Caribbean - Central America Weather

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cycloneye
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Re: Caribbean - Central America Weather

#19101 Postby cycloneye » Fri Nov 24, 2017 5:54 am

Area Forecast Discussion
National Weather Service San Juan PR
452 AM AST Fri Nov 24 2017

.SYNOPSIS...An upper level ridge dominates and moderates activity
in the pattern. A weak trough leaving the area will increase
shower activity-- mainly across northwest Puerto Rico this
afternoon. Drier weather will follow over the weekend, then a
moisture patch will pass through before general moisture
increases considerably Tuesday through Thursday.

&&

.SHORT TERM...Today through Sunday
Model guidance indicates moisture will move in from the east and
keep precipitable water values near 2.0 inches today. Later today
a trough of low pressure will move to the west of Puerto Rico
which will shift surface winds to an east southeast to southeast
direction. Isolated showers are expected across the the U.S.
Virgin Islands and Puerto Rico during the afternoon and evening
hours with the strongest showers over portions of northwestern
Puerto Rico. This activity is dependent on the surface winds
becoming more southerly today. At the mid to upper levels a
strong ridge of high pressure will suppress thunderstorm growth
across the region. Water Vapor imagery overlaid with 500 to 200
mb heights shows drier air in the mid to upper levels which also
coincides with San Juan Skew-T sounding last night.

Saturday, the moisture surge will be replaced by drier air, but
scattered showers will be possible across the northwest interior
Saturday afternoon. Sunday, models indicates a small patch of
moisture will grow southeast of the area and cross the island of
Puerto Rico but confidence is low in such fine detail.

.LONG TERM...Monday through Saturday... A patch of moisture
develops just southeast of Puerto Rico and moves onto the island
during the day. Then ridging at 700 mb dries the pattern out for
another 12 to 24 hours. Then modest moisture then prevails through
the end of the work week. At upper levels high pressure dominates
the southern Caribbean and a deep polar trough over the United
States shears out and moves across the Atlantic in a greatly
weakened condition, passing just to the north accompanied by an 65
knot jet late Wednesday. The trough passage at upper levels will
enhance shower activity somewhat with good precipitable water
values, but dynamics are weak. The jet will hang just south of the
area in northwest flow until it lifts back across the area on
Saturday. Patchy moisture Thursday through Saturday will bring
showers but mainly in the west and interior portions of Puerto
Rico.

&&

.AVIATION...VFR conditions will prevail across all terminal
sites through the rest of the period. But VCSH is possible across
most terminal sites by 23/15Z with MVFR possible at TJMZ due to
isolated VCTS. SFC winds prevailing out of the E at 5 to 10 kts
through the period. FL250 TO FL500 winds out of the west at 15 to
30 kts.

&&

.MARINE...7 foot seas relaxed during the day on Thursday, and seas
will follow a downward trend during much of the next 7 days. No
small craft advisories are foreseen through the end of November.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 78 87 75 / 40 40 40 10
STT 85 77 86 74 / 40 40 30 20
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Re: Caribbean - Central America Weather

#19102 Postby cycloneye » Fri Nov 24, 2017 5:30 pm

Area Forecast Discussion
National Weather Service San Juan PR
522 PM AST Fri Nov 24 2017

.SYNOPSIS...Mid to upper level ridge will continue for the next
several days. Drier air and fair weather will persist through the
weekend. Overall moisture will increase by mid-week next week as
an induce trof moves over the area.

&&

.SHORT TERM...Today through Sunday...Showers and isolated
thunderstorms over western Puerto Rico are expected to diminish
during the evening hours. Ridge aloft and a drier air mass will
move over the region during the weekend. This will limit shower
activity across the islands. Therefore, mostly sunny to partly
cloudy skies will prevail with shallow afternoon convection over
sections of western PR during the afternoon hours. An east to
southeast wind flow will keep day time temperatures between the
high 80s to low 90s across the lower elevations. Overnight
temperatures will drop to the low 60s across the higher
elevations.


.LONG TERM...From previous forecast...Monday through Saturday...
A patch of moisture develops just southeast of Puerto Rico and
moves onto the island during the day. Then ridging at 700 mb dries
the pattern out for another 12 to 24 hours. Then modest moisture
then prevails through the end of the work week. At upper levels
high pressure dominates the southern Caribbean and a deep polar
trough over the United States shears out and moves across the
Atlantic in a greatly weakened condition, passing just to the
north accompanied by an 65 knot jet late Wednesday. The trough
passage at upper levels will enhance shower activity somewhat with
good precipitable water values, but dynamics are weak. The jet
will hang just south of the area in northwest flow until it lifts
back across the area on Saturday. Patchy moisture Thursday through
Saturday will bring showers but mainly in the west and interior
portions of Puerto Rico.


&&

.AVIATION...VFR conds...SCT-BKN lyrs nr FL025...FL050 with VCSH
at most terminals til 24/23z. Few SHRA en route btw islands and ovr
coastal waters. Few tops nr FL150. L/lvl wnds fm E-NE 10-15 kts blo
FL250...SFC wnds mainly fm E 5-15 kts...except for local sea breeze
variations. No sig wx impacts at local terminals attm.


&&

.MARINE...A 4-5 feet northeast swell is expected to reach the
local waters on Sunday. This will cause a moderate to high risk of
rip currents across the Atlantic beaches of the islands. Overall,
seas should continue between 3-5 feet across the offshore waters
and passages and at 4 feet or less across the nearshore waters of
the islands. East winds will continue between 5-15 knots.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 87 77 / 40 40 40 10
STT 85 77 86 75 / 40 40 30 20
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Re: Caribbean - Central America Weather

#19103 Postby cycloneye » Sat Nov 25, 2017 5:42 am

Area Forecast Discussion
National Weather Service San Juan PR
532 AM AST Sat Nov 25 2017

.SYNOPSIS...Mid-level dryness will continue through mid-week next
week, keeping transient patches of low level moisture from
generating any more than passing showers under upper level
ridging. There are some indications that a front may be able to
pass through the area late next week bringing a better chance of
rain to the islands.

&&

.SHORT TERM...Today through Monday...
The Puerto Rico 25/00Z sounding and model guidance indicate low
level moisture has lingered from Friday`s moisture surge from the
west. This is also evident by scattered showers moving across the
U.S. Virgin Islands and eastern Puerto Rico early this morning.
At the surface easterly to southeasterly trade winds at 5 to 10
mph will cause showers across portions of interior and northwest
Puerto Rico during the afternoon and early evening hours.
Elsewhere isolated showers will diminish during the afternoon
hours across portions of eastern Puerto Rico and the U.S. Virgin
Islands.

