Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
339 AM AST Mon Nov 25 2019

.SYNOPSIS...
A trade wind perturbation will increase moisture across the
islands today and tomorrow. However, the lack of upper level
support and dry air at mid levels will limit the potential for
thunderstorm development. Pleasant temperatures will prevail
throughout the week.

&&

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

The short-term period is forecast to be tranquil with few passing
showers during the morning hours across the U.S. Virgin Islands and
eastern Puerto, then isolated to scattered showers during the
afternoons over portions of the U.S. Virgin Islands and Puerto Rico.
Rainfall amounts are expected to be light due to the lack of
sufficient moisture. Thunderstorm development is not expected at
this time due to warmer 500 temperatures, limited low-level moisture
as well as upper-level forcing.

Today a slight increase in moisture is expected as a result of a
weak perturbation within the easterly flow. Guidance shows moisture
increasing from 1.1. inches this morning to 1.5 inches this
afternoon. The 24/00Z TJSJ Skew-T shows a strong inversion from 810
to 700 mb, this drier air has remained in the mid to upper levels of
the atmosphere through the weekend. Analysis of the relative
humidity values from 500, 700 and 250 mb depict values ranging from
10 to 30 percent today. The drier air and relatively limited
moisture will hinder shower development this afternoon.
Nevertheless, shallow convection is expected to develop as a result
of local and diurnal effects. Also, limited instability as well as
moisture will cause showers to be short-lived.

Tuesday, low-level moisture is expected to continue to increase
across the region and erode the drier air in place. Precipitable
water values are forecast to peak at 1.8 inches before slightly
falling again. A short-wave trough is expected to begin to develop
across the western Atlantic Tuesday night.

Wednesday, the short-wave trough will continue to deepen due to
several jet streaks which will round the base of the trough. The
base of the trough is expected to remain to the northwest of Puerto
Rico, but will cause the mid and upper-level ridges to flatten. Then
late Wednesday night the trough is expected to move east of the area.

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

Stable, cold and quite weather conditions should prevailed through
the beginning of the long-term period. GFS/ECMWF are suggesting a
drying trend Thursday and Friday, with TPW values between 1.0 and
1.55 inches. Under a northeasterly wind flow, occasional trade
wind showers cannot be ruled out over the windward sections of
Puerto Rico and the U.S. Virgin Islands. However, the lack of
upper level support and the presence of dry air at mid levels will
limit vertical development.

GFS and ECMWF are suggesting the arrival of the remnants of a
frontal boundary, increasing moisture and lowering air
temperatures on Saturday and Sunday. This feature will linger
through at least late Sunday, when the leading edge of a tropical
wave is forecast to reach the islands Monday morning or afternoon.
The axis of this wave is forecast to move over or near the region
by Tuesday. The weather picture is not clear due to the amount of
uncertainty present at this time.

&&

.AVIATION...

VFR conds expected over the next 24 hrs. Easterly winds of 10 to
15 kts with sea breeze variation by 25/12Z. VCSH/SHRA are
forecast to develop by 25/16Z across the interior and northern PR
followed by showers across the western PR by 25/18Z. SHRA should
increase across the USVI terminals by 26/03Z.

&&

.MARINE...

Seas will continue to improve across the local waters today. After
tonight, mariners can expect tranquil marine conditions
throughout the work-week, with seas below 6 feet and winds at 18
knots or less.

Marine guidance are suggesting a northerly swell moving across the
local Atlantic Waters and Caribbean Passages by Saturday or
Sunday. Stay tuned to follow the evolution of this event.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 76 88 76 / 40 40 30 50
STT 86 77 86 76 / 40 40 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
339 AM AST Tue Nov 26 2019

.SYNOPSIS...

A tropical wave will increase the potential for shower activity
across the islands today, especially across the western sections
during the afternoon hours. Although moisture will increase
across the islands, ridge and dry air at mid/upper-levels will
suppress the vertical development of showers across the region.

&&

.Short-Term...Today through Thursday...

A tropical wave and its associated moisture will increase low-level
moisture convergence over the region. Current guidance shows
precipitable water reaching 1.9 inches this afternoon. Later today
low-level moisture, sea breeze convergence, and diurnal effects will
aid in the development of showers over the U.S. Virgin Islands and
Puerto Rico. The TJSJ 26/00Z sounding shows light low-level winds
less than 10 knots. This wind flow will cause showers to move slowly
this afternoon, which could lead to urban and small stream flooding
as well as ponding of water on roadways. Similar to yesterday, deep
convection is not expected to develop as a result of drier air mass
and ridging in the mid and upper-levels of the atmosphere. The
ridging aloft will suppress the vertical development of showers
across the region. Therefore, thunderstorm development is not
anticipated this afternoon.

Wednesday, the short-wave trough will continue to deepen due to
several jet streaks which will round the base of the trough. The
base of the trough is expected to remain to the northwest of Puerto
Rico, but will cause the mid and upper-level ridges to flatten. Then
late Wednesday night, the trough is expected to move east of the
area. Stratiform showers are expected to develop during the
afternoon as a result of local and diurnal effects. This activity
will produce light rainfall amounts. A weak trough is expected to
move through the area on Wednesday, turning surface winds to the
east or northeast. Also, these winds will disperse a dry air mass
from the Central Atlantic over the region. The drier air mass will
cause precipitable water values to slowly fall on Wednesday night
through early Thursday morning, with the precipitable water value
bottoming out to 1.36 inches.

Thursday, a drier air mass is expected to remain over the area;
however, precipitable water values are forecast to stabilize, but
still rank below the climatology for November. Although, a drier
air mass and limited low-level moisture will be over the area;
showers are still expected to develop during the afternoon due to
local and diurnal effects.

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

Stable and tranquil weather conditions are forecast on Friday.
The drying trend will persist until Friday afternoon when
GFS/ECMWF are indicating TPW values between 1.0 and 1.55 inches,
which are below normal conditions for this time of the year. Under
a northeasterly wind flow, occasional trade wind showers cannot be
ruled out over the windward sections of the islands.

On the onset of the arrival of the remnants of a frontal boundary
passing showers are forecast to increase across the northern
coast of Puerto Rico and the U.S. Virgin Islands late Friday night
into the weekend. TPW is forecast to increase above 1.6 inches by
Saturday and Sunday.

By early Monday morning, subsidence ahead of a tropical wave will
result in clear skies with little or no rain. Then, moisture will
increase once again, but this time from the east. GFS/ECMWF,
both, are suggesting a tropical wave reaching the local region
late Monday into Tuesday. On Wednesday, after the passage of the
aforementioned tropical wave, winds will return from the northeast
and another frontal boundary is forecast to stall north of the
islands. It will be inducing a prefrontal trough over the
northeast Caribbean. In addition, a polar trough will move near
the region by Tuesday or Wednesday, which would erode the ridge
aloft. Therefore, the upper-level dynamics could enhance the
formation of organize convection, especially across the east half
portion of PR and the U.S. Virgin Islands. Although the weather
picture is not clear at this time due to the amount of
uncertainty, a wet and unstable weather pattern will remain
possible for the first part of the upcoming week, if the guidance
is right.

&&

.AVIATION...

VFR conds expected over the next 24 hrs. Winds will be out of the
east at 5 to 10 kts. VCSH/SHRA are forecast to develop today
across the USVI and PR eastern terminals by 26/12Z. This activity
will spread to TJBQ/TJMZ by 26/18Z. SHRA/VCSH should begin to
diminish by 27/06z. Sea breeze variations expected along the west
and north coast of PR after 26/13Z.

&&

.MARINE...

Mariners can expect tranquil marine conditions with seas at 5
feet or less and east winds around 15 knots through most of the
work-week. However, winds are forecast to shift from the northeast
by Thursday and more from the north by the upcoming weekend.

The forerunners of a northerly swell is forecast to reach the
islands by Saturday, peaking on Sunday. Marine guidance are then
suggesting a second swell by Tuesday or Wednesday of next week.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 86 76 / 50 50 40 30
STT 87 77 86 76 / 40 40 40 40

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
426 AM AST Wed Nov 27 2019

.SYNOPSIS...
A tropical wave propagating across the Caribbean Sea will bring
passing showers across the local waters, the U.S. Virgin Islands
and north and east Puerto Rico through the morning hours. Local
effects, diurnal heating and sea breeze variations will result in
afternoon convection mainly across the southwest quadrant of
Puerto Rico and downwind from the U.S. Virgin Islands. Stable and
quiet weather conditions are forecast for Thursday and Friday.

&&

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

This morning showers matured to thunderstorms mainly across the
Atlantic and Caribbean waters. The 18Z risk assessment yesterday
increased Puerto Rico risk for thunderstorms, and flooding rains by
20 percent. Isolated thunderstorms developed yesterday with a
similar synoptic set up with moisture from a weak tropical wave
converging across the island, and local and diurnal effects
combining to create enough instability for showers to mature to
thunderstorms. Due to the current synoptic setup, latest infrared
satellite imagery, as well as current 00Z GFS, which shows more
moisture and instability across the area this afternoon; required
the addition of isolated thunderstorms to todays forecasts for the
portions of southern, interior, and eastern areas of Puerto Rico.
However, the forecast lies on the conservative side and keeps
thunderstorm development in the aforementioned areas above. Also,
light low-level steering flow this afternoon could lead to urban
and small stream flooding as well as ponding of water on roadways.

A surface high pressure moving over the western Atlantic will
promote an east to northeast wind flow across the forecast area
before becoming northerly later today through Friday. The northerly
wind flow will advect a drier air mass into the area and erode low-
level moisture. The drier air and limit low-level moisture will
promote stable and tranquil weather conditions late tonight through
Friday. However, locally and diurnally induced showers can not be
ruled out during the afternoons. Also, patches of moisture will
transverse the region from time to time over the next several days.

