Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
447 AM AST Sat May 29 2021

.SYNOPSIS...A mid and upper level ridge moving in on Sunday will
make today the wettest of the next three days. But, Tuesday
will mark the beginning of a moistening trend that will not end
until Saturday. Our most unstable conditions will occur Thursday
and Friday and we expect a noticeable increase in thunderstorms
accompanied by heavy rains then.

&&

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

For today, a surface high pressure extending across the north
Atlantic will maintain a generally moderate east to east-southeast
wind flow across the region. At mid to upper levels, a short-wave
trough to the west, with an axis extending southward over
Hispaniola, will maintain somewhat favorable conditions aloft. This
along with near-normal moisture levels fluctuating between 1.5 and
1.7 inches, diurnal heating and local effects will support another
active afternoon with shower and isolated thunderstorm development.
Under a southeasterly component of the steering flow, the bulk of
the activity is expected to favor the interior and northwestern
quadrant of Puerto Rico, as well as portions of the San Juan
metropolitan area and eastern Puerto Rico. Until afternoon
convective development begins by the late morning and early
afternoon hours, expect showers moving from the waters into portions
of eastern Puerto Rico and the US Virgin Islands. Although today`s
activity is expected to be slightly faster and more focused than
previous days, prolonged periods of moderate to heavy rains over
already saturated soils will result in urban and small stream
flooding and possible mudslides near areas of steep terrain. Daytime
high temperatures are forecast to reach the mid-80s to near 90
degrees across coastal areas, with heat indices as high as 100
degrees across coastal areas of northern Puerto Rico.

For Sunday and Monday, a weak mid-level ridge is forecast to roll in
as the aforementioned short-wave trough lifts to the east-northeast
and away from the region. This will sustain a trade winds inversion
that may be strong enough to inhibit deep convection, but not strong
enough to suppress shallow development. As the plume of moisture
meanders away, intermittent pockets of relatively drier air and
shallow moisture, with moisture fluctuating between 1.10 to 1.80
inches, will dominate the local weather conditions. If the timing of
enhanced moisture coincides with peak afternoon hours, which is,
so far, anticipated, intense diurnal heating and local effects
will aid in the development of showers and possible isolated
thunderstorms. Since the local wind flow is expected to display an
east-southeast and an east-northeast component on Sunday and
Monday, respectively, expect the bulk of the activity to shift
accordingly. Localized urban and small stream flooding remains
possible, especially with the heaviest rain expected each
afternoon.

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

Troughing at upper levels over Cuba and the Bahama Islands
develops a cut-off low on Wednesday. The trough will continue in
the same general area while the cut-off low weakens and lifts to
the northeast. This in turn will cause a relatively weak
southwesterly jet, again at upper levels, to brush the area and
increase the instability. At the same time 500 mb temperatures
will lower to nearly minus 8 degrees. As mentioned precipitable
water values will drop to around 1.10 inches on Monday and will
increase until Saturday. Moisture between the 850 and 700 mb
levels is the weakest part of the profile during the period and
this will likely suppress some of the rain over the area, but in
general rainfall will increase--especially on Thursday and periods
of heavy rainfall are expected each day over western and interior
Puerto Rico. Showers will also increase for the U.S. Virgin
Islands, but amounts will be limited compared to Puerto Rico.
Areas of urban and small stream flooding will become more
widespread Wednesday and Thursday, but will continue through the
end of the period, sustained by the high moisture content of the
atmosphere over the area.

&&

.AVIATION...Mainly VFR conditions are expected across all terminals.
However, brief MVFR conditions can be expected with VCSH affecting
TJSJ and USVI terminals through 29/14Z and TSRA/SHRA affecting
mostly TJSJ/TJBQ with VCSH/VCTS at TJMZ/TJPS between 29/15-23Z due
to low ceilings and reduced visibility. Winds will be light and
variable through 29/12Z, bcmg ESE at 10-15 knots with higher
gusts through 29/23Z. Maximum winds W 50-62 kts btwn FL425-495
strongest at FL470.

&&

.MARINE...Moderate trade winds over the local area will allow
seas to remain 5 feet or less through the next 7 days.
Thunderstorm activity will increase on Thursday and continue into
Friday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 77 88 77 / 40 50 40 50
STT 87 77 87 76 / 40 40 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
456 AM AST Sun May 30 2021

.SYNOPSIS...Bands of moisture will move through a modestly
unstable atmosphere today through Tuesday, then moisture will
increase and an upper level trough will stall over Cuba leaving
better instability on Thursday and Friday to increase showers and
thunderstorms--mainly over Puerto Rico. Moisture continues to
improve over the weekend prolonging the wet trend through at least
next Sunday.

&&

.SHORT TERM...Today through Tuesday...
For today, a surface high pressure extending across the north
Atlantic will continue to maintain a moderate east to slightly east-
southeast wind flow across the region. A weak tropical wave is
forecast to stream across the region, generating slight variations
in the general wind flow and enhance low-level moisture convergence.
At mid to upper levels, a weak mid-level ridge will build over the
area. As a result, a trade wind inversion will gradually envelop
the region. This inversion may inhibit organized deep convection,
but it will not be strong enough to suppress shallow convective
development. Even so, there is still a chance of thunderstorm
development resulting from the combination of near normal moisture
levels around 1.70 inches, intense diurnal heating and local
effects in the afternoon. Preceding the arrival of the
aforementioned tropical wave, an area of relatively drier air will
maintain generally fair weather conditions through the mid
morning hours.

As pockets of moisture reach the forecast area, expected a slight
increase in showers moving from the waters into the US Virgin
Islands and eastern Puerto Rico through late in the morning, when
lines of showers are expected to develop and extend further west
from the local islands and El Yunque area into eastern Puerto Rico
and the San Juan metropolitan area thereafter. The bulk activity
will then shift to portions of the interior and western Puerto Rico,
where periods of moderate to heavy rains over already saturated
soils will result in urban and small stream flooding and possible
mudslides near areas of steep terrain. This activity should
dissipate around sunset, but remnants may linger over western Puerto
Rico and the Mona Passage through the evening hours. Daytime high
temperatures are forecast to reach the mid to upper 80s across
coastal areas, with heat indices peaking to around 100 degrees
across coastal areas.

For Monday and Tuesday, intermittent pockets of relatively drier air
and shallow moisture, with moisture levels fluctuating between 1.30
to 1.80 inches, are expected to stream across the region from weak
perturbations in the trade winds. Mid level ridging will hold over
the region, but weakening of the trade wind inversion is anticipated
on Tuesday due to the proximity of a mid-to-upper level trough to
the west. Showers will follow a seasonal pattern, but somewhat
favorable conditions may enhance deeper convective development on
Tuesday. As a result, urban and small stream flooding remains
possible, especially with the heaviest rain expected each afternoon.

.LONG TERM...Wednesday through Sunday...
Troughing at upper levels over Cuba and the Bahama Islands
develops a cut-off low on Wednesday. The trough will continue in
the same general area while the cut-off low weakens and lifts to
the northeast. This in turn will cause a relatively weak
southwesterly jet, again at upper levels, to brush the area and
increase the instability. At the same time 500 mb temperatures
will lower to just under minus 7 degrees. Precipitable water
values will be on the rise during most of the period with a peak
on Saturday afternoon of 2.2 inches aided by tropical waves
passing to the south and a persistent ridge at 700 mb to our west.
Moisture between the 850 and 700 mb levels is the weakest part of
the profile during the period and this will likely suppress some
of the rain over the area, but in general rainfall will increase--
especially on Thursday and periods of heavy rainfall are expected
each day over western and interior Puerto Rico. Showers will also
increase for the U.S. Virgin Islands, but amounts will be limited
compared to Puerto Rico. Areas of urban and small stream flooding
will become more widespread Wednesday and Thursday, but will
continue through the end of the period, sustained by the high
moisture content of the atmosphere over the area. At this time
surface and low to mid level flow is east or east southeast and
this will tend to favor afternoon showers and thunderstorms over
northwest and north central Puerto Rico with the possibility of a
streamer just southwest of the Greater San Juan and Bayamon
Metropolitan areas.

&&

.AVIATION...Mainly VFR conditions are expected across all terminals.
However, brief MVFR conditions can be expected with VCSH affecting
TJSJ, USVI and Leeward terminals through 30/14Z and VCTS/VCSH with
MVFR conds affecting all PR terminals between 30/14-23Z due to
low ceilings and reduced visibility. Winds will be light and
variable through 30/13Z, turning from the E at 10-20 knots with
higher gusts thereafter. Max winds WSW-W 45-50 kts btwn FL385-480.

&&

.MARINE...Marine condtions will remain relatively tranquil with
seas up to 5 feet except for Tuesday in the outer Atlantic waters
when 6 foot seas are possible along the northern border of the
local waters. Showers and thunderstorms with locally gusty winds
will increase Wednesday and Thursday and some heavy shower
activity is likely to be seen through the weekend as moisture
continues to increase.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 76 88 76 / 40 30 40 40
STT 86 76 88 76 / 50 50 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
432 AM AST Mon May 31 2021

.SYNOPSIS...Isolated to scattered brief showers will continue
during the morning hours, mostly over the windward and northern
sections of Puerto Rico and the U.S. Virgin Islands. In the
afternoon, diurnally induce shower activity with isolated
thunderstorms are forecast across the interior and western
portions of Puerto Rico. During the long term period, Thursday
looks like a transitional day into a more unstable weather pattern
across the forecast area.


&&

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

A weak mid-level ridge will continue over the region through at
least Tuesday, but a gradual erosion of the trade wind cap is
expected between Tuesday and Wednesday as a mid-to-upper level
amplifies west of the area. At lower levels, a broad surface high
pressure anchored over the central Atlantic will promote moderate
east winds. Areas of shallow moisture and showers embedded in
this flow will reach the islands from time to time through the
short term period. Models suggest that precipitable water
content will range from 1.30-1.70 inches today, gradually
increasing on Tuesday up to 1.80 inches and just under 2.00 inches
by Wednesday, seasonal climatology is about 1.75 inches.

