Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
454 AM AST Mon Apr 12 2021

.SYNOPSIS...Generally fair and stable weather conditions with
limited shower activity, if any, will prevail through Tuesday.
This scenario will support elevated fire danger conditions.
Local conditions will shift to a more wetter and unstable weather
pattern beginning on Wednesday as above average moisture moves
into the region. Simultaneously, warmer temperatures can be
expected as winds become more southeasterly. Choppy seas and
hazardous surf zone conditions will continue today.


&&

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

Dry air interacting with a mid level ridge will promote stable
weather conditions with sunny skies today. Model suggest little to
no rainfall over the forecast area. Therefore, shower activity, if
any, could be expected in the afternoon over parts of interior
Puerto Rico and across the Caribbean waters. Winds are shifting now
more to the east southeast. Therefore, expect slightly warmer
daytime temperatures across the region, compared to what has been
observed in the past couple of days.

For Tuesday, the aforementioned ridge will start to erode and
moisture will increase somewhat. The chance for isolated
thunderstorms remains marginal as latest model guidance shows
moisture content below normal values and the dynamic aloft looks
less favorable. Therefore, sunny skies will be observed across the
islands during the morning hours. Once the moisture embedded in the
southeasterly flow reaches the islands in the afternoon, partly
cloudy skies with isolated to scattered showers will be noted mainly
over parts of interior and eastern interior of Puerto Rico. Rainfall
activity is expected to lead to minor rainfall accumulations.

For Wednesday, a large polar trough will pass to our north during
the day. Therefore, dynamics aloft look more favorable for the
development of isolated thunderstorms. Also, models continue to
suggest a westerly component in the wind flow pattern from 250-
700mb, but light southeasterly winds at sfc. This weather scenario
will interact with a surge in moisture advecting across the local
islands. Thus, diurnally induced afternoon showers with isolated
thunderstorm activity will focus mainly over parts of interior and
eastern interior Puerto Rico. Showers as well as isolated
thunderstorms over the San Juan metro area cannot be ruled out. This
activity could result in ponding of water over roadways and in poor
drainage areas and possible localized urban and small stream
flooding with the heaviest and most persistent rains.

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

Recent model guidance continues to suggest that a somewhat wetter
and unstable weather pattern will continue on Thursday, but now a
bit drier than previously expected and lasting through late
Friday night since the area of enhanced moisture is expected to
stall over the region. A delay in the peak of moisture is once
again presented, suggesting highest model-estimated precipitable
water around 1.80 inches by Friday evening. Over land, the bulk of
the activity will favor southern and eastern sections of Puerto
Rico, as well as the US Virgin Islands during the overnight and
early morning hours, shifting to the interior and northern
sections of Puerto Rico in the afternoon, with the potential for
isolated thunderstorm development since 500 mb are expected to
fall as low as -8 degrees Celsius. This scenario, under a
generally weak steering flow, presents the potential for ponding
of water to localized urban and small stream flooding through
late Friday night.

Thereafter, global models are now in strong agreement
with a drying tendency dominating the local weather conditions
Saturday into early next week, with peak drying expected on
Monday. So far, this will result from a mid-to-upper ridge moving
into the area, strengthening the trade wind cap while limiting
any chance for organized shower development. Nevertheless, limited
afternoon convection cannot be ruled out. As conditions dry out
and the general wind flow becomes more southeasterly, expected
warmer temperatures that could reach the lower to mid 90s with
possible heat indices into the upper 90s to lower 100s by Friday
onwards.


&&

.AVIATION...Mainly VFR conditions are expected to prevail across TAF
sites during the next 24 hours. Winds will be from the ESE at 10-15
kt, with sea breeze variations through 22z. Then, light and variable
winds are expected overnight.


&&

.MARINE...A weak northerly swell spreading across the Atlantic
waters and local passages will continue to result in choppy seas
through tonight. Recent buoy observations (41043) suggest the
peak of the swell will occur early this morning, with seas in the
outer Atlantic waters approaching but not quite reaching Small
Craft Advisory conditions. As a result, small craft operators are
urged to exercise caution across these waters. Similarly, surf
zone conditions will be approaching but not quite reaching High
Surf Advisory criteria, with breaking waves expected to remain
just below 10 feet. However, occasionally higher waves may briefly
result in higher breaking waves. Therefore, beachgoers are urged
to exercise caution when visiting north-facing beaches of Puerto
Rico, Culebra and the northern US Virgin Islands due to the
potential for brief dangerous breaking waves and expected
dangerous rip currents conditions. In fact, a High Risk of Rip
Currents remains in effect for these areas through at least late
tonight.

Marine and surf conditions are expected to improve late tonight
into Tuesday, with tranquil seas prevailing through the end of
the workweek.


&&

.FIRE WEATHER...A generally dry and stable weather pattern with no
chance for significant wetting rains is expected today, with the
potential for further deterioration of soils and fuels. Relative
humidities are expected to fall into the upper 30s to lower 40s,
under a generally east to southeast wind flow that may remain
below 15 mph with higher gusts. However, sea breeze variations
may generate locally higher winds around 15 mph or higher between
the late morning and early afternoon hours. Since recent KBDI and
10-hour fuel moisture reports have remained above 600 and as low
as 8 per cent, respectively, this scenario will support elevated
fire danger conditions. Therefore, a Fire Danger Statement has
been issued due to elevated fire danger conditions expected across
the southern coastal plains and hills, as well as the west coast
of Puerto Rico.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 73 88 75 / 0 0 30 20
STT 84 74 85 74 / 0 20 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
531 AM AST Tue Apr 13 2021

.SYNOPSIS...Moisture will increase until a weak front moves into
the area on Wednesday bringing northerly flow. Tropical air will
be held just southeast of the island, but as southeast flow
returns it will move through quickly on Friday. Then mostly drier
air with a few patches of moisture will pass by in east to east
southeast flow into early next week.

&&

.SHORT TERM...Today through Thursday...
A shift to a somewhat wetter weather pattern is expected to begin
today as dynamics aloft become favorable for shower development
along with an increase of available moisture. This will result
from the passage of a deep polar trough, pushing a mid-to-upper
level ridge eastward and away from the region while weakening the
trade wind cap. As the polar trough streams across the area,
expect a generally light and variable surface wind flow with a
southwesterly to westerly component above the 850 mb layer. In the
meantime, tropical moisture will slowly make its way into the
region from the south. Although the bulk of the moisture is
expected to remain over the Caribbean waters, normal precipitable
water values around 1.5 inches are expected over land areas by
13/18-21Z. This scenario supports a higher potential for shower
development, but conditions aloft may not necessarily support
deep convective development nor significant rainfall accumulations
since mid-levels are expected to remain quite dry. However, under
a weak steering flow, rains from slow-moving showers may result
in ponding of water on roadways and low-lying areas, particularly
along the eastern interior and eastern sections of Puerto Rico
this afternoon, where the strongest showers are expected.

By Wednesday, a similar weather pattern is expected. However, the
combinations of the remnants of an old frontal boundary crossing the
local islands from the north along with continuous moisture
advection from the south and favorable dynamics aloft with full
erosion of the trade wind cap will support an increase in the extent
of the afternoon shower activity. Shallow-convective development is
still expected, but the persistent weak steering flow will continue
to support slow-moving showers that may generate ponding of water
and even localized urban and small stream flooding. Even though a
similar weather pattern can be expected on Thursday, a brief
erosion of the available moisture and less favorable conditions
aloft will limit the potential for shower development.

.LONG TERM...Friday through Monday...
With high pressure over the western tropical Atlantic,
southeasterly flow develops Friday and continues Saturday. This
will cause the old frontal boundary south of the area to cross
over the islands again for another shot of showers. However drier
air follows directly. Then high pressure at 700 mb moves east
north of the area and brings the almost completely washed out
front back over the area again and also ends the warming trend.
Better moisture does not then build back until mid week next week.

At mid levels, high pressure builds over the Greater Antilles west
of the area and moves into the Atlantic waters north of us by late
Monday.

At upper levels lower pressure persists over the Atlantic and a
the passage of a weak upper level trough and companion jet accompanies
the last passage of the very weak cold front on Saturday. High
pressure then builds over the western Caribbean.

Moisture and stability conditions are not particularly favorable
for heavy rains during the period, however some local effects
could invigorate showers that drive up eastern mountains in the
overnight and morning periods and local convergence in the
northwest portion of Puerto Rico will also favor showers in the
afternoons.

At no time is flow found to be favorable to bring significant ash
to the local area from the Soufriere Volcano on Saint Vincent.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across
all TAF sites during the next 24 hours. However, VCSH may result in
brief MVFR conditions with SCT-BKN between FL020-040 at TKPK/TNCM
through 13/14Z, TJSJ between 13/16-22Z and TIST/TISX between 13/14-
24Z. Winds will be generally light and variable through 13/14Z,
turning from the ESE at 10-15 kt with sea breeze variations
thereafter.

&&

.MARINE...Marine conditions are generally subsiding although weak
swell continue to invade the local waters from the north.
Conditions are expected to remain below small craft advisory
criteria for at least the next 7 days. A moderate risk of rip
currents will persist for much of the period on coasts with
northerly exposures.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 74 87 74 / 50 10 60 60
STT 86 73 85 73 / 40 40 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
439 AM AST Wed Apr 14 2021

.SYNOPSIS...An old cold front boundary that moved through the area
on Tuesday will make several passages through the area before the
weekend is over. High pressure to the north will cause the
easterly trade winds to increase Sunday through Tuesday and create
somewhat less favorable marine conditions.

&&

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

A somewhat wetter pattern is expected to continue today as the
remnants of an old frontal boundary move across the region from the
north. The combination of local effects and diurnal heating along
with near-normal precipitable water values (model-estimates up to
1.40 inches) will support locally-induced shower development over
Puerto Rico, with highest impact expected across the interior and
southeastern sections of the island under a generally west-northwest
to northwest wind flow. Isolated shower activity can be expected
elsewhere. Isolated thunderstorm development, if any, will be
possible due to 500 mb temperatures falling to nearly -8 degrees
Celsius. Nevertheless, flooding is not expected today, but the
persistent weak steering flow will support slow-moving showers that
could result in ponding of water on roadways and poorly drained
areas and even localized urban and small stream flooding are
possible with the heaviest activity. Daytime highs are forecast
to peak into the mid to upper 80s across coastal areas.

