward sections will be due to the
advection of patches of moisture, and the afternoon convection due
to the intense heating, local effects, and sea breeze variations.

Beachgoers, a northerly swell will maintain the risk of rip currents
high along the north-facing beaches of Puerto Rico, Culebra and St
Thomas, and the east corner of St Croix. Exercise caution!

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

For Tuesday through at least early Thursday, model guidance suggests
a relatively stable weather pattern. A dry air mass will move in
over the area decreasing precipitable water content at or below
normal levels. More specifically, relative humidities within the 850-
700 mb layer are expected to drop between 30% to 40%, which is two
standard deviations below normal, serving as a limiting factor for
shower development. However, the proximity of a short wave trough
aloft will provide sufficient instability to, combined with patches
of moisture passing across the area from time to time, enhance
convective activity, especially during afternoon hours where diurnal
heating and local effects are at a maximum. Therefore, expect
isolated showers over U.S. Virgin Islands, Vieques, Culebra and
eastern third of Puerto Rico during the morning hours and, in the
afternoon, isolated to scattered showers and isolated
thunderstorms. This activity will depend on the available low-
level moisture in the atmosphere.

For the end of the workweek through the weekend, uncertainty remains
regarding the prevailing weather pattern due to differences between
model cycles. Models agree on a polar trough and surface frontal
boundary exiting the Eastern Seaboard of the United States by mid
week. In latest model runs of both GFS and ECMWF, the frontal
boundary stalls northwest of the forecast area through Sunday.
Previous runs would show a surface trough north of the region
pulling deep moisture from the ITCZ across the northeast
Caribbean. However, the latest runs are consistently showing an
opposite solution with much drier mid to upper levels. Upper-
levels still look unstable, as the polar trough slowly moves
eastward and a cut-off low develops and remains over the area.
The GFS has a much stronger solution with a deeper cut-off low
cooling 500 mb temperatures to below -8 degrees Celsius, which is
below normal for this time of year. This feature could provide
steep lapse rates and an elevated potential for organized
convection. The limiting factor would be the available moisture.
To sum up, models consistently show unstable upper-level
conditions by the end of the workweek through the weekend. This
will definitely aid in any convective development across the area.
However, uncertainty remains regarding the amount of available
moisture which could mean the difference between very localized
deep convective activity to more widespread and organized
convection. And thus there is continued low confidence in the
forecast details at this time.


&&

.AVIATION...VFR conds with hazy skies due to Suspended dust
particles are expected today. However, P6SM will prevail. Expect
VCSH and maybe an Isol-TSRA near TJBQ btwn 23/18-22z. Winds will
prevail from the ESE at 10 to 18 kt with higher gusts and sea breeze
variations after 23/13z.


&&

MARINE...The combination of moderate to locally fresh easterly
winds and a northerly swell will continue to produce choppy seas
across the regional waters throughout the weekend. Therefore,
small craft operators should exercise caution. As a result of the
northerly swell, a high risk of rip currents is expected across
the north-facing beaches of Puerto Rico, Culebra, and St. Thomas
as well as eastern St. Croix during the weekend.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 90 78 / 30 10 50 60
STT 88 79 88 78 / 20 20 40 50
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Re: Caribbean - Central America Weather

#20647 Postby cycloneye » Sun Oct 24, 2021 5:31 am

Area Forecast Discussion
National Weather Service San Juan PR
451 AM AST Sun Oct 24 2021

.SYNOPSIS...A ridge aloft will continue to promote mainly dry and
stable conditions aloft through at least the early portion of
this week, limiting the potential for deep, organized convective
activity from materializing. Patches of low-level moisture,
however, will move over the area aiding in trade wind shower
activity across the area from time to time. Choppy marine
conditions will prevail across the regional waters through at
least tonight due to the combination of a long dominant period
northerly swell and moderate to fresh easterly winds.


&&

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

Unfavorable atmospheric conditions for deep convection continue
across the islands due to a mid to upper-level ridge. However, a
surge of moisture detected with GOES-E will move across the islands,
increasing low-level moisture and shower activity today and
tomorrow. This activity will affect the windward sections of Puerto
Rico and the U.S. Virgin Islands, moving into the interior and west-
PR by late morning into the afternoon. Although atmospheric
conditions are hostile for thunderstorm development, low-level
convergence, sea breeze, and local effects could produce periods of
moderate to heavy showers to result in urban and minor stream
flooding.

Model guidance suggests the erosion of the available moisture by
Tuesday and the winds shifting from the east-southeast in response
to a low-pressure surface moving across the western Atlantic. Under
this weather pattern, above-normal temperatures could be expected,
especially during the peak of maximum heating.

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

Despite earlier wetter solutions, latest global model runs continue
to trend on the dry side for most of the long term period. However,
certain features close to the forecast area keep changing slightly
which could result in differences on the prevailing weather pattern.
Both GFS and ECMWF keeps on showing a weak upper-level short wave
trough crossing the area from Wednesday through at least Friday.
This will provide marginal instability aloft throughout the earliest
part of the forecast period. At low levels, a weak frontal boundary
over western Atlantic will approach the area on Wednesday. As it
continues its eastward motion, winds will shift south southeast.

Although this setup usually allows moisture advection into the
area by pulling it from the ITCZ, the pressure gradient will
weaken and that will allow winds to die down. GFS has a slightly
stronger southerly wind flow throughout this period compared to
ECMWF. This means that GFS brings some of the moisture content
closer to the area, over the Caribbean waters, and in the latest
run brings it even closer than earlier recent runs. Whereas ECMWF
maintains the moisture well south of the area with normal to below
normal moisture prevailing instead. Although discrepancies lie
regarding the amount of moisture, it seems that weather conditions
will be slightly unstable and this could trigger convective
development each afternoon when combined with surface heating and
sea breeze convergence. A gradual shift of focus area of rainfall
accumulations could be observed from western portions to northern
half of Puerto Rico from Wednesday through the end of the workweek
as winds shift to a more southerly flow. Low-steering winds will
produce higher rainfall accumulations. Therefore, expect urban and
small stream flooding as well as ponding of waters on roadways
and in poor drainage areas.

By the weekend, a mid to upper ridge builds across the area bringing
back stable weather conditions. However, models still suggest a cut-
off low close to the area by Sunday through Monday. Once again,
the positioning of this cut-off low differs between both GFS and
ECMWF reintroducing uncertainty into the forecast, this time
regarding the unstable weather conditions. Nevertheless, expect at
least a seasonal weather pattern with enhanced deep convection
development each afternoon and possible passing showers across the
windward coastal areas during the night and morning hours.
Forecast confidence is low to moderate given that some similar
weather features continue to appear between each model cycle.


&&

.AVIATION...VFR conds predominating today. However, VCSH with a
few of them moving into the terminals are expected. SHRA/-SHRA will
increase in frequency across IST/ISX/JSJ after 24/13z, spreading
into the interior and W-PR btwn 24/15-22z. Winds will prevail from
the E at 10-20 kt with higher gusts and sea breeze variations after
24/13z.


&&

.MARINE...Moderate to locally fresh trade winds along with a
northeasterly long dominant period are combining to produce
confused seas of 4-6 feet mainly across the Atlantic waters and
passages. Therefore, small craft operators should exercise caution
as choppy seas will continue through at least tonight. Seas will
gradually improve Monday into Tuesday as the swell and winds start
to subside.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 87 76 / 60 60 60 30
STT 88 78 88 77 / 50 60 60 40
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Re: Caribbean - Central America Weather

#20648 Postby cycloneye » Mon Oct 25, 2021 5:15 am

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Mon Oct 25 2021

.SYNOPSIS...A ridge aloft will persist into Tuesday, resulting in
stable conditions aloft and thus limiting the potential for deep,
organized convective activity. However, patches of low-level
moisture riding the trade wind flow will be sufficient to generate
isolated to scattered shower activity from time to time during
the next couple of days. The ridge aloft is expected to weaken by
the middle to latter half of the week as a shortwave trough moves
across and depending on the amount of moisture, it may allow for
better convective activity.


