Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
432 AM AST Fri Sep 24 2021

.SYNOPSIS...
Above normal temperatures with heat indices up to 106 degrees are
expected to continue today. A seasonal pattern, with afternoon
showers and thunderstorms, is expected to continue through the
next few days. A small northerly swell will continue to invade the
local waters through tomorrow.

&&

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

After 10 PM AST on Thursday, showers drifted northeast through
the Mona Channel. Thunderstorms were seen migrating moving toward
the northeast at 7 mph 30 to 35 miles north of northeast Puerto
Rico. And, a few very strong showers with frequent lightning were
seen just north of 19.5 north moving almost due east just outside
of our local outer Atlantic waters. Winds in both the observed
sounding last night at 24/00Z and the forecast soundings through
25/00Z were all less than 15 knots from the surface through 54
kft, which is something rarely seen here. As might be surmised
from the very light flow, moisture features have moved very slowly
in the last 24 hours. A ball of precipitable water, the remnants
of Peter, is drifting northeast to the right of a trough, likely
of its own making, and this moisture extends south along the
entirety of the Lesser Antilles.

The GFS suggests that easterly flow will appear in our area today
where the flow was quite variable Thursday, but wind speeds will
remain below 10 knots up through 700 mb. But much as was forecast
yesterday, the better moisture to our east will slide in over the
area on Saturday and precipitable water will peak on Sunday.

This will bring a few showers and slow moving thunderstorms to
the area today with an increase in showers and thunderstorms--
still mainly over the interior of Puerto Rico--Saturday and
Sunday.

The high temperatures that we saw Tuesday and Wednesday will
gradually face into early next week, but relief will be quite slow
in coming, especially on the north coast of Puerto Rico. Highs in
the lower 90s will be common in the lower elevations and heat
indices in the low and mid 100s are expected to continue.

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

A mid-level ridge centered over Hispaniola will begin to lose its
grip over the local area as a polar trough exits the eastern coast
of the United States digs into the western Atlantic. The trough
should linger near the U.S. Eastern coast for most of the week,
maintaining a loose gradient and hence a light to locally moderate
wind flow. This feature will act to enhance afternoon convection as
well, mainly over the interior and western Puerto Rico.
Additionally, small patches of moisture at the low levels will be
dragged by the trade winds, with precipitable water values around
1.4 to 1.8 from Monday through Wednesday. Taking these factors
into consideration, expect the development of showers and
thunderstorms each day, with the potential for urban and small
stream flooding.

The second half of the long-term forecast period will be more
challenging, as it will depend on how close or how far recently
upgraded Hurricane Sam moves from the area. As it has been in
previous days, the ECMWF has the system closer to the islands,
while the GFS recurves the cyclone further away. So far, in both
solutions, the bulk of the system will remain north of the
forecast area. If the cyclone gets close enough, as the ECMWF is
suggesting, then an increase in shower activity can be expected on
Thursday and Friday. On the other hand, if the storm stays far
away (the solution the GFS has) a seasonal pattern will continue,
with early showers moving over Puerto Rico and the U.S. Virgin
Islands, followed by active afternoons over the interior and
western portions of Puerto Rico. Nevertheless, users are advised
to follow the latest forecast on Hurricane Sam by checking the
latest National Hurricane Center updates on hurricanes.gov.


&&

.AVIATION...
Some MVFR conds with mtn obscurations are psbl aft
24/17Z in interior PR as sct SHRA/Isold TSRA dvlp across the area
during max heating in southerly flow, but TAF sites are expected to
remain VFR. Sfc winds will be generally less than 10 kt except near
TSRA and dominated by sea breezes in the southeasterly flow. Maximum
winds are variable less than 15 kt blo FL540 thru 25/00Z.

&&

.MARINE...
Recent buoy observations show that a small northerly swell
continues to invade the local waters, with a period of 13 seconds
and seas generally around 2 to 4 feet nearshore. In general, seas
up to 5 feet are expected for the offshore Atlantic waters, and up
to 4 feet elsewhere. Conditions could deteriorate again by
midweek as a swell from Hurricane Sam reaches the local waters.

For the beaches, today, the risk of rip currents is moderate for
the northern coast of Puerto Rico, Culebra, and northwestern coast
of St. Thomas, with a moderate risk appearing for Saint Croix`s
Cramer Park tonight.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 94 79 93 77 / 30 20 20 40
STT 89 80 89 79 / 20 20 20 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
458 AM AST Sat Sep 25 2021

.SYNOPSIS...

A typical shower pattern is expected today, despite decreasing
moisture and instability. Tomorrow, a tropical wave will bring an
increase to the shower activity; this trend will continue for
Monday, as an induced surface trough maintains moisture over the
region. Lingering patchy moisture will help sustain showers into
midweek.

&&

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

Showers and isolated thunderstorms developed through the overnight
hours, mainly across the Atlantic waters due to a lingering upper
level trough northwest of the region. This activity is expected to
linger through the morning hours, and remain offshore due to the
light southeasterly steering winds. Meanwhile, a weak upper level
ridge will continue to build west of the region, and moisture
content is expected to decrease somewhat later today into Sunday
morning. Having said that, afternoon shower and thunderstorm
development is still expected across the Cordillera Central and
western sections of Puerto Rico, due to the combination of the
available low-level moisture content with daytime heating, and the
sea breeze convergence. Steering winds will continue light with a
more easterly wind component than previous days, therefore, there is
slight risk for urban and small stream flooding.

For Sunday, the ridge is expected to further weaken, and a tropical
wave currently over the Leeward Islands will bring a small surge in
moisture content to increase the areal coverage of the diurnally
induced afternoon convection over the islands. The flood threat will
remain elevated through the short term period due to light steering
easterly winds. For Monday, models are suggesting a further increase
in moisture content due to an induced surface trough moving across
the region from the east. The heat index for the next few days will
range mainly from the high 90s to low 100s across the lower
elevations.

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

Patches of near-normal moisture will track across the region through
midweek next week, with PWATs of around 1.7 to 2.1 inches.
Otherwise, moisture levels are forecast to be below normal.
Meanwhile, a large upper-level trough is forecast to be west of the
region, centered over eastern North America (likely in the vicinity
of the Gulf of St. Lawrence). This trough is expected to swing a
little eastward, which could allow for some increased ventilation
over the area, leading to better instability. That being said, with
ridging in the mid-levels, instability levels on the whole are
unlikely to be particularly high. The moisture, especially when
patches are traversing the region, will combine with local effects
and modest instability to promote a typical pattern of showers. This
will continue through Wednesday. Confidence is near average in the
forecast to this point.

The forecast for the end of the week has much lower confidence. This
is associated with the effects of Hurricane Sam. The forecast still
shows the system passing by the area to the northeast. How close or
far away that passage will be remains to be seen. As has been the
case for some time now, the ECMWF has a track that is closer to the
islands, which would suggest increased potential for impacts,
including enhanced moisture and significant shower activity.
Meanwhile, the GFS has very little in the way of additional moisture
making its way into the area. It is worth noting that the GFS is
further north of the official forecast from the NHC than the ECMWF
is to the south. As such, it is likely that the GFS is overly dry
for over the local islands. The forecast reflects additional
moisture for Thursday and Friday, as well as the substantial
uncertainty that remains.

A tropical wave is forecast to arrive late Saturday/early Sunday,
with a dry slot ahead of it. As such, drying is expected during the
day on Saturday, with increased activity overnight into Sunday.

&&

.AVIATION...

Mainly VFR conditions expected to prevail across all terminals
during the next 24 hours. However, isolated thunderstorms are
developing across the Atlantic waters, and they could last through
early in the fcst period. Also, SHRA/TSRA expected to develop
over the interior and western PR fm 16z-22z, which may cause tempo
MVFR conds at TJBQ. ESE winds should prevail around 10 kt, with a
northerly sea breeze variation aft 14z across the northern PR
terminals.

&&

.MARINE...

Seas are forecast to remain at around 4 feet or less through early
next week, with generally light winds up to 10 knots.

Deteriorating conditions are likely around midweek or just after,
associated with the passage of Hurricane Sam to the northeast of
the region.

There is a moderate risk of rip currents for north-facing beaches of
Puerto Rico, as well as beaches of Culebra and eastern Vieques.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 93 80 91 78 / 10 40 40 20
STT 89 79 89 78 / 20 50 50 30

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
453 AM AST Sun Sep 26 2021

.SYNOPSIS...

Moisture persists over the region, while conditions aloft are
becoming more conducive to convective development. As such, another
active afternoon is expected, as well as tomorrow, when moisture
will increase. The forecast beyond midweek has significant
uncertainty, associated with the (indirect) impacts of Hurricane
Sam, as it passes by the region well to the northeast. Deteriorating
marine conditions are likely for Wednesday and Thursday.

&&

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

Moisture associated with a tropical wave will linger over the
local area today, and another round of showers and thunderstorms
are expected to develop this afternoon along the Cordillera
Central, with isolated to scattered showers expected across the
regional waters and portions of the USVI. Light winds are expected
to prevail once again, but a northeasterly wind component is
forecast for late this afternoon, and showers will drift southward
and affect the southern municipalities of PR. Slow-moving showers
will cause urban and small stream flooding, especially late this
afternoon into the evening hours.

Meanwhile, the mid-to upper-level ridge over the region will
collapse under pressure from a building upper-level trough across
the western Atlantic by Monday. This will further allow the
vertical development of afternoon convection, over the same areas
that have received rainfall these past few days; therefore, the
flooding risk will remain elevated through most of the short term
period. For Tuesday, a drier air mass between 800-500mb should
decrease the areal coverage of the diurnally-induced afternoon
convection. However, there is still a slight disagreement between
global models in the time of arrival of this drier air mass.

As moisture content is expected to increase through Monday, the heat
indices should range from 100-108 degrees across urban areas and the
lower elevations.

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

On Wednesday, patches of moisture will remain over the region; these
patches are expected to have near-normal moisture content, with
PWATs of 1.8 to 2.1 inches. These patches will help to sustain
shower activity across the region. Additionally, troughing is
forecast in the mid-levels, with a large upper-level trough
extending from around the Gulf of St. Lawrence to just west of the
region. This will also support convective development over the
region. As such, relatively active weather is expected during the
day on Wednesday. Forecast confidence is high, but will rapidly fall
off as we move into Thursday.

