Caribbean - Central America Weather

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cycloneye
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Re: Caribbean - Central America Weather

#19721 Postby cycloneye » Thu Jan 10, 2019 5:12 am

Area Forecast Discussion
National Weather Service San Juan PR
445 AM AST Thu Jan 10 2019

.SYNOPSIS...A mid to upper level trough will provide some instability
through Friday to result in cloudiness and periods of scattered
to numerous showers across the local isles. A more seasonal weather
pattern is expected the upcoming weekend into early next week with
trade wind showers across the eastern coastal areas of Puerto Rico
and the outlying islands.

&&

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

A cold front over the western Atlantic is expected to stall north of
the area through Friday. Meanwhile, a surface high over the central
Atlantic will continue to loose influence over the region. Winds are
expected to decrease and a deep layer southerly wind flow will
prevail. A mid to upper level trough will provide some instability
through Friday and in combination with the available low level
moisture, will result in cloudiness with periods of scattered to
numerous showers over portions of the regional waters and across the
U.S. Virgin Islands and Puerto Rico. For this afternoon, light
steering south-southwest winds and sea breeze convergence over
northern PR should lead to shower development along the northern
slopes as well across the eastern sections of the islands.

Moisture is expected to peak from tonight through Friday morning and
periods of intermittent showers are possible across the USVI and the
eastern sections of PR. A more southeasterly wind flow is expected
on Friday afternoon and shower development is expected mainly over
the northwest quadrant of PR. A mid to upper level ridge is forecast
to build from the west on Saturday and moisture content is expected
to erode. A surface high pressure is also expected to build over the
western Atlantic and northeast trades will return across the region.

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

The mid to upper level ridge pattern will prevail much of the forecast
period across the local isles with a brief weakening anticipated
Wed-Thu as a deep mid to upper level trough moves across the
western Atlantic into the central Atlantic. At lower levels, a
moderate easterly wind flow will prevail Sunday into early next
week, becoming southeast by midweek as a frontal boundary approaches
from the west. Under the aforementioned pattern, trade wind
showers will prevail Sunday followed by fair weather Mon-Tue as a
drier airmass encompasses the forecast area.

There is a better chance for shower activity Wednesday and Thursday
as the ridge aloft erodes and the frontal boundary approaches
from the west. A more seasonal weather pattern with trade wind
showers will prevail Friday into the weekend. Pleasant temperature
to continue, particularly by the end of the forecast period.

&&

.AVIATION...Mainly VFR conditions are expected early in the forecast
period across all the terminals. SHRA and sct/bkn layers btw FL030-
FL250 are expected this afternoon and through the evening hours
across portions of the islands and the surrounding coastal waters.
Tempo MVFR conds are possible across the PR/USVI terminals with this
activity. Low level southerly winds are expected between 5-10 kt,
sea breeze variations expected at TJMZ/TJBQ/TJSJ after 14z.

&&

.MARINE...A light to gentle east southeast wind flow will prevail
across the local waters through Friday, becoming more easterly
during the weekend. Although seas are expected to subside
throughout the day, another northerly swell is forecast to move
into the local waters during the weekend. However, seas will
remain below SCA criteria.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 84 73 / 40 50 50 20
STT 83 72 83 72 / 50 50 50 30
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Re: Caribbean - Central America Weather

#19722 Postby cycloneye » Fri Jan 11, 2019 5:22 am

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Fri Jan 11 2019

.SYNOPSIS...An approaching upper level trough over the western
Atlantic with an associated frontal boundary at the surface will
provide some instability over the region today. A more seasonal
weather pattern is expected the upcoming weekend into early next
week with trade wind showers across the eastern coastal areas of
Puerto Rico and the outlying islands.

&&

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

An approaching upper level trough over the western Atlantic with an
associated frontal boundary at the surface will provide some
instability over the region today. However, the front is expected to
stall just north of the region for the next day or so. This will
continue to induce a southerly wind flow and increase low level
moisture over the islands. Therefore, another round of afternoon
showers, are expected to develop mainly over portions of the
interior, the northwest and western Puerto Rico. Some of these
showers could be heavy at times and produce localized urban and
small stream flooding. Across the U.S. Virgin Islands, fair weather
conditions are expected but isolated showers can`t be ruled out.

Meanwhile, a surface high pressure is expected to build over the
western Atlantic and promote a moderate east to northeast wind flow
on Saturday and Sunday. In addition, an upper level ridge is
expected to build from the west and promote drier air aloft. During
this period, fragmented low level clouds from the old frontal
boundary and light trade wind showers are expected across the
USVI/northeastern sections of PR. Followed by diurnally induced
scattered showers over western PR each afternoon. A small surge in
low level moisture is expected briefly on Sunday morning.