&&

.SHORT TERM...TODAY THROUGH WEDNESDAY...

A trade wind perturbation will continue to result in passing showers
across the islands today. While a ridge aloft will limit the
vertical development of these showers. However, residents in the
Virgin Islands and the east and north portions of Puerto Rico can
expect showery weather this morning. These showers may produce
ponding of water on roadways and in low-lying areas. Later in the
afternoon, local effects, diurnal heating, and sea breeze variations
will give way to convection across the western sections of PR,
downwind from the El Yunque and the Virgin Islands.

A drier air mass with Suspended Particles from the Africans` Deserts
will limit moisture and produce hazy skies through at least mid-
week. Nevertheless, the trade winds will bring patches of moisture
at times; therefore, pesky showers cannot be ruled out through the
forecast period.

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

Model guidance continues to be consistent on a marginally unstable
weather pattern for most of the long term period. Thursday starts
with an upper-level short wave trough crossing the area and low-
level winds shifting to southeast through Friday. Discrepancies
still exist regarding the amount of moisture convergence through the
end of the workweek as mentioned in previous discussions. GFS
continues to have better moisture advection due to a southerly flow
than ECMWF. However, winds are still expected to weaken as pressure
gradient decreases over the area. Therefore, uncertainty still
exists on how much moisture will converge over the forecast area.

Recent GFS model runs are consistent that the bulk of the
moisture plume will stay south of the region but close enough for
above normal moisture content to reach the area. If this plays
out and with enough instability in the atmosphere, widespread
convective development would be likely with the potential for
isolated to scattered thunderstorms across the area. The bulk of
the activity could be observed by Thursday night with showers and
thunderstorms developing over the Caribbean waters and being
advected towards the southern and southeastern coastal
municipalities of Puerto Rico and St. Croix. During the day,
surface heating and sea breeze convergence could produce showers
and scattered thunderstorms over interior and northern half of
Puerto Rico and occasionally affecting the local islands. Light
steering winds will increase the potential of flooding threat
especially in urbanized regions such as the greater Bayamon and
San Juan Metropolitan area. If the ECMWF run plays out instead,
then a more less widespread and more localized activity could be
observed as moisture intrusion over the forecast area will be
greatly reduced.

The weekend also looks marginally unstable with the northeast
Caribbean under the boundary of an upper-level building ridge and
trough. By Sunday through the end of the forecast period, both
global models are consistent in the development of an upper cut-off
low lingering over Puerto Rico and U.S. Virgin Islands but strength
and positioning still not completely agreeing within each model
solution. Moisture still does not look impressive, at times both
models showing below normal values. Hence, continue to expect a more
seasonal weather pattern for the weekend through Tuesday with deep
convection developing during each afternoon depending on the
available moisture and the evolution of unstable weather conditions
aloft. Although models are consistent on the progress of weather
features for this week and early next week, location differences of
these features continue to bring forecast uncertainty. Therefore,
confidence continues to be low to moderate.


&&

.AVIATION...Prevailing VFR conds expected through the forecast
period. However, VCSH will continue to arrive across the local
terminals, and there is a possibility of brief SHRA at times. SHRA
may form later in the afternoon across the interior and W-PR. A
Saharan Air Layer will result in hazy conditions late this afternoon
through the rest of the forecast period. Wind will remain from the
east at around 10 to 15 knots with sea breeze variations after
25/13z.


&&

.MARINE...The combination of a long dominant period northerly
swell and moderate easterly winds will result in seas between 3
to 6 feet through at least this afternoon, with the highest seas
expected across the offshore Atlantic waters. Seas are expected to
subside tonight through Tuesday as the wind and swell decrease. A
high risk of rip currents will continue across the northwestern
beaches of Puerto Rico and Culebra through this afternoon.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 76 88 76 / 50 30 30 30
STT 88 77 87 78 / 50 40 30 30
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Re: Caribbean - Central America Weather

#20649 Postby cycloneye » Wed Oct 27, 2021 4:40 am

Area Forecast Discussion
National Weather Service San Juan PR
445 AM AST Wed Oct 27 2021

.SYNOPSIS...

Generally fair weather is expected across the region over the next
few days, with below normal moisture over the area. Even so, a
typical diurnal pattern of showers, though suppressed, is expected
each day. Increasing moisture is expected by early next week, though
PWAT values are forecast to remain below normal to normal at times.


&&

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

A polar trough is approaching the islands weakening the mid-level
ridge aloft. However, the lack of tropical moisture will limit
shower activity across the islands, and hazy skies will dominate due
to suspended dust particles from the Africans` deserts. At the
surface, southerly winds will aid in above-normal temperatures
between 1000 and 1500 AST. Heat indices will rise into the 100`s
degrees Fahrenheit, especially across the urban areas of northern
Puerto Rico.

Overall model guidance consensus is a fair-weather pattern with
below-average moisture content and above-normal temperatures. The
rainfall activity, if any, will be limited to the local waters,
quick burst of showers, and sea breeze convergence. Hazy skies will
also continue through much of the workweek.

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

The period will be mostly defined by easterly low level flow with
patchy moisture and an upper-level cut-off low meandering over the
area through Thursday of next week. A mid-level ridge will maintain
700-500 mb relative humidities below 50% through at least Sunday
which could hinder convective development. However, the ridge will
gradually erode as the cut-off low predominates the environmental
conditions aloft. The moisture throughout the period will fluctuate
as alternating wet and dry bands move across the northeast Caribbean
bringing a pattern of variable moisture. Precipitable water values
are forecast to alternate between below normal to normal levels. The
cut-off low at upper-levels will enhance the activity as 500 mb
temperatures cool to -7 to -8 degrees celsius and 700-500 mb
lapse rates gradually increase throughout the long- term period.
Other than the typical diurnal pattern of showers and isolated
thunderstorms in western Puerto Rico, only moderate confidence
should be placed in the timing of any of these features as they
could change considerably in the next several days. Nevertheless
the expected pattern will bring early morning showers with each
passing band. Then typical showers and thunderstorm development
each afternoon should occur through the period. By early next week
through Thursday, these bands will bring more moisture with
favorable conditions at upper-levels. Therefore, urban and small
stream flooding can be expected in areas with the heaviest
showers, especially during afternoon hours where localized deep
convective activity could develop producing significant quantities
of rainfall.


&&

.AVIATION...Prevailing VFR conds expected through the forecast
period. Hazy skies will continue, but VIS will remain P6SM. Rain
activity, if any, will not have significant impact on operations.
Wind will remain from the S-SE at around 10 knots with sea breeze
variations after 27/13z.


&&

.MARINE...

Winds out of the east to southeast continue, with speeds to 10
knots. Seas will remain 4 feet or less through the end of the
workweek, with calmer conditions in the Caribbean than the
Atlantic. A northerly swell is forecast to affect the local waters
this weekend.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 92 76 92 75 / 20 10 10 10
STT 85 78 85 77 / 20 0 0 10
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Re: Caribbean - Central America Weather

#20650 Postby cycloneye » Thu Oct 28, 2021 4:44 am

Area Forecast Discussion
National Weather Service San Juan PR
415 AM AST Thu Oct 28 2021

.SYNOPSIS...Mainly fair weather conditions with generally below
normal moisture will prevail through Friday, which will result in
limited shower activity. More patchy moisture is expected during
the upcoming weekend, which could result in an increase in trade
wind showers, however, no significant rainfall is anticipated.
More unstable conditions with an increase in convective activity
is possible by next week as a TUTT (Tropical Upper Tropospheric
Trough) settles over the eastern Caribbean.