Once the remnants cross the local islands and move into the Caribbean
waters by late tonight, a drier air mass is expected to move into
the area, causing precipitable waters values to drop below an inch.
Although this scenario will result in a generally dry and stable
weather pattern across the local islands, limited afternoon
convection is still expected by Thursday afternoon, clustering along
the interior and western interior sections of Puerto Rico as winds
veer from the northeast. Since the remnants are expected to converge
with another area of enhanced tropical moisture and stall just south
of the local islands through at least late Thursday night, showers
moving from the waters into southern and eastern Puerto Rico, as
well as the US Virgin Islands, cannot be ruled out. On Friday, winds
are expected to become more southeasterly. Not only warmer
temperatures can be expected under this flow, but southeasterly
trade winds will push the aforementioned area of enhanced moisture
northward over the local islands through late Friday night. Model
guidance suggests that peak moisture will coincide with the time
of peak daytime temperatures, with precipitable water values
ranging around 1.5 and 1.7 inches. This combination will result in
a higher chance for shower and possible thunderstorm activity,
with the potential for urban and small stream flooding.

.LONG TERM...Saturday through Tuesday...
Flow is mostly northerly during the short-term period near the
surface, but on Friday flow begins to become easterly and by
Saturday, flow in the lower levels is southeast. This pulls the
old frontal boundary north over the area again. This had been
anticipated for Friday earlier, but now seems to be delayed until
Saturday morning. During this time flow at 700 mb is even somewhat
southwest. This abruptly shifts back to north and then northeast
late Saturday as high pressure moves east over the open waters of
the Atlantic to our north and the still weaker cold front makes
another pass through Puerto Rico and the U.S. Virgin Islands. At
this point the warming also reverses and cooler temperatures, as
indicated by the return and strengthening of the of easterly trade
wind flow and the decline of 1000-850 mb thickness values through
the end of the period, are indicated.

Precipitable water values will have peaked on Friday, but a
secondary peak, also above 1.6 inches, is expected to occur
Saturday evening as the frontal boundary makes another pass
through the area. With mid layers remaining very dry due to the
proximity of a 500 mb high pressure through out the forecast
period, this is not promising for significant rainfall during
this time, but patches of good moisture do pass in the increasing
low level flow and passing showers will continue during the
period. Nevertheless the overall moisture values will drop through
late Tuesday, and current models are forecasting precipitable
water to be near 1.1 inches by Tuesday night.

At upper levels a weak short wave trough moves through the area
north of Puerto Rico and the U.S. Virgin Islands and pulls a jet
of west northwest flow over the area Friday night. This is
expected to enhance shower activity Friday night and into
Saturday--especially on the southeast coast due to the low level
winds. High pressure at upper levels then builds over the
southwestern Caribbean turning flow over the local area northwest
and then north by Tuesday night.

&&

.AVIATION...Mainly VFR conditions are expected to prevail across
all TAF sites during the next 24 hours. However, VCSH may result in
brief MVFR conditions with SCT-BKN between FL020-040 at TIST through
14/14Z, TJPS between 14/15-23Z, and TISX between 13/14-21Z. Winds
will be generally light and variable through 14/14Z, turning from
the N-NW at 5-15 kt with sea breeze variations thereafter. Maximum
winds W 60-75 knots btwn FL340-490--strongest at FL470 and FL355.

&&

.MARINE...Seas are light and generally below 5 feet at the moment.
As surface winds become a little more northerly winds and seas in
the Mona Channel will necessitate that mariners exercise caution--
mainly close to shore south of Mayaguez. More favorable conditions
return until late in the weekend. At that time winds gradually
increase and make seas rough. But before that a minor swell event,
but still one a little stronger that the one passing through late
Thursday and Friday will enter the area Friday night and Saturday.
At this time seas are expected to remain below 7 feet through the
next 7 to 10 days.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 72 87 75 / 10 20 20 20
STT 86 74 85 74 / 20 30 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
421 AM AST Thu Apr 15 2021

.SYNOPSIS...
Mainly tranquil weather and marine conditions are expected for
today, but conditions should become more favorable for shower and
thunderstorm development on Friday. A Saharan Air Layer is
expected then by the weekend and early next week, resulting in
another round of hazy skies and limited rainfall activity over the
islands.

&&

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

A surface high pressure over the southwestern Atlantic will promote
a light to moderate northerly wind flow through this afternoon. As
the high moves quickly northeast of the region, winds will shift
from the east-southeast through Saturday. A drier air mass will
continue across the region today, promoting fair weather conditions.
Limited shower development is possible over portions of central
Puerto Rico due to diurnal effects. However, precipitable water
content (PWAT) is forecast to drop to near 0.75 inches, and minor
rainfall amounts are anticipated, if any.

The remnants of an old frontal boundary, currently located
south/southeast of the region over the eastern Caribbean Sea, are
expected to move back across the islands on Friday. PWAT content is
then expected to increase significantly compared to previous days
between 1.50-1.75 inches. Meanwhile, at upper levels a 80 kt jet
segment is forecast to move just north of the islands, providing
divergence aloft for possible isolated thunderstorm development
during the afternoon hours over portions of central and the northern
half of PR. Across the USVI and Caribbean waters, scattered shower
activity is expected, with possible brief periods of moderate to
locally heavy rainfall. For Saturday, the remnants of the frontal
boundary are expected to move over the Atlantic waters, while a
building ridge east of the Leeward Islands will promote drier air
intrusion and the arrival of a Saharan Air Layer should cause hazy
skies and limit shower activity once again across the region.

.LONG TERM...
The region will continue to be dominated by the presence of a mid
to upper level ridge over the Caribbean. At the surface, an
elongated surface high pressure over the eastern Atlantic will
maintain a southeasterly wind flow through Monday. At the mid
levels, the wind flow will stay from the east, with a dry air mass
in place. This will act to suppress any significant rainfall
activity over the local islands. Also, the Saharan Air Layer will
keep entraining over the region, resulting in hazy skies, at
least through the beginning of the workweek.

By Tuesday, and Wednesday, the mid level ridge will move into the
central Atlantic, while an upper level trough deepens to the
northeast of the islands. So far, both the GFS and the ECMWF are
showing that the forecast area will remain on the subsidence side
of this feature, hence it should not have an impact on shower
development. Also, by Tuesday and Wednesday, a surface high
pressure over the central Atlantic will strengthen, shifting the
low level winds from the east and tightening the gradient, which
will result in stronger winds. Even though conditions are not
particularly favorable for any significant rainfall events, local
effects should trigger shower development during the afternoon
hours across the interior and western portions of Puerto Rico,
while brief isolated activity cannot be ruled out elsewhere.


&&

.AVIATION...
Mainly VFR conditions are expected to prevail across all
the terminals during the next 24 hours. Surface winds from the E-ENE
at 10-15 kts, with a southerly sea breeze at TJPS aft 14z.

&&

.MARINE...
Seas up to 4 feet are forecast for today, except for the Mona
Passage, where seas are expected to reach 5 feet. Winds will be
from the northeast up to 10 knots. A weak northerly swell will
impact the Atlantic waters and passages later tonight and early
Friday, and another pulse will reach the waters by the weekend,
but seas are expected to remain up to 5 feet. A moderate rip
current risk is expected for the north-facing beaches of Puerto
Rico, without including Vieques and Culebra.

&&

.FIRE...
Relative humidities in the 30s and 40s are expected today under a
northeasterly wind flow. Although some rains fell yesterday across
southeastern Puerto Rico, KDBI values are still well above the
critical threshold at Camp Santiago and Guanica. The general wind
flow should remain light, but sea breezes may make the flow reach
15 mph or more. As a result, an Elevated Fire Weather message
(RFDSJU) was issued today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 88 73 / 0 10 50 40
STT 86 76 86 74 / 10 30 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
421 AM AST Sat Apr 17 2021

.SYNOPSIS...A surface high pressure over the central Atlantic will
continue to promote light to moderate east to southeast winds for
the next several days. Hazy skies due to a Saharan Air Layer are
expected during the weekend. Normal to above normal daytime
temperatures are expected in general through next week. Isolated
to scattered showers could develop each afternoon over portions of
the interior/western PR, but no significant rainfall amounts are
anticipated at this moment.


&&

.SHORT TERM...Today through Monday...
A southeasterly wind flow is expected to prevail across the islands
today due to surface high pressure located over the central
Atlantic. The ridge extend through the mid levels as well,
promoting stable conditions over the eastern Atlantic, and this
pattern should prevail through at least early in the workweek. For
today, the remnants of a frontal boundary will linger around,
which could cause some passing showers early in the day across
eastern Puerto Rico and the U.S. Virgin islands. In the afternoon,
as is usual, some showers may develop over the interior and
western Puerto Rico. Conditions aloft are not favorable for strong
rainfall accumulation, but some ponding of water will be possible
in low- lying areas.

The recent guidance also suggest the presence of a Saharan Air
Layer that should remain in place for the rest of the short-term
forecast period, resulting in hazy skies. On Sunday, as the
remnants of the old frontal boundary lifts into the Atlantic
Ocean, the air mass will turn even drier. The forecast soundings
are showing precipitable water values at 1.1-1.2 inches. As a
result, shower activity should be very limited. In terms of
temperatures, on Saturday, the wind flow will be very well
established from the south up to 750 mb, meaning that temperatures
should be warmer than in the past few days, with highs in the
upper 80s and low 90s across urban areas and low level elevations.
On Sunday and Monday, the low level wind flow remains from the
east-southeast, hence, above normal temperatures should continue.


.LONG TERM...Tuesday through Saturday...
A mid level ridge will promote stable conditions and drier air
intrusion through much of the long term period. The ridge is
forecast to move just north of the region on Tuesday and hold
northeast of the Leeward islands through Friday. At lower levels,
a surface high over the central Atlantic will continue to promote
east-southeast flow through Friday, with a slight increase in
winds expected by midweek. During the second part of the workweek,
a few pulses of moisture carried by the trade winds will reach
the region from the east, causing an increase in precipitable
water content. Therefore, expect trade wind showers to move at
times during the night time across the USVI and eastern sections
of PR, followed by afternoon shower development over western PR.
Otherwise, fair weather conditions are expected to prevail across
the islands. At the end of the long term period...a polar trough
is expected to move over the western Atlantic by Friday, and the
ridge is then expected to erode by Friday into Saturday. This
should cause an increase in low level moisture content and give
better chances for measurable rainfall in diurnal activity.