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

The mid to upper level ridge pattern and limited low level moisture
will result in fair weather conditions Monday and Tuesday. Passing
showers, if any, will be focused mainly across the outlying islands
and the eastern third of Puerto Rico. The ridge aloft is then
expected to erode by the end of the work week as a mid to upper
level trough moves across the western Atlantic into the central
Atlantic. Surface frontal boundary associated with the trough aloft
will approach the local isles from the west Wed-Thu. Therefore,
under eroding ridge and approaching frontal boundary, there is a
chance for shower activity both days. Although ridge aloft is
expected to rebuild by the end of the work week, showery
conditions are possible as the east northeast wind flow brings
the remnants of the aformentioned frontal boundary.

&&

.AVIATION...Mainly VFR conditions are expected to prevail during
the next 24 hours across all the terminals. However, SHRA over
western PR could cause tempo MVFR cigs at TJBQ/TJMZ btw 16z-22z.
ESE winds will prevail at less than 10 kt with sea breeze
variations after 14z across the north/west coast of PR.

&&

.MARINE...A light to gentle south to southeast wind flow will
prevail across the local waters through today with seas below 4
feet. Winds will become east to northeast on Saturday through
early next week. A northerly swell is forecast to move into the
local waters during the weekend, which will increase seas across
the local waters. However, seas will remain below SCA criteria.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 83 74 / 20 10 10 30
STT 83 74 83 74 / 50 20 30 50
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Re: Caribbean - Central America Weather

#19723 Postby cycloneye » Sat Jan 12, 2019 5:54 am

Area Forecast Discussion
National Weather Service San Juan PR
522 AM AST Sat Jan 12 2019

.SYNOPSIS...A weak surface high pressure over the western Atlantic
will promote a northeast steering wind flow through Monday. Lighter
winds return once again early next week. Low level moisture will
increase from the east later tonight through Sunday morning. A
drier air mass will promote fair weather conditions during the
first part of the workweek.


&&

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

A weak inverted trough is found from the Mona passage to 28 North 60
west, but will fade as high pressure over the eastern United States
gradually fills into the western Atlantic. That building high
pressure is arrested on Monday by a rapidly deepening low that moves
up the eastern U.S. coast leaving weak trade wind flow over the
forecast area. At mid levels, a weak and broad trough over the area
will slowly move southeast of the forecast area. By Monday a ridge
will extend from the western Caribbean. Drying at mid levels will
peak on Monday. At upper levels, flow will become more northwesterly
as a trough over the area moves into the Leeward Islands Sunday
morning. The approaching ridge flattens out on Monday although west
northwest flow will continue.

An area of moisture is seen just east of the Leeward Islands and is
expected to enter the forecast area from the east northeast Saturday
night and Sunday. Drier air returns late Sunday night and Monday.
Showers will not be as heavy over western Puerto Rico as they were
yesterday and owing to a shift in the low level flow to east
northeast that is already underway, those showers will form mainly
in the west and southwest portion of Puerto Rico and over the
northern USVI. Some showers may also be seen around and downwind
of the Luquillo range today. Scattered shower spread over saint
Croix tonight and will continue on Sunday area-wide before drying
begins.

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

Dry air in the mid to upper levels will keep moisture confined
below 750 MB on Tuesday and fair weather conditions should
prevail across the islands. However, an approaching upper level
trough and associated cold front across the western Atlantic are
expected to increase the chance of showers across the regional
waters and over the islands during the middle of the week. Winds
will gradually decrease and turn from the east to southeast during
this period. A building surface high over the western Atlantic
will return a northeast wind flow and push the remnants of the
front across the region through the weekend.


&&

.AVIATION...VFR conds to prevail at all TAF sites. Brief MVFR conds
due to CIGS may occur aft 12/12Z at TNCM/TKPK and at TJMZ aft 12/18Z
in SHRA. Mtn obscurations in HIR trrn of PR aft 12/16Z. Sfc winds 5-
15 kt in ENE flow. Maximum winds WNW 40-50 kt FL400-490.


&&

.MARINE...A northerly swell will arrive later today and spread
across the Atlantic waters and passages. This swell will increase
seas up to 6 feet and small crafts should exercise caution from
this afternoon through at least Sunday night. This swell will
increase breaking waves along the north facing beaches of the
islands, increasing the potential for rip currents. A high rip
current risk was issued for the north coast of PR, Culebra and St.
Thomas. Please refer to the latest surf zone forecast (SRFSJU)
and coastal hazard message (CFWSJU) for detailed information. A
moderate east to northeast wind flow will prevail through the rest
of the weekend with winds increasing between 10 to 15 knots.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 82 73 83 73 / 20 50 50 10
STT 83 72 83 72 / 50 50 30 30
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Re: Caribbean - Central America Weather

#19724 Postby cycloneye » Sun Jan 13, 2019 6:38 am

Area Forecast Discussion
National Weather Service San Juan PR
527 AM AST Sun Jan 13 2019

.SYNOPSIS...A weak surface high pressure north of the region will
continue to promote moderate northeasterly trade winds. A surge
in low level moisture today, will bring passing showers along the
northern sections of PR and across the USVI through the morning
hours and aid in the development of afternoon showers over
southwestern PR. Fair weather conditions are expected on Monday
and Tuesday. An upper level trough and associated surface front
will increase showers once again by midweek. An upper level ridge
is forecast to build from the west during the end of the week.