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

Taking in consideration discrepancies with moisture advection
minor adjustments were made to the long term grids. However, in
general, the weather pattern continues as forecasted during the
last few days. Model guidance continues to suggest an old frontal
boundary approaching the region from the northwest. This boundary
(shear line) will stall north of the islands resulting in pleasant
temperatures and increasing the available moisture throughout the
weekend. The remnants of this front would then be lifted north by
the arrival of a tropical wave from the southeast on Monday.
Subsidence ahead of this wave will result in little or no rain for
a brief period. Then, moisture will increase once again, as both
GFS/ECMWF are suggesting, late Monday into Tuesday.

On Wednesday, another cold front, which GFS is stalling it north
of the islands across the Western Atlantic Ocean, will continue
to pool tropical moisture over the region. Also, a polar trough
will move near the region by Tuesday or Wednesday, eroding the
ridge aloft and breaking the trade wind cap. This upper-level
feature will enhance the formation of organize convection,
especially across the east half portion of PR and the U.S. Virgin
Islands.

Although a moist and unstable weather pattern seems to be possible
through the long-term, there still too much uncertainty in the
position of these features and their final impacts across the
islands.

&&

.AVIATION...

VFR at all terminals durg prd, expect VCSH across E PR
and USVI terminal sites from 27/10Z to 28/02Z. SHRA/VCTS are
possible across southern, interior and eastern PR by 27/18Z
persisting until 28/02Z. Brief MVRF conds are possible across
western, interior and eastern areas of PR due to SHRA/VCTS til
28/02Z. Wnds fm E-NE 10-15 kts with sea breeze variations by
27/12Z.

&&

.MARINE...

Mariners can expect tranquil marine conditions with seas at 5
feet or less and east to northeast winds around 15 knots. A
frontal boundary is forecast to approach the islands from the
north increasing the potential for showers and thunderstorms
across the local Atlantic waters late Saturday into Sunday.

A long period northerly swell is forecast to reach the islands by
Saturday, peaking on Sunday. Marine guidance are then suggesting
a second swell by late Tuesday or Wednesday of next week. These
swells could deteriorate marine conditions by increasing wave
heights. Stay tuned for additional information about these events.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 85 75 / 40 40 20 20
STT 86 77 85 75 / 30 30 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Thu Nov 28 2019

.SYNOPSIS...A fairly stable weather pattern is expected to
prevail across the area through Friday, however, some showers are
still expected across south and southwestern PR during the
afternoon hours due to local and diurnal effects. A weak frontal
boundary is expected to move near the area during the weekend,
bringing a slight increase in showers. A more unstable weather
pattern is possible during the early to middle portion of next
week as deeper moisture in combination with another frontal
boundary results in more enhanced rainfall potential.

&&

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

Weak SFC high pressure north of the local area will promote
northeasterly winds at around 10-15 mph today. However, the latest
guidance is suggesting weaker winds on Friday and Saturday as a
strong SFC low pressure enters the western Atlantic, causing a COL
over the local area. In the upper levels, a ridge should dominate
for the next couple of days, causing northwesterly winds. Even
though the available moisture is near or slightly below normal, the
local effects and diurnal heating may cause locally induced showers
and isolated thunderstorms across the S-SW sections of PR this
afternoon, while the rest of PR and across the USVI mainly fair
weather and possible brief showers is expected, except central and
portions of eastern PR where scattered showers are expected. That
said, the more significant rainfall accumulations are expected
across the SW quadrant of PR this afternoon.

For Friday and Saturday, the forecast becomes a tad more uncertain,
or confidence decreases. The reason is that the COL that is expected
over the area is forecast by the different models to have the winds
from different direction for the same time period. That said, this
is the nature of the COL, the winds decrease and become more
variable. However, the models agree that the available moisture will
be lower over PR and USVI but higher over the local waters for the
most part. According to the WRF and GFS though, showers are
possible across the north and eastern sections of PR on Friday
afternoon, and then on Saturday afternoon, more significant
showers and even thunderstorms are forecast for the southern
sections of Puerto Rico.

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

A weak frontal boundary is expected to be located near or just
north of the area on Sunday. This feature will increase the low-
level moisture slightly, and produce more shower activity,
especially across the northern half of Puerto Rico. However, the
mid to upper-levels do not appear to be particularly conducive
for any organized convective activity. Therefore, significant
rainfall accumulations are not expected.

The weather pattern, however, is expected to change by the early
to middle portion of next week. Latest model guidance continues
to show a highly amplified polar trough moving over the western
Atlantic, with the base reaching into the northern Caribbean. At
lower-levels, a frontal boundary is expected to move into the
western Atlantic and be located near the region by Tuesday and
Wednesday. The low-level flow is expected to be from the
southeast, which will serve to advect deeper moisture into the
region with precipitable water values ranging between 1.7 and 2.0
inches. Therefore, the potential will exist for more organized
showers to materialize given the more favorable conditions aloft
and the frontal boundary, which will be located near the region.
Some thunderstorm activity is also likely given that 500 mb
temperatures are expected to drop to around -7 Celsius.

Conditions look to improve by the latter portion of next week as
the polar trough lifts towards the north. This will allow ridging
to build aloft, eroding the moisture.

&&

.AVIATION...Prevailing VFR conds expected across the local
terminals today. ISOLD/SCT SHRA activity expected across the local
area will cause VCSH across the local terminals. Possible TSRA
across SW-PR after 28/17Z may cause VCTS at TJPS and TJMZ. Winds of
5-10KT expected through 28/12Z, increasing thereafter from the ENE-
NE at 10-15 KT with sea breeze variations expected today.

&&

.MARINE...Tranquil marine conditions are expected to continue
across the regional waters through Friday, with seas less than 5
feet expected. Conditions, however, are expected to deteriorate
significantly by the weekend due to the arrival of a northerly
swell. This swell event is expected to produce hazardous seas
greater than 7 feet across the Atlantic waters and local passages.
Therefore, small craft advisories will likely be needed. The
hazardous seas are expected to last through early next week.

For beachgoers, there is a moderate risk of rip currents for most
of the northern beaches of Puerto Rico and Culebra as well as
across Botany Beach in Saint Thomas for today. The rip current
risk will become high during the weekend for the north-facing
beaches as a result of the northerly swell.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 77 87 77 / 40 30 30 30
STT 87 77 87 76 / 30 20 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
454 AM AST Fri Nov 29 2019

.SYNOPSIS...Fair weather conditions are expected to prevail across
the local area for today with very limited shower activity
expected. A weak frontal boundary is expected to be located near
the area over the weekend, with an increase in low-level moisture
and shower activity expected. A more unstable weather pattern is
still on tap during the early to middle portion of next week as
deeper moisture and another frontal boundary could enhance the
rainfall potential across portions of the local area.

&&

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

Weak SFC high pressure has weakened and a SFC low pressure has
entered the western Atlantic, which put us in a COL today. Because
of this, the local winds may be light and variable through the day.
This COL will move slightly east on Saturday as the high pressure
gradually strengthens north of the local area, promoting a more
northerly wind flow, then east to northeast wind on Sunday. The
available moisture will remain near normal for the next several days
as a weak frontal boundary approaches the local area this weekend.
In the upper levels, a ridge should dominate today and Saturday,
causing northwesterly winds, but it will flatten considerably by
Sunday. At this time, the forecast is mainly for fair weather with
isolated to scattered showers. The shower activity may be a bit more
significant late tonight as a band of showers moves through, then on
Sunday afternoon, with the combination of the local effects and
diurnal heating, moderate to locally heavy showers could develop
across central and western PR. The latest WRF model is bullish on
the rainfall for Sunday, but the model has overdone it a bit the
past few days, so we held of on the thunderstorm potential for
Sunday. However, it shouldn`t be completely ruled out to have
isolated thunderstorms on Sunday afternoon.

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

As the surface high pressure moves eastward into the east-central
Atlantic and a frontal boundary moves into the western Atlantic,
the low-level flow will become southeasterly by Monday. This will
advect deeper moisture into the area with precipitable water
values expected to increase to up to 1.8 inches. Therefore, an
increase in afternoon convection is expected, especially across
northwestern Puerto Rico. More widespread rainfall activity is
possible by Tuesday and Wednesday as the frontal boundary
approaches the area and a polar trough amplifies across the
western Atlantic. These features will serve to increase the
vertical motion. Thunderstorms are also more likely given that
the 500 mb temperatures are expected to cool to around -7 degrees
celsius. At this point, it is still too early to pinpoint how
much rainfall and which locations have the best potential to
receive the heaviest activity.

Weather conditions are expected to improve by the latter half of
next week as the polar trough lifts to the north and a mid-level
ridge builds overhead. This will result an erosion of the moisture
content.

&&

.AVIATION...Prevailing VFR conds expected across the local
terminals today. ISOLD/SCT SHRA activity expected across the local
area may cause VCSH across the local terminals. Possible SHRA across
southern PR after 29/18Z may cause TEMPO -SHRA at TJPS, while brief
SHRA could also affect TJBQ. There is uncertainty so VCSH was
written on TAF. Somewhat variable winds at around 5 KT are expected
today, with possibly a strong sea breeze influence.

&&

.MARINE...Tranquil marine conditions are expected to continue
today with seas of less than 4 feet expected. Seas, however, are
expected to rapidly deteriorate by Saturday afternoon as a
northerly swell invades the local waters. At this time, seas are
forecast to increase to as high as 8 to 10 feet the Atlantic
waters and local passages. These hazardous marine conditions are
expected to continue into Monday. A small craft advisory has been
issued for the outer Atlantic waters starting Saturday afternoon.
Small craft advisories are expected to be issued for the rest of
the local Atlantic waters and passages later today.

For beachgoers, there is a low risk of rip currents across all of
the local beaches for today. However, the rip current risk will
quickly become high for the north-facing beaches by Saturday and
continuing through early next week as a result of the northerly
swell. In addition, to the high risk of rip currents, there will
also be high surf conditions as breaking wave heights are expected
to surpass 10 feet across many of the north-facing beaches.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 86 75 / 50 50 30 30
STT 88 75 88 76 / 20 40 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
448 AM AST Mon Dec 2 2019

.SYNOPSIS...
Hazardous marine conditions continue across the area until
Tuesday. An increase in moisture is expected later today and
through tomorrow with a mid-level trough enhancing local rainfall
activity. Weather conditions are expected to improve by the second
half of the workweek.