Similar to previous days the mid to upper levels of the atmosphere
remain relatively dry due to an upper level ridge of high
pressure that has entrenched itself over the forecast area. This
ridge has stunted thunderstorm development by creating sinking
motion at the mid to upper levels of the atmosphere over the
islands.

On Monday a long wave trough to the west of Puerto Rico will
cause the the upper level ridge to shift eastward away from the
islands. Then low level moisture will return and will prevail out
of the southeast which will trigger more showers.

.LONG TERM...Tuesday through Friday...
Relatively high precipitable water values will continue over the
forecast area Monday night through Thursday. The long wave trough
over Florida on Tuesday leans into the western Atlantic and
becomes strongly positively tilted by Wednesday. As it does so it
weakens considerably. Nevertheless the jet that passes south of
it and the trough axis will cross over Puerto Rico and the U.S.
Virgin Islands on Thursday afternoon. At this time it is expected
to generate some good divergence aloft over eastern Puerto Rico
just after a maximum in moisture occurs. This means that showers
will increase Monday night through Thursday as dynamics become
more favorable and mid level moisture returns from the southwest.
For Friday and beyond, although the jet remains close to the
area, dynamics are weak and moisture falters somewhat from the
higher values, leaving showers, but no extraordinary conditions
other than the possibility of the first frontal passage of the
season several days into December, that will not bring much
clearing or drying.

&&

.AVIATION...VFR conditions will prevail across all terminal
sites through the rest of the period. But VCSH is possible across
most terminal sites by 25/16Z due to patches of low level moisture
moving in from the east. Some brief MVFR is possible over TJMZ
from 25/17-21Z with mtn obscurations in most of the higher terrain
of Puerto Rico. sfc winds prevailing out of the E at 5 to 10 kts
through the period with sea breeze variations and ocnl 15 kt with
higher gusts. Maximum winds are WNW at 40 kt at 26/12Z at FL410.

&&

.MARINE...With the strongest weather features remaining in the
northwest part of the Atlantic seas will continue at 5 feet or
less through next week. Small craft advisories are not
anticipated.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 78 88 77 / 40 10 10 30
STT 85 76 85 75 / 30 20 10 20
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Re: Caribbean - Central America Weather

#19104 Postby cycloneye » Sat Nov 25, 2017 4:23 pm

Area Forecast Discussion
National Weather Service San Juan PR
350 PM AST Sat Nov 25 2017

.SYNOPSIS...A seasonal weather pattern will continue to prevail
across the forecast area during the next few days. Although ridge
aloft will continue to hold, patches of low level moisture are
expected at times. The chance for shower activity will increase
by midweek next week.

&

.SHORT TERM...Tonight thru Mon...

Mostly sunny to partly cloudy skies prevailed across the forecast
area throughout the day with a few showers noted across the
western interior of Puerto Rico in the afternoon. Coastal temps
were in the mid to upper 80s under easterly winds at 15 mph or
less. Although a mid to upper level ridge will continue to hold
across the forecast area, easterly winds will continue to bring
patches of low level moisture at times. Therefore, expect a fair
and generally stable weather pattern with a few morning and late
evening passing showers across the USVI and eastern PR. Locally
induced afternoon showers across western sections of Puerto Rico
cant be ruled out each afternoon.

.LONG TERM...Tue thru Sun/issued 532 AM AST Sat Nov 25 2017/

Long wave trough over Florida on Tuesday leans into the western
Atlantic and becomes strongly positively tilted by Wednesday. As
it does so it weakens considerably. Nevertheless the jet that
passes south of it and the trough axis will cross over Puerto Rico
and the U.S. Virgin Islands on Thursday afternoon. At this time
it is expected to generate some good divergence aloft over eastern
Puerto Rico just after a maximum in moisture occurs. This means
that showers will increase by midweek as dynamics become more
favorable and mid level moisture returns from the southwest. For
Friday and beyond, although the jet remains close to the area,
dynamics are weak and moisture falters somewhat from the higher
values, leaving showers, but no extraordinary conditions other
than the possibility of the first frontal passage of the season
several days into December, that will not bring much clearing or
drying.

&&

.AVIATION...VFR conds...SCT-BKN lyrs nr FL025...FL050 with VCSH
at most terminals til 25/23z. Few SHRA en route btw islands and
ovr coastal waters. L/lvl wnds fm E 10-15 kts blo FL300...SFC
wnds mainly fm E 5-10 kts...except for local sea breeze
variations...bcmg lgt/vrb aft 25/23z. No sig wx impacts at local
terminals attm.

&&

.MARINE...A 4-5 feet northeast swell is expected to reach the
local waters on Sunday. This will cause a moderate to high risk
of rip currents across the Atlantic beaches of the islands.
Overall, seas should continue between 3-5 feet across the offshore
waters and passages and at 4 feet or less across the nearshore
waters of the islands. East winds will continue between 5-15
knots.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 78 88 77 87 / 20 20 30 30
STT 76 85 75 86 / 40 20 20 20
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Re: Caribbean - Central America Weather

#19105 Postby cycloneye » Sun Nov 26, 2017 7:10 am

Area Forecast Discussion
National Weather Service San Juan PR
517 AM AST Sun Nov 26 2017

.SYNOPSIS...

Mid-level dryness will continue until Wednesday with patches of
low level moisture creating isolated showers under a strong upper
level ridge. At this time model guidance is showing a front
passing through the forecast area late next week which will
increase rain chances across the islands Wednesday through
Saturday.

&&

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

The MIMIC product and the low level 7.34 micron water vapor
imagery showed drier air moving through the U.S. Virgin Islands
and into Puerto Rico early this morning. Showers were also
weakening over eastern Puerto Rico and the Caribbean waters just
west of the USVI. Clouds were thinning over the area as they moved
west. Precipitable water is expected to reach a minimum just
after noon and may drop briefly below 1 inch according to the GFS.
The 26/00z sounding from San Juan showed an inversion accompanied
by a dry slot from 6900 to 9800 feet and this was stopping most
cloud growth in the area. Relative humidities do not return to 50
percent until almost 35 kft. The atmosphere at mid levels only
slowly recovers good moisture by Wednesday 29/12Z. During the
period, the upper level ridge moves into the Leeward Islands from
almost over Puerto Rico and a few weak perturbations run over the
top today through Tuesday with little effect. This will yield only
isolated showers over most of the forecast area through Monday
and some increase in showers on Tuesday. Local effects may produce
scattered showers each day in western or northwestern Puerto
Rico, but elsewhere accumulations will be minor.


.LONG TERM...Wednesday thru Monday....