&&

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

Hazy skies with limited shower activity is expected today and Friday
as Saharan dust prevails over the local area. South to southeast
winds are expected today, which will cause high temperatures to be
in the lower 90s across the lower elevations of Puerto Rico, while
mid to upper 80s can be expected elsewhere in PR and across the
USVI. Winds will then start to gradually become more easterly on
Friday and Saturday. Patches of moisture will start to move in on
Saturday, causing an increase in the shower activity across the local
area.

Surface high pressure across the eastern Atlantic, and a surface low
across the northwestern Atlantic, will cause the local pressure
gradient to be weak, and the local winds to be light and southerly
today. The SFC low will slowly move east and into the central
Atlantic, causing a SFC high to gradually develop to the NNE of the
local islands, and causing the local winds to gradually become
easterly and slightly stronger by Saturday. Upper trough is located
over the local islands, but the dry air and mid level ridge are not
conducive to an enhanced shower or thunderstorm development.

The latest guidance still insists in drier than normal moisture
today and Friday, with limited shower activity. For today, portions
of the western interior of PR have a chance of showers in the
afternoon due to the combination of the diurnal heating and sea
breeze convergence, but this shower activity is expected to be
focused in a relatively small area, while the rest of PR and the
USVI is expected to observe fair weather. Similarly, only a slight
chance of showers is expected on Friday, but a small patch of
moisture may bring brief showers to Saint Croix on Friday afternoon.
Then the patches of moisture become more noticeable on Saturday, and
thus an increase in the chances of showers across the local area.
That said, the rainfall totals are expected to be modest on
Saturday.

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

A TUTT is expected to settle across the eastern Caribbean south of
the area on Sunday and Monday, however, the mid-level ridge will
continue to remain strong enough to limit convective activity.
Nevertheless, patches of moisture will be moving across to result in
trade wind shower activity across portions of the local waters
during the overnight and early morning hours, with some of the
activity affecting portions of eastern Puerto Rico and the USVI
followed by locally and diurnally induced activity across western
Puerto Rico during the afternoon hours. The low-level flow is
expected to be easterly on Sunday but then become northeasterly
during the first half of next week as a low-level ridge settles
over the western Atlantic north of the area. Conditions aloft then
become more favorable for higher instability between late Monday
and Thursday as the TUTT amplifies over the eastern Caribbean
with an inverted mid-level trough developing and settling near
and south of the area. This will be strong enough to displace the
mid-level ridge north and become less of an influence in the
weather pattern. Having said this, there is uncertainty in terms
of how the moisture field will evolve as model guidance differs in
this aspect. The GFS shows moisture levels to be in the near
normal range most of the time while the ECMWF model shows more
patchy moisture, fluctuating between near and below normal at
times. Therefore, convective coverage will be dependent on the
evolution of the moisture field with the GFS model favoring more
activity compared to the ECMWF model. Given these differences,
overall confidence in the forecast for the early to middle portion
of next week is low to moderate at this time.

&&

.AVIATION...Prevailing VFR conds expected through the forecast
period. Hazy skies will continue, but VIS will remain P6SM. Slight
chance of -SHRA is forecast, but not expected to affect the
terminals. Wind will remain light and variable early today, becoming
S-SE at around 10 knots with sea breeze variations developing after
28/13z.

&&

.MARINE...Mainly tranquil marine conditions with seas of less than
4 feet are expected to prevail through Friday. Choppy seas are
then expected during the upcoming weekend, especially over the
Atlantic waters and local passages, as a northerly swell moves
across. For beachgoers, there is a low risk of rip currents across
all of the local beaches for today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 77 88 75 / 10 10 20 20
STT 87 77 87 75 / 0 10 30 30
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Re: Caribbean - Central America Weather

#20651 Postby cycloneye » Fri Oct 29, 2021 4:56 am

Area Forecast Discussion
National Weather Service San Juan PR
425 AM AST Fri Oct 29 2021

.SYNOPSIS...Mainly fair weather conditions are expected to prevail
for today as a drier than normal air mass and a lingering Saharan
Air Layer will limit rainfall activity. Then, during the upcoming
weekend, patches of low-level moisture will move across resulting in
an increase in trade wind showers, however, no significant rainfall
accumulations are expected. A closed mid and upper-level low will
meander across the eastern Caribbean during the early to middle
portion of next week, helping to result in more unstable weather
conditions.

&&

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

Hazy skies with isolated shower activity is expected today as a
small concentration of Saharan dust prevails over the local area.
Southeast winds are expected today, which will cause high
temperatures to be in the upper 80s to lower 90s across the lower
elevations of Puerto Rico, while mid to upper 80s can be expected
elsewhere in PR and across the USVI. Winds will then start to
gradually become more easterly tonight and Saturday. Patches of
moisture will move into the local area on Saturday and Sunday, which
will cause an increase in the shower activity.

Surface high pressure across the eastern Atlantic, and a surface low
across the northwestern Atlantic, will cause the the local winds to
be light to moderate from the southeast today. However, the SFC low
will slowly move east southeast into the central Atlantic, causing a
SFC high to gradually develop to the NNE of the local islands, and
causing the local winds to become easterly and slightly stronger by
Saturday. An upper trough is located over the local islands, but the
dry air and mid level high pressure are not conducive to an enhanced
shower or thunderstorm development.

For today, the western interior of PR has a chance of showers in the
afternoon due to the combination of the diurnal heating and sea
breeze convergence, but the overall coverage is expected to be
small, while the rest of PR and the USVI is expected to observe fair
weather. A chance of showers is expected late tonight for the USVI
as brief patches of moisture start filtering into the local area.
Moisture increase will become slightly more noticeable on Saturday
as additional patches of moisture move into the local area, and thus
an increase in the chances of showers is expected. That said, the
rainfall totals are expected to be modest on Saturday, and also
Sunday.

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

A closed upper-level low is expected to settle near the Windward
Islands on Monday with a strong reflection in the mid-levels in
the form of a closed low as well. However, the mid-level ridge
will be strong enough still to inhibit convective activity across
the area. This changes by Tuesday and Wednesday as the mid and
upper level low retrogrades slightly, closer to the area. This
will be sufficient to displace the mid-level ridge far enough
north. As a result, conditions aloft will become more unstable
and thus more conducive for convective activity to materialize.
Low-level winds will become more east- northeast as a low-level
ridge settles to the north. Moisture is expected to increase to
near normal, with precipitable water values ranging between 1.7
and 2.0 inches. The combination of all of these factors will aid
in the enhancement of overnight and morning shower activity across
portions of the USVI as well as eastern and northeastern portions
of Puerto Rico followed by enhanced afternoon convection across
portions of interior, western, and southwestern Puerto Rico.

Then, by Thursday and lasting through the end of the long term
period, the mid and upper level low is expected to weaken and
this will allow the mid-level ridge to bounce back once again to
result in drier and more stable conditions. As a result, a
decrease in the convective activity can be expected during this
time period.

&&

.AVIATION...No significant hazards expected. VFR conds expected
to prevail through the forecast period. Hazy skies may be
observed, but VIS will remain P6SM. Slight chance of -SHRA is
forecast, which could affect the vicinity of TJBQ after 29/18Z,
and TISX after 30/06Z. Wind will remain light and variable early
today, becoming SE at around 10 knots with sea breeze variations
developing after 29/13Z.

&&

.MARINE...Tranquil marine conditions are expected to prevail for
today with seas of less than 4 feet expected. By late tonight and
continuing into the upcoming weekend, a northerly swell is
expected to invade the local waters, with choppy seas expected
across the Atlantic waters and local passages.

