Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion...UPDATED
National Weather Service San Juan PR
502 AM AST Tue Dec 29 2020

.SYNOPSIS...

The pattern is trending generally wetter as we make our way into
midweek. Scattered to locally numerous showers are possible today,
mostly in the interior of Puerto Rico, and into the west. Tomorrow,
a frontal boundary will bring additional moisture and showers to the
area, especially for northern and eastern Puerto Rico. Drying is
expected by this weekend, with generally fair weather into the start
of next week. Hazardous marine conditions are expected, starting
tonight, with increasing winds across the local waters leading to
increases in wave heights. Seas of up to 10 feet are expected for
portions of the local waters by Wednesday, with further increases
possible in the second half of the week.

&&

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

Scattered showers are expected today, with locally numerous showers
across central portions of Puerto Rico. A trend to a wetter pattern
is expected for Wednesday and Thursday.

A SFC shortwave just to the north and east of the local area is
causing a disorganized light wind flow over the local area tonight,
but will gradually lead to a predominantly northerly wind flow
through the day across the local islands. This northerly wind will
bring drier air as the day progresses. That said, there is a mid
level trough that would provide some forcing, and there is also
relatively strong winds aloft, so the instability is expected to
increase today. Therefore, scattered to locally numerous showers are
forecast today, with the numerous showers mainly expected across
central to western interior of PR in areas of convergence.

As the mid level trough amplifies over the local area on Wednesday
into Thursday, the available moisture is expected to increase as a
frontal boundary is pushed in by a SFC high across the western
Atlantic. The expected setup would then lead to a wide area of
cloudiness and numerous showers across the Atlantic waters,
gradually moving in and affecting the north and eastern sections of
PR as well as the USVI. Wednesday looks like the wettest day with
persistent rain through the day across the aforementioned areas,
while the rest of the local area would have some rain, but is not
expected to observe as much as the north and east sections of PR
and the USVI. Lingering moisture is expected on Thursday, but by
Thursday the local wind is expected to increase and become more
northeasterly. Therefore, the northeast sections of PR and the
northern USVI have the best chance of rain, but more in the way of
brief and numerous showers, while brief and scattered showers are
expected elsewhere.

Once again there is some discrepancy among the model guidance, but a
bit more weight was given to the Hi-Res models this time around.
Given the expected pattern of the frontal boundary pushing in with
above normal moisture and a mid level trough with an upper jet, it
seems like the GFS model is a bit dry, so we leaned wetter than the
GFS this time around.

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

A large area of high pressure will be sinking southward over the
area from the west central Atlantic on Friday. As the ridge moves,
it will help push the remnants of a frontal boundary over the area
late in the day on Friday, into the night; however, moisture levels
will remain below average or on the low end of average for the month
of December. The arrival of the ridge will bring dry, stable air to
the region, with precipitable water values forecast to be around 0.7
to 0.9 inches, well below seasonal normals. Occasional patches of
moisture will push over the area, embedded in the trade winds, which
will aid in the development of passing showers during the night, and
a few afternoon showers due to local and diurnal effects. On the
whole, generally fair weather is expected through the weekend, and
into the start of the next workweek. Forecast confidence through the
weekend is moderate to high.

On Monday, a frontal boundary will begin to approach the region from
the northwest, associated with a potential Nor`easter off the east
coast of the United States. Model guidance is now suggesting a
slower approach for this feature than it previously had, and hints
at the potential for a pre-frontal trough developing and impacting
the area Tuesday into midweek. Confidence in the forecast diminishes
through the early part of the week next week. Currently, the most
likely scenario is for an increase in shower activity, likely to
near-normal levels, for Tuesday.

&&

.AVIATION...

VFR conditions are expected across the local terminals today.
However, VCSH expected across the local terminals today with
possible brief TEMPO SHRA. Winds are trending northerly to NE
generally at around 5 to 10 kts. However TJPS is expected to have
more variable winds with the possibility of light WSW winds.

&&

.MARINE...

Winds are forecast to increase over the western local waters this
afternoon, spreading across the area. Moderate to fresh winds, up to
around 25 knots sustained, will lead to rapid increases in wave
heights late today through tomorrow. Hazardous marine conditions are
likely starting tonight for the Atlantic waters and Mona Passage,
and starting tomorrow for the waters near the USVI/east of Puerto
Rico and the Anegada Passage. Seas of up to 11 feet are possible for
the offshore Atlantic waters, and up to 10 feet elsewhere. Small
Craft Advisories are in effect starting tonight with the offshore
Atlantic waters and Mona Passage, with others following; additional
advisories will be necessary in the future. Anyone with marine
interests should monitor future forecasts and advisories for
updates.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 82 74 80 74 / 50 40 60 60
STT 83 74 83 74 / 50 40 60 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
519 AM AST Wed Dec 30 2020

.SYNOPSIS...

Scattered to locally numerous showers are expected today and
tomorrow, mostly for northern and eastern Puerto Rico. Showers
are likely to be relatively brief, as winds will become
increasingly brisk across the area. A drying trend is expected for
the end of the week, as a surface high pressure pushes southward
over the area, bringing with it a drier air mass and increased
stability. Hazardous marine conditions will affect most of the
local waters. Moderate to strong winds are leading to building
seas today and tomorrow, and the rough conditions will persist
into the weekend. Small Craft Advisories, High Surf Advisories,
and a High Risk of Rip Currents are in effect.

&&

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

Scattered showers are expected today, with locally numerous showers
across north and eastern portions of Puerto Rico. Variably to mostly
cloudy skies and shower activity is expected today across most of
PR and across the USVI.

A SFC high pressure will be entering the western Atlantic today,
tightening the pressure gradient and causing an increase in wind
speed from the NE across the local islands. The remnants of a
frontal boundary will push through today. That said, the latest
model guidance is suggesting that the deeper moisture will stay to
our east, so there will be scattered to numerous showers, but they
will likely be brief and move fast with the strong NE winds. Even
though the showers may cover a good portion of north and east PR as
well as the USVI, the rainfall accumulations may be limited as they
are expected to be brief. Based on the latest guidance and
observations, ponding of water in poor drainage areas would be
possible.

A mid level trough will position itself over the local area today,
which may help in the development of the shower activity that will
affect the local area. However, by Thursday, a mid level ridge gets
closer and decreases instability. But there may be lingering
moisture or maybe even a slight increase, so scattered to locally
numerous showers continue to be forecast for the northern USVI and
north and east PR, yet once again the shower activity is expected to
be brief. The winds are expected to continue to be from the NE and
relatively strong, at around 20 mph and gusty across the general
area. A line of drier air moves in very early on Friday, but also a
quick line of moisture associated with an old secondary frontal
boundary will move in through the day on Friday, causing some
cloudiness and light rain across the local islands. The wind will
remain strong on Friday as well.

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

A large area of high pressure sinking southward over the region will
bring generally dry, stable conditions to the area on Saturday.
Precipitable water values will be on the order of 0.8 to 1.2 inches,
below seasonal normals. Ridges aloft will also contribute to
stability over the area. Fair weather will dominate the region
through the weekend, though a few isolated showers cannot be ruled
out due to patches of moisture being carried across the region
embedded in the trade winds. Forecast confidence through the weekend
is moderate to high.

On Monday, a frontal boundary will begin to approach the region from
the northwest, associated with a potential Nor`easter off the east
coast of the United States. There is some disagreement between the
models on the trajectory and strength of this feature, which
could have impacts on the conditions that we see for the local
islands, though those possible effects are presently unclear.
There is consistency between runs of the GFS, however, which does
give a slight increase in confidence to the forecast, though
confidence does remain relatively low. The most likely scenario
remains for the approach to stall northwest of the region, with a
pre-frontal trough developing nearby or over the area Tuesday into
Wednesday. Increasing shower activity is anticipated. This
increase is also supported by some weakening of the ridge at the
mid- and upper- levels around midweek. It appears likely presently
that shower activity will be near-normal levels, though could be
slightly above seasonal normals. As mentioned above, though, the
confidence in this forecast is relatively low, though marginally
increased.

&&

.AVIATION...

SHRA is expected across the local area, but would be moving quickly
and prevailing VFR conditions are expected across the local
terminals today with brief periods of SHRA and CIGs near FL050.
However, VCSH expected to prevail across the local terminals today.
Winds will be from the N to NE generally at around 10 to 20 kts with
occasional gusts. That said TJPS is expected to have more easterly
winds.

&&

.MARINE...