&&

.Short term... Today through Wednesday...

Showers continued mainly over the offshore coastal water overnight
as a slot of drier air moved across the region. This will however be
short lived as a gradual increase in low level moisture is expected
later today and through Tuesday. Gradually increasing low-level
moisture convergence and mid to upper level instability is forecast
for most of the period, as a broad polar trough and associated cold
front will sweep across the west and southwest Atlantic late today
through Tuesday. In addition a mid level short wave trough is also
forecast to move through the region by Tuesday to also increase the
potential for active weather conditions across the forecast area.

The interaction of the polar trough and cooler temperatures aloft,
along with good low level convergence and warm moisture advection
caused by an approaching easterly perturbation; all suggest
deteriorating conditions beginning later today and continuing
through Tuesday or early wednesday. That said, expect good potential
for enhanced shower activity later this afternoon and into the early
evening hours. Isolated thunderstorm will be possible mainly over
parts of the central interior and north to northwest sections of
Puerto Rico steered by the south to southeasterly low level wind
flow.

On Tuesday, the increasing moisture convergence will support
continued advection of moisture into the area. Therefore the best
potential for showers and thunderstorm development is still for
Tuesday with enhance convection expected across the islands and
coastal waters. Recent model guidance continued to suggest
increasing layered precipitable water values near 2 inches by
Tuesday, which would be near 2 standard deviations above normal for
the month of December. During the morning hours, showers and
thunderstorms are forecast to affect portions of eastern Puerto Rico
and the USVI, then spreading west and northwards across the rest of
Puerto Rico through the day. The potential for heavy rainfall will
be high, as well as for prolonged rainy conditions. There is also
high the risk of urban and small stream flooding.

By Wednesday model guidance still suggest a gradual improvement in
the weather condition due to more stable conditions aloft as the
upper trough lifts northwards, as well as diminishing low level
moisture advection. However, still expect sufficient moisture
availability for the development of afternoon showers along with
with a few thunderstorms, mainly across parts of the central
interior and northwest sections of Puerto Rico. Isolated to
scattered afternoons showers are also expected over the USVI on
Wednesday.

.LONG TERM...Thursday through Tuesday...
Mid-level ridge begins to build from the west, while surface high
pressure continues to hold in place in the middle of the Atlantic
Ocean. Under this pattern, patches of moisture are expected to
filter into the islands from time to time, with no significant
weather feature on sight. By Sunday, the mid-level ridge begins to
retreat to the west and, at the upper levels, a trough will begin
to approach from the north. However, at least trough the long-
term forecast period, the system seems to remain far enough to
have any real impact over the forecast area. In general, the
weather pattern will favor isolated to scattered showers in the
overnight and early morning hours across portions of eastern
Puerto Rico and the U.S. Virgin Islands, while locally induced
showers will remain possible over the western half of Puerto Rico.

&&

.Aviation...VFR conds at the local sites durg prd. Brief MVFR psbl
in SHRA and low cig at and vcty TKPK/TNCM as tropical moisture
increase from the east. SCT-BKN lyrs nr FL022...FL050...FL080 ovr
regional waters and en route btw islands. Isold SHRA vcty
TISX/TIST/TJSJ/TJPS til 02/14Z. Isol TSRA psbl fm 02/16Z-02/23Z
mainly over the interior sections of Puerto Rico and vcty
TJSJ/TJNR/TJBQ/TJMZ. Sfc winds will be calm to light and variable
bcmg fm E-SE 5-15 knots with sea breeze variations aft 02/14z.


&&

.MARINE...
A northerly swell continues to create hazardous marine conditions
across the local waters. Seas of 8 to 10 feet, with occasional
seas up to 13 feet are expected today. These conditions are
expected to persist until tomorrow. Please refer to the latest
Marine Weather Message (MWWSJU), Coastal Hazard Message (CFWSJU)
and Surf Zone Forecast (SRFSJU) for the latest updates.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 88 76 / 50 30 60 40
STT 86 78 85 74 / 50 60 60 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
414 AM AST Wed Dec 4 2019

.SYNOPSIS...
A drier weather pattern is expected for the second half of the
workweek and early in the weekend. However, passing showers are
expected over the islands with afternoon isolated thunderstorms
possible across the northwestern quadrant of Puerto Rico. Choppy
marine conditions continue for the Atlantic waters.

&&

.SHORT TERM...Today through Friday...
Deep layered trough across the west and southwest Atlantic will
continue to lift further northwards into the northwest Atlantic, and
allow a mid to upper level ridge to reestablish and strengthen its
hold across the region today through the end of the work week. This
changing weather pattern will promote drier and stable conditions
with increasing subsidence aloft. In the meantime, the broad surface
high pressure north and east of the region will continue to build
west and south across the forecast area to help strengthen the trade
wind cap inversion. Consequently a more dominant easterly trade wind
flow will prevail.

Moisture transport and low level convergence is therefore forecast
to erode and diminish, as the low level wind flow becomes more east
southeast today, then more easterly on Thursday and Friday as the
ridge builds north of the area. That said, expect limited moisture
availability for any widespread convection during the day. However
local effects and good daytime heating will give way to afternoon
shower development mainly across parts of the interior and west to
northwest sections of Puerto Rico. There is a slight chance for
isolated thunderstorms today in the northwest section of Puerto Rico
,as daytime temperatures are expected to increase to slightly higher
than normal today. Any afternoon showers that develop are expected
to steer northwest towards the coastal areas.

Drier conditions expected on Thursday and Friday as the mid to upper
level ridge relocates across the areas and dominant easterly trades
will prevail. Afternoon convection if any will be limited to parts
of the central interior and west sections of Puerto Rico each day.
Lesser showers activity is forecast in and around the USVI during
the rest of the day through the end of the week as mostly fair
weather conditions and sunny skies should prevail. However a few
light to moderate afternoon showers may form mainly on the west end
of the islands or just offshore.

.LONG TERM...Saturday through Thursday...
For the first half of the weekend, a mid-level high pressure will
continue along the western Caribbean Sea. Drier air in the mid-
level should prevent strong convection over the area. However,
there is enough moisture at the lower levels to promote the
formation of afternoon showers over western Puerto Rico while
isolated activity will be possible over the eastern half of the
forecast area. The environment looks a bit more favorable on
Sunday as better moisture arrive into the islands. In addition,
the ridge at the mid-levels begins to retreat.

Getting into the first half of the next workweek, an upper level
trough will move north of the area. Although this system does not
look to be positioned in the best position to support rain
activity, at least some upper level divergence is possible, which
should increase the chance for isolated thunderstorm formation
across western Puerto Rico in the afternoon hours. For Wednesday
and Thursday, an upper level ridge builds over the region. At the
lower levels, winds are expected to shift from the east-northeast,
promoting morning showers over the northern and eastern half of
Puerto Rico and over and around the U.S. Virgin Islands.

&&

.Aviation...VFR at all terminals. Isold SHRA ovr regional waters and
en route btw the local islands. Mostly SCT lyrs nr FL.
025...FL050. Sfc wnds lgt/vrb bcmg fm E-SE btw 5-15 kts with sea
breeze variations. No sig operational wx impacts attm.


&&

.MARINE...
A weak northwesterly swell will maintain choppy seas across the
Atlantic waters with seas up to 6 feet. Southeasterly winds at 10
to 15 knots continue with showers from time to time. Small craft
operators are urged to exercise caution. For the beachgoers, the
high rip current risk continues for the northern coast of Puerto
Rico and Culebra.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 77 89 77 / 30 30 30 40
STT 86 79 86 79 / 50 20 30 30

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
444 AM AST Thu Dec 5 2019

.SYNOPSIS...A gradual drying trend is forecast across the region
during the next few days and into the weekend. High pressure
ridging aloft will reestablish across the region to maintain
overall stable conditions, while the Atlantic high will strengthen
north and east of region to promote a light to moderate easterly
wind flow across the region. Early morning passing showers will
remain possible over the local waters and around a few of the
islands but will be less frequent. Afternoon shower development
and isolated thunderstorms will remain possible mainly across the
northwestern quadrant of Puerto Rico today. The easterly trade
winds are forecast to increase over the weekend into early next
week and consequently increase the chance of more frequent passing
trade wind showers.

&&

.SHORT TERM...Today through Saturday...
A mid-level ridge will continue to hold across the local area for
the rest of the workweek. At the low levels, high pressure located
over the Atlantic Ocean will continue to extend over the area,
promoting a more easterly wind flow during the next several days.
These features should work against strong convection development
over the area. However, as usual groups of clouds and showers moving
embedded in the trade winds will supply enough moisture for a few
passing showers across portions of eastern Puerto Rico and the U.S.
Virgin Islands, while scattered showers and isolated thunderstorm
may develop over western Puerto Rico during the afternoon. Moving
into the last part of the workweek and early in the weekend, the
pattern looks even drier across the region. So far, the latest GFS
guidance suggest precipitable water values dropping to near 1.2 to
1.5 inches, which should limit any significant rainfall activity
across the islands.

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

The environment looks a bit more favorable and late Sunday into
early next week, as the east to northeast trade winds increase
along with low level moisture convergence across the forecast
area. In addition, the mid to upper level ridge is forecast to
erode as a polar trough moves across the west Atlantic and north
of the region. The breaking own of the upper ridge will weaken
the trade wind cap inversion and support better chance for
afternoon shower development across the islands. Most of the
moisture however will be advective and brought in form old
frontal remnants north of the region. Therefore no significant
rainfall accumulations are anticipated this time for most of the
long term period.

During the first half of the period, as previously mentioned, the
upper level trough will move north of the area. In doing it will
weaken the ridge and destabilize conditions aloft providing
better ventilation and a weakening of the trade wind cap
inversion. This will favor a better chance for early morning and
afternoon showers and thunderstorm development mainly across
central and southwest Puerto Rico. For Wednesday through Friday,
an upper level ridge is again forecast to build over the region.
At the the same time the local pressure gradient will tighten and
winds will become more northeasterly while increasing due to a
surface trough and associated area of low pressure forecast to
develop northeast of the region over the tropical Atlantic. This
will also promote more frequent morning passing showers over the
northern and eastern half of Puerto Rico, as well as over and
around the U.S. Virgin Islands.