For the second half of the week, conditions across the region will
depend heavily on the track of Hurricane Sam. The system is forecast
to track by the region well to the northeast; direct impacts
presently appear quite unlikely. However, bands of moisture
associated with this system, pulling moisture up from the south,
could affect the region, especially for late Thursday into Friday.
Minor changes in the trajectory of the hurricane could greatly
impact whether or not additional moisture makes its way into the
region, as well as how much. As has been the case throughout, the
GFS has Hurricane Sam tracking further away from the local islands,
while the ECMWF has a somewhat closer track - these two tracks lie
on either side of the official track from the NHC. The Euro brings
more moisture into the region than does the GFS, which keeps the
area relatively dry through the end of the workweek. Looking at the
CMC, which takes Sam closer to the official forecast track,
additional moisture makes its way into the area, bringing PWAT
values to near or above normal levels for Friday afternoon. With all
of this in mind, the forecast reflects additional moisture over the
region, moreso for Friday than Thursday. Considering additional
impacts small changes in the trajectory could have on the region, in
the form of wind direction, there is also uncertainty with the
location of precipitation maxima, even if the moisture materializes
as anticipated. As such, the forecast confidence through the end of
the workweek is low.

On Saturday, a tropical wave is forecast to arrive, bringing
increased moisture to the region, likely starting during the second
half of the day. This moisture will traverse the region through the
night and into Sunday morning. Active weather is expected, with
shower activity in a typical pattern. Lingering moisture is expected
to persist over the region on Sunday, though the trend will be
towards drying Sunday into Monday. Forecast confidence is low to
average, considering potential uncertainty with the timing and the
dynamics, due to the affects of Hurricane Sam in the vicinity.

&&

.AVIATION...

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, SHRA/TSRA expected to develop
over the interior sections of PR fm 16z-23z, which may cause tempo
MVFR conds at TJPS and vcts across the rest of the PR terminals.
Light east winds should prevail around 10 kt or less, with sea
breeze variations aft 14z.

&&

.MARINE...

Seas of generally 4 feet or less continue across the local waters,
with winds up to around 10 to 12 knots out of the east/east-
northeast through the day today and into tomorrow.

Deteriorating marine conditions are expected around midweek,
associated with the passage of Hurricane Sam well to the northeast.
Hazardous conditions are likely, and future forecasts may bring
further increases in wave heights for Wednesday and Thursday.

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

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 90 77 / 40 40 30 20
STT 89 78 89 77 / 50 50 50 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
417 AM AST Mon Sep 27 2021

.SYNOPSIS...Seasonable weather conditions are expected to prevail
through midweek, with afternoon showers and thunderstorms
developing each day. Urban and small stream flooding is expected
due to light steering winds. During the latter part of the
workweek into Saturday, moisture content should increase, but will
depend on the track of Sam and from a tropical wave passage on
Saturday. Thereafter, weather conditions are expected to improve
as a drier air mass moves over the region through at least Monday.
Swells generated by Hurricane Sam will cause hazardous seas and
rough surf conditions late in the workweek.


&&

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

Patches of moisture will continue to stream across the region; this
will bring precipitable water values to within seasonal normals,
around 1.7 to 1.9 inches. Meanwhile, conditions aloft will become
more favorable for convective development today. An upper-level low
to the southeast will combine with a large trough extending
southward across the eastern US/western Atlantic from Hudson Bay.
The steering flow remains weak across the region, at less than 10
knots; as such, showers will likely be very slow-moving. This will
maintain the risk for urban and small stream flooding.

Drier air will be over the region tomorrow. This drier airmass is
apparent on Total Precipitable Water Imagery from GOES-16, located
upstream, east of the Windward Islands. Precipitable water values
are likely to be below normal, around 1.3 to 1.6 inches. Even so,
the combination of local effects, diurnal heating, favorable
conditions aloft, and the available moisture will result in showers
and thunderstorms for interior and western Puerto Rico. The weak
steering flow could result in locally significant rainfall.

Moving towards midweek, the upper-level trough over Hudson Bay will
drift southeastward to over southern Quebec/New England. This will
bring the trough to just west of the region. Meanwhile, the mid-
level ridging is forecast to erode under the influence of Hurricane
Sam, which will remain well to the northeast. Conditions are
therefore likely to become more favorable for convective development
around midweek. Low-level moisture convergence also seems likely on
Wednesday. Increasing shower activity is expected. Though some small
increases in the mean flow over the area are anticipated, speeds
will remain on the low end, and slow-moving showers are likely, yet
again, increasing the potential for locally high rainfall amounts.


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

At least for Thursday and Friday, the forecast across the islands
will depend on the track of Hurricane Sam. Currently, the official
forecast for Sam is to pass about 400 miles northeast of the islands
on Thursday. Based on this track, a northeast steering wind flow is
expected on Thursday, with patches of moisture moving at times over
the region. Meanwhile, an upper level trough west of the region
should provide some instability over the area. This should favor an
advective pattern during the night/early morning hours, with showers
moving over the USVI and east/northeast sections of PR. Then in the
afternoon, diurnally induced afternoon showers with isolated
thunderstorms should develop along the Cordillera Central and
southern sections of PR. As Sam pulls away further north on Friday,
a low-level trough is forecast to develop over the area, and winds
are expected to turn from the east-southeast, favoring diurnal
convection along the interior and northern slopes of PR.

For Saturday, a tropical wave is forecast to cross the region,
increasing moisture content and the areal coverage of showers across
the islands. Moisture is expected to quickly erode on Sunday, as a
ridge builds from the east, promoting drier air and more stable
conditions through Monday. However, typical afternoon convection
cannot be ruled out over the western interior sections of PR, and
from streamers downwind of the USVI. Moderate trade winds are
expected to return during the weekend.


&&

.AVIATION...Generally VFR conditions are expected across all
terminals for the next 24 hours. VCSH until 27/14Z for
TIST/TISX/TJSJ are not expected to have operational impacts at
terminals. Peak afternoon convection is expected for interior into
western Puerto Rico. Cannot entirely rule out VCTS for TJBQ, but
VCSH more likely, with activity largely staying south/southwest of
the terminal. Winds picking up out of the east after sunrise to
near 12 knots, with sea breeze variations.


&&

.MARINE...Seas up to 4 feet are expected to prevail through at least
Tuesday. Trade winds up to 12 knots should continue for the next
several days. There is a moderate risk of rip currents for the
northern beaches of Puerto Rico, including Culebra and the eastern
beaches of St. Croix. Deteriorating and hazardous seas are expected
by midweek, due to swells generated by Major Hurricane Sam. These
swells will also cause rough surf conditions and life-threatening
rip currents along the east and north facing beaches of the islands
through the end of the week.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 79 88 78 / 40 40 30 20
STT 89 78 88 78 / 50 40 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
415 AM AST Tue Sep 28 2021

.SYNOPSIS...Diurnally induced afternoon convection is expected to
develop each day over portions of the interior of PR through the end
of the week. An upper level trough west of the area will promote
instability on Wednesday. Light steering winds will cause slow
moving showers, increasing the potential for urban and small stream
flooding. A tropical wave is forecast to increase moisture content
through the weekend. Weather conditions are expected to improve
early next week, due to a building ridge and drier air intrusion.
Swells generated by Hurricane Sam will cause hazardous seas and
rough surf conditions late in the workweek.


&&

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

Patches of moisture continue to filter in over the area from time to
time. This morning, there is a patch making its way westward over
the southern half of the CWA, and is presently located over/around
St. Croix. Based on satellite estimates, this patch has precipitable
water values in the neighborhood of 1.8 to 2.0 inches or more. There
has been widespread isolated to scattered shower activity through
the night, with stronger and more concentrated activity, as well as
some thunderstorms, associated with this area of enhanced moisture.
Occasional showers pushing onshore will continue this morning, with
a typical pattern of shower activity dominating the region
throughout the coming days. Steering flow remains light over the
area; as such, showers will be generally slow-moving. Portions of
interior Puerto Rico could see locally high rainfall amounts from
afternoon convection because of this.

Aloft, conditions are becoming more favorable for supporting
convective development, as the mid-level ridge continues to erode,
giving way to some weak troughiness over the area today. Tomorrow,
this increase in instability continues. A strong deep-layer trough
extending south from over northern Quebec/Labrador this morning will
gradually shift southward and then eastward, to be over New
England/the Canadian Maritimes by Thursday, when it will begin
slowly moving away. This trough will extend to just west of the
region on Wednesday, supporting additional increases in instability,
providing further support to convection over the region.

For Thursday, model guidance suggests decreasing moisture. There is
a region of dry air just west to southwest of Hurricane Sam, as is
visible on satellite imagery. It is likely that we will see at least
some drying effects from this airmass during the storm`s passage
well to the northeast of the islands. That being said, there will be
sufficient moisture in the low levels to support shower activity.
The influence of Hurricane Sam will also lead to additional
weakening of the steering flow over the area, and the trend
continues - slow-moving showers largely affecting the interior of
Puerto Rico during the afternoon causing locally significant
rainfall, causing an enhanced risk for urban and small stream
flooding.

Forecast confidence is generally high for today and tomorrow, but is
lessened on Thursday, due to the impacts of Hurricane Sam`s passage
to the northeast.

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

As Hurricane Sam lifts further north on Friday, a low-level trough
is forecast to develop over the area, and winds are expected to turn
from the east-southeast, favoring diurnal convection along the
interior and northern slopes of PR. Urban and small stream flooding
can be expected with the heaviest showers. The weak southeasterly
steering wind flow should promote warmer than normal temperatures.
During the weekend, a tropical wave is forecast to cross the region,
increasing moisture content and the areal coverage of showers across
the islands with isolated thunderstorms expected to develop across
the local waters and over portions of the islands each day.
Therefore, the flood threat will remain elevated through the weekend.

Moisture content is expected to quickly erode by early next
week, as a ridge builds from the east, promoting drier air and more
stable conditions. However, typical afternoon convection cannot be
ruled out over the western interior of PR, and from streamers
downwind of the USVI. Moderate to fresh trade winds are expected to
return during this period in response to the building ridge to our
northeast.