Therefore, expect showers with possible isolated thunderstorms to
develop each afternoon over the interior and western sections of
Puerto Rico, with showers increasing in areal coverage on
Wednesday due to higher moisture content and increasing
instability aloft due to the mid-to-upper level trough west of the
area. Urban and small stream flooding will be the main threat
each day with the heaviest showers. Across the U.S. Virgin Islands
and the eastern sections of PR, expect trade wind showers to move
at times through the period during the overnight/early morning
hours, followed by diurnal development of streamers downwind of
the islands and from the eastern mountains of PR.


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

An unsettled weather pattern will prevail for most of the long
term period. According to model guidance from the ECMWF and GFS,
a mid-to-upper level trough located over the southwestern
Atlantic will approach the region from Thursday into Saturday. As
this feature moves over the region, it will create instability
aloft, increasing the potential for heavy shower activity. At the
same time, according to the GFS model, 500 mb temperatures will
range between -6 to -8 degrees. These temperatures will increase
the potential for isolated thunderstorm development with the heaviest
activity.

Meanwhile, at the surface, a high pressure located over the north
central Atlantic will maintain a moderate east-southeasterly wind
flow through the period. Following this wind flow, an increase in
moisture is expected due to the passage of a few weak tropical waves.
This increase in tropical moisture will keep precipitable water
values between 1.90 to 2.0 inches (according to the GFS model). If
model guidance is correct, heavy shower activity will prevail on
Thursday into Friday, mainly during the afternoon hours over the
interior and northwest sections of Puerto Rico and the San Juan
Metro area. The typical morning and evening activity over the
windward regions and the U.S. Virgin Islands will prevail for the
rest area. As a result, ponding of water to urban and small
stream flooding can be expected, especially with each afternoon`s
heavy rainfall activity.

Additionally, as the surface ridge promotes an east to southeasterly
wind flow, warmer than normal temperatures are expected from Thursday
into the weekend.


&&

.AVIATION...Trade wind showers across the coastal sections of
northeastern PR may cause tempo MVFR conds thru 10z at TJSJ.
Another area of showers is expected to move over TIST/TISX early
in the morning, and could also cause brief MVFR cigs. From 16z-22z
SHRA/TSRA should develop over the western interior sections of
PR, causing mainly VCSH/VCTS at TJBQ/TJPS. Otherwise, mainly VFR
through the rest of the forecast period. East winds 10-15 kt with
sea breeze variations and higher gusts at times.


&&

.MARINE...Across the regional waters, choppy marine conditions
will prevail for the Atlantic offshore waters with seas increasing
up to 6 feet tonight. For the rest of the local waters and
Passages, seas will range between 3-5 feet, and winds will be up
to 15 knots from the east. There is a moderate risk of rip
currents for the east and north facing beaches of Puerto Rico,
Vieques, Culebra and across St. Croix.


&&

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

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
445 AM AST Tue Jun 1 2021

.SYNOPSIS...A seasonal weather pattern is expected to prevail
today, with brief passing showers in the morning hours over the
windward sections of the islands and local waters. Then, in the
afternoon hours, heavy shower activity is expected over western
Puerto Rico due to diurnal effects. A cut-off low will open into
a trough and remain west of the region during the second part of
the week. This will promote unstable conditions aloft and enhance
afternoon shower development across the islands. A broad surface
high over the central Atlantic will hold through early next week.


&&

.SHORT TERM...Today through Thursday...
A weak mid-level ridge over the Caribbean Sea will continue to
loose influence over the region today, as a trough pattern
develops west of the area. Further weakening of the trade wind cap
is expected on Wednesday and Thursday, and afternoon showers are
expected to gradually increase in areal coverage each day. A broad
surface high across the central Atlantic will continue to promote
patches of low-level cloudiness and passing showers across the
U.S. Virgin Islands and the eastern sections of Puerto Rico, and
as well across the regional waters during the next several days.
This influx of moisture will keep precipitable water content
(PWAT) at or above normal levels through the short term period,
and enhance the diurnally induced afternoon showers and isolated
thunderstorms over portions of central and western PR each
afternoon.

Instability will increase late Wednesday into Thursday due to the
mid-to-upper level trough west of the area. The 500 mb
temperatures are forecast to drop around -8C by 06z Thursday and
PWAT is expected to peak to near 2 inches during the day on
Thursday. Urban and small stream flooding will be the main threat
each day with the afternoon thunderstorms and enhanced overnight
shower activity across eastern PR.

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

A mid-to upper-level trough located over the southwestern
Atlantic will continue to move southward more into the region.
According to model guidance from the ECMWF and GFS, the trough
axis is expected to stand over the Hispanola from Friday into the
weekend. This will result in instability aloft, increasing the
potential for more widespread shower activity. Also, the potential
for isolated thunderstorm activity is still on track due to 500
mb temperatures between -7 and -8 degrees Celsius, according to
the GFS model.

At the surface, a strong high pressure located over the north
central Atlantic will keep a moderate east-southeasterly wind flow
through the period bringing from time to time cloudiness and
moisture over the region on Friday into Saturday. As the surface
ridge moves eastward, an increase in tropical moisture from a weak
easterly wave will move over the region on Sunday. This will
promote moisture content at all levels, increasing the potential
for widespread shower activity. If model guidance is correct, the
heaviest shower activity will prevail on Saturday into Sunday,
mainly during the afternoon hours over the interior and northwest
sections of Puerto Rico and the San Juan Metro area. The typical
morning and evening shower activity will prevail across the
windward regions and the U.S. Virgin Islands. As a result,
ponding of water to urban and small stream flooding can be
expected. Additionally, as the surface ridge promotes an east to
southeasterly wind flow, warmer than normal temperatures are
expected during the long term period.


&&

.AVIATION...Mainly VFR conditions are expected to prevail across
all terminals. However, SHRA/TSRA will cause areas of MVFR conds
across western PR btw 16z-22z, impacting TJBQ and the vcty of
TJPS. Elsewhere, -RA/VCSH expected at times. East winds 10-15 kts
with sea breeze variations aft 14z.


&&

.MARINE...Choppy marine conditions will continue with seas up to
6 feet and winds between 15-20 knots across most of the local
waters. Therefore, small craft operators should exercise caution
across the Atlantic offshore waters and the waters between eastern
PR and the USVI. There is a moderate risk of rip currents across
the north and southeastern exposed beaches of Puerto Rico, some
beaches at Culebra and Vieques, as well most of the St. Croix
beaches.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 76 87 76 / 40 50 40 60
STT 87 76 87 76 / 40 40 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
452 AM AST Wed Jun 2 2021

.SYNOPSIS...A surface high pressure will dominate the local
pattern today, resulting in easterly winds. This wind flow will
push isolated to scattered showers for the rest of the morning
hours, mostly over eastern sections of Puerto Rico and the U.S.
Virgin Islands. In the afternoon hours, the forecast includes
heavy shower activity and isolated thunderstorms over the interior
and western areas of Puerto Rico.

&&

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

No significant change in the synoptic pattern through the short
term period from previous forecasts. For today, a weak mid-level
ridge over the Caribbean Sea and a deepening trough west of the
region will continue to promote west-southwest flow aloft.
Embedded in this flow, mid-to-upper level cirrus clouds will
continue to stream over the region. In addition, moderate to
locally fresh trades are expected to prevail. This should cause a
delay of the onset of diurnally induced afternoon convection over
mainland PR, and from streamers developing off the USVI and
eastern mountains of PR.

At lower levels, a broad surface high pressure across the central
Atlantic will continue to promote an easterly wind flow across
the region, with patches of moisture moving at times through the
forecast cycle. Instability will increase on Thursday and Friday
as the upper level trough moves over Hispaniola and promotes
divergence aloft and a drop in 500 mb temperatures to -8 degrees
C. This will also promote further weakening of the trade wind cap,
and showers should increase in areal coverage. The main threat
will continue to be urban and small stream flooding with the
heaviest showers each afternoon, mainly across portions of the
interior and west/northwest PR, as well across the San Juan metro
area.


.LONG TERM...Saturday through Wednesday

A strong surface ridge located over the central Atlantic will
continue to dominate the low levels for the long term period. As
the surface ridge stalls over the Atlantic waters, it will create an
east-southeasterly wind flow over the forecast area. This wind
flow will bring tropical moisture from a weak tropical wave over
the Caribbean. The GFS model guidance suggests that precipitable
water values on Sunday and early next week will range between 2.0-
2.2 inches with plenty of humidity between 700-500 MB. At the
same time, to reinforce the forecast of an unsettled pattern, an
upper level trough is expected to linger across the northwestern
Atlantic for most of the long term period. According to the GFS
and Ecmwf model guidance, the upper trough axis will stall and
start to elongate over Hispanola from Saturday into Tuesday when
it merges with another upper level trough. Also, on Sunday into
the upcoming week, 500 mb cold temperatures will prevail
(suggested by the GFS) between -7 to -8 degrees Celsius. Given all
these conditions, an unstable weather pattern is expected with
afternoon showers and isolated thunderstorm development. Urban
and small stream flooding will be the main threat each day with
the afternoon thunderstorms and enhanced overnight shower activity
across eastern PR.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across
all terminals through the forecast period. However, SHRA/TSRA
will cause areas of MVFR conds across western PR btw 02/17z-23z,
impacting TJBQ and the vcty of TJPS. Elsewhere, -RA/VCSH expected
at times. Low-level winds will continue from the east at 10-20
kts with sea breeze variations aft 02/14z.


&&

.MARINE...Relative tranquil marine conditions will continue with
seas up to 5 feet and wind up to 15 knots across all the local
waters. These marine conditions will continue for the next several
days. There is a moderate risk of rip currents across the north
and southeastern exposed beaches of Puerto Rico, some beaches at
Culebra and Vieques, as well most of the St. Croix beaches.



&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 86 76 / 40 50 50 40
STT 88 77 87 76 / 40 40 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Thu Jun 3 2021

.SYNOPSIS...Upper level trough pattern west of the region will
promote unstable conditions through next week. A tropical wave
will move well south of the area during the weekend, and another
one by midweek next week. A broad surface high pressure across the
central Atlantic will promote moderate to locally fresh trade
winds for the next several days. Moisture content will remain high
through the short and long term period.