&&

.AVIATION...Mainly VFR conditions expected to prevail across all
terminals. Hazy skies are expected due to Saharan Dust, but
visibilities should remain at P6SM. VCSH are expected for TJBQ
after 17/17Z, which could result in brief MVFR conditions due to
low ceilings and reduced VIS. Winds are expected from the SE at
less than 10 knots from the surface to FL050.


&&

.MARINE...A northerly swell will move across the Atlantic waters
today, causing seas up to 6 feet across the offshore waters and a
high risk of rip currents across the northern beaches of Puerto
Rico. A surface high pressure over the central Atlantic will
continue to promote light to moderate east to southeast winds
through the rest of the weekend. Seas will improve through early
next week, before a wind surge brings choppy seas across the
offshore waters and passages by midweek.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 90 76 90 75 / 30 20 10 20
STT 85 77 85 76 / 20 20 20 10

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
305 AM AST Sun Apr 18 2021

.SYNOPSIS...A surface high pressure over the central Atlantic will
continue to promote light to moderate east to southeast winds for
the next several days. Locally higher winds due to the sea breeze
are expected across the northern and southern coastal areas of PR.
Hazy skies due to a Saharan Air Layer are expected to continue
through early next week. Above normal daytime temperatures are
expected in general through next week. Limited shower activity
will continue across the islands through next week.


&&

.SHORT TERM...Today through Tuesday...
The eastern Caribbean is still under the influence of a mid level
ridge, and a surface high pressure extending from the western to the
central Atlantic. This will continue to generate an east-southeast
wind flow through early in the workweek. The Total Precipitable
Water product, derived from GOES-16, indicates that an even drier
air mass is making its way into Puerto Rico and the U.S. Virgin
Islands, with values around 1.2 inches. In fact, the GFS forecast
soundings are showing that these dry conditions at the low and mid
levels should persist at least through Tuesday, with a trade wind
cap inversion evident around 900 to 850 mb. As a result, mainly fair
weather is expected to prevail. There is a chance that isolated to
scattered showers may develop over northwestern Puerto Rico each
afternoon, due to local effects, but without leaving significant
rainfall accumulation. Additionally, this dry air mass contains
Saharan dust, hence skies will stay hazy through Tuesday as well.
Under the influence of the mid-level ridge and the southeasterly wind
flow, temperatures will stay on the warm side, with maximum
temperatures as high as the low 90s over coastal elevations across
the islands.

.LONG TERM...Wednesday through Sunday...
A mid level ridge will promote stable conditions and drier air
intrusion through the end of the workweek. The ridge is forecast
to move northeast of the Leeward islands by Friday, as a polar
trough moves across the western Atlantic. At lower levels, a
surface high over the central Atlantic will continue to promote
east to southeast winds through Friday, with a slight increase in
winds expected by midweek. Another surface high will enter the
western Atlantic and move into the central Atlantic during the
weekend, this will cause a more easterly wind flow across the
region.

During the second part of the workweek, a few pulses of moisture
carried by the trade winds will reach the region from the east,
causing a slight increase in precipitable water content. In
particular on Thursday and Friday, as the polar trough presses
against the upper level ridge. Therefore, expect trade wind
showers to move at times during the night time across the USVI and
eastern sections of PR, followed by better chances for afternoon
shower development over northwestern PR. The weekend looks
similar, however, a drying trend is expected once again, and due
to a more easterly trade wind flow, afternoon showers are expected
to develop over the western interior and west coast of PR.


&&

.AVIATION...VFR conditions expected to prevail across all
terminals. Skies remain hazy due to Saharan dust, but VIS will
remain at P6SM. VCSH may form after 18/18Z across TJBQ, which
could lead to brief MVFR conditions. Winds will be out of the ESE
at 5-12 knots at FL050, with sea breeze variations and stronger
gusts.


&&

.MARINE...A surface high pressure over the central Atlantic will
promote moderate east to southeast winds for the next several days.
Seas will continue to improve through early in the week, before a
small wind surge brings choppy seas across the offshore waters
and passages by midweek. A north swell around 4 feet will continue
across the local Atlantic waters and passages today. This will
cause a moderate risk of rip currents for most of the northern
and east facing beaches of the islands, and across the southwest
coast of PR.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 91 75 89 76 / 10 20 20 10
STT 87 76 86 76 / 10 10 10 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
452 AM AST Mon Apr 19 2021

.SYNOPSIS...

A surface high pressure system over the region will continue to
promote east to southeasterly wind flow pattern. Also, a dry
weather pattern with hazy skies will continue to hold for the next
several days. Trade wind showers will move at times during the
second part of the work week across the islands. Tranquil to
somewhat choppy Marine conditions will continue for the next
several days across the regional waters.

&&

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

A mid-level high pressure and an upper-level ridge are promoting
stable weather conditions in the short term. These features are
promoting a trade wind inversion, subsidence, and dry air aloft.
Also, lingering Saharan air particulate will continue over the
region, creating hazy skies and limiting night-time cooling. While
at the surface, a high-pressure, anchored over the central and
eastern Atlantic Ocean, is inducing an east-southeast wind flow that
is pushing below-normal moisture over the islands. Under these
weather conditions, expect hazy skies, little or no rain, and warm
to hot temperatures today. A similar weather pattern will continue
Tuesday and Wednesday. However, haziness should be diminishing this
afternoon, clearing somewhat the suspended particles. Although rain
will be scarce, it may form each afternoon across the western
portions, mainly due to the combination of sea breeze and local
effects. Also, winds will rarely bring one or two showers across the
local waters and windward sections.

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

Drier conditions will persist until Friday, as the mid level
ridge moves to northeast of the Leeward islands and polar trough
moves across the western Atlantic. At lower levels, a surface high
over the central Atlantic will continue to promote east to
southeast winds. This will result in warmer daytime high
temperatures across the islands. A slight increase in winds
expected by midweek. Another surface high will enter the western
Atlantic and move into the central Atlantic during the weekend,
this will cause a more easterly wind flow across the region.

An increase in moisture is expected by the second part of the
workweek. Thus, expect trade wind showers to move at times during
the overnight across the USVI and eastern sections of PR,
followed by diurnally induced afternoon showers over northwestern
PR on Thursday and Friday. The weekend looks similar, however, a
drying trend is expected once again. Winds will shift more to the
east, and afternoon showers are expected to develop over the
western interior and west coast of PR.

&&

.AVIATION...

VFR conditions will prevail today. Hazy skies will persist over the
local flying area. However, we are not expecting VIS below 6 SM.
Some showers may develop near JBQ between 19/18-22z, without
significant impact, at this time. No ashes from yesterday`s
eruptions from La Soufriere in St Vincent nor any possible later
today or tomorrow will affect PR/USVI. Calm to light and variable
winds will continue until 19/13z, returning from the ESE at 10 to 15
knots with sea breeze variations and occasional gusts after
19/13z.

&&

.MARINE...

A surface high pressure over the central Atlantic will
promote moderate east to southeast winds for the next several days.
Seas will continue to improve through early in the week. However,
a small wind surge brings somewhat choppy seas across the
offshore waters and passages by midweek.

For the beachgoers, there is a moderate risk of rip currents for
most of the northern and east facing beaches of the islands, and
across the southeast and southwest coasts of PR.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 76 89 75 / 10 10 20 20
STT 86 76 87 75 / 10 10 10 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
436 AM AST Wed Apr 21 2021

.SYNOPSIS...

Dry pattern continues over the local area. Hazy skies as result
of African dust incursion will continue through Saturday.
Moisture content will pick up over the weekend promoting showery
weather across the region. Choppy marine conditions will prevail
today with seas up to 6 feet mainly over the outer Atlantic
waters.

&&


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

Stable weather conditions will continue today with a mid to
upper-level ridge aloft. Somewhat hazy skies will continue due to
the remnants of suspended dust from Africa`s desserts. Winds will
turn more from the east today. In general, expect hazy and mostly
sunny skies today. Once again, moisture will develop across the
western portions of Puerto Rico during the afternoon.

A polar trough moving across the western Atlantic will weaken the
ridge aloft. In addition to the weakening of the trade wind cap,
surges of low-level moisture will increase the frequency and
intensity of showers in the typical seasonal pattern Thursday and
Friday. Therefore, expect passing showers embedded in the trades
across the local waters and windward sections during the morning
and evening hours. Then, diurnal-heating and sea breeze variations
will aid in the formation of showers over the western portions.
Also, the U.S. Virgin Islands could expect afternoon showers due
to low-level convergence, and rains in the form of streamers from
El Yunque could impact the San Juan metro area.

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

A polar trough moves across the western Atlantic. The mid to upper
level ridge is expected to stall northeast of the Leeward
islands. At lower levels, a surface high will move into the
central Atlantic. This will result in a showery weekend with
patches of moisture reaching the islands during the morning hours,
followed by afternoon convection over parts of interior and
northern Puerto Rico. The wind pattern will be from the southeast,
thus daytime high temperature are expected to be just above normal
values. For the second half of the forecast period, winds will
shift more to the east. This will result in fragments of moisture
embedded in the trade winds to reach the local islands from time
to time.

&&

.AVIATION...
Conditions will remain VFR thru the next 24 hrs. Skies will
continue hazy, but with more than 6 SMi of Visibilities. Showers
may affect or move near JBQ/JSJ between 21/18-22z. Calm to light
and variable winds will continue until 21/13z, returning from the
E at 10 to 20 knots with sea breeze variations and higher gusts.

&&


.MARINE...

A surge in winds as resulted in seas reaching up to 6 feet over
the local outer Atlantic waters and in local areas of the inner
waters surrounding Puerto Rico today. Therefore, small crafts are
urged to exercise caution.