&&

.AVIATION...VFR conditions are expected to prevail across all
terminals. VCTS are expected after 05/17Z across TJMZ/TJBQ which
could result in TEMPO groups with MVFR/IFR conditions. Winds will
stay out of the ESE at 10 to 15 knots.

&&

.MARINE...Moderate east-southeast winds will persist today becoming
more east- northeast by Friday and into the weekend. A small northwest
swell affecting portions of the local Atlantic today will continue
to subside. Another northeast swell is forecast to move across the
Atlantic and Caribbean Passages late Saturday or Sunday. Local winds
will gradually increase over the next few days into the upcoming
weekend becoming moderate to fresh resulting in choppy seas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 87 75 / 30 40 40 20
STT 86 76 86 75 / 30 30 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
415 AM AST Fri Dec 6 2019

.SYNOPSIS...A gradual drying trend is expected to continue today
and through the weekend as a mid to upper level ridge will
strengthen and hold across the region. This in turn will
increase the trade wind cap inversion and limit shower and
thunderstorm development across the forecast area. However,
locally and diurnally induced convection is expected to develop
during the afternoons, but due to modest instability and shallow
moisture showers are expected to be short- lived. Increasing east
to northeast trade winds is expected over the next several days as
the surface high pressure ridge will build and spread across the
Atlantic north and east of the region.

&&

.SHORT TERM...Today through Sunday...
A mid-level ridge is expected to hold over the area through the
short-term forecast period. As a result of this feature and dry air
at the mid levels, the trade wind cap will strengthen. Therefore,
thunderstorm formation is not favored across the area. Winds will
remain out of the east to east-northeast and, under this flow
however, patches of moisture at the low levels will continue to move
across the region. For each day, passing showers will move across
portions of eastern Puerto Rico and the U.S. Virgin Islands during
the overnight and morning hours. Then, in the afternoon, due to the
available moisture, diurnal heating and local effects, showers are
expected to develop across the interior and western Puerto Rico.

In terms of temperatures, a more easterly to east-northeast wind
flow means that temperature will be slightly cooler over the area
than what has been observed during the previous days. Normal highs
for this of year are between 84 to 86 degrees.

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

Recent model guidance continued to suggest a better chance for
showers and isolated thunderstorms by Monday and possibly on
Tuesday, as the east to northeast trade winds will increase low
level moisture convergence across the forecast area. In addition,
the mid to upper level ridge is forecast to slightly erode as a
polar trough moves across the west Atlantic and north of the
region. The breaking down of the upper ridge will weaken the
trade wind cap inversion and support better chance for afternoon
shower development across the islands. Most of the moisture however
will be advective and brought in from old frontal remnants north
of the region. Therefore no significant or widespread rainfall
accumulations are anticipated over land areas at this time.

During the latter part of the period through Friday, an upper
level ridge is again forecast to build over the region. At the
same time the local pressure gradient will tighten and consequently
winds will increase and become more northeasterly due strong
surface high pressure ridge north of the region, and a weak
induced surface trough forecast to develop northeast of the area
over the tropical Atlantic. This will also promote more frequent
morning passing showers which should affect the northern and
eastern half of Puerto Rico, as well as the U.S. Virgin Islands.
In addition late Friday through Saturday, weak perturbation in
the prevailing trades will bring an increase in low level moisture
and therefore increase the chance for shower development during
the early morning and afternoon hours.

&&

.AVIATION...VFR conditions are expected across all terminals.
Passing showers are expected across the area through 06/16Z. After
06/18Z, SHRA could briefly reduce visibility to MVFR across TJMZ/TJBQ.
Winds will be out of the ENE at 5 to 15 knots.

&&

.MARINE...
Moderate easterly winds are expected to persist through the
weekend. This will create a light to moderate chop across portions
of the local waters and passages through today.Another northerly
swell is forecast to move across the Atlantic and Caribbean Passages
late Sunday into Monday. This along with increasing east to northeast
winds will create choppy and hazardous seas. In the meantime, local
seas will be up to 5 feet for the next few days with easterly
winds up to 15 knots. There is a low or moderate risk of rip
currents across the local beaches.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 76 85 75 / 40 30 20 30
STT 86 76 85 74 / 20 30 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
428 AM AST Sat Dec 7 2019

.SYNOPSIS...

Fairly benign weather conditions are expected for the next week,
with no major weather systems expected. However, showers will
continue to move inland from local waters for the nighttime and
morning hours, with more showers developing in the afternoon for
western Puerto Rico. Faster than average trade winds for the next
week will help to keep these showers moving along. These winds
will also induce rough seas during the next workweek.

&&


.SHORT TERM...Today through Monday

The mid-level ridge will continue to dominate our local region
through Sunday night and Monday. This weather pattern will generate
an easterly wind flow as well as relatively stable weather
conditions across the local forecast area. Although stable and dry
conditions will prevail across the area, showers are still expected
to develop due to sea breeze convergence and diurnal heating. Most
of these showers will develop over the interior and western areas
of Puerto Rico during the afternoons.

Satellite imagery and models are suggesting low level moisture
advection across the local forecast area for the next few days.
Most of the showers associated to these patches will occur over
the eastern coastal sections of Puerto Rico and adjacent islands.


.LONG TERM...Tuesday through Sunday

Fairly uneventful weather conditions are expected to prevail in the
longterm forecast. Near average moisture will be with us, with
precipitable water values mostly between 1.4 and 1.7 in. Also, trade
winds stay fairly brisk as well, helping to keep showers moving
along and reducing the amount of rainfall accumulations. No major
fronts or tropical waves are expected at this time for the next
week. Furthermore, upper-level dynamical forcing remains fairly
uninspiring until possibly Friday...and fairly briefly even then.

Despite the generally average conditions in the long-term, there
will still be plenty of opportunity for passing showers. Advective
showers will develop in the nighttime and morning hours, threatening
the east coast of Puerto Rico and the USVI, particularly Tuesday
night through Friday when the highest moisture content will
occur. Furthermore, the usual afternoon shower activity is
possible, particularly for western Puerto Rico. However, for
reasons mentioned in the last paragraph, these showers will likely
have minimal impact. Very long range models suggest possibly a
tropical wave clipping us to our south for next weekend. However,
there is minimal confidence in that forecast this far out.

&&


.AVIATION...

Mainly VFR conditions are expected to prevail across all
terminals for the next 24 hours. However, SHRA developing from 16z-
22z could cause tempo MVFR at TJMZ. Winds will continue from the
east at 10 to 15 knots with higher gusts at times.

&&


.MARINE...

In the short-term, seas remain fairly calm with wave heights
generally between 3-5 feet. However, with high pressure building in
the central Atlantic, this will result in choppy seas heading into
next week. Wave heights up to 6 feet are expected for Sunday, and
increasing to 7 feet for much of the next workweek.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 86 76 / 30 30 30 40
STT 85 75 86 75 / 30 40 30 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
503 AM AST Sun Dec 8 2019

.SYNOPSIS...

Isolated to scattered showers are possible for the next few days
across the region, though conditions will generally be drier. In
fact, no frontal passages or tropical waves are expected for the
foreseeable future. However, stronger than average trade winds
will be with us for most of this week, so breezy winds are
expected. These winds will drive hazardous seas heading into the
next workweek, and a Small Craft Advisory is likely at some point.

&&


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

An approaching upper level trough will usher in a westerly jet up to
55 knots Monday through early Tuesday morning. At mid levels, a cold
pool accompanying the upper level trough will approach the area and
pass to our northeast, but not without bringing 500 mb temperatures
of minus 8 degrees to the area on Tuesday. This will also be the
time when the driest mid level air will be encountered. At the
surface, high pressure over New York early Sunday morning will move
into the western Atlantic tonight and strengthen to as much as 1043
mb in the central Atlantic near 40 north by Monday evening. This
will increase the local pressure gradient and also the east
northeast winds in the lower levels. Surface winds over the local
waters will increase to around 20 knots. Bands of moisture are
interspersed in this flow over the western tropical Atlantic with
areas of drier air between. One of those drier areas is moving over
Puerto Rico this morning and will reduce the shower activity from
levels seen yesterday. Other bands of moisture will bring windward
showers during the overnight and early morning periods, and some
activity in southwest and western Puerto Rico during the mid
afternoons. Weak mid level moisture along with rapidly moving
showers will considerably limit amounts of rain received during the
period.


.LONG TERM...Wednesday through Monday

The long term forecast continues to look fairly uneventful for the
foreseeable future, as no major tropical waves or fronts are
forecasted. The threat for urban and small stream flooding will
still exist, though that threat is expected to be minor. We will
see a minor increase in low to mid-level moisture content for
Wednesday. This moisture increase will not be associated with any
organized system, but simply patches of moisture riding in with the
easterly trade winds. Fairly vigorous easterly trade winds at
around 20 knots from 850 to 700 mb will help to keep these showers
moving along, and keeping rain amounts to a minimum. However,
persistent showers over a given area could drive some localized
flooding.

Similar conditions are expected to prevail for Thursday and Friday
as well. The steering flow stays above average, and precipitable
water values stay around average. Upper level atmospheric conditions
will be rather unfavorable for thunderstorm development for the
middle to end of the week as well. Slightly drier conditions are
forecasted for next weekend, though uncertainty is high in that
regard. However, even very long range models expect uneventful
weather for the beginning of next week as well.

&&


.AVIATION...

VFR conditions are expected to prevail across all
terminals. Sct SHRA will develop in SW PR aft 08/17Z with highest
trrn obscured. Brief MVFR may be seen in TJMZ. Sfc winds ENE 5-15 kt
with sea breeze influences. Max winds W-WNW 40 kt at FL410
increasing to 55 knots at FL540.


&&

.MARINE...