&&

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

For Today into Friday, a more seasonal pattern will prevail over the
forecast area. A deepening upper trough located over the
northwestern Atlantic will promote divergence and unstable
conditions aloft. These conditions mentioned above with the
available moisture and diurnal heating will result in afternoon
convection mostly over interior and western sections of Puerto Rico.
According to satellite imagery, the limiting and timing factor for
afternoon activity could be the cloudiness at the upper level due to
the southwesterly wind flow resulting from the upper level trough.
In the morning hours, brief passing showers will continue in the
over the windward and northern sections of the islands, as well
local waters.

As the upper level trough sinks slowly into the Caribbean, weather
conditions are expected to deteriorate. Therefore, on Saturday, a
more unstable weather pattern is expected to prevail. As the broad
surface ridge continues across the central Atlantic, the low-level
steering flow will become from the east-southeast as well as
slightly stronger. This wind flow will push fragments of tropical
moisture, increasing the precipitable water content between 1.6 and
1.8 inches. As the upper level trough axis approaches over the
Hispanola, this will promote further divergence and instability
aloft over the forecast area. If model guidance (GFS and
Ecmwf)remains on track, Saturday looks like the wettest day of
the short term with heavy shower activity and possible
thunderstorms due to 500 MB temperatures rounding between -7 to -8
degrees Celsius. Therefore, urban and small stream flooding with
the heaviest showers is expected, mainly across northwest sections
of PR and across the San Juan metro area due to the streamer from
eastern mountains.

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

Broad surface high pressure across the central Atlantic will
continue to promote east to southeast trade winds through next
week. Embedded in this flow, areas of low-level clouds and showers
will continue to stream over the islands and surrounding waters.
This will continue to maintain a similar weather pattern each day,
with passing showers across the USVI and eastern sections of PR
during the night/early morning hours, followed by afternoon
convection along the interior/northwestern sections of PR, as well
as from showers developing over the east and streaming across San
Juan and vicinity. A tropical wave is forecast to move between
Tue-Wed, further enhancing the available low-level moisture.
Meanwhile, troughiness aloft west and north of the area will
prevail through much of the long term period. This will maintain
unstable conditions and favor the development of thunderstorms
across portions of the local waters and in diurnal activity over
mainland PR.


&&

.AVIATION...Mainly VFR conditions will prevail for all TAF sites
until 04/06Z. However, SHRA and TSRA could be possibles over TJBQ
between 03/18Z to 03/22Z due to afternoon convection across w PR.
VCSH will prevail for most of the sites. Winds will become more E
up to 15 kts.


&&

.MARINE...Choppy seas up to 6 feet are expected across the
offshore Atlantic waters from later today into the weekend.
Elsewhere, seas up to 5 feet are expected. Easterly trades up to
20 knots are expected across the regional waters, therefore, small
crafts should exercise caution. A moderate risk of rip currents
will prevail across all the islands for the next several days.


&&

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

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
408 AM AST Sat Jun 5 2021

.SYNOPSIS...
An upper-level trough will remain west of Puerto Rico through the
middle of next week and yield wet and unstable weather conditions
over the local islands. Moisture content coupled with local
effects and instability will aid in the development of organized
convection today through early next week.

&&

.SHORT TERM...Today through Monday...
The west half portion of Puerto Rico mainly had clear to partly
cloudy skies but without rain activity. The eastern half of Puerto
Rico and the U.S. Virgin Islands had frequent passing showers
overnight. This activity is due to plenty of tropical moisture and
the proximity of a mid to upper-level trough. Winds were from the
east at 10 mph or less with stronger gusts. Overnight low
temperatures were in the mid-70s across the coastal areas and in the
mid-60s across mountains and valleys.

Unsettle weather conditions will persist today and through the rest
of the short-term as the mid-to upper-level trough amplifies near
the Hispanola. Instability parameters are indicating favorable
atmospheric conditions for the development of thunderstorms and
inclement weather. Expect steep lapse rates at mid-levels, pooling
of moisture, low-level convergence, and cooling temperatures between
-7 and -8 degrees Celsius. The interaction between the good-dynamic
aloft, the sea breeze variations, local effects, and diurnal heating
will aid in the development of thunderstorms with heavy rainfall
each afternoon. Additionally, the available moisture will continue
to increase with PWAT values between 1.7 and 2.20 inches. Therefore,
expect widespread rainfall activity with isolated to scattered
thunderstorms, especially each afternoon. Persistent wetting rains
over saturated soils and urban areas could produce localized runoff,
possibly causing significant flooding. Minor urban and small stream
flooding as well as ponding of waters on roadways and poorly drained
areas will likely be elsewhere.

&&

.LONG TERM...Tuesday through Saturday...
Model guidance continues to show a wet and unsettled weather
pattern during the beginning of the period. At the upper-levels,
a trough is forecast to remain positioned to the west of Puerto
Rico through late Wednesday. During this time several short-waves
will round the base of the trough, helping the trough maintain
it`s position near Puerto Rico. The position of the upper-level
trough will create unstable conditions aloft and promote organized
convection mainly across portions of the interior, western, and
northwestern areas of Puerto Rico. An induced surface trough and
easterly winds will pull rich moisture across the local islands.

Thursday and Friday, upper-level instability is expected to decrease
as the upper-level trough slowly lift northeast of the local
islands. The GFS and ECMWF has a weak disturbance lifting north
out of the southwestern Caribbean, with moisture spreading across
the local islands. The moisture coupled with significant heating
and sea breeze convergence will induce showers across the western
and interior areas of the island during the afternoon. Saturday,
guidance advects a drier air mass over the local islands, the
drier air should cause a decrease in afternoon convection, and
keep showers mainly across the interior and western areas of
Puerto Rico.

&&

.AVIATION...
SHRA will continue to move across the local flying area, with some
of them moving over the TAF from time to time. TSRA/+TSRA are likely
across the mountain areas/west PR between 05/15-22z, and they could
impact the VCTY of JSJ/JPS/JBQ. IST/ISX can expect brief periods of
+SHRA/SHRA at times, especially this afternoon. Winds will continue
calm to light and VRB thru 05/13z, when they will return from the E
at 15 to 20 kt with higher gusts and sea breeze variations.

&&

.MARINE...
Hazardous marine conditions will continue across the outer
Atlantic and northern near-shore waters of Puerto Rico through
this evening. Seas up 7 feet with occasional seas up to 9 feet
across the outer Atlantic and northern near-shore waters of Puerto
Rico. Therefore, Small Craft Advisory will be in effect tonight
through this evening. Elsewhere, seas up to 6 feet with easterly
winds up to 20 knots the next several days. Therefore, small crafts
should exercise caution. There is high risk of rip currents for the
northwestern beaches of Puerto RIco.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 87 76 / 60 60 70 40
STT 86 77 86 76 / 50 60 60 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
403 AM AST Sun Jun 6 2021

.SYNOPSIS...
A mid to upper-level trough will amplify to the west of Puerto
Rico the next several days and cause wet and unstable weather
conditions across the region. Above-average moisture content and
mid to upper-level instability, and local effects will aid in the
development of organized convection across the local area through
the middle of next week. Therefore, urban and small stream
flooding and ponding of water on roadways is expected.

&&

.SHORT TERM...Today through Tuesday...
Model guidances continue suggesting the local region moving into
unstable weather conditions. The amplification of a mid to upper-
level trough will enhance instability over the northeast Caribbean
today. Both GFS and ECMWF are in a much better agreement concerning
the evolution of this feature. The guidance indicated plenty of
tropical moisture over the islands, with GFS suggesting TPW between
2 and 2.5 inches across Puerto Rico and the U.S. Virgin Islands.

The weather scenario mentioned above will result in frequent showers
across the eastern half of Puerto Rico and the U.S. Virgin Islands
today, followed by afternoon convection across the western half of
PR. Thunderstorm development is likely, as temperatures at 500 MB
could drop below -7 degrees C. Periods of moderate to heavy rains
could trigger urban and small-stream flooding each day.
Additionally, flash flooding and mudslides will remain possible due
to soil saturation associated with the previous rainfall
accumulations.

Tuesday seems the most active day in the short-term period due to
the atmospheric features mentioned above combined with max in low-
level moisture and the formation of an induced surface trough. The
only limiting factor suggested by weather guidance is the formation
of mid to upper-level clouds, limiting max daytime heating,
inhibiting convection across the islands.

&&

.LONG TERM...Wednesday through Sunday...
The GFS and ECMWF continues to show a wet and unsettled pattern
through Thursday. An upper-level trough is expected to remain in a
favorable position to the west of Puerto Rico and provide unstable
upper-level conditions, which will support the development of deep
convection during the afternoon, mainly across the western,
interior, and northwestern areas of Puerto Rico. Wednesday, the GFS
and ECMWF show a weak surface trough north of Puerto Rico and to the
southwest a weak disturbance lifting north out of the southwestern
Caribbean, with moisture spreading across the local islands. The
deluge of moisture and local effects will cause scattered to
numerous showers and isolated thunderstorms across most of the
local islands through Thursday.

Thursday and Friday, global models diverge with the ECMWF keeping
the upper-level trough near Puerto Rico, while the GFS lifts the
upper-level trough to the northwest of Puerto Rico. The ECMWF
keeps 500 mb temperatures around minus 7 to 8 degrees celsius
through Sunday, while the GFS show 500 mb temperatures minus 6 to
7 degrees celsius. Either way, persistent showers are expected to
affect the local islands due to above-average moisture and local
effects. However, if the GFS solution comes to fruition,
instability will decrease over the area.

Saturday and Sunday, Global models show sfc and mid-level winds
advecting a drier air mass into the area, this should limit
organized convection but, shallow convection will produce isolated
to scattered showers.

&&

.AVIATION...
SHRA will continue to move across the local flying area, and some of
them will move over the TAF occasionally. TSRA/+TSRA are likely
across the mountain areas/west PR between 06/15-22z, and they could
impact the VCTY of JSJ/JPS/JBQ. +SHRA/SHRA will occasionally move
over IST/ISX today, especially this afternoon. Winds will continue
calm to light and VRB thru 06/13z, when they will return from the E
at 15 to 20 kt with higher gusts and sea breeze variations.

&&

.MARINE...
Choppy marine conditions will continue across the near and
offshore waters through early next week. Seas will range from 4
to 6 feet and winds will be from the east up to 20 kts. There is a
moderate risk of rip currents for the most of the local beaches
except for the western and southwestern beaches of Puerto Rico.
Showers and isolated thunderstorms are expected to develop each
day across the regional waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 88 76 / 60 60 60 70
STT 86 76 85 77 / 60 60 60 70

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
423 AM AST Mon Jun 7 2021

.SYNOPSIS...

