Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 111953

Area Forecast Discussion
National Weather Service San Juan PR
353 PM AST Tue May 11 2021

A mid to upper-level ridge will promote stable weather conditions
through Thursday, with a few showers moving across eastern Puerto
Rico and the U.S. Virgin Islands during the overnight and morning
hours. Sea breeze convergence and local effects will induce a few
showers during the afternoon which will yield light rainfall


.SHORT TERM...Tonight through Thursday...
Partly cloudy skies prevailed across Puerto Rico and the local
islands today. GOES-16 imagery shows low to high clouds moving
rapidly over the local islands. A few showers developed over the
eastern and western areas of Puerto Rico; this activity was a
result of easterly trade winds and local effects. A mid to upper-
level ridge will promote a fairly stable weather pattern through
Wednesday due to dry sinking air in the mid levels of the
atmosphere and limited moisture content. Nevertheless, a few
passing showers are possible during the overnight and early
Wednesday morning. Then, showers due to sea breeze convergence and
local effects will appear during the afternoon. Mid to upper-
level coupled with limited moisture content will inhibit the
development of deep convection and cause showers to produce light
rainfall amounts. Thursday, the upper-level trough currently to
the west of Puerto Rico is forecast to lift north of the area
resulting in a modest uptick in upper-level instability during the
afternoon. The modest instability and local and diurnal effects
will induce showers across interior, eastern, and northern Puerto
Rico during the afternoon.


.PREV DISCUSSION... /issued 302 AM AST Tue May 11 2021/

.LONG TERM...Friday through Tuesday..
A mid-to-upper level ridge is forecast to hold over the region
through the long term period. A polar trough and associated
surface front are expected to remain north of area, while a
surface high pressure over the central Atlantic moves further east
late in the period. This will cause winds to turn more from the
southeast during the weekend. Warmer than normal temperatures are
expected with the southeasterly winds. Hazy skies due to Saharan
dust are possible early next the week, as a Saharan Air Layer is
forecast to enter the southeastern Caribbean. The upper level
ridge will promote drier air aloft and more stable conditions in

At lower levels, moisture is expected to be capped below 700 mb,
and this shallow layer of moisture will bring occasional passing
showers across the USVI and eastern sections of PR during the
overnight/early morning hours. During the afternoon hours, the
combination of the available low-level moisture, daytime heating
and the sea breeze convergence will cause showers to develop
mainly over the west/northwest sections of PR, and from streamers
downwind of the USVI.


Mainly VFR conditions expected. VCSH are expected across
the terminals, but showers are moving quickly. VCSH expected for
TJBQ after 11/17Z. BKN/OVC sky expected at FL050 or so, but lower
CIGS is possible at times near SHRA, which could result in MVFR
conditions. Winds are out of the E at 15 to 20 knots with stronger
gusts. BKN layers will continue at FL050 to FL080 through
around 12/02Z.



Choppy seas up to 6 feet will continue across the Atlantic waters
and local passages. Winds will continue from east up to 20 kts
through Thursday, then decrease to 10 to 15 kts later this week. A
northerly swell is forecast to invade the Atlantic waters late
Wednesday night into Thursday. A moderate rip current risk will
continue across the north, east, and western beaches of Puerto
Rico, and across all the beaches of the U.S. Virgin Islands,
Vieques and Culebra.


SJU  78  87  77  89 /  40  20  30  30
STT  76  87  77  87 /  30  20  30  20




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