&&

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

A weak high pressure decays at lower levels north of the area as low
pressure develops along the coast of North Carolina and moves
rapidly northeast while deepening. The cold front associated with
this low will move to within 350 miles of Aguadilla (480 miles of
Saint John) with a weak ridge intervening just north of the local
waters during the period. This will maintain east to east northeast
flow over the area. The best moisture is just southeast of Puerto
Rico and has been responsible for the rains noted over Saint Croix
overnight. This moisture will move west southwest so that the bulk
of it misses Puerto Rico. A weak boundary has moved over the area
and the air behind it is slightly drier. The boundary may stall over
the southeast quadrant of the forecast area. Meanwhile the drier air
behind the weak boundary will continue to move over Puerto Rico from
the north as evidenced by the water vapor imagery and the GFS
precipitable water which drops from 1.44 inches at 13/00Z to 0.84
inches at 14/12Z. Part of this drop is due to mid level drying and
subsidence that is compressing an already shallow layer of lower
level moisture. This will lower shower activity. Showers are still
expected over western and southwestern Puerto Rico during the
afternoons, and over eastern Puerto Rico during the late night and
early mornings, but accumulations will diminish and in some areas
measurable amounts will not be seen.

At upper levels west northwest flow ill continue, but flow at 35
knots tonight will increase to 50-60 kts on Tuesday. With such
dryness intervening at mid levels this is not expected to have
much affect on the conditions near the surface.

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

An upper level trough and associated surface front moving from the
western Atlantic into the central Atlantic are expected to
increase shower activity through midweek. A weak southeasterly
wind flow is expected on Wednesday and on Thursday and with the
surge in low level moisture...showers are expected to increase
across the USVI and the east/southeast sections of PR. Afternoon
showers and light steering winds could result in urban and small
stream flooding in isolated areas of the interior and western PR.
A surface high pressure will move into the western Atlantic and
promote light to moderate northeast trades once again through
early in the weekend. An upper level ridge is forecast to build
from the west during the weekend, promoting drier air aloft and
fair weather conditions across the region.


&&

.AVIATION...VFR conds to prevail at all TAF sites. Brief MVFR conds
psbl due to CIGS may occur at TJMZ aft 12/19Z in SHRA. Mtn
obscurations in HIR trrn of PR aft 12/16Z. Sfc winds 5-15 kt in ENE
flow. Maximum winds NW 40-50 kt FL330-500.


&&

.MARINE...Northerly swell will keep seas between 4-6 feet across
the Atlantic waters and passages through at least tonight and
small crafts should exercise caution. Winds will continue from the
east to northeast between 10-15 kt in general. Locally higher
winds are expected early this afternoon over portions of the
coastal Caribbean waters and northwestern waters of Puerto Rico.
There is a high risk of rip currents along the northern beaches of
PR, Culebra and St. Thomas. Seas and winds will gradually decrease
through next week.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 74 84 72 / 60 40 20 20
STT 84 72 83 71 / 40 20 10 20
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Re: Caribbean - Central America Weather

#19725 Postby cycloneye » Mon Jan 14, 2019 8:02 am

Area Forecast Discussion
National Weather Service San Juan PR
453 AM AST Mon Jan 14 2019

.SYNOPSIS...After a brief dryer period today, moisture will
increase Wednesday through Sunday, to continue a pattern of
scattered showers in easterly flow. Some heavier showers may be
expected in western Puerto Rico during that wetter period.

&&

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

A weak surface high pressure north of the region will keep a
moderate east-northeast wind flow through late tonight. A mid level
ridge and dry air aloft will dominate the weather conditions in
general today. Mostly sunny skies are expected during the morning
hours across the islands. For this afternoon, daytime heating
combined with the sea breeze and shallow low level moisture will
result in scattered showers over the southwest quadrant of PR. Light
to moderate rainfall amounts could result in ponding of water and
urban flooding in isolated areas. A surface low and associated front
moving from the western Atlantic into the central Atlantic will turn
winds more easterly on Tuesday and Wednesday. A surge in low level
moisture is also expected and scattered showers are expected by
Tuesday morning across the USVI and the eastern sections of PR,
followed by diurnally induced afternoon showers along the interior
and western PR. A similar pattern is expected on Wednesday with
better rainfall amounts across the USVI and PR.