For the beachgoers, there is a moderate risk of rip currents for
most of the northern and east facing beaches of the islands,
including the southeast and southwest coasts of Puerto Rico,
Vieques, Culebra and the U.S. Virgin islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 75 87 76 / 20 40 30 50
STT 87 75 85 76 / 10 40 40 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Thu Apr 22 2021

.SYNOPSIS...

The ridge pattern aloft will weaken as a polar trough moves across
the western Atlantic. Easterly winds will return today, shifting
more from the southeast on Friday. An advective pattern will
dominate the local weather during the next few days, with the
arrival between pockets of moist and dry air. Afternoon convection
is expected each day, mainly across the mountain and western
areas. In the long term, a moist and unstable weather pattern
seems possible for the second part of next week.

&&

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

Today, they will remain lingering moisture over the area, with some
additional patches of moisture being carried in, embedded in the
trade winds. Aloft, the polar trough will weaken the upper level
ridge today. Thus, expect partly to variably cloudy skies across
the eastern half of Puerto Rico and the US Virgin Islands, with a
slight chance for isolated to scattered showers during the early
morning hours. Then in the afternoon hours, moisture confined at
the low levels, diurnal heating and local effects will aid in the
development of showers across interior and northwestern parts of
Puerto Rico, as well the San Juan metro area. Streamer-like
showers cannot be ruled out downwind from the U.S. Virgin Islands.
It is possible that persistent showers over a given area could
lead to ponding water on roadways.

Another tropical disturbance is expected to arrive Friday and
lingering into Saturday. This will enhance shower activity across
the forecast area. Thus, expect a similar weather pattern with
showery weather conditions in and around the local islands. Winds
will continue to blow from the east at 10-15 mph. Temperatures are
expected to be relatively warm, with day temperatures reaching the
mid to upper 80s.

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

A polar trough will move into the western Atlantic late Sunday
night and early Monday morning, and then eastward close to the
northeast Caribbean by Tuesday. The mid to upper-level trough will
then amplify over PR/USVI Wednesday through Friday, increasing
instability. In the meantime, a surface-high pressure will build
across the Atlantic Ocean north of the Greater Antilles Sunday and
Monday. A cold front will then swing eastward across the Western
Atlantic, weakening the high pressure. The remnants of the cold
front will sink southward near PR/USVI by midweek until it
dissipates, enhancing tropical moisture. Another surface-high will
build over the Western Atlantic Thursday and onward.

That said, expect the advective pattern to continue Sunday and
Monday, which could bring passing showers across the windward
sections in PR/USVI during the overnight and morning hours,
followed by afternoon convection across the northwest quadrant and
interior portions of Puerto Rico. But in general, mostly tranquil
weather conditions. However, we will be transitioning to a more
unstable weather pattern by Tuesday and onward as the polar trough
moves closer and moisture increase across the islands. The
potential to observe inclement weather due to thunderstorms, urban
and small stream flooding could increase by that time (as long as
GFS is correct, which was the model chosen for the long term
forecast).

&&

.AVIATION...

Mainly VFR conds expected across all terminals drg the next 24 hr
prd. Afternoon convection will result in an increase in cloud
cover and VCSH in/around TJSJ/TJBQ. Winds will continue from the
E at 10-15 knots with higher gusts in sea breeze variations. Winds
will become calm to light and variable aft 22/23z. No sig
operational wx impacts durg prd at this time.

&&

.MARINE...

Small craft operators are urged to exercise caution across most
of the local waters due to expected seas up to 6 feet and east
winds up to 20 knots. Thereafter, marine conditions will improve
with winds around 15 knots and seas below 5 feet; conditions that
will hold through the weekend into early next week.

For beachgoers, there is a moderate risk of rip currents for most
local beaches.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 75 86 75 / 30 50 30 30
STT 86 76 84 74 / 20 40 40 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
454 AM AST Fri Apr 23 2021

.SYNOPSIS...

An easterly perturbation will move across the islands today,
providing enough low-level moisture promoting passing showers
across the windward portions of PR/USVI in the morning, followed
by afternoon convection during the afternoon across the western
sections. A dry air mass will arrive on Saturday, and a ridge will
build aloft, resulting in fair weather conditions. In the long
term, a moist and unstable weather pattern could be the weather
story between Tuesday and Thursday next week.

&&

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

An easterly perturbation will promote somewhat unstable weather
conditions for today. Passing showers will continue to affect
portions of eastern Puerto Rico and the U.S. Virgin islands during
the morning hours. This activity will be followed by afternoon
convection over parts of interior and northwestern quadrant of
Puerto Rico, as well over the San Juan metro area. This activity
could lead to at least ponding of water on roadways and poor
drainage areas. Showers will diminish by sunset.

For tomorrow, mainly fair weather conditions with limited rainfall
activity is expected across the forecast area. Model guidance now
suggest a drier air mass coupled with a surface high pressure that
will yield to less available moisture content at the low levels.
Aloft, stable conditions expected due to a building upper-level
ridge. Precipitable water values are forecast to be below normal.
Hence, Saturday seems to be the driest day of the short term
period. Incursion of African dust particles is suggested by
observations, thus somewhat hazy skies could be notice.

Patches of moisture will reach the islands by Sunday afternoon
due to the influence of a polar trough, located in the western
Atlantic. However, these showers are not expected to be impactful
as they will not lead to significant rainfall accumulations. The
most active part of the day will be in the afternoon, as local
effects and diurnal heating can spawn showers over parts of
northwestern Puerto Rico.

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

A polar trough will move from the western to the eastern Caribbean
Monday through Tuesday. This mid to upper-level trough will then
amplify over PR/USVI Tuesday through Thursday, to be then
displaced by a ridge building from the west on Friday. Meanwhile,
a surface-high pressure will push disturbance in the easterly
winds over the islands early next week. Then, a cold front will
approach the islands from the northwest Tuesday through Thursday,
enhancing tropical moisture over us. Another surface-high will
build over the Western Atlantic Thursday and onward.

That said, expect the advective pattern to continue Monday and
early Tuesday, which could bring passing showers across the
windward sections in PR/USVI during the overnight and morning
hours, followed by afternoon convection across the northwest
quadrant and interior portions of Puerto Rico. The weather pattern
should be transitioning to a more unstable one Tuesday through
Thursday as the polar trough amplifies and tropical moisture
increase across the islands. Therefore, the potential to have
inclement weather due to thunderstorms, urban and small stream
flooding could increase, especially Tuesday through Thursday, as
model guidance continues to suggest. A more stable pattern should
return by Friday.

&&

.AVIATION...

Mostly VFR conditions expected to prevail over the next 24 hours
across all terminals. VCSH and brief gusty winds with and around
SHRA expected for TJSJ and TJPS through 23/10. Afternoon convection
will yield in SHRA for TJBQ/TJSJ til 23/22. Winds out of east-
southeast at 10 to 15 knots, with sea breeze variations with
occasionally higher gusts during the afternoon.

&&

.MARINE...

Mariners can expect tranquil marine conditions during the next
several days. Seas will range between 3 and 5 feet most of the
time. Light to moderate east to southeast winds will prevail
through early next week.

Beachgoers, a moderate risk of rip currents is expected to
continue across some of the east, northern and southern beaches
of the islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 75 88 74 / 40 30 10 20
STT 87 75 87 75 / 50 20 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
448 AM AST Sat Apr 24 2021

SYNOPSIS...A patch of moisture will produce isolated to scattered
showers in the morning hours over the local area and shower
activity over western Puerto Rico in the afternoon. Much drier air
will move in tonight and tomorrow. In the long term, a moist and
unstable weather pattern will prevail between Tuesday and Thursday
next week. Tranquil marine conditions persist.


&&

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

A patch of moisture will linger in the morning across the local
islands, but western PR will have enhanced moisture into the
afternoon hours. This will result in scattered showers in the
morning hours across the local area, becoming more isolated in the
mid morning hours. However, the lingering moisture will combine
with the local effects and diurnal heating to cause shower
development across western Puerto Rico. Some of the showers this
afternoon could persist over urban areas and cause minor flooding.
That said, while western PR will have lingering moisture and
showers, the USVI and the eastern portions of PR will have drier
air moving in, especially late in the afternoon into the evening.
Therefore there is only a slight chance of brief showers tonight
across the local area as drier air moves in. For tomorrow, drier
than normal moisture is expected, but a narrow band of moisture
may affect the USVI early in the morning hours. This band of
moisture will move west during the day, causing a slight increase
in moisture across PR, eventually causing the development of
scattered showers across western PR in the afternoon, but perhaps
less persistent than what is expected for today Saturday.
Thunderstorms are not expected this weekend since the mid and
upper levels will not be conducive to thunderstorm development.
That said, the story may change staring early in the workweek.

For Monday, a mid and upper level trough starts to develop to our
west and northwest. At the same time, a patch of moisture will move
in from the east and encompass the local islands. This will cause
moderate showers across most of the local area through the day, but
once again western and northwestern PR may have the most significant
showers on Monday afternoon. That said, the latest guidance suggests
that eastern PR may have significant shower activity on Monday
afternoon as well.

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

A polar trough from the west will move and build over the northeast
Caribbean on Tuesday setting favorable dynamical conditions aloft
for shower and deep convection development. As the upper-level
trough moves over our area, temperatures are expected to cool down
at 500 mb between -8 degrees celsius on Tuesday to -12 degrees
celsius on Thursday. This will cause an increase in instability
aloft, especially if the divergent side of the upper-level trough
coincides with diurnal surface heating. At low-levels, a frontal
boundary will approach from the north pushing moisture southwards
over to our region. So far, most indicators including precipitable
water and the GDI (Galvez-Dadidson Index) will favor the best
chance of thunderstorms and heavier showers on Tuesday. This would
also be the day for highest potential of widespread urban and
small stream flooding. Wednesday and Thursday look similar
accompanied by the potential of thunderstorm activity but less
widespread each day owed to a steady decrease of low-level
moisture and the eastward movement of the polar trough over
central Atlantic. Expect urban and small stream flooding in areas
with the heaviest showers. Weather conditions improve on Friday
and Saturday as the trough at upper levels pulls away and a ridge
aloft builds in along with an associated surface high pressure
north of the forecast area. This will result in drier and more
stable conditions. Lingering moisture could aid in some shower
development across the area, especially during afternoon hours due
to induced local effects, but drier air and stable weather above
the 700 mb layer will limit any significant rainfall
accumulations.