For beachgoers, a low risk of rip currents is expected for all of
the local beaches for today. However, due to the aformentioned
northerly swell, the rip current risk for the northern beaches
of Puerto Rico and Culebra will increase to moderate tonight and
to high during the upcoming weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 75 87 76 / 20 20 30 30
STT 86 76 86 76 / 30 30 30 30
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Re: Caribbean - Central America Weather

#20652 Postby cycloneye » Fri Oct 29, 2021 12:56 pm

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Re: Caribbean - Central America Weather

#20653 Postby cycloneye » Sat Oct 30, 2021 4:57 am

Area Forecast Discussion
National Weather Service San Juan PR
415 AM AST Sat Oct 30 2021

.SYNOPSIS...A weak surface high pressure is gradually developing
to the north of the local islands before dissipating on Tuesday,
which will cause the ESE winds expected today to gradually become
ENE by Monday. A weak mid level high pressure will maintain some
stability across the local area through the weekend. Upper level
ridge to the north of the local area and an upper trough to the
east southeast, will keep the local islands in the subsident side
of said trough through the weekend. The Saharan dust
concentration is diminishing and some haze could be observed until
tonight, but patches of moisture will move in this weekend, but
the increase in moisture will become more persistent early in the
following workweek. The shower activity is expected to increase
next week with this increase in moisture.

&&

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

A west to east oriented upper-level trough is currently enveloping
the eastern Caribbean with a mid-level ridge prevailing overhead.
This ridge will continue to result in dry and stable conditions
aloft, inhibiting the development of deep and organized convective
activity during the short-term period. At low-levels, patches of low-
level moisture riding the trade wind flow, being enhanced somewhat
by the upper-level trough, are moving across the western Tropical
Atlantic into the eastern Caribbean. A patch of low-level moisture
is currently moving across the area, which has resulted in shower
activity across portions of the local waters as well as across
portions of Vieques into extreme northeast Puerto Rico during the
overnight hours. This patch of moisture is expected to move westward
during the day and will combine with daytime heating and local
effects to spark afternoon shower activity across northwest Puerto
Rico as the steering flow will be from the east-southeast. Across
the rest of the area, mainly fair weather conditions are expected as
an area of drier air in between moisture patches moves in,
inhibiting shower activity. With winds taking more of an easterly
component compared to previous days, high temperatures are
expected to be slightly cooler, in the upper 80s to around 90
degrees. Skies will also be somewhat hazy through this afternoon
as a Saharan Air Layer lingers. The dust concentration is expected
to diminish by tonight, putting an end to the hazy conditions.

For Sunday and Monday, additional patches of moisture will be moving
across the area, resulting in trade wind showers from time to time.
The steering flow during the day on Sunday will take more of an
easterly component and then more of an east-northeast component late
Sunday through Monday as a low-level ridge settles to the north.
Therefore, shower activity during the overnight and early morning
hours will be concentrated across portions of the local waters, with
some of the activity expected to affect portions of the USVI as well
as the eastern and northeastern third of Puerto Rico followed by
locally and diurnally induced activity across portions of interior,
western and southwestern Puerto Rico during the afternoon hours. As
mentioned, given that the mid-level ridge will continue to result in
unfavorable conditions for the development of deep and organized
convective activity, only light to locally moderate rainfall
accumulations are expected with ponding of water on roadways and in
low-lying areas expected to be the main hazard.

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

A noticeable increase in moisture and in shower activity is
expected in the long term period. The local winds are forecast to
be from the ENE on Tuesday, but from Wednesday onward, the winds
will be mainly from the east. With this increase in moisture and
easterly winds, we can expect trade wind showers every morning and
night, mainly affecting the local waters, USVI, and eastern PR.
However, the latest guidance indicates that the rainiest days
would be Tuesday through Thursday, as patches of moisture, of
over 2 inches of precipitable water, would move through the local
area. There is some hints in the guidance that would suggest that
isolated thunderstorms could be observed, but the confidence is
higher on isolated thunderstorms over land areas, with less
confidence on thunderstorms over the waters. Then for Friday into
next weekend, essentially tradewind showers with locally induced
showers in the afternoons over PR are expected. The temperature
guidance is suggesting milder temps, with highs in the mid to
upper 80s across the lower elevations, but a few areas with upper
80s could also be expected.

&&

.AVIATION...VFR conditions expected to prevail throughout the
period. Sct SHRA expected across northwestern PR between 30/17z and
30/22z, resulting in VCSH across TJBQ. Winds light and variable
through 30/12z, increasing to 10 to 15 kts from the ESE with sea
breeze variations after 30/14z.


&&

.MARINE...Seas are becoming choppy, up to 6 feet. The choppy seas
are expected to continue into next week, due to a northerly swell.
There is a high risk of rip currents today across the north coast
of Puerto Rico, and a moderate risk across many other beaches of
PR and the USVI.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 75 88 77 86 / 30 30 40 50
STT 76 87 76 87 / 20 20 30 50
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Re: Caribbean - Central America Weather

#20654 Postby cycloneye » Sun Oct 31, 2021 5:12 am

Area Forecast Discussion
National Weather Service San Juan PR
443 AM AST Sun Oct 31 2021

.SYNOPSIS...A weak surface high pressure to the NNE of the local
area will gradually dissipate as a broad and much stronger high
pressure moves into the northwestern Atlantic by Tuesday. This
will cause the local winds to go from ESE today to ENE late Monday
into Tuesday, then Easterly on Wednesday and onward. A mid level
high pressure will maintain some stability across the local area
through Monday, but a weak mid level low pressure will approach
the area on Tuesday and Wednesday, at the same time that an upper
level low moves over the local area. The available moisture is
also expected to increase for the following workweek. This setup
could cause rainy conditions, with perhaps a few thunderstorms,
particularly on Tuesday through Thursday.

&&

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

Not much has changed in the overall weather pattern during the next
couple of days. A west to east oriented upper-level trough continues
enveloping the eastern Caribbean with a mid-level ridge sitting
overhead. This mid-level ridge will continue to result in mainly dry
and stable conditions aloft, inhibiting the development of deep and
organized convection. This overall pattern will prevail through
Monday. The low-level wind flow for today will be from the east to
east-southeast, switching to the east-northeast by late tonight and
continuing through the rest of the short-term period as a low-level
ridge settles just northwest of the area. The overall wind flow
pattern will continue to transport patches of low-level moisture
from the western Tropical Atlantic into the eastern Caribbean from
time to time resulting in trade wind showers, which is expected to
move across the local waters, with some of the activity moving
inland across eastern portions of Puerto Rico and the USVI, mainly
during the nighttime and early morning hours. This will be followed
by the development of afternoon convection across western Puerto
Rico. Only very minor rainfall accumulations are expected with the
trade wind showers moving across eastern Puerto Rico and the USVI,
with heavier accumulations across western Puerto Rico with the
afternoon convection.

On Tuesday, the weather pattern undergoes changes. The upper-level
low will retrograde to a position near the area with a strong
reflection in the mid-levels in the form of a inverted trough. This
inverted trough will be sufficient to displace the mid-level ridge
to the north and thus conditions aloft are expected to become more
unstable and moist with precipitable water values climbing to
between 1.7 and 1.9 inches, which is in the near normal range for
this time of the year. As a result, an increase in convective
activity is likely with western and southwestern Puerto Rico
observing more enhanced shower and thunderstorm activity during the
afternoon. Enhanced nocturnal convection is likely across the local
waters, with some of the activity moving inland across portions of
the USVI as well as across eastern and northeastern portions of
Puerto Rico. Some of the heaviest activity, especially with the
afternoon convection, will have the potential to result in areas of
urban and small stream flooding.

