Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 041544

Area Forecast Discussion
National Weather Service San Juan PR
1144 AM AST Thu Mar 4 2021

.UPDATE...Fair weather has prevailed across the local area as
below normal moisture prevails. isolated showers have been
observed over the waters, and only very light and brief showers
were observed this morning across eastern PR. The winds are now
from the SE and lighter today than they have been over the past
few days. This SE wind direction and lighter wind speed is
expected tomorrow as well. The daytime high temps so far have been
in the mid 80s. The latest guidance still suggests that drier than
normal conditions are expected through Friday morning, with deep
moisture moving in from a tropical wave late on Friday, and some
moisture lingering into the weekend.


.AVIATION...VFR conds expected through today into Friday morning.
VCSH is possible at TJBQ after 04/16. Prevailing SE winds around
10KT with sea breeze variations, causing east winds at TJSJ and
north winds at TJBQ. Winds will become light and variable


.MARINE...Choppy seas up to 5 or 6 feet expected this afternoon
and tonight. There is a moderate risk of rip currents today, but
a high risk of rip currents for north central PR tonight. Winds
generally up to 10 knots today and tonight.


.PREV DISCUSSION... /issued 422 AM AST Thu Mar 4 2021/

SYNOPSIS...Fair weather conditions due to a drier than normal air
mass will prevail through early Friday. Moisture will increase in
southeasterly flow later Friday through Saturday, resulting in an
increase in shower activity. Drier conditions expected for Sunday
before low-level moisture gradually increases through most of
next week. Winds are expected to increase as well by early next
week as another surface high pressure moves across the western

SHORT TERM...Today through Saturday...

Drier than normal conditions will prevail across the islands today
and early Friday morning, as indicated by the GOES-East water vapor
channels. At mid-levels, a high-pressure over the northeast
Caribbean is promoting subsidence and dry air at those levels. At
the surface, the interaction of a frontal boundary over the western
Atlantic and a surface-high pressure across the central Atlantic is
inducing a weak southerly wind flow across the northeast Caribbean.
Under these weather conditions, expect above-normal temperatures
north of the Cordillera Central of Puerto Rico, little or no rain
activity, and calm to light and variable winds across Puerto Rico
and the U.S. Virgin Islands.

The weather pattern will persist through at least late in the
morning or the afternoon of Friday when an easterly disturbance,
forecasted to propagate across the islands, enhance rain formation
across PR/USVI. Dynamic aloft could be reinforced by an eastward
propagating mid to upper-level trough forecast to reach the islands,
as both GFS and ECMWF suggest. The trailing moisture of this
disturbance will promote rainy conditions through at least Saturday.
If the timing is correct, urban and small stream flooding will be
likely Friday afternoon through Saturday evening.

LONG TERM...Sunday through Thursday...

Fair weather conditions are expected to return on Sunday as a
drier air mass moves across the area, limiting shower activity.
On Monday, a frontal boundary is expected to be situated northwest
of the area, with an increase in low-level moisture expected.
This will cause shower activity to increase somewhat with isolated
to scattered showers across eastern Puerto Rico and the USVI
during the morning hours followed by locally induced activity
across western Puerto Rico during the afternoon hours. The low-
level winds will then increase on Tuesday and Wednesday as a
surface high pressure builds across the western Atlantic. This
will favor a cool advective pattern with patches of moisture
moving across the area from time to time, resulting in trade wind

Then, by the end of the long term period, the weather pattern
begins to undergo changes aloft as a mid and upper-level trough
amplifies across the central and eastern Caribbean. If model
guidance is correct on this solution, then a more unstable
weather pattern is more likely by the latter half of next week
with more enhanced shower activity possible across portions of
the area.

AVIATION...VFR conditions will prevail today. Winds will persist
from the ESE- SE at 10 kt or less, with sea breeze variations
after 04/13z. VCSH will remain possible without any impact on

MARINE...A northerly swell is expected to impact the Atlantic
waters and local passages later today through Friday. This will
result in choppy seas of up to 6 feet, mainly across the offshore
Atlantic waters. Across the rest of the local waters, seas of up
to 5 feet are expected. Seas are expected to remain below 6 feet
through the upcoming weekend.

For beachgoers, there is a moderate risk of rip currents across
all the northern beaches of Puerto Rico and Culebra as well as the
easternmost beaches of Vieques and Saint Croix for today. The rip
current risk increases to high across the north-central beaches
of Puerto Rico for tonight due to the aformentioned northerly


SJU  86  73  86  74 /  20   0  40  50
STT  85  73  85  73 /  20  20  50  60


PR...High Rip Current Risk from 6 PM AST this evening through late
     tonight for North Central.



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