Caribbean - Central America Weather

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
436 AM AST Thu Mar 25 2021

.SYNOPSIS...A ridge over the southwestern Atlantic will promote
moderate east to northeast steering winds today. Winds will
increase gradually through the weekend into early next week as the
ridge moves north of the area. An upper level trough should remain
to our northeast, inducing a few trade wind perturbations through
at least Sunday. Drier mid-level air and more stable conditions
are expected through the first part of next week.


&&

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

We have seen some active weather over the past few days, yet
moisture content really has not been all that impressive. Rather, it
has been the presence of an upper-level trough that has acted to
enhance shower activity across the region, particularly in the
afternoon. However, that trough is moving away to the east and will
no longer be a factor. There will an upper-level low to our east for
the next few days that will maintain cooler temperatures aloft,
which is conducive for enhanced shower activity, but otherwise its
position relative to our region is not favorable for shower
enhancement. The moisture content however, will be below average the
next few days, and the mid-level troposphere in particular will be
very dry. Thus any shower activity will be driven by patches of low
level moisture that move in from time to time from the east.
Finally, surface high pressure to our north will strengthen,
resulting in breezy winds during the short term period, particularly
Friday and Saturday.

For today, only isolated showers are expected in the morning, with
scattered showers over southwest Puerto Rico in the afternoon. No
thunderstorms are expected. These showers may produce ponding of
water over roadways, but flooding is not expected. Breezy winds will
blow the showers over the southwest coastal waters, so boaters
should monitor conditions in the area this afternoon. Overnight,
isolated to scattered showers are possible, likely impacting the
northeast Puerto Rican coastal areas. More showers are likely for
Friday over southwest Puerto Rico in the afternoon, similar to
today. Low-level winds will be even stronger, so the quick moving
showers will likely be even less impactful than today.

Similarly for Saturday, moisture will be limited with a continuation
of east-northeast breezy winds. Scattered somewhat weak showers will
likely impact southwestern PR once again. One interesting note is
that the aforementioned upper-level trough that will reside to our
east the next few days may induce some showers and possibly isolated
thunderstorms out near the Leeward Islands and possibly the USVI
Saturday and into Saturday night. At this point the trough influence
does not look like it will extend to Puerto Rico, but this will be
monitored in subsequent forecasts.

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

A TUTT induced low-level perturbation is expected to move from
the east across the region on Sunday. Precipitable water content
is expected to peak to around 1.40 inches through the day,
favoring early morning showers across the U.S. Virgin Islands and
eastern Puerto Rico. However, the 500 mb temperature is expected
to warm to around -6.5C and trade winds will increase to around
20-25 kt, these two factors will limit the vertical development of
the afternoon showers over western PR and flooding is not
anticipated.

For the rest of the workweek, a drying trend is currently expected
as an upper level ridge over the western Caribbean promotes
convergence aloft and the trade wind cap intensifies across the
northeastern Caribbean. Therefore, fair weather conditions are
expected at this moment across the islands, with mostly light
rainfall amounts in diurnal shower activity through the long term
period.


&&

.AVIATION...Mostly VFR conds expected during prd. VCSH posible
through 25/14z for TJSJ/TIST, with a smaller chance for
TIST/TNCM/TKPK. Afternoon SHRA possible near TJMZ. SFC wnds will be
light and variable bcmg fm E-NE between 10-15 kts with sea breeze
variations aft 25/14Z.


&&

.MARINE...Relative tranquil seas are expected during the next day
or so, with seas ranging mainly from 3 to 5 feet. East winds will
continue at 10-15 kts in general today, with higher winds across
the southern coastal waters due to the sea breeze. Winds and seas
will gradually increase during the weekend, and small craft
operators should exercise caution across most of the regional
waters. There is a moderate risk of rip currents across most of
the east and north facing beaches of Puerto Rico and St. Croix,
and across the northwestern beaches of St. Thomas.


&&

.FIRE WEATHER...A Fire Danger Statement(RFDSJU) was issued for
the southern coastal plains today. The relative humidity is
forecast to drop around 45% across the southeastern coastal plains,
and moderate easterly winds are expected during the day. The KBDI
was above 600 yesterday at Camp Santiago.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 75 85 75 / 30 30 40 50
STT 85 73 85 74 / 30 30 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Fri Mar 26 2021

.SYNOPSIS...Scattered trade wind showers will continue across the
region through the weekend. Providing low-level moisture for
afternoon shower development over west/southwestern PR. Winds and
seas will continue to gradually increase through early next week.
Drier conditions are currently expected through much of next week.


&&

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

Despite below average precipitable water values across the region
this morning, fast-moving scattered showers have been observed over
the local waters and impacting northern and eastern Puerto Rico, as
well as the USVI. Many of these showers are producing brief moderate
to heavy rain, and seem to be enhanced by the upper-level low to our
northeast, whose trough resides over the region. The sounding from
earlier this evening measured a 500mb temperature of near -10C, a
full degree colder than what the GFS model suggested. Given that
conditions will not change much into the afternoon, it is likely
that fast moving moderate to heavy showers will impact western and
southwestern Puerto Rico, and it is even possible that some
lightning is associated with some of the most vigorous showers.
However, there is very dry air at mid-levels that should hinder the
development of thunderstorms. Flooding is not expected due to the
dry air aloft and fast low-level winds that will keep showers moving
along. However, there will likely be some areas where persistent
showers occur, leading to ponding water over roadways and low-lying
areas.

Conditions do not really change much into tomorrow. The upper level
trough will still be there. Surface high pressure to our north will
continue to help produce breezy east-northeasterly winds. Moisture
content will remain uninspiring, yet continue to be enhanced by
upper-level atmospheric conditions. Thus more scattered showers are
expected overnight tonight and into tomorrow, again impacting
primarily eastern and northern Puerto Rico. Afternoon showers will
again be expected for southwestern Puerto Rico. By Sunday, the upper-
level trough will move off towards the east, yet moisture from the
trough will decouple from it and move towards us. So better moisture
is expected for Sunday, which will once again lead to morning
showers for north and east Puerto Rico and afternoon showers for
western Puerto Rico. Ponding water is again possible for both
Saturday and Sunday afternoon in southwestern and western Puerto
Rico. Winds will remain breezy with gusty winds up to 30 mph
associated with the showers.

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

The upper-level trough should move further east of the Leeward
Islands on Monday and an upper-level ridge pattern is forecast to
hold aloft through the end of the workweek. A 700 mb ridge over
the southwestern Atlantic will promote brisk northeasterly winds
and drier air will filter across the region from Tuesday through
at least Friday. This should promote an overall fair weather
pattern across the islands. Also, precipitable water content is
currently forecast to remain below normal values through Thursday,
with a slight increase by late Friday.

Overall, a cool advective pattern will bring the occasional trade
wind showers across portions of the USVI and east/northeast PR
during the overnight/early morning hours...followed by shallow
afternoon convection over portions of west/southwest PR each day.
Across the USVI, streamers with light rainfall amounts are
expected to develop off the islands. Breezy conditions are
forecast for Tuesday and Wednesday, with latest guidance
suggesting 20-25 kt trades across the region.


&&

.AVIATION...Mostly VRF conds expected with fast-moving VCSH for
TJSJ/TIST/TISX/TNCM/TKPK through 26/14z. In the afternoon, SHRA
possible for TJMZ. Winds from the ENE continue at 5 to 13 kts, with
gusty winds associated with the passing SHRA. Winds increase to 10
to 20 kts after 26/14z, with gusts to 25 to 30 kts.


&&

.MARINE...As winds increase during the next few days across the
regional waters, choppy seas up to 6 feet are expected through at
least Saturday and increasing up to 7 feet from Sunday and onwards
through much of next week across the offshore waters and
passages. East to northeast trades should continue through the
weekend at 15-20 kt, with higher gusts. A moderate risk of rip
currents will continue for all the islands for the next several
days. The risk is expected to be high on Monday across the
northern beaches of Puerto Rico.


&&

.FIRE WEATHER...A Fire Danger Statement (RFDSJU) was issued for
the southern coastal plains today, due to the expected low RH`s
and moderate to strong winds across these areas.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 85 75 / 60 50 50 50
STT 85 74 85 74 / 50 50 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
451 AM AST Sat Mar 27 2021

.SYNOPSIS...

A generally typical weather pattern will persist across the region
over the next several days. However, relatively strong winds will
help to carry patches of moisture across the region, aiding in
sustaining passing shower activity. On the whole, though, generally
fair weather is expected. The aforementioned enhanced winds are
causing building seas, becoming choppy to hazardous, which will last
through at least Tuesday

&&

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

A mid to upper-level trough lingering near the northeast Caribbean
will promote frequent passing showers across the local islands each
day of the short-term period. A surface high pressure across the
Atlantic Ocean will tighten the local pressure gradient,
increasing the trade winds. Under this weather pattern, expect
periods of sunshine but with patches of moisture embedded in the
trades affecting the windward sections at times. Local effects,
sea breeze variations, and diurnal-heating will result in
afternoon convection across the mountains and southwest portion of
the islands today, and more into the west Sunday and Monday, as
the wind shifts more from the east.

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

Moisture at near-normal levels is expected for Tuesday. Conditions
aloft will be relatively stable, with a mid- to upper-level ridge in
place over the area. Winds are forecast to be stronger than normal,
up to around 20 knots, which will help to bring patches of
additional moisture across the islands, promoting further passing
shower activity. As such, isolated to scattered showers are
expected, in a typical pattern, but significant organized
convection is not currently anticipated. For Wednesday and
Thursday, decreasing moisture is expected, though patches of
moisture will help to sustain some shower activity. Calmer, drier
weather conditions are therefore likely, though stronger winds
will persist on Wednesday. On Friday, the remnants of an old
frontal boundary are forecast to approach the region from the
northeast. Presently, model guidance suggests that the greatest
affects of this boundary will be seen in northern portions of the
CWA, before the moisture that it brings is swept away to the
west/northwest. An increase in shower activity is expected. With
the moisture pulling away from the region late on Friday into
Saturday, generally fair weather is expected, with patchy moisture
helping to sustain occasional showers. Moisture is forecast to be
approaching the region from over the Caribbean, but is set to
arrive the following week.