Unstable weather conditions are likely early this workweek. Above-
normal tropical moisture and a mid to upper-level trough are the
perfect ingredients to promote numerous showers and scattered
thunderstorms over Puerto Rico and the U.S. Virgin Islands. Urban
and Small stream flooding will be possible, especially each
afternoon across mainland Puerto Rico. The Virgin Isles can also
expect periods of moderate to strong showers due to thunderstorms.

&&

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

Frequent passing showers will continue to affect the eastern and
northern areas of Puerto Rico this morning. Afternoon showers and
isolated thunderstorms will develop across the interior and
southwestern regions of the islands. East to southeast wind flow
at the surface and mid-levels will advect higher moisture content
over the island during peak heating today. The moisture from a
weak tropical wave and sea breeze convergence will promote the
development of organized convection.

Tuesday and Wednesday, the GFS and ECMWF show a wet and unsettled
weather pattern due to an upper-level trough that will intensify
west of Puerto Rico due to short-waves rounding its base and modest
jet streaks up to 40 kt. The trough will be in a position that will
cause upper-level divergence over the local area. The upper-level
instability and above-average moisture content advecting over the
local area from the Atlantic and Caribbean waters will induce
scattered to numerous showers and isolated thunderstorms each day.
The organized convection redeveloping over the local islands the
next several days would likely cause urban and small stream flooding
and mudslides in higher terrain.

One factor that could change the outcome of the forecast is mid
and upper-level clouds developing and inhibiting significant
heating at the surface. The GFS has consistently shown a saturated
profile Tuesday through Wednesday. The saturated atmosphere will
inhibit organized convection from developing from the lack of
forcing at the surface to cause parcels to lift. Additionally, the
GFS MOS guidance keeps temperatures near the low 80s across the
area due to the saturated profile due to rich moisture content and
mid and upper-level clouds. However, the GFS Skew-T shows winds
veering with height by Tuesday afternoon, and the winds could
possibly break the cloud deck at the mid-levels and allow surface
heating needed to promote organized convection.

.LONG TERM...THURSDAY THROUGH MONDAY...

A cutoff low will swing near the northeast Caribbean over the
Atlantic Ocean. This feature lingering aloft will induce a set of
surface troughs over the islands, pooling tropical moisture from
the southeast Caribbean over PR/USVI. Therefore, Thursday through
at Saturday seems to continues with an unstable weather pattern.
A drier airmass with Suspended African Dust could replace this
moist airmass late-Saturday into early next week.

That said, expect unsettled weather conditions through at least
Saturday, with much less shower activity Sunday into Monday. The
potential to observe strong thunderstorms with downpours events
will remain possible Thursday and Friday. Therefore, if the short-
term rains saturated soils and increase river levels, the
possibility of observing flooding and even mudslides will remain
high for the end of the workweek. Then, hazy skies with much less
rain activity will be possible for the Sunday into Monday.

&&

.AVIATION...

SHRA will continue to move across the local flying area, and
affect the eastern and northern terminal sites. TSRA/+TSRA are
expected to develop by 07/15Z over the interior, western, and
southwestern areas of Puerto Rico. Winds from the east to
southeast up to 20 kts with higher gusts and sea breeze
variations by 07/15Z.

&&

.MARINE...

Easterly winds between 15 and 20 knots are creating choppy seas
up to 5 feet. Winds are forecast to drop below 18 knots tonight,
and seas will slowly improve. However, small craft operators
should exercise caution across the Offshore waters through tonight
due to winds up to 20 knots.

Due to the upper-level trough, thunderstorm formation will
remain likely throughout the workweek, especially each afternoon
through early in the evening.

Beachgoers, the risk of rip currents will persist moderate across
the beaches in the north, east, and southeast coast of Puerto
Rico, Vieques, Culebra, and the U.S. Virgin Islands through at
least late Tuesday night. Then, it`s forecast to become low at the
northern USVI by Wednesday and the rest of the islands by Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 84 74 / 70 80 70 60
STT 86 76 87 74 / 60 80 70 70

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
408 AM AST Tue Jun 8 2021

.SYNOPSIS...

Favorable weather conditions for the development of showers and
thunderstorms will persist through much of the week. The
combination of above-average tropical moisture and a lingering mid
to upper-level trough with its associated induced surface trough
are the perfect ingredients to promote numerous showers and
scattered thunderstorms over Puerto Rico and the U.S. Virgin
Islands. Urban and Small stream flooding will be possible,
especially each afternoon across mainland Puerto Rico and the U.S.
Virgin Islands.

&&

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

During the overnight hours, showers affected the eastern and
northern areas of Puerto Rico and the U.S. Virgin Islands and
produced light rainfall amounts. Shower activity will increase later
this morning across the areas mentioned above then spread westward
over the interior and the western regions of Puerto Rico this
afternoon.

The short-term period will have above-normal moisture content and
adequate instability. The sufficient moisture and sea-breeze
convergence will yield showers and thunderstorms across the local
islands through Thursday. Despite the favorable conditions across
the region, a limiting factor that could delay and inhibit the
continuation of organized convection is mid and upper-level clouds.

The GFS continues to show saturated layers aloft, and the saturated
layers will delay heating and decrease instability; and cause some
areas of the islands not to reach the convective temperature needed
for thunderstorm development. If the GFS solution comes to fruition,
the continuation and expansion of organized convection will not
occur. However, scattered to numerous showers will cause urban and
small stream flooding and possible mudslides in higher terrain
through Thursday.

.LONG TERM...FRIDAY THROUGH TUESDAY...

A TUTT-low will promote a jet stream aloft through at least late
Saturday night. Although model guidance suggests the jet weakening
by Saturday night, the trough will linger over the region through
at least Tuesday. Meanwhile, at low levels, the upper-level
feature will induce a set of induced surface trough Friday through
Sunday, and moisture will pool over the islands through late
Saturday or Sunday. Then, a drier airmass with Suspended African
Dust would replace this moist airmass by late Saturday night into
early next week. At this time, there is some discrepancy in how
fast the atmosphere will dry out, but something is inevitable, and
it is that the unstable and wet pattern could last through at
least the upcoming weekend. Model guidance suggests a tropical
wave arriving at the local islands by late Monday night or early
Tuesday.

That said, expect unsettled weather conditions through at least
Saturday, with much less shower activity Sunday into Monday. The
potential to observe strong thunderstorms with downpours events
will remain possible Thursday and Friday. Therefore, if the short-
term rains saturated soils and increase river levels, the
possibility of observing flooding and even mudslides will remain
high for the end of the workweek. Then, hazy skies with much less
rain activity will be possible for the weekend and through
Monday. Then on Tuesday, if the dense and extensive dry air mass
with African Dust does not consume the tropical wave, a better
chance to observe wetting rains and thunderstorms will be possible
with the wave`s arrival.

&&

.AVIATION...

VFR conds at all terminals, but Isold-SCT SHRA will effect TJSJ,
TIST/TISX thru 08/15Z. SHRA/VCTS will develop across the
interior/W/NW areas of PR by 08/15Z. SHRA/VCTS could cause brief
MVFR conds across terminals sites TJBQ/TJMZ til 08/23Z. VCSH/SHRA
will move across the rest of the terminals til 08/23Z. Brief Mtn
TOP-obscr/MVFR ovr E-PR due to low cld lyrs til 08/23Z. E-winds up
to 10 kt, then bcmg 15-20 kts by 08/15z. Sea breezes aft 08/13Z
with gusts up to 25kt over the nrn coasts of PR.

&&

.MARINE...

Mariners can expect easterly winds around 15 knots and choppy
seas up to 5 feet across the offshore waters. Seas will range
between 2 and 4 feet across protected waters.

An upper-level trough will promote the formation of thunderstorms
throughout the week, especially each afternoon through early in
the evening. Mariners should exercise caution.

Beachgoers, the risk of rip currents will persist moderate across
the beaches in the north, east, and southeast coast of Puerto
Rico, Vieques, Culebra, and the U.S. Virgin Islands through at
least tonight. Then, it`s forecast to become low at St Thomas and
St John tomorrow, and the rest of the islands by Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 75 85 75 / 80 60 70 50
STT 86 75 86 75 / 80 70 70 80

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
406 AM AST Wed Jun 9 2021

.SYNOPSIS...Higher than normal moisture is expected to move in
from the south today. Upper level trough and associated low across
the southwestern atlantic, with its axis to the west of the local
area will keep unstable conditions for the local islands for the
next few days. Surface high pressure across the central Atlantic
will keep moderate easterly winds. Relatively active weather is
expected today, with numerous showers and isolated thunderstorms
over Puerto Rico, where most soils are already saturated.

&&

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

The unsettled weather pattern across the region will continue due to
above-normal moisture content and upper-level instability. A broad
trough west of Puerto Rico will deepen west of the area through
Friday. Due to several short-waves and subtropical jet maxima, which
will round the base of the trough. Puerto Rico will be in the right
entrance region of the trough, which favors upper-level divergence.
The upper-level divergence aloft will help sustain shower activity
and thunderstorms that develop during the afternoon. The above
features coupled will sea breeze convergence and heating will
produce isolated to numerous showers and isolated thunderstorms
during the afternoon across most of the area. Urban and small stream
flooding is likely, and mudslides in higher terrain are possible
through Friday as soils are saturated across most of the island. Any
additional rainfall will trigger flooding especially across the
interior, western, and northwestern Puerto Rico and the metro areas
of San Juan.

.LONG TERM...Saturday through Thursday...
The local winds are expected to be light to moderate this coming
weekend and early start to next week, with an ESE component. This
is because a series of SFC low pressure systems are forecast to
enter the western Atlantic and move north, causing the local
pressure gradient to weaken and for winds to have that ESE
component. A weak upper trough could still affect the local
islands on Saturday into early Sunday, but by Sunday afternoon
onward, an upper level ridge will dominate the local area, which
will promote stability, especially when the mid levels will also
have a ridge over the local area. That said, the available
moisture will still be near or above normal for the weekend and
the early part of next week, which could promote scattered showers
in the morning and nighttime hours over eastern PR and the USVI.
In the afternoon hours, showers and isolated thunderstorms are
forecast across western PR. A tropical wave is expected to move in
on Tuesday, keeping the above normal moisture, but drier air will
follow late Tuesday into Wednesday, causing a reduction in shower
activity across the local islands.