&&

.AVIATION...VFR conditions expected over the next 24 hours across
all terminals. VCSH and brief gusty winds with and around SHRA
expected for TJSJ TIST, and TISX through 24/13Z. SHRA to develop
after 24/17Z across western PR, that could cause VCSH at TJBQ this
afternoon. Wind will be light and variable through 24/12Z, becoming
easterly at around 10-20 knots with occasional gusts thereafter.
Sea breeze variations may be observed today.


&&

.MARINE...Tranquil to slightly choppy marine conditions are expected
for the next several days with wave heights of up to 5 feet in the
forecast. The local winds will be mainly from the east at 10 to 20
knots.

Beachgoers, a moderate risk of rip currents is expected to continue
across some of the east, northern and southern beaches of the
islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 74 87 73 / 10 20 20 50
STT 85 74 86 74 / 10 30 30 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
436 AM AST Sun Apr 25 2021

.SYNOPSIS...Mainly dry air is expected today for most areas,
although patches of moisture will be filtering in from time-to-
time and scattered to locally numerous showers can be expected across
western PR this afternoon. During the workweek, conditions look
more favorable for shower and thunderstorm activity, especially
from Tuesday through Thursday and possibly Friday as well. Marine
conditions will continue relatively tranquil for the next few
days.


&&

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

A patch of moisture will move through the local islands very early
in the morning, then dry air will move in later in the morning,
reaching central PR by noon. However, scattered to locally numerous
showers are forecast across western PR this afternoon due to the
combination of the limited moisture with the local effects. Some of
the showers this afternoon could persist over urban areas and cause
minor flooding. That said, while western PR will have showers this
afternoon, the USVI and the eastern portions of PR will have mainly
fair weather with perhaps isolated and brief showers. However,
moisture starts increasing tonight from the east, which will cause
scattered showers to affect the USVI and local waters overnight,
then eastern PR by Monday morning.

On Monday, a mid and upper level trough starts to develop to our
west and northwest. At the same time, a patch of moisture will move
in from the east. This will cause moderate scattered showers across
most of the local area through the day, but once again western and
northwestern PR may have the most significant showers on Monday
afternoon. That said, the latest guidance suggests that eastern PR
may have significant shower activity on Monday afternoon as well.
For Tuesday, the mid and upper level troughs may be positioned
favorably for enhanced shower activity with a few thunderstorms. The
overall moisture also encompasses the local islands. For that
reason, in the short term period, Tuesday is expected to be the
rainiest day, possibly causing urban flooding.

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

Model guidance continues to indicate the presence and
intensification of a tilted deep upper level trough over Puerto Rico
and U.S. Virgin Islands. On Wednesday, a broad frontal boundary
engulfing most of northern and northeastern Caribbean will be
supplying moisture into the upper trough with axis located just west
of Puerto Rico according to both GFS and ECMWF models. GFS has the
trough deepening into a cut-off upper low on Thursday that
eventually stalls across Puerto Rico through Saturday and pulls away
while weakening on Sunday. This latest run also shows an induced low
to mid level cut-off low just north of Puerto Rico causing low-level
winds to shift to more southeasterly on Friday, pulling deeper
moisture close to the forecast area. Meanwhile ECMWF has a less
bullish solution with the trough deepening as well into a cut-off
upper low and moisture pulling from the south but weakens much
faster on Saturday.

Both models are showing a wetter weekend than previous runs while
simultaneously exhibiting discrepancies in the evolution of the
cut-off low after late Friday. Therefore confidence is low for the
long range forecast for the weekend. However, models continue to
be in agreement on a wet and active weather for the latter part of
the week. From Wednesday through Friday, upper level conditions
will be conducive for deep convection together with high
precipitable water content (PWAT), thus, expect widespread showers
and thunderstorm activity. This will increase the risk of heavy
rainfall across Puerto Rico and U.S. Virgin Islands causing urban
and small stream flooding as well as ponding of waters on roadways
and in poor drainage areas.


&&

.AVIATION...VFR conditions expected over the next 24 hours across
all terminals. VCSH expected for TJSJ TIST, and TISX through 25/14Z.
SHRA to develop after 26/17Z across western PR, that could cause
VCSH at TJBQ this afternoon, perhaps even TEMPO SHRA at TJBQ. Wind
will be light and variable through 25/12Z, becoming easterly at
around 10-20 knots with occasional gusts thereafter. Sea breeze
variations may be observed today.


&&

.MARINE...Tranquil marine conditions with seas below 5 feet and light
to moderate winds up to 15 knots are expected across the regional
waters through early in the workweek. This will maintain
conditions below small craft advisory criteria. There is a
moderate risk of rip currents across the northern, eastern and
southeastern beaches of the islands. Passing showers will affect
the local waters for the next several days.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 88 73 86 74 / 30 50 50 30
STT 87 75 85 73 / 30 50 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
455 AM AST Mon Apr 26 2021

.SYNOPSIS...
A wetter pattern is expected this week with weather conditions
becoming favorable for shower and thunderstorm activity,
especially from Tuesday through the end of the workweek. Rainfall
activity may result in urban and small stream flooding these days.
Marine conditions will remain tranquil through much of the week,
although with a moderate rip current risk for some beaches.

&&

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

A patch of moisture will move through the local islands today.
However, the increase in moisture is not expected to be as much as
the model guidance was suggesting in the past couple of days. That
said, scattered showers are forecast through the day across eastern
PR and the USVI, while locally numerous showers are forecast across
the northwestern quadrant of PR this afternoon. Some of the showers
this afternoon could persist over urban areas and cause minor
flooding. Patches of drier air move in this evening, causing a
slight decrease in the shower activity, but a more significant
increase in moisture is expected for Tuesday. Thunderstorms are
possible on Tuesday, especially starting in the afternoon hours as a
mid and upper level troughs would be in a favorable area for local
instability. The unstable conditions may persist for most of the
workweek thereafter, and scattered to locally numerous showers with
isolated thunderstorms are forecast across different sections of the
local area on Wednesday as well. It will be possible to observe
areas with urban flooding each of the afternoons in the short term
forecast period.

As far as temperatures go, highs in the upper 80s and around 90
degrees are expected today across the lower elevations today, with
the higher elevations observing highs in the low to mid 80s.
However, a significant increase in cloud cover is expected on
Tuesday and Wednesday, and based on the latest guidance, the lower
elevations could observe high temps in the low to mid 80s.

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

The long-term period will be mostly wet and unsettled as a result of
moisture convergence in the low-levels, and persistent mid to upper-
level moisture over the region particularly for the end of the
workweek. The low-level moisture is a result of remnants of a
frontal boundary and easterly disturbance. Latest GFS run keeps
precipitable water values around 1.50 to 1.76 through the entire
long-term period with an occasional drop to 1.36 inches on Saturday
early morning.

The upper trough and sub-tropical jet will continue enhancing upper-
level divergence over the forecast area. Also, the upper-level
divergence will cause the upper-levels of the atmosphere to be
unstable thus conducive for thunderstorm development especially
during each afternoon when combined with local effects. Both GFS and
ECMWF have the trough deepening into a cut-off low between Thursday
and Friday inducing a low-level trough. This will shift low-level
winds to more southeasterly which in turn cause moisture pulling
from the south possibly extending the effects of the trough across
the region. GFS again is more bullish maintaining a wetter
weekend than ECMWF, the latter showing a quicker dissipation with
the bulk of moisture slightly eastern than GFS. However, it seems
that shower and thunderstorm activity could extend through Monday
with lesser intensity each day as the trough pulls away.

To sum up, the combination of moisture availability through most of
the atmospheric column and instability aloft combining with local
and diurnal effects will cause wet and unsettled weather conditions
across the region through at least Saturday. Additionally, deep
moisture convection could lead to urban and small stream flooding
across many areas especially during the afternoon. As a result of
model discrepancies regarding the final evolution of the cut-off
low, the forecast at this time is low for Sunday onwards.


&&

.AVIATION...SHRA expected across the local flying area, but VFR
conditions expected across the local terminals today. That said,
VCSH expected for TJSJ, TIST, and TISX today. SHRA to develop after
26/17Z across northwestern PR, that could cause VCSH at TJBQ this
afternoon, perhaps even TEMPO SHRA at TJBQ. Wind will be light and
variable through 26/12Z, then from the E-ESE at around 10 knots with
occasional gusts and sea breeze variations.


&&

.MARINE...Seas up to 5 feet are expected for the Atlantic waters and local
passages, with seas up to 4 feet elsewhere. These conditions should
continue for the next several days. There is a moderate rip current
risk for most of the local beaches.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 89 74 84 74 / 50 30 60 60
STT 84 73 84 72 / 40 50 50 60

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
503 AM AST Tue Apr 27 2021

.SYNOPSIS...A mid-to-upper level trough will promote unstable
conditions across the region during the next several days.
Thunderstorms are forecast for today through Friday, the most
active days are currently expected for Wednesday and Thursday.
Urban and small stream flooding can be expected with this
activity. Moderate risk of rip currents continue across the
northern and eastern beaches of the islands.

&&

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

A rather complicated forecast in for the short term period, with
slightly lower confidence than normal for this time period, as the
latest model guidance appears to be slightly warmer and drier than
was the case over the past couple of days.

A deepening trough in the mid and upper levels will provide
sufficient instability from this afternoon through Thursday to cause
the development of thunderstorms across the local islands. This in
combination with an increase in moisture and combining with the
local effects, could cause some areas with persistent rainfall, some
of which could be heavy at times. The overall picture looks like a
change to a more unsettled weather pattern is in store for the local
islands for the rest of this week. However, the latest model
guidance does not look as exceptional as it did over the past few
days. To start, the increase in moisture expected, according to the
00Z GFS would bring precipitable water up to the 1.5 to 1.6 inch
range, which is very near average for this time of year, the
instability profile looks decent but not exceptional. Some questions
have arisen about the possibility of small hail in isolated areas
with the strongest thunderstorms on Wednesday and Thursday, mainly
because of the very cold 500mb temps, close to -11C on Wednesday
into Thursday, and the relatively low heights of the freezing level
and wet bulb zero. But, considering the latest forecast soundings,
the jury is still out on that, though certainly in the realm of
possibilities and not to rule it out at all, but the CAPE is
unimpressive, and while other instability parameters look good,
again, not particularly impressive. Make no mistake, showers and
thunderstorms, some with heavy rainfall are expected starting this
afternoon and especially through the late morning and afternoon
hours of Wednesday and Thursday. However, to say more than that
would be difficult at this time. We will continue to monitor the
situation closely. That said, some areas will likely observe urban
and small stream flooding while others, including the USVI, could
observe ponding of water on roadways and poor drainage areas with
the shower activity expected over the short term period.