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

After a weak upper level trough passage on Wednesday, upper level
flow becomes west northwest and increases through Saturday night.
An upper level ridge builds in over the weekend. Mid levels
remain dry through the period, but lower level moisture deepens
Wednesday through Friday and intrudes into that drier air up to 15
to 16 kft. This raises the precipitable water which will remain
above present levels Thursday through Sunday, before it begins a
steep decline on Monday.

Lower level flow will remain east to east southeast during the
period and will keep most of the best showers in the afternoons in
western and northwestern Puerto Rico. Some showers will continue
to dampen eastern Puerto Rico--mainly on the slopes of the
Luquillo range--during the late night and early morning hours each
day, although showers on Monday will be diminished due to the
limited moisture.

In the longer range the latest GFS (14/00Z run) is showing a
frontal passage Tuesday night. Run to run consistency on this and
other features is not particularly good and the model did shift
winds from east northeast flow to east southeast flow past day 4
in the last 24 hours, so will consider the long term forecast of
medium confidence only. No major features are expected through
Monday however.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, SHRA are expected to
develop between 16z-22z over the interior and southwestern PR,
impacting TJPS/TJMZ with possible RA/VCSH and tempo MVFR cigs. Low
level winds will continue form the ENE at 7-14 kt. Sea breeze
variations are expected at TJPS/TJMZ aft 14z. Max winds WNW 30-40
kt btwn FL310-480.

&&

.MARINE...Seas are subsiding at this time and are expected to
remain mostly below 6 feet through the next 7 days.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 71 83 72 / 20 0 20 20
STT 85 72 83 72 / 20 40 40 30
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Re: Caribbean - Central America Weather

#19726 Postby cycloneye » Tue Jan 15, 2019 4:58 am

Area Forecast Discussion
National Weather Service San Juan PR
516 AM AST Tue Jan 15 2019

.SYNOPSIS...A dryer day today, but moisture will increase
Wednesday through Friday. Then showers will taper off over the
weekend and into early next week. Weak surface high pressure will
maintain easterly flow that will briefly become east southeast
Thursday and Friday. Temperatures will vary little from day to
day.

&&

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

Mainly fair weather conditions are expected across the region
throughout the day as a drier than normal air mass will be moving
over the area with precipitable water values dropping below 1 inch,
(2 standard deviations below normal for this time of the year). A
few showers may attempt to develop over western Puerto Rico this
afternoon due to daytime heating and local effects. However, given
the drier than normal airmass, these showers should be short-
lived and produce minor accumulations.

Model guidance continues to indicate that an increase in low-level
moisture is expected by Wednesday and Thursday with precipitable
water values increasing up to 1.4-1.5 inches. Therefore, more
frequent shower activity is expected. Winds will veer to the
southeast as the surface high pressure will shift eastward into
the tropical Atlantic. As a result, during the overnight and
morning hours scattered showers are expected across portions of
the USVI and across portions of eastern and southeastern Puerto
Rico. This will be followed by the development of additional
showers across the northwest quadrant of Puerto Rico, where
activity could be enhanced by daytime heating and local effects.
Thunderstorms are not expected due to the very dry mid to upper-
levels.

.LONG TERM...Friday to Tuesday...
Moisture peaks near 1.6 inches on Friday and then drops
irregularly through Tuesday as low-level moisture generated by
convergence over the area on Wednesday and Thursday dissipates
and is replaced by drier air from the northeast Saturday through
Wednesday. Moisture on Friday and Saturday intrudes into the mid-
levels up to 16 kft, but moisture becomes more shallow and mid
levels become extremely dry according to the GFS solution Monday
and Tuesday just above 700 mb. This is due to high pressure at 500
mb moving in from the west over the weekend and settling over
Puerto Rico and the U.S. Virgin Islands Monday and Tuesday. Upper
level flow is west to west north west through the period with a
ridge developing over the central Caribbean on Saturday and moving
over the area early next week. This pattern will tend to suppress
convection over the area especially after Sunday.

Showers will be active on Friday and are expected to diminish each
day through the period. Showers that form in the afternoon will
generally be in west and southwest Puerto Rico. Late night and
early morning showers will mostly fall over El Yunque with some
slight accumulations over the northeast coast of Puerto Rico and
very limited shower activity over the U.S.Virgin Islands.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across all
terminals throughout the forecast period. A few SHRA may develop
across western PR after 15/16z, affecting TJMZ. Winds expected to be
light and variable through 15/13z, increasing to 10 to 15 kts from
the E with sea breeze variations. Maximum winds increasing to W
50-60 knots btwn FL335-465 by 16/00Z.