&&

.AVIATION...VFR conds at all terminals, but Isold-SCT SHRA will affect
TJSJ, TIST/TISX thru 09/15Z. SHRA/VCTS will develop across the
interior/W/NW areas of PR by 09/15Z. SHRA/VCTS could cause brief
MVFR conds across TJBQ til 09/23Z. VCSH/SHRA will move across the
rest of the terminals til 09/23Z. Brief Mtn TOP- obscr/MVFR ovr
E-PR due to low cld lyrs til 09/23Z. E-winds up to 10 kt, then
bcmg 15-20 kts by 09/15z. Sea breezes aft 09/13Z with gusts up to
25kt over the nrn coasts of PR.

&&

.MARINE...Showers and thunderstorms are forecast across the local
waters today and Thursday due to deep moisture moving in and
combining with the instability of an upper trough. The local seas
will be slightly choppy with heights up to 5 feet and winds up to
15 knots, but higher winds near the showers and thunderstorms.
There is also a moderate risk of rip currents for the northern and
southeastern beaches of PR, most of Culebra and eastern Vieques.
For the USVI, a moderate risk of rip currents is expected today
for all except the western beaches of St. Croix.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 76 87 74 / 60 50 60 60
STT 86 75 85 75 / 70 80 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
422 AM AST Sun Jun 13 2021

.SYNOPSIS...A seasonable weather pattern is expected to prevail
across the area through at least the middle of the week, with
afternoon convection affecting mainly the western half of Puerto
Rico. Marine conditions will continue to remain fairly tranquil
through at least early this week, however, choppier conditions
are expected beginning by the middle portion of the week as winds
increase. Increase in shower activity can be expected by next
weekend.

&&

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

A decrease in the Saharan Dust concentration is expected today, so
skies are expected to be less hazy then they were yesterday. Above
normal moisture is still expected today, and the upper trough is
still positioned favorably for thunderstorm development this
afternoon. Showers and thunderstorms are forecast this afternoon,
mainly across western and northwestern PR, while scattered showers
are expected elsewhere in PR and isolated showers for the USVI. The
local wind flow will be mainly from the east to slightly ESE. The
daytime high temperatures are expected to be warmer today than we
have observed the past few days, with highs in the upper 80s to
around 90 across the lower elevations.

Drier air and Saharan Dust return to the local area on Monday
morning, just ahead of a tropical wave that is expected in the late
morning and early afternoon hours on Monday. Even though there is a
tropical wave moving in, and moisture will increase once again on
Monday afternoon, the latest guidance is not suggesting significant
rainfall in the afternoon, which could be due to drier air at the
700mb level and Saharan dust present. That said, scattered showers
and isolated thunderstorms are in the forecast for the afternoon,
but the rainfall accumulations are expected to be modest compared to
what we have observed over the past few days. Then for Tuesday, even
drier air moves in, this time the dry air and Saharan dust will
persist through the day, causing hazy skies and warm to hot
temperatures. The forecast soundings suggest relatively dry layer at
700mb as well, and not much more than isolated to scattered showers
are expected. In terms of temperatures, the daytime high temps could
reach 90 at the San Juan airport, as the lower elevations are
expected to have temps in the upper 80s to low 90s.

This means that there will be mainly fair weather, with brief
showers during the morning and overnight hours for eastern PR and
the USVI, while showers and thunderstorms may affect central and
western PR each afternoon. Soils are still saturated though, so
significant showers could cause at least some urban and small
stream flooding, which is possibly particularly across the
northwestern quadrant of PR since that is the area that is
expected to have the highest amounts of rain this weekend and on
Monday.

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

A surface high pressure across the north central Atlantic will yield
east southeasterly winds across the local islands midweek through
the weekend. The forecast for the long-term period continues mostly
on track with Wednesday and early Thursday looking warm and somewhat
dry with a 500 mb high pressure ridge and hazy skies due to the
presence of Saharan dust particulate. At lower levels, moisture will
reach below normal levels, however, enough will be present for
daytime heating and local effects to produce showers and possibly
some isolated thunderstorms mainly over the northwestern quadrant
of Puerto Rico during afternoon hours.

Slight discrepancies exist between the GFS and ECMWF models by
Thursday onwards. GFS shows two easterly waves affecting the area;
one arriving late Thursday through early Saturday and the other
moving in by Sunday through Monday. Conversely, ECMWF has a more
continuous transition between both easterly waves but much weaker
intensity affecting the area Friday through Monday. Both models
show 500 mb temperatures between -6 to -8 degrees, normal to
slightly above normal levels for this time of year. Dynamically
speaking, upper-level conditions are not extraordinary but enough
to aid in convection development with sufficient available deep
layer moisture. Precipitable water values will increase to more
than 2.0 inches with each easterly wave event, raising moisture to
above normal levels.

Despite model discrepancies, we could expect the wettest days of
the long-term forecast to occur by Friday through the weekend.
Thus, shower and thunderstorm activity may increase with each wave
passage, raising the available moisture. The moisture will
combine with diurnal heating and local effects to cause more
significant shower or thunderstorm development across portions of
Puerto Rico, but also the waves will bring shower activity to the
local area overall, affecting the USVI as well.


&&

.AVIATION...

VFR conds expected across the local terminals today. SHRA/TSRA
activity may be observed near TJBQ this afternoon, causing at least
some VCTS. SCT SHRA is forecast for the TJSJ terminal, so VCSH is
possible this afternoon as well. Winds will be light early in the
morning, becoming e to ese with sea breeze variations after 13/13Z
at around 10-15KT.

&&

.MARINE...Tranquil marine conditions are expected to prevail
across the local waters through at least early this week with
seas of up to 4 feet expected and slightly increasing by tomorrow
nigh over the offshore Atlantic waters. Winds are expected to
increase during the middle portion of this week, resulting in
choppier seas. There is a moderate risk of rip currents for most
of the north facing beaches of Puerto Rico as well as the eastern
tip of Saint Croix today.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 78 90 78 / 40 30 30 30
STT 88 79 88 79 / 30 30 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
444 AM AST Mon Jun 14 2021

.SYNOPSIS...

A trend towards generally drying conditions continues over the next
few days. Some hazy skies are also possible around midweek, with a
Saharan Air Layer expected to impact the region. A tropical wave is
forecast to arrive late Thursday into Friday, bringing an uptick in
shower activity.

&&

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

Passing tradewind showers will continue to affect the local
waters and mainly the windward side of the islands during the
early morning hours. This will be followed by a drier airmass and
accompanying Saharan dust particulates which is forecast to spread
across the region through the short term period. A weak tropical
wave will cross the eastern caribbean and local region later today
through Tuesday bringing with it a quick surge of low to mid
level moisture along with an increase in the easterly trade winds.
Although local effects and good daytime heating will aid in
afternoon shower development in some areas,expect the dry Saharan
air layer to aid in suppressing organized convection. However,
isolated thunderstorm development will remain possible in isolated
areas of the interior sections of Puerto Rico, but activity of
short duration is anticipated. The east to southeast winds today
will again yield to near or slightly above normal daytime high
temperatures especially along the north coastal areas.

On Wednesday, a continued drying trend is forecast with the Saharan
air layer and suspended dust particulates expected to spread across
the region along the drier airmass and moderate easterly trade
winds. Therefore, only shallow patches of moisture embedded in the
easterly trades will favor periods of quick passing showers during
the early morning across eastern and northern sections of Puerto
Rico and the U.S. Virgin Islands. This will be followed by limited
afternoon shower development over the interior and west sections of
Puerto Rico. Limited or no significant shower activity can be
expected including for the U.S. Virgin Islands, where any afternoon
showers should be mainly on the west-end or downwind of the islands
over the coastal waters during the afternoon.

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

On Thursday morning, the area will be under the influence of a
relatively dry airmass ahead of an approaching wave to the east.
Meanwhile, an upper-level trough is forecast to be over or just
to the east of the region, providing subsidence to the region. As
such, generally fair weather is expected for the first part of the
day on Thursday. However, moisture is likely to increase as the
wave presses closer to the region. Though the bulk of the wave is
forecast to remain to the south of the region, enough is likely
to make its way over the islands to bring moisture levels at least
to the high end of normal, if not above normal. Meanwhile, a mid-
level ridge will persist over the region, maintaining conditions
aloft that are not particularly favorable for convection. An
increase in shower activity is anticipated, though likely not
substantially above normal, with the greatest impacts likely to be
seen Friday into Saturday morning.

During the day on Saturday, the wave is forecast to ext the region.
Though there will remain some patches of moisture that will be
carried into the region embedded in the trade winds, most of this
moisture will be in the lowest levels, and total moisture content
will likely be on the low end of normal, if not below normal, by
Sunday. A decrease in shower activity is expected, though local
effects and diurnal heating will likely still lead to afternoon
convection, and a few passing showers also cannot be ruled out
during the overnight and morning hours.

There is decent agreement between the model guidance up until this
point in the forecast period - late Sunday/early Monday. Beyond this
point, there remains some general agreement on the scenario
expected; however, timing and exact details become less certain.
This is not unexpected, of course, given a week of lead-time, but it
is worth noting that the confidence in the forecast quickly falls
off around the start of next week.

The expectation is for another easterly wave to approach and enter
the region during the early part of next week, bringing a
significant increase in moisture, with precipitable water values
likely to be above seasonal normals. Additionally, model guidance
suggests that an upper-level trough will be nearby the region
during this time. There is a decent chance that this feature will
be to the west of the region, placing us on the favorable side for
convective development. As such, deep layer moisture is likely,
and an increase in activity is anticipated. The timing is quite
uncertain, and there has been a not-insignificant amount of inter-
run variability on this from the GFS, and the agreement just isn`t
there with the ECMWF, either. Presently, sometime around Monday
into Tuesday seems like a reasonable expectation for the timing of
the arrival of the wave, as well as for the more favorable
conditions aloft. If the forecast scenario proceeds as expected,
it is likely that urban and small stream flooding would be an
increasing concern during this time period.