A positively tilted longwave trough on Wednesday will move off
into the Gulf of Mexico and the Atlantic waters. This trough will
bring a strong jet of 80 to 90 kts across Puerto Rico during the
middle of the week. GFS and ECMWF models show weak perturbations
in the flow Wednesday through Friday. These perturbations combined
with easterly trade winds at the surface will trigger showers
across Puerto Rico and the U.S. Virgin Islands. Divergence aloft
remains weak through the period so the only trigger for showers
will be low level moisture, weak disturbances in the flow and
local orographical effects.

Friday, the GFS and ECMWF are picking up on a weak short wave
north of the forecast region. If this short wave does occur, it
could increase instability across the area which could help bring
isolated thunderstorms to the northern Puerto Rico and the
Atlantic waters. During the weekend there is a possibility that we
will see the first frontal passage of the season several days
into December.

&&

.AVIATION...With drier air now approaching Puerto Rico from the
east, VFR conds are expected at all TAF sites through 27/04Z except
at TJMZ where brief MVFR due to CIGS may occur. Sct SHRA are
expected to dvlp aft 26/17Z in wrn PR and hir trrn may be obscured.
Winds are east at 5 to 15 kt at the sfc with sea/land breeze
influences. Winds alf are easterly 10-20 kt up through FL170
southerly thru FL300 and westerly up to FL460. Maximum winds
280/45kt at FL410 arnd 27/06Z.


&&

.MARINE...A 4-5 feet northeast swell is expected to reach the
local waters today. This will cause a moderate to low risk of rip
currents across the Atlantic beaches of the islands. Overall,
seas should continue between 3-5 feet across the offshore waters
and passages and at 4 feet or less across the nearshore waters of
the islands. East winds will continue between 5-15 knots.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 87 76 / 30 30 30 30
STT 85 75 86 76 / 40 40 10 20
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Re: Caribbean - Central America Weather

#19106 Postby cycloneye » Mon Nov 27, 2017 5:35 am

Area Forecast Discussion
National Weather Service San Juan PR
503 AM AST Mon Nov 27 2017

.SYNOPSIS...Drier conditions will last through Wednesday, then
moisture will return to the forecast area. A short wave trough
will cause the upper level ridge to flatten and allow tropical
moisture to return across Puerto Rico and the U.S. Virgin Islands.


&&

.SHORT TERM...Light trade wind showers moved at times across portions of the U.S.
Virgin Islands and eastern Puerto Rico during the overnight hours.
However, no significant rainfall amounts were observed. Upper ridge
and dry mid levels will continue to suppress/limit convection across
the islands. Best chance for showers is during the afternoon hours
over portions of western Puerto Rico each day, increasing on
Wednesday as an upper trof approaches from the western Atlantic.

Otherwise, light showers embedded on the trade winds should continue
at times to move across the regional waters and briefly over land
areas. High temperatures for the next few days are expected to be in
the mid to upper 80s across the lower elevations and from the low
70s to low 80s across the higher elevations. Overnight temperatures
are expected to reach the low 60s across the higher elevation to
the mid 70s across coastal areas.

.LONG TERM...Thursday through Tuesday....A positively tilted long
wave trough will be in the Atlantic waters on Thursday. This
trough will bring a jet of 50 to 60 kts across the islands through
Sunday. On Friday a short wave trough will form north of Puerto
Rico and cause surface winds to veer to the southeast. These
veering winds late Thursday and Friday will bring moist tropical
air across Puerto Rico and the U.S. Virgin Islands thus increasing
precipitable waters values. Divergence aloft remains weak through
the period so the only trigger for showers will be low level
moisture, the induced trough and local orographically effects.


&&

.AVIATION...Mainly VFR conditions will prevail during the next 24
hours. However, -SHRA developing over western PR this afternoon
could affect the vcty of TJBQ/TJMZ. Sfc winds will prevail from the
east at 10-15 kts with sea breeze variations aft 15z.


&&

.MARINE...A 4-5 feet northerly swell will continue to invade the
local waters and cause a moderate to high risk of rip currents
across the north facing beaches of the local islands. Easterly
winds will continue between 5-15 knots.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 87 77 / 20 20 30 30
STT 83 79 83 79 / 30 30 40 40
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Re: Caribbean - Central America Weather

#19107 Postby cycloneye » Mon Nov 27, 2017 4:32 pm

Area Forecast Discussion
National Weather Service San Juan PR
416 PM AST Mon Nov 27 2017

.SYNOPSIS...Drier than normal moisture will prevail over the local
area through Tuesday, with moisture increasing on Wednesday
morning. The upper ridge is still expected to flatten by midweek.
Shower activity is expected to increase slightly for the latter
part of the week.

&&

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

Fair weather has prevailed today across the local
area and is expected to continue through Tuesday. Scattered
showers are expected this afternoon across western PR and then
some brief showers are possible across the local waters, USVI and
eastern PR tonight and Tuesday morning, then some showers across
western PR Tuesday afternoon as well. Due to the relatively dry
air over the area, these showers are not expected to produce
flooding. Moisture returns on Wednesday and the shower activity
and coverage is expected to increase a bit, but the upper levels
will not be conducive for long lasting showers or thunderstorm
development. Winds will be from the ESE to E at 10-15 mph for the
most part with sea breeze variations during the daytime.

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

.From previous discussion...

A positively tilted long
wave trough will be in the Atlantic waters on Thursday. This
trough will bring a jet of 50 to 60 kts across the islands through
Sunday. On Friday a short wave trough will form north of Puerto
Rico and cause surface winds to veer to the southeast. These
veering winds late Thursday and Friday will bring moist tropical
air across Puerto Rico and the U.S. Virgin Islands thus increasing
precipitable waters values. Divergence aloft remains weak through
the period so the only trigger for showers will be low level
moisture, the induced trough and local orographically effects.

&&

.AVIATION...Mainly VFR conditions will prevail during the next 24
hours across the local flying area. However, SHRA developing over
western PR late this afternoon could affect the vcty of TJBQ/TJMZ.
Sfc winds will prevail from the east at 10-15 kts with sea breeze
variations. After 27/23Z only VCSH are possible across the Leewards,
USVI and TJSJ TAF sites.


&&

.MARINE...A 3-5 feet northerly swell is expected to continue to
affect the local waters and cause a moderate to high risk of rip
currents across many beaches of the local islands through
Wednesday. East to ESE winds will continue between 5-15 knots
tonight and Tuesday.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 76 87 77 87 / 20 30 30 30
STT 79 83 79 83 / 30 40 40 30
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Re: Caribbean - Central America Weather

#19108 Postby cycloneye » Tue Nov 28, 2017 5:28 am

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Tue Nov 28 2017

.SYNOPSIS...

Drier than normal moisture will prevail over the local
area through Tuesday, with moisture increasing on Wednesday
morning. The upper ridge is still expected to flatten by midweek.
Shower activity is expected to increase slightly for the latter
part of the week.

&&

.SHORT TERM...