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

The long range models continue to suggest an increase in moisture
and in shower activity for the long term forecast period. The
local winds are forecast to become easterly on Wednesday and for
the next following days. With this increase in moisture and the
easterly winds, we can expect trade wind showers every morning and
night, mainly affecting the local waters, USVI, and eastern PR.
However, the latest guidance indicates that the rainiest days
would be Tuesday through Thursday, as patches of moisture, of over
2 inches of precipitable water, would move through the local
area, though the GFS model is now suggesting Thursday to be the
day with the deepest moisture and overall wider coverage of
rainfall. Isolated thunderstorms could be observed on Tuesday
through Thursday, as an upper low starts to approach the local
area from the south, and the high pressure in the mid levels
weakens. No significant change in the forecast for Friday into
next weekend. Tradewind showers with locally induced showers in
the afternoons over PR are generally expected for those days.

The temperature guidance is suggesting milder temps for Wednesday
and Thursday, with highs in the mid to upper 80s across the lower
elevations, mainly due to the cloud cover and rainfall expected.
Then for Friday onward, the daytime high temp is forecast to get
close to 90 across the lower elevations once again. The overnight
minimum temperatures are expected to be seasonable, generally in
the mid to upper 70s across the lower elevations, and in the 60s
to low 70s across the higher elevations.


&&

.AVIATION...VFR conditions will prevail across the local area
throughout the period. SHRA activity expected across western PR
between 31/17z and 31/22z, resulting in VCSH across TJBQ. Winds
light and variable through 31/12z, increasing to 10-15 kts from the
E-ESE with sea breeze variations after 31/14z.


&&

.MARINE...The northerly swell is expected to continue affecting
the local waters for the next few days, causing choppy seas up to
5 or 6 feet. Light to moderate winds from the east are also
expected for the next few days. There is a high risk of rip
currents today for the north coast of Puerto Rico and Culebra,
while a moderate risk exists for other beaches of northeast and
northwest Puerto Rico, Vieques, and the USVI.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 77 88 76 / 30 40 40 40
STT 87 76 87 76 / 20 30 20 40
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Re: Caribbean - Central America Weather

#20655 Postby cycloneye » Mon Nov 01, 2021 4:41 am

Area Forecast Discussion
National Weather Service San Juan PR
444 AM AST Mon Nov 1 2021

.SYNOPSIS...Broad surface high pressure across the northwest
Atlantic will continue to build and spread eastward across the
southwest Atlantic through Wednesday. This will induce an east to
northeast wind flow across the region. Low level moisture
fragments from old frontal boundaries/shear lines will be
transported across the region by the prevailing trade winds. In
the upper levels, a cutoff tutt low just south of the region will
continue to shift westward towards the east central Caribbean,
while an upper ridge just north of the region will continue to
erode in response to a polar trough approaching the eastern
seaboard of the United States by Wednesday. This in turn, will
maintain a moderate to strong east to southeast wind flow aloft
along promoting marginally unstable condition due to the cooler
air aloft.

&&

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

For the rest of the morning, expect the prevailing east to northeast
trades to bring periods of passing low level clouds and showers
across the coastal waters, with some brushing the north and east
coastal areas from time to time. During the afternoon, the available
pockets of moisture along with local effects and daytime heating
will favor afternoon convection but mainly over portions the central
and southwest sections of Puerto Rico. For the rest of the islands
including the U.S. Virgin Islands shower activity if any should be
mainly on the west-end or just downwind of the islands, as mostly
fair weather conditions should prevail. Overall no significant or
widespread rainfall is anticipated, however a few of the afternoon
shower activity in the southwest may result in minor ponding of
water on roads and in poor drainage areas.

For Tuesday and Wednesday, recent model guidance continued to
suggest increasing trade wind moisture along with low level moisture
convergence and the cooler temperatures aloft to linger. This
pattern will therefore enhance morning shower activity along the
north and east coastal areas. The increasing moisture is also
suggested by higher precipitable water values which will be between
1.70 to near 2.00 inches also thus supporting a wetter patten with
good change for more frequent early morning and afternoon shower
activity each day across the islands. Afternoon showers will
therefore be enhanced and with better potential for thunderstorm
development along with periods of moderate to locally heavy rains
in and around the islands and over the coastal waters. That said
there will be a moderate to high chance for urban and small stream
flooding but mainly in isolated areas and especially along the
east, central and southwest section of Puerto Rico.


.LONG TERM...Thursday trough Tuesday...

An unsettled pattern is forecast for the long term period. On
Thursday, both model guidance continues to suggest the axis of an
upper level trough drifting westward and moving over Hispaniola,
providing some divergence aloft. This some unstable conditions
along with plenty of moisture with precipitable water values above
climatological normal will result in a rainy pattern over the
local region. The heaviest shower activity is expected for the
afternoon hours over the interior and northwestern sections of
Puerto Rico. That said, the development of this pattern will
result in urban and small stream flooding with the heaviest
shower activity. Additionally, urban flooding could be possible
for the San Juan metro area due to the southeasterly component in
winds. On Friday into Saturday, a ridge is expected to take the
place of the upper level trough and turn more stables the
conditions aloft. However, advective moisture will continue over
the area, as a building surface high pressure over the eastern
Atlantic dominate the moderate wind flow from the east-southeast.
This wind flow will push fragments of moisture over the CWA.
Taking all these factors into consideration, for the weekend,
cloudiness and shower activity is anticipated to continue each
afternoon. In terms of temperatures, near normal readings will
continue across the islands, with highs in the mid 80s to low 90s.

For Monday onward, a variable pattern is expected. In the upper
levels, a deepening polar trough, reflecting in the upper and mid
levels suggested by the model guidances would result in
divergence over the local area, thus, an increase in widespread
activity is very likely.

&&

.AVIATION...VFR conds durg the prd. Occasional tradewind SHRA
will continue ovr the regional waters en route btw islands and psbl
along the north and east coastal sections of the islands til 01/13Z
with SCT ocnl BKN lyrs nr FL025...FL050. SFC wnds...calm to lgt/vrb
bcmg E-NE 10-15 kts with sea breeze variations aft 01/14Z. Aftn
convection will affect mstly portions of ctrl mtn range of PR and
the SW sections of PR fm 01/16Z-22Z, with VCSH mainly at TJPS/TJMZ.
&&

.MARINE...

A northerly swell will continue to invade the local waters and
resulting in hazardous coastal conditions across all the north
exposed beaches of Puerto Rico. Therefore, there is a high risk of
rip current, including beaches across Culebra. For the rest of
the area the risk will remain moderate. Across the regional
waters, seas will remain between 5-6 feet and with winds up to 15
knots. Marine conditions will improve for the upcoming weekend. An
increase in shower and thunderstorm activity is expected for late
today into Tuesday.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 76 87 74 / 40 40 50 70
STT 87 76 87 74 / 30 40 60 60
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Re: Caribbean - Central America Weather

#20656 Postby cycloneye » Tue Nov 02, 2021 5:07 am

Area Forecast Discussion
National Weather Service San Juan PR
447 AM AST Tue Nov 2 2021

.SYNOPSIS...
Broad surface high pressure ridge across the western Atlantic will
continue to spread eastward into the central Atlantic through
Thursday. This will promote a prevailing northeast wind flow today,
then becoming more easterly by Wednesday and Thursday. Remnant
moisture fragments from old frontal shear lines will be transported
across the region by the prevailing trade winds through the end of
the week. In the upper levels, a TUTT low extending northwards
across the region from the eastern Caribbean, will continue to shift
westward into the east central Caribbean the next few days, while
maintaining a moderate to strong southerly wind flow and marginally
unstable conditions with cooler air aloft. A fairly moist and
unstable weather pattern is forecast Wednesday through Thursday.