The easterly trade winds are expected to increase over the next few
days as a strong area of high pressure is forecasted to develop over
the central Atlantic, thus enhancing pressure gradients. With winds
of at least 15-20 knots beginning Monday, seas will become choppy
and hazardous, with small craft advisory conditions likely.
Though the buoy just offshore of San Juan is showing seas around
3-4 feet, buoy 41043 in the outer Atlantic waters is showing wave
heights of around 6 to 7 feet and is definitely higher than model
forecasts. At this point, a Small Craft Advisory is not expected
till Monday night, but the situation will be monitored closely in
case the advisory needs to come out sooner.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 84 74 / 40 40 40 40
STT 86 75 86 74 / 30 50 50 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
446 AM AST Mon Dec 9 2019


.SYNOPSIS...

The threat for isolated to scattered showers continues across the
region, but a few factors will minimize the threat for urban and
small stream flooding. Though some localized flooding is possible,
decent low level wind flow will keep the showers moving, and
unfavorable atmospheric conditions will limit the strength of the
showers. No major weather systems are expected for the next week.
However, a strong Atlantic high pressure system will drive breezy
easterly winds and rough seas.

&&


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

An approaching upper level trough will usher in a westerly jet up to
55 knots Monday night through early Tuesday morning. At mid levels,
a cold pool accompanying the upper level trough will approach the
area and pass to our northeast, but not without bringing 500 mb
temperatures of minus 9 degrees to the area on Tuesday. This will
also be the time when the driest mid level air will be encountered.
At the surface, high pressure north of the area near 40 north this
morning will strengthen to as much as 1044 mb in the central
Atlantic by Tuesday morning. This will increase the local pressure
gradient and also the east northeast winds in the lower levels.
Surface winds over the local waters will increase to 15 to 20 knots
and continue through beyond Wednesday. Bands of moisture are
interspersed in this flow over the western tropical Atlantic with
areas of drier air between. One of those bands moved across the U.S.
Virgin Islands overnight and is entering Puerto Rico this morning.
Shower activity is expected to increase from levels seen yesterday.
Because of the stronger winds, showers will be more significant over
the windward slopes of Puerto Rico even during the typically drier
daytime hours. Weak mid level moisture along with rapidly moving
showers will considerably limit amounts of rain received during the
period but amounts up to an inch are possible. Temperatures at 500
mb are expected to fall to minus 8 this afternoon and so
thunderstorms cannot be ruled out in central and western Puerto
Rico, while drier mid levels may inhibit deep convection on Tuesday.


.LONG TERM...Thursday through Tuesday

Uneventful weather conditions are expected to prevail in the
longterm forecast. Near average moisture will be with us, with
precipitable water values mostly between 1.5 and 1.7 inches.
Also, trade winds stay fairly brisk as well, helping to keep
showers moving along and reducing the amount of rainfall
accumulations. No major fronts or tropical waves are forecasted
for the next week. Furthermore, the upper levels of the
atmosphere remain less conducive to thunderstorm activity with
plenty of ridging aloft.

Despite the generally average conditions in the
long-term, there will still be plenty of opportunity for passing
showers. Advective showers will develop in the nighttime and
morning hours, threatening the east coast of Puerto Rico and the
USVI, particularly Thursday and Friday when the highest moisture
content will occur. Furthermore, the usual afternoon shower
activity is possible, particularly for western Puerto Rico.
However, for reasons mentioned in the last paragraph, these
showers will likely have minimal impact. Long range models suggest
drier conditions heading into the next week, with the chance for
some Saharan dust working into the region. However, there is
minimal confidence in that forecast this far out.

&&


.AVIATION...

VFR conditions are expected to prevail across all
terminals. Sct SHRA will develop in SW PR aft 08/17Z with highest
trrn obscured. Isold TSRA psbl. Brief MVFR may be seen in TJMZ. Sfc
winds ENE 5-15 kt with sea breeze influences and gusts to 25 kt. Max
winds W increasing to 50-65 kt btwn FL380-510--highest near FL460.

&&


.MARINE...

The easterly trade winds are increasing as expected, due to a
strong area of high pressure developing in the Atlantic. Seas will
become choppy and hazardous, with Small Craft Advisory conditions
beginning later this evening and lasting at least into Friday.
Isolated to scattered showers are possible across local waters,
with only a small threat for thunderstorms.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 75 84 76 / 50 50 70 70
STT 85 75 86 75 / 40 40 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
529 AM AST Tue Dec 10 2019

.SYNOPSIS...

Somewhat calmer weather is expected today and tomorrow as some
drier air works in from the east. Wetter conditions are projected
for Thursday and Friday however, as a decent batch of moisture
moves in. Stronger than normal easterly trade winds will continue
for the next several days, helping the showers to move along
quickly. However, these winds will drive hazardous seas at least
into Friday. Drier weather is possible for next week.

&&


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

An approaching upper level trough has just crossed through the area
with a westerly jet up to 65 knots. Flow will be turning more
northwesterly later today and tomorrow. At mid levels, a cold pool
accompanying the upper level trough is passing to our northeast, and
will cause 500 mb temperatures to drop to around minus 9 degrees
today. Precipitable water is expected to fall to 1.1 inches this
afternoon however, and this will limit strong convection over land.
Nevertheless, a few thunderstorms are possible over the local
waters.

At the surface, high pressure has developed in the north central
Atlantic with as much as 1044 mb. It will continue to drift east
with central pressures of 1042-1044 mb fueling surface winds over
the local waters of 15 to 20 knots that will last beyond Thursday.
Bands of moisture are interspersed in the flow over the western
tropical Atlantic with areas of drier air between. One of those
bands moved across the local area overnight and was enhanced by the
upper level trough. It is being followed by the driest air of the
week. Better moisture is immediately on its heels. Moisture is also
expected to increase Wednesday and Thursday and models show better
shower activity driven across the local islands Thursday and Friday
although timing of the best showers is uncertain.

Moisture is rich below 850 mb throughout the period and well beyond,
but little is seen above 500 mb. Moisture between 850 mb and 500 mb
will increase Thursday and will generate better showers. Winds will
keep these moving quickly so excessive rainfall amounts are not
expected.


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

Coming off what appears will be a wet Thursday, Friday will still
provide scattered showers across the region. These showers will
not be due to any organized weather system, but rather just a
decent batch of moisture being advected in by the trade winds. The
wettest period for Friday appears to be in the early morning
hours, and trending drier for the rest of the day. The usual
afternoon shower activity is likely in western Puerto Rico, though
atmospheric conditions do not look favorable for thunderstorms at
this point. A high chance for showers also exists for the east
coast of Puerto Rico. Low level wind flow is still forecast to be
fairly strong, so these showers will likely be moving fairly
fast.

Conditions do not change much heading into the weekend. Though the
chance for showers remains, slightly less moisture is forecast to
move in, so a drier few days are expected. In fact, this drier
trend continues into the next workweek. Forecast models still hint
at the chance for some Saharan dust to move in by the middle of
next week, though dust concentrations look unimpressive at this
point.

&&

.AVIATION...

VFR conditions are expected to prevail across all
terminals. SHRA will spread across the USVI aft 10/16Z and over ern
PR aft 10/17Z with highest trrn obscured and brief MVFR at
TJNR/TJMZ/TJBQ. Isold TSRA psbl mainly ovr the lcl waters aft
10/18Z. Sfc winds ENE 10-20 kt with sea breeze influences and gusts
to 25 kt. Max winds WNW 50-65 kt btwn FL350-520--highest near FL400.

&&


.MARINE...

Windy conditions as a result of a strong area of high pressure in
the central Atlantic has caused rough and hazardous seas across
the region. Thus, Small Craft Advisories are in effect for several
zones across the region, with two more going into effect later
today for the offshore waters of southern Puerto Rico, and the
Rincon area. This looks to be a fairly long lasting event, as seas
will be impacted at least through Friday, with another swell event
possibly occurring for next weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 76 84 74 / 70 70 50 80
STT 87 75 85 75 / 70 40 40 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
543 AM AST Wed Dec 11 2019

.SYNOPSIS...

Showers will increase across the region over the
next few days as moisture works in from the east, with a slight
chance of thunderstorms for today. Breezy easterly trade winds
continue for the next several days, driving hazardous seas and a
high risk for rip currents. A trend to drier weather will ensue
for next week.

&&


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

A cut-off low has formed in the passing upper level trough and it
will hold about 400 miles east northeast of San Juan through
tonight before receding northeastward. Upper level winds will be
northwest and subside through the period. 500 mb temperatures will
be around minus 8 to minus 9 degrees today to create a slight
chance of thunderstorms. Chances will decrease on Thursday and
Friday.

At the surface, high pressure of around 1042 mb will be
just west of the Azores today. It will continue to drift east and
fade as another high moves out of the eastern United States and
into the western Atlantic north of 40 degrees north latitude
Thursday and Friday. This will drive surface winds over the local
waters of 15 to 20 knots that will last beyond Friday. Pockets of
moisture are interspersed in the flow over the western tropical
Atlantic with areas of drier air between. One of those pockets is
moving across the Leeward Islands this morning. Although
precipitable water values are modest, they will increase through
Friday, and the lowest levels of the atmosphere will remain quite
moist bringing periods of showers to most of the forecast area--
but especially the windward slopes of higher terrain in Puerto
Rico.

Moisture is rich below 850 mb throughout the period and well
beyond, but little is seen above 500 mb. Moisture between 850 mb
and 500 mb will increase Thursday and Friday and will generate
better showers. Winds will keep these moving quickly so excessive
rainfall amounts are not expected. Rainfall amounts over the next
3 days should not exceed 1.5 to 3.0 inches even in the wettest
areas.

&&


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

A fairly wet weather pattern continues into the weekend as
moisture gets pulled up from the southeast into our region. For
the weekend, Sunday looks to be the wetter of the two days. Under
the direction of the forecasted wind flow, southern and eastern
Puerto Rico will see the bulk of the shower activity, with a
second maximum in rainfall for northwestern Puerto Rico in the
afternoon under the convergent windflow around the island. The
atmosphere looks to be more stable for the weekend compared to the
short term period, so the thunderstorm threat will be minimal.
Low level winds are expected to slow down a little bit, but still
have decent speed to keep showers moving along. Thus the threat
for local flooding should be rather low.