&&

.AVIATION...

VFR conds will prevail durg prd. Sfc wnds light and variable,
becoming fm E at 10 to 15 knots aft 14/14Z with sea breeze
variations and occasionally higher gusts. Aftn convection with
SHRA and slght chc for isold TSRA mainly across the interior and
west sections of PR and VCSH/VCTS psbl at TJBQ/TJMZ fm 14/17Z-22Z.
Isold SHRA elsewhere with SCT lys nr FL025...FL050 en route btw
islands and ovr regional waters. No other sig operational wx
impacts at local terminals attm.

&&

.MARINE...


Relatively tranquil marine conditions continue today, with seas of
less than 5 feet. Winds are generally out of the east at up to 15
knots. Increasing winds are expected tonight into tomorrow, lasting
through much of the week, which will lead to building seas; there is
the potential that around midweek, criteria for hazardous conditions
will be met.

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

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 79 90 78 / 30 20 20 20
STT 89 80 87 78 / 30 20 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
512 AM AST Tue Jun 15 2021

.SYNOPSIS...

Relatively dry, stable weather conditions are expected to continue
over the next couple of days, accompanied by some hazy skies.
However, local effects and daytime heating will still likely fuel
afternoon convection each day, and isolated to scattered passing
showers are possible overnight and into the morning. On Thursday,
increasing moisture is expected with an approaching easterly wave,
and a corresponding increase in shower activity is likely.

&&

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

The mid- to upper-level ridge will linger and remain the dominant
upper level feature during the period, maintaining a moderate
trade wind cap inversion and subsidence aloft. Strong surface high
pressure across the north central Atlantic will maintain moderate
to fairly strong easterly trades during the period, with
increasing east to southeast trade winds expected today and
through Wednesday. Moisture trailing a departing tropical wave,
which is moving well south of the region this morning, will be
sufficient to aid in locally- and diurnally-induced afternoon
convection; however, the activity should be focused mainly over
the central interior and western sections of Puerto Rico. There
is slight chance of afternoon streamers in and around the San
Juan metro, but activity will be of short duration. Mostly hot and
hazy conditions are expected elsewhere, including around the U.S.
Virgin Islands with limited or no shower activity expected.

The Saharan Air layer will also persist across the region though the
period, with moderate to high concentrations of suspended dust
particulates to hover over the region. This will also aid in
inhibiting strong shower development over the area; but, still
expect a period of locally and diurnally induced afternoon
showers each day mainly over eastern Puerto Rico and the U.S.
Virgin Islands during the early morning hours,followed by limited
afternoon convection, mainly across interior and northwestern
Puerto Rico. Daytime high temperatures will be near normal or
slightly higher, under the expected east to southeast wind flow,
with heat indices approaching the 100 degree mark.

On early Thursday, the area will remain under the influence of a
relatively dry airmass ahead of an approaching wave to the east.
Meanwhile an upper-level ridge is to slightly erode, as an upper
level trough is forecast to be just to the west of the area. This in
turn will support better ventilation aloft and provide a better
chance for afternoon shower development. Later in the afternoon
and through the rest of the day, the tropical wave will approach
the eastern caribbean, and gradually bring an increase in low-level
moisture. This will also increase the potential for afternoon
shower development, though most of the activity should still be
focused over the central interior and western sections of Puerto
Rico, as the Saharan air layer will persist across the region and
thus aid in maintaining dry condition aloft. That said, an
increase in shower development is anticipated, as well as possibly
some isolated thunderstorms, although the activity is not
expected to be widespread on Thursday.

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

On Friday morning, a wave is forecast to be over the region,
providing above-normal levels of moisture, with precipitable water
values around or above 2.0 inches. Increased shower activity is
expected. However, conditions aloft are not likely to be very
favorable for convective activity, with subsidence likely,
associated with an upper-level trough that is forecast to be located
just east of the region. This will likely inhibit a significant
uptick in showers, especially those associated with afternoon
convection. There is good confidence in the forecast up to this
point.

For this weekend - drying is expected for Saturday, though how much
dry air will make its way over the region is up in the air (pun
absolutely intended). Model guidance has been trending towards less
drying for Saturday, though there does remain at least a modest
decrease in moisture over the area. Another tropical wave looks
poised to follow hot on the heels of Friday`s, though, so any period
of dry or more stable weather is unlikely to last very long. Exact
timing of the arrival of the next wave is uncertain. By Sunday
morning is possible, and Monday is likely to be wet, as well.
Additionally, at the upper levels, a trough is forecast to develop
to the west/northwest of the region, and will likely be in place
near Hispaniola, placing the area favorable for convective
development over the local islands, by early next week. Therefore, a
significant uptick in shower activity is likely for early next week,
including an increase in afternoon convection. Urban and small
stream flooding are likely to be a concern.

Beyond that, the upper-level trough is forecast to retreat westward,
with another trough aloft approaching from the east, making
conditions less favorable for convection, likely by around Tuesday.
Additionally, moisture is expected to decrease behind the wave, as a
drier air mass filters in over the region in its wake. By midweek,
drier, more stable weather is likely.

&&

.AVIATION...

VFR conds will prevail durg prd. Light and variable winds will become
mainly fm east 15-20 kts but with sea breeze variations and higher
gusts aft 15/14Z. Locally and diurnally induced afternoon convection
btw 15/17-22z mainly over the interior and west sections of PR...with
VCSH nr TJSJ/TJMZ/TJBQ TIL 15/22z. Few -SHRA with SCT- BKN clds nr
FL025...FL050 will affect the coastal waters and en route btw islands
durg prd. Suspended saharan dust particulates will linger across the
region durg prd but no restrictions to VSBY expected.

&&

.MARINE...

Increased winds have fueled building seas for the local waters,
especially for the offshore waters. Seas of up to 6 feet are
possible, though seas of 5 feet or less are more likely for
nearshore waters. These conditions will persist for the next couple
of days, with the potential for hazardous conditions after midweek.

There is a moderate risk of rip currents for most local beaches. The
exceptions are beaches of south central Puerto Rico, and most
beaches of western Puerto Rico, where there is a low risk.

&&

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

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
450 AM AST Thu Jun 17 2021

.SYNOPSIS...
Upper level trough extending southwards across the Mona Passage
will lift east northeast across the area and erode the ridge
today into Friday. However, a mid-level ridge will hold across
the region; this, along with the upper-level ridge, will be
reinforced on Friday into the weekend, and consequently
strengthen the trade wind cap inversion. The broad surface ridge
spread across the north central Atlantic will maintain east to
southeast winds across the areas. Meanwhile, a tropical wave will
continue to enter the eastern Caribbean and make its way across
the region today through Friday, increasing tropical moisture and
instability across the forecast area. Choppy seas will continue
due to moderate to fresh trade winds. The Saharan dust layer will
diminish but will linger across the region through Friday but with
lesser concentration.

&&

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

A tropical wave is approaching the region this morning, bringing
with it ample moisture. Some of this moisture has already arrived
over the region, which has led to a marked increase in shower
activity. Passing showers over the water have spread westward; these
showers have pushed onshore in windward portions of the islands from
time to time. This will continue through the morning. Aloft, the mid-
to upper-level ridge is forecast to weaken through the day today,
which will provide a modest increase in instability for the region.
Lingering dust could inhibit some of the daytime heating, which
would limit convective activity. Considering this, as well as the
fact that conditions aloft are fairly marginal, thunderstorms have
been left out of the forecast for today. That being said, the
potential for a thunderstorm or two is not nonexistent.

The tropical wave continues through the region today into tomorrow,
with lingering moisture behind the wave likely for Friday afternoon.
As such, relatively active weather is anticipated, with the
potential for some isolated thunderstorms. Decreasing activity is
likely, however, through the afternoon, as moisture decreases in the
wake of the wave.

Relatively dry conditions are expected for Saturday. A drier air
mass will be in place through the day, though there will be
sufficient low-level moisture to sustain some activity in the
typical pattern. Increasing moisture is expected Saturday night,
ahead of the arrival of another tropical wave. As such, increasing
passing shower activity is forecast through the night on Saturday.

.LONG TERM...Sunday through Friday...
By early Sunday, a tropical wave will enter the eastern Caribbean,
and move across the region during the rest of the day through
Monday. Recent model guidance initialized well and continued to be
in good agreement, with all suggesting significant increase in
moisture and instability, with the layered precipitable water
values to increase to 2.0 inches or slightly higher Sunday into
early Monday. Therefore, a moist and unstable weather pattern is
expected through at least Monday, with good potential for active
weather, especially during the afternoon and evening hours. This
increase in convection is also supported by an upper level low
forecast to develop just west-northwest of the region, which will
weaken the mid- upper level ridge and favor unstable conditions
aloft.

By Monday afternoon and through the middle of the week, a gradual
drying trend is forecast, as the wave and trailing moisture is
forecast move out of the area. However, fragments of moisture
will continue to move across the region, and will be sufficient
to help to maintain relatively active conditions during the
afternoon hours, mainly due to local and diurnal effects. The
conditions aloft are also likely to become less favorable for
significant convection as the upper- level low is forecast to
weaken while moving away from the region and is to be replaced
once again by the mid-upper level ridge over the area. Only the
typical periods of passing clouds and tradewind showers are
expected to affect the area, carried by moderate to fairly strong
easterly tradewinds. The relatively stable conditions forecast
to prevail aloft and a moderate trade wind cap inversion that is
forecast to hold will limit daytime convection.

By Thursday into Friday, model guidance suggest a moderate
increase in tropical moisture accompanying an weakly induced
surface trough, which is forecast to develop and cross the
region. However, significant or widespread convection is not
anticipated at this time, favoring the more typical weather
pattern of early morning passing showers over the coastal waters
followed by locally and diurnally induced afternoon convection,
mainly over parts of the west and northwest sections of the
islands and downwind of orographic features, steered by a
prevailing east to southeast wind flow.

&&

.AVIATION...

Generally VFR conditions expected for the next 24 hours. VCSH for
TJSJ/TIST/TISX continue this morning, due to passing showers, with
limited operational impacts at the terminals. Winds increase,
generally out of the east, after around 17/14Z, to around 15 to 20
knots, with stronger gusts. Afternoon showers causing VCSH for most
terminals, except TJPS.