Hazardous marine conditions continue to spread across the local
waters. At 4 AM AST, Buoy 41043 reported seas of 8.9 feet, and San
Juan Buoy reported seas of 6.6 feet. With sustained winds of up to
25 knots, seas will continue to build through the day and into
tomorrow. In the Atlantic waters, seas of 10 to 12 feet are possible
by tomorrow. These conditions will continue through the week. Small
Craft Advisories are in effect for most of the local waters.

There is a high risk of rip currents at north-facing beaches of
Puerto Rico, as well as Culebra, and northern and eastern beaches of
St. Croix. The area affected by the high risk is forecast to spread
with the building seas as we move into the second half of the week.
High surf conditions are also forecast to affect the north coast of
Puerto Rico, with breaking waves of 10 feet or higher.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 81 74 81 74 / 70 60 30 20
STT 84 74 84 72 / 60 60 30 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Fri Jan 1 2021

.SYNOPSIS...Surface high pressure across the western Atlantic is
causing fresh to strong E-NE winds, which will continue into the
weekend. Weak band of moisture will move through today, causing a
brief increase in moisture, dry air moves in behind it this
weekend. Mid to upper level ridge and dry air will persist for the
next several days, causing a stable atmosphere. Marine and surf
zone conditions are hazardous, and will continue hazardous through
the weekend.

&&

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

The pressure gradient continues be relatively tight over the
region with the approaching ridge, causing breezy conditions.
The strong winds will persist at least through Sunday. Moisture
continues to decrease, as the surface high pressure sinks
southward over the area, but a narrow band of moisture will move
in today, which is expected to be south of the local islands by
late this afternoon. Thereafter, a relatively dry air mass will
persist through the weekend. However, any available moisture will
be mainly limited to the lower levels, and the strong winds
present, the shower activity is expected to be brief. Most of the
shower activity is expected to affect the local waters, USVI, and
the north and eastern sections of PR, a lower chance of rain for
the interior and western sections of PR.


.LONG TERM...Monday through Saturday...
Surface high pressure will persist north of the local islands
until early in the week, then a SFC low will enter the NW Atlantic
for the middle of the week, causing lighter winds locally, but
then towards the end of the week, another but weak SFC high will
be to the north of the local islands. Relatively dry air mass
will persist on Monday, but a patch of moisture will move in on
Tuesday into Wednesday. The shower activity will be limited to a
few brief tradewind showers on Monday. Then with the increase in
moisture, Tuesday and Wednesday should have more shower activity,
but with stable mid and upper levels, the shower activity will
likely be shallow and scattered. Thursday looks like it could have
some afternoon shower development over central PR in the afternoon
due to light winds allowing for sea breeze convergence.
Thereafter, isolated to scattered brief showers are expected, but
it looks like it will be limited to the USVI and eastern PR,
while fair weather persists elsewhere. There was little change in
the long term forecast.

&&

.AVIATION...Mainly VFR conds are expected drg the 24 hr prd. Quick
showers will continue to enter the local islands, but only VCSH
are expected for the northern terminals til 01/16Z. Showers will
decrease as drier air filters in and no major impacts to
operations are anticipated. SFC winds are continue from the ENE
between 15 and 20 kts, with higher gusts.


&&

.MARINE...The marine and surf zone conditions continue to be
hazardous, and are expected to be hazardous through the weekend.
The local nearshore buoy north of San Juan is still reporting
seas of 8 to 9 feet, which could be causing breaking waves up to
12 feet. For this reason no significant change was done to the
marine forecast as the latest guidance and the observations
continue in good agreement. The Small Craft Advisory, High Surf
Advisory, and a High Risk of Rip Currents continue in effect.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 82 73 82 72 / 60 40 40 40
STT 83 72 84 72 / 50 30 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
416 AM AST Sat Jan 2 2021

.SYNOPSIS...

Windy conditions are expected to continue today as high pressure
dominates the regional weather pattern. These winds will continue
producing rough seas, with a separate swell expected to arrive
for Sunday. Some moisture is expected to make it into our region
for the middle of next week which will help to enhance shower
activity across the region.

&&

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

Deep layered high pressure ridging will be the dominant feature
across the region through Monday. The strong Atlantic surface ridge
will continue to induce a moderate to strong northeasterly wind flow
which will continue to bring patches of shallow trade wind moisture
and occasional light to moderate showers across the region from time
to time. Recent satellite imagery as well as the National Weather
Service doppler weather radar and recent model guidance all
suggest an overall dry and stable air mass will prevail during the
period with no significant rainfall accumulations expected for
the islands. A strong 3-4 degree subsidence cap inversion will
maintain shallow moisture below 850 millibars with an overall dry
airmass aloft. Therefore for the entire period, expect mostly
isolated passing morning showers. This will be followed by limited
afternoon showers in and around the islands as mostly sunny and
fair weather skies should prevail during the entire period. As the
winds will remain relatively brisk through the weekend, any
shower activity will be quick-moving and of short duration. As
such, rainfall accumulations will be generally low. The areas most
likely to be impacted by any showers will be mainly north and
east of Puerto Rico with lesser activity expected during the
afternoon hours in the west and south sections of the islands.

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

Overall the long-term forecast looks wetter for mid-week and more
uneventful for the next weekend. On Tuesday, a strong high
pressure ridge will continue to dominate the mid to upper levels
of the atmosphere, with high surface pressure to our north. Low-
level winds will be near normal intensity, with around 10 to 20
knot winds from the east-northeast. Thus the normal isolated to
scattered showers can be expected Tuesday morning and Tuesday
night into Wednesday, impacting primarily the north and east
coasts of Puerto Rico. Wednesday however, that upper-level ridge
shifts off to the east, and an upper-level shortwave trough will
approach from the west. Models suggest this trough will help to
induce a surface trough over the region with an enhanced area of
moisture. Currently models suggest this moisture will push into
the region and drive scattered showers from Wednesday to Friday.
The upper-level trough and surface feature do not last long over
the region, as upper-level ridging is once again expected to take
hold and produce fairly uneventful conditions heading into the
weekend, with again the usual weak showers impacting the east
coast of Puerto Rico.

&&

.AVIATION...
VFR conds durg prd. SCT lyr nr FL025...SCT-BKN nr FL050. Isold SHRA
en route ovr regional waters and en route btw islands til 02/12Z.
Sfc winds fm ENE 12-15kt w/ocnl gust to nr 20kts bcmg fm NE 15-20
kts w/ocnl gust btw 25-30 kts aft 02/14Z. L/Lvl wnds fm NE 20-30 kts
blo FL200,then bcmg northerly and incr w/ht ABV.

&&

.MARINE...
Hazardous marine conditions are expected to continue due to the
fresh to strong winds. Today and tomorrow the winds will be fresh
to strong, yet moderate winds are back in the forecast for Monday.
Another swell from the northeast will move into the region for
Sunday and last into Monday, so confused seas are possible.
However, calmer seas are expected after Monday with seas at around
or below 5 feet for Tuesday.

&&

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

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
330 AM AST Sun Jan 3 2021

.SYNOPSIS...

Fairly seasonal weather conditions are expected for the next few
days, with passing showers impacting primarily the north and east
coasts of Puerto Rico and the USVI. Brisk winds will continue
today, yet calm down to near normal levels by tomorrow. Wetter
conditions are expected for midweek as an area of enhanced
moisture moves in from the east. Marine conditions remain
hazardous today and into tomorrow.

&&

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

A broad subtropical ridge will continue to be the dominant
feature across the region, promoting dry and stable conditions
aloft while maintaining a fairly strong tradewind cap inversion
and moderate to strong east northeasterly winds. This will favor a
continued advective weather pattern which will transport frequent
patches of shallow trade wind moisture with occasional light to
moderate showers across the region through at least Monday.

Latest satellite imagery and the National Weather Service doppler
weather radar initialized well with most recent model guidance, and
all continue to suggest an overall dry and stable air mass will
prevail at least until Monday except for periods of quick passing
showers mainly during the overnight and early morning hours.
Previous 03/00Z TJSJ upper air sounding, as well as the satellite
derived precipitable water product both suggest precipitable water
values around one inch with a strong 3-4 degree cap inversion
maintained and shallow moisture trapped below 850 millibars.

For today through Monday, expect mostly isolated passing morning
showers followed by limited afternoon shower development over the
islands with no significant rainfall accumulations anticipated. A
mixture of sunshine and clouds will prevail across the islands with
moderate to strong east northeast trade winds. However, by late
Monday into Tuesday the Atlantic surface ridge will relax across the
region resulting in loosening of the local pressure gradient and
consequently diminishing trade winds. In addition, a weak easterly
perturbation will approach the region and bring a quick surge of low
level moisture to the forecast area. As a result there will be a
better chance and increase potential for shower activity with
wetting rains across portions of the islands. At this time
widespread rainfall is not expected at this time with this feature.
Areas most likely to be impacted by any showers will be mainly north
and east sections of Puerto Rico and the adjacent islands during the
morning hours, followed by isolated to scattered afternoon shower
development mainly in the west and southwest sections of the islands.