&&

.MARINE...Relatively tranquil conditions are expected to continue
through early next week with seas mostly below 6 feet until
Sunday. A north northwest swell of 4 to 5 feet will return to the
area on Wednesday night and will provoke a high risk of rip
currents along the north coast of Puerto Rico and isolated spots
on the northwest beaches of Culebra and Saint Thomas Wednesday
night and Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 73 83 71 / 10 20 30 30
STT 84 72 84 71 / 10 40 40 50
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Re: Caribbean - Central America Weather

#19727 Postby msbee » Tue Jan 15, 2019 2:37 pm

Thanks for your regular updates, Luis.
The St Maarten Met Office has issued it's forecast for January to March 2019.

http://www.meteosxm.com/wp-content/uplo ... 0JeCj-EdZM

In summary,
Jan-Feb-Mar, rainfall totals are expected to be lower than usual. Daytime temperatures are expected to be warmer than usual while night-time temperatures are expected to be as usual and become warmer by March. Drought is not expected to become a major concern until the end of May 2019.
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Re: Caribbean - Central America Weather

#19728 Postby cycloneye » Wed Jan 16, 2019 5:04 am

Area Forecast Discussion
National Weather Service San Juan PR
453 AM AST Wed Jan 16 2019

.SYNOPSIS...Low-level moisture is expected to increase across the
area today and prevail through Saturday, with passing showers
across eastern Puerto Rico and the USVI during the overnight and
morning hours followed by the development of additional showers
across interior and western Puerto Rico during the afternoon
hours. Mainly fair weather conditions are expected by the second
half of the weekend through the first part of next week as a mid
to upper-level ridge amplifies overhead, eroding the low-level
moisture.

&&

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

A surge of low level moisture will continue to cross the region
today through early Thursday steered by a fairly light easterly
trades. Recent satellite imagery as well as the Doppler weather
radar suggests showers of mostly light to moderate intensity
accompanying the cloudiness now mainly over the Caribbean waters.
Expect a few showers to brush the USVI particularly Saint Croix from
time to time, but no significant rainfall accumulations is
anticipated. Some passing showers may also reach the east and
southeast sections of Puerto Rico and the adjacent islands but
rainfall will be brief with minimal accumulations.

For the rest of today expect mixture of sunshine and clouds with
some locally and diurnally induced afternoon convection mainly over
parts of the interior and north central to northwest sections of
Puerto Rico including isolated areas in the San Juan metro. Some
showers may be locally heavy especially in the west to northwestern
sections of the island. Model guidance and present conditions all
suggest that the mid to upper levels should remain fairly dry and
stable, therefore no significant or widespread convection is
expected today or during the entire period.

On Thursday and Friday...An overall drying trend is forecast as
model guidance suggests a strengthening of the mid to upper level
ridge overhead. This in turn will increase the trade wind cap
inversion and limit daytime convection. Nevertheless , still expect
isolated to scattered afternoon showers mainly over parts of the
interior and west sections of Puerto Rico each day with mostly fair
weather skies expected to prevail elsewhere. In additions periods of
early morning passing trade wind showers will remain possible over
the coastal waters and on the windward side of the islands.

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

Enough low-level moisture will remain present on Saturday to
result in brief passing showers across portions of eastern Puerto
Rico and the USVI during the morning hours. This will be followed
by the development of locally and diurnally induced showers
across interior and western portions of Puerto Rico during the
mid to late afternoon hours.

As the aformentioned mid to upper-level ridge amplifies overhead
late in the weekend through the first part of next week, the low-
level moisture is expected to gradually erode. This will result in
mainly fair weather conditions with very limited shower activity
expected across the region. By the middle of next week, model
guidance is suggesting an increase in the winds from the northeast
as a strong surface high pressure moves off the northeast coast
of the United States into the western Atlantic, tightening the
pressure gradient somewhat.


&&

.AVIATION...VFR durg prd. SCT-BKN cld lyrs nr FL025...FL050.
Mostly SKC ovr land areas. Few tops FL090...w/Isold SHRA en route
btw PR and Nrn Leeward Islands...VCSH at TIST/TISX/TNCM/TKPK til
16/14z. Sfc wnds calm to LGT/VRB bcmg mainly fm E 10-15KT with
sea breeze variations aft 16/14Z.


&&

.MARINE...Light to moderate easterly winds will continue to
maintain seas between 2 and 4 feet across the regional waters for
today. A northerly swell is forecast to spread across the Atlantic
waters by late tonight into Thursday, slightly increasing the
seas. There is a moderate risk of rip currents for the northwest
to north-central beaches of Puerto Rico for today. The rip
current risk is expected to increase starting tonight into
Thursday for the north facing beaches of the islands as the
northerly swell arrives.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 71 84 72 / 60 30 40 40
STT 84 72 84 71 / 40 50 50 40
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Re: Caribbean - Central America Weather

#19729 Postby cycloneye » Thu Jan 17, 2019 5:12 am

Area Forecast Discussion
National Weather Service San Juan PR
419 AM AST Thu Jan 17 2019

.SYNOPSIS...Low-level moisture will continue to result in periods
of showers across the region through Saturday. A drier and more
stable weather pattern is expected starting Sunday and continuing
through the middle of next week as a mid to upper-level ridge
amplifies overhead. Winds are expected to increase from the
northeast by the middle portion of next week as a strong surface
high pressure moves across the western Atlantic, tightening the
pressure gradient.