&&

.AVIATION...

Northeasterly winds will dominate the local weather. Winds will
increase between 15 and 20 knots with gusts between 25 and 30 knots
and sea breeze variations after 27/13z. The trade winds will push
showers and clouds across the terminals at times. Therefore, though
VFR conditions will prevail, periods of SHRA/-SHRA could produce
brief SCT-BKN ceilings Btwn FL020-FL040 at times.

&&

.MARINE...

Moderate to fresh winds are forecast for the local waters over the
next several days, which is leading to building seas. Choppy to
hazardous conditions are forecast through the weekend and well into
next week. Small Craft Advisories are in effect starting late
tonight/early tomorrow morning for the offshore Atlantic waters and
Anegada Passage.

For the beachgoers, there is a moderate risk of rip currents for
most local beaches, with the exception of those sheltered to the
east, mostly those of the southern west coast of Puerto Rico.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 73 85 74 / 30 50 60 40
STT 85 73 85 75 / 30 50 60 30

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
429 AM AST Sun Mar 28 2021

.SYNOPSIS...

A typical pattern is expected over the next few days. Enhanced winds
will pull additional moisture across the region, similarly to
yesterday, and similar conditions are expected again today. A drying
pattern is anticipated for midweek into the second half of the
workweek. For the local waters, the enhanced winds are causing
building seas; choppy to hazardous marine conditions are expected,
and there is a moderate to high risk of rip currents for most local
beaches.

&&

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

The combination of a mid to upper-level trough (which is lingering
near the northeast Caribbean) and a surface-high pressure across the
central Atlantic will promote frequent passing showers across the
regional waters and windward sections of the islands each day
through at least Monday. The surface high pressure will reinforce
the local pressure gradient creating windy easterlies during the
next few days. Therefore, expect a mixture of sunshine with
passing clouds over the north, east, southeast portion of PR and
the U.S. Virgin Islands, with mostly sunny skies across the west
and south PR through the morning hours. Then, rains will make
their way into the western and interior sections of PR during the
afternoon. Do not anticipate significant rainfall accumulations
due to the nature of these showers (fast-moving rains).

The mid to upper-level trough is forecast to weaken after Monday
night, as a mid-level high pressure moves over the northeast-
Caribbean from the west.

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

Relatively dry conditions are expected across the region at midweek,
with precipitable water values forecast to be below normal. With a
strong surface ridge maintaining a tightened pressure gradient over
the region, enhanced winds are also anticipated through midweek
across the area. These winds will aid in the advection of low-level
moisture into the area, which will help to sustain shower activity.
Aloft, the dominant feature is a mid-level ridge, which is
providing stability and therefore inhibiting convective
development. Generally fair weather is expected, with some
isolated to scattered shower activity possible, in a typical
pattern.

On Friday, a weak mid-level trough will push into the area from over
the Caribbean, weakening stability over the region. Meanwhile, the
remnants of an old frontal boundary will approach the area from the
northeast Thursday into Friday, increasing moisture by Friday
morning, especially in northern portions of the CWA. On Saturday, a
weak upper level trough is forecast to approach from the west,
leading to increases in instability for the weekend. Saturday night
into Sunday, moisture is forecast to arrive in the region from the
south. Shower activity is likely to be generally increasing starting
on Friday through the upcoming weekend, with a typical pattern
maintained across the region.

&&

.AVIATION...

Easterly winds will dominate the local weather. Winds will continue
between 10 and 15 knots, increasing between 15 and 20 knots with
gusts between 25 and 30 knots and some sea breeze variations after
28/13z. The trade winds will push showers and clouds across the
terminals at times. Though VFR conditions will prevail, periods of
SHRA/-SHRA could produce brief SCT-BKN ceilings Btwn FL020-FL060 at
times. SHRA will form across the interior/W-PR Btwn 28/16z-29/02z.

&&

.MARINE...

Enhanced winds persist, associated with a surface ridge located to
the north of the region, which is tightening the pressure gradient
over the area. Wind speeds upwards of 20-22 knots are anticipated
for the local waters today through the first part of the workweek.
Building seas are expected in response to these winds, and choppy to
hazardous conditions are anticipated. Hazardous conditions will
spread across the offshore waters and local passages today, with
some hazardous conditions likely in portions of the nearshore
waters, especially near the Anegada Passage. This will persist for
the next few days, and possibly late into the week.

For the beachgoers, there is a high risk of rip currents for the
north coast of Puerto Rico and eastern beaches of St. Croix, as well
as Culebrita. Most of the rest of the local beaches have a moderate
risk of rip currents.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 74 86 76 / 60 40 40 40
STT 85 75 85 75 / 50 30 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
456 AM AST Mon Mar 29 2021

.SYNOPSIS...

A seasonally typical pattern of showers is expected to continue,
though strong winds will hasten the showers` traversal of the
islands. This will likely prevent significantly high rainfall
amounts. Decreased shower activity, due to drier conditions, is
forecast to arrive by midweek. The stronger winds will also
maintain choppy to hazardous conditions for most of the local
waters for the next few days, as well.

&&

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

A surface high pressure across the central Atlantic will maintain
a tight local pressure gradient, inducing windy easterlies. Winds
will have an east-southeasterly component that will aid in the
afternoon activity across the northwest quadrant and northern
portions of Puerto Rico today. However, the U.S. Virgin Islands
can expect a mixture of sunshine and clouds, with most rain
activity across the surrounding waters. Winds will return more
from the east Wednesday.

Another surface high pressure will move into the western Atlantic
later tonight, and will spread eastward through mid-week. A mid-
level high pressure will build over the islands limiting the
vertical development of any shower activity. This weather scenario
will promote an advective pattern pushing patches of moisture
from time to time into the region. At this time, model guidance is
suggesting moisture erosion by Wednesday.

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

Relatively dry air is forecast to be in place over the region on
Thursday morning. Later in the day, the remnants of an old frontal
boundary will approach the region from the northeast. Aloft, there
is a mid- to upper-level trough that will sweep by the region to the
north; this could improve instability for Thursday, but in the
absence of significant moisture, especially for western Puerto Rico,
this will likely to lead to any substantial increase in shower
activity during the day on Thursday. Increasing shower activity is
likely for Friday, as the boundary remnants arrive and then stall
out. This is expected to lead to some moisture convergence,
especially at the lower levels, further increasing precipitable
water values, to the high end of seasonal normals or above normal
levels. At the mid-levels, however, a ridge will dominate,
especially at the lower mid-levels, which will maintain
relatively stable conditions aloft. This will prevent
significant/organized convective activity, and will persist
through the weekend.

The moisture from the old frontal boundary is forecast to start
moving away from the region, towards the north/northwest late on
Saturday. This could lead to a temporary decrease in shower
activity. Another frontal boundary is forecast to sweep off of the
coast of the US southeast/Florida, and approach from the northwest
by late Sunday, moving moisture back over the CWA. Meanwhile,
additional moisture convergence is expected - both from the
aforementioned boundaries, as well as some moisture being pulled up
with a perturbation from the southeast. Presently, the GFS suggests
precipitable water values that are well above climatological
normals. As such, an increase in shower activity is quite likely.
Additionally, stability aloft will be eroded during the early part
of next week. A weak upper-level trough is forecast to move to north
and west of the islands by late Monday or early Tuesday. Divergence
aloft is therefore likely. And, at the mid-levels, the ridges will
be gradually eroded, as well. Should this pattern hold, this could
lead to significant rain from both passing showers and afternoon
convection early in the next workweek. Considering, however, that
this is a week out, confidence is not especially high.

On the whole, the general trend is passing showers on Thursday,
followed by a general increase in shower activity through the rest
of the forecast period.

&&

.AVIATION...

Once again, windy easterlies will dominate the local weather. Winds
will continue between 10 and 15 knots, increasing between 15 and 20
knots with gusts between 25 and 35 knots and some sea breeze
variations after 29/13z. The trade winds will push showers and
clouds across the terminals at times. Though VFR conditions will
prevail, periods of SHRA/-SHRA could produce brief SCT-BKN ceilings
Btwn FL020-FL060 at times. SHRA will form across the interior/NW/N-
PR Btwn 29/16z-29/02z, which could impact JBQ/JSJ.

&&

.MARINE...

Enhanced winds persist across the region, with surface high pressure
to the north maintaining a tightened pressure gradient over the
area. Moderate to fresh, and locally strong, winds will persist for
a few days more, still. This will maintain choppy to hazardous seas
across most of the local waters. Winds are forecast to start
gradually subsiding Wednesday into Thursday, and the seas will
follow. In the meantime, though, hazardous conditions will persist,
likely into the late week for some zones - especially the offshore
Atlantic waters, as well as portions of the Anegada Passage and
nearby waters.

For the beachgoers, there is a high risk of rip currents for
northern beaches of Puerto Rico, as well as beaches of Culebra and
St. Croix. These conditions are forecast to continue for a few days
more, and possibly spread to include other local beaches as well,
and interested parties should plan accordingly.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 86 74 / 50 50 50 30
STT 85 75 85 73 / 20 50 20 20

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
450 AM AST Wed Mar 31 2021

.SYNOPSIS...