As far as temperatures go, the models have adjusted to less cloud
coverage than was expected before, so today`s highs will be in the
mid to upper 80s across the lower elevations today, with the higher
elevations observing highs in the low 80s. However, high temps in
the low to mid 80s are forecast on Wednesday and Thursday.

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

An unstable weather pattern is forecast to continue through the long-
term period due to low level moisture convergence produced by
remnants of a frontal boundary and easterly disturbances embedded in
the trades, along with continued mid to upper-level instability
supported by a jet maxima which will round the base of the
amplifying upper trough. Both GFS and ECMWF continue to suggest
further amplification of the upper trough into a closed cut-off low
on Friday that will stall close to the forecast area and slowly pull
away eastward. While doing so, both models continue showing the
induced surface low pulling moisture from the south maintaining
low-level moisture convergence through the weekend. Model
guidance suggests temperatures at 500 mb to still be close to -9
degrees celsius on Friday and steadily decline through Tuesday
promoting favorable conditions aloft for thunderstorm activity.

Although models still remain in disagreement as far as the
overall final evolution of the upper level trough, all suggest a
fairly moist and unstable weather conditions through the weekend.
Current guidance still maintains precipitable water values between
1.5 to 1.7 inches through most of the period. The best potential
for increased and enhanced convective development still looks like
Friday afternoon through Saturday. There still exists a high
uncertainty for the early part of next week depending how quickly
the upper low pulls away while a high pressure ridge builds aloft.

All in all, the overall expected persistence of somewhat deep
layered moisture and convection development over the islands may
lead to urban and small stream flooding across many areas each
afternoon, at least through the weekend. Continue to follow this
discussion as we keep monitoring the expected weather pattern.

&&

.AVIATION...SHRA expected across the local flying area, but VFR
conditions are still expected across the local terminals today. That
said, VCSH expected for TJSJ, TIST, and TISX. SHRA/TSRA to develop
after 27/17Z could cause VCSH/VCTS at TJPS and TJSJ. CIGs at around
FL060-080 possible today. Wind will be light and variable through
26/12Z, then from the east at around 10 knots with occasional gusts
and sea breeze variations.


&&

.MARINE...Relative tranquil marine conditions are expected to
prevail across the regional waters during the next several days.
However, marine conditions will become somewhat choppy for a short
period of time tomorrow especially over the Anegada Passage where
seas up to 6 feet are expected. East winds will momentarily increase
to 20 kts tomorrow, but overall will continue at 10-15 kts for most
of the workweek. The risk of isolated thunderstorms will increase
tomorrow through the rest of the week across the coastal waters,
which could turn seas dangerous locally. A moderate risk of rip
currents is expected across the northern and eastern beaches of the
islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 73 83 73 / 50 60 60 30
STT 86 73 84 72 / 50 60 60 60

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
455 AM AST Wed Apr 28 2021

.SYNOPSIS...Increasing instability aloft from a digging upper
level trough and enhanced low-level moisture convergence will
promote a generally unsettled weather pattern, with the potential
for thunderstorm development, during the next several days. As a
result, a threat for urban and small stream flooding can be
expected with this activity. Increasing winds will generate
somewhat choppy marine conditions, but seas will remain below
small craft advisory criteria. Moderate risk of rip currents
continues across the northern, eastern, and southeastern beaches
of the islands.


&&

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

An unsettled weather pattern is expected today, the models are
significantly different in this latest 28/00Z run compared to this
time yesterday, indicating for a much drier Thursday in the latest
model run. Today looks like the most active day, with thunderstorms
in the forecast that could lead to urban and small stream flooding
in several sectors of PR, especially across some areas of the San
Juan metro, as well as central and W-SW PR. The USVI is expected
to observe shower activity with nearby thunderstorms also, which
may cause minor flooding or ponding of water in poor drainage
areas.

A deepening trough in the mid and upper levels and an increase in
moisture will provide sufficient instability today through late
tonight or very early Thursday, causing the development of
thunderstorms across the local islands. The areas with the most
persistent showers and thunderstorms are expected to be across
portions of the San Juan Metro, central PR and portions of W-SW PR
due to the combination of the weather pattern and the local
effects observed in PR. The latest global and hi-res models are
now suggesting lower rainfall amounts for today, but given the
fact that they under-estimated yesterday`s rainfall, and the
overall pattern still would suggest active weather, we are still
forecasting numerous showers and isolated thunderstorms across the
aforementioned areas. With the expected rainfall, urban and small
stream flooding can be expected across several sectors of Puerto
Rico by this afternoon and evening. As far as the USVI is
concerned, showers and thunderstorms in the general area are also
expected, but it is expected to be with a shorter duration, and
perhaps intermittently, so ponding of water in some areas, to
minor flooding in areas of poor drainage is what seems most likely
at this time, though more significant flooding would be possible
if more rain than expected is observed, there is some degree of
uncertainty with this event.

The details for today are that, the latest guidance has higher
moisture forecast, near 1.8 inches of precipitable water, the 500mb
temp will be at its coldest this afternoon with a temp around -11.5C,
the axis of the mid and upper level troughs will be to our WNW.
All of these parameters are conducive to thunderstorms over the
local area. That said, CAPE is expected to be good, but not
particularly impressive, peaking at around 1600 and a Lifted Index
of no less than -6, which is also not too impressive but still a
measure of decent instability. This is all using the model
guidance, so a more thorough assessment of today`s instability
will be done after the 28/12Z sounding this morning.

Perhaps one of the most interesting things in the short term
forecast was how drastically the models dried up for Thursday. The
GFS model is now forecasting below normal moisture and a rainfall
pattern consistent with those of locally induced showers and
thunderstorms over PR. Depending on how much it rains today across
central and western PR, the rainfall on Thursday, although not
impressive, it may still cause some flooding since some soils may be
saturated by then. The models are also suggesting that Friday will
be similar to Thursday, but with a higher moisture content. That
said, we will still have an upper trough in the area, which may mean
that the models may be under-estimating the rainfall total. This has
been a difficult event to forecast, and confidence is lower than
normal.

As far as temperatures go, highs will be mainly in the mid 80s
across the lower elevations, upper 70s to low 80s across the higher
elevations.

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

The 00Z GFS run now is in somewhat more agreement with latest
ECMWF regarding the final stages of the upper trough showing a
less active weekend than previous model runs. For Saturday, both
models develop the upper trough into two short wave troughs; one a
strong closed cut-off low located northeast of the Caribbean and
another closed cut-off low south or close to La Hispaniola.
Temperatures at 500 mb would be close to -6 degrees Celsius, less
conducive for thunderstorm activity. Models now put the plume of
moisture from the south pulled by the induced surface trough
furthest east diminishing moisture convergence over the area. This
is corroborated with the Galvez- Davison Index where it is now
suggesting a few isolated thunderstorms for Saturday afternoon
over the west of Puerto Rico mainly owed to lingering moisture and
diurnal heating.

Meanwhile an upper-level ridge is building that will eventually
push the northern most cut-off low eastward. Regarding the
southern most cut-off low, some discrepancies arise with both
models with the upper ridge completely (partly) eroding the cut-
off low in ECMWF (GFS) by Sunday morning. Shower activity
especially for the U.S. Virgin islands and eastern Puerto Rico
will heavily depend on the development of this closed cut-off low
and moisture availability on Sunday. Given that global models are
still struggling with the development of the upper-level trough,
forecast confidence for this weekend is still low to moderate.

Having said that, it seems that conditions will improve by early
next week as the upper trough pulls away and the ridge aloft
continues to build overhead. This will result in a decrease in
shower activity across the area. However, patches of moisture
will be advected from time-to-time to result in some passing
showers across eastern portions of PR and the U.S. Virgin Islands
during overnight and morning hours followed by more enhanced
showers across interior and western portions of Puerto Rico during
the afternoon hours due to daytime heating and local effects.
This activity will be shallow in nature, therefore no significant
accumulations are expected. This ridging pattern is expected to
hold through Wednesday.


&&

.AVIATION...SHRA expected across the local flying area, but VFR
conditions are still expected across the local terminals today. That
said, VCSH is expected for most of the local terminals, and SHRA
will be observed from time to time at the terminals. VCTS is
possible across the local terminals after 28/16Z. CIGs at around
FL040-070 possible today. Wind will be light and variable through
28/12Z, then from the east at around 10-15 knots with sea breeze
variations and some gusts, especially near SHRA and TSRA.


&&

.MARINE...Tranquil marine conditions are expected to prevail
across the local waters during the next several days. Increasing
winds up to 20 knots will generate somewhat choppy conditions, but
seas will remain below small craft criteria. However, they should
exercise caution due to the possibility of observing thunderstorms
across the local waters, which may produce hazardous marine
conditions. A moderate risk of rip currents is expected across
the northern, eastern and southeastern beaches of the islands.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 85 74 / 60 60 50 50
STT 84 73 86 73 / 60 60 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
405 AM AST Thu Apr 29 2021

.SYNOPSIS...
Amplified mid-upper trough with strong upper jet max, deep layered
moisture, and low level convergence are all in place to maintain
a moist and unstable environment today through at least Friday.
Lesser upper dynamics by Saturday but still good moisture pooling
for locally induced convection over the weekend. Mariners should
exercise caution over the Caribbean waters and Anegada Passage due
to choppy marine conditions.