As has been discussed over the past few days, a strong area of
high pressure in the Atlantic has been driving stronger than
normal easterly trade winds across the region. These winds are
expected to subside a bit as this high moves off to the east over
the weekend. However, another area of high pressure will move out
over the Atlantic for Monday, and this will once again enhance the
low level wind flow. This will impact marine conditions once
again, and will keep fairly breezy winds in the forecast. Along
with that area of high pressure, drier and more stable air is
expected to move in for next week. Long range models are even
hinting at some Saharan dust that could work in for the middle of
next week. Shower activity is of course possible, but these
showers will be less prevalent than what we have seen over the
past few days.

&&


.AVIATION...

VFR conditions are expected to prevail across all terminals. Sct
SHRA will continue over the area and spread into SW PR aft 11/15Z.
Hir trrn will be obscured. Isold TSRA are psbl. Sfc winds
increasing to 10-20 kt with gusts to 26 kt on nrn coasts. Max
winds WNW 50-60 knots btwn FL430-480 and diminishing during the
day.

&&


.MARINE...

Hazardous seas continue across the region. As such, a
Small Craft Advisory is in effect for all the local and outer
waters except for the southern nearshore waters of Puerto Rico.
Seas will range from 6 to 10 feet with seas occasionally reaching
11 feet. Seas are forecast to remain choppy into the weekend.
Though the hazardous conditions will subside a bit for the
beginning of next week, it appears another area of high pressure
to our north will drive windy conditions producing more rough seas
for next week. There is a high risk of rip currents for the
northern beaches of Puerto Rico and the eastern beaches of
Culebra. In addition, there is a high risk of rip currents for the
northeastern beach of the U.S. Virgin Islands, and the
northwestern beach of Saint Thomas.

&&



.PRELIMINARY POINT TEMPS/POPS...
SJU 85 76 84 74 / 80 80 80 80
STT 87 76 85 74 / 60 60 50 70

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Thu Dec 12 2019

.SYNOPSIS...

Continuing passing showers are expected to prevail across the
forecast area today and through the end of the week. Deeper
moisture combined with an induced low-level trough are expected to
enhance somewhat the shower activity today and tomorrow. Brisk
easterly trade winds will also persist today, under the influence
of a surface ridge stretching across the central Atlantic.

&&

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

A surface high pressure building north of the area will maintain
breezy conditions through the short term period. Meanwhile, a mid to
upper level trough northeast of the Leeward Islands is forecast to
gradually weaken, as an upper level ridge builds from the west by
Saturday. At low levels, an induced trough will increase shower
activity across the USVI and over the northeast/eastern coast of PR
through the day, with possible isolated thunderstorms developing
this afternoon across these areas and over the west coast of PR.
Maximum temperatures should stay at normal values today due to the
breezy northeast winds.

Low level moisture will linger over the region on Friday and trade
wind showers moving from the eastern waters of the islands will
continue to affect portions of the USVI and eastern PR. This
moisture will feed diurnally-induced afternoon showers over
western PR and over the San Juan metro area from streamers
developing off el Yunque area. Drier conditions are expected on
Saturday as the ridge builds aloft, and fair weather conditions
should prevail across the USVI and eastern sections of PR. Only
light to moderate showers are expected to develop over the western
coast of PR on Saturday afternoon.

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

A surface ridge over the central Atlantic, stretching westward
toward the southeastern United States will maintain its influence
over the area, with moderate, generally easterly flow expected over
much of next week. A somewhat drier airmass is expected over the
forecast area Sunday and Monday. At the same time, a TUTT low is
forecast to be to our east; this, combined with a persistent mid-
level ridge over the area will likely act to inhibit upward motion
over the area. Afternoon showers due to local effects and diurnal
heating are still expected, however, especially in western portions
of Puerto Rico, as well as passing showers.

In the early part of the week, an upper level trough is forecast to
move towards the east from over the Gulf of Mexico. By Tuesday
afternoon, it is anticipated to be stretched over Hispaniola. At
this same time, a perturbation is expected to make its way into the
area from the east, associated with deep, enhanced moisture.
Increased shower activity is likely to be associated with this. On
Wednesday, the upper level trough is expected to have shifted
eastward, passing over the forecast area. A slight trend to drier
conditions is expected for the second half of the week, as well;
however, passing showers as well as afternoon showers due to local
effects and diurnal heating, are still likely.

&&

.AVIATION...

Mainly VFR conditions are expected. However, +SHRA across
the regional waters could move at times across the USVI/northern PR
terminals through the forecast period. Also, MVFR conditions are
possible between 16z-22z at TJSJ/TJMZ due to TSRA/SHRA. Northeast
winds will increase between 15-20 kts with higher gusts after 14z.

&&

.MARINE...

Continuing easterly winds, with speeds over the local waters of up
to 20 knots, are expected. Associated with these stronger winds is a
continuing increase in wave heights today, with heights upwards of 9
feet possible overnight tonight in northeastern local Atlantic
waters. Hazardous conditions are expected to last into the weekend,
and Small Craft Advisories are in effect for all zones of the local
waters with the exception of southern and western coastal areas of
Puerto Rico. Rip current will continue to be a concern, as well,
with a high risk at beaches along the north coast of Puerto Rico and
Culebra, and a moderate to high risk at the beaches of the U.S.
Virgin Islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 75 85 73 / 70 70 60 40
STT 85 75 85 75 / 70 60 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
441 AM AST Fri Dec 13 2019

.SYNOPSIS...

Passing showers will continue to affect the area for the next few
days, as well as afternoon shower activity due to local and
diurnal effects. Winds are expected to subside somewhat as the
high to our north pulls away, but with another ridge making its
way into the Atlantic to take its place, this will be short-lived,
and the enhanced winds - and therefore waves - will return early
next week. The start of the work week looks slightly drier, but
sufficient moisture is likely to maintain some shower activity.

&&

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

An induced surface trough is forecast to move across the region
today; this will increase shower activity across the U.S. Virgin
Islands and the eastern sections of Puerto Rico during the morning
hours. As the trough cross the region from east to west, it will
enhance the diurnally induced afternoon showers over western
Puerto Rico, and streamer type activity off the USVI and from el
Yunque area into the San Juan metro area. As the trough exits the
region, easterly trades will turn more from the east-southeast.
Surface winds are expected to slightly decrease during the
weekend, from 15- 20 kts today to 10-15 kt by Sunday.

For the weekend, wind flow turns more from the southeast as a
surface high moves from the northern Atlantic into the central
Atlantic and a surface low moves over the northeastern coast of
USA, while its associated front remains over the western
Atlantic. At upper levels, a ridge building from the west will
provide some drier air and stability aloft. The 500mb temps are
forecast to increase from -8 degrees C today to -5C by Sunday.
This should inhibit thunderstorm development, but not the
development of moderate to locally heavy rain showers, as
tropical moisture is forecast to increase across the Caribbean Sea
during the weekend. Therefore, under a southeast steering wind
flow expect showers to reach portions of southern and southeastern
PR during the night and early morning hours, followed by
diurnally induced showers over the NW quadrant of PR and over the
San Juan area each afternoon.

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

A surface ridge stretched across the central Atlantic will continue
to be the dominant feature on Monday. As it weakens and pulls away
to the northeast, a ridge stretching from James Bay in Canada to the
southeastern United States will build into the Atlantic - a process
that is expected to repeat near the end of the week next week.
Because of this, a zonal ridge is expected to be the major feature
to our north through the forecast period. This will aid in the
persistence of moderate, generally easterly trade winds, which
are forecast to weaken somewhat later in the week as the ridge
weakens its hold over the Atlantic somewhat. At the mid-levels, a
ridge is expected to dominate over the area through the week next
week; a trough to our north will weaken this ridge slightly later
in the week. Aloft, the TUTT will be located to the east of the
local islands on Monday. These conditions will likely act to
inhibit upward motion over the area. Even so, passing showers are
still expected, as well as afternoon showers due to local effects
and diurnal heating, especially in western Puerto Rico.

A weak disturbance is forecast to push westward into the area on
Tuesday, associated with deep, enhanced moisture. An upper level
trough will make its way eastward at the same time, stretching over
Hispaniola by Tuesday afternoon. Because of this, increased shower
activity is likely. As the upper level trough passes over and past
us on Wednesday, a dry slot is expected to push over the area.
Though the typical pattern of passing showers during the overnight
and morning hours, and afternoon showers due to local effects and
diurnal heating will still persist over the area, activity will be
lessened. As we move into the latter half of the week, patches of
moisture will push into the area, carried in on the trade winds.
Associated with this moisture is the potential for increased shower
activity over the area.


&&

.AVIATION...

Mainly VFR conditions are expected. However, trade wind
showers will move at times across the USVI/Eastern PR terminals
through the morning hours, causing brief periods of -SHRA/MVFR cigs.
SHRA this afternoon developing over west PR could cause tempo MVFR
conds at TJMZ/TJBQ. East winds will increase between 15-20 kts with
higher gusts along coastal areas after 14z.

&&

.MARINE...

Enhanced easterly trade winds associated with a strong Atlantic high
pressure system continue to blow across the region at around 15-20
knots. Associated with these winds are waves of roughly 5 to 9
feet, with occasional seas of up to 11 feet. Continuing hazardous
marine conditions will persist this weekend, and Small Craft
Advisories are in effect for all zones of the local waters, with
the exception of nearshore waters of southern/southwestern Puerto
Rico. At the beaches, there is a high risk of rip current along
northern beaches of Puerto Rico and Culebra, and a moderate to
high risk of rip current at beaches of the U.S. Virgin Islands.
Though winds and seas are forecast to subside briefly, as the
current ridge moves off to the east, another high will push in
over the central Atlantic early next week, heralding a return to
the increased winds and waves across the region.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 73 87 76 / 50 40 10 40
STT 85 76 85 76 / 40 20 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
508 AM AST Sat Dec 14 2019

.SYNOPSIS...