A typical weather pattern will continue across the local islands.
Instability aloft, however, brings the potential for some
afternoon thunderstorms today, mostly in western Puerto Rico.
There is the potential for urban and small stream flooding. Winds
will gradually subside for the second half of this week, and
rainfall activity will also decrease. Increasing shower activity
is expected for this weekend.

&&

.SHORT TERM...Wednesday through Friday...

Isolated to scattered showers will continue moving across the
surrounding waters of St Croix, the Atlantic and Caribbean Waters,
and the northern and eastern portions of Puerto Rico. Moisture will
erode later this morning, leaving a mixture of sunshine and clouds
across most of the islands of Puerto Rico and the U.S. Virgin
Islands. However, local effects will trigger afternoon convection
across the interior and west PR, where isolated thunderstorms may
form, especially near Mayaguez and Cabo Rojo. This activity will
likely move over the shoreline, creating hazardous marine
conditions. Furthermore, some areas with persistent rainfall
activity may observe urban and small-stream flooding.

Windy conditions will persist due to a surface high pressure
across the Atlantic Ocean. An upper-level short wave will linger
aloft, with a jet stream, leading to an increase in instability.
This jet will exit the islands by Thursday afternoon as a mid to
upper-level ridge build-in. A somewhat drier air mass is possible
on Thursday.

Patches of moisture will continue to move in embedded in the trades
on Friday, which interacting with diurnal heating and sea breeze
variations will result in afternoon convection across the western
portions, the San Juan Metro area, and downwind from the U.S. Virgin
Islands.

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

On Saturday morning, the remnants of an old frontal boundary will be
affecting the region, lingering and then drifting northward. With
the slow movement of the front, moisture convergence is likely. The
front is forecast to stall out near the northern extent of the CWA
during the weekend. This is due to the approach from the
west/northwest of a front moving off the east coast of the US. This
newer front will make its way towards the region, bringing
additional moisture. Aloft, a mid- to upper-level ridge will be
gradually eroded, from the top and bottom. The surface trough with
which the newer frontal boundary is associated is expected to be
reflected aloft, as well. This will lead to decreasing stability
across the region, which will also support increasing shower
activity during the weekend, in a typical pattern.

A small dry slot is forecast to be south of this frontal boundary,
and is likely to affect the region on Monday. Aloft, a weak mid- to
upper-level trough is forecast to move to just east of the region
before diminishing; this would then cause an increase in stability
for the region. As such, a (temporary) decrease in shower activity
is expected.

On Tuesday, a disturbance is forecast to approach the region from
the southeast, bringing significant moisture with it. The
aforementioned dry slot is expected to diminish and nearly
disappear, with the frontal boundary stalled out in the north, as
the surface low with which it is associated is forecast to have its
progression eastward halted by a blocking high in the north central
Atlantic, leaving it to churn off the coast of Atlantic Canada.
Model guidance continues to suggest that this increase will push
precipitable water values to significantly above normal levels,
possibly as high as around 2.0 inches. Aloft, a deep-layer trough
approaching from the west will help return instability to the
region, allowing for moisture to extend through the mid-levels by
Tuesday into Wednesday. There has been generally good consistency
between model runs of the GFS for this scenario, and both the Euro
and the CMC suggest similar solutions. This does increase confidence
somewhat, though the timing is relatively uncertain still, and has
changed a little between model runs, and it is still several days
out. And with this increased confidence, the potential that midweek
next week will bring significant, and possibly hazardous levels of,
rainfall to the region also increases. Future forecasts should be
monitored for updates.

&&

.AVIATION...

Expect winds between 10 and 15 knots, increasing between 15 and 20
knots with higher gusts, even around the mid-30s after 31/13z. Also,
sea breeze variations may form after 31/13z. These breeze conditions
will push showers and clouds across the terminals at times. SHRA
will develop across the interior/SW-PR and in the VCTY of JSJ/JPS
between 31/16z-31/02z.

&&

.MARINE...

Breezy conditions continue across the region, under the persisting
influence of a surface ridge to the north of the islands. These
winds are still causing choppy to hazardous conditions for most of
the local waters, and will continue to do so for a couple days yet,
still. Hazardous conditions are expected to persist for the offshore
Atlantic waters and Anegada Passage into tomorrow night. Diminishing
winds are forecast for the second half of the week, which will cause
gradual subsiding of the seas.

For the beachgoers, there is a high risk of rip currents for beaches
of northern Puerto Rico, northern and eastern St. Croix, as well as
Culebra. Most other local beaches have a moderate risk of rip
currents.

&&

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

&&

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
456 AM AST Thu Apr 1 2021

.SYNOPSIS...

Near normal weather conditions are expected the next several
days, with patches of moisture advecting over the local islands
during the early morning and afternoon. This weekend, an uptick
in showers is expected as a through stalls north of Puerto Rico
through early next week.

&&

SHORT TERM...Today through Saturday.

The local weather is expected to gradually become rainier into the
weekend as the available moisture increases. Today, the available
moisture will be below normal, with precipitable water of around 1
inch, increasing to near normal on Friday, and then slightly above
normal on Saturday. However, some rain is expected every day in the
short term period.

A Surface high pressure north of the local area will keep an
easterly breeze today and Friday, but by Saturday another high
pressure will move in from the west, causing the local pressure
gradient to relax and thus winds to weaken slightly. The mid levels
are expected to be fairly dry these next few days, and the upper
levels do not appear to be particularly conducive for deep
convection or thunderstorms. Even though the mid level temps could
be below normal on Saturday, the best chances of thunderstorms, and
isolated at that, appear to be over the waters on Saturday night
into Sunday. That said, there could be a very isolated thunderstorm
in the afternoon hours, especially over western PR during these next
few days. Otherwise, we can expect isolated to scattered and brief
showers in the local waters, USVI, and eastern PR in the morning
hours, with scattered to locally numerous showers in the afternoon
across western PR. The daytime high temperatures are expected to be
near normal over the next few days.

&&

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

An unsettled weather pattern is forecast for Puerto Rico and local
islands through most of the long-term period; guidance shows
moisture content ranging from 1.5 to 1.8 inches which are above
average for April. A frontal boundary moving through the
southeastern U.S. will push into the western Atlantic waters on
Friday. The frontal boundary is forecast to move eastward across the
Atlantic waters before stalling just north of Puerto Rico on
Saturday. The boundary will weaken the mid to upper-level ridge,
promote troughiness aloft, and gradually moisten the atmosphere
mid and upper-levels across the Caribbean.

Saturday, a shear line/prefrontal trough stalls over Puerto Rico
through Sunday evening. The shear line/prefrontal trough is forecast
to lift north of the island by Sunday afternoon. The uptick in
moisture coupled with local effects will bolster shower activity
during the afternoons for most of the islands.

Monday through Thursday,

Weather conditions remain unsettled as residual moisture from the
shear line lingers north of Puerto Rico and easterly trade winds
advect moisture into the local islands. The GFS shows rich tropical
moisture in the southern Caribbean and Pacific. The GFS pulls the
rich moisture over the area by the southerly winds at 700, 500, and
250 mb. Relative humidities for the above layers will range from 50
to 80 percent. The significant moisture throughout the atmospheric
column and moderate divergence aloft will induce deep convection
over most of the local islands leading to urban and small stream
flooding and ponding of water on roadways.

Forecast confidence: Medium

&&

.AVIATION...

Winds will increase to around 15-20 knots and gusty after 01/13Z,
mainly from the east with sea breeze variations. VCSH are
expected as SCT SHRA activity is expected across the local flying
area. That said, the shower activity is expected to be brief with
the quick passing showers. The afternoon convection across western
PR is expected to keep the SHRA activity in the vicinity of TJBQ.

&&

.MARINE...

Hazardous marine condition will continue through Friday due to
moderate and fresh easterly winds. Small Craft Advisory
conditions will continue for most local waters through late
tonight. A high risk of rip currents for the northern beaches of
Puerto Rico and Culebra. There is a high risk of rip currents for
Botany beach in Saint Thomas and Cramer Park beach in Saint
Croix.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 85 73 87 74 / 20 30 40 30
STT 83 73 84 74 / 30 30 30 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
446 AM AST Fri Apr 2 2021

.SYNOPSIS...

Relatively fair weather is expected today across most of the local
area today due to relatively dry conditions at the surface and
aloft. This weekend, a frontal boundary is forecast to stall north
of Puerto Rico, with a shear line/pre-frontal boundary moving along
the islands`s northern coastal areas. The moisture convergence
coupled with upper-level instability and mid-level moisture will
cause unsettled weather conditions Saturday through the middle of
next week.

&&

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

The available moisture will gradually increase today, becoming much
above normal on Saturday, and holding steady on Sunday. Instability
will gradually increase over the next few days as well, peaking on
Saturday as an upper level jet, with about 80-90 knot winds, moves
over the local area, which will also increase the chances of
thunderstorms. The upper jet will relax a bit on Sunday, but there
will still be a chance of isolated thunderstorms. The surface winds
will decrease gradually over the next few days, with the following
day having lighter winds than the day before, as a surface high
moves into the western Atlantic, creating narrow COL over the local
area. Based on the latest guidance, scattered showers will be
expected today, especially across the USVI, and north and east
Puerto Rico in the morning and early afternoon, but it seems as
though Saturday could be the day with the most significant rainfall
this weekend. This is because it will have the deepest moisture and
the upper jet, increasing the chances of thunderstorms, with heavy
rainfall at times.