&&

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

For the rest of the morning, the prevailing northeast trade winds
will bring occasional patches of clouds an accompanying showers to
the regional waters and parts of the islands from time to time. No
significant accumulations are expected. During the afternoon, the
available moisture along with local effects, daytime heating and
favorable conditions aloft will give way to afternoon convection
over the central and southwest sections of Puerto Rico as well as
portions of the northeast later in the afternoon and early evening.
For the rest of the islands periods of passing clouds and mostly
isolated showers can be expected including the U.S. Virgin Islands,
where the shower activity should be mainly on the west-end or just
downwind of the islands. Otherwise mostly fair weather conditions
should prevail. No widespread rainfall is anticipated for today,
however some of the afternoon convection in southwest Puerto Rico
may cause minor urban flooding as well as ponding of water on roads
and in poor drainage areas. Isolated afternoon thunderstorms will
also be possible in some areas in the central interior and
southwest sections of Puerto Rico.

For Wednesday and Thursday, recent model guidance continued to
suggest increasing low level moisture advection along with low level
convergence and continued unstable conditions aloft. This fairly
moisture environment along with the cooler temperatures aloft and
divergent pattern will support periods of enhanced convection across
the region for the rest of the short term. This expected pattern
will therefore increase the chance for showers and thunderstorm
development over the islands, but particularly along the north and
east coastal areas during the morning hours followed by enhanced
afternoon convection over parts of the interior and west to
southwest sections of Puerto Rico. Model guidance suggests a marked
increase in precipitable water values, peaking to slightly higher
than 2.00 inches Wednesday through Thursday. Consequently plenty of
moisture to maintain a somewhat active weather pattern with good
chance for more frequent early morning trade wind showers along with
afternoon shower activity each day across the islands. Afternoon
showers will be enhanced and with good potential for isolated
thunderstorm development along with periods of locally heavy rains
across portions of the islands and over the coastal waters.
Consequently ,there will be a moderate to high probability for urban
and small stream flooding but in isolated areas and especially along
the east, central and southwest sections of Puerto Rico.

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

Model guidances continues to suggest a strong deepening
upper level trough sinking southwestward into the central
Atlantic. This trough will reflect on almost all the levels and
will generate a surface trough far away over the central Atlantic,
generating a moderate east-southeast wind flow over the region.
This wind flow will result in advective moisture pattern and will
keep the available moisture moving in the area of the long term
period. This evolving pattern will turn favorable conditions for
shower development over the interior and western sections of
Puerto Rico each afternoon, as well the passing showers from time
to time in the morning and evening hours over the local waters and
windward sections. However, starting on Friday onwards, stable
conditions will prevail in the mid to upper levels as a westward
high pressure establish over the area.

In general, a seasonal pattern is expected for Friday through
Monday, with the typical afternoon shower activity due to the
local effects and diurnal heating. Then, on late Monday onwards,
the precipitable water values will remain near normal, and as a
result, less coverage in the shower activity is expected. Daytime
temperatures are expected to remain warmer between mid 80s to low
90s, due to the east-southeast wind flow over the forecast area.


&&

.AVIATION...VFR cond are expected at all terminals durg the prd.
Occasional SHRA with wdly SCT cld lyrs ovr regional waters and en
route btw islands. Some showers may move inland ovr E-NE Puerto Rico
with VCSH for TJSJ/Tist/TISX. Brief Mtn top obscr ovr Ern PR due to
low clds/-SHRA til 02/13Z. Sfc wnd calm to lgt/vrb bcmg ENE 10-15
kts with sea breeze variation aft 02/14Z. Afternoon convection
expected ovr the central interior and southwestern PR, with
VCSH/psbl VCTS for TJPS. VCSH also psbl at TIST/TJSJ/TJBQ durg
aftn. No other sig operational wx impact attm.

&&

.MARINE...Marine conditions will continue choppy as a northerly
swell persists over the offshore waters of Puerto Rico through at
least late today. As a result, seas will continue between 4-6 feet
across most of the local waters and passages with with up to 15
knots. Additionally,coastal conditions will continue hazardous and
a high risk rip current will remain in effect for all the north
exposed beaches of Puerto Rico and Culebra. For the rest of the
local beaches the risk will remain low to moderate. An increase in
isolated to scattered showers are expected to affect portions of
the local waters for the next few days.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 87 76 / 50 70 70 70
STT 87 76 87 76 / 40 70 60 60
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Re: Caribbean - Central America Weather

#20657 Postby cycloneye » Wed Nov 03, 2021 4:54 am

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Wed Nov 3 2021

.SYNOPSIS...

Unstable conditions will prevail for most of the short term
period. A upper level trough is expected to moves into a favorable
area for instability across the area through at least Thursday.
This unstable conditions aloft and the available moisture with
precipitable water values of 2.06 inches(GOES-16) will result in a
active afternoon with shower activity and isolated thunderstorms.
Therefore, expect ponding of water in roadways and poor drainage
areas, and urban and small stream flooding with the heaviest
activity. A seasonal pattern is expected for the long term period,
with the typical shower activity in the afternoon hours.

&&

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

TUTT low now centered across the Mona passage and extending
southwards into the eastern Caribbean will maintain cool
temperatures and unstable conditions aloft today into Thursday. The
Tutt is forecast to gradually weaken while lifting northeastwards
across the area through Friday. Surface high pressure ridge will
continue to shift eastwards towards the west central Atlantic while
a weakly induced surface through sets up and crosses the region
today into Thursday. This scenario along with a moist east-northeast
low level wind flow, will maintain a fairly active and unstable
weather pattern across the regional least into Thursday. The surface
winds are forecast to become more east southeast by Friday as the
Atlantic ridge spreads into the central Atlantic while sinking
southwards across the region.

For today and on Thursday, moist and unstable conditions will
persist with periods of scattered to numerous showers and isolated
thunderstorms expected to affect the islands and coastal waters.
Intervals of passing showers will continue to affect the coastal
waters and portions of the islands during the morning hours
producing periods of moderate to locally heavy rains mainly along
the north and east coastal areas. This may lead to minor ponding
of water on roads and in poor drainage areas but only in isolated
spots. During the afternoon hours, increasing low level moisture
convergence along with daytime heating and the unstable/divergent
upper level pattern will continue to support favorable conditions
for enhanced convection across portion of the islands and coastal
waters. Today the focus of the afternoon shower activity should be
over the central interior and west sections of Puerto Rico. A
better chance for increase convection and showers development over
parts of the east interior of Puerto Rico over the U.S. Virgin
islands is expected later in the afternoon and into early Thursday
as the upper per trough lift northwards across the region.
Afternoon showers and thunderstorms development over Puerto Rico
during the day will increase the chance for urban and small stream
flooding due to periods of heavy rains in isolated areas. over
the interior and west sections of Puerto Rico. Over the U.S.
Virgin Islands, only brief periods of passing showers is expected
most of the day. However, as previously mentioned during the late
afternoon and into Thursday expect an increasing chance for cloud
coverage and shower development in and around the islands. By then
this , this may lead to ponding of water on roads and in poor
drainage areas with the periods of moderate to locally heavy
rains.

By Friday, latest model guidance in agreement and all suggest
gradual weakening of the upper trough along with erosion of low
level moisture and diminishing instability aloft as an upper ridge
gradually builds across the region. This in turn will erode low
level moisture and increase the east to southeast tradewinds leading
to a more seasonal weather pattern. Expect sufficient advective
moisture however for the development of passing nocturnal showers
over the coastal waters with some affecting the portions of the
north and east coastal areas of the island. This will be followed by
isolated to scattered afternoon convection mainly over the west to
northwest and interior sections of Puerto Rico steered by the
prevailing east southeast wind flow. Lesser shower activity can be
expected for the rest of the forecast area including the U.S. Virgin
islands, and should be fast moving in the form of streamers as the
tradewinds are expected to increase as the local pressure gradient
gradually tightens across the region.

