National Weather Service San Juan PR
414 AM AST Mon Dec 7 2020
.SYNOPSIS...A patch of shallow moisture will enhance shower
activity today, particularly over the northwestern quadrant of
Puerto Rico in the afternoon. Thereafter, fair and stable weather
conditions will persist through at least Thursday. Thereafter, an
increase in moisture and somewhat favorable conditions aloft will
enhance shower activity. Winds will be out of the southeast
during the next few days, turning from the east-northeast by the
end of the workweek.
&&
.SHORT TERM...Today through Wednesday...
A patch of deeper moisture is currently affecting the local area,
causing mostly cloudy skies over the local islands and light brief
showers across the USVI into eastern PR this morning. This patch of
moisture will continue moving slowly west today, causing light to
moderate rain across the local area and variably to mostly cloudy
skies for most of the day. Afternoon showers are expected across NW-
PR, but the showers expected are expected to cause little
accumulation. High pressure in the mid and upper levels will keep a
stable atmosphere, that is why the shower activity that is expected
will likely be light to moderate for the next few days. Winds today
are expected to become lighter as they gradually shift SE, then
drier air moves in starting late tonight into Tuesday, and
essentially having dry air through Wednesday. The SE winds continue
into Tuesday and Wednesday, but are expected to be light.
Essentially fair weather is expected for most of the short term
period, with clouds and some rain today, drying off by Tuesday and
remaining dry on Wednesday. If shower activity occurs on Tuesday and
Wednesday, it is expected to be light.
.LONG TERM...Thursday through Sunday...
Recent model guidance now suggests that ridging aloft will hold
over the region through earlier than expected, holding strong
through Thursday and gradually weakening late Thursday night into
Friday. Regardless, expect stable weather conditions under a
strong trade wind cap and limited available moisture while ridging
holds. In the meantime, a strong mid-to-upper level trough is
expected to sink southward across the western Atlantic, with
developing low over the northeastern Caribbean during the
weekend. This feature will displace the ridge well to our east,
while weakening the trade wind cap. As a result, deeper moisture
content is forecast to move over the area, with model- estimated
precipitable water peaking between 1.7 and 1.9 inches between
Friday morning and Saturday evening. At the surface, an induced
surface trough, followed surface high pressure moving into the
western Atlantic from the continental United States, will maintain
a generally east-northeast wind flow. This flow will favor
overnight and early morning passing showers moving over eastern
and northern Puerto Rico and the USVI, while afternoon convection
development, if any, will cluster along the interior and
southwestern sections of Puerto Rico. If this forecast
materializes, environmental conditions will be somewhat favorable
to support enhanced shower activity by the end of the workweek
into the upcoming weekend.
&&
.AVIATION...Prevailing VFR conds expected across all local terminals
for the next 24 hours. Brief SHRA may result in VCSH across TJSJ,
TISX and TIST through 07/16Z. Sct SHRA forecast across NW PR between
07/18Z and 08/22z, possibly resulting in VCSH at TJBQ. BKN SKY will
cause CIGS at around FL070 today, but TEMPO CIGS at FL020-030 is
possible through 07/13Z mainly at IST and TISX. Light and variable
winds expected through 07/12z, increasing to up to 10 kts or so from
the ESE to SE with sea breeze variations after 07/14Z.
&&
.MARINE...A northerly swell will continue to cause choppy seas up
to 6 feet across the Atlantic waters and Anegada passage, where
small craft operators should exercise caution through late Monday
night. Elsewhere, tranquil marine conditions with seas at 5 feet
or below will prevail. As the swell subsides, tranquil marine
conditions will return to all regional waters. There is a high
risk of rip currents for the northern and eastern beaches of
Puerto Rico and the beach of eastern St. Croix through Monday
night.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 83 73 85 73 / 30 30 30 20
STT 84 74 84 74 / 50 50 20 40