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

Increased shower activity is still expected for Wednesday as the
aforementioned moisture perturbation persists over the region.
The moisture also might be enhanced a bit by an upper level
shortwave trough moving in from the west with its associated
surface trough. The showers are not likely to be very strong,
since a lot of dry air will be in place aloft to work against
development. However, wind speeds at low levels also will not be
very strong, so the concern is for slow moving showers that drop a
lot of rainfall. At this point, it appears likely that in the
morning for Wednesday the showers will focus over eastern Puerto
Rico and the USVI. Then in the afternoon, due to the light winds,
the high terrain of interior Puerto Rico will be the area of
greatest shower activity. Ponding of water over roadways and even
some localized flooding is possible.

Patches of moisture will linger over the area between Thursday and
Friday, so again showers will be possible. These will likely be less
impactful than those on Wednesday since low level winds will pick up
a bit, helping the showers to move along. At this point, Saturday
morning looks a bit drier with very long range models suggesting
a weak tropical wave passing through for late Saturday and Sunday.

&&

.AVIATION...

Prevailing VFR conds durg prd. SCT cld lyrs nr FL028...SCT ocnl BKN
nr FL050...mstly SKC ABV. Isold SHRA en route btw islands and ovr
regional waters til 02/12Z. Sfc winds fm ENE 5-10kt bcmg fm NE 10-20
kts w/ocnl gust btw 20-25 kts aft 03/14Z. L/Lvl wnds fm ENE 20-25
kts blo FL200, then backing and bcmg northerly and incr w/ht ABV.

&&

.MARINE...

Marine conditions remain hazardous due to fresh to strong winds
across the region. However, these winds are expected to slow down
slowly throughout the day today. Another swell will invade the
local waters today from the northeast, and last into tomorrow.
Thus tomorrow will be a transition day as we transition to calmer
seas by Tuesday. Thereafter seas will be around 5 feet or less for
the next few days.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 72 83 73 / 30 30 30 40
STT 84 72 85 74 / 20 20 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
433 AM AST Mon Jan 4 2021

.SYNOPSIS...
High pressure ridge remained the dominant weather feature across
and continued to produce very dry and stable conditions aloft.
Recent satellite derived precipitable water products and previous
upper air sounding for San Juan both suggested precipitable water
values less than an inch across the region. The prevailing winds
have continued to diminish during the overnight hours as the
local pressure gradient relaxed resulting in light to moderate
northeasterly winds overnight. Satellite imagery and the present
doppler radar imagery depicted only patches of shallow moisture
and mostly isolated showers moving over the local waters. A few
of these shower reached the windward parts of the islands from
time to time.


&&

.SHORT TERM...Monday through Wednesday...

Currently our weather pattern is being dominated by a mid to upper-
level ridge with its associated surface high to our north.
Thankfully, pressure gradients over our region associated with the
surface ridge have relaxed, helping the winds to weaken over the
past several hours, and should generally be around 10 to 15 mph from
the ENE today. This ridge is producing very dry air aloft, with
satellite measurements of precipitable water suggesting less than an
inch across the region.

Despite the dry air, there has been some light shower activity near
the USVI and eastern Puerto Rico, and more is expected today as weak
moisture perturbations move in from the east. Thus light to moderate
showers will be a threat through out the day today, specifically for
the aforementioned areas of E. PR and the USVI. Some showers are
also possible over interior PR, but ought not to be very impactful.

Later this evening, forecast models suggest a somewhat more
ambitious patch of moisture that will move in and produce scattered
showers across the region. At the same time, the ridging will move
eastward along with the surface high, thus weakening winds across
the region. Once the area of enhanced moisture arrives early
Tuesday, it will not be in a hurry to leave since there will not be
much large-scale flow to push it anywhere. As the moisture lingers
on Tuesday and Wednesday, scattered showers can be expected across
the region. The biggest threat for Tuesday and Wednesday will be
over interior Puerto Rico in the afternoon, since showers may
develop over the high terrain and persist over the area for several
hours, leading to ponding of water and even isolated areas of
flooding. At this point, the moisture looks a bit better for
Tuesday, but atmospheric dynamics look better for enhanced shower
activity on Wednesday. Thus both days have a similar threat for
rainfall.

.LONG TERM...Thursday through Monday

Recent model guidance continued to suggest increasing moisture
transport by the latter part of the work week as an induced low
level perturbation will approach and cross the region. The best
best chance for increased and enhanced shower activity across the
region so far will be on Thursday, as the ridge aloft is forecast
to erode, along with the tradewind cap inversion in response to
a shortwave trough which will move just north of the region along
with an weakly induced surface induced trough. The prevailing
winds will also diminish while becoming more easterly from Friday
onwards into the weekend.

Another easterly perturbation/tropical wave is also forecast to
bring another surge of tropical moisture Saturday through Sunday
and therefore the potential for increased shower activity will
persist through the weekend. So far most of the expected activity
should be focused over parts of eastern Puerto Rico and portions
of the USVI during the overnight and morning hours, followed by
locally enhanced shower development mainly over parts of the
central and west sections of Puerto Rico during the afternoon
hours. Due to the fairly light winds, rainfall may be moderate to
locally heavy at times and therefore ponding of water on roadways
and poor drainage areas or even some localized flooding will be
possible. A gradual improvement is expected by Monday onwards,
with a drier airmass will filter in and the easterly trade winds
are forecast to increase once again.

&&

.AVIATION...
Mostly VFR conds expected during prd. Fast-moving VCSH possible at
all terminals except TJPS/TJMZ thru 04/13z. During daytime, unimpactful
VCSH possible for all terminals, but better chance for -SHRA aft
04/21z again for all terminals except TJPS/TJMZ. After 04/13z, NE
winds 8-18 knots with higher gusts and local sea breeze variations
expected.

&&

.MARINE...

Recent data from the surrounding buoys have continued to suggest
gradually improving conditions with diminishing northeasterly swell
action, as well as the northeasterly trade winds. However, choppy
seas and hazardous conditions will persist until later today. At
the San Juan buoy, seas have fluctuated between 6 to 6.6 feet during
the past few hour with periods between 9-11 secs. Meanwhile seas
at buoys 41043 and 41044 was around 6 and 7 feet respectively.
Small Craft Advisories will therefore remain in effect for some
areas with conditions expected to improve by tonight. Seas of 6
feet or less are anticipated thereafter and over the next several
days.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 81 73 81 73 / 40 70 70 60
STT 83 73 82 71 / 50 60 60 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
433 AM AST Tue Jan 5 2021

.SYNOPSIS...
Mid to upper level ridge will continue to erode across the region
today through Thursday, as a broad polar trough and associated short
wave will enter and cross the west and southwest Atlantic. Surface
high pressure ridge will lift slightly north and east of the region
allowing a weak easterly perturbation to cross the forecast area today.
This will favor an increase in low level cloudiness with periods
of passing showers especially during the morning hours. The tradewinds
will continue to diminish through Thursday as the local pressure
gradient relaxes and a weak surface trough forms across the region.

&&

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

Currently a ridge of high pressure exits at mid- to upper-levels
over the region, with a weakening area of high surface pressure to
our north. Due to the weakening surface high, winds have also been
weakening over the last day and have returned to near normal intensity.
Robust mid- to upper- level troughing coming off the U.S. will push
this high pressure eastward during the short term period. This will
help to further weaken wind speeds over the region, and increase
instability for Wednesday and into Thursday as the associated surface
trough settles over the region.

An enhanced area of moisture currently resides at low levels, and
due to the relaxed winds it will be in hurry to exit the region. It
will thus be with us today and tomorrow, with drier air in place for
Thursday until the next moisture perturbation arrives overnight
Thursday into Friday.

Putting this all together, today is expected to be the wettest day
of the short term period. Mostly scattered showers can be expected
this morning primarily across the local waters, but also impacting
eastern Puerto Rico and the USVI. Winds look weak at low levels in
the afternoon hours, and it is likely that slow moving showers
develop over the Puerto Rican interior and northwest quadrant.
Though the showers ought not to be intense, they may be somewhat
stationary and persistent, thus leading to water ponding. Isolated
to scattered showers will continue over the nighttime primarily over
the local waters. Less moisture will be in place for Wednesday, but
instability will be a bit better. Models currently suggest the best
moisture will reside over the western end of the forecast area for
Wednesday morning, so that is where the bulk of the showers will be,
with less activity near the USVI. Afternoon showers are once again a
threat for western Puerto Rico, with light winds again leading to
slow-moving showers. Thereafter, Thursday looks much drier as the
moisture finally moves out, so only mostly isolated showers are
expected.