Fair weather conditions are expected to prevail today due to ridge
aloft and dry mid levels. Showers are expected to develop over
western PR this afternoon due to day time heating and sea breeze
convergence. However, this activity should be light to moderate as
moisture is very limited and there is no upper level forcing. High
temperatures are expected to range from the mid to upper 80s across
the lower elevations and from the low 70s to low 80s across the
higher elevations. Overnight temperatures are expected to reach the
low 60s across the higher elevation to the mid 70s across coastal
areas.

On Wednesday and Thursday, an upper level trof will move to the
north of the area as the ridge erodes. This will allow for low level
moisture content to increase across the region. A weak easterly
perturbation is expected to reach the USVI and eastern PR coastal
areas by 06z on Wednesday and moisture will linger over the region
through early Thursday morning. Therefore, shower coverage is
expected to increase on Wed afternoon across the interior and
western sections of PR. Although the ridge collapses...no
significant upper level forcing will be present and therefore
decided to keep thunderstorms out of the forecast.

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

A long wave trough will move into the Atlantic waters but remain
to the north of the Islands. This trough will cause the upper
level ridge that has brought fairly nice weather to Puerto Rico
and the U.S. Virgin islands to flatten south of the islands on
Thursday. Weak pertubations within the flow and an induced trough
will form and move northeast of Puerto Rico which will trigger
showers across the forecast area starting on Friday through the
weekend. Divergence aloft remains weak through the period so the
only trigger for showers will be low level moisture, the induced
trough and local orographically effects. At the surface low level
winds will be out of the east to southeast at 5 to 10 mph.

Currently our confidence is low regarding the precipitation
across the region due to GFS and ECMWF guidance reducing the rain
across the area Friday and Saturday. The previous mentioned
models have decreased the amount of tropical moisture across the
area too. Also, both models indicate precipitable waters values
falling between 1.0 to 1.5 during this period which falls in the
25th percentile for climatology. Monday another long wave trough
will move into the Caribbean and Atlantic waters with the
possibility for showers and isolated thunderstorms.



&&

.AVIATION...

Mainly VFR conditions will prevail during the next 24
hours. However, iso-sct SHRA developing over western PR this
afternoon could affect the vcty of TJBQ/TJMZ. Winds will prevail
from the east-southeast at 5-15 kts blo FL150, sea breeze variations
mainly across west/northwest PR after 15z.


&&

.MARINE...

A 3-5 feet northerly swell is expected to continue to
affect the local waters and cause a moderate to high risk of rip
currents across many beaches of the local islands through
Wednesday. East to ESE winds will continue between 5 to 15 knots
today and Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 87 76 / 30 30 30 40
STT 81 80 81 79 / 40 40 30 30
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Re: Caribbean - Central America Weather

#19109 Postby cycloneye » Tue Nov 28, 2017 3:34 pm

Area Forecast Discussion
National Weather Service San Juan PR
359 PM AST Tue Nov 28 2017

.SYNOPSIS...Conditions continue drier than normal for the rest of
today with a patch of higher moisture quickly passing through on
Wednesday morning, before drier air moves once again for the rest
of the next several days thereafter. Surface high pressure north
of the local area will drift east for the next couple of days.
Upper levels continue to be stable, which will inhibit
thunderstorm development over the local area.

&&

.SHORT TERM...Today through Thursday...
Fair weather is expected across the local area for the next
several days with mainly brief showers affecting the islands. The
only exception may be on Wednesday morning when a patch of
moisture moves in and shower activity may increase during those
hours. Having said that, mainly scattered and passing showers is
what is expected.Thereafter, as the moisture decreases and the
atmosphere continues to be relatively stable, brief showers in the
morning and evening hours with scattered showers across areas of
sea breeze convergence is what is expected.

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

.From Previous discussion...

A long wave trough will move into the Atlantic waters but remain
to the north of the Islands. This trough will cause the upper
level ridge that has brought fairly nice weather to Puerto Rico
and the U.S. Virgin islands to flatten south of the islands on
Thursday. Weak pertubations within the flow and an induced trough
will form and move northeast of Puerto Rico which will trigger
showers across the forecast area starting on Friday through the
weekend. Divergence aloft remains weak through the period so the
only trigger for showers will be low level moisture, the induced
trough and local orographically effects. At the surface low level
winds will be out of the east to southeast at 5 to 10 mph.

Currently our confidence is low regarding the precipitation
across the region due to GFS and ECMWF guidance reducing the rain
across the area Friday and Saturday. The previous mentioned
models have decreased the amount of tropical moisture across the
area too. Also, both models indicate precipitable waters values
falling between 1.0 to 1.5 during this period which falls in the
25th percentile for climatology. Monday another long wave trough
will move into the Caribbean and Atlantic waters with the
possibility for showers and isolated thunderstorms.


&&

.AVIATION...Mainly VFR conditions will continue to prevail across
the local flying area for the next 24 hours. However, SHRA will
develop this afternoon over western PR inducing VCSH across TJBQ
and TJMZ. Surface winds will continue from the east to east-
southeast at 10-15 kts decreasing to around 10 mph after 28/23Z.
Only VCSH are possible across the Leewards, USVI and TJSJ TAF
sites overnight.

&&

.MARINE...A 3-4 foot northeasterly swell will continue to affect
the local waters and cause a moderate to high risk of rip currents
across many beaches of the local islands through Wednesday. East
winds will prevail between 5 to 15 knots today through Wednesday.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 77 87 76 86 / 20 20 30 10
STT 80 81 79 80 / 30 30 20 10
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Re: Caribbean - Central America Weather

#19110 Postby cycloneye » Wed Nov 29, 2017 5:31 am

Area Forecast Discussion
National Weather Service San Juan PR
508 AM AST Wed Nov 29 2017

.SYNOPSIS...A surge in low level moisture will favor better
chances for showers this afternoon across western PR. Drier
conditions return on Thu-Fri. Another small surge in moisture is
expected on the weekend and early next week, but a fair weather
pattern will persist for the next several days.

&&

.SHORT TERM...Today through Friday...
Satellite imagery and model guidance showed a fair weather pattern
through at least Friday. A surge of moisture increased trade wind
showers across the islands overnight, this moisture is expected to
erodes through the morning hours. For the afternoon, some showers
are expected to develop across the western sections during the
afternoon, elsewhere sunny skies with little or no shower activity.
In general, a dry air mass with a relative stable atmosphere will
result in brief showers in the morning and evening hours with
scattered showers across the western sections due to sea breeze
convergence.

.LONG TERM...Saturday to Thursday...