&&

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

Occasional clusters of low to mid level moisture will continue to
make its way across the forecast area and bring periods of passing
showers to the coastal waters and the windward side of the islands
during the rest of the morning hours. A weak low level trough just
west and north of the region will maintain a light east to southeast
wind flow across the area through at least Friday, then become more
east to northeast by Saturday as a surface high pressure ridge will
builds north of the region across the west and southwest Atlantic.

For the rest of today, expect cloud cover and shower activity to
diminish by late morning leaving partly sunny skies across the
forecast area. Locally and diurnally induced afternoon convection
is however expected again during the afternoon mainly over parts of
the interior and west sections of Puerto Rico as well as around the
San Juan metro. Some showers will be locally heavy especially in the
west to northwestern sections of the island. Model guidance and
present conditions now suggest that a mid to upper level trough will
linger across the region through Friday but will slowly lift east
northeast into the tropical Atlantic. Therefore expect the shower
activity in the easterly trades to be further enhanced as they
are steered west northwest producing periods of locally heavy
rains. This in turn may lead to minor ponding of water on roadways
and in poor drainage areas. However, widespread convection is
still not expected during the entire period. This cool advective
pattern of early morning passing trade wind showers followed by
isolated to scattered afternoon convection will continue though a
least Friday. Conditions will gradually improve by Saturday as the
low level trough pulls away from the region and a high pressure
ridge builds both aloft as well as at the surface inducing an east
to northeast low level wind flow and a gradual strengthening of
the trade wind cap inversion.

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

A drier and more stable weather pattern is expected by the second
half of the weekend through at least the middle of next week as
the aformentioned mid to upper-level ridge amplifies overhead,
eroding the low-level moisture. In fact, both the GFS and ECMWF
models indicate precipitable water values dropping below 1 inch at
times during the period, which would be close to 2 standard
deviations below normal for this time of the year. As a result,
mainly fair weather conditions can be expected across most of the
region with very limited shower activity. An increase in the winds
from the northeast is expected by the middle of next week as a
strong surface high pressure moves off the northeastern coast of
the United States into the western Atlantic, tightening the
pressure gradient somewhat.

&&

.AVIATION...Prevailing VFR at local terminals durg prd but VCSH at
TJSJ/TJNR/TISX/TIST/TNCM/TKPK. BKN-OVC lyrs nr FL030... FL060...
FL080...and SHRA en route btw PR and northern Leeward Islands til
17/14Z. SHRA and low cld lyrs may cause brief MVFR and Mtn top obscr
ovr E PR As patches of moisture move across the region. Sfc winds
light and variable bcmg fm E-SE 10-15 kts aft 17/14Z with sea breeze
variations through 17/22Z.

&&

.MARINE...Tranquil marine conditions are expected to prevail
with seas ranging between 2 and 5 feet and east to southeast
winds up to 15 knots. A northerly swell is moving across the
Atlantic waters and local passages and will continue through
Saturday. A high risk of rip currents is in effect for the beaches
located across north-central Puerto Rico and San Juan and
Vicinity through 6 AM AST Friday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 71 82 73 / 30 20 20 40
STT 83 72 83 72 / 40 40 30 40
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Re: Caribbean - Central America Weather

#19730 Postby cycloneye » Fri Jan 18, 2019 5:14 am

Area Forecast Discussion
National Weather Service San Juan PR
415 AM AST Fri Jan 18 2019

.SYNOPSIS...A surge of low to mid level moisture transported in the
prevailing east to northeast low level wind flow will continue to
move across Puerto Rico and the Mona passage this morning as a slot
of drier air will enter the forecast area from the east. A mid to
upper level short wave trough will continue to weaken and lift east
northeast of the region today as an upper level ridge will build
across the west Atlantic and spread across the region through the
upcoming weekend. Few passing shower continued to move west southwest
across the local waters this morning with a few brushing mainly parts
of the northeast coastal areas of Puerto Rico while a gradual clearing
was noted over the USVI.

&&

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

Residual low-level moisture will remain across the forecast area today.
This will result in some passing showers across the coastal waters,
possibly affecting portions of eastern PR during the rest of morning
hours. This will be followed by the development of showers across
interior and western PR during the afternoon hours, where activity
could be enhanced due to daytime heating and local effects. Some
additional activity may also develop across southern portions of
the San Juan metro area. At this moment, the greatest hazard with
these showers will be ponding of water on roadways and in poor
drainage areas. Rest of the area, including the USVI, is expected
to observe mainly fair weather conditions.