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

By Friday into Saturday another surge of moisture is forecast to
move across the area, in association with a weak surface trough
and an easterly wave. This pattern along with weak ridging aloft
will increase the chance for enhanced overnight and early morning
showers, as well as providing better potential for afternoon
shower development over parts of the interior and west sections of
Puerto Rico and mainly on the west-end of the U.S. Virgin Islands.
The prevailing easterly winds will diminish on Friday and Saturday,
also supporting better potential for rainfall accumulations and
ponding of water on roadways and in poor drainage areas with any
moderate or locally heavy rains.

By Sunday through Tuesday, the low pressure gradient will again
tighten across the region in response to a surface high pressure
ridge, which will build north of the region favoring an increase
in the easterly trade winds. This along with the building of the
mid to upper level ridge by Sunday, will aid in eroding moisture
transport and the frequency of shower activity across the region.
That said, and based on the most recent model guidance, expect
improving weather condition by Sunday with breezy conditions so
far forecast favoring brief periods of quick passing early morning
showers with limited afternoon shower activity over the islands
under a prevailing east-southeast low level wind flow.

&&

.AVIATION...
VFR conds expected during prd. However, VCSH/SHRA expected at
TJSJ and terminals further east, especially before 05/18z.
VCSH/SHRA then possible for TJBQ/TJMZ in afternoon, with a smaller
chance for VCSH at other terminals. Sfc winds ENE 10-15 kt after
05/14z, gusting to 20 kt near coasts and passing showers.
Overnight winds generally light and variable and modified by land
breezes.

&&

.MARINE...

Overall marine conditions will continue to improve today with light
to moderate easterly winds forecast to prevail through the middle of
the work-week. A small northeasterly swell will arrive across the
local Atlantic Waters and Caribbean Passages later tonight into
early Wednesday morning. Seas of 6 feet or less will continue for
the next few days with prevailing easterly winds between 5 to 15
knots.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 80 71 84 72 / 70 30 20 20
STT 81 71 82 71 / 60 20 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
444 AM AST Thu Jan 7 2021

.SYNOPSIS...

Generally fair weather is expected to continue, under the influence
of a mid-level ridge bringing dry, stable air aloft. Passing showers
are still anticipated, however, and there is also the potential for
some afternoon showers in western Puerto Rico. An increase in
showers is possible in eastern Puerto Rico late tonight into
tomorrow morning with a modest increase in moisture. &&

.SHORT TERM...Thursday through Saturday...

Weak high pressure across the Atlantic, between 20 and 30 degrees
north latitude, will shift north somewhat, but will also be
somewhat anchored by high pressure in the northeast Atlantic. The
gradient across Puerto Rico and the U.S. Virgin Islands will also
be maintained by a stationary low in the Gulf of Darien to bring
easterly flow of 8 to 16 kt through the period. High pressure at
700 mb developing ahead of a weak frontal boundary over the
Dominican Republic will bring in some moisture to Puerto Rico in
weak northwest flow, but it remains slightly disconnected from the
lower levels, whose moisture will remain shallow through the
period. That said, patches of weak moisture at lower levels will
bring periods of scattered light showers. The main impact of these
will be mostly focused on the eastern side of Puerto Rico and
mainly in the late night and early morning hours. Some showers are
also expected to develop over western Puerto Rico in the
afternoon hours. All the showers should yield only lighter
accumulations. A weak trough at upper levels accompanied by a 70
knot jet over the forecast area will pass through the area today
and will offer limited enhancement to the showers in the west this
afternoon. High pressure to the southeast will continue as an
upper level trough moves into the western Atlantic later on
Saturday.

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

On Sunday, there will be a deep-layer mid- to upper-level ridge
located generally east of the region, stretching across to the area.
This ridge will remain the dominant feature aloft through the week.
This will provide stability, and the moist layer will be capped
between 850 and 700 hPa. Generally dry air ahead of a rapidly
decaying frontal boundary to the northwest will be over the region
on Sunday. Patches of moisture embedded in the trade winds will make
their way across the islands from time to time through the week.
Precipitable water values will vary, from around 0.9 inches to
around 1.5 inches; this is from below seasonal normals to near
normal levels. The timing and locations affected by these patches
are uncertain. As such, the timing and location of precipitation
cannot be reasonably ascertained. Therefore, the forecast is for
near climatological average, or slightly drier. Though forecast
confidence in terms of the trend is relatively high, the details
remain quite uncertain, and confidence is below normal.

&&

.AVIATION...

Spotty SHRA over lcl waters but dry ovr land areas til aft 07/16Z
then SHRA forming hir trrn mostly in wrn PR. Aft 07/22Z mstr movg
in fm E will bring VCSH to TIST/TISX. Sfc winds lgt and vrb with
land breezes. Aft 07/14Z ENE wnds bcmg 6-12 kt with sea breezes
prevailing. Max winds W 55-70 kt btwn FL320-475.

&&

.MARINE...

Seas of 6 feet or less will continue through the weekend, even as a
weak northeasterly affects the local waters today. Winds are out of
the east to east-southeast at around 10 to 15 knots. Late in the
weekend, another swell will push into the area. Seas look poised to
become hazardous early on Monday for portions of the local waters.

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

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 72 83 73 85 / 40 40 20 40
STT 73 82 73 83 / 30 20 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
448 AM AST Sat Jan 9 2021

.SYNOPSIS...

Generally fair weather will continue over the next several days.
Shallow, patchy moisture will likely bring some occasional showers
to the region, mostly in the form of overnight and early morning
passing showers in the east. Though some afternoon convection cannot
be entirely ruled out, it will be limited. Choppy marine conditions
are expected through the weekend, with hazardous conditions likely
for the start of the next workweek. At the local beaches, there
is a high risk of rip currents at northern beaches of Puerto Rico
and Culebra, and eastern beaches of St. Croix

&&

.SHORT TERM...Saturday through Monday...

A surface low migrating to the northeast across the western
Atlantic will maintain a weak cold front to our north and
northwest during the period. High pressure over the northeastern
Atlantic and low pressure in the Gulf of Darien also maintain
moderate easterly trade wind flow with relatively shallow patchy
moisture. These trade winds will increase and become locally fresh
on Monday as high pressure builds into the western Atlantic. High
pressure continues over the area at 700 and 500 mb. High pressure
at upper levels is centered over the eastern coast of Venezuela
during the period.

Models were too optimistic about rain over western Puerto Rico
yesterday and the day before. Also the strong capping at the top of
the marine layer near 8 kft remained relatively strong. Therefore
have backed away from the higher end of the scattered showers
category over western Puerto Rico this afternoon. By Sunday, the cap
should be sufficiently gone so as to allow a fair chance of rain
over interior Puerto Rico. Monday also looks somewhat drier and will
keep only isolated showers there. Otherwise some shower activity on
the eastern slopes of Puerto Rico during the overnight and early
morning hours are expected.

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

The mid-level ridge will remain stretched over the region from the
east on Tuesday. Though some weakening of this ridge is possible
late in the week, it will likely remain a dominant feature for the
region. The stability aloft provided by this ridge will lead to a
fairly strong cap on the moisture, keeping the bulk of it in the
lower levels. There will also be a relatively dry airmass in place,
though shallow, patchy moisture will stream into the area from time
to time. The majority of rainfall that is seen through the week will
likely be from passing showers in the east during the overnight
and morning hours. Afternoon convection will be limited, but still
possible. The GFS suggests a brief weakness in the ridge at lower
mid-levels for Friday afternoon, allowing for a slightly deeper
moist layer. As such, that looks to be one of the best times for
rain; however, considering how brief this increase is, there is
some uncertainty in just how realistic the shift is, and it also
makes the forecast very sensitive to the exact timing. Given the
patchiness of the moisture that will be affecting the area, exact
timing and location remains uncertain. Because of this, the
forecast remains as near climatological average, or slightly
drier.

&&

.AVIATION...

Spotty SHRA moved ovr ern PR earlier this morning, but remain
only over the local waters from just east of Saint John to well
south of Ponce. Spotty SHRA to cont ovr ern PR with a chc ovr wrn
PR aft 09/17Z with some lcl MVFR CIGs and mtn top clds away from
TAF sites. Patches of mstr to bring ocnl MVFR CIGs to TNCM/TKPK
til 09/18Z. Sfc winds light easterly with land breezes bcmg east
5- 15 kt with sea breeze influences by 09/14Z. Max winds WSW 45-60
kt btwn FL380-490 strongest at FL445.

&&

.MARINE...