&&

.AVIATION...Generally VFR conds are expected across all terminals for the next
24 hours. SHRA/TSRA activity near TISX has diminished, MVFR conds no
longer likely. VCSH after 28/18Z for TJBQ; cannot entirely rule out
VCTS, but most activity will likely be S/SE of terminal, outside of
vicinity. Winds generally east to 10 to 12 knots, with sea breeze
variations, after 28/14Z. Winds subside after sunset, becoming
light.


&&

.MARINE...Seas up to 4 feet are expected to prevail today, gradually
building between 6-8 feet by Thursday across the northern and
eastern waters of the islands. Light trade winds will continue to
prevail around 10 knots or less through much of the workweek. There
is a low risk of rip currents across all the islands today, as the
primary wave direction is from the east to southeast with the 4 ft
seas across the Atlantic waters. However, deteriorating and
hazardous seas are expected by late Wednesday night through Friday,
due to swells generated by Hurricane Sam. These swells will also
cause rough surf conditions and life-threatening rip currents along
the east and north facing beaches of the islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 89 78 / 30 10 30 40
STT 88 78 88 77 / 20 30 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
425 AM AST Wed Sep 29 2021

.SYNOPSIS...An upper level trough west of the area will promote
unstable conditions today. Light steering winds will cause slow
moving showers during the afternoons, increasing the potential
for urban and small stream flooding through Friday. A tropical
wave is forecast to increase moisture content through the weekend.
Weather conditions are expected to improve early next week, due to
the arrival of Saharan Air Layer and a building ridge from the
east. Swells generated by Hurricane Sam will cause hazardous seas
and life-threatening rip currents on Thursday and Friday.


&&

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

Not much in the way of change in the forecast, or its reasoning, and
it continues much as it has for the last few days. There are patches
of moisture that are traversing the region, which will sustain
shower activity. Dynamics are improving today, with a deep-layer
trough to the west, which is forecast to extend south from southern
Quebec to over Hispaniola. What ridging remained over the island in
the mid levels has effectively been eroded away in the squeeze
between the aforementioned trough at the broad troughing generated
around Hurricane Sam. And speaking of Hurricane Sam, though the
system will pass by the region well to the northeast, it is likely
to assist in the advection of moisture into the area. Even with
moisture expected to decrease on the whole across the region for
tomorrow into Friday, there will be plenty of low-level moisture to
support continuing active weather. The favorable dynamics will
persist, as the trough stalls to the west; model guidance suggest
that the center of that system will make it only as far as the
Canadian Maritimes and then churn for a while, with a ridge over the
Central Atlantic holding in place. And, to complete the sense of
deja vu that is this forecast, steering flow over the region remains
light. Guidance from the GFS has the mean winds for the cloud layer
at speeds approaching 5 knots through the period. This is well
supported by other guidance. Though winds are likely to be a little
bit stronger at certain layers, it`s still really only ever as high
as being on the order of about 10 knots. So, on the whole, once the
storms develop due to local effects, they`re not going to be
absconding anywhere too quickly. So, again, expect the majority of
the convective activity to be over the interior of Puerto Rico then
drifting; today, the drifting will be generally more towards
northwestern portions of the island. And, again, locally high
rainfall amounts are likely, and there remains an enhanced risk for
urban and small stream flooding, especially as showers are generally
likely over the same areas yet again (and again, and again for
Thursday and Friday). Forecast confidence is high.

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

A tropical wave is forecast to cross the region on Saturday,
increasing tropical moisture content and the areal coverage of
showers across the islands with isolated thunderstorms expected to
develop across the local waters and over portions of the islands
through at least early Sunday morning. The lingering moisture in
combination with daytime heating and the sea breeze convergence will
lead to showers and thunderstorms developing in the afternoon,
mainly over the interior and northwestern Puerto Rico. Therefore,
the flood threat will remain elevated through the weekend.

Global models are indicating a quick drying trend from late Sunday
through at least Tuesday, due to the arrival of a Saharan Air Layer
and building ridge from the east, promoting drier air intrusion and
more stable conditions aloft. However, shallow patches of moisture
embedded in the trade winds will move from time to time across the
eastern Caribbean. This should keep seasonable weather conditions
across the forecast area, with passing showers during the night and
early morning hours across the USVI and portions of east/southeast
PR, followed by diurnally induced afternoon convection over western
PR. Moderate to fresh trade winds are expected to return early in
the week. Another tropical wave is forecast to move across the
eastern Caribbean on Wednesday, increasing moisture content once
again over the area.


&&

.AVIATION...Generally VFR conds expected next 24 hrs across all
terminals, though there is potential for brief MVFR at TJBQ due to
SHRA/TSRA in afternoon, after 29/17Z. Afternoon convection expected
mostly over interior PR, but likely to drift generally northwest.
VCSH expected for TJSJ/TJPS with minimal operational impacts at
terminals. Winds generally from the east to 10 to 12 knots, with
sea breeze variation, subsiding and becoming light after sunset.


&&

.MARINE...Seas up to 5 feet are expected to prevail today, gradually
building between 6 to 10 feet by Thursday across portions of the
northern and eastern waters of the islands. Light trade winds will
continue to prevail at 10 knots or less through the end of the
week. Deteriorating and hazardous seas are expected overnight
through Friday, due to swells generated by Hurricane Sam. These
swells could also cause rough surf conditions and life-threatening
rip currents along the east and north facing beaches of the
islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 89 77 / 30 30 40 20
STT 89 78 87 77 / 30 40 40 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
423 AM AST Thu Sep 30 2021

.SYNOPSIS...Trofiness will continue to remain in place west of
the area through at least the weekend. The proximity of the
trough and sufficient low-level moisture will result in afternoon
convection across the interior and west Puerto Rico Thu-Fri.
More widespread convective activity is expected on Saturday as a
tropical wave moves across the area. Under a building ridge early
the next workweek, a drying trend is then expected. Hazardous
marine conditions due to swells generated from Hurricane Sam
continue.

&&

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

A broad upper trough will remain in place across the region through
Friday then gradually shift westward by Saturday as an upper level
ridge builds northwards across the region. This will maintain
unstable conditions aloft. In the low levels, a fairly light north
northeasterly flow disrupted by the major Hurricane Sam as it tracks
northeast of the region; is forecast to become more easterly later
today into Friday, then southeasterly by Saturday as a tropical wave
approaches the region.

Mostly clear skies and fair weather conditions expected for the rest
of the morning hours except for a few passing showers over the
coastal waters which may brush parts of the north and east coastal
sections from time to time. Significant rainfall accumulations are
however not anticipated. Otherwise skies will become mostly sunny by
late morning into the early afternoon with limited shower activity.
Another active afternoon is expected due to the near normal moisture
content along with favorable conditions aloft and daytime heating.
This pattern will favor enhanced shower and thunderstorm development
mainly over parts of the interior and west sections of Puerto Rico.
Isolated showers cannot be ruled out elsewhere, especially in and
around the San Juan metro area and on the west-end or just downwind
of the U.S. Virgin Islands. Urban and small stream flooding as well
as mudslides in areas of steep terrain will be possible with the
heaviest and most persistent rainfall activity over Puerto Rico.

For Friday a somewhat drier pattern is so far forecast as drier air
will filter in, and winds will become more easterly while remaining
fairly light. The overall weather pattern however still calls for
some afternoon convection, but mainly over parts of central and
northwest sections of Puerto Rico, including the San Juan metro
area. Across the USVI, shower activity is expected to be limited to
none, as mostly sunny skies should prevail.

By late Friday into Saturday the weather pattern changes, with the
approach of a tropical wave and thus an increase in tropical
moisture. The combination of upper level diffluence due to upper
trough shifting westward and the ridge building northwards, will
create an overall moist and unstable weather pattern across the
region, with good chance for enhanced early morning and afternoon
convection in and around the islands and over the coastal waters.
That said , the potential for urban and small stream flooding will
be high for Saturday so far based on most recent model guidance.

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

As trofiness across the western Atlantic into the central Caribbean
weakens, a mid to upper level ridge is expected to build across the
eastern Caribbean early the next workweek. This feature is expected
to extent across the central and west Caribbean by Wednesday,
holding across the area through the end of the forecast cycle. At
lower levels, moderate to fresh easterly winds will prevail Sunday
through Tuesday, becoming gentle to moderate by the end of the
workweek. Under the building ridge, a drying trend is expected
Monday and onwards. Nevertheless, shallow patches of moisture
embedded in the trade winds will move from time to time across the
eastern Caribbean.

This weather pattern should keep seasonable conditions across the
forecast area, with passing showers during the night and early
morning hours across the USVI and portions of east/southeast PR,
followed by diurnally induced afternoon convection over western
PR. Heat indices will be into the 100s with temperatures in many
areas ranging from the upper 80s to lower 90s. In addition,
Saharan dust particles continue this way, and some haziness is
expected early the next workweek.

&&

.AVIATION...VFR conds will prevail durg prd. SCT-BKN lyrs nr
FL025...FL050 over regional waters and en route btw islands with
wdly SCT SHRA. Afternoon convection will result in brief MVFR conds
due to reduced visibility and SCT-BKN lyrs btw FL020-050 with psbl
SHRA/Isold TSRA ovr most PR terminals btw 30/14Z-22Z. Elsewhere,
VCSH psbl. SFC wnds light/variable bcmg fm E-NE at 10-15 knots with
sea breeze variations aft 30/14Z.

&&

.MARINE...Seas are expected to gradually deteriorate as the swell
energy generated by Hurricane Sam approaches the area. Seas of
between 5 and 8 feet with occasionally higher seas can be expected
across the Atlantic waters and the waters east of the U.S. Virgin
Islands, including the Anegada Passage. For beachgoers, there is
a moderate to high risk of rip currents across north- and east-
facing beaches of the local islands today into the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 91 77 / 30 20 20 30
STT 89 78 89 78 / 30 30 30 70

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
420 AM AST Sat Oct 2 2021


.SYNOPSIS...Unstable condtions with showers and thunderstorms
will continue over the area today. A gradual drying trend is
expected Monday and onwards as stability and winds increase.
Saharan dust particles continue this way, and some haziness
expected early the next week.