A surface ridge over the Atlantic continues to promote breezy
conditions over the local islands and waters through the weekend.
Passing showers as well as afternoon locally- and diurnally-
induced showers are expected both days as well. Some drying is
expected for Monday, but another round of enhanced moisture on
Tuesday will likely bring another increase in shower activity.

&&

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

A moist east to southeast wind flow will prevail through the rest of
the weekend across the region, as a surface high builds over the
central Atlantic and a trough lingers west of the area. This will
cause showers to continue across the Caribbean waters and move over
portions of the USVI and the south/southeast coast of PR during the
overnight and early morning hours. This will be followed by
diurnally induced afternoon showers over the NW quadrant of PR and
over the San Juan area each day. A low to mid level ridge is
forecast to build quickly on Monday over the southwestern Atlantic
and into the region, this will promote drier air and the return of
brisk northeasterly winds across the local area. Therefore, the
focus of showers will shift across the northern USVI and the NE
quadrant of PR during the night and early morning hours, with
diurnally induced afternoon showers forming over west/southwest PR.

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

A ridge stretching across the Atlantic on Tuesday to our north will
continue to be the dominant feature for the region. It will help to
maintain moderate easterly trade winds; as the high pulls away to
the east Wednesday into Thursday, winds are forecast to subside
somewhat and shift slightly to out of the east-southeast. In the mid-
levels, a ridge will persist over the area through the week next
week, weakening and pulling away over the weekend as a trough pushes
into the area on Sunday. On Tuesday, a weak disturbance making its
way into the forecast area will bring enhanced moisture. Meanwhile,
a weak upper-level trough will move eastward, stretching over
Hispaniola by late Tuesday. This will aid in the development of
afternoon shower activity due to local effects and diurnal heating.
Passing showers are also likely during the overnight and morning
hours. Behind this disturbance is a dry slot that will push into the
area on Wednesday. Though the drying trend will continue on
Thursday, patches of moisture will begin to filter in. The upper
level trough will make its way over us, proceeding eastward
Wednesday, pulling away in the latter part of the week. While these
factors will likely serve to inhibit somewhat shower activity, the
usual pattern of afternoon showers are still likely both days.

Increasing moisture is expected Friday and into the weekend, with
the moisture anticipated to extend into the mid-levels. A
perturbation pushing into the Caribbean will begin to develop into
an inverted trough as it makes its way westward. From here, the
certainty in the synoptic patter diminishes significantly. The GFS
suggests that this inverted trough will deepens and develop a low
that will undergo rapid cyclogenesis off the coasts of New
England and Nova Scotia on Sunday. While the ECMWF does show some
development of a trough, its solution is much less bullish with
this, instead maintaining a strong ridge over the eastern coast of
North America. Especially with this being more than a week out, I
am somewhat incredulous of the scenario the GFS presents.
However, with some developing trough still anticipated, enhanced
shower activity is likely for the weekend.

&&

.AVIATION...

Mainly VFR conditions are expected. However, SHRA moving along the
southern coast of PR could cause tempo MVFR cigs at TJPS with brief
gusty winds. SCT-BKN cigs should continue through the morning hours
over mainland PR btw FL030-FL060. Afternoon SHRA, over northwest PR
may cause tempo MVFR to brief IFR conds at TJBQ. Elsewhere, RA/VCSH
expected through the fcst period. Low level winds will be from the
ESE at 10-15 kt with higher gusts after 14z.

&&

.MARINE...

Choppy, hazardous marine conditions, associated with the enhanced
easterly trade winds, continue. There could be some slight
improvement over the weekend, but this would be brief, with
reinvigorated winds forecast for early next week. Small Craft
Advisories remain in effect for most of the local waters, with the
exception of the nearshore waters of southern and southwestern
Puerto Rico, lasting into late Sunday night/early Monday morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 86 76 / 40 50 40 40
STT 85 76 85 76 / 50 40 40 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
538 AM AST Sun Dec 15 2019

.SYNOPSIS...

A moist southeasterly flow will continue to promote passing
showers across the area today. Winds will diminish slightly today,
picking up again tomorrow out of the east. The pattern of passing
showers overnight and in the morning, with afternoon showers due
to local and diurnal effects will persist, and is likely to be
enhanced with the passage of a surface trough on Tuesday.

&&

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

A trough over Hispaniola and weak surface ridge northeast of the
region are promoting a moist southeast wind flow across the region,
which has caused showers to move across the USVI and over the
southeast/eastern interior sections of PR. Gusty winds around 25 mph
and rainfall amounts up to one inch were observed with the heaviest
showers, mainly over SE PR during the overnight hours. Low level
moisture will continue high through early in the afternoon and
passing showers in a 10-15 kt southeast steering wind flow are
expected to move at times over the USVI and east/southeast sections
of PR. Locally induced afternoon showers are expected to develop
mainly over NW PR. Precipitable water content (PWAT) is forecast to
drop from near 2 inches this morning to around 1.20 inches tonight
and mostly isolated shower activity is expected across the region.

For Monday, a low to mid-level ridge is forecast to build just north
of the islands, this will promote a brisk east to northeast wind
flow and trade wind shower activity moving across the USVI and
northeast sections of PR through the day. Diurnally induced showers
are expected to develop mainly over the SW quadrant of PR. On
Tuesday, a surface trough is forecast to move from the east, while a
broad surface high anchors over the central Atlantic. This will
cause winds to shift once again from the southeast and showers with
periods of moderate to heavy rainfall are expected on Tuesday
afternoon over the eastern sections as well over the NW quadrant of
PR.

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

The large zonal ridge continues to influence conditions over the
local islands on Wednesday. As it is forecast to be pulling away
from the area, moving to the east, winds over the local area will
veer slightly to out of the SE, while also diminishing somewhat
through the day and into Thursday. A dry slot will push through
the area on Wednesday into early Thursday; combined with
unfavorable conditions aloft, this will act to inhibit somewhat
shower activity over the local islands. Brief passing showers are
still anticipated, as well as afternoon showers due to local
effects and diurnal heating. Patches of moisture carried in on the
trade winds will begin filtering into the area on Thursday,
associated with the passage to our south of a developing
disturbance. These patches of moisture will continue passing over
the area into Friday, and an increase in shower activity is
likely. Another small dry slot is anticipated for late Friday into
Saturday, again associated with a decrease in - but not an
elimination of - shower activity across the forecast area.

On Saturday, an inverted trough is expected to develop over the
western Caribbean, stretching northward to off the coast of the
Carolinas by Saturday afternoon. Beyond this point, there is
increasing uncertainty in the synoptic pattern. This trough will
slowly approach the area from the west during the day on Sunday, and
begin sweeping through on Monday. Cyclogenesis of some kind is
likely in the western Atlantic, off the coast of the United States,
within this trough; the location, timing, and intensity are
uncertain, though, at this time. Both the ECMWF and the GFS now show
some notable development of a low, with a front that would extend
southward enough to impact the local islands. Today, it is the ECMWF
that is more bullish with the development and intensification of
this low, showing very rapid cyclogenesis, while the GFS solution
suggests a somewhat more modest intensification, taking place
further south. Given that this is all a week out, and the lack of
good consensus from the models, or even good consistency between
runs, there remain plenty of reasons to be skeptical of this
theoretical future low, especially in terms of its intensity or
the potential for explosive cyclogenesis. All of this to say that,
presently, it looks likely that there will be a trough to our
west on Sunday that will pass over the area on Monday, though
there is uncertainty in the magnitude of the impacts. A more
southerly flow is therefore likely Sunday into Monday, with a
northwesterly flow behind the trough. Increased shower activity is
likely for Sunday and especially Monday, and with winds out of
the south on those days, the most affected areas will be southern
Puerto Rico during the overnight and morning, and northern Puerto
Rico during the afternoon.

&&

.AVIATION...

Mainly VFR conditions are expected to prevail across all
terminals. However, trade wind showers could move at times across
the USVI terminals as well at TJSJ/TJPS through the morning hours.
Between 16z-20z SHRA over west PR could cause tempo MVFR conds at
TJBQ. East to southeast winds expected at 10-15 kts with higher
gusts and sea breeze variations after 14z.

&&

.MARINE...

Moderate to fresh easterly trade winds continue this morning, with
speeds between 15 and 20 knots; this will result in continuing
rough, choppy seas and hazardous conditions across a large portion
of the local waters. Though winds are forecast to diminish slightly
later in the day today, tomorrow will see a resumption of these
enhanced winds. Small Craft Advisories continue for the majority of
the local waters, except for nearshore waters of southern and
western Puerto Rico. With the increase in winds tomorrow, building
seas are anticipated as well. As such, Small Craft Advisories will
be required for Monday afternoon in the offshore Caribbean waters,
Mona Passage, and the nearshore waters surrounding the U.S. Virgin
Islands. There remains a high risk of rip currents at most northern
beaches of Puerto Rico, and a moderate to high risk at the beaches
of St. Croix and Culebra. With the exception of southwestern Puerto
Rico, a moderate risk of rip currents is expected today for the rest
of the local beaches.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 85 74 / 50 50 50 40
STT 85 76 86 76 / 40 50 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
421 AM AST Mon Dec 16 2019

.SYNOPSIS...

A strong mid to upper-level ridge will hold over the area through
the middle of the week. The surface ridge will cause fresh
easterly wind flow across the area, thus resulting in hazardous
seas and breezy conditions. The middle of the week a weak trough
will cause the surface high to become elongated as it slides to
the northeast of the area. As the high weakens and moves northeast
of the region a east to southeast wind flow will prevail over
Puerto Rico. This flow will usher in patches of moisture across
the region from time to time.

&&

.SHORT TERM...Today through Wednesday...
A strong high-pressure building north of the islands is promoting
breezy and windy easterly trade winds across the region of the
U.S. Virgin Islands and Puerto Rico. This wind surge, pushing a
patch of moisture, will bring occasional pesky showers from the
regional waters into the Virgin Isles and the eastern half of PR
throughout the day. However, periods of sunshine will be observed
too. These showers will makes their way into the interior and
western section by the afternoon hours. The low- to mid-high
pressure ridge will be the main weather feature across the North
Atlantic Ocean through the short term period.