&&

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

The high amplitude mid to upper level trough with the base now
extending southwest across Puerto Rico, and the upper level jet
max just east of the U.S. Virgin islands over the northern Leeward
islands, will continue to slowly lift northeastward through Friday.
This instability aloft along with deep layered moisture and good
low level convergence associated with the induced low level trough,
will maintain a moist and unstable environment through Friday with
a gradual improvement expected by Saturday.

For the rest of the overnight and into the morning hours, showers
and isolated thunderstorms will continue to affect the local waters
and portions of the coastal areas of the islands from time to time.
However,most of the activity should be over the coastal waters and
between eastern Puerto Rico and the U.S. Virgin Islands. Rainfall
in these areas will be moderate to locally heavy at times and may
reach the coastal areas from time to time. For the rest of the
day, as cloud cover diminishes, expect another active afternoon
with increasing flood potential due to saturated soils, local and
diurnal effects and the instability aloft. Mudslides in areas of
steep terrain will also be possible. Recent GFS model guidance
which now initialized well with the placement of the upper level
feature and the present weather pattern, both suggest that this
unstable weather pattern will persist through at least Friday,
although a gradual depletion of low level moisture is expected.
This in turn should begin to limit widespread convection across
the local islands. On Saturday, winds are forecast to become more
easterly, and the mid to upper level trough should continue to
weaken while lifting northwards. This should then result in
increasing stability aloft as the forecast area becomes situated
on the subsident side of the upper trough. However, local and
diurnal effects and available moisture will support afternoon
convection, some of which may still lead to minor urban and small
stream flooding as well as ponding of water on roadways and in
poor drainage areas.

.LONG TERM...Sunday through Thursday

The long term forecast looks like the transition term between the
unstable to a more typical weather pattern. As both model guidances
agree, the upper level trough will continue to move out of the region,
pushed by a building mid to upper level ridge located over the western
Atlantic. On Sunday, GFS model guidance localizes the upper level axis
just at east of the Island, leaving the maxima jet just at our southeast
near the U.S Virgin Islands. That being said, for Sunday, only a slightly
unstable pattern will prevail with shower activity and still the
possibility of isolated afternoon thunderstorms.

An improvement in weather conditions will begin next week as the
mid-level ridge continues to sink into the Central Atlantic. This
ridge will provide more stable conditions aloft, limiting the
potential for long life and widespread shower activity over the
forecast area. However, low-level patches of moisture embedded in
the trade winds combined with the local effects could result in
goods rounds of showers activity, mostly over western sections of
Puerto Rico. If model guidance is correct, the best days for
shower activity are Monday into late Tuesday.

As the high surface pressure shifts more into the central-east
Atlantic, drier airmass will filter into the region. The drier air
mass combined with the stable conditions aloft and a northeast
low level wind flow, will result in less potential for a
widespread shower activity. As a result, afternoon convection, if
any, is expected to drift mainly over western and southwestern
sections of Puerto Rico.


&&

.AVIATION...VFR conditions expected most TAF sites, except for TISX
where SHRA/VCTS will be psbl til at least 29/10Z. Thereafter,
VCSH are expected for TJSJ, TJBQ, USVI and Leeward terminals
through 29/14Z. This may result in brief MVFR conds with reduced
visibility and SCT-BKN lyrs nr FL025...FL050...FL090. Aftn
convection will bring another round of SHRA/Isold TSRA mainly at
TJSJ, TJBQ and TJPS between 29/16-22Z. Winds will be calm to light
and variable...bcmg fm E at 10-20 knots aft 29/14Z.

&&

.MARINE...
An upper level trough will continue to generate showers, with
isolated thunderstorms and areas of heavy rainfall on occasions
over the local waters. Mariners should exercise caution over the
exposed waters for the next few days. Choppy marine conditions
will prevail for some of the local waters due to moderate to fresh
easterly winds the next several days. Therefore, small craft operators
should exercise caution. There is a moderate risk of rip current for
the northern beaches of Puerto Rico, beaches over Culebra and Vieques,
and St. Croix as well.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 86 76 / 40 40 70 40
STT 84 74 85 74 / 40 40 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
434 AM AST Fri Apr 30 2021

.SYNOPSIS...
Shower activity and isolated thunderstorms will continue today as
the upper level trough moves out of the forecast area. There is a
potential for minor flooding over the interior and western
sections of the Island. Tranquil marine conditions will continue
with seas between 2 to 5 feet across all the local waters.

&&

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

A mid to upper trough will continue to meander and extend aross the
region today through Saturday while gradually weakening and lifting
northeastward. It is then forecast to be replaced by an upper level
ridge which will build across the region from the west on Sunday,
resulting in increasing stability aloft and a continued drying of
the mid to upper levels.

In the meantime, the proximity and placement of the upper trough
along with the available moisture in place today, will support
shower development over the coastal waters during the rest of the
morning hours. Some showers will reach the coastal areas of the
islands from time to time and bring periods of moderate to locally
heavy rains. Afternoon convection will again be likely due to good
moisture convergence, local effects and the influence of the mid
to upper trough. Urban an small stream flooding as well as ponding
of water on roadways and in poor drainage will again be likely
with the expected isolated thunderstorms activity and locally
heavy rains. In addition, the already saturated and loose soils
in areas of steep terrain may also cause mudslides.

On Saturday recent model guidance all suggest a slow but gradual
drying trend along with weakening of the upper trough. However,
still expect sufficient trade wind moisture transport across the
region to support early morning passing showers, followed by
locally and diurnally induced afternoon convection. The activity
should be focused more over the interior and west to southwest
sections of Puerto Rico as low level winds are forecast to become
more east northeast by then.

By Sunday, a continued filling/weakening of the upper trough is
forecast, as well as the erosion of low level moisture with the
layered precipitable water values so far forecast to decrease and
range between 1.00-1.50 inches. In addition, low level winds are
expected to become more northeasterly as well as the a gradual
strengthening of the trade wind cap inversion as the ridge builds
aloft. Therefore, expect a more typical daytime weather pattern
with a mostly fair weather pattern to prevail except for some
locally and diurnally induced afternoon convection mainly over the
interior and west to southwest sections of Puerto Rico. Elsewhere
including around the U. S. Virgin Islands, expect mostly isolated
afternoon showers if any which should be mainly on the west end
or just downwind of the islands.

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

Both model guidance suggests a mid to upper ridge and the
associated surface high pressure dominating the local weather
pattern for a most long-term period. As a result, an improvement
in weather conditions is expected on Monday due to the stable
conditions aloft and a relatively drier environment. On the other
side, for Tuesday, the GFS precipitable water model suggests
slightly increased moisture over the region. If model guidance is
correct, Tuesday afternoon looks quite active, mainly for the
interior and western sections of the Island.

As the surface ridge moves more into the central Atlantic,
beginning on Wednesday, relatively drier air will filter into the
region with some patches of low level clouds and moisture. Those
patches will slightly increase the potential for shower activity
but only in the afternoon hours combined with the local effects
due to the stable conditions aloft. As a result, ponding of water
in roadways and poor drainage areas could be possibles.

A lighter of uncertainty enters the last parts of the long term
with an upper-level trough near the Atlantic waters for Thursday
into Friday. According to the latest model guidance, the solution
for this feature mentioned above, has different for both models.
In the GFS, the upper level trough looks like it will move closely
to the Atlantic waters more on Thursday. Besides, the ECMWF
solution has the upper level trough more into Friday and a little
farther away from the forecast area. This discrepancy will turn
low the confidence on how the weather pattern will be affected on
Thursday into Friday. So far today, Thursday into Friday looks
with the typical pattern of afternoon convection mostly over
northwestern sections of Puerto Rico due to the south component in
winds as the surface ridge moves into the eastern Atlantic.


&&

.AVIATION...
SCT ocnl bkn lyrs nr FL025..FL040 en route btw islands with BKN-
OVC lyrs nr FL250 between the USVI and the Nrn Leeward Islands
due to the proximity of the upper level trough. Few tops nr FL160
w/SCT SHRA and brief MVFR psbl ovr the Atl waters and en route
btw PR and the Lesser Antilles durg prd. VCSH will be psbl at
TJSJ/TISX/TIST/TJNR til 30/14Z with Mtn top obscr psbl ovr Ern PR
due to low cld lyrs and -SHRA. SFC wnds calm to lgt/vrb bcmg fm
E-NE 10-15 kts with ocnl hir gusts and sea breeze variation aft
30/14Z.

&&

.MARINE...
Tranquil marine conditions will prevail with seas between 2 to 5
feet across the local waters for the next several days. There is a
moderate risk of rip current for the northern beaches of Puerto
Rico, beaches over Culebra and Vieques, and St. Croix as well.
Shower activity is forecast to continue over the local waters as
the upper level trough moves out of the region today.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 75 87 77 / 70 40 40 30
STT 86 75 86 75 / 40 30 30 30

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
429 AM AST Sat May 1 2021

.SYNOPSIS...
Mid to upper level trough with axis extending southwest across Puerto
Rico will continue to gradually weaken while lifting northeast across
Puerto Rico today through Sunday, as a high pressure ridge will build
and spread across the region from the southwest Atlantic. Surface high
pressure over the central and northeast Atlantic will be reinforced
by another high pressure forecast to enter and spread across the
southwest Atlantic. This in turn will maintain moderate east northeast
trade winds. The moderate trades will continue to bring fragments of
shallow trade wind moisture across the region from time to time during
the period.

&&

.SHORT TERM...Today through Monday

Weather conditions will continue to gradually improve as the
upper level trough now with the axis over the region continues to
move more eastward out of the region. That said, unstable weather
conditions will persist today. This upper level feature will
continue to induced brief passing showers across the local waters
and the islands at times in the morning and evening hours. Then,
due to the local effects and the available moisture, afternoon
convection will develop mainly across the interior and western
sections of Puerto Rico. Given the proximity of the upper level
trough, cold temperatures at 500 MB between -7 to -6 degrees C
will maintain the treat for isolated thunderstorms with the
heaviest rainfall activity over interior and western sections of
Puerto Rico this afternoon.

Meanwhile, a building high pressure in the mid to upper levels and the
associated surface ridge will relocate over the region by Sunday. Model
guidance at this moment suggests stable conditions aloft for the
forecast area. In addition, as the surface high pressure moves more
into the Central Atlantic, a drier airmass will filter into the region,
limiting the widespread shower activity. However, afternoon convection
is forecast primarily in the afternoon hours for western and interior
sections of the Island. Elsewhere including around the U.S.Virgin
Islands, expect mostly isolated afternoon showers, if any, and should
be mainly on the west end or just downwind of the islands.