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

A seasonal pattern is expected to prevail for the long term
period. On Friday, the prevailing low level moisture with
precipitable water values near normal will combine with the local
effects, as a result, expect passing showers in the morning hours
over the local waters and the windward sections of the islands.
Then, the shower activity will drift more into the interior and
northwestern sections of Puerto Rico. This activity could result
in minor ponding of water in roadways and poor drainage areas. The
limiting factor for widespread shower activity in the afternoon
hours will be stable conditions aloft from a mid ridge establish
over the area. On Sunday into Monday, a upper level trough moving
northeastward will erode the upper level ridge and will create
some unstable conditions aloft with cooler temperatures at 500 mb.
That said, in afternoon hours, shower activity is expected to
become more intense, but the coverage will be affected of a low to
mid ridge. This instability in the upper levels is expected to be
for a short period, as the TUTT moves eastward on late Monday
afternoon, and the subsidence side will move over the area. After
that, on Monday onwards, a mid to upper levels ridge is forecast
to dominate the upper dynamics.

Model guidances suggest a slight decrease in the available
moisture over the forecast area for Monday into Wednesday. That
could result in less cloudiness and shower activity over the local
Islands, however, the local effects with the diurnal heating are
expected to be enough for the typical afternoon showers. The
activity would affect the southwestern sections of the island, as
the wind flow become more to the northeast influenced by a strong
building surface ridge moving eastward into the north-central
Atlantic. On Thursday, conditions will turn wet again with patches
of moisture moving over the region with precipitable water values
above normals, thus, shower activity is likely for the afternoon
hours.


&&

.AVIATION...VFR cond at all terminals durg the prd. FQT passing
SHRA with SCT-BKN lyrs ovr regional waters and en route btw islands.
Some showers will move inland ovr north and east coastal areas of PR
with VCSH for TJSJ/TIST/TISX. Brief Mtn top obscr ovr Ern PR due to
low clds/-SHRA til 03/12Z. Sfc wnd calm to lgt/vrb bcmg fm E 10-15
kts with sea breeze variation aft 03/14Z. Afternoon convection ovr
the central interior and western PR fm 03/16z-22Z, psbl VCTS at
TJSJ/TJMZ/TJPS and VCSH at the remaining terminals durg prd.
No other sig operational wx impact attm.

&&

.MARINE... Choppy marine conditions are expected to prevail mainly
over the Atlantic offshore waters, with seas up to 6 feet and
winds up to 15 knots from the east. Therefore, small craft
operators urge to exercise caution. For the rest of the local
waters and passages, seas will remain in 5 feet or less with winds
up to 15 knots. Marine condtions are expected to become more
tranquil for the night hours and for the rest of the week. An
increase in the frequency of shower is expected for today as a
upper level trough moves over the area and result in more shower
activity.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 86 76 / 50 70 50 40
STT 87 77 87 77 / 60 60 50 30
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Re: Caribbean - Central America Weather

#20658 Postby cycloneye » Thu Nov 04, 2021 5:10 am

Area Forecast Discussion
National Weather Service San Juan PR
516 AM AST Thu Nov 4 2021

.SYNOPSIS...
A Tutt will continue to lift east northeast and gradually weaken
across the region this morning into the afternoon hours,as a mid to
upper level ridge will build and spread across the area from the
west later today. A surface high pressure ridge will shift eastwards
into the east central Atlantic while a surface low and associated
cold front moves across the west and northwest Atlantic. This
pattern will maintain an east to southeast tradewind flow across
the area through Friday. The proximity of the weakening Tutt and
good moisture availability will continue to favor a moist and unstable
environment, sufficient for development of passing morning showers
followed by diurnal convection across portions of the islands today.
A more seasonal weather pattern is so far forecast for the long term,
with the typical passing nocturnal showers over the local waters
followed by limited diurnally induced afternoon shower activity
each day.

&&

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

A seasonal pattern is expected to prevail for most of the short term
period. In the surface (low-level), GOES-16 shows an area of
moisture with precipitable water values between 1.95 to 2.02 inches.
Meanwhile, a upper level trough will continue to move northeastward
as a upper level ridge builds and spread over the area. As the upper
ridge move northeastward, some diffluence in the upper level could
enhanced the instability aloft. As a result, the combination of the
aforementioned conditions could result in shower activity for today
and localize isolated thunderstorms activity in the afternoon hours.
The heaviest activity are forecast to affect the interior and
northwestern sections of Puerto Rico, where ponding of water in
roadways is expected, as well minor flooding with the heaviest
activity. For the U.S. Virgin Islands, a variably pattern of weather
is forecast with the typical passing showers and cloudiness in the
morning and evening hours.

For Friday onwards, a ridge will establish and reflect in the mid-
upper levels, this may affect the intensity and coverage of the
shower activity. Nevertheless, more low level patches of moisture
embedded in the trade winds will continue to reach the CWA. This
moisture are forecast to combine with the local and diurnal effects
and result in the typical shower activity focus over the
northwestern and interior sections of the islands, due to the wind
direction. On Saturday, model guidances suggest a slight decrease in
the available moisture over the forecast area. Given the presence of
the mid-level ridge and in some way the lack of moisture, that could
result in less cloudiness and shower activity over the local
Islands, however, the local effects with the diurnal heating are
expected to be enough for the typical afternoon showers over the
interior sections. Daytime temperatures are forecast to increase by
Friday into Saturday due to a southeasterly components in the winds.


.LONG TERM...Sunday through friday...
A seasonal pattern is expected to continue in and around the
islands For the early part of the long term period. Sunday into
Monday the broad mid to upper level ridge will hold across the
area and therefore limit nocturnal and diurnal convection across
the forecast area. However,the light to moderate easterly winds
will bring occasional patches of low level moisture across the
region resulting in periods of passing morning showers followed by
localized afternoon convection, mainly over parts of the interior
and western sections of Puerto Rico. Some of this activity may
result in ponding of Water in roadways and poor drainage areas due
to isolated areas of moderate to locally heavy rains. Mostly fair
weather conditions and sunny skies should prevail elsewhere.

By late Monday through Wednesday, a polar trough is forecast to move
northeastward across the western Atlantic. This will erode the upper
ridge forecast to be in place and therefore create marginally unstable
conditions aloft along with cooler 500 millibar temperatures. As a
result, afternoon shower activity should be more enhanced also due
to the weakening of the tradewind cap inversion and better local
and diurnal effects. However, widespread coverage and significant
rainfall accumulations are still not anticipated at this time as
recent model guidance all agree and continue to suggest limited
moisture advection across the region.

For Thursday through Friday winds are expected to become more
east to northeast and fairly light as a weakly induced surface
trough is forecast to set up across the region, in response to an
area of low pressure and associated cold front moving across the
western Atlantic, and a high pressure ridge moving farther
eastwards into The north central Atlantic. This overall scenario
should result in a somewhat wetter pattern as trade wind moisture
transport and low Level moisture convergence will return to the
region thus increasing the chance for more frequent passing morning
showers followed by better chance for convective development the
afternoon hours each day. As a result, urban and small stream flooding
will again be possible in isolated areas but mainly over the interior
and west sections of Puerto Rico during the afternoon hours.

&&

.AVIATION...VFR conditions expected across the local terminals. Some
passing showers will cause brief VCSH conditions for TJSJ, TIST and
TISX, in the morning hours. For TJBQ around 04/17z VCTS are forecast
due to the afternoon convection. Wind will remain light winds until
04/13z, but will increase after 04/14Z, from the east up to 15KT with
sea breeze variations. Light winds will return around 04/22z for most
of the TAF sites. No other sig operational wx impact attm.

