Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 271522
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1122 AM AST Sat Feb 27 2021

.UPDATE...

Windy easterly trades will result in quick passing showers,
clouds, and gusty winds. TJSJ detected an increase in moisture
(1.35 inches of precipitable water) and E-ENE winds between 25 and
35 (between the surface and 3 k ft) knots across Puerto Rico and
the U.S. Virgin Islands. At mid-levels, dry air continues above
700 MB. This weather pattern will continue to advect clouds and
showers the next few days across most of the islands, resulting in
periods of low to moderate rains at times, especially across the
windward portions.

&&

.AVIATION...

VFR conditions will prevail today. However, easterly winds between
20 and 25 knots with gusts from 25 and 35 knots will affect the
local terminals. Winds will drop around 15 knots after 27/23z.
Should not rule out a few showers at times.

&&

.MARINE...

Seas and winds continue between 6 and 10 feet and out of the east
at 20 to 25 knots. Therefore, Small Craft Advisories are in effect
for the local waters.

Beachgoers, the risk of rip currents continues high for the north-
facing beaches of Puerto Rico, the southeast coast of PR, Culebra,
the eastern third of Vieques, the northwestern beaches of St
Thomas, and the north and east coast of St Croix.

&&

.PREV DISCUSSION... /issued 437 AM AST Sat Feb 27 2021/

SYNOPSIS...
Strong winds will continue across the region due to a surface high
pressure to the north, with sustained winds 20 to 25 mph expected.
These winds are causing hazardous marine conditions through early
in the workweek. A group of showers is expected to move across the
islands later tonight, increasing the potential for passing
showers. In the long term, significant rainfall are not expected.

SHORT TERM...Today through Monday...
An easterly perturbation moved overnight across the region and
scattered shower activity was observed across much of northern and
eastern half of Puerto Rico. The Doppler radar estimated between
half to an inch of rain, mainly over the northeast to north
central coastal areas of the island. Gusty winds between 25-32 mph
were observed with the showers and minimum temperatures ranged
from the mid 60s across the higher elevations to the mid 70s
across coastal areas in general.

Strong east to northeast winds will continue across the region
through the short term period, in response to a building high
pressure at the surface to our north. This will promote a cool
advective pattern across the region, favoring shower development
along the northern and eastern sections of Puerto Rico and across
the U.S. Virgin Islands. Sustained winds between 20-25 mph and gusts
up to 35 mph are expected through the weekend, mainly across coastal
areas. Another easterly perturbation is expected to move tonight
into Sunday morning across the islands, enhancing once again shower
activity over northeastern and north central Puerto Rico. Across
west/southwest PR, overall fair weather conditions should prevail
with gusty winds through the period. By early Monday morning, the
remnants of a front are forecast to move quickly across the Atlantic
waters and across the islands, increasing shower activity once again
during the overnight hours and a drier air mass will follow during
the day and promote more stable conditions across the region.

LONG TERM...Tuesday through Sunday...
A low to mid level high pressure will continue to be the dominant
feature as we extend into the long-term period. The global models
show an upper level trough developing over the central Atlantic,
but this feature won`t appear to have a strong influence over the
local islands. In fact, the mid-level ridge will maintain the
trade cap inversion through at least mid-week. Additionally, at
the lower levels precipitable water values are expected to range
from 0.8 to 1.3 inches of water. During this period, only shallow
moisture embedded in the trade winds will drag a few showers
across the islands, but without leaving significant rainfall
accumulation.

By the latter part of the workweek, a polar trough will exist the
eastern coast of the U.S., causing the ridge to flatten out. By
late Thursday into Friday, the forecast sounding from the GFS
shows a weaker trade wind cap. As a result, moisture a little
deeper will be able to enter the forecast area, increasing shower
activity a little bit. Moving into the weekend, another mid to
upper level ridge is expected to develop over the western
Caribbean, which once again will act to limit the potential for
vertical development across the islands. Precipitable water values
are expected to remain on the low side, with only occasional
patches of moisture being displaced from the east from time to
time.

AVIATION...Mainly VFR conditions are expected to prevail across all
terminals during the next 24 hours. However, SHRA may cause brief
MVFR conds at TJSJ and TJBQ through the period and mtn top obscd
ovr eastern and north central PR. SCT/BKN cigs from FL040-FL090.
Surface winds from the east at 20-25 kt with higher gusts expected
through the weekend.

MARINE...
Hazardous marine conditions continue across most of the local
waters, except southwestern Puerto Rico, with building seas up to
10 feet. This is due to a strong surface high pressure that is
causing fresh to strong winds across the waters, 20 to 25 knots
and stronger gusts. These conditions are expected to continue
through early in the workweek. As a result, Small Craft Advisories
are in effect.

For the beaches, there is a High Rip Current Risk statement for
the the northern, eastern, and southeastern Coast of Puerto Rico,
as well as for Vieques, Culebra, and St. Thomas and St. Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  84  73  84  73 /  70  60  50  50
STT  85  73  84  73 /  40  50  50  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late Sunday night for Central
     Interior-Culebra-North Central-Northeast-Northwest-San Juan
     and Vicinity-Southeast-Vieques.

VI...High Rip Current Risk through late Sunday night for St Croix-
     St.Thomas...St. John...and Adjacent Islands.

AM...Small Craft Advisory until 2 AM AST Monday for Caribbean Waters
     of Puerto Rico from 10 NM to 17N-Anegada Passage Southward
     to 17N-Atlantic Waters of Puerto Rico and USVI from 10 NM
     to 19.5N-Coastal Waters of Northern Puerto Rico out 10 NM-
     Coastal Waters of Northern USVI and Culebra out 10 NM-
     Coastal Waters of Northwestern Puerto Rico out 10 NM-
     Coastal Waters of Southern Puerto Rico out 10 NM-Coastal
     Waters of Southern USVI Vieques and Eastern Puerto Rico out
     10 NM-Mona Passage Southward to 17N.

&&

$$

SHORT TERM...CAM
LONG TERM....LIS


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