Seas of 6 feet or less continue through the weekend. A northeasterly
swell will lead to building seas, which may become hazardous as soon
as Monday morning for the offshore Atlantic waters. Winds continue
out of the east to east-southeast at up to around 15 knots. There is
a high risk of rip currents for the northern coasts of Puerto Rico
and Culebra, as well as for beaches of eastern St. Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 73 85 74 / 20 10 30 30
STT 83 74 85 75 / 10 10 10 10

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
509 AM AST Sun Jan 10 2021

.SYNOPSIS...

Generally fair weather persists across the region. Passing showers
are expected to affect eastern Puerto Rico and the USVI during
the overnight and early morning hours. During the afternoons, the
occasional isolated shower is possible in western and interior
Puerto Rico due to local effects. For the local waters, a
northeasterly swell is forecast to push into the local waters,
with the offshore Atlantic waters and Anegada Passage becoming
hazardous by Monday morning. Also, there is a high risk of rip
currents for northern beaches of Puerto Rico and Culebra, as well
as St. Croix.

&&

.SHORT TERM...Sunday through Tuesday...

High pressure at the surface in the northeastern Atlantic retreats
to the northeast. Low pressure north of the U.S. Virgin Islands at
40 north also moves northeast allowing high pressure over the mid
western United States to follow across into the western Atlantic
Sunday night through Monday. This will increase the pressure
gradient and the trade wind flow as the low in the Gulf of Darien
remains while pressure to the north increases. High pressure
continues at 700 and 500 mb levels with either a ridge or the high
itself directly over the area. The ridge at 250 mb continues off the
coast of Venezuela affecting all of the eastern and central
Caribbean. This makes the main forecast problem one of timing the
multitude of shallow moisture minimums and maximums running with the
low level flow between the surface and just above 850 mb.

Models were too optimistic about rain over western Puerto Rico
yesterday and the day before and the day before that. Also the
strong capping at the top of the marine layer near 8 kft remained
relatively strong. Therefore have continued to suppress most POP
values above 30 percent and used the GFS when it was lower than
that. Although the GFS wants to bring in a moisture spike in the
precipitable water values between 1.3 and 1.45 inches tonight, it
also forecasts the lowest value of this week at 00Z Tuesday of 0.87
inches.

There have been a few moderate showers over eastern Puerto
Rico this morning, but they have been tiny and brief. Much less
shower activity is being seen over the local waters this morning
compared to yesterday. Therefore, expect a continuation of the fair
weather pattern, with increasing winds Monday and Tuesday and some
shower activity on the eastern slopes of Puerto Rico early Monday
and Tuesday.

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

Relatively dry air with shallow, patchy moisture continues to be the
dominant pattern through the weekend. A mid-level ridge will be
stretched over the region during this time, limiting the vertical
extent of moisture, and therefore inhibiting shower development.
Still, patches of moisture will likely bring passing showers to
eastern Puerto Rico and the USVI during the overnight and morning
hours. A few isolated afternoon showers in western and interior
Puerto Rico also cannot be ruled out. Additionally, occasionally
there will be periods where the moist layer is somewhat deeper due
to temporary weaknesses in the cap. During these times, showers
will become somewhat more prevalent. The GFS continues to suggest
Friday afternoon as a potential time for this to occur, and
therefore there may be more shower development during that time.
However, this scenario would be quite sensitive to minor changes.
The forecast for the long-term period remains, as it has for the
last few days, near climatology.

&&

.AVIATION...

Spotty -SHRA ovr ern PR this morning, but VFR conds are
expected to prevail at all TAF sites. A patch of moisture with
clouds is apchg TNCM/TKPK and may bring some MVFR CIGs by 10/16Z.
Few SHRA psbl ovr wrn PR aft 10/17Z. Sfc winds consist of land
breezes less than 6 knots to bcm east 5-15 kt with sea breezes and
some hir gusts aft 10/14Z. Max winds W 45-55 kt btwn FL380-460.

&&

.MARINE...

Seas remain at 6 feet or less across the local waters today through
tonight. The arrival of a northeasterly swell by early tomorrow
morning, will bring increasing seas, especially to the offshore
Atlantic waters and Anegada Passage. In these areas, hazardous
conditions are expected to begin in the morning on Monday, and there
is a Small Craft Advisory in effect. An increase in winds is
expected later in the day on Monday, associated with a tightening
pressure gradient due to a surface high moving into the western
Atlantic. This will lead to further increasing wave heights.
Additional Small Craft Advisories are likely to become necessary as
we move nearer to the event.

For the beachgoers, there is a high risk of rip currents at northern
beaches of Puerto Rico and Culebra, as well as eastern St. Croix.
This risk will persist, likely into midweek.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 74 84 74 / 10 30 20 20
STT 84 74 84 73 / 10 30 10 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
449 AM AST Mon Jan 11 2021

.SYNOPSIS...
A mid-level high pressure system will dominate the weather
conditions through must of the period. Only a few showers are
expected to filter in over the area through the next few days.
Hazardous marine conditions are expected due to a northeasterly
swell and stronger winds.

&&

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

A mid-level high pressure is expected to build over the region from
the east, while a surface high builds and strengthen across the
western Atlantic during the next few days. This will promote a
stronger trade wind cap, drier air intrusion and more stable
conditions aloft. Precipitable water content is forecast to remain
below climatology today(less than 1.35 inches) and below 1.00 inch
on Tuesday. Therefore, expect mostly fair weather conditions with
the trade winds carrying the occasional patch of moisture that could
result in light showers across the USVI and eastern sections of
Puerto Rico during the overnight/early morning hours, followed by
limited shower development over portions of western PR during the
afternoon hours. Breezy east to northeast trades should promote
seasonable temperatures during the day. On Wednesday, precipitable
water content is forecast to increase around 1.50 inches, as the mid-
level ridge moves a little further west creating a weakness in the
trade wind cap and allow for better low-level moisture to temporary
increase from the east. Therefore, better chances for showers are
expected on Wednesday but no significant rainfall amounts are
anticipated at this moment.

.LONG TERM...Thursday through Monday

A westerly flow at the upper levels will drag an area of higher
moisture and high clouds to the area through Saturday. At the
mid-levels, high pressure over the eastern Caribbean will hold
through the long term forecast period. This will result in a trade
wind cap, lasting all the way through Monday, that will inhibit
strong and organized convection to develop over the local islands.
At the surface, a high pressure centered to the north of the area
will maintain a generally easterly trade wind flow. Additionally,
the latest guidance show precipitable water values ranging
between 0.8 to 1.3 inches, which is below the climatological
values for early January. The moisture that does reach the region
will be in the form of patches of clouds carried by the trade
winds from time to time. However, due to these unfavorable
environmental conditions and the low moisture, only limited
shower activity is anticipated, with light to locally moderate
accumulation expected. As is usual under an easterly wind flow,
the U.S. Virgin Islands and eastern Puerto Rico could receive some
showers early in the day and in the overnight hours, followed by
diurnally induced showers over western Puerto Rico.

&&

.Aviation...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. VCSH likely at times due to
trade wind showers across the USVI/eastern PR terminals. East winds
increasing to 12-18 kt with higher gusts and sea breeze variations
after 14z.


&&

.MARINE...
An increase in winds and a northeasterly swell will result in
choppy to hazardous seas today, continuing to mid-week. Small
craft advisories are in effect for the offshore Atlantic waters
today, spreading to most of the area by later tonight. For the
beaches, the risk of rip currents is high for the northern coast
of Puerto Rico, Culebra, eastern St. Croix and northwestern St.
Thomas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 84 73 / 20 20 30 30
STT 84 73 84 74 / 20 10 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
401 AM AST Tue Jan 12 2021

.SYNOPSIS...
A surface high pressure will generate moderate to fresh winds
through Wednesday, and in combination with a northeasterly swell,
choppy and hazardous seas continue. No significant rain event is
anticipated through the next several days, with only patches of
moisture reaching the islands from time to time.

&&

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

A mid-level ridge will hold and continue to build over the region
for the next several days. Promoting a moderate trade wind cap,
drier air and stable conditions aloft. At low-levels, a weak surface
front will remain north of the area and a weak ridge is forecast to
gradually build across the central and eastern Atlantic at the end
of the short term period. Easterly trades between 15-20 kts are
forecast to prevail through Wednesday, winds turn more from the east
to southeast by Thursday as the surface ridge builds over the
Atlantic. Latest infrared and total precipitable water satellite
imagery indicated areas of low-level clouds across the tropical
Atlantic. These areas of shallow moisture will continue to move west
and reach portions of the islands each day. However, today is
expected to be the driest day in the short term forecast with
forecast soundings still forecasting around 1 inch of precipitable
water content across the islands. Overall, the areas that will
experience some periods of light rain showers are the USVI and the
eastern/northern sections of PR during the night and early morning
hours and over the west coast of PR each afternoon.