&&

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

Doppler Radar and Satellite imagery detected showers and thunderstorms
moving across the region due to a tropical wave. This wave moving
across the islands will increase moisture and instability through
at least Sunday. Therefore, expect enhanced convection, which
could produce urban and small stream flooding and strong thunderstorms
across Puerto Rico and the U.S. Virgin Islands. Soils are already
saturated, and any persistent rain could trigger mudslides,
especially during the afternoon hours. The lingering moisture
associated with this wave will remain until tomorrow afternoon,
resulting in a seasonal weather pattern driven by showers
advection and sea breeze variations.

A ridge pattern will build aloft, stabilizing the atmosphere and
promoting sinking air aloft. In addition, a dry air mass with
Saharan dust particulate will filter from the east by Sunday
afternoon into next week. This air mass will result in hazy skies.
The maximum temperatures will continue in the low 90s, with heat
indices rising into the 100s degrees Fahrenheit, especially between
10 am and 4 pm, across urban and coastal areas.

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

A mid to upper level ridge will hold across the local islands much
of the forecast cycle with some weakening expected by the upcoming
weekend. At lower levels, a surface high pressure north of the area
will yield moderate to fresh easterly winds Tue-Wed, becoming gentle
to moderate Thursday and onwards. Under ridge pattern aloft,
precipitable water values are expected to remain below the normal
range through at least Friday. However, as the ridge aloft weakens,
moisture advection is then expected Sat-Sun.

This pattern should keep a seasonable weather conditions, with
mostly fair weather conditions and diurnally induced convection
over western PR each afternoon. Breezy...Tue-Wed. Heat indices
will be into the 100s with temperatures in many areas ranging from
the upper 80s to lower 90s. Some haziness early in the cycle.

&&

.AVIATION...SHRA/TSRA will move across the islands due to a tropical
wave. This activity could impact terminals at times. Brief MVFR
conditions will remain possible across IST/ISX and by 02/15z
across JSJ/JBQ. TSRA will form across the Cordillera Central
between 02/15-22z, causing mountain obscuration and producing
frequent lightning. Winds will be light and variable overnight,
increasing to 10 to 15 knots from the ESE-SE with sea breeze
variations after 02/14z.

&&

.MARINE...A moderate to fresh easterly wind flow will prevail across
the local waters during the next several days. Scattered showers
and isolated thunderstorms will continue from time to time today.
Wind-driven seas of up to 8 feet will result in hazardous marine
conditions early the next week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 91 77 / 60 50 40 30
STT 88 75 89 76 / 50 50 40 20

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
420 AM AST Sun Oct 3 2021

.SYNOPSIS...A seasonal weather pattern is expected to prevail
much of the forecast cycle with afternoon convection each
day. Saharan dust particles continue this way with some haziness
expected through at least Monday. Breezy.

&&

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

The lingering moisture of yesterday`s tropical wave will bring a
few passing showers. This moisture, combined with local effects
and sea breeze variations, will result in some afternoon
convection across the islands later during the afternoon hours. In
the meantime, a ridge pattern will continue to build aloft,
promoting a more stable atmosphere. In addition, the derived Total
Precipitable Water from GOES-16 detected a dry air mass moving
into the northeastern Caribbean Sea. This air mass had a high
concentration of African suspended dust particulate, and the
Leeward Islands and the Virgin Islands are reporting hazy skies
and reduced visibilities since last night. Therefore, expect hazy
skies and drier conditions spreading across the U.S. Virgin
Islands and Puerto Rico from today and through the short term.

A mid to upper-level ridge will hold through at least mid-week.
Therefore, an advective pattern will prevail through the rest of
the short-term, and afternoon convection should not be ruled out
across the western portions each afternoon. At this time, an
easterly perturbation seems to bring an increase in moisture by
Tuesday. The maximum temperatures will continue in the low 90s, with
heat indices rising into the 100s degrees Fahrenheit, especially
between 10 am and 4 pm, across urban and coastal areas.

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

A seasonal weather pattern is expected to prevail much of the
forecast cycle as a ridge pattern aloft remains in place across
the forecast area combined with precipitable water values below
the normal range which is 1.90 inches. As the ridge aloft weakens
by the end of the workweek, better moisture advection is expected
with precipitable water values near 2.0 inches. At lower levels,
a surface high pressure north of the area will yield moderate to
fresh easterly winds on Wednesday, becoming gentle to moderate
Thursday and onwards. Under this evolving pattern, continue to
expect mostly fair weather conditions with diurnally induced
convection over western PR each afternoon. However, by the end of
the cycle under better moisture advection, expect an increase in
passing showers during the night and early morning hours across
the USVI and portions of east/southeast PR. Breezy on Wednesday.
Heat indices continue near 100 degree with temperatures in many
areas ranging from the upper 80s to lower 90s.

&&

.AVIATION...Suspended dust particulate will reduce VIS across the
islands between 3-6 SM. However, SHRA will move across the islands
from time to time. TSRA will then develop across the northwest
quadrant of PR between 03/17-22z, causing mountain obscuration.
Winds will be light and variable overnight, increasing to 10 to 20
knots from the E-ESE with sea breeze variations after 03/14z.

&&

.MARINE...A building surface high pressure north of the region will
promote a moderate to fresh easterly wind flow during the next
several days. Wind-driven seas of up to 7 feet will result in
choppy to hazardous marine conditions through early the next
workweek.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 78 91 77 / 40 30 20 30
STT 89 75 90 75 / 40 10 10 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
507 AM AST Mon Oct 4 2021

.SYNOPSIS...Surface high pressure across the central western
Atlantic will cause moderate to fresh easterly winds. Some Saharan
dust is still over the area, causing hazy conditions. Scattered
showers are expected in the early morning hours across the USVI
and eastern PR, with scattered showers forecast across western and
northwestern PR in the afternoon. High risk of rip currents
expected for some of the local beaches, small craft advisories are
also in effect.

&&

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

A mid to upper-level ridge pattern will hold through Wednesday. The
below-normal dry air mass with suspended aerosol particles will
continue filtering across the islands. Therefore, hazy conditions
with limited shower activity will dominate local weather conditions.

Surface winds will increase somewhat across the region over the next
few days. These breezy conditions will promote an advective pattern
that will push patches of moisture embedded in the trades from time
to time. Then, local effects and sea breeze variations will result
in isolated to scattered convection across the western portions.
Moisture will peak Tuesday into Wednesday due to a weak perturbation
increasing the likelihood to observe more frequent passing showers
and most vigorous afternoon convection.

Like previous days, maximum temperatures will continue in the low
90s, with heat indices rising into the 100s degrees Fahrenheit,
especially between 11 am and 4 pm, across urban and coastal areas.

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

A typical weather pattern is expected through most of the long
term forecast period. Therefore, isolated to scattered showers
are expected every morning and during the night across the local
waters, USVI, and eastern PR. Meanwhile, afternoon showers and
thunderstorms are expected across portions of PR, especially
across the central and western PR. However, things could get very
rainy on Monday into Tuesday of next week if the model guidance
were to verify as a tropical wave moves through.

A weak trough in the upper levels will prevail through the end of
the week, but high pressure in the mid levels is expected to keep
things fairly stable. This mid level high pressure, combined with
precipitable water values below the normal, will limit the
thunderstorm development to isolated areas in the afternoons.
Better moisture advection is expected with precipitable water
values near or above 2.0 inches starting late Monday into Tuesday
of next week. The latest model guidance is also suggesting a broad
coverage of shower activity across the local forecast area. A
surface high pressure north of the area will cause moderate
easterly winds through the long term period. Temperatures will be
near normal, and heat indices will continue near 100 degrees
across the lower elevations.

&&

.AVIATION...Although visibilities will remain P6SM, suspended aerosol
particulate will continue reducing visibilities. VFR conditions will
prevail through most of the forecast period. A few -SHRA/SHRA will
move from time to time, without impacts. SHRA/ and maybe Isolated-
TSRA will then develop across the northwest quadrant of PR between
04/18-22z. Winds will be light and variable overnight, increasing to
10 to 20 knots from the E-ESE with sea breeze variations and gusts
after 04/14z.

&&

.MARINE...Hazardous seas are expected through Wednesday due to
moderate to fresh winds up to 20 knots and seas up to 8 feet.
Therefore, there is a small craft advisory in effect. There is
also a high risk of rip currents through late Tuesday night for
the northern beaches of PR, Culebra and eastern St Croix.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 78 90 80 / 20 30 50 50
STT 89 79 89 79 / 10 20 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
435 AM AST Wed Oct 6 2021

.SYNOPSIS...

A ridging pattern aloft will hold until Friday. An increase in
moisture content due to remnants of Victor will aid in the
development of showers and thunderstorms Thursday and Friday.
Choppy to hazardous marine conditions will continue at least
through early Thursday.


&&

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


At lower levels, a surface high pressure north of the area will
continue to promote east to east northeast winds. This will drive
patches of low-level moisture into the area from time to time,
resulting in brief showers across the local waters, USVI and
portions of eastern and northern Puerto Rico during the overnight
and early morning hours. A weak mid level ridge will continue to
hold over the area through Friday. An upper level ridge will weaken
as an upper low starts moving in on Thursday, and by Friday, the
upper low will weaken and become a weak trough with its axis over
the local islands. This will promote somewhat stable conditions,
hindering widespread development of deep convection. That being
said, scattered to locally numerous showers are forecast across
parts of the local forecast area, but only isolated thunderstorms
are expected. This overall pattern, in combination with the daytime
heating and local effects, will cause shower, and isolated
thunderstorm activity, across western Puerto Rico during the
afternoon hours. However, due to the relatively fast steering flow,
rainfall activity is not expected to be significant, therefore, the
flooding potential is expected to remain low, though ponding of
water in poor drainage areas is expected.

As far as temperatures, we can expect near normal highs and lows,
possibly within 2 degrees of normal. Highs in the upper 80s to low
90 across the lower elevations, with lows in the mid 70s to near 80.
The higher elevations could observe highs and lows about 5 to 10
degrees cooler than the lower elevations, even slightly cooler in a
few isolated areas. The heat index values could reach the low 100s
across some areas in the lower elevations each day through the end
of the workweek.