&&

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

The GFS 02/00Z has trended closer to the ECMWF with a relatively
drier air mass over Puerto Rico and a weaker frontal boundary across
the area. Additionally, the 02/00z GFS slowly lifts the tropical
moisture from the southwestern Caribbean over Puerto Rico on
Wednesday, and this guidance cycle is about 48 hours slower than the
GFS 01/00Z run. Therefore, I kept higher pops in the long-term
period but lowered them slightly. If the GFS continues to slow the
moisture progression across the southwestern Caribbean or weakens
the shear line/pre-frontal boundary early in the period, pops will
be lowered again.

The guidance supports an unsettled weather pattern Wednesday through
Friday for Puerto Rico and adjacent islands. Upper-level instability
and moisture content will increase each day; moisture content will
range from 1.4 to 2.0 inches, which is above average for April.

A polar trough will stall north of Puerto Rico this weekend. On
Sunday, the GFS moves a pre-frontal boundary near the northern
coastal regions of Puerto Rico. The moisture convergence coupled
with divergence aloft and scant mid-level moisture will cause an
uptick in shower activity. The shear line/pre-frontal trough will
gradually lift north of Puerto Rico through Wednesday before
becoming diffused on Thursday. The GFS model shows rich moisture
moving over the area Wednesday through the end of the period due to
the southerly winds at 700, 500, and 250 mb. Relative humidities for
the above layers will range from 50 to 80 percent. The significant
moisture throughout the atmospheric column and moderate divergence
aloft should support light to moderate shower activity. Light winds
will cause convection to move slowly and lead to urban and small
stream flooding and ponding of water on roadways.

Forecast Confidence: Medium

&&

.AVIATION...


&&

.MARINE...

A Small Craft advisory in effect for the Atlantic waters until 8
AM this morning. Across the rest of the regional waters, small
crafts should continue to exercise caution due to seas up to 6
feet and winds up to 20 knots. Seas will continue to subside this
afternoon across the local waters. There is a high risk of rip
currents along the northern and eastern beaches of Puerto Rico,
Culebra and the eastern beaches of St. Croix through late Friday
night.

&&

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

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
455 AM AST Sat Apr 3 2021

.SYNOPSIS...The available moisture will increase this weekend,
the shower activity and thunderstorm potential will also be
higher over the next several days, compared to last week. Upper
level low to the north of the local area will cause an upper level
jet that will cause an increase in instability, which could lead
to developing thunderstorms across the local area this weekend,
and then again for the latter part of next week. Light to moderate
ESE winds expected today as a surface high pressure enters the
western Atlantic and meets the surface low across the central
Atlantic, causing a brief COL over the local area. Marine
conditions will gradually improve this weekend, but a northerly
swell will invade the waters again on Sunday night.

&&

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

GOES-16 total precipitable water shows a moist plume of 1.5
inches moving across eastern Puerto Rico and adjacent islands.
Moisture content will remain above average through the short-term
period. Light southerly wind flow and a pre-frontal trough, as
well as favorable upper-level conditions will yield showers and
isolated thunderstorms for most of Puerto Rico today. The shower
activity will be focused across portions of eastern and
southeastern Puerto Rico and the U.S. Virgin Islands this morning;
then, the action shifts to the northwestern and interior areas of
Puerto Rico this afternoon.

The GFS sounding shows a moist layer from 850 to 700 mb this
afternoon, the saturated low-levels will spawn frequent showers over
the same areas today. Convection that develops will move slowly due
to light steering winds around 10 mph. Frequent showers and
relatively light winds increase the likelihood that urban and small
stream flooding will occur across areas that receive the highest
rainfall amounts.

Sunday and Monday,

The pre-frontal/shear line remains draped across the Atlantic and
northern coastal areas of Puerto Rico and cause unsettled weather
across the local islands and regional waters. Modest instability
coupled with above normal moisture will enhance convection across
the northern, eastern and interior areas of Puerto Rico. Soils will
be saturated therfore expect urban and small stream flooding and
ponding of water on roadways.

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

Near normal moisture is expected on Tuesday, but a frontal
boundary will be to our north, mainly causing shower activity
over the Atlantic waters. However, things change for Wednesday
onward. The available moisture will increase for the second half
of next week, starting on Wednesday as the frontal boundary
remains to our north, but also additional moisture will move in
from the south. In addition, the upper level dynamics become more
conducive for thunderstorm development as a strong upper level low
moves across the Atlantic, causing the upper level winds to be
stronger across the local area, similarly a mid level low will
cause the mid level winds to be stronger locally, which will
cause instability to increase. This pattern of stronger mid and
upper level winds as well as near normal to higher than normal
moisture may be present from Wednesday to Sunday according to the
latest long range models. In fact, the latest forecast soundings
indicate that the moisture will increase across all levels of the
atmosphere, so there may be enough moisture and instability to
have a few days with the potential of significant rainfall,
especially in the afternoon hours.

&&

.AVIATION...VFR/MVFR conditions are expected over the next 24 hours. Southerly
low level winds will advect moisture over eastern, northern,
southeastern areas of PR and the USVI through 03/17Z. SCT-BKN lyrs
nr FL025...FL050 w/SHRA across terminals TJSJ, TIST, TISX, TIL
03/17Z. +SHRA/VCTS are forecast to develop across northern, eastern,
and western areas of PR by 03/17Z and last until 04/00Z. Sfc winds
will range from 5 to 15 kts today.


&&

.MARINE...Seas will subside gradually, though they will be up to 6
feet and choppy today, the local seas are expected to be up to 5
feet by tonight, continuing into Sunday. Therefore, small craft
operators are urged to exercise caution today. Winds will also be
up to 20 knots today, but will decrease to 10-15 knots tonight
into Sunday. However, a brief northerly swell will move in Sunday
into Monday, causing hazardous seas up to 7 feet for a brief
period across the Atlantic waters. As far as the surf zone, there
is a moderate risk of rip currents today across most of the local
beaches.



&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 84 74 84 74 / 60 40 40 30
STT 81 76 82 74 / 40 40 40 40

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
451 AM AST Sun Apr 4 2021

.SYNOPSIS...Moisture is below normal early today but increasing to
near normal by this afternoon, which could enhance the
probability of rainfall across central, western and northern
Puerto Rico this afternoon when combined with the diurnal heating
and southeast winds. Winds will continue to be on the lighter side
today as a surface high pressure across the western Atlantic and
meets a surface low across the south central Atlantic, causing a
COL over the local area today. Marine conditions will be tranquil
this morning, but will gradually become choppy as a northerly
swell invades the local waters starting this afternoon.

&&

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

Partly cloudy skies with a few showers across eastern and northern
areas of Puerto Rico is forecast this morning. This afternoon a pre-
frontal trough and favorable upper-level conditions will enhance
shower activity across portions of north, northwestern, and interior
areas of Puerto Rico. The proximity of the trough and increasing
moisture content could cause some showers to mature into
thunderstorms but, the mid-levels of the atmosphere remain devoid of
moisture with relative humidities ranging from 8 to 15 percent.
Nevertheless, showers that develop today will move slowly due to
light steering winds and possibly lead to urban and small stream
flooding and ponding of water on roadways.

Monday and Tuesday, high-res and model guidance pushes a frontal
boundary currently northwest of Puerto Rico into our northern
coastal waters; east to northeast winds will advect patches of
moisture over northern and eastern areas of Puerto Rico, with the
bulk of the showers remain across the outer Atlantic waters. An
uptick in shower activity is forecast over the next several days due
to the increase in moisture content throughout the atmospheric
column and the location of the trough to Puerto Rico.

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

The global models have been backing off a little bit on the
moisture and rainfall expected in the mid and latter part of this
week, compared to what they were suggesting over the past few
runs. That said, they still suggest an increase in shower and
possible thunderstorm activity on Wednesday onward, just not as
much as suggested before. Based on the latest model guidance, near
normal to slightly higher moisture is expected on Wednesday, with
the deeper moisture plume being pushed back to Thursday onwards,
with Saturday having the deepest moisture with over 2 inches of
precipitable water, which is close to 2 standard deviations above
normal. The models still suggest that a frontal boundary will
stall to our north on Wednesday into Thursday, mainly causing
shower activity over the Atlantic waters. However, the frontal
boundary will weaken and the remnants are pushed south and into
the local area late Friday into Saturday. That said, the increase
in moisture during this time will combine with local effects and
diurnal heating, to cause the development of showers and isolated
thunderstorms across portions of central and western Puerto Rico.

The upper level winds continue to look like they will be
relatively strong during this time as an upper level low moves
across the Atlantic. In addition, a mid level low across the
Atlantic will cause the mid level winds to be stronger across the
local area. The latest forecast soundings still indicate that the
moisture will increase across all levels of the atmosphere, though
mainly so there may be enough moisture and instability to have a
few days with the potential of significant rainfall, especially
in the afternoon hours.


&&

.AVIATION...VFR conditions expected across the local terminals
through 04/15Z. A few Iso SHRA are possible over eastern and
northern Puerto Rico and the USVI through 04/15z. Iso/Sct SHRA
will develop across western and interior areas of PR by 04/16Z.
SHRA could cause MVFR conds near terminal sites TJBQ and TJMZ;
this activity is forecast to diminish by 05/01Z. Sfc winds will be
from the ESE-SE ranging from 5 to 15 kts, with seas breeze
variations aft 04/14z.


&&

.MARINE...Seas will be tranquil this morning, up to 5 feet, but a
northerly swell will start moving in this afternoon, and seas will
be up to 6 feet across the Atlantic waters starting this
afternoon. The choppy seas up to 6 feet will continue through at
least early Tuesday. Winds will be light to moderate today from
the east to southeast. There is a moderate risk of rip currents
across many of the local beaches today, but starting this evening
there will be a high risk of rip currents across the north central
and northwestern beaches of Puerto Rico.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 87 75 84 74 / 30 50 50 30
STT 84 74 83 74 / 30 30 30 30

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
421 AM AST Mon Apr 5 2021

.SYNOPSIS...A frontal boundary is expected to linger near the area
through much of the week, resulting in enhanced afternoon
convection, especially over interior and western Puerto Rico. The
most significant rains appear to come during the latter part of
the work week as deep moisture moves in. Choppy to hazardous
marine conditions are expected through early Tuesday as a
northerly swell invades the local waters.