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

The model guidance has not change significantly for the long term
forecast period. A mid-level ridge will hold over the eastern
Caribbean through Tuesday. This will translate in a trade wind cap
inversion that will maintain all the moisture confined to the
lower 850 mb of the atmosphere. Also, this feature will promote a
generally fair weather pattern and dry air at the mid-levels. At
the upper levels, a westerly flow associated with a high pressure
developing to the east of Venezuela will bring high level clouds
to the islands from Friday through Sunday. Then, as this high
moves to the west and over South America, the high clouds will be
displaced to the north of the area. Any rain activity that may
move over the islands will be associated with patches of clouds
embedded in an easterly flow generated by a surface high pressure
north of the area. For now, the forecast soundings are showing
precipitable water values remaining below 1.3 inches through
Sunday, thus only limited shower activity are expected across the
area. By Monday, a wider patch of clouds could increase showers a
little, especially over eastern Puerto Rico and the U.S. Virgin
Islands, but only moderate accumulation is expected. Once this
area of moisture moves from the area, fair weather should return
by Tuesday.

&&

.Aviation...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. East winds increasing 15-20 kt
with higher after 14z.

&&

.MARINE...
A northerly swell and moderate to fresh winds are resulting in
choppy and hazardous seas through Wednesday. Small craft
advisories are in effect for some of the local waters due to seas
up to 7 feet. Elsewhere, small craft should exercise caution due
to seas up to 6 feet and winds up to 20 knots. For the beaches, there
is a high rip current risk for the northern coast of Puerto Rico,
Culebra, and St. Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 85 74 / 30 30 40 40
STT 84 73 84 73 / 30 30 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
421 AM AST Wed Jan 13 2021

.SYNOPSIS...
A shallow area of clouds and showers will continue to move across
the area today. A generally stable weather pattern is expected to
prevail through the weekend, with limited rainfall activity.
Hazardous marine conditions continue today for the Caribbean and
Mona Passage, but seas will diminish later this afternoon.

&&

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

A shallow layer of moisture moved from the east during the overnight
hours across the region and low-level cloudiness and light showers
were observed across the islands. Rainfall accumulations were in
general from a few hundredths to less than half an inch in some
areas of eastern Puerto Rico. This area of moisture will continue to
move west and aid in the development of afternoon showers over
western PR, however, a persistent mid-level ridge will maintain
stable conditions aloft. This ridge is expected to remain in place
over the region for the next several days, and max precipitable
water content is forecast to range between 1.2-1.4 inches through
the short term period. Latest model guidance continues to suggest
that the best chance for showers is on Thursday, with PWAT values
around 1.40 inches and steering winds will have a more east to
southeast component, causing showers to develop over portions of
northwestern PR and across San Juan and vicinity due to diurnal
effects and the small surge in moisture. Thereafter, drier air will
filter once again by Thursday night and persist through Friday,
causing fair weather conditions across the islands.

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

From Saturday through Monday, the mid-level high pressure will
remain anchored over the eastern Caribbean. As a result, the trade
wind cap inversion will hold, maintaining the moisture at the
lower levels. The latest guidance are suggesting patches of
moisture crossing the islands through this period, especially on
Sunday and Monday. Some passing showers could then be expected
over the eastern half of Puerto Rico and the U.S. Virgin Islands.
In the afternoon, additional activity could develop over western
Puerto Rico, aided by local effects and diurnal heating. However,
due to the lack of support in the mid and upper levels, only light
to locally moderate rainfall accumulation can be expected. By
Tuesday and Wednesday, the mid-level high pressure will finally
begin to migrate toward the western Caribbean. However, this
feature will not lose its influence over the area, thus
maintaining a generally fair weather pattern, with, again, just
shallow areas of clouds and light showers reaching the forecast
area.


&&

.Aviation...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, -SHRA early in the
period will cause SCT-BKN cigs from FL030-FL070. East winds 15-20 kt
with higher gusts expected after 14z.


&&

.MARINE...
The northeasterly swell is subsiding across the local waters,
while winds should remain moderate to fresh today, especially over
the Caribbean waters. A Small Craft Advisory remains in effect
until 2 PM AST today due to seas up to 7 feet. Elsewhere, small
craft operators are urged to exercise caution due to choppy seas
up to 6 feet and winds up to 20 knots. Marine conditions will
continue to improve toward the end of the workweek. For the
beaches, there is a High Rip Current Risk for the northern coast
of Puerto Rico and for St. Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 74 84 73 / 20 50 50 40
STT 85 76 83 73 / 20 40 40 40

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
438 AM AST Thu Jan 14 2021

.SYNOPSIS...An area of shallow moisture moving over the region
today will promote variably cloudy skies and light rainfall
activity across the islands. A mid-level ridge will continue to
remain as the dominant weather feature for the next several days,
promoting drier air aloft and stable conditions. Areas of low-
level moisture embedded in the trades will move at times through
the long term period, bringing the occasional passing shower
across the islands.


&&

.SHORT TERM....SHORT TERM...Today through Saturday...
Total Precipitable Water from GOES-16 shows an area of enhanced
moisture crossing Puerto Rico and the U.S. Virgin Islands. This
feature has been responsible for leaving mostly cloudy skies and
passing showers. High resolution and global models indicate that
this activity should continue through the rest of the morning hours,
with the eastern half of Puerto Rico receiving most of the showers.
At the mid-levels, however, a high pressure system continues to hold
over the eastern Caribbean, with a trade wind cap inversion in
place. As a result, the moisture being advected into the islands is
shallow in nature, and rainfall accumulation is expected to be
generally light. Later in the afternoon, the available moisture
could combine with local effects to fuel additional showers over the
northwestern corner of Puerto Rico, but again, no significant
activity is forecast.

For the rest of the short-term forecast period, due to the constant
presence of the mid-level high pressure, the weather pattern will
not be conducive for significant rainfall activity to develop. For
Friday, another area of shallow moisture is expected to reach the
islands, with precipitable water values around 1.0 to 1.4 inches.
Another round of light to locally moderate showers can be expected
to affect the local islands. Then, on Saturday, a drier air mass is
expected to filter in, and fair weather is anticipated through most
of the day, with very limited shower activity.

.LONG TERM...Sunday through Thursday...
No significant change in the long term forecast is expected as the
mid-level ridge is expected to remain in place over the region
through late next week. Global models and forecast soundings are
indicating precipitable water values fluctuating from one inch
and peaking to around 1.30-1.40 inches each day. This is due to
the arrival of patches of low-level moisture moving from the
tropical Atlantic. Therefore, the same weather conditions from the
short term period will carry on through much of the long term
period.

By the end of the forecast period, a surface high pressure is
expected to build over the western Atlantic and promote an east to
northeast steering wind flow. In this flow, models suggest that
fragments of a lingering surface front over the Atlantic waters
may reach the northern portions of Puerto Rico and the northern
U.S. Virgin Islands.


&&

.AVIATION...Mainly VFR conditions expected today. Passing showers
may result in brief MVFR conditions due to low ceilings through
14/18Z across the terminals of PR/USVI. Winds will be out of the
ESE at 10 to 20 knots.


&&

.MARINE...Choppy seas up to 6 feet due to moderate to locally
fresh trades are expected to continue today across the offshore
waters and passages. Winds and seas will improve through the
weekend, before a northerly swell moves across the Atlantic waters
by early next week. A moderate risk of rip currents will prevail
across most of the east, north and southern beaches of the
islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 74 86 74 / 50 20 30 20
STT 82 74 83 72 / 40 20 40 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Fri Jan 15 2021

.SYNOPSIS...A mid-level ridge will continue to be the dominant
weather feature through next week. Moisture embedded in the trade
winds will bring the occasional passing showers across the
islands with areas of drier air in between. A northerly swell will
increase seas briefly up to 7 feet by early next week.


&&

.SHORT TERM...Today through Sunday

The story for the short term forecast period remains virtually
unchanged from previous discussions. A mid-level high pressure still
holds over the eastern Caribbean, maintaining a trade wind cap
inversion in place, which translate to stable weather conditions
aloft. However, at the surface, a high pressure to the north of the
islands will drag groups of clouds to the region from time to time.
Currently, the first patch of clouds is located over the Leeward
Islands, and Total Precipitable Water product, from GOES-16, shows
this area on enhancing moisture moving toward Puerto Rico and the
U.S. Virgin Islands. As a result, passing showers are expected
throughout the day over eastern PR/USVI. For the afternoon, the high
resolution models are suggesting that additional activity could
develop near the San Juan metro area and over northwestern Puerto
Rico. Due to the lack of upper level support, only light to moderate
rainfall accumulation is anticipated.