&&

.MARINE...
Seas will be choppy due to moderate to fresh tradewinds between 15
and 20 knots. Mariners can expect seas up to 7 feet across the offshore
waters and local passages, and 4 feet or less elsewhere. An approaching
tropical wave will increase winds and seas today through Friday;
therefore small craft advisories are in effect for portions of
the Atlantic, Caribbean waters and the Anegada passage. Small craft
operators should exercise caution over most of the remaining local
waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 78 89 79 / 50 60 60 20
STT 88 78 88 79 / 60 60 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
456 AM AST Sun Jun 20 2021

.SYNOPSIS...
A tropical wave is expected to increase shower activity across the
area through tomorrow night. A seasonal weather pattern is
expected for the workweek, with another tropical wave reaching the
area by Friday and Saturday. Choppy marine conditions will
continue through Tuesday.

&&

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

Satellite imagery showed two distinct bands of moisture over the
region, both oriented northeast southwest. Puerto Rico and the U.S.
Virgin Islands are currently sandwiched between these two bands.
Moisture is much better in the band to our southeast and even
overnight this area continued to have episodes of widely scattered
thunderstorms. Isolated tops were running 35-40 kft there. Although
some weakening is expected, the band to our southeast is edging
toward the forecast area and some of the better moisture has already
entered the southeast corner of the forecast area. The GFS is also
showing 500 mb temperatures of minus 7 to 8 degrees with some
divergence at upper levels today. The GFS was also showing some
weakness in moisture fields above the lower 7000 feet which will
limit the potential for widespread shower and thunderstorm growth
during the period of maximum heating today. But, as was the case
yesterday, a few thunderstorms have the potential to unleash
torrential rains and isolated amounts of 3-4 inches cannot be ruled
out today either. Some local urban and small stream flooding should
be expected this afternoon. Moisture and periods of showers will
continue into the overnight hours tonight with eastern Puerto Rico
continuing to be wet. Moisture at 700 mb, however will diminish
considerably early tomorrow morning and some of this drying will be
reflected at 850 mb by 21/12Z.

After the main band of moisture has passed early on Monday, winds
will again increase and some Saharan dust is expected to accompany
these winds. At upper levels the area will be under a weak ridge
from high pressure to our southeast. This will not be enough,
however, to eliminate night and early morning passing showers in
eastern Puerto Rico or afternoon showers and isolated thunderstorms
in western and interior Puerto Rico, but will greatly diminish
shower activity in the U.S. Virgin Islands.

On Tuesday an upper level cut-off low to our northeast will extend a
trough to its west that will approach Puerto Rico and the U.S.
Virgin Islands. This, and patches of good low-level moisture, will
allow shower activity across the area to continue in a seasonable
manner.

.LONG TERM...Wednesday through Monday...
A mid-level ridge over the western Caribbean will begin to weaken,
while an upper level low digs from the northeast. However, the ridge
will still promote dry air in the mid levels, with moisture being
trapped at the lower levels of the atmosphere. On the other hand,
very shallow areas of clouds should be advected by the trade winds
over the area from time to time, which should result in a typical
pattern of passing morning showers over eastern PR/USVI, followed by
afternoon activity over western Puerto Rico, and downstream from the
isles toward the west.

By Friday and Saturday, an approaching tropical wave will work to
increase moisture across the islands. There is some uncertainty in
the forecast, since the GFS is keeping most of the moisture field
associated with the wave over the Caribbean waters, but the ECMWF
brings the bulk of the system over the area, especially late Friday
and on Saturday. Regardless, a period of increased shower and
thunderstorm activity can be anticipated. After the passage of this
wave, another layer of dry air with suspended Saharan dust should
arrive to the area, limiting the potential for showers, then
followed by a weaker wave that could reach the area by Monday.

&&

.AVIATION...

VFR conditions are expected thru the period, except briefly MVFR
under sct SHRA ovr ern PR. Aft 20/16Z SHRA ovr wrn and interior PR
and down stream from El Yunque. Mtn obscurations. Isold TSRA psbl
btwn 20/16-22Z. Easterly flow will influence sfc winds less than 10
kt in land breezes. Then, aft 20/14Z, sea breezes of 10-20kt with
gusts to 28 kt psbl. Max winds E 20-30 kt btwn FL015-085.


&&

.MARINE...
Choppy seas up to 6 feet and winds up to 20 knots are expected to
continue through Tuesday. A tropical wave will increase shower and
isolated thunderstorm activity through tomorrow night, and seas
could become hazardous quickly withing a thunderstorm. For the
beaches, there is a moderate rip current risk for most of the
local area.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 78 87 79 / 70 60 50 60
STT 88 78 88 77 / 60 60 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Mon Jun 21 2021

.SYNOPSIS...A general drying trend is in progress and will
continue through Wednesday night. Thursday through Saturday will
gain moisture with another tropical wave passing through the area
Friday night bringing good moisture and instability behind it.
Even during the drier weather scattered showers and isolated
afternoon thunderstorms will continue.

&&

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

The Total Precipitable Water (PWAT) product from GOES-16 shows an
area of enhanced moisture currently covering the eastern
Caribbean, with infrared satellite imagery showing patches of low-
level clouds moving from the east across the area. This will
result in morning showers affecting the U.S. Virgin Islands and
eastern Puerto Rico. The High Resolution and Global models agree
that rainfall accumulations should stay around or below a quarter
of an inch this morning.

The synoptic picture is dominated by a surface high pressure over
the central Atlantic currently resulting in an east to east-
southeast moderate wind flow across the area. A mid level ridge is
also present to the north of the Greater Antilles, while an upper
level trough is currently located between Haiti and Cuba, which
could promote some divergence aloft. For today, the GFS forecast
soundings are showing PWAT values around 1.8 to 2.0 inches, which is
above the climatological values for this time of year. Additionally,
it is suggesting a very weak trade wind cap around 850 mb. Thus, the
upper level trough and local effects should still act to generate
afternoon activity, mainly over the interior and western Puerto
Rico, with lines of showers also developing around sections of
eastern Puerto Rico and downstream from the Virgin Isles. Urban
and small stream flooding is also likely in western and interior
Puerto Rico this afternoon. The aerosol models also show
suspended Saharan dust advancing into the area, but with most of
it making its way by late Monday into the middle of the workweek.
On Tuesday, however,an upper level low to the northeast will
induced additional patches of low- level moisture that will move
from the east, fueling another round of seasonal showers around
the area. By Wednesday, the dry air layer becomes deeper, and as
result, the coverage and intensity of the rain should decrease,
but still with the potential for some showers affecting the local
islands.

.LONG TERM...Thursday through Monday...
Moisture begins to rise after reaching a nadir of 1.2 inches of
precipitable water Wednesday night. By Saturday it should be
nearly 1.9 inches. The GFS is showing a tropical wave moving into
the area Friday night. Better moisture and instability will follow
behind it Saturday and Sunday when shower and thunderstorm
activity will increase again. These conditions are expected to be
sufficiently strong to bring urban and small stream flooding both
Saturday and Sunday afternoons, mainly in western and interior
Puerto Rico and will favor scattered showers continuing through
the overnight hours in eastern Puerto Rico and around the U.S.
Virgin Islands.

After a weak upper level trough passage on Wednesday, a trough
will extend out of a cut-off low southwest over the lesser
Antilles chain at the east end of the Caribbean. This would be
considered less favorable to convection over Puerto Rico and the
U.S. Virgin Islands. However, on Thursday, the low pressure
begins to move west at around 28 degrees north latitude and passes
north of the area Saturday night and Sunday, favoring an already
moistened situation and creating an environment with more
thunderstorm activity that the previous several days.

After Sunday, somewhat drier air is again manifest and the upper
level trough will also be found to the east allowing activity to
subside somewhat.

&&

.AVIATION...Mainly VFR conditions expected to prevail through the
forecast period. VCSH expected early in the day for TJSJ/TIST/TISX,
then VCTS after 21/17Z for TJBQ which could result in TEMPO groups
due to reduced VIS and low ceilings. FL050 winds from the ESE
expected at 10 to 21 knots with stronger gusts. Maximum winds SSW
30-40 knots btwn FL400-450.

&&

.MARINE...Marine conditions continue choppy with seas just below 7
feet for the next day or so. Conditions do improve and exercise
cautions are expected to come down no later than Tuesday night.
Small craft advisories are not expected this week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 79 88 77 / 50 50 50 50
STT 89 79 89 77 / 40 50 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
521 AM AST Wed Jun 23 2021

.SYNOPSIS...Moisture gradually returns through Monday evening, but
mid-levels remain fairly weak in moisture. High surface pressure
will continue in the central Atlantic, but winds will become more
southeasterly on Saturday. Weak upper level dynamics with good
solar heating and low level moisture will allow showers and
isolated thunderstorms to grow each afternoon, with the best
activity expected Sunday and Monday. Overnight and early morning
showers in eastern Puerto Rico will increase through Monday.

&&

.SHORT TERM...Today through Friday...
An upper to mid level low continues to the northeast of the Lesser
Antilles, with another upper level low located between Cuba and
Jamaica. At the same time, a mid-level ridge north of the Bahamas
begins to weaken. The mid-level ridge will maintain a trade wind
cap inversion around 850 mb, but the cap should weaken as the day
progresses. There is dry air at the mid-levels, but the upper to
mid level low will continue to induce shallow patches of moisture
across the area. These patches are evident on infrared satellite
imagery, and GOES-16 satellite-derived precipitable water products
show areas with values around 1.5 inches, which is close to the
climatological value for this time of year. Even with the mid-
level dry air layer, showers with isolated thunderstorms, are
expected to develop this afternoon, mainly over the interior and
western Puerto Rico, and also streamers from El Yunque over
eastern sections. Urban and small stream flooding will be possible
with this activity.

The mid to upper level low will linger, while moving westward to the
north of the area. On Thursday, moisture decreases a little bit, but
then again, seasonal showers could still develop over the region.
Then, on Friday, a surface high pressure and an approaching tropical
wave will cause the wind flow to gradually shift from the east-
southeast. Additionally, moisture will gradually increase across the
region with the GFS forecast soundings not showing any significant
trade wind cap and PWAT values increase to around 1.7 inches, hence
promoting additional shower activity over the area.