Low level moisture increases somewhat during the weekend and this
will only favor scattered showers across the western interior
portions of PR. Zonal flow aloft will then persist from Mon-Wed
with a ridge building late in the forecast period. This will
continue to inhibit widespread shower activity across the region.
Although PWAT content will increase, it will remain below
climatology values. Best chance for showers during the long range
period will be across the western sections of PR where diurnally
induced afternoon showers are expected to develop each day. Light
to moderate trade wind showers will continue at times moving
mainly across the Caribbean waters and over portions of the USVI
and eastern PR. Overall, fair weather conditions are expected to
continue through the long term period.


&&

.AVIATION...Mainly VFR conditions will continue to prevail
across the local flying area for the next 24 hours. SHRA could
develop this afternoon over western PR affecting the VCTY of
TJBQ/TJMZ. Surface winds will continue from the E to ESE at around 5
kts increasing at around 10 kt with sea breeze variations after
29/13Z.


&&

.MARINE...Seas will range between 3-5 feet across the offshore
waters and less than 4 feet across the nearshore waters of the
islands. Light to moderate easterly winds will continue for the
next several days. A long period northeasterly swell between 3-4
feet will result in a high rip current risk across the northwest
to north central beaches of Puerto Rico. Moderate risk continues
for much of the north and east facing beaches of the islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 87 75 / 20 10 10 10
STT 86 76 85 75 / 30 20 10 20
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Re: Caribbean - Central America Weather

#19111 Postby cycloneye » Wed Nov 29, 2017 3:31 pm

Area Forecast Discussion
National Weather Service San Juan PR
357 PM AST Wed Nov 29 2017

.SYNOPSIS...Drier than normal available moisture will once again
filter in tonight through Friday. Easterly winds to continue for
the rest of today and Thursday but light winds expected late
Thursday into Friday as a surface low develops north of the local
islands.

&&

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

Afternoon showers occurred today across the western
sections of PR due to local effects combining with the available
moisture. A patch of moisture passed through the islands today but
drier air is already moving in. The general pattern through Friday
is expected to be that of mainly fair weather with isolated to
scattered and brief showers across the USVI and eastern PR in the
morning and overnight hours with a slight chance of showers across
western PR in the afternoons. Winds will remain from the east at
10-15mph with sea breeze variations. There is really no particular
feature that would disrupt this pattern through Friday, with the
exception of a sfc low developing just north of the local islands
which will cause the winds to diminish on Friday.

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

.From Previous discussion...

Low level moisture increases somewhat during the weekend and this
will only favor scattered showers across the western interior
portions of PR. Zonal flow aloft will then persist from Mon-Wed
with a ridge building late in the forecast period. This will
continue to inhibit widespread shower activity across the region.
Although PWAT content will increase, it will remain below
climatology values. Best chance for showers during the long range
period will be across the western sections of PR where diurnally
induced afternoon showers are expected to develop each day. Light
to moderate trade wind showers will continue at times moving
mainly across the Caribbean waters and over portions of the USVI
and eastern PR. Overall, fair weather conditions are expected to
continue through the long term period.


&&

.AVIATION...Mainly VFR conditions will continue to prevail across
the local flying area for the next 24 hours. SHRA could develop late
this afternoon over western PR affecting the VCTY of TJBQ/TJMZ with
only VCTY SHRA expected elsewhere. Surface winds will continue from
the E to ESE at 10-15 kts decreasing to around 10 kts after
29/22Z.


&&

.MARINE...Seas will range between 3-5 feet across the local offshore
Caribbean and Atlantic waters and less than 4 feet across the
nearshore waters of the islands. easterly winds between 5-15 knots
expected today and Thursday, decreasing even more on Friday. Moderate
risk continues for much of the north and east facing beaches of
the islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 77 87 75 87 / 10 10 10 20
STT 76 85 75 86 / 20 10 20 20
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Re: Caribbean - Central America Weather

#19112 Postby cycloneye » Thu Nov 30, 2017 5:57 am

Area Forecast Discussion
National Weather Service San Juan PR
536 AM AST Thu Nov 30 2017

.SYNOPSIS...Fair weather conditions should prevail through
Saturday. Diurnally induced afternoon showers are expected each
day over western Puerto Rico. However, showers will be light to
moderate. Low level moisture will increase during the first half
of the week. An upper level ridge builds during the second part of
the week and dry conditions will return across the islands.


&&

.SHORT TERM...Today through Saturday...A mid level ridge will
continue to favor a fair weather pattern across the islands today.
As a result expect mostly sunny skies with little or no shower
activity through the morning hours. The combination of the local
effects with the available moisture will result in shallow shower
activity across the west interior sections of Puerto Rico during the
afternoon hours, elsewhere mostly sunny to partly cloudy skies.
Maximum temperatures are forecast in the upper 80s along the coastal
areas and around the low 80s across the mountain areas. Although a
fair weather pattern is expected, surges of moisture will bring
clouds with embedded showers across the islands Friday and Saturday.

.LONG TERM...Sunday through Friday...Surface low will continue to
move into the Central Atlantic. Shearline to the east northeast of
the area will allow for low level moisture to increase across the
region. A surface high pressure building across the western
Atlantic will push a weak front north of the area and turn winds
more northeasterly by the middle of the week. Overall, shower
activity will increase during the first part of the week due to
these features. By the second part of the week, a return to drier
and fair weather conditions is expected...as a mid to upper level
ridge builds over the region.

&&

.AVIATION...VFR conditions today. -SHRA/SHRA are expected across the
interior and west portions of Puerto Rico during the afternoon btwn
30/16-23z. Mount obsc across the interior and VCSH possible at
TJBQ/TJMZ. Easterly winds at less than 6 kt increasing at around 10-
12 knots aft 30/13z with sea breeze variations.


&&

.MARINE...Seas will continue to subside across the regional
waters. Tranquil marine conditions are expected through the
Saturday. Another pulse of a small northeast swell is expected to
reach the local waters on Sunday. Surface low pressure developing
over the Atlantic waters will maintain a light 5-10 kt easterly
wind flow across the region through the weekend. Moderate to fresh
trades return by early next week.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 76 87 77 / 30 10 40 40
STT 85 76 85 75 / 10 40 40 40
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Re: Caribbean - Central America Weather

#19113 Postby cycloneye » Thu Nov 30, 2017 4:43 pm

Area Forecast Discussion
National Weather Service San Juan PR
400 PM AST Thu Nov 30 2017

.SYNOPSIS...Mainly fair weather is expected to persist for the
next few days with only brief showers in the morning and overnight
hours. Afternoon showers possible across western PR due to local
effects. Below normal moisture expected through Saturday, moisture
increasing gradually on Sunday and into the first few days of the
upcoming workweek.

&&

.SHORT TERM...Fair weather persisted today and it is expected to
continue through at least Saturday. Overnight and early morning
brief showers across the local waters, USVI, and eastern PR are
possible with afternoon showers across western PR due to local
effects. However, this activity should be very limited due to the
lack of upper level instability and below normal available
moisture. Winds will diminish on Friday, becoming variable as a
surface low develops north of the local islands, then on Saturday
winds are expected to be mainly E to ENE by Saturday evening.