On Saturday, as the surface high pressure migrates toward the east,
the wind flow will begin to acquire a more east-southeast component.
Additionally,a drier air mass is expected to filter in from the
east, with precipitable water values ranging between 0.8 to 1.0
inch. Therefore, mainly fair weather is expected to prevail with
very limited shower activity over the islands. On Sunday, another
patch of clouds should move across the area, which will increase the
chance of showers, but again, environmental conditions will remain
unfavorable for significant rainfall accumulation.

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

A mid-level ridge will continue to be dominant weather feature
through the long term period, providing stable conditions and
promoting the trade wind cap inversion. Therefore, similar
weather conditions are expected each day through at least
Thursday, with areas of shallow layer moisture and pockets of dry
slots moving from the tropical Atlantic with the trade winds.
This will continue to result in mostly fair weather conditions
across the region. The best chance for showers are across portions
of the U.S. Virgin Islands and eastern Puerto Rico, with rainfall
accumulations generally at less than half an inch each day. By
the end of the week, fragmented moisture from a lingering weak
front across the Atlantic is expected to be push across the
region by a surface high pressure over the western Atlantic. This
advective pattern should favor light to moderate rainfall amounts
across the northern and eastern sections of PR and the northern
USVI as winds turn more from the east to northeast.


&&

.AVIATION...Mainly VFR conditions expected through the forecast
period. Passing showers may affect the terminals of USVI and the
Leeward Islands early in the period, but no impacts are anticipated.
VCSH are expected after 15/15Z for TJSJ/TJBQ, and could cause brief
MVFR conditions due to reduced ceilings and lower VIS. Winds will be
of the ESE at 5 to 10 knots.


&&

.MARINE...Relative tranquil seas are expected through the weekend,
highest seas are expected to range between 3 to 5 feet in general
across the offshore waters and Anegada Passage. A northerly swell
is forecast to gradually build on Monday and Tuesday across the
Atlantic waters and passages and seas between 5 to 7 feet are
possible across portions of these waters. Moderate trades between
10 to 15 knots are expected to prevail. There is a moderate risk
of rip currents across the northern and eastern beaches of Puerto
Rico and St. Croix.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 86 73 / 30 20 10 20
STT 84 73 83 74 / 20 20 20 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
346 AM AST Sat Jan 16 2021

.SYNOPSIS...A mid to upper-level ridge will continue to prevail
through the period. This will continue to result in dry and stable
weather conditions aloft, with mainly fair weather conditions
expected. However, patches of low-level moisture embedded within
the easterly trade wind flow may bring some passing showers to the
region from time to time. Mainly tranquil marine conditions are
expected through weekend, however, conditions are expected to
deteriorate somewhat by early next week as a northerly swell
arrives.

&&

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

A strong-high-pressure system at mid to upper-levels is promoting
subsidence and dry air aloft. Model guidance suggests this weather
feature anchored over Puerto Rico and the U.S. Virgin Islands
through the short term period. As a result, expect stable weather
conditions with mostly clear skies and limited rain activity.
Showers, if any, will be due to small pockets of moisture embedded
in the trades.

The best chance for shower activity is possible on Sunday when a
trade wind perturbation will increase somewhat the available surface
moisture. Therefore, more frequent morning showers are forecast
over the eastern half of PR and the USVI and scattered afternoon
convection across the western and central portions of PR.

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

The ridge pattern aloft is expected to hold through the long term
period, resulting in very dry and stable conditions aloft.
Therefore, mainly fair weather conditions will continue to prevail
across the local area. However, patches of low-level moisture
embedded within the easterly trade wind flow will move over the
area from time to time. These patches will bring with it low-level
cloudiness as well as some passing showers, with activity
possible across portions of the USVI and eastern Puerto Rico
during the overnight and into the early morning hours followed by
some locally and diurnally induced afternoon activity across
western Puerto Rico. Rainfall accumulations for the most part with
any activity should remain on the light side.

&&

.AVIATION...VFR conditions will prevail through the forecast period. Expect
mostly clear skies with limited SHRA/-SHRA activity, without impacts
to operations. Winds will be mainly from the E between 5-15 kt with
sea breeze variations after 16/13z.

&&

.MARINE...Fairly tranquil marine conditions will prevail through
the weekend with seas of up to 5 feet expected. A northerly swell
is expected to invade the Atlantic waters and local passages by
early next week, resulting in choppy seas. A moderate risk of rip
currents is expected for the northern beaches of Puerto Rico and
Culebra, the east-facing beaches of Vieques, the northwestern
beaches of Saint Thomas and some of the north and east-facing
beaches of Saint Croix for today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 74 85 74 / 10 20 40 30
STT 85 73 84 73 / 10 10 40 10

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
352 AM AST Sun Jan 17 2021

.SYNOPSIS...Ridge aloft will continue to prevail during the next
several days, resulting in mainly fair weather conditions across
the area. However, occasional patches of low-level moisture will
move in from time to time, resulting in isolated to scattered
showers with only light rainfall accumulations expected. Tranquil
seas are expected for today, however, a northerly swell arriving
by the early portion of the upcoming work week will deteriorate
seas.

&&

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

Ridge pattern aloft will maintain a strong trade wind cap near 850
MB and subsidence at upper levels. Although stable conditions will
prevail early this morning, a trade wind perturbation will advect
moisture with clouds and showers late this morning into the
afternoon hours. Therefore, shower activity will slowly ramp-up
by this afternoon across the islands. Significant flooding is
unlikely due to the fast-moving nature of these showers.

As the strong-high-pressure system persists at mid to upper-levels
stable weather conditions will prevail across Puerto Rico and the
U.S. Virgin Islands. Therefore, mostly clear skies and limited rain
activity will continue Monday and Tuesday. Showers, if any, will be
due to small pockets of moisture embedded in the trades.


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

No change in the overall synoptic pattern is expected during the
long term period. Mid-level ridge will continue to hold across the
area, resulting in very dry air and stable conditions aloft.
Therefore, fair weather conditions are expected to prevail
through period. However, as it is typical during this time of the
year, patches of low-level moisture riding the easterly trade wind
flow will move across the area from time to time. This will
result in areas of isolated to scattered showers, with activity
across portions of eastern Puerto Rico and the USVI mainly during
the overnight and early morning hours followed by some activity
across western Puerto Rico during the afternoon hours. In general,
any activity is expected to be light to moderate in intensity and
brief, resulting in light rainfall accumulations for the most
part.

&&

.AVIATION...VFR conditions will prevail through the morning hours. Then,
cloud cover and -SHRA/SHRA will increase by mid-morning and
through the evening. Therefore, VCSH and possibly SCT to BKN
ceilings between FL020-FL070 is possible after 17/15z across the
terminals. Winds will be mainly from the E between 5-15 kt with
sea breeze variations after 17/13z.

&&

.MARINE...Tranquil marine conditions will continue to prevail for
today with seas of less than 5 feet expected. A northerly swell is
still forecast to spread across the Atlantic waters and local
passages Monday into Tuesday, resulting in choppy to potentially
hazardous seas, especially across the offshore Atlantic waters.
For beachgoers, there is a moderate risk of rip currents across
the northern beaches of Puerto Rico and Culebra as well as the
eastern tip of Vieques and St. Croix for today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 85 74 / 40 50 20 30
STT 85 73 84 74 / 50 50 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
413 AM AST Mon Jan 18 2021

.SYNOPSIS...

Expect stable weather conditions through much of the work-week,
with trade wind showers affecting the windward sections, mainly
during the night and morning hours, followed by afternoon
convection across the western portions. Marine-wise, a northerly
swell will deteriorate marine and coastal conditions late this
afternoon and through mid-week across the local Atlantic.

&&

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

A mid-level ridge will continue to prevail through the short-term,
promoting dry and stable conditions aloft. Therefore, organized
convective activity is not expected. Meanwhile, at lower-levels,
patches of moisture will be moving across the area from time to time
through the period. One such patch of moisture moved across the area
overnight, resulting in isolated to scattered passing shower
activity across portions of eastern Puerto Rico will very minor
rainfall accumulations observed. Behind this patch of moisture, an
area of dry air will be moving across throughout the day. Therefore,
most of the area should see mainly dry weather conditions under
mostly sunny to partly cloudy skies. Another patch of moisture is
then expected to move across very late tonight into the day on
Tuesday and linger into early Wednesday. This will result in an
increase in cloudiness as well as isolated to scattered passing
shower activity with only minor rainfall accumulations expected. The
areas most likely to be affected by these showers will be across the
eastern half of Puerto Rico and the USVI. Drier air is then expected
to move in on Wednesday, resulting in a decrease in activity.