.LONG TERM...Tuesday through Sunday

Based on recent model guidance...A mid to upper ridge along with the
a strong surface high pressure spread across the central and northeast
Atlantic, will continue to dominate the low weather pattern for
most of the period. Therefore at least through Wednesday the moderate
trade winds mainly from the east northeast will bring occasional patches
of shallow moisture across the region from time to time during the
early morning hours. On Tuesday and Wednesday expect locally and
diurnally induced afternoon shower activity to be focused mainly
over the central interior and west to southwest section of Puerto
Rico with lesser activity elsewhere including the U.S. Virgin
Islands. Some of the afternoon shower activity may cause minor
ponding of water on roadways and in poor drainage areas but no
widespread rainfall is forecast so far.

By Thursday and Friday winds become more east southeast and tropical
moisture returns accompanying a weak easterly perturbation. This
increasing moisture along with the approach of an upper level trough,
will erode the ridge aloft and favor unstable condition. As a result,
expect a better chance for overnight showers with increased potential
for enhanced afternoon convection mainly over the central and west
to northwest sections of Puerto Rico as well as around parts of
the San Juan metro and the U.S.Virgin islands. Urban and small
stream flooding will be possible with the heavy rainfall.

By the following weekend, conditions are forecast to gradually improve
as the ridge will build aloft and the mid to upper trough should lift
further northeastward and away form the region. Local surface winds
by then forecast are again forecast to become more northeasterly with
a somewhat drier airmass so far expected to filter in across the region
with Sunday being the driest day and lesser chance for widespread or
significant rainfall accumulations.

&&

.AVIATION...
VFR conds durg prd at all TAF sites. wdly SCT SHRA ovr regional waters
and en route btw islands. SCT ocnl BKN lyrs nr FL025...FL050 mainly
ovr regional waters,,,mstly SKC ovr land areas. VCSH psbl at
TJSJ/TJPS/TISX/TIST til 01/12Z with Brief Mtn TOP obscr ovr E PR
due to low passing CLDS/-RA. Aftn SHRA/Isold TSRA psbl ovr
interior and W pr fm 01/16Z-01/22Z. SFC wnds calm to lgt/vrb bcmg
fm E-NE 10-15 kts aft 01/14Z with sea breeze variations.

&&

.MARINE...The moderate east northeast trade winds will persist with
overall tranquil seas forecast to continue across the regional waters
and local passages through the period. However a light winds chop will
remain possible over the offshore waters and local passages.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 77 87 77 / 40 20 30 20
STT 86 75 87 76 / 30 20 30 30

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
459 AM AST Sun May 2 2021

.SYNOPSIS...A building mid and upper-level ridge today will promote
dry and stable conditions aloft, which will persist through the middle
of next week. Surface high pressure will dominate the local weather
pattern. Shower activity will therefore be limited to early morning
trade wind showers from time to time. This will be followed by locally
and diurnally induced afternoon shower development mainly over parts
of the interior and west sections of Puerto Rico, with mostly fair
weather and sunny skies to prevail elsewhere. Overall tranquil seas
will continue during the next several days.

&&

.SHORT TERM...Today through Tuesday

The combination of a building mid and an upper-level ridge with a
drier airmass filtering in during the morning hours will result
in fair weather conditions across Puerto Rico and the U.S. Virgin
Islands. The presence of the ridge will create stable conditions
aloft, limiting the widespread shower activity. However, the
daytime heating and the available moisture should result in
shower activity over the western and interior sections of Puerto
Rico. The Galvez Davidson Index (GDI) is near five today. Therefore
there is only a slight threat for isolated thunderstorms with the
heaviest activity. Minor flooding and ponding of water on roadways
will be possible with the afternoon activity. Elsewhere, including
the USVI, mainly fair weather conditions with just a few showers
are expected.

On Monday into Tuesday, model guidance suggests the mid to upper
level ridge and the associated surface high pressure will dominate
the forecast area for the latter part of the short term period.
These stable conditions aloft with some moisture break should
result in a mixture of clear skies and occasional cloudiness with
passing showers in the morning hours. During the afternoon hours,
shower activity mainly over the interior and west sections of
Puerto rico may result in ponding water in roadways and poor
drainage areas.


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

A strong surface high pressure will spread across the central and
northeast Atlantic, will continue to dominate the low weather pattern
at least through Wednesday. The moderate east-northeast trade winds
will bring occasional patches of shallow moisture across the region
from time to time. During the afternoon expect locally and diurnally
induced afternoon shower activity to be focused mainly over the central
interior and west to southwest sections of Puerto Rico. Lesser shower
activity is expected elsewhere including around the U.S. Virgin Islands.
Some afternoon shower activity may cause minor ponding of water on
roadways and in poor drainage areas over the interior and west section
of PR but no widespread rainfall is forecast so far.

By Thursday and Friday winds become more east southeast and tropical
moisture returns accompanying a weak easterly perturbation. This
increasing moisture along with the approach of an upper level trough,
will erode the ridge aloft and favor unstable conditions. As a result,
expect a better chance for overnight showers and increased potential
for enhanced afternoon convection, mainly over the interior and
west to northwest sections of Puerto Rico, as well as around the
San Juan metro and on the west end-and downwind of the U.S.Virgin
islands. Urban and small stream flooding will be possible with
the heavy rainfall.

By late Saturday and on Sunday, conditions are forecast to gradually
improve as the ridge aloft will hold and the mid to upper trough
should lift northeastward and away from the region. Local surface
winds by then are again forecast to become more east northeast
with a somewhat drier airmass expected to filter in across the
region with Sunday being the driest day. By Monday, based on recent
model guidance, expect increasing tropical moisture and instability
aloft across the region with the approach of an easterly wave and
an upper trough. Consequently, there will be better chance for morning
and afternoon shower development with periods of locally heavy
rains. Stay tuned as we will continue to monitor and see how this
pattern unfolds.

&&

.AVIATION...VFR conditions are expected for all TAF sites for the
forecast period. Some VCSH is expected over the TJPS btw 02/16Z
to 02/22Z. Winds will continue VRB at 5 knots or less with land
breeze variation, and then by 02/12z, winds will increase from
E-NE with sea breeze variation btw 10-15 knots.

&&

.MARINE...Tranquil seas up to 4 feet expected today. Winds will
be between 10-15 knots with a ht and Sunday. Late Monday into
Tuesday a slight increase in seas is still expected due to a
small northerly swell. There is a moderate risk of rip currents
across northern PR and Culebra as well as portions of the north
and eastern beaches of St Croix. There is a low risk elsewhere.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 76 86 77 / 30 20 30 20
STT 87 76 88 76 / 20 30 20 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
456 AM AST Mon May 3 2021

.SYNOPSIS...Relatively stable weather will be seen across the
region with showers developing across the local islands during the
afternoon. A surface high pressure north of Puerto Rico will
create easterly winds and advect patches of moisture periodically
over the local islands. Late this week an uptick in shower
activity is expected, then early next week unstable weather is
expected for Puerto Rico and the U.S. Virgin Islands.

&&

.SHORT TERM...Today through Wednesday...High pressure over the
central Atlantic at lower levels will continue to generate
moderate--locally fresh--trade winds through the period that will
carry patches of moisture across the area at fairly regular
intervals for night and morning showers in eastern Puerto Rico and
around the U.S Virgin Islands and afternoon showers in western
Puerto Rico during each afternoon. A weak short wave trough at
upper levels will cause weakness in the mid level pressures and
cooling of several degrees C on Wednesday which will increase the
chances of thunderstorms over western Puerto Rico during the
afternoon.

&&

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

Thursday and Friday, moderate east to southeast winds will pull
modest moisture across the local islands which will lead to
showers across portions of eastern and northern Puerto Rico,
Culebra, Vieques and the U.S. Virgin Islands. The uptick in
moisture coupled with local and diurnal effects will cause showers
and a slight chance thunderstorms across the interior, western,
and northwestern areas of Puerto Rico. The enhanced convection
will increase the likelihood for urban and small stream flooding
for the aforementioned areas.

Saturday and Sunday, The GFS moves a frontal boundary into the
western Atlantic waters on Saturday, which is forecast to slowly
deepen and create troughy conditions aloft north of Puerto Rico.
Guidance shows low-level moisture increasing throughout the day on
Saturday and peaking early Sunday morning at 1.7 inches. Weak
instability and increasing moisture will yield light to moderate
showers for most of Puerto Rico and the U.S. Virgin Islands.

Monday and Tuesday, a deluge of tropical moisture is expected to
effect the local islands due to an easterly perturbation moving
across the southern Caribbean waters. Additionally, an upper-level
trough is forecast to deepen to the north of Puerto Rico; the two
features will cause unstable weather conditions for most of the
region. Moderate to heavy rainfall and urban and small stream
flooding is expected. The GFS and EURO are in agreement with the
above scenario. The GFS cross-section shows relative humidities
ranging from 70 to 90 percent from 750 to 250 mb, this is
significant moisture throughout the atmospheric column that would
support the development of deep convection. Furthermore, global
models has 500 mb temperatures cooling to minus -7 to -8 degrees
celsius Monday through Tuesday.

&&

.AVIATION...VFR conds to prevail across the forecast area. Sct SHRA
across NE PR thru 03/16Z and dvlpg SHRA across wrn PR aft 03/16Z
will cause brief MVFR and mtn obscurations some that will affect
TJMZ/TJBQ. Sfc winds less than 10 knots in land breezes bcmg aft
03/14Z 10-15 kt with sea breeze influences. Max winds WNW 40-50 kt
btwn FL380-450.

&&

.MARINE...A northerly swell will cause seas to reach 6 feet
mainly across the Atlantic waters. Elsewhere, seas will range from
3 to 5 feet today. There is a moderate risk of rip currents
tonight across the north coast of PR and Culebra, eastern Vieques
and eastern Saint Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 77 88 77 / 40 60 60 60
STT 89 77 88 75 / 20 40 40 40