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

.From previous discussion.

Surface low will continue to move into the Central Atlantic.
Shearline to the east northeast of the area will allow for low
level moisture to increase across the region. A surface high
pressure building across the western Atlantic will push a weak
front north of the area and turn winds more northeasterly by the
middle of the week. Overall, shower activity will increase during
the first part of the week due to these features. By the second
part of the week, a return to drier and fair weather conditions is
expected...as a mid to upper level ridge builds over the region.


&&

.AVIATION...VFR conditions today. Isold mtn obscurations and -
SHRA/SHRA psbl btwn 30/18-22Z, but conds much drier today. Isold
SHRA arnd and south of TKPK. Aft 01/04Z moisture to spread across
southeastern portion of Forecast area with isold SHRA expected vcnty
TISX/TIST. East southeast winds around 10-12 knots til 30/22Z then
mainly land breezes dominating at less than 7 knots. Winds alf bcmg
westerly abv FL140 and increasing to 60 kt by FL400.


&&

.MARINE...Relatively tranquil marine conditions expected through
Saturday. A NE swell is expected for Sunday but it should be short
lived and subsided by Monday, only increasing seas up to 5 feet.
However, a more significant swell may invade the local waters
later in our forecast period by the following Wednesday.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 76 87 77 86 / 10 40 40 30
STT 76 85 75 85 / 40 40 40 30
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Re: Caribbean - Central America Weather

#19114 Postby cycloneye » Fri Dec 01, 2017 5:48 am

Area Forecast Discussion
National Weather Service San Juan PR
532 AM AST Fri Dec 1 2017

.SYNOPSIS...Dry mid to upper levels will continue through the
weekend. This will favor fair weather conditions across the
islands and local waters. Remnants of a frontal boundary are
forecast to move across the islands and northeast trades will
increase by early next week.


&&

.SHORT TERM...Today through Sunday...Under a mid level ridge and a
dry air mass, fair weather conditions are expected into the
weekend. However, the trade wind inversion is expected to relax
this afternoon giving way to shower development mainly along and
to the west of the Cordillera Central, as well as trade wind
showers across the U.S. Virgin Islands and E-PR. A surface low is
expected to develops just to the north of the local islands to
result in light and variable winds. As the low drift eastward
winds are expected to return from the ENE to E by late Saturday
into Sunday. The lack of instability will continue to promote fair
weather conditions with a few overnight and early morning brief
showers across the local waters, USVI, and eastern PR with
afternoon showers across western PR due to local effects.

.LONG TERM...Monday through Friday...No significant change from
previous forecast. A shearline and remnants of a frontal boundary
are expected to move across the region behind a moderate to fresh
northeast trade wind flow. Surface high pressure will establish
north of the region and will result in breezy and cooler
conditions than previous days. Shower activity will increase
during the first part of the week due to these features. By the
second part of the week, a return to drier and fair weather
conditions is expected...as a mid to upper level ridge builds over
the region.

&&

.AVIATION...VFR conds with some mtn obscurations btwn 01/17-23Z.
Psbl brief VCSH at TJPS/TJMZ. Calm to light and VRB winds at less
than 6 kt with sea breeze variations aft 01/13z.


&&

.MARINE...Tranquil seas are expected through Saturday. A small
pulse of a northeasterly swell will reach the local waters on
Sunday. Higher seas are expected by mid-week as trade winds
increase across the local waters and a long period Northeast swell
fills in across the Atlantic waters and passages. Small craft
advisories will be required across some of the regional waters.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 76 86 76 / 40 40 30 20
STT 86 78 86 76 / 40 40 30 30
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Re: Caribbean - Central America Weather

#19115 Postby cycloneye » Fri Dec 01, 2017 5:54 pm

Area Forecast Discussion
National Weather Service San Juan PR
558 PM AST Fri Dec 1 2017

.SYNOPSIS...Dry mid to upper levels will continue through the
weekend. This will favor fair weather conditions across the
islands and local waters. Remnants of a frontal boundary are
forecast to move across the islands and northeast trades will
increase by early next week.


&&

.SHORT TERM...Tonight through Sunday...

Under precipitable water below the normal range, continue to expect
a fair weather pattern across the forecast area tonight through at
least early Sunday. A few trade wind showers across the USVI and E
Puerto Rico are likely in the early morning and late evening hours
followed by some locally induced afternoon showers across west
Puerto Rico. As a digging trough across the Greater Antilles
continues to press against an upper level ridge across the eastern
Caribbean, deeper moisture will begin to pool across the area late
Sunday and into Monday morning. As a result, a better chance for
shower activity is expected late the upcoming weekend.



LONG TERM...Monday through Friday...

.From Previous discussion...

No significant change from previous forecast. A shearline and
remnants of a frontal boundary are expected to move across the
region behind a moderate to fresh northeast trade wind flow.
Surface high pressure will establish north of the region and will
result in breezy and cooler conditions than previous days. Shower
activity will increase during the first part of the week due to
these features. By the second part of the week, a return to drier
and fair weather conditions is expected...as a mid to upper level
ridge builds over the region.



&&

.Aviation...VFR conditions are expected to prevail at all TAF sites
through the forecast period with some mtn obscurations and brief
SHRA possible in and around TJPS/TJMZ till 01/22z. Calm to light and
VRB winds at less than 6 kt with sea breeze variations to
continue.


&&

.MARINE...Tranquil seas are expected through Saturday. A small
pulse of a northeasterly swell will reach the local waters on
Sunday. Winds increasing across the local waters and a long
period Northeast swell fills in across the Atlantic waters and
passages. Small craft advisories will be required across some of
the regional waters.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 76 86 76 86 / 40 30 20 20
STT 78 86 76 86 / 40 30 30 40
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Re: Caribbean - Central America Weather

#19116 Postby cycloneye » Sat Dec 02, 2017 5:44 am

Area Forecast Discussion
National Weather Service San Juan PR
601 AM AST Sat Dec 2 2017

.SYNOPSIS...
A surface low pressure will continue to drift into the Central
Atlantic as a surface trough move into the region and weaken.
However, at mid to upper levels a dry air mass will continue over
the islands. This surface trough will bring some passing showers
mainly across the southern USVI and the eastern half portion of
Puerto Rico today. Remnants of a frontal boundary are forecast to
move across the islands and northeast trades will increase by
next week.