A trade wind perturbation will shift winds from the ESE Tuesday and
more from the SE by Wednesday. This wind shift could increase
somewhat the maximum temperatures along the northern sections of the
islands. Moisture will erodes by Wednesday, although quick passing
showers should not be ruled out at times.

&&

.LONG TERM...Thursday through Tuesday...
A strong mid to upper-level ridge is forecast to hold over the
area Thursday through the weekend. Thursday, a weak perturbation,
is forecast to will transverse the southern Caribbean waters and
pull deep tropical moisture across Puerto Rico and adjacent
islands through Friday. Guidance shows precipitable water values
reaching 1.50 inches during this time. The deep tropical moisture
is progged to combine with local and diurnal effects to yield
isolated to scattered showers across the U.S. Virgin Islands and
eastern Puerto Rico during the mornings. Followed by scattered
showers across southern, interior, western areas of Puerto Rico
during the afternoons. As for thunderstorm development due to the
mid to upper- level ridge suppressing the vertical development of
showers, as well as limited divergence aloft. Therefore
thunderstorms are not forecast to develop at this time. Daytime
high temperatures may exceed the daily record as a result of the
east to southeast wind flow, which typically causes temperatures
to soar.

Saturday and Sunday, the weak perturbation in the easterly flow is
progged to continue to move west, and away from the region, however,
moisture behind the feature may pool over the area through early
Sunday morning. However, patches of moisture in the easterly flow
could induce showers during the afternoon on Sunday. The GFS shows
precipitable water values falling to the 1.2 inches on Sunday; this
ranks near the 50th percentile for December. Also, several weak
boundaries and their associated moisture are forecast to stall well
north of Puerto Rico through the weekend and early next week.

Monday through Tuesday, the beginning of the week is were the GFS
and ECMWF diverge. The GFS shows an upper-level low deepening near
Nova scotia with the base of the trough reaching the central
Atlantic waters. As the trough deepens well north of the area, its
progged to push a weak front through the region. The GFS shows
abundant moisture ahead of the front, with the moisture filtering
into the U.S. Virgin Islands and Puerto Rico. Also, the GFS develops
a low which as warm-core characteristic similar to a tropical
cyclone over the central Atlantic waters.

On the other hand, the ECMWF shows a low getting cutoff from the
main flow across the southern coastal areas of the U.S. on Monday.
As the low transverse, the coastal locations of the northern Gulf of
Mexico the ECMWF has it undergo cyclogenesis while it continues
to sink south across the Peninsula of Florida. The ECMWF shows the
low east of the Florida Peninsula by Tuesday afternoon with the
bulk of the remaining moisture positioned northeast of Puerto
Rico. At this time a wait and see approach to should be taken with
the long-term forecast. The forecast picture should become clear
over the next several days. Nevertheless, an increase in showers
is progged can on Monday and Tuesday as moisture increases across
the region.

&&

.AVIATION...
VFR conditions will prevailed today. Gusty easterly winds are
expected at times across the islands. Therefore, expect E to ENE
winds at 15 to 20 kt gusting between 25 and 30 kt. SHRA/+SHRA will
move en route from the Leeward islands and E-PR throughout the
day, spreading into central and western PR between 16/16z-20z.

&&

.MARINE...
Hazardous marine conditions will continue to prevail
through the middle of the week. A surface high pressure is
creating fresh easterly trade winds across most of the regional.
As a result, small craft advisories are in effect for the offshore
and nearshore waters except for the southern nearshore waters of
Puerto Rico. Seas will range from 7 to 9 feet with seas
occasionally reaching 10 feet. A high risk of rip currents
continues in effect for the northern, eastern and southeastern
beaches of Puerto Rico. There is a high risk of rip currents for
the beaches of Culebra and Saint Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 86 74 / 50 60 60 40
STT 88 76 85 75 / 50 60 50 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
428 AM AST Tue Dec 17 2019

.SYNOPSIS...

A surface high will continue to hold firm across the Atlantic
waters through Thursday. The surface high is creating fresh to
strong winds as well as moderate to rough seas across Atlantic and
Caribbean waters. In fact, this surface high is ushering in
moisture from the Atlantic waters over the area. The high is
forecast to slightly weaken on Thursday as it slides east of
Puerto Rico. This will result in a east to southeast wind flow on
Thursday and Friday. The southerly wind flow will drag moisture
over the U.S. Virgin Island and Puerto Rico, and cause an increase
in showers during the afternoons. Saturday, the surface and mid-
level ridge reestablishes themselves over the area again and
increase the trade wind cap.

&&

.SHORT TERM...Today through Thursday...
A broad ridge tightening the local pressure gradient is promoting
breezy and windy easterly winds across the northeast Caribbean,
including U.S. Virgin Islands and Puerto Rico. Satellite data
indicate a plume of moisture with embedded clouds and showers. As a
result, occasional passing showers producing periods of moderate to
locally heavy rains will affect the Virgin Isles and the eastern
half of PR throughout the day. Periods of sunshine will remain
possible at times. This activity will makes its way into the
interior, north and western section by the afternoon hours. A short
wave upper-level trough will swing by the region inducing a jet
aloft. Therefore the development of an isolated thunderstorm should
not be ruled out late this morning or early in the afternoon. The
strongest activity is expected across the eastern and southern
sections of Puerto Rico.

The pressure gradient is expected to loose by mid-week, promoting a
southeast wind flow. Moisture is also expected to erode across the
islands. Under this weather pattern, maximum temperature will
increase somewhat along the northern sections of the islands.
Although moisture will continue to erode quick passing showers
cannot be ruled out at times.

&&

.LONG TERM...Friday through Wednesday...
The GFS and ECMWF have been persistent in showing the surface and
mid-level ridges holding firm across the U.S. Virgin Island and
Puerto Rico Friday, and through the weekend. A short-wave trough
across the northern Atlantic waters will cause the surface ridge
to weaken. The surface winds are forecast to turn to the east to
southeast through Saturday morning due to the surface high
pressure shifting east.

Friday, lingering moisture from a weak perturbation is progged to
pull across the area, with the bulk of the moisture coming on Friday
afternoon. Guidance continues to show precipitable water values
reaching 1.50 inches during this time. The tropical moisture,
diurnal heating as well as orographic effects will yield isolated to
scattered showers across the U.S. Virgin Islands and eastern Puerto
Rico during the mornings. Followed by scattered showers across
southern, interior, western areas of Puerto Rico during the
afternoons. Also, Daytime high temperatures may exceed the daily
record as a result of the east to southeast wind flow, which
typically causes temperatures to soar.

Saturday and Sunday, guidance shows the surface to mid-level ridge
reestablishing themselves across the area. The strengthening of
the ridges could cause an increase in the trade wind cap through
the Sunday. Both global models depicted this when analyzing the
Skew-T diagrams. The strengthening of the trade wind cap should
inhibit the vertical development of showers into thunderstorms
area-wide, as a result of the mid-level ridge causing sinking air
in the mid- level of the atmosphere.Therefore thunderstorms are
not forecast to develop at this time. Nevertheless, both the GFS
and ECMWF show showers developing during the afternoon across the
U.S. Virgin Islands and Puerto Rico.

The GFS shows precipitable water values falling to the 1.3 inches
early Sunday morning with a continues fall to 1.00 inches by Sunday
afternoon. Sunday afternoon, the precipitable water value is
forecast to be near the 25th percentile for December. Also, several
weak boundaries and their associated moisture are forecast to stall
well north of Puerto Rico through the weekend and early next week.

Next week model guidance continues to diverge on a clear solution
when it comes to the development of the upper-level low or cutoff
low moving across Florida. However, the GFS and ECMWF continue to
show the solution described below.

Monday through Tuesday, the beginning of the week is were the GFS
and ECMWF diverge. The GFS shows an upper-level low deepening near
Nova scotia with the base of the trough reaching the central
Atlantic waters. As the trough deepens well north of the area, its
progged to push a weak front through the region. The GFS shows
abundant moisture ahead of the front, with the moisture filtering
into the U.S. Virgin Islands and Puerto Rico. The GFS has surface
winds out of the west; these winds are forecast to converge with the
frontal boundary just north of Puerto Rico on Tuesday.

On the other hand, the ECMWF shows a low getting cutoff from the
main flow across the southern coastal areas of the U.S. on Monday.
As the low transverse, the coastal locations of the northern Gulf of
Mexico, it should undergo cyclogenesis while it continues to sink
south across the Peninsula of Florida. The ECMWF shows the low east
of the Florida Peninsula by Tuesday afternoon with the bulk of the
remaining moisture positioned northeast of Puerto Rico.

Wednesday, the GFS and ECMWF have the frontal boundary moving
through the area. However, the models don`t agree on the timing of
the frontal passage. What we do know is an increase in showers, and
isolated thunderstorms are possible early next week as a result of a
frontal boundary, which will either stall just north of the area
or a boundary that pushes through Puerto Rico. We should wait to
see how the synoptic pattern evolves across the eastern U.S. and
the Atlantic so that we can determine the effects the frontal
boundary and abundant moisture will have on the forecast.

&&

.AVIATION...
Winds are forecast to shift more from the E to ESE, with
occasional gust between 20 and 30 kts. Passing SHRA will continue en
route between the Leeward Islands and Puerto Rico. SHRA/-SHRA are
possible across the terminals of USVI, E/S-PR and TNCM/TKPK
throughout the day, spreading into central and western PR between
17/16z-20z. Isold TSRA will be possible mainly across E/S PR during
the afternoon.

&&

.MARINE...
A firm surface high pressure over the Atlantic waters is creating
fresh to strong winds as well as moderate to rough seas across
Atlantic and Caribbean waters. Sea up to 8 feet are expected this
afternoon, with occasional seas to 10 feet for most local waters.
A high risk of rip currents for the northern, eastern, and
southeastern beaches of Puerto Rico. Also, there is a high risk of
rip currents for the beaches of Saint Croix, the southern beaches
of Vieques, and the northeastern beaches of Culebra.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 89 75 / 60 60 30 30
STT 86 75 85 75 / 30 20 30 30