.LONG TERM...Saturday through Wednesday...
A tropical wave will move through the area Friday and Friday night
with moisture moving northwest behind it, The GFS continues to
show the best moisture moving northeast of the local area and
across the southwestern corner of the forecast area Saturday night
and Sunday. This will also provide enough sun to drive
temperatures up a little in the southeast flow, and lower
elevations could easily reach the lower 90s over the weekend. Then
Sunday night the band of moisture closes the gap over the U.S.
Virgin Islands and Puerto Rico and the best moisture of the week
will move through. Precipitable water values remain above 1.9
inches Sunday noon until Tuesday morning. But high pressure
remains over the area at mid levels with weak flow in a poorly
defined ridge at upper levels working against vigorous shower
activity. Nevertheless sufficient moisture and energy exist to
bring a good chance of showers and thunderstorms each day in the
usual diurnal pattern of night and early morning showers over
eastern Puerto Rico and around the U.S. Virgin Islands and
afternoon showers and isolated thunderstorms in western and
interior Puerto Rico and downstream from El Yunque Saturday
through Wednesday. Currently we are expecting a whiff of Saharan
dust on Sunday, with a larger puff on Tuesday and Wednesday, which
will also help diminish the shower activity.

&&

.AVIATION...Mainly VFR conditions expected to prevail through the
forecast period. VCSH expected to affect TJSJ and the Leeward and
USVI terminals through 23/13Z. VCTS expected for TJSJ/TJMZ after
17Z, which could result in TEMPO groups due to reduced VIS and low
ceilings. Scattered to numerous showers expected to continue
across the area, mainly each afternoon. Winds are expected from
the E at 10 to 16 knots till aft 23/22Z. Maximum winds WSW 15-30
kt btwn FL400-500 and E 15-22 kt btwn sfc and FL110.

&&

.MARINE...Marine conditions including rip current risk are
expected to gradually subside through Saturday as winds diminish.
At this time seas are expected to remain less than 5.5 feet for
the rest of the seven day period.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 88 78 / 40 40 40 40
STT 90 78 89 78 / 50 40 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
409 AM AST Thu Jun 24 2021

.SYNOPSIS...A seasonable weather pattern is expected to prevail
through Friday, with overnight and early morning passing showers
across eastern Puerto Rico and the USVI followed by afternoon
convection across western Puerto Rico. Weather conditions will
then turn more unstable during the weekend as the combination of
deeper moisture and mid and upper-level trofiness will result in
more widespread convective activity across the local area.

&&

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

A Tropical Upper Tropospheric Trough (TUTT) is currently located to
the northeast of the eastern Caribbean while another upper level low
lingers near Cuba and Jamaica. This will continue to induce patches
of moisture at the low levels that will be dragged over the islands
by the trade winds. The GFS forecast soundings show precipitable
water (PWAT) values around 1.4 to 1.7 inches for today with a very
weak trade wind cap around 850 mb. These PWAT values are near normal
for this time of year, while 500 mb temperatures are around -6 to -7
degree Celsius, which is also near normal. At the surface, high
pressure over the central Atlantic is generating an easterly wind
flow. Taking all these factors into consideration, showers with
isolated thunderstorms are expected again today, especially over the
interior and western Puerto Rico, as well as over portions of the
east. Isolated urban and small stream flooding will be possible with
this activity.

On Friday, the TUTT begins to moves westward, while a tropical wave
east of the Lesser Antilles begins to approach the region. The winds
will shift from the east-southeast, while moisture begins to
gradually increase. Therefore, another seasonal pattern is
anticipated for tomorrow, with advective showers early in the day
for eastern PR/USVI, and afternoon convection over western PR (and
possible near the San Juan metro area). Then on Saturday, as the
waves get closer, and with the mid and upper level trough north of
the islands, conditions should become increasingly more favorable
for shower and thunderstorm activity to develop across the islands.
It should be noted, however, that there is some uncertainty between
the guidance on when and how much this feature will affect the
islands, with the ECMWF bringing the moisture early on Saturday, and
the GFS having the best activity later that day.

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

Weather conditions will remain unstable on Sunday as the upper-
level trough will remain north of the area and moisture will be
near to above normal, with precipitable water values ranging
between 1.8 and 2.0 inches. Therefore, enhanced shower and
thunderstorm activity is expected with activity expected across
portions of eastern Puerto Rico and the USVI during the morning
hours, extending into interior and northwestern portions of Puerto
Rico during the afternoon hours as the low-level flow be from the
southeast. Urban and small stream flooding will be possible with
the heaviest and most persistent activity.

On Monday, weather conditions are expected to improve as a mid-
level ridge builds from the tropical Atlantic into the northeast
Caribbean. Therefore, shower activity is expected to diminish in
coverage. However, moisture will remain sufficient in the low-
levels to combine with local and diurnal effects and generate
afternoon convection across northwest Puerto Rico as the low-level
flow will remain from the southeast. A drier air mass along with
a Saharan Air Layer is expected for both Tuesday and Wednesday,
resulting in mainly fair weather conditions with limited shower
activity. Then, by the end of the long-term period, another
tropical wave may impact the area bringing an increase in shower
and thunderstorm activity.

&&

.AVIATION...Mainly VFR conditions expected to continue for the
forecast period. VCSH expected for TJSJ, the Virgin Islands and
Leeward terminals through 24/14Z. VCTS expected for TJSJ after
17Z, which could lead to TEMPO groups due to reduced VIS and low
ceilings. Winds will be out of the E at 11 to 17 kts with stronger
gusts.

&&

.MARINE...More tranquil marine conditions with seas of up to 5
feet and winds up to 15 knots are expected through the end of the
work week. For the beachgoers, there is a moderate risk of rip
currents for the north and southeast coasts of Puerto Rico, as
well as the beaches of Culebra, most beaches of Vieques and St.
Croix, and northwestern beaches of St. Thomas.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 77 86 78 / 40 50 40 40
STT 88 78 86 77 / 40 50 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
433 AM AST Fri Jun 25 2021

.SYNOPSIS...A seasonable weather pattern will prevail across the
local area today with morning passing showers across portions of
eastern Puerto Rico and the USVI followed by afternoon convection
across interior and western portions of Puerto Rico. A more
unsettled weather pattern is expected for the upcoming weekend as
the combination of a Tropical Upper Tropospheric Trough (TUTT)
and moisture from a tropical wave will result in an increase in
shower and thunderstorm activity across portions of the local
area. A decrease in shower activity is expected for the first half
of the upcoming work week.

&&

.SHORT TERM...Today through Sunday..

A TUTT low northeast of the region will move into the western
Atlantic through the short term period. A TUTT induced low-level
trough across the Atlantic waters will bring a small surge in
moisture today. This, in combination with daytime heating and the
sea breeze convergence will lead to the development of afternoon
showers and thunderstorms, mainly over the interior and western
sections of PR, and showers from streamers developing downwind of
the islands, and from el Yunque into the San Juan metropolitan area.
Urban and small stream flooding is expected with the heaviest
showers this afternoon.

Meanwhile, a tropical wave moving across the Windward Islands will
enter the eastern Caribbean later today, and further increase the
available moisture content across the local area through the
weekend. Shower and isolated thunderstorm activity is expected to
gradually increase from the Anegada Passage and across the eastern
waters of the islands from late tonight into Saturday. As the wave
moves across the region on Saturday, expect cloudiness and scattered
to locally numerous showers with isolated thunderstorms to affect
portions of the islands through at least late Saturday night. Urban
and small stream flooding will be the main threat. Lingering
moisture on Sunday in a southeasterly wind flow will aid in the
development of diurnally induced afternoon convection, mainly over
northwestern PR. Drier air is expected to quickly fill from the east
by Sunday night.

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

Model guidance is in relatively good agreement in showing
improving weather conditions on Monday. A mid-level ridge is
expected to build in from the central Atlantic into the northeast
Caribbean, resulting drier and more stable conditions aloft.
Therefore, the coverage of shower activity is expected to diminish
substantially. However, sufficient low-level moisture will still
remain in place to result in afternoon convection across the
northwestern quadrant of Puerto Rico as the low-level steering
flow will be from the east-southeast.

On Tuesday into at least the first half of Wednesday, the low-
level moisture content decreases with a plume of suspended Saharan
Dust Particulates expected to move across, resulting in hazy
skies. Therefore, mainly fair weather conditions with limited
shower activity is expected.

Weather conditions then change late Wednesday into Thursday as a
tropical wave approaches the area with moisture expected to
increase significantly, increasing shower and thunderstorm
activity. Then, on Friday, another tropical wave is expected to
move across the eastern Caribbean, however, model guidance is in
disagreement in terms of how far north this wave will move with
the GFS model maintaining the wave well to the south while the
ECMWF model brings the wave towards the area. Therefore, given
these differences, confidence is rather low as to the expected
weather conditions for next Friday.

&&

.AVIATION...Mainly VFR conditions expected across most of the
terminals through the forecast period. However, SHRA/TSRA expected
to develop in and around the western terminals of PR fm 16z-22z,
causing tempo MVFR conds. VCSH expected mainly across the
USVI/Eastern PR terminals through the fcst period, increasing aft
22z, with SCT/BKN cigs fm FL030-FL060. East winds will prevail at 10-
15 kt with sea breeze variations aft 14z.

&&

.MARINE...Moderate winds of up to 15 knots and seas of up to 5
feet are expected to prevail across the regional waters through
the upcoming weekend. For beachgoers, there is a moderate risk of
rip currents for the northern beaches of Puerto Rico and most of
Culebra as well as the eastern tip of Vieques and Culebra.

&&

.FIRE WEATHER...Little to no shower activity is expected today
across most of the southern coastal plains of Puerto Rico with
relative humidity values expected to drop into the upper 40s to
low 50s for a period of time later this morning into early this
afternoon. In addition, due to the lack of wetting rains, 10-hour
fuel moisture is around 10% with KBDI values remaining above 700
for both Guanica and Camp Santiago. Winds are expected to peak at
around 15 mph with frequent higher gusts. Therefore, there is an
elevated fire danger threat today across the southern coastal
plains.

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 77 87 77 / 40 50 40 40
STT 88 78 86 76 / 40 60 60 60