&&

.SHORT TERM...Today through Monday... A surge of moisture arriving
with a surface trough will increase shower activity across the
southeast portion of the forecast area and this moisture is expected
to approach eastern Puerto Rico by 02/12Z. An upper level jet, with
convergent flow over the area, and weak humidity above the marine
layer will keep shower activity to a minimum today and tonight.
Moisture increases Sunday and Monday as a shear line northwest of
the area approaches and the tropical air from the southeast moves
around the high to our southeast and into the area keeping a band of
moisture over the area into the long term period. Mid and upper
levels of the atmosphere will also moisten at this time and
precipitable water values will rise to 1.90 inches by Monday
evening.

.LONG TERM...Tuesday through Saturday...
A surface high pressure will establish north of the islands. The
interaction of this high and a cold front, exiting the eastern
U.S., will enhance moisture pooling over the region. There are
some discrepancies in the time of arrival between GFS and ECMWF.
GFS solution was chosen, because most of the frontal systems are
not moving far over the area. As the high pressure establish north
of the area breezy trade winds and cooler temperatures are
possible during the end of the work week. By the next weekend, a
return to drier and fair weather conditions is expected...as a mid
to upper level ridge builds over the region.

&&

.AVIATION...Moisture moving into the area will approach eastern PR
by 03/12Z bringing sct SHRA to areas east of there and brief MVFR to
TNCM/TKPK and aft 03/00Z TIST/TISX. Hir trrn in Cordillera Central
and the Luquillo range obscured aft 02/18Z. Sfc winds less than 6 kt
til arnd 02/15Z then 5 to 15 kt til aft 02/21Z. Max winds west 50-70
kts btwn FL350-FL500.

&&

.MARINE...Tranquil seas are expected through today. A small pulse
of a northeasterly swell will reach the local waters on Sunday.
Seas are forecast to increase by Tuesday or Wednesday as trade
winds increase across the local waters. In addition, a long
period Northerly swell is forecast to move across the islands the
upcoming week. Small craft advisories will be required across some
of the regional waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 86 76 / 10 20 20 30
STT 85 76 86 76 / 30 30 30 30
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Re: Caribbean - Central America Weather

#19117 Postby cycloneye » Sat Dec 02, 2017 5:20 pm

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
412 PM AST Sat Dec 2 2017

.SYNOPSIS...

At the surface a low pressure area will move into the
central Atlantic waters on Monday but closer to home an inverted
trough will form and remain north of the forecast area. The mid to
upper levels will remain relatively dry but this will change late
Monday and early Tuesday with precipitable water values
increasing due to patches of tropical moisture moving in from the
east southeast. A weak shear line is forecast to move over the
islands with increasing northeast trade winds.


&&

.SHORT TERM...TONIGHT THROUGH MONDAY...

Precipitable water still below the normal range, therefor
continue to expect a fair weather pattern across the forecast area
tonight. Low level moisture is then expected to gradually
increase Sunday into Monday as an induced trough establishes
north of the area. This will bring a better chance for showers
development across the local Isles. As a result, expect frequent
passing showers across east and southeast Puerto Rico as well as
Saint Croix under an east southeast wind flow Sunday afternoon
and Monday with showers also developing each afternoon over
central Puerto Rico. Intensity and coverage should increase Monday
afternoon under PLenty of moisture and Favorable upper level
dynamics.



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

.From Previous Discussion...

A surface high pressure will establish north of the islands. The
interaction of this high and a cold front, exiting the eastern
U.S., will enhance moisture pooling over the region. There are
some discrepancies in the time of arrival between GFS and ECMWF.
GFS solution was chosen, because most of the frontal systems are
not moving far over the area. As the high pressure establish north
of the area breezy trade winds and cooler temperatures are
possible during the end of the work week. By the next weekend, a
return to drier and fair weather conditions is expected...as a mid
to upper level ridge builds over the region.

&&

.AVIATION...

VFR conditions are expected to prevail at all TAF sites through
the forecast period with some MTN obscurations and brief SHRA
possible in and around TJSP/TJMZ till 02/22Z. ENE winds less than
10 kts to continue.


&&

.MARINE...

Tranquil marine conditions expected to continue across
the local waters with seas up to 4 feet and east to northeast
winds up to 10 knots.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 75 86 76 85 / 20 20 30 50
STT 76 86 76 84 / 30 30 30 50
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Re: Caribbean - Central America Weather

#19118 Postby cycloneye » Sun Dec 03, 2017 5:48 am

Area Forecast Discussion
National Weather Service San Juan PR
523 AM AST Sun Dec 3 2017

.SYNOPSIS...A surface trough approaching from the southeast and a
frontal boundary to the north of the islands will slowly increase
showers and thunderstorm activity across the local region today.
Dry air will persist at mid to upper levels through at least
Monday afternoon, when precipitable water is forecast to increase.
A wetter pattern is expected between Monday into Thursday. A
backdoor front is forecast to bring a cold and dry air mass Friday
into the upcoming weekend.

&&

.SHORT TERM...Today through Wednesday...
The leading edge of the moisture surge was punctuated by a few
thunderstorms early this evening around Saint Croix. These have
re-emerged this morning. The moisture has been retarded by the
approach of a shear line from the northwest which has induced
subsidence ahead of it and kept the moisture from advancing as
rapidly as models have suggested. Nevertheless both the GFS and
the ECMWF agree that better moisture will eventually arrive and
current thinking is that this will be sometime this evening for
the U.S. Virgin Islands and later Monday afternoon for western
Puerto Rico. Moisture then increases overnight Monday with the
first intrusion of tropical moisture. Then, a band of subsidence
at 700 mb will intervene after the moisture surge moves west of
the area on Tuesday when moisture associated with the tail of the
shear line will invade from the northeast. This moisture will be
forced toward the area by high pressure that will have moved out
of South Carolina on Monday to a position north of Puerto Rico on
Wednesday. That moisture band will remain over the area into the
long term forecast.

.LONG TERM...Thursday through Monday...
The moisture from the shear line will continue through early
Friday morning when model guidance suggested the arrival of a
backdoor front. If models are right the islands will observe
clear skies with pleasant below normal temperatures through the
upcoming weekend. A surface high pressure will build over the
eastern Atlantic Ocean inducing an east to north northeast wind
flow over the region with the typical winter popcorn showers from
time to time.

&&

.AVIATION...
Moisture moving into the area has brought isold SHRA
into the Caribbean waters. By 03/16-18Z some areas of MVFR are psbl
as SHRA dvlp across wrn and interior PR with some mtn obscurations.
SHRA will persist til arnd 04/02Z. VFR conds expected at TIST/TISX
thru byd 04/02Z. Brief MVFR expected TNCM/TKPK due to CIGS with
isold TSRA psbl thru 04/12Z. Sfc winds less than 6 kt til arnd
03/15Z then 5 to 15 kt til aft 03/21Z. Max winds west 55-65 kts btwn
FL350-FL500. incrg to 85 knots at FL500 by 04/18Z.