&&

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

Recent satellite imagery and model guidance suggests high zonal flow
in the mid to upper levels with a dominant west to southwest wind
flow. This is expected to continue thru the period, as a broad polar
trough will shift eastward across the west and central Atlantic.
A frontal boundary/shearline will linger just north of the region
while a weakly induced trough is to persist across the area
through Tuesday, to maintain a light east southeast wind flow.
Winds are to forecast to become more easterly by Wednesday and
slightly increase as a surface high builds north of the region. In
the meantime, pockets of low to mid level moisture will converge
across the region to aid in the development of mostly isolated to
scattered afternoon convection mainly over portions of central and
northern half of Puerto Rico. Lesser rainfall and shower activity
is forecast for the U.S Virgin Islands.

For today and Tuesday , available moisture accompanying the frontal
shearline and low level convergence will aid in the development of
afternoon showers and possibly isolated thunderstorms, mainly over
parts of the interior and northern half of Puerto Rico. Precipitable
water values are forecast to range between 1.50-1.60 inches during
the period and this would be sufficient to aid the development of
afternoon convection. Although widespread rainfall is not
anticipated, the available moisture will favor an increase in
afternoon convection in northwestern and interior section of Puerto
Rico as well as around the San Juan metro. During the morning hours,
expect occasional passing showers but no significant rainfall is
expected at this time as the winds are to remain fairly light.
However, due to the light winds, there is increased potential for
localized flooding with any heavy rains and isolated thunderstorms,
especially in the form of urban and small stream flooding.

By Wednesday, the winds become more easterly and a weak perturbation
is to bring another surge of moisture to the region. This will also
maintain the potential for afternoon convection across portions of
the islands. Again, shower development should be mainly focused over
the interior and west sections of Puerto Rico and just on the west
end or downwind of the U.S. Virgin Islands. The potential for minor
urban and small stream flooding during the afternoon hours will also
be possible especially over the interior and west sections of Puerto
Rico.

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

The frontal boundary is expected to linger over the area Thursday
and Friday. With it, deep moisture is also expected with
precipitable water values rising to above normal levels, in the
1.8 to 2.0 inch range. Therefore, enhanced convection is expected
for both of these days. In addition, the steering flow is expected
to remain very light, at around 5 knots or less. As a result, the
convection that develops will be slow-moving with the potential
to observe urban and small flooding.

Thereafter, model guidance begins to diverge significantly for the
upcoming weekend. The GFS model lingers the frontal boundary over
the area with very high moisture content remaining and thus the
threat for enhanced shower activity continuing. The ECMWF model,
on the other hand, pushes the frontal boundary south of the local
islands with much drier air penetrating in and thus fair weather
conditions would be the result. The difference comes down to the
model handling of a mid-level trough that is expected to be
located over the central Atlantic during this time period. The
ECMWF model is much more amplified with this mid-level trough than
the GFS model is and thus the frontal boundary is forced south of
the local islands. As a result of these differences, there is
high uncertainty of the weather conditions for the upcoming
weekend. More unstable weather conditions are possible by the end
of the long-term period as models are hinting at another mid-
level trough moving near the area.

&&

.AVIATION...VFR at all terminals durg prd. Sfc wnd calm to
lgt/vrb bcmg 5-15 kts fm ESE w/sea breeze variations aft 05/14Z.
Frontal boundary over the Atl waters north of the local islands
bring SCT-BKN lyrs nr FL030...FL050..FL080 ovr regional waters and
en route btw islands with mstly isold SHRA til 05/14z. Aftn SHRA
with Isold TSRA psbl ovr ctrl interior PR fm 17Z-22Z w/ Isold SHRA
elsewhere with VCSH mainly at TJSJ/TJBQ/TJMZ. No sig operational
wx impacts attm durg prd.

&&

.MARINE...Choppy to hazardous marine conditions with seas ranging
between 5 and 7 feet are expected across the Atlantic waters and
local passages through early Tuesday due to a northerly swell.
Therefore, Small Craft Advisories are in effect for the Atlantic
waters and Mona Passage. Across the Caribbean waters, more
tranquil seas of up to 4 feet are expected. For beachgoers, as a
result of the northerly swell, there is a high risk of rip
currents across the north-facing beaches of Puerto Rico and
Culebra.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 86 75 86 74 / 50 40 40 20
STT 85 74 85 73 / 30 30 40 10

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
509 AM AST Tue Apr 6 2021

.SYNOPSIS...A frontal boundary will linger across the area through
the end of the work week, resulting in enhanced afternoon
convection mainly over Puerto Rico. Lingering northerly swell will
continue to result in rough marine and coastal conditions today.

&&

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

High zonal westerlies will continue across the region in the mid to
upper levels under the dominant anticyclonic flow, while a broad
polar trough slowly shifts eastwards across the Atlantic. A frontal
shear-line and elongated band of moisture will slowly sink
southeastward across the region, as a surface high pressure ridge
builds across the southwest Atlantic. This pattern will induce a
more east-northeast wind flow today through Thursday. Moisture
fragments from the old boundary/Shear-line will converge across the
area to aid in the development of isolated to scattered over the
regional waters during the overnight and early morning hours.
Diurnal heating and local affects will aid in promoting afternoon
convection each day but mainly over the interior and southern slopes
of Puerto Rico. Winds will remain fairly light today but is forecast
to gradually increase becoming more northeasterly on Wednesday and
Thursday.

For today, afternoon showers and isolated thunderstorm activity
should be focused over parts of the interior sections of Puerto Rico
then later drift towards the southwest and southern slopes. However,
portions of the San Juan metro may also experience some early
afternoon shower development. Due to the light steering winds, the
potential for urban and small stream flooding will remain high, as
well as ponding of water on roadways and in poor drainage areas
with the heavy rains.

By Wednesday and Thursday, much of the same is forecast, however
expect the shower activity to be somewhat more enhanced as low level
moisture convergence increases along with better ventilation aloft
provided by the anticyclonic flow in the upper levels. In addition,
the increasing low level winds will be more northeasterly and
therefore the passing showers should be more frequent along the
north and east coastal sections during the morning hours. This will
be followed by afternoon convection over the central and southwest
sections of Puerto Rico. The potential for urban and small stream
flooding will continue throught the period especially over Puerto
Rico during the afternoon hours. For the U.S. Virgin islands, while
lesser shower activity is expected, early morning passing showers
can still be expected from time to time each day followed by
isolated to scattered showers during the afternoon but mainly on the
west end and downwind of the islands.

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

The frontal boundary will linger over the area on Friday.
Therefore, another round of afternoon convection is expected,
mainly across the interior and southern portions of Puerto Rico as
the low-level flow will remain from the northeast. Once again,
given the light steering flow expected, convection that develops
will be slow-moving leading to the potential for urban and small
stream flooding.

Model guidance has come into better agreement on the weather
pattern for the upcoming weekend. The GFS model, which in
previous runs lingered the frontal boundary over the area during
the weekend, has now corrected towards the ECMWF model solution
and now pushes the boundary south of the area with a drier air
mass now expected. Therefore, improving weather conditions are
now expected during the upcoming weekend with more limited shower
activity.

Even though model guidance has come into better agreement on the
overall pattern for the upcoming weekend, they disagree once
again on the pattern during the early portion of next week. The
GFS model wants to bring the remnants of the frontal boundary back
towards the area Monday and Tuesday of next week, which would
increase the moisture and thus shower activity. The ECMWF model,
on the other hand, maintains the boundary well south of the area
with a relatively drier than normal air mass prevailing and thus
fair weather conditions. Therefore, there is high uncertainty of
the weather conditions for early next week.

&&

.AVIATION...Prevailing VFR at all terminals durg prd. Sfc wnds lgt/vrb
to calm bcmg 10-15 kts fm ENE wITH sea breeze variations aft
06/14Z. L/lvl moisture along a frontal boundary over the Atl
waters just north of PR, will bring SCT-BKN lyrs nr FL025...FL050
FL080 ovr regional waters and en route btw islands w/wdly SCT SHRA
til 05/14z. Mtn top obscr psbl ovr E PR w/SHRA til 06/12Z. Fm
06/17-06/22Z...SHRA w/Isold TSRA psbl ovr ctrl interior and
southern slopes of PR. VCSH/Isold TSRA psbl at TJSJ/TJBQ/TJMZ durg
aftn. Isold SHRA elsewhere.

&&

.MARINE...Northerly swell will continue to result in rough marine
and coastal conditions today for the Atlantic zones. The latest
nearshore buoys continue to indicate seas of near 7 feet with a
period of 10-11 seconds. Therefore, it was decided to extend the
High Surf and Small Craft Advisories. The High Surf Advisory is
in effect for all of the north-facing beaches of Puerto Rico
through late this morning due to breaking waves of up to 10 feet
possible. The Small Craft Advisories for the nearshore Atlantic
and Mona Passage are in effect through early this afternoon for
seas of up 7 feet and across the offshore Atlantic until this
evening for seas of up to 8 feet. Across the Caribbean waters,
seas of up to 5 feet are expected. In addition to the High Surf
and Small Craft Advisories, there is also a high risk of rip
currents for all of the north-facing beaches of Puerto Rico,
Culebra, and Saint Thomas.

