Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 200905

Area Forecast Discussion
National Weather Service San Juan PR
505 AM AST Fri Apr 20 2018

.SYNOPSIS...Broad surface high pressure will continue across the
eastern Atlantic through early next week. Patches of moisture
embedded in the trades will move occasionally across the region
for the next several days, inducing the development of showers and
thunderstorms each afternoon across interior and western Puerto
Rico with isolated to scattered showers across the U.S. Virgin
Islands and eastern Puerto Rico during the nights and early
morning hours.


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

Slightly drier air made its way into the local area last night,
causing a decrease in shower activity across the local islands.
However, an increase in moisture is expected today, which will
combine with the local effects and diurnal heating to cause showers
and isolated thunderstorms over Puerto Rico this afternoon. High
resolution model guidance suggests that with the exception of the
south coastal sections of PR, the rest of the island may observe
some rain with isolated sports of heavy rain across NW-PR and
portions of the interior and north central. For that reason only
minor modifications were made tot he inherited forecast and left
good probability of precip with isolated thunderstorms for the
forecast for this afternoon.

Scattered showers may affect the USVI but the western sections of St
Thomas and St Croix have a slightly higher chance of rain because
showers are expected to develop over the islands and stream off to
the west, so parts of those showers could affect the western

Another patch of moisture is expected tonight into Saturday, which
may cause scattered to locally numerous showers overnight tonight
across the local waters, USVI and eastern PR with isolated
thunderstorms once again in the afternoon hours over the interior
into NW-PR. There is also an upper trough that will be moving in
from the west which may increase instability over PR and cause
slightly more persistent thunderstorms. Bu Sunday, drier air has
moved in and wind flow may shift a bit to the ENE, which may cause
afternoon convection across SW-PR with isolated showers elsewhere.

.LONG TERM...Monday through Friday...
Moisture peaks on Monday and Tuesday and an upper level trough
will support thunderstorm development each day. But overall the
same weather pattern is expected to prevail each day. Shower and
thunderstorm development is expected to develop each afternoon
over portions of western Puerto Rico. Trade wind showers will
persist across the USVI and eastern portions of PR during the
overnight and early morning hours. Drier air is expected to move
once again from the east by Friday. Day time maximum temperatures
are expected to reach the high 80s to low 90s across the lower
elevations and overnight minimum temperatures are expected to
range from the low 60s across the higher elevations to low 70s
along the lower elevations.


.AVIATION...VFR conds in the morning hours across the local
terminals. SHRA/SHRA expected this afternoon may cause moments of
MVFR across TJSJ, TJMZ, and TJBQ after 20/16Z. TEMPO groups were
left out due to exact timing uncertainty except TJBQ which may have
convection after 20/19Z. Winds will be from the east becoming breezy
at 15-20kt and gusty.


.MARINE...A long period northeast swell will continue to result
in life threatening rip currents across the north, east and
southeast facing beaches of Puerto Rico, Culebra, Vieques and St.
Croix. Small craft advisories are in effect for the offshore
waters and passages due to seas up to 7 feet. East winds will
continue at 15 to 20 knots across the region through the weekend.


SJU  88  75  86  75 /  60  40  40  20
STT  86  76  85  75 /  40  20  20  20


PR...High Rip Current Risk through late tonight for North Central-
     Northeast-Northwest-San Juan and Vicinity-Southeast-Western

     High Rip Current Risk through this afternoon for Central

VI...High Rip Current Risk through late tonight for St Croix.

AM...Small Craft Advisory until 2 PM AST this afternoon for
Anegada Passage Southward to 17N-Caribbean Waters of Puerto Rico
from 10 NM to 17N-Mona Passage Southward to 17N.

Small Craft Advisory until 6 PM AST Saturday for Atlantic Waters
of Puerto Rico and USVI from 10 NM to 19.5N.



LONG TERM....DS is the U.S. government's official web portal to all federal, state and local government web resources and services.