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

A seasonal weather pattern is expected for this upcoming weekend
with lingering moisture across the area through Sunday. A weak upper-
level trough over the area will maintain some instability aloft
with 500 mb temperatures remaining between -7 to -6 degree
Celsius. However, the mid-level ridge will make a comeback with
dry air filtering in at these levels. This will mainly support
shallow convection and reduce coverage in thunderstorm activity.
Therefore, isolated to scattered showers are expected during night
hours and each morning across the local waters, USVI, and eastern
PR. Meanwhile, diurnal heating and local effects will produce
afternoon showers and isolated thunderstorms mainly across the
central and western sections of PR.

Model guidance diverge for next Monday throughout the week. Both GFS
and ECMWF agree on the existence of a deepening cutoff low over
Florida. However, discrepancies start with GFS having a much
stronger upper low moving eastward while settling west of the
forecast area and persisting through the week. Meanwhile ECMWF has
the low weakening into a trough and staying a bit farther west.
At low levels, a vigorous tropical wave will stream across eastern
Caribbean with precipitable water values increasing to near and
above 2.0 inches across Puerto Rico and U.S. Virgin Islands by
early Monday. GFS also combines this event with the upper low
pulling deeper moisture from the ITCZ into the forecast area
supporting a very moist and unstable environment throughout the
week. This suggests a broad coverage of shower and thunderstorm
activity across the local forecast area through the end of the
workweek. On the other hand, ECMWF has the tropical wave passing
through but downplaying on the moisture pulling from the ITCZ,
hence delaying deeper moisture in the air column and appearing
much later in the workweek supporting a more seasonal weather
pattern for most days. Therefore, confidence in the forecast is
low. We will need to closely monitor the evolution of this
forecast as there still exist the potential for a significant rain
event by next week.


&&

.AVIATION...VFR conditions expected to prevail across the local
terminals through the forecast period. However, SHRA will be
observed through at least 06/12Z, causing -SHRA at the local
terminals. That being said, no significant impacts are expected. In
the afternoon, after 06/16Z SHRA and ISOLD TSRA expected across
western PR, causing VCTS at TJBQ. Winds will continue from the ENE
at 10 KT or less through 06/12Z, increasing to 15 to 20 kts with
gusts up to 25 kts and sea breeze variations after 06/14z.


&&

.MARINE...

Choppy to hazardous seas between 5 to 8 feet due to wind driven
seas and a northeasterly swell are expected to continue across
most of the regional waters through early Thursday. Therefore,
there is a Small Craft Advisory in effect until Thursday morning.
There is a high risk of rip currents across the northern and
eastern beaches of PR, Culebra, eastern beaches of St.Croix and
northern St. Thomas .


&&

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

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
352 AM AST Sat Oct 9 2021

.SYNOPSIS...Fair weather conditions along with hazy skies due to a
Saharan Air Layer will prevail over the area today, with limited
afternoon convection over western Puerto Rico. A tropical wave
will affect the area late Sunday through Monday, resulting in more
widespread shower and thunderstorm activity. The long-term period
will remain unsettled with multiple days of widespread shower and
thunderstorm activity looking likely.

&&

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

Hazy skies and a relatively dry airmass will continue across the
region due to the Saharan air layer and suspended particulates
spread across the region, along with limited moisture advection. A
mid to upper trough will continue to weaken and lift northeast of
the region, and be replaced by high pressure ridge aloft on Sunday.
Surface high pressure will continue to build north of the region
today into Sunday to maintain moderate to locally strong easterly
winds with somewhat breezy conditions expected to continue
especially along the coastal areas. A tropical wave still east of
the Lesser Antilles is forecast to enter the eastern Caribbean and
cross the region late Sunday through Monday.

For today into early Sunday morning, expect overall stable and
generally dry conditions to prevail across the region with only a
few passing early morning showers expected, followed by limited
afternoon convection. Precipitable water values are forecast to
range between 1.0 to 1.6 inches, which is below the normal
climatological value. Regardless, patches of shallow trade wind
moisture will cross the regional waters and reach the coastal
areas from time to time. This, in combination with local effects
and good daytime heating, will aid in the development of some
showers and possibly isolated thunderstorms, mainly over the
interior and northwestern quadrant of Puerto Rico. Elsewhere
activity will be mainly downwind of the islands if any at all.

By late Sunday into Monday, moisture advection is expected to
quickly increase as the aforementioned tropical wave crosses the
Lesser Antilles and approaches the region. This expected moist and
unstable pattern will therefore increase the chance for showers and
isolated thunderstorm development across the U.S. Virgin Islands and
east sections of Puerto Rico. During the day on Monday, the
arrival of the tropical wave and increasing instability, along
with precipitable water values in excess of 2.0 inches and a
significantly moist southeasterly wind flow, will all favor high
potential for urban and small steam flooding across the islands
due to heavy rains and thunderstorm activity, along with mudslides
which will be possible in areas of steep terrain due to unstable
and saturated soil. Stay tuned as we will continue to monitor to
see how this pattern unfolds during the later part of the period.

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

Not much has changed in the overall weather pattern during the long
term period. As mentioned in previous discussions, a wet weather
pattern continues to look likely. A mid and upper-level trough is
expected to cutoff and amplify over Cuba. This will induce a broad
low-level trough, which is expected to be located north of
Hispanola, near the southeastern Bahamas. This feature will induce a
southerly wind flow, which will drag deep ITCZ moisture over the
area through the period. Model guidance continues to suggest very
high moisture content, with precipitable water values expected to
range between 2.1 and 2.5 inches. Climatology speaking, these values
are between 75th and 99th percentile for this time of the year.
Therefore, environmental conditions appear to be quite favorable for
deep and organized convective activity to materialize, especially
during the afternoon time period when the activity will be fueled by
daytime heating and local effects. One somewhat concerning aspect in
this overall weather pattern is that due to the broad low-level
trough expected to set up north of the area, the steering flow will
become very light, less than 5 knots, especially from Friday
through next weekend. Therefore, the convection that develops will
be slow-moving and prolonged.

To sum everything up, it is becoming increasingly likely that
significant rainfall activity will materialize during most of next
week. Given that this is going to be multiple days of active
conditions, the soils are likely to become saturated, leading to
flooding and mudslide concerns.

&&

.AVIATION...VFR conds will prevail at all terminals durg prd. Area
of Saharan dust spread across the region will maintain prevailing
vsby at most terminals between 5-7 SM. However No restrictions to
flight vsby anticipated. Isold SHRA en route btw islands with mstly
SCT lyrs nr FL025...FL050...FL250. SFC wnds generally light and
variable, bcmg fm E-SE around 15 KTS with ocnly hir gusts fm 09/14Z-
09/23Z. SHRA/Isold Tsra psbl ovr interior and west sections of PR fm
09/17Z-09/22Z. No sig operational wx impact attm.

&&

.MARINE...A long dominant period northerly swell will result in
choppy seas across the Atlantic waters and local passages today
through Sunday. A tropical wave is expected to affect the area
late Sunday through Monday, increasing the winds and seas even
further with seas of up to 7 feet possible across the offshore
Atlantic waters. As a result, a Small Craft Advisory has been
issued for this zone beginning Sunday afternoon and lasting
through at least Monday evening.

For beachgoers, there is a high risk of rip currents across the
north-facing beaches of Puerto Rico for today. The high risk of
rip currents will extend into the beaches of Culebra and eastern
St. Croix by tonight. The high risk of rip currents will prevail
across these areas through Monday Afternoon.


&&

.FIRE WEATHER...Although the general wind flow is expected to remain
at 15 mph or below, sea breeze variations may cause winds to peak at
15 to 20 mph between the late morning and early afternoon hours.
Minimum relative humidities may briefly fall into the mid to upper
50s, but lack of wetting rains and further drying is expected to
keep fuel moisture values at 10% or below. Given the expected
scenario, a Fire Danger Statement has been issued for elevated fire
weather conditions expected today, particularly in the vicinity of
Guanica, where KBDI remains above 550.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 90 77 / 20 20 30 50
STT 88 78 88 78 / 20 30 50 60

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
452 AM AST Sun Oct 10 2021

.SYNOPSIS...
An increase in cloudiness and moisture is expected as a tropical
wave move more into the forecast area. Given the presence of this
low level moisture an active afternoon is forecast with shower
activity over western and southwestern Puerto Rico. Therefore,
ponding of water in roadways and urban and small stream flooding
is expected with the heaviest activity. Across the regional
waters, marine conditions will deteriorate as a northerly swell
arrives over the local waters.

&&

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

A mid to upper trough will continue to slowly lift northward across
the area to maintain marginally unstable conditions aloft. A surface
high pressure ridge across the Atlantic, will lift farther north of
the region and relax the local pressure gradient, as a tropical wave
crosses the Lesser Antilles and enters the northeastern Caribbean
today through Monday. Another vigorous tropical wave will approach
the region By Tuesday to maintain a moist and unstable weather
pattern across the forecast area through the short term period.

For the rest of the morning into the afternoon hours, occasional
bands of moisture along the leading edge of the tropical wave, with
axis now crossing the Lesser Antilles, will move across the coastal
waters and affect parts of the U.S. Virgin Islands and eastern
Puerto Rico. A gradual increase in moisture is expected throughout
the day and on Monday as the tropical wave approaches the region.
Recent guidance as well as satellite imagery, continued to suggest a
significant increase in tropical moisture with precipitable water
values expected to exceed 2.0 inches through-out the day. The
marginal instability aloft along with good daytime heating, local
effects and the increasing low level moisture, will all support
enhanced late morning and afternoon convection across the area.
Showers and isolated thunderstorms can therefore be expected in some
areas, first over portions of the U.S Virgin islands and eastern
Puerto Rico during the morning hours. By early afternoon and into
the evening, this activity should spread to the interior and west
sections of Puerto Rico. So far all guidance suggest an increasingly
moist and unstable environment with a good potential for shower
development and organized convection across portions of the islands.
Urban and small stream flooding, as well as ponding of water on
roads and in poor drainage areas will be possible especially during
the afternoon and into the evening hours.