&&

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

[cycloneye]

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
509 AM AST Tue Apr 6 2021

.SYNOPSIS...A frontal boundary will linger across the area through
the end of the work week, resulting in enhanced afternoon
convection mainly over Puerto Rico. Lingering northerly swell will
continue to result in rough marine and coastal conditions today.

&&

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

High zonal westerlies will continue across the region in the mid to
upper levels under the dominant anticyclonic flow, while a broad
polar trough slowly shifts eastwards across the Atlantic. A frontal
shear-line and elongated band of moisture will slowly sink
southeastward across the region, as a surface high pressure ridge
builds across the southwest Atlantic. This pattern will induce a
more east-northeast wind flow today through Thursday. Moisture
fragments from the old boundary/Shear-line will converge across the
area to aid in the development of isolated to scattered over the
regional waters during the overnight and early morning hours.
Diurnal heating and local affects will aid in promoting afternoon
convection each day but mainly over the interior and southern slopes
of Puerto Rico. Winds will remain fairly light today but is forecast
to gradually increase becoming more northeasterly on Wednesday and
Thursday.

For today, afternoon showers and isolated thunderstorm activity
should be focused over parts of the interior sections of Puerto Rico
then later drift towards the southwest and southern slopes. However,
portions of the San Juan metro may also experience some early
afternoon shower development. Due to the light steering winds, the
potential for urban and small stream flooding will remain high, as
well as ponding of water on roadways and in poor drainage areas
with the heavy rains.

By Wednesday and Thursday, much of the same is forecast, however
expect the shower activity to be somewhat more enhanced as low level
moisture convergence increases along with better ventilation aloft
provided by the anticyclonic flow in the upper levels. In addition,
the increasing low level winds will be more northeasterly and
therefore the passing showers should be more frequent along the
north and east coastal sections during the morning hours. This will
be followed by afternoon convection over the central and southwest
sections of Puerto Rico. The potential for urban and small stream
flooding will continue throught the period especially over Puerto
Rico during the afternoon hours. For the U.S. Virgin islands, while
lesser shower activity is expected, early morning passing showers
can still be expected from time to time each day followed by
isolated to scattered showers during the afternoon but mainly on the
west end and downwind of the islands.

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

The frontal boundary will linger over the area on Friday.
Therefore, another round of afternoon convection is expected,
mainly across the interior and southern portions of Puerto Rico as
the low-level flow will remain from the northeast. Once again,
given the light steering flow expected, convection that develops
will be slow-moving leading to the potential for urban and small
stream flooding.

Model guidance has come into better agreement on the weather
pattern for the upcoming weekend. The GFS model, which in
previous runs lingered the frontal boundary over the area during
the weekend, has now corrected towards the ECMWF model solution
and now pushes the boundary south of the area with a drier air
mass now expected. Therefore, improving weather conditions are
now expected during the upcoming weekend with more limited shower
activity.

Even though model guidance has come into better agreement on the
overall pattern for the upcoming weekend, they disagree once
again on the pattern during the early portion of next week. The
GFS model wants to bring the remnants of the frontal boundary back
towards the area Monday and Tuesday of next week, which would
increase the moisture and thus shower activity. The ECMWF model,
on the other hand, maintains the boundary well south of the area
with a relatively drier than normal air mass prevailing and thus
fair weather conditions. Therefore, there is high uncertainty of
the weather conditions for early next week.

&&

.AVIATION...Prevailing VFR at all terminals durg prd. Sfc wnds lgt/vrb
to calm bcmg 10-15 kts fm ENE wITH sea breeze variations aft
06/14Z. L/lvl moisture along a frontal boundary over the Atl
waters just north of PR, will bring SCT-BKN lyrs nr FL025...FL050
FL080 ovr regional waters and en route btw islands w/wdly SCT SHRA
til 05/14z. Mtn top obscr psbl ovr E PR w/SHRA til 06/12Z. Fm
06/17-06/22Z...SHRA w/Isold TSRA psbl ovr ctrl interior and
southern slopes of PR. VCSH/Isold TSRA psbl at TJSJ/TJBQ/TJMZ durg
aftn. Isold SHRA elsewhere.

&&

.MARINE...Northerly swell will continue to result in rough marine
and coastal conditions today for the Atlantic zones. The latest
nearshore buoys continue to indicate seas of near 7 feet with a
period of 10-11 seconds. Therefore, it was decided to extend the
High Surf and Small Craft Advisories. The High Surf Advisory is
in effect for all of the north-facing beaches of Puerto Rico
through late this morning due to breaking waves of up to 10 feet
possible. The Small Craft Advisories for the nearshore Atlantic
and Mona Passage are in effect through early this afternoon for
seas of up 7 feet and across the offshore Atlantic until this
evening for seas of up to 8 feet. Across the Caribbean waters,
seas of up to 5 feet are expected. In addition to the High Surf
and Small Craft Advisories, there is also a high risk of rip
currents for all of the north-facing beaches of Puerto Rico,
Culebra, and Saint Thomas.

&&

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

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
424 AM AST Wed Apr 7 2021

.SYNOPSIS...A frontal boundary will linger over the area through
Friday with afternoon convection expected across interior Puerto
Rico. A drier air mass moves in over the weekend. A lingering
northerly swell will result in choppy seas across the Atlantic
waters as well as a high risk of rip currents for the north-facing
beaches of Puerto Rico for today.

&&

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

Mid to upper level anticyclonic flow will continue during the period
with a broad polar trough north of the region to continue eastwards
into the central Atlantic. A band of moisture along a frontal shear-
line will continue to sag and drift southwards across the region
through Thursday while gradually eroding, then finally dissipating
by Friday. Winds will also gradually increase from the northeast
with a drier and more stable airmass so far expected to filter in
from the north.

For the rest of the morning hours showers will continue to reach the
north coastal sections of Puerto Rico and the coastal waters mainly
around the northern U.S. Virgin Islands. Some showers will be
moderate to locally heavy at times and will cause minor
inconveniences with ponding of water on roadways and in poor
drainage areas. Afternoon shower development will be focused over
parts of the interior sections of Puerto Rico, then later drift
towards the southwest and southern slopes. Portions of the San Juan
metro may also again experience a few showers from time to time.
During the afternoon hours, the potential for urban and small stream
flooding will remain high as well as ponding of water on roadways
and in poor drainage areas with the heavy rains.

By Thursday, expect sufficient moisture availability to maintain the
pattern of early morning passing showers along the north and east
coastal areas. This will be followed by afternoon convection over
the central interior and southwest sections of Puerto Rico with a
few afternoon steamers possible around the San Juan metro area. The
increasing low level winds will be more northeasterly and therefore
the early morning showers should be more frequent along the north
and coastal sections of the islands. The potential for urban and
small stream flooding during the afternoon hours as well as
ponding of water on roads and poor drainage areas will continue
but mainly over Puerto Rico. Lesser shower activity is expected in
and around the U.S. Virgin Islands but early morning passing
showers can still be expected from time to time followed by
isolated showers during the afternoon mainly on the west end and
downwind of the islands. Improving conditions are so far expected
by Friday with a gradually drying trend as moisture will erode in
response to a drier airmass and more stable conditions filtering
in from the north, as a surface high pressure ridge will build
across the west Atlantic and north of the region.

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

With the frontal boundary being forced south of the area, a drier
than normal air mass will take hold throughout the weekend.
Therefore, relatively tranquil weather conditions with very
limited shower activity are expected. Some locally induced shower
activity cannot be ruled over portions of interior Puerto Rico
during the afternoon hours, otherwise, most of the region should
remain mostly dry.

Major discrepancies continue with the model guidance for the
early portion of next week. The GFS model continues to show the
scenario that brings the deep moisture associated with the
remnants of the frontal boundary back north once again, towards
the area on Monday into Tuesday, as winds switch from the
southeast as a surface high pressure moves across the Central
Atlantic and a surface low pressure with an associated frontal
boundary moves across the western Atlantic. Under this scenario,
an increase in rainfall activity would occur over the area. The
ECMWF model, on the other hand, maintains the moisture field south
of the area and thus the dry air mass lingers. Under this
scenario, a fair weather pattern would thus occur. Other models,
such as the Canadian and German model, support more of the ECMWF
model solution of maintaining the moisture field south of the area
with the dry air mass persisting. Thus, it appears that the GFS
model solution may be an outlier scenario at this time. Forecast
at this time sides more with the ECMWF solution in showing low
rain chances for Monday and Tuesday. Thereafter, model guidance
agrees that moisture increases by Wednesday and Thursday, with an
increase in diurnal convection expected.

&&

.AVIATION...VCSH at most terminals except TJMZ/TJPS til 07/14Z as
remnants of an old frontal boundary will linger across the local
areas. SCT-BKN lyrs nr FL022...FL050...FL090 with BKN lyr btw
FL200-FL250. Mtn Top obscr ovr E interior of PR due to low clds
and -SHRA til 07/12Z. Sfc Wnds generally fm ENE but light and
variable bcmg fm NE 10-15 kts aft 07/14Z. SCT-BKN lyrs will
continue across the region during the entire prd with Isold-SCT
SHRA ovr regional waters en route btw islands. L/Lvl wnds fm NE
5-15 kts blo FL100 but bcmg fm W and incr w/ht abv with max winds
of 60-65 kts btw FL300-FL350.