&&

.MARINE...Choppy seas expected to continue with wave up to 6 feet
over the Atlantic offshore waters and 5 feet or less elsewhere.
Winds will be from the east at 10 to 15 knots. There is a moderate
risk of rip currents for northern facing beaches of PR, all beaches
of Culebra, and most beaches in Vieques. The USVI will also have
a moderate risk of rip currents, across all of St Thomas, northern
St John, and most of St Croix except the SW beaches.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 77 88 76 / 50 40 40 30
STT 87 76 87 77 / 50 50 30 40
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Re: Caribbean - Central America Weather

#20659 Postby cycloneye » Fri Nov 05, 2021 5:11 am

Area Forecast Discussion
National Weather Service San Juan PR
415 AM AST Fri Nov 5 2021

.SYNOPSIS...
A mid-upper level ridge will build and hold across the region
through the weekend. This will help to maintain a fairly strong
trade wind cap inversion and limit early morning and afternoon
convection. As a result, a more seasonal weather pattern is likely
and will promote mainly stable weather conditions, with some isolated
to scattered locally and diurnally induced showers and only a slight
chance for isolated thunderstorms development each afternoon. Light
to moderate easterly winds will prevail for the next several days.

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

An improvement in weather conditions is forecast to prevail for
the short term period. For today, according to GOES-16 PWAT
imagery the moisture content is expected to remain between 1.40
to 1.5 inches, as a fragment of clouds move across the region in
the early morning and early afternoon hours. This slight increase
in cloudiness and moisture will maintain the pattern of passing
showers over the local waters and windward sections of the
islands. Meanwhile, in the upper levels, a upper level trough is
expected to maintain very stable conditions aloft. As a result,
limited and short-live activity is expected to dominated the
weather pattern for this afternoon. However, the local effects and
the diurnal heating, will be enough for scattered showers over
the northwestern sections of Puerto Rico, resulting in ponding of
water in roadways and poor drainage areas. On Saturday, a mid-
upper ridge establish over the CWA will result in a more strong
trade wind inversion cap over Puerto Rico and local islands. This
will promote drier air and stable conditions aloft. This
conditions and the lack of moisture will result in a more dry
pattern. Nevertheless, afternoon convection is forecast for the
interior and western sections of Puerto Rico, due to the local
effects.

On Sunday, a surface high pressure across the central Atlantic
will cause the the local winds to be light to moderate from the
east- southeast. According to GFS model guidance, the moisture
content is expected to fluctuate below the climatological normals
with precipitable water vales around 1.10 inches. That in combination
with the presence of the mid level high pressure will inhibit the
enhanced shower or thunderstorm development. However, the local
effects could result in some afternoon convection. Daytime temperatures
are forecast to increase by Friday into Saturday due to a southeasterly
components in the winds.


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

A seasonal pattern is expected to persist through Monday as the mid
to upper level ridge will hold across the area and therefore limit
nocturnal and diurnal convection across the forecast area. A light
to moderate easterly wind flow will bring occasional patches of low
level moisture across the region resulting in periods of passing
morning showers. This will be followed by localized afternoon
convection, mainly over parts of the interior and western sections
of Puerto Rico. Overall fair weather conditions can be expected
elsewhere including over the U.S. Virgin islands where mostly fair
weather skies will prevail.

By Tuesday through Thursday the upper ridge will erode in response
to a polar trough moving northeastward across the west Atlantic.
This will aid in creating marginally unstable conditions aloft with
the trade wind inversion to slightly erode. As a result, afternoon
shower activity should be more enhanced mainly due to local and
diurnal effects. Widespread coverage and significant rainfall
accumulations are still however not anticipated at this time as
recent model guidance all continue to suggest only occasionally
patches of trade wind moisture to move across the region in the
prevailing moderate easterly wind flow. Consequently other than
passing early morning showers over the coastal waters , afternoon
convection should also be focused over parts of the interior and
west to northwest sections of Puerto rico with mostly fair weather
skies to prevail in and around the U.S. Virgin Islands.

For Friday and into the weekend winds are expected to become more
east to northeast and fairly light as a weakly induced surface
trough is forecast to set up and cross the region. This is in
response to an area of low pressure and associated cold front moving
across the western Atlantic, and a high pressure ridge moving
farther eastwards into The north central Atlantic. This overall
scenario should result in a somewhat wetter pattern as trade wind
moisture transport and low Level moisture convergence will return to
the region thus increasing the chance for more frequent passing
morning showers as the tradewinds gradually increase. This will be
followed by a better chance for convective development during the
afternoon hours each day. The activity by then should be focused
over the central interior and west to northwest sections of Puerto
Rico steered by the prevailing east to southeast winds. Activity
for the rest of the region should be limited with mostly isolated
afternoon showers possible in and around the U.S. Virgin islands
but mainly downwind and on the west-end, in the form of streamers
and of short duration.

&&

.AVIATION...VFR conditions expected across the local terminals.
VCSH expected at TJSJ until 05/14Z. Aftn convection fm 05 /17z-
22z would result in VCSH mainly at TJMZ/TJBQ. SCT ocnl BKn cld
lyrs nr FL025..FL050 with wdly SCT SHRA en route btw islands. Wind
will remain light, increasing to up to 15 KT fm E with sea breeze
variations. No other sig operational wx impact attm.

&&

.MARINE...Seas of 5 feet or less are anticipated across the local
Atlantic waters and passage waters today. For the Caribbean waters
seas will generally be 3 feet or less.

There is a moderate risk of rip currents for beaches of northern
Puerto Rico, as well as most beaches of Vieques and St Croix and
some of the northwest beaches of St Thomas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 77 88 75 / 30 30 40 20
STT 88 76 87 76 / 40 40 40 20
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cycloneye
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Re: Caribbean - Central America Weather

#20660 Postby cycloneye » Sat Nov 06, 2021 7:05 am

Area Forecast Discussion
National Weather Service San Juan PR
514 AM AST Sat Nov 6 2021

.SYNOPSIS...Easterly trade winds with some variations in direction
and moisture content will continue to bring passing showers from
time to time across the area. The wettest period appears to be
Monday night and Tuesday, but dry mid layers will impede very
heavy amounts and greatly reduce the chances of thunderstorms.


&&

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

A mid-upper level ridge will maintain a relatively dry and
stableenvironment acrossthe northeast Caribbean through at
least early next week. The high pressure aloft will hold over the
forecast area while strengthening during the weekend. In terms of
moisture, operational models suggest that the precipitablewater
values across the local area will remain below normal, ranging
between 1.0-1.5 inches. In addition to these dry and stable
conditions, the warm mid- level temperatures will likely suppress
the development of thunderstorms across the region through early
next week. However, remnants of an old frontal boundary
carriedin on the trade winds will reach the U.S. Virgin Islands
and eastern Puerto Rico at times. Under this pattern, only light
accumulations are anticipated through at least Monday.

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

High pressure at the surface over the central Atlantic Ocean will
maintain moderate easterly flow across the area with limited
variations. Patches of moisture will cross through with
alternating moist and dry patterns in the lower levels, but the
mid layers of the atmosphere remain dry pretty much between 700
and 300 mb through the end of the period. This will bring steady
temperatures and passing showers to Puerto Rico and the U.S.
Virgin Islands with precipitable water values that alternate
between 1.2 and 1.8 inches on a daily though irregular basis.
Although flooding is not expected during the next 7 days, showers,
some locally heavy are possible across the area, especially over
eastern Puerto Rico during the night and early morning hours and
over western Puerto Rico during the afternoons.

&&

.AVIATION...VFR conditions will prevail through the forecast period.
Wx conditions are fairly stable across the local area, therefore no
significantimpacts to operations are anticipated during the
weekend. SHRA, if any, will form near TJBQ and TJMZ. As a result,
VCSH was included at TJBQ between 17Z-21Z. E to ESE winds of 10-20
kts will continue below FL150.


&&

.MARINE...Wave heights will remain around 3 to 5 feet in the
unprotected waters and a northeasterly swell through mid week next
week.Small craft advisories are not expected during the next 10
days. There could be a high risk of rip currents next weekend for
the eastern tip of Saint Croix, otherwise most northern coasts
will have a moderate risk of rip currents.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 75 88 75 / 30 20 20 10
STT 87 76 86 77 / 30 20 20 10
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