By Monday, a moist southeasterly flow will continue trailing the
tropical wave, with layered precipitable water values expected to
exceed 2.0 inches throughout the day. As a result, widespread
convection will be likely with good potential for enhanced showers
and thunderstorms across the islands, especially during the early
morning over the east sections of the islands, then over the
interior and west sections during the afternoon hours. For the rest
of the period, another tropical wave is expected to approach the
local area by Tuesday. Therefore expect this moist and unstable
weather pattern to continue with the likely-hood of urban and small
stream flooding as well as ponding of waters on roads and in poor
drainage areas to remain high across the islands due to heavy rains
and thunderstorm activity, along with mudslides which will be
possible in areas of steep terrain.

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

An unstable weather pattern is expected for most of the long term
period. On Wednesday into Friday, a mid and upper-level trough is
expected to cutoff and amplify western of the forecast area. As a
result, an induce surface trough is expected to be located north
of the area and will drag ITCZ moisture to the area. This feature
will induce a southerly wind flow over the CWA for most of the
long term period. Meanwhile, according to both model guidances, at
the surface, a vigorous tropical wave with Precipitable water
values above climatological normals will moves into the local
islands. As this low level moisture from the aforementioned
tropical wave spreads over the local region, a more frequent
showers and isolated thunderstorms are forecasted mainly over the
interior sections of Puerto Rico in the afternoon hours. Given the
presence of the induce trough just at north of the area, the
steering flow is expected to remain light to gentle and in less
than 10 mph. That said, the afternoon convection will be slow
moving and will enhance the threat for flooding with the long live
activity.

On Friday into Sunday, a slight decrease in water content is
expected as the upper level trough and the associate moisture
moves to the east. However, enough lo level moisture in
combination with the local effects and some unstable conditions
aloft would result in afternoon convection each day and will
increase the potential for urban ans small streams flooding with
the heaviest activity once again. Daytime temperatures are
expected to increase and fluctuate between the upper 80s to the
low 90s due to a south component in winds. That said, expect some
heat indices between the low 100s to the 105 Fahrenheit degrees
across all the north coast of Puerto Rico and some sections across
the U.S. Virgins Islands.

&&

.AVIATION...VFR cond will prevail at most terminals durg the morning
hours, except for TKPK and TNCM, where brief MVFR due to SHRA/ISLD
TSRA will cont durg prd. SCT ocnl Bkn lyrs nr FL025...FL050... FL090
en route btw islands and ovr regional waters, as a tropical wave
crosses the Lesser Antilles, then moves ovr the Northeast Caribbean
today. SFC wnds fm E at 5-10 kts...bcmg E-SE at 10-20 kts aft
10/14z. The tropical wave will increase the chance for SHRA/TSRA
across the local flying area with VCSH/VCTS psbl at most terminals
fm 10/16Z-10/23Z except for TNCM/TKPK as previously mentioned.

&&

.MARINE....Across the regional waters, a long dominant period
northerly swell will continue to produce choppy seas up to 7 feet
across the Atlantic waters and local passages starting through at
least Sunday. An increase in the frequent of passing showers is
expected as a tropical wave filters into the region. Also, an increasing
the winds and seas are forecast across the regional waters. As a
result, Small Craft Advisories have been issued for these zones
beginning today at 8 AM AST and lasting through at least Monday
evening. There is a high risk of rip currents across the north-
and east-facing beaches of the local islands through at least
Monday afternoon.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 77 89 76 / 50 80 90 60
STT 90 81 88 77 / 70 80 70 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
532 AM AST Tue Oct 12 2021

.SYNOPSIS...
Mid to upper level high pressure ridge will remain in place
overhead with a TUTT and associated cut off low just west of the
area to provide good ventilation and marginally unstable conditions
aloft. A broad plume of moisture trailing a tropical wave will
continue to lift northwards across the region in a prevailing
southeasterly wind flow. Another vigorous tropical wave will
enter the eastern Caribbean later tonight through Wednesday and
bring another swath of tropical moist across the region. This will
maintain a very moist and unstable local environment through the
end of the work week. Periods of scattered to numerous showers and
potential for thunderstorm development will continue across the
region for the next several days. Choppy seas will continue due to
moderate east southeast winds.

&&

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

An unsettled weather pattern is expected for the short term
period. In the upper levels, just over the local region a high
pressure will be in place and will result in some stable
conditions aloft. However, the presence of an upper level
trough/TUTT located over Cuba could provide some marginal
unstable conditions, especially for the last part of the short
term period. Meanwhile, at the surface today, a slight decrease in
moisture is expected to reach the islands in the morning hours.
However, this will be a short break and for the afternoon hours
plenty of low level moisture from a previous tropical wave and the
leading edge of another tropical wave (Invest 93L), which at this
time have a low tropical cyclone formation in the next 5 days. As
a result, for this afternoon into evening hours, widespread
activity is expected over the interior and northwestern sections
PR, as well the San Juan metro area. The heaviest activity could
result in urban and small streams flooding as well mudslides over
the interior sections.

On Wednesday into Thursday, according to both model guidance, the
upper level trough located at west of the area will resut in an
induce trough just at north of the region. This through will
induce a weakness in the pressure gradient over the forecast area.
As a result, winds are expected to become more lights from east-
southeast. In the surface, on Wednesday, the axis of the vigorous
tropical wave (Invest 93L) is expected to cross the region
increasing even more the water content with precipitable water
values around 2.4 inches (Pwat from GOES-16 Satellite). That
said, expect widespread shower activity over eastern, the interior
and western sections of Puerto Rico, as well the San Juan metro
area. Therefore, an increase in the threat for flooding is
expected over the region due to the combination of the slow-moving
showers and the saturated soils. Daytime temperatures are
expected to remain in the mid 70s to the upper 80s due to the
cloud coverage.

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

Recent model guidance continued to suggest that the fairly moist
and unstable pattern is expected to continue into the upcoming
weekend. On Friday, the TUTT and associated cutoff low will
continue west of the forecast area while an induced surface
trough and weak area of low pressure is expected to linger north
of the region. This overall pattern will aid in lifting another
plume of moisture across the forecast area and will also maintain
a light southerly wind flow over the region through at least
early Sunday. Meanwhile, considerable amounts of tropical moisture
will be drawn up across the region to maintain precipitable water
values well above the climatological normals. The deep layered
moisture field with precipitable water values ranging between 1.80
to 2.20 inches will persist though Sunday and thus increase the
potential for more frequent showers and isolated thunderstorm
development across the islands and regional waters. This afternoon
convection should be focused mainly over the interior and north
sections of the islands, especially Puerto Rico and the northern
U.S. Virgin Islands during the afternoon hours. Due to the presence
of the induced troughiness across the area, a light south to southwest
wind component is expected with enhanceed sea breezes and near
normal temperatures. That said, afternoon convection will be slow-
moving and will be enhanced therefore increasing the threat for
urban and small stream flooding.

By late Sunday into early next week...an upper level ridge is
forecast to build and spread across the region from the west. Low
level moisture is then expected to erode, resulting in less
potential for widespread convection. However, there will still be
sufficient low level moisture to combine with local and diurnal
effects for afternoon convection each day mainly over parts of the
interior and west to northwest sections of Puerto Rico. Daytime
temperatures are expected to fluctuate between the upper 80s to
the near 90s due to a southerly component in winds at least until
Sunday. Thereafter winds are to remain light but become more easterly
as the aforementioned surface trough is forecast to weaken in response
to a high pressure ridge building over the west and central Atlantic.

&&

.AVIATION...Mainly VFR conditions will prevail for all the TAF sites
at least until 12/16Z, with VCSH forecasted. Sfr winds will remain
VRB until 12/10z, and becoming from E-SE at 10 Knots with wind gust
and with seas breeze variation. After 12/18Z TSRA will start to develop
near TJSJ, TJBQ, TIST & TISX and could result in MVFR conditions.

&&

.MARINE...Choppy seas up to 6 feet expected today through Wednesday,
with winds up to 15 knots. There is a high risk is of rip currents
for the north facing beaches of PR today, and moderate risk for
the remaining northwest, northeast and east facing beaches as well
as for the beaches of Culebra, Vieques and most of the north and
east beaches of the U.S. Virgin islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 90 75 / 70 50 60 60
STT 87 79 86 78 / 50 70 50 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
511 AM AST Wed Oct 13 2021

.SYNOPSIS...
An extensive area of low to mid level moisture will accompany a
tropical wave with axis now crossing the Lesser Antilles. This
wave will bring deep moisture to the area and continue to support
the moist and unstable weather environment already in place for
the next several days. An induced surface trough and associated
area of low pressure will continue to develop north of the region,
while lifting farther north through Friday. This overall pattern
will maintain a light south to southwest wind flow and therefore
favor unstable conditions, with good potential for enhanced convection
into the weekend. Consequently moderate to high potential for urban
and small stream flooding can be expected across portions of the
islands, along with mudslides in areas of steep terrain especially
over Puerto Rico. Choppy seas will continue today due to gentle
to moderate southeasterly winds.

&&

.SHORT TERM... Today through Friday...
An unsettled weather pattern is expected to prevail through the
forecast period. At the mid and upper levels, a trough located just
north of Cuba and a high pressure over the Leeward Islands will
maintain a southwesterly wind flow over the local islands. This will
result in a divergent, favorable, upper level pattern through at
least Thursday. At the surface, a trough north of Hispaniola is
generating a southerly wind flow that will continue to drag plenty
of moisture over the region. In fact, Total Precipitable Water from
GOES-16 shows values around 2.1 to 2.4 inches, which is above the
climatological value for this of year. Also adding to the mixture, a
tropical wave over the eastern Caribbean will also combined with
this feature. The trail of moisture associated with these systems
will affect the U.S. Virgin Islands and the southern and
southeastern municipalities of Puerto Rico through the morning
hours, and some urban flooding cannot be ruled out. In the
afternoon, diurnal heating will combine with the available moisture
to generate showers and thunderstorms along the Cordillera Central
and northern Puerto Rico.