&&

.MARINE...A lingering northerly swell will result in choppy seas
of up to 6 feet across the Atlantic for today. Therefore, small
craft operators should exercise caution. Across the rest of the
local waters, seas of less than 5 feet are expected. For
beachgoers, there is a high risk of rip currents across the
beaches from Pinones to Aguadilla along the north coast of Puerto
Rico. There is a moderate risk of rip currents across the rest of
the north and some east-facing beaches of the islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 73 83 72 / 40 50 30 30
STT 86 72 86 70 / 40 30 50 50

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Thu Apr 8 2021

.SYNOPSIS...High level clouds along with the remnants of a frontal
boundary will linger across the region today into Friday. Surface
high pressure will continue to build across the southwest Atlantic
resulting in a prevailing northeast wind flow across the area.
Available moisture along with local effects and brief breaks in cloud
cover will support shower development mainly across the interior and
southwest Puerto Rico. Diminishing cloud cover and a drier air mass
is expected by the weekend. Another northerly swell will invade the
local Atlantic waters resulting in choppy seas as well as a moderate
to high risk of rip currents for the north- facing beaches of Puerto
Rico for today.

&&

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

Surface high pressure across the southwestern Atlantic will continue
to produce a northeasterly wind flow through the period. A frontal
boundary will continue to linger over the area through today with
abundant low-moisture as precipitable water values remain between
1.7 and 1.8 inches. Therefore, expect additional shower activity to
affect the area today, mainly across mainland Puerto Rico. Some
activity may affect the north coast of the island during the morning
hours followed by the development of afternoon activity across
interior and southwestern portions of the islands. Recent satellite
imagery continues to show an abundance of mid to high level clouds
over the area moving in an west to east fashion and this cloudiness
is expected to linger through much of the day. Therefore, this may
limit the amount of heating that occurs over the land and thus may
also limit the intensity of the afternoon convection. Nevertheless,
given that the steering flow remains very light, any activity that
develops will move slowly and thus may have the potential to result
in isolated areas of urban and small stream flooding as well as
ponding of water on roadways. Across the USVI, very little shower
activity is expected once again.

On Friday, the frontal boundary will have pushed south of the area
with the moisture content gradually decreasing throughout the day.
However, there will be sufficient moisture in the low-levels to
combine with daytime heating and local effects to generate some
afternoon shower activity across interior and southwestern Puerto
Rico with rainfall accumulations expected to be less than today.

Conditions really dry out by late Friday night through Saturday as a
much drier than normal air mass moves in. In fact, precipitable
water values drop to around 0.7 inches, which is more than two
standard deviations below normal for this time of the year. In
addition, the dewpoint depression between the 850-700 mb layer will
be in the 20-30 Celsius range. Therefore, the environment will be
very hostile for shower development and thus all of the area should
remain dry under fair weather skies.


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

A much drier air mass will continue through Sunday and Monday as
surface high pressure and weak mid to upper level ridge will dominate
the local weather pattern. Therefore, relatively tranquil weather
conditions with limited shower activity are so far forecast. Some
locally induced afternoon shower activity still cannot be ruled over
mainly over portions of interior Puerto Rico. Otherwise the rest of
the region should remain mostly sunny and fairly dry. Much warmer
temperature can be expected by Tuesday and through most of the
following next week, as winds become more southeasterly.

By Tuesday and through the middle of next week, the pattern however
changes based on recent model guidance. The prevailing winds become
more east to southeast resulting in a much warmer and moist environment
as low level moisture returns and an upper level short wave trough
moves across the region. This will result in unstable conditions
and cooler temperatures aloft. Moisture remnants from the old frontal
boundary returns once again, as the local winds become southeasterly
and the a surface high pressure moves further into the central Atlantic
while a low pressure system with an associated frontal boundary
enters the the western Atlantic. Therefore expected a fairly wet
and unstable weather pattern at least through Thursday with potential
for enhanced showers and isolated thunderstorms development across
the islands and coastal waters. The potential for urban and small
stream flooding will therefore increase during that time.

BY Friday, models guidance suggest a drier weather pattern as low
level winds become more southerly and moisture decreases across
the region and a weak ridge builds aloft. This will result in lesser
shower development across the islands with mostly fair weather to
prevail. In fact with the expected prevailing wind flow, a low
concentration of saharan dust will be possible during the latter
part of next week.

&&

.AVIATION...
Mainly VFR conditions expected across all area terminals through the
period. VCSH possible across TJSJ, mainly between 08/10z and 08/16z
and across TJPS between 08/16z and 08/23z. SCT-BKN layers between
FL050 and FL080 are expected at times through the period. Winds will
be from the ENE-NE up to 10 kts through 08/14z, increasing to between
12 and 18 kts with some higher gusts afterwards with sea breeze
variations.

&&

.MARINE...
Seas will range between 3-5 feet today with prevailing northeast winds
between 10 to 15 knots expected to prevail through the end of the
workweek. However by later tonight a northerly swell will increase
seas up to 6 feet once again small crafts should therefore exercise
caution. A moderate to high risk of rip currents is expected during
the next few days, across the northern beaches of Puerto Rico and
a moderate risk of rip currents for most of the remaining beaches
along the north and east coasts of the islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 80 72 81 71 / 40 30 30 20
STT 85 71 84 67 / 20 20 20 10

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
431 AM AST Fri Apr 9 2021

.SYNOPSIS...
Surface high pressure ridge will build north of the region to
increase the northeast wind flow into the weekend. A broad mid to
upper level trough will lift further north into the north central
Atlantic, as a high pressure ridge will build across the region.
Diminishing mid to upper level cloud cover and increasing dry
and stable conditions is expected to continue and spread across
the region today and through the weekend. A northerly swell will
continue to invade and spread across the Atlantic and Mona passage
today.

&&

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

A surface high pressure building over the southwestern Atlantic is
providing a northeasterly wind flow across the area, which is
expected to prevail through much of the upcoming weekend. This
feature is also pushing the remnants of a frontal boundary south of
the area, with a drier air mass beginning to move in. As a
result, mostly fair weather conditions are expected to prevail
through much of the area for today. However, some residual
moisture will still be in place to combine with daytime heating
and local effects to generate some afternoon shower activity
across southwestern Puerto Rico. Rainfall accumulations for the
most part should remain on the light side.

Thereafter, by later tonight and prevailing through much of the
upcoming weekend, a much drier than normal air mass is expected to
penetrate into the area from the north with precipitable water
values falling to between 0.7 and 0.9 inches, which is around two
standard deviations below normal for this time of the year. In
addition, the dewpoint depression at lower levels, in the 850-700 mb
layer, is expected to solidly range between 20 and 30 degrees
Celsius. As a result, environmental conditions are expected to
become extremely hostile for shower development through much of the
upcoming weekend and thus, mostly dry conditions under fair weather
skies are expected.

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

Overall dry and stable conditions will persist through Monday as
surface high pressure and a mid to upper level ridge will hold in
place across the local area. Mostly fair weather conditions with
limited shower activity is so far forecast for most areas. However,
locally induced afternoon showers will remain possible through at
least Tuesday but should be focused mainly over portions of interior
Puerto Rico. Much warmer temperature can be expected by Tuesday
and through the rest of the following next week, as winds become
more southeasterly.

By Late Tuesday and through at least Thursday, model guidance
still suggests a shift in the weather pattern due to increasing
moisture and the approach of a short wave trough just north of the
region. The prevailing winds will become southeasterly resulting
in a much warmer and moist environment, as low level moisture
returns and the upper trough crosses just north of the region.
This scenario will result in unstable conditions and cooler
temperatures aloft. Therefore expect a fairly wet and unstable
weather pattern at least through Thursday with potential for
enhanced showers and isolated thunderstorm development across the
islands and coastal waters. The potential for urban and small
stream flooding will therefore be high especially during the
afternoon hours.

By Friday and Saturday, models guidance continue to suggest a
drier weather pattern as low level winds become more east southeast
and moisture decreases across the region as a weak ridge builds
aloft. Therfore a seasonal weather pattern is expected with lesser
afternoon shower development forecast for the islands as mostly
fair weather should prevail. The potential for significant
rainfall accumulations and flooding is not expected across the
islands during that time.

&&

.AVIATION...VFR conditions expected across the area throughout the
period. Sct SHRA possible across SW PR between 09/17z and 09/22z,
possibly resulting in VCSH across TJPS. Otherwise, fair wx
conditions will prevail. Winds will continue from the NE below 10
kts through 09/12z, increasing to 12-20 kts with sea breeze
variations after 09/14z.


&&

.MARINE...Small craft should exercise caution during the morning
hours, due increasing northeasterly winds and the arrival of a
northerly swell. Seas increasing 5 to 7 feet and winds up to 20
knots can be expected by this afternoon. Therefore, Small Craft
Advisories will be in effect starting this afternoon. Please refer
to the latest Coastal Waters Forecast (CWFSJU) and Marine Weather
Message (MWWSJU) issued by WFO San Juan PR for the latest
updates.

There is a high risk of rip currents for the northwest to northeast
beaches of Puerto Rico, northern beaches of Culebra and northwest
beaches of St Thomas. These is a moderate risk of rip currents for
some east facing beaches of PR and most of the remaining beaches
of the USVI, Vieques and Culebra. Please refer to the latest Coastal
Hazard Forecast (CFWSJU) and Surf Zone Forecast (SRFSJU) for the
most up to date info.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 81 71 82 71 / 10 10 0 10
STT 85 70 83 70 / 10 0 0 10

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
443 AM AST Sat Apr 10 2021

.SYNOPSIS...Generally fair and stable weather conditions with
limited shower activity will prevail through early next week as
drier air moves in from the north and ridging aloft holds over
the region. A slight increase in moisture may enhance shower
activity on Sunday, but it is not until midweek when
environmental conditions are forecast to become favorable for
shower and possible thunderstorm development across the region.
Under a generally southeasterly wind flow, warmer temperatures can
be expected by the mid to latter part of the workweek.