A drying trend is expected to commence starting tonight and continuing
through the upcoming weekend as the mid to upper-level ridge begins
to build and amplify overhead. This will result in the erosion of
the low- level moisture that has been in place across the region
since mid- week. Therefore, mainly fair weather conditions can be
expected across most of the region throughout the weekend. Some
showers, however, cannot be ruled out portions of eastern PR and
the USVI during the overnight and early morning hours followed by
some activity across interior and western PR during the afternoon
hours due to daytime heating and local effects. Given, however,
that a drier air mass will be overhead, the shower activity that
does develop should be short-lived and only lead to minor rainfall
accumulations.

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

A much drier airmass and more stable weather pattern is expected by
Monday and through at least the middle of next week, as the aformentioned
mid to upper-level ridge will continue to build and amplify overhead.
This will erode low-level moisture pooling and at the same time strengthen
the trade wind cap inversion. Recent model guidance all suggest a gradual
decrease in layered precipitable water values dropping to less than
an inch during the early part of the period. However the local pressure
gradient is to tighten across the region Wednesday through Friday,
as the surface high builds north of the region. This in turn will
cause an increase in the east to northeast trade winds. As a result,
mostly fair weather and somewhat breezy conditions can be expected
across much of the region, with limited shower activity each day
except for early morning cool advective passing showers along the
north and east coastal sections. This will be followed by isolated
afternoon showers over parts of central and southwest PR, and mainly
downwind of the USVI each day. No significant weather feature is
so far forecast for the long term at this time.

&&

.AVIATION...Mainly VFR conditions expected across all local terminals
throughout the period. A few brief SHRA may affect NE PR during
the early morning hours, resulting in VCSH at TJSJ. SHRA expected
to develop across interior and western PR after 18/17z, affecting
TJMZ and TJBQ terminals through 18/23z. Brief MVFR conditions are
possible with the heaviest SHRA. Light and variable winds through
18/13z, becoming E between 10 and 15 knots with sea breeze variations
developing afterwards.

&&

.MARINE... Gentle to moderate east to northeast winds will prevail
across the regional waters through the upcoming weekend. Seas
will range between 2 to 5 feet and winds 10 to 15 kts. A northerly
swell will continue across the Atlantic waters through at least
Saturday. Seas are expected to increase late Monday night or early
Tuesday when a long period northwest swell is forecast to reach
the local Atlantic Waters and local Passages along with the increasing
easterly trades.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 81 72 83 72 / 40 20 20 20
STT 80 71 83 73 / 20 20 20 20
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Re: Caribbean - Central America Weather

#19731 Postby cycloneye » Sat Jan 19, 2019 5:24 am

Area Forecast Discussion
National Weather Service San Juan PR
431 AM AST Sat Jan 19 2019

.SYNOPSIS...
Surface high pressure across the northeast Atlantic and a weakening
low pressure system north of the area moving eastward across the
western Atlantic will help to maintain light to moderate east to
northeast wind flow. A mid to upper level ridge will continue to
build northwards across the region from the central Caribbean while
maintaining stable conditions aloft. A cold front and the associated
area of low pressure is forecast to enter and move across the western
Atlantic Sunday through Monday.

&&

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

Drier than normal air mass will prevail over the local area for the
next few days. There will be a few patches of moisture across the
area that will bring slightly higher moisture, but it is not
expected to have that big of an impact other than scattered showers
over the local waters and around the USVI. In the afternoon hours
for the next few days, showers are expected to develop across
western PR, but mainly locally induced. The high resolution models
indicate decent amounts of rain today and on Monday, but less rain
on Sunday because of even drier air moving in. Nevertheless, some
showers are forecast each afternoon across portions of western PR.
There is no particular synoptic feature at the surface or the upper
levels that would help enhance shower development. The forecast
soundings indicate that the little moisture there is will be limited
to the lower levels, and the other instability parameters indicate a
fairly stable atmosphere is expected. Therefore, the main pattern
will be mostly fair weather with a few brief and mainly light
showers across the local waters, near the USVI and eastern PR in the
morning and overnight hours, then locally induced showers across
portions of western PR in the afternoons.

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

Overall dry and stable conditions is forecast to continue at
least through Wednesday, as the mid to upper level ridge will
build and extend northward across the region. This in turn will
erode low- level moisture convergence and at the same time strengthen
the trade wind cap inversion. Model guidance also continued to suggest
decreasing layered precipitable water values to less than an inch
at least until Wednesday. By the latter part of the week the local
pressure gradient is to tighten across the region as the surface
high builds north of the forecast area while spreading across the
west and central Atlantic. This will cause an increase in the east
to northeast trade winds and consequently increase the moisture
advection from an old frontal boundary which is forecast to sink
southward into the tropical Atlantic. As a result, an increase in
moisture transport is forecast for the latter part of the week and
into the weekend with breezy conditions and periods of quick
passing clouds and showers during the overnight and early morning
hours. During the daytime, isolated to scattered afternoon showers
will remain possible mainly over parts of central and west to
northwest sections of PR, and mostly downwind of the USVI.