By Thursday, the pressure gradient loosens, thus winds become light,
and also more from the southwest as the surface trough evolves into
a low pressure and begins to move to the east. Additionally,
conditions aloft still expected to be favorable for shower and
thunderstorm develop. However, under a southwesterly wind flow, the
focus of rainfall in the afternoon hours will shift to the San Juan
metro area and northeast Puerto Rico. Light winds will promote the
rain to linger longer, hence enhancing the potential for flooding
and sharp water surges along streams and rivers. By Friday, the
surface trough will also interact with a gyre located north of
Panama, dragging additional moisture content over the area. Under a
still light west to southwest wind flow, expect another round of
rain to affect the area and the potential for flooding to continue.

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

The aforementioned surface trough is to lift northeast across the
region to maintain light south to southwest wind flow and moist low
level convergent zone through at least early Sunday. The local winds
are forecast to become more east to northeast by Sunday afternoon
onwards, with the moisture convergence to focus over the eastern
and and southeastern sections of Puerto Rico as well as over the
U.S.Virgin Islands through Tuesday. Winds will again shift and
become more easterly and increase on Wednesday and Thursday when
the the easterly trades will return with accompanying periods of
passing clouds and showers across the region with a more typical
weather pattern to follow.

That said, expected high moisture content to continue with PWAT
values up to 2 inches to linger across the region through Sunday.
The upper level ridge is forecast to erode, as a short wave trough
crosses north and east of the region and will therefore maintain
marginally unstable conditions aloft. This along with local effects
and good daytime heating, expect the possibility of enhanced convection
to continue with showers and thunderstorms development likely especially
during the afternoon and evening hours across portions of the islands.
Therefore the potential for urban and small stream flooding will remain
moderate to high across the islands.

By Monday and for the latter part of the period, the weather pattern
will continue to gradually change and improve with an erosion of low
level moisture and the building of the surface high pressure ridge
north of the region. This in turn will increase the easterly trade
wind which is expected by Tuesday, followed by a wind surge so far
forecast to cross the region Wednesday through Thursday. By then a
more seasonal weather pattern can be expected, with periods of
quick passing morning cloud and showers across the regional waters,
followed by locally and diurnally induced afternoon showers and mostly
isolated thunderstorm over the interior and west sections of Puerto
Rico.

&&

.AVIATION...
VCTS are expected to affect the Leeward terminals through 14Z, and
the USVI terminals through most of the period, which could cause
TEMPO groups due to reduced VIS and low ceilings. VCTS are also
expected for TJSJ/TJBQ after 17Z. SHRA/TSRA expected after 17Z for
most of Puerto Rico, resulting in mountain obscuration. Winds
will be out of the south at 5 to 10 knots, with stronger gusts.

&&


.MARINE...Small craft advisory continues in effect for the
offshore Atlantic waters until this afternoon due to seas up to 7
feet. However, seas up to 5 or 6 feet can be expected elsewhere
through today into Thursday. There is a high risk of rip currents
tonight for the northern beaches of PR and Culebra and a moderate
risk of rip currents for most of the U.S. Virgin islands beaches.

&&

HYDROLOGY...Deep tropical moisture will continue to be drawn
northward across the region as a tropical wave crosses the region
today, along with a surface trough which will linger across the
forecast areas at least through the end of the week. This
moisture, will combine with marginally unstable condition aloft
and local and diurnal effects to enhance shower development and
rainfall activity across the local islands each day. There is
moderate to high potential for rainfall accumulations between 1-2
inches each day with localized higher amounts, particularly across
portions of the east and northern half of Puerto Rico as well
over portions of the U.S. Virgin Islands where isolated amounts
between 1 to 2 inches of accumulative rainfall amounts cannot be
ruled out at least through Thursday. The probability of urban and
small stream flooding will therefore remain high and also the
possibility of mudslides in area of steep terrrain and where the
soil remains saturated.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 77 89 77 / 70 60 80 70
STT 86 79 86 79 / 60 70 70 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
434 AM AST Thu Oct 14 2021

.SYNOPSIS...
Showers and thunderstorms continue over and around Saint Croix
but will fade during the day. Showers and thunderstorms will
redevelop over Puerto Rico each of the next several days in light
flow. Moisture will decrease over the next seven to 10 days while
flow across the area returns to normal next week. Minor river
rises and localized urban and small stream flooding may be
expected today and tomorrow, but the highest amounts likely
occurred yesterday.


&&

.SHORT TERM...Today through Saturday...
Low pressure at lower levels will remain north of the forecast area.
High pressure has built at 700 mb just south of the forecast area
while a ridge extends toward the west also south of the forecast
area at 850 mb. This will create an unusual flow pattern through the
forecast area that will translate into light south and west flow
over the U.S. Virgin Islands and Puerto Rico. Skies are mostly clear
at the moment over Puerto Rico except for scattered cirrus, but
showers and overcast persist over the U.S. Virgin Islands and
thunderstorms west southwest of Saint Croix are drifting slowly east
southeast. Moisture will continue to diminish across the area, but
will remain above normal with precipitable water values not dropping
much below 2 inches during the period. On Friday, the low pressure
will weaken and move northeast as high pressure from just north of
20 north in the tropical Atlantic ridges in over the U.S. Virgin
Islands and Puerto Rico. The resulting col will prolong the light
winds with daytime showers and thunderstorms likely each day.

The cut-off low at upper levels over the Bahama Islands will move
toward the Florida Strait during the period allowing high pressure
to become centered over Puerto Rico and the U.S. Virgin Islands by
Saturday. Although 500 mb temperatures will warm several degrees
during the period, the increase in divergence aloft due to the high
will allow some thunderstorms to develop each afternoon and warm
waters around the area will allow them to continue into the
nighttime hours.

.LONG TERM...Sunday through Friday...
A mid to upper level ridge will hold over the local islands on
Sunday. However, it will remain pretty moist at the lower levels,
with precipitable water values around 2.0 inches and mid-level
relative humidities around 70%. At the surface, the pressure
gradient will remain weak due to a trough well to the north, and
therefore, light winds should continue into mid-week. Under this
pattern, the GFS, ECMWF and the National Blend Model (NBM) all
show showers developing over the interior and spreading along the
northern portions of the region. Although 500 mb are expected to
remain around -5 degree Celsius, the Galvez-Davison Index (GDI)
does show values around 30 for that day, which translate into
possible isolated thunderstorms.

Moving into Monday and Tuesday, the mid-level ridge will begin
to migrate toward the Dominican Republic as a trough approaches
from the east. The induced reflection of this feature to the
northeast of the Leeward Islands will also maintain a wind flow
from the east-northeast. Additionally, it will generate patches
of moisture that will move across the islands, favoring a
seasonal pattern with overnight and early morning showers moving
over the northern municipalities of Puerto Rico and over the U.S.
Virgin Islands, and then fueling additional activity in the
afternoon for the interior and southwestern portions of Puerto
Rico. Then, on Wednesday and Thursday, winds will pick up a little
bit, with the GFS forecast soundings showing a low level steering
flow at about 10 to 15 knots. On Wednesday, the frequency of
showers could increase as an easterly wave moves across the
islands. By the end of the workweek, as the surface high pressure
moves toward the east and merges with another cell over the
central Atlantic, the wind flow will shift more from the east,
while carrying additional patches of moisture across the islands
and promoting showers from time to time each day.

&&

.AVIATION...
Thunderstorms continue over the Caribbean and well south of the
Leeward Islands with isolated tops up to FL500 WSW of TISX and up to
FL350-450 elsewhere in the band. These are expected to dissipate into
SHRA by 14/12Z. A few SHRA remain nr TJNR. TSRA/SHRA to re-dvlp aft
14/14Z ovr PR with residual activity over the lcl waters. Sfc winds
sly til 14/14Z then bcmg sly ovr the Carib and wly ovr the lcl
Atlantic less than 12 knots. Max winds W 25-30 kt btwn FL460-500.

&&

.MARINE...
As the northerly swell continues to fade, seas 3 to 5 feet are
expected across the regional waters, under a wind flow out of the
south to southwest at 5 to 15 knots. Unsettled weather conditions
will result in showers and thunderstorms over the local waters,
and seas could become locally hazardous within a thunderstorms.
For the beaches, the risk of rip currents is high for the northern
coast of Puerto Rico, and low to moderate elsewhere.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 77 89 78 / 80 40 80 70
STT 88 79 87 78 / 60 60 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Fri Oct 15 2021

.SYNOPSIS...
Showers and thunderstorms continue over the local waters
and will redevelop over interior Puerto Rico each afternoon today
through Sunday with localized urban and small stream flooding.
Winds will become easterly and increase only slightly next week. A
very gradual cooling and drying trend will continue through early
next week, but temperatures will increase afterward.

&&

.SHORT TERM...Today through Sunday...
As low pressure at lower levels retreats to the northeast, high
pressure will build in over the area from the east. This will
continue a pattern of light winds, which will be westerly today, but
will be in the process of returning to a more seasonal easterly flow
by late Sunday. Moisture will be abundant during the period with
precipitable water values remaining almost entirely above 2 inches.
With westerly flow at lower levels this will also keep the focus of
showers and thunderstorms toward the eastern part of Puerto Rico and
later the U.S. Virgin Islands and cause the best precipitable water
values of the next 10 days to be today in the late afternoon today.

The cut-off low at upper levels over central Cuba will move toward
the Florida Strait on Saturday and rejoin the southwesterly flow
there on Sunday. High pressure at upper levels will become centered
over Puerto Rico and the U.S. Virgin Islands by later on Saturday.
Although 500 mb temperatures will warm several degrees today and
Saturday no further warming is expected. The increase in divergence
aloft due to the high will allow some thunderstorms to develop each
afternoon and warm waters around the area will allow them to
continue into the nighttime hours.

.LONG TERM...Monday through Saturday...
A mid-level ridge will continue to hold by the beginning of the
workweek, while an upper level trough digs east of the Leeward
Islands. The trough will have a reflection extending to the surface,
that will cause local winds to shift from the east-northeast. This
will cause the pressure gradient to remains weak as well, with a low
level steering flow around 4 to 5 knots on Monday, and 8 to 10 knots
on Tuesday. Even under the presence of the mid-level ridge, moisture
content is expected to remain high below 500 mb, with precipitable
water values around 1.7 to 2.0. Therefore, a northeasterly wind flow
will translate into showers being advected over the northern
portions of Puerto Rico and the U.S. Virgin Islands, especially in
the overnight and early morning hours. In the afternoon, local
effects will combine with the available moisture to generate showers
and isolated thunderstorms across the interior and southwestern
Puerto Rico. Due to the weak steering flow, this shower activity
could linger, resulting in urban and small stream flooding.