&&

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

A mid-to-upper level ridge and the associated surface high
pressure located over the western Atlantic will dominate the local
weather pattern for the short term period. For today, a drier air
mass is expected to filter into the region. According to
satellite GOES-16 derived data, the dry air mass that will
dominate the island today has precipitable water values of 0.70 to
1.0 inches. As a result, rain activity for the island is expected
to be light to moderate. However, the combination of the moisture
available and the local effects could result in localized
isolated to scattered showers throughout the interior and
southwest sections of Puerto Rico. As the high pressure moves
eastward into the Atlantic, the generated northeast wind flow will
push a band of cloudiness and moisture over the island on Sunday.
The aforementioned band, in combination with an area of moisture
in the 850 mb layer, could result in shower activity. If model
guidance is correct, this increase in showers for Sunday could
result in ponding water on roadways and poor drainage over the
interior and western sections of Puerto Rico.

On Monday, as the ridge mentioned above moves eastward into the
central Atlantic and merge with an elongated high pressure across
the eastern Atlantic, a drier airmass will push in the region.
The presence of the ridge will dominate the local region, bringing
stable conditions aloft. According to both model guidances (GFS
and ECMWF), unfavorable conditions will be in place for
widespread activity over the forecast area due to the limited
available moisture. However, isolated to scattered shower activity
will be possible in the afternoon hours due to local effects,
favoring the interior and northwestern sections of Puerto Rico.
Additionally, a southeasterly component is forecast for early
afternoon on Monday. This wind flow will promote slightly warmer
temperatures over the region on Monday.

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

Recent model guidance suggests that dry and stable weather
conditions with limited shower activity will prevail through early
Tuesday. Then, weather conditions are to gradually shift into a
wetter and unstable weather pattern beginning Tuesday evening and
continuing through late Thursday night, with peak moisture
expected by Thursday afternoon with model- estimated precipitable
water peaking around 1.90 inches. Thereafter, model guidance
suggest that drier and stable weather conditions will return and
hold through the weekend as a ridging builds aloft.

Initially, a mid to upper level ridge along with the presence of
drier air will maintain mostly fair weather conditions early
Tuesday. As the ridge moves eastward and away from the region, a
weakening in the trade wind cap is expected by. This, along with
the passage of a short wave trough just north of the region, will
support favorable conditions for shower and possible thunderstorm
development, with 500 mb temperatures falling below -8 degrees
Celsius. The bulk of the moisture will stall over the Caribbean
waters and south of the local islands Tuesday into Wednesday,
crossing the region Wednesday into Thursday as winds increase and
turn more from the southeast. This scenario presents the potential
for urban and small stream flooding across the local islands,
favoring portions of eastern and southern Puerto Rico and the US
Virgin Islands through the overnight and early morning hours, and
northern Puerto Rico in the afternoon. Drier air along with
unfavorable conditions aloft are expected to return by Friday into
the weekend. Under a generally southeasterly flow, warmer
temperatures can also be expected.


&&

.AVIATION...Mainly VFR conditions all forecasts for all the TAF
sites until 1106Z. Winds will remain VRB and from NE until 1012Z,
then mostly E-NE are expected for all the TAF sites. VCSH
conditions are possibles on TJPS around 1118Z to 1021Z.


&&

.MARINE...Seas continued to subside, but small craft operators
are urged to exercise caution across the Atlantic Waters and local
passages due to choppy seas up to 6 feet. Elsewhere, tranquil
seas up to 5 feet are expected. A small northerly swell is
expected to invade the local waters Sunday into Monday, but Small
Craft Advisory criteria is not expected. Winds will remain from
the east to northeast at 10-15 knots today.

For beachgoers, a high risk of rip currents will continue for
north-facing beaches of Puerto Rico, Culebra and Saint Thomas.
Surf zone conditions will improve by this afternoon into late
tonight.



&&

.PRELIMINARY POINT TEMPS/POPS...
SJU 83 71 84 73 / 10 10 20 10
STT 85 71 84 72 / 10 20 20 20

[cycloneye]

Eagered to see our friend in Barbados abajan as that island is being bigtime affected by thick ash.

[cycloneye]

Area Forecast Discussion
National Weather Service San Juan PR
431 AM AST Sun Apr 11 2021

.SYNOPSIS...Generally fair and stable weather conditions with
limited shower activity, if any, will prevail through early next
week as drier air moves in from the north and ridging aloft holds
over the region. Favorable environmental conditions along with an
increase in low-level moisture are expected to enhance shower and
thunderstorm development beginning on Tuesday, with highest
impact expected on Thursday. Under a southeasterly wind flow,
warmer temperatures can be expected by the mid to latter part of
the workweek. Hazardous surf zone conditions will continue.
Elevated fire danger conditions are also expected today.


&&

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

A surface high pressure north of the area continues to induce a
northeasterly wind flow, expected to become more easterly later
today. Meanwhile, a very dry air mass remains over the entire region
with the GOES-16 Total Precipitable Water product showing values of
around 0.7-0.8 inches. A band of slightly higher low-level moisture,
with a precipitable water value of around 1.0 inch, is located just
to the northeast of the region and will move over Puerto Rico later
this morning into this afternoon. This may spark a few showers
across interior and western Puerto Rico this afternoon with only
very minor accumulations, if any, expected. Elsewhere, dry
conditions should prevail.

On Monday, the low-level winds are expected to switch from the
southeast as the aformentioned surface high pressure moves farther
east. The air mass will continue to remain very dry with
precipitable water values expected to range between 0.8 and 1.0 inch
and the dewpoint depression at the 850-700 mb level expected to
solidly range between 20-30 degrees Celsius, signifying that a
strong trade wind cap will remain in place. Therefore, another
mostly dry day is expected across the entire region.

Conditions then begin to change somewhat on Tuesday. Low-level
moisture is expected to increase from the southeast with
precipitable water values expected to climb to between 1.3-1.5
inches. In addition, the trade wind cap will weaken considerably.
The combination of these factors should allow for an increase in
afternoon convection. With the winds at 850 mb and higher up
expected to be out of the southwest, the afternoon convection will
be concentrated across the eastern half of Puerto Rico. Elsewhere,
including the U.S. Virgin Islands, just isolated showers are
expected.

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

Recent model guidance suggests that a shift from a relatively dry
and stable to a wetter and unstable weather pattern will take
place on Wednesday and continuing through at least late Thursday
night. A delay in the peak of moisture is now presented,
suggesting highest model-estimated precipitable water around 1.90
inches by Thursday night. Thereafter, global models suggest
different scenarios. The GFS calls for a building surface high
pressure centered over the north central Atlantic and extending
into the northeastern Caribbean to remain as the dominant feature.
The high will block a short-wave trough from approaching the
region, resulting in improved weather conditions with ridging
aloft and the entrance of drier air Friday onwards. In contrast,
the ECMWF calls for a weak surface high, with the short-wave
trough to the north and the remnants of an old frontal boundary
pushing southward across the area. As a result, the latter
scenario calls for a wetter and unstable weather pattern through
the weekend.

As a mid-to-upper level ridge continues to move eastward and away
from the region early Wednesday, further weakening in the trade
wind cap is expected. This, along with the passage of a short
wave trough just north of the region, will support favorable
conditions for shower and possible thunderstorm development, with
500 mb temperatures falling below -7 degrees Celsius. The bulk of
the moisture is forecast to move over the region Wednesday into
Thursday under a generally light to moderate southerly wind flow.
This scenario, under a weak steering flow, presents the potential
for urban and small stream flooding across the local islands, with
highest impact across portions of eastern and southern Puerto
Rico and the US Virgin Islands through the overnight and early
morning hours, and northern Puerto Rico in the afternoon. At 850
mb, model guidance is suggesting a southwesterly component in the
wind, which may result in afternoon convection focusing over the
northeasterly quadrant of the island. Under a generally southerly
flow, warmer temperatures that could peak into the lower to mid
90s can also be expected. Since global models are suggesting two
very different scenarios, there is low confidence on what
conditions can be expected by the end of the workweek into early
next week. For now, the local forecast will favor improved weather
conditions with enhanced locally-induced shower and isolated
thunderstorm development due to increased diurnal effects.


&&

.AVIATION...Mainly VFR conditions with fair wx conditions expected
to prevail during the next 24 hours. Winds light and variable
through 11/12z, increasing to 10 to 15 kts from the ENE-NE with sea
breeze variations after 11/14z.


&&

.MARINE...Small craft operators are urged to exercise caution
across the offshore Atlantic waters due to choppy seas up to 6
feet, resulting from a northerly swell invading the local waters.
Elsewhere, tranquil seas up to 5 feet are expected. A surface
high pressure to the north will maintain a moderate east-
northeast wind flow through Sunday, turning from the east to
southeast on Monday. Limited shower activity, if any, is expected
through the beginning of the workweek.

For beachgoers, there is a high risk of rip currents for beaches
along the north coast of Puerto Rico and Culebra. For other
north- and east-facing beaches of Puerto Rico, Vieques, and the US
Virgin Islands, a moderate risk continues. The risk will elevate
to high for beaches along the north coast of Saint Thomas by this
evening.


&&

.FIRE WEATHER...Recent soil and fuel moisture reports have
supported further drying across the local islands, with KBDI
values above 600 and 10-hour fuel moisture as low as 8 per cent.
Today`s forecast calls for another day of generally dry and stable
weather conditions, under mostly sunny skies and no chance for
significant wetting rains. As a result, relative humidities are
expected to fall once again into the upper 30s to lower 40s. The
general wind flow may remain below 15 mph, but sea breeze
variations may generate winds of 15 mph or higher between the late
morning and early afternoon hours. Therefore, a Fire Danger
Statement was 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 84 71 86 73 / 10 0 0 0
STT 85 72 84 72 / 10 0 0 20

[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