&&

.MARINE...
A small pulse of a northeasterly swell is moving across the local
Atlantic Waters and Anegada Passage. Mariners can expect seas at 2
to 4 feet and easterly winds around 10 knots. Seas are forecast
to increase after Tuesday as trade winds increase across the local
waters. Then, a long period Northerly swell is forecast to move
across the islands by the end of the work week into the weekend.
Small craft advisories will be required across some of the
regional waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 75 86 77 / 30 30 50 50
STT 85 75 86 75 / 40 40 50 50
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Re: Caribbean - Central America Weather

#19119 Postby cycloneye » Sun Dec 03, 2017 3:27 pm

Area Forecast Discussion
National Weather Service San Juan PR
403 PM AST Sun Dec 3 2017


.SYNOPSIS...

A surface trough moving in from the southeast and a frontal
boundary to the north of the islands will increase instability
over the forecast region. A weak shear line will form across the
area and cause showers and isolated thunderstorms thru Wednesday.
A backdoor front is forecasted to bring a cold and dry air mass
late Friday and through the weekend with precipitable water values
once again falling to 1.0 to 1.5 inches.

&&

.SHORT TERM...Tonight through Wednesday...

Limited moisture has returned today across Puerto Rico and the
U.S. Virgin islands. At this time drier air still remains in the
mid to upper levels of the atmosphere which limited area wide
showers. Under influence of a shear line and meandering front the
lower level winds are to back from the east southeast early on
Monday and then to the east northeast late Tuesday and early
Wednesday morning.This pattern will favor a cool advective pattern
across the forecast area. On Wednesday, cool advection over the
warm Atlantic water will increase the instability and cause trade
wind showers.

&&

LONG TERM...Thursday through Monday...

From Previous Discussion...

The moisture from the shear line will continue through early
Friday morning when model guidance suggested the arrival of a
backdoor front. If models are right the islands will observe clear
skies with pleasant below normal temperatures through the
upcoming weekend. A surface high pressure will build over the
eastern Atlantic Ocean inducing an east to north northeast wind
flow over the region with the typical winter popcorn showers from
time to time.

&&

.AVIATION...

Mostly VFR conditions at all TAF sites through the
forecast period with some mtn obscurations and SHRA/TSRA possible in
and around TJPS/TJMZ/TISX/TIST till 03/22z. VCTS/VCSH likely
overnight across the USVI terminals as well as JSJ. ENE winds less
than 10 knots to continue.

&&

.MARINE...

A small pulse of a northeasterly swell is moving across the local
Atlantic Waters and Anegada Passage. Mariners can expect seas at 2
to 4 feet and easterly winds around 10 knots. Seas are forecast
to increase after Tuesday as trade winds increase across the local
waters. Then, a long period Northerly swell is forecast to move
across the islands by the end of the work week into the weekend.
Small craft advisories will be required across some of the
regional waters.

&&


.PRELIMINARY POINT TEMPS/POPS...
SJU 75 86 77 86 / 30 50 50 50
STT 75 86 75 85 / 40 50 50 50
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cycloneye
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Re: Caribbean - Central America Weather

#19120 Postby cycloneye » Mon Dec 04, 2017 5:35 am

Area Forecast Discussion
National Weather Service San Juan PR
531 AM AST Mon Dec 4 2017

.SYNOPSIS...
A surface trough will move across the islands and a frontal
boundary will stall north of the region. This will enhance
moisture pooling through the end of the work-week. A backdoor
front is forecast to bring a cold and dry air mass late Friday
through the weekend.

&&

.SHORT TERM...Today through Thursday... Moisture that was pulled
up from the tropics in southerly low level flow that was southwest
at 700 mb and southeast at 850 mb on Sunday will create a
favorable environment for increasing clouds and showers today
through Thursday. An old boundary and pre-frontal zone, now being
stretched over the area from a rapidly forming low pressure over
the central Atlantic that is in full retreat to the northeast,
will enhance the dynamics of the situation. High pressure north of
the area at 700 mb will slowly drive the boundary between the
moist air that is over and north of us, and the drier air just
north of 25 north, toward the area and focus some of the dynamics
in the band over the area on Wednesday and Thursday. With flow at
lower levels and the surface becoming more easterly Tuesday
through Thursday, showers will be more concentrated over interior
portions of Puerto Rico and will be scattered around the U.S.
Virgin Islands. Instability was good on Sunday, but trigger
mechanisms were lacking for more widespread convection. Lifted
indices of around minus 8 over San Juan in the GFS are expected
briefly during the afternoon today, but instability slowly
decreases through the end of the week thereafter. Nevertheless the
atmosphere favors the formation of a few afternoon thunderstorms
each day over Puerto Rico, and over the local waters and around
the U.S. Virgin Islands each night. The drier air to our north
will begin filtering into the forecast area overnight on Thursday
leading to a more dramatic change in weather in the long term
period.

.LONG TERM...
As the surface high pressure over the Central Atlantic and a
surface low pressure over the Eastern Atlantic squeeze together
to induce a wind surge pushing a backdoor front with a modified
cooler air mass with patches of moisture across the islands.
However, weather guidance is suggesting an area of low-level
convergence induced by the approaching backdoor front on Friday.
As a result, showers are possible across the U.S. Virgin Islands,
east PR and the surrounding waters during this period. Then, the
air mass behind the backdoor front will bring mostly clear skies
with pleasant below normal temperatures late Friday through the
weekend. A surface high pressure will build over the eastern
Atlantic Ocean inducing an east to north northeast wind flow over
the region with the typical winter popcorn showers from time to
time.

&&

.AVIATION...
Isold TSRA cont ovr Local waters and will redevelop over interior
Puerto Rico aft 04/16Z. Sct SHRA cont ovr local waters and ern
PR, but will incrs ovr interior and wrn PR aft 04/16Z with areas
of MVFR and mtn obscurations. Only brief MVFR for the USVI and
Leeward Islands. Winds east 5 to 15 kt with sea breeze influences
aft 04/14Z. Winds alf bcm WSW-W abv FL150 and winds incrs to max
77 kts at FL410 by 05/00Z.

&&

.MARINE...
Mariners can expect seas at 2 to 5 feet and easterly winds at 5 to
15 knots. Seas are forecast to increase by Tuesday afternoon as
trade winds increase across the local waters. For that reason, a
small craft advisory is in effect for the Atlantic Offshore Waters
after Tuesday afternoon. Then, a long period Northerly swell is
forecast to move across the islands by Thursday through the
weekend. Mariners are urge to follow our marine products because
small craft advisories will be required across some of the
regional waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 77 85 75 / 60 60 60 40
STT 85 75 85 76 / 50 50 50 50
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