By mid-week, the mid-level ridge flattens out in response of another
trough that exits the eastern coast of the United States. From the
east, another low to mid-level trough moves across the region,
dragging additional patches of moisture across the region. In the
meantime, a surface high pressure will begin to exit the eastern
coast of the United States, causing the steering flow to increase,
first to normal values, around 10 to 15 mph. Then, as the high
migrates toward the central Atlantic, the steering flow will pick up
a bit more. The weather pattern will be more seasonal, with morning
activity affecting the eastern sections of the forecast area,
followed by convection developing in the afternoon over western
Puerto Rico.

&&

.AVIATION...
A band of SHRA over the outer Atlantic waters has a cluster of TSRA
north of Vega Baja. Some TSRA will cross the Mona Channel into the
lcl area. SHRA will remain widely scattered across the area
including the Caribbean in wly flow moving 10-15 kt. Aft 15/15Z
SHRA/TSRA will dvlp ovr interior PR and move ENE carrying MVFR/IFR
conds and mtn obscurations. Sfc winds mainly sea breezes 8-12 knots
with gusts to 23 kts nr TSRA. Maximum winds SW-W bcmg less than 23
kts blo FL540 due high pressure alf movg into the area.

&&

.MARINE...
Seas will remain at 4 feet or less for the next several days
across the local waters. Winds will be out of the south at 5 to 10
knots. Unsettled conditions will result in showers and
thunderstorms, that could cause seas to become hazardous within
the thunderstorms. For the beaches, the risk of rip currents is
moderate for the northern coast of Puerto Rico and Culebra and for
eastern St. Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 89 77 / 80 50 70 40
STT 87 78 87 78 / 40 60 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
451 AM AST Sat Oct 16 2021

.SYNOPSIS...Surface low pressure will gradually move away to the
northeast, bringing a return to our normal easterly trade winds
late Sunday and into Monday. Abundant moisture will continue
through mid week promoting relatively active weather days during
the weekend and the first half of next week, then a gradual drying
trend will ensue.

&&

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

A mid to upper level trough remains in place over Cuba, while
upper level high pressure is currently located over the Leeward
Islands. This will continue to create a divergent pattern aloft,
favoring thunderstorm formation over the islands. Additionally, a
polar trough continues to dominate over the central Atlantic,
inducing a surface low to the northeast of the region. This
feature will maintain light winds through early in the workweek,
while pulling moisture from the south across the eastern
Caribbean. As the trough moves out to the northeast, winds will
gradually shift to a more typical direction: out of the southeast
by late Sunday and more from the east on Monday. The steering
flow, however will remain very light. On Sunday, high pressure
builds over the region at the mid and upper levels, however,
moisture levels will continue to be higher than normal, with the
GFS-forecast soundings showing precipitable water values above 2.0
inches.

For each day, advective showers will move across the southern and
eastern portions of Puerto Rico and the U.S. Virgin Islands, mainly
in the overnight and morning hours. Then, in the afternoon, due to
local effects showers and thunderstorms are expected to develop for
the interior, western and northern Puerto Rico, although due to the
light wind flow, some of this activity could also spread across the
southern slopes. Urban and small stream flooding, as well as water
surges along rivers and mudslides in steep terrain are likely to
continue.

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

An upper level trough digs into the western tropical Atlantic
Sunday, allowing a weak TUTT low to be established just east of
the Leeward Islands by Tuesday, but high pressure at upper levels generally
remains established over the Caribbean waters, bringing northerly
flow to the local area. Mid levels, as well, show a center of high
pressure never far from the local area and generally across much
of the Caribbean. At lower levels areas of moisture move through
as high pressure builds over the western Atlantic and high
pressure remains in control of the eastern Atlantic waters. This
allows easterly flow modulated by weak waves to be the predominate
influence in the weather pattern. While 500 mb temperatures are
cooler during the midweek, they warm after Thursday. This and the
fact that precipitable water values drop considerably after
Friday, as mid levels become quite dry, will mean that shower
activity will decrease considerably over the next weekend.

&&

.AVIATION...Mainly VFR conditions are expected to prevail through
the forecast period. VCTS are expected for TJSJ/TJBQ/TJPS after
17Z, which could result in TEMPO groups for TJSJ/TJBQ due to low
ceilings and reduced visibilities. VCSH will be possible for the
USVI terminals. Winds will remain light, out of the southwest at
around 5 knots with sea breeze influences. Maximum winds SW 21-26
kts btwn FL430-500.

&&

.MARINE...Benign conditions will prevail through Wednesday, but
easterly winds will begin to rise during the latter part of next
week forcing seas as high as 6 feet by next weekend as a
northeasterly swell is added to the mix. This will also bring a
high risk of rip currents to the eastern end of Saint Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 77 88 76 / 50 40 70 50
STT 87 77 88 78 / 40 40 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
506 AM AST Sun Oct 17 2021

.SYNOPSIS...Light winds, owing to a weak ridge just north of the
area opposing the southerly flow around the tropical Atlantic
ridge nosing into the Caribbean, and some of the best moisture of
the fortnight, will bring another round of showers and
thunderstorms with localized heavy rains to Puerto Rico, and
lighter rains to the U.S. Virgin Islands, today. Decreasing
showers will continue Monday through Wednesday accompanied by
increasing winds. A drying trend thereafter will be briefly
interrupted on Sunday next week by the approach of a weak
tropical wave.

&&

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

A mid to upper level ridge built north of the local islands and
should linger through early in the workweek, while the upper high
weakens by Monday. At the surface, an induced trough to the
northeast of the Leeward Islands is still maintaining a weak
pressure gradient, and therefore, a very light wind flow. At the
surface, the winds are from the southeast, but remain from the
southwest between 800 to 600 mb. As the trough moves toward the
region, the wind flow is expected to gradually turn more from the
southeast on Monday, and then gradually turn more from the east on
Tuesday, while strengthening a little bit. Through the short-term
forecast period, moisture content below 500 mb will remain high,
with the GFS-forecast sounding shows precipitable water values
ranging between 1.9 to 2.4 inches, and these are the values
currently confirmed by Total Precipitable Water from GOES-16.

Recent satellite and radar imagery early this morning showed a
line of showers that developed over the Caribbean waters. This
activity could be advected across the U.S. Virgin Islands and the
southern municipalities of Puerto Rico in the morning hours. In
the afternoon, as has been the case in the previous days, showers
are expected to develop along the Cordillera Central. Due to
light winds, these showers are expected to be slow moving, and due
to soil saturation from previous rainfall, this activity will
result in an enhanced risk of flooding, mudslides and rapid river
and stream rises. Since the wind flow between 800 to 600 mb is
forecast to be from the southwest, this activity is expected to
move into the northern and eastern part of Puerto Rico including
the Greater San Juan and Bayamon Metropolitan Areas, and also
over the Virgin Islands area later in the afternoon hours. For the
rest of the short-term forecast period, the weather pattern is
not expected to change much, but with the winds backing toward the
southeast on Monday, and from the east on Tuesday, the focus of
afternoon convection is expected to be more seasonal.

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

By early Wednesday the cold front making its way south over the
western Atlantic will have stalled about 500 miles north of San
Juan with a band of moisture between it and the local islands.
This will open a path for tropical waves to once again migrate
through the area with one at about 57 degrees west on Wednesday
morning. This particular wave is depicted as have a forward area
of moisture and a following band, with rather dry conditions along
the axis most prominently at 700 mb. Moisture at lower levels
will still be rich over the forecast area and allow for good
shower and some thunderstorm activity, especially since 500 mb
temperatures will be bottoming out about this time near minus 6.5
degrees. The forward band of moisture will be arriving early
Thursday with the crest of the wave expected to pass through
Puerto Rico later that afternoon. Those in the U.S. Virgin Islands
need only subtract 2 to 3 hours. The moisture field behind the
wave will stretch and thin out and pass through during the
evening on Thursday. Between Friday and Sunday good moisture
dapples the forecast like sunlight on the forest floor and will
allow for scattered showers in our typical diurnal pattern of
night and early morning showers in the east and showers and
isolated thunderstorms in the west. Flow will by then, be nearly
easterly, favoring neither the north nor the south. Then, to wrap
up the weekend, a band of drier air passes through the area
Sunday night and Monday morning. Showers should be much more
sparse then, although this far out there is considerable
uncertainty with regard to the survivability of the band of such
dry air.

At upper levels high pressure dominates the Caribbean, but its
influence is weaker east of the Leeward Islands and by Sunday into
Monday a strong TUTT low digs south southwest into the tropical
Atlantic Ocean east of 50 degrees west. This will force winds
from the north at upper levels over the local area. The ridge of
high pressure at 500 mb never leaves the local area during the
period and in general supports the formation of a modestly drier
mid-level layer over the weekend that will also stifle but not
strangle shower formation over the area--especially over western
Puerto Rico during the afternoons.

&&

.AVIATION...Mainly VFR conditions expected to prevail til 17Z.
VCSH are expected to continue for the USVI and Leeward terminals.
Areas of SHRA/TSRA are expected to form aft 17/17Z leading to
VCTS for TJBQ/TJSJ with mtn obscurations and MVFR/IFR conds.
Winds will remain light, out of the southeast at the surface at
around 5 knots, with sea breeze variations and stronger gusts nr
TSRA. Winds alf will be variable and less than 15 knots blo FL
540.

&&

.MARINE...Seas will remain relatively tranquil through mid-week
this week. East to east southeast winds will increase during the
week and a northerly swell will arrive mid week, pushing seas up
to 5 feet by Thursday. Seas should remain below 7 feet Friday and
Saturday, but at this point small craft advisories for the outer
Atlantic waters and the Anegada Passage cannot be ruled out.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 77 88 77 / 80 50 50 40
STT 86 78 87 78 / 60 60 50 50

[cycloneye]

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

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


&&

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

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

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

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

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

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

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


&&

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


&&

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


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 78 88 78 / 40 40 30 40
STT 88 78 89 79 / 60 50 50 50