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

A mid-level-high pressure will hold aloft through at least this
weekend. Then, model guidance had a polar trough moving across the
western Atlantic, weakening the ridge pattern during the weekend
into early next week. Meanwhile, a set of surface-low-pressures
moving across the Western Atlantic will loosen the local pressure
gradient and decreasing the easterly winds. Under this weather
pattern, the islands will be at the mercy of what the winds advect
over us. Therefore, areas of isolated to scattered showers, with
activity across portions of eastern Puerto Rico and the USVI,
mainly during the overnight and early morning hours, followed by
some activity across western Puerto Rico during the afternoon
hours, are possible each day.

Surface-high pressure, moving from the Eastern Seaboard into the
Atlantic, will push the remnants of a frontal boundary over the
islands Monday into Tuesday next week. As a result, moisture will
possibly increase as well as cloudiness and shower activity.

&&

.AVIATION...

Mainly VFR conditions expected across the local area.
Passing SHRA will affect portions of eastern PR through 18/12z,
resulting in VCSH at TJSJ. Otherwise, mainly fair wx conditions
expected through the rest of the period. Winds will be light and
variable through 18/12z, increasing to up to 15 kts from the E with
sea breeze variations after 18/14z.

&&

.MARINE...

Mariners can expect seas of up to 6 feet across the Atlantic Waters,
and 5 feet or less elsewhere. A northerly swell will increase seas
between 5 and 7 feet across the Atlantic Offshore waters this
evening. As a result, a Small Craft Advisory (SCA) is in effect from
tonight and extending through Wednesday morning. Winds will continue
from the east at 10 to 20 knots through at least Thursday.
Therefore, small craft operators should exercise caution.

Beachgoers, the risk is moderate across the north, east, and
southeast beaches of PR, Culebra, and Vieques. Also, it is
moderate across portions of south St. John and eastern St Croix.
This swell will increase the risk of rip currents to high across
the north-facing beaches of Puerto Rico tonight.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 73 84 74 / 10 40 40 50
STT 84 74 85 73 / 10 20 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
421 AM AST Tue Jan 19 2021

.SYNOPSIS...

Stable weather conditions will prevail through much of the
forecast period. However, patches of moisture will move from time
to time, resulting in passing showers mainly across east and north
PR and the U.S. Virgin Islands during the night and morning hours,
followed by limited afternoon convection over west PR. A northerly
swell will deteriorate marine and coastal conditions across the
local Atlantic through mid-week.

&&

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

Not much change in the overall synoptic pattern is expected through
the short term period as a mid-level ridge will continue to hold.
This will result in dry and stable conditions aloft and thus will
inhibit any potential for any organized convective activity. At
lower-levels, patches of moisture embedded within the trade wind
flow will continue to affect the area from time to time. For today,
a patch of moisture will move over the area. This will increase the
low-level cloudiness as well as result in some passing showers
moving across portions of eastern Puerto Rico during the morning
hours with some activity potentially developing across western
Puerto Rico during the afternoon hours. Then, later this afternoon
into tonight, a more decent area of moisture will move across with
precipitable water values expected to range between 1.5 and 1.7
inches. As a result, more frequent passing showers will affect
portions of the USVI and northern and eastern Puerto Rico. Rainfall
accumulations potentially up to one quarter of an inch are possible
in some areas, especially in northern and eastern Puerto Rico,
overnight tonight. A drier air mass is then expected to penetrate
across the region on Wednesday, with precipitable water values
falling to below normal, between 1.0 and 1.2 inches. Therefore,
mostly dry conditions with very limited shower activity, if any, are
expected. Another patch of moisture will then move over the area on
Thursday, resulting in isolated to scattered shower activity.

.LONG TERM...Friday through Tuesday

The new model solution keeps the Polar-trough well north of the
region. Therefore, the mid-level high will remain in place,
promoting subsidence and dry air aloft. GFS has a set of surface
low-pressures moving across the Western Atlantic, which will
loosen the local pressure gradient, decreasing the easterly winds.
That said, no much change is forecast in the weather story.
However, a trade wind disturbance is now forecast to reach the
islands by the weekend, increasing cloudiness and showers.

Surface-high pressure, moving from the Eastern Seaboard into the
Atlantic, will sink southward the remnants of an old boundary,
keeping it to the north of the islands Sunday through Tuesday.
Model guidance had some discrepancy about the possible position
and the impacts of this system over the islands.

&&

.AVIATION...

Mainly VFR conditions expected to prevail across the
area through the period. However, brief periods of MVFR conditions
cannot be ruled out across TJSJ, USVI, and Leeward Islands terminals
due to passing SHRA. Winds will be from the E-ENE below 10 knots
through 19/12z, increasing to 15 to 20 kts with higher gusts and
some sea breeze variations, especially in passing SHRA, after 19/14z.

&&

.MARINE...

A northerly swell is producing hazardous seas across the Atlantic
Waters. Therefore, a small craft advisory for the Offshore waters
is currently in effect due to seas between 5 and 7 feet.
Elsewhere, mariners should exercise caution due to seas of 6 feet
or less and easterly winds between 15 and 20 knots. Marine
conditions are forecast to improve after mid-week.

Beachgoers, the risk is high across the north-facing beaches of
PR, Culebra, and St Thomas. The risk is moderate for most of the
local beaches.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 73 85 74 / 40 50 30 30
STT 85 73 85 72 / 40 40 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
432 AM AST Wed Jan 20 2021

.SYNOPSIS...

A moist air mass will promote passing showers across the windward
sections through the morning hours. Shower activity is then
forecast to diminish by this afternoon into the evening hours when
a drier air mass is forecast to arrive. Although stable weather
conditions will continue through the forecast period, pockets of
moisture embedded in the trades will reach the islands from time
to time.

&&

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

Latest GOES-16 Total Precipitable Water imagery shows an area of
enhanced moisture moving across Puerto Rico. This has resulted in
passing shower activity affecting mainly the northern half of Puerto
Rico during the overnight hours. This pocket of moisture is expected
to quickly move out of the area during the early morning hours, with
an area of drier air quickly following behind and remaining over the
area through tonight. Therefore, from the mid-morning hours onwards,
mainly fair weather conditions with very little shower activity are
expected. A few showers cannot be ruled out across western Puerto
Rico this afternoon.

At mid to upper-levels, a polar trough is forecast to move across
the western Atlantic later today into tomorrow, weakening the mid-
level ridge somewhat. The polar trough will drive a surface low-
pressure and an associated front across the western Atlantic,
weakening the pressure gradient and thus the low-level steering
flow. Another patch of low-level moisture is expected to move across
the area on Thursday and combined with a lighter steering flow,
there is a better potential to observe afternoon convection across
interior, western and southwestern portions of Puerto Rico as the
available moisture will combine with diurnal heating and local
effects. Below normal moisture then moves across the area for Friday
and thus limited shower activity can be expected once again.
However, some afternoon convection cannot be ruled out across
portions of western Puerto Rico.

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

The mid-level high will remain in place, promoting subsidence and
dry air aloft. At the surface, pockets of moisture embedded in the
trades will bring clouds and showers from time to time. However,
due to the mid-level high, do not anticipate organized convection
across the region.

A surface-high pressure, moving from the Eastern Seaboard into the
Atlantic, will sink southward the remnants of an old boundary,
keeping it to the north of the islands Sunday through mid-week.
Model guidance has been very inconsistent with the moisture field
through the long-term period.

&&

.AVIATION...

Mainly VFR conditions expected across the local terminals. Passing
SHRA will continue to affect portions of the northern half of PR
through 20/12z, resulting in VCSH across TJSJ and TJBQ. Brief MVFR
conditions cannot be ruled with these passing SHRA. Thereafter,
mainly fair wx conditions expected through the rest of the period.
Winds will continue from the E-ENE below 10 kts through 20/12z,
increasing to up to 15 kts with sea breeze variations after
20/14z.

&&

.MARINE...

The northerly swell is subsiding across the local waters. However,
moderate to locally fresh easterly winds will create choppy seas
of up to 6 feet today. Therefore, small craft operators should
exercise caution across most of the local waters.

A surface-low moving across the western Atlantic will loosen the
local pressure gradient, promoting light to moderate trades across
the local islands. As a result, the seas will also improve.

Beachgoers, there is a high risk of rip currents along the north-
facing beaches of Puerto Rico and Culebra. It`s moderate for most
of the north and east-facing coasts.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 73 84 74 / 30 30 30 30
STT 85 73 84 72 / 10 30 30 10