&&

.AVIATION...VFR conds expected for the local terminals for the next
24 hours, with the exception of possible MVFR conds at some point
between 19/19Z and 19/22Z at TJMZ. Winds will be light and variable
through 19/13Z, thereafter winds will become mainly easterly at
around 10-15KT with sea breeze variations.

&&

.MARINE...Marine conditions will remain unchanged through the
weekend with seas of 2 to 4 feet, with easterly winds of 10 to 15
kts. A northerly swell will continue to fade across the Atlantic waters
and local passages today while another long Dominant period northwesterly
swell is forecast to arrive across the local Atlantic Waters by Tuesday.
A low to moderate risk of rip currents for the northern beaches
of Puerto Rico and the U.S. Virgin Islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 73 85 74 / 10 20 20 20
STT 82 72 83 73 / 10 20 20 20
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Re: Caribbean - Central America Weather

#19732 Postby cycloneye » Sun Jan 20, 2019 5:19 am

Area Forecast Discussion
National Weather Service San Juan PR
541 AM AST Sun Jan 20 2019

.SYNOPSIS...Doppler weather radar,recent satellite imagery and satellite
derived total precipitable water product all suggest a a drier air
mass will continue to spread across the region today through Monday.
A mid to upper level ridge will also build and hold across the region
for the next several days and therefore support a strengthening of
the cap inversion while limiting convective development across the
islands. Surface high pressure is expected to move across the western
Atlantic by the middle of the upcoming week and increase the winds
across the area as the local pressure gradient tightens. This will
result in breezy conditions.

&&

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

A generally drier than normal air mass is still expected to prevail
over the local area for the next few days. There will be patches of
moisture across the area that will bring slightly higher moisture,
especially on Monday, which may cause scattered showers over the
local waters and around the USVI in the morning, then allowing for
moderate to locally heavy showers in the afternoon across western
PR. That said, for the next few days in the afternoon hours, showers
are expected to develop across western PR, but mainly locally
induced. In the next few days, Monday looks to be the day with the
most significant afternoon rainfall, today and Tuesday looks like
less rainfall accumulations are to be expected. There is still no
particular synoptic feature at the surface or the upper levels that
would help enhance shower development. There is a frontal boundary
that will approach from the northwest, but this is expected to
remain far enough to not have an impact locally. Only a change in
wind direction from the northeast ahead of the front can be expected
on Tuesday. Also, the model guidance suggests that we will be under
some moisture on Tuesday. However, the moisture is still forecast to
be below normal, so isolated to scattered showers could be expected
on Tuesday.

.LONG TERM...By Wednesday local pressure gradient is to tighten
across the region as the surface high builds north of the forecast
area while spreading across the west and central Atlantic. This
will cause an increase in the east to northeast trade winds and
consequently increase the moisture convergence from remnants of an
old frontal boundary which is forecast to sink southward into the
tropical Atlantic. As a result, breezy conditions with an increase
in moisture transport is forecast for the latter part of the week
and possibly into the weekend. Periods of quick passing clouds and
showers can therefore be expected during the overnight and early
morning hours followed by isolated to scattered afternoon showers.
The shower activity should be focused mainly over parts of central
and west sections of PR, and mostly down wind of the U.S.Virgin
Islands. Still no significant weather feature is expected across
the forecast areas during the period.

&&

.AVIATION...VFR conds expected for the local terminals for the next
24 hours, with the exception of possible brief MVFR conds at some
point between 20/18Z and 20/21Z at TJMZ. Winds will be light and
variable through 20/13Z, thereafter winds will become easterly at
around 10-15KT with sea breeze variations.

&&

.MARINE...
Marine conditions will remain relatively quiet through Monday
with seas of 3 to 5 feet, with easterly winds between 10 to 20
knots. Small craft operators should exercise caution due to the
stronger winds across portions of the local waters.

There is a moderate risk of rip currents for the northwestern to
northeastern and some of the southern beaches of Puerto Rico as
well as Vieques and Culebra. There is also a moderate risk of rip
currents for the some of the northern beaches of St. Thomas as
well as the north and south beaches of St.Croix.

&&

.FIRE WEATHER...
Elevated fire weather conditions expected for south coastal plains
of Puerto Rico today. A continued drying of fuels is expected across
the south coastal plains as drier air will move in across the region.
RH and winds may briefly near critical threshold values along
with KBDI which were already above critical threshold. Therefore
fire behavior danger will be elevated today and possibly on
Monday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 85 75 / 20 30 30 20
STT 84 73 83 73 / 30 30 20 20
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