Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 161522
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1122 AM AST Tue Jan 16 2018

.UPDATE...Near normal moisture is expected today across the local
area with some brief showers moving in from the east, while the
western interior and southwestern sections of PR could observe
showers due to the combination of the local effects with diurnal
heating. The short term forecast for this afternoon was adjusted a
little to account for the agreement of the different high
resolution models and latest observations. The southwestern
quadrant of Puerto Rico, particularly around the municipality of
Maricao. Eastern PR to the USVI also has a chance of showers but
the activity is expected to be somewhat brief, causing mainly
ponding of water. The significant showers are expected to have
dissipated by this evening, leaving the isolated to scattered
brief showers for tonight.

&&

.AVIATION...Mainly VFR conds with TEMPO MVFR possible at TJMZ
after 16/17Z. VCSH possible in the rest of the terminals,
especially the USVI terminals and TJSJ. Winds will be from the
east at 10-15KT, with sea breeze variations and variations in
direction and speed near the showers. Winds to diminish for the
overnight hours and SHRA activity decreasing tonight, leaving
mainly ISOLD to SCT brief SHRA.

&&

.MARINE...There is still a small craft advisory in effect until
Wednesday and there is also a high risk of rip currents. The
northeasterly swell invading the local waters is expected to
subside on Wednesday and seas are expected to be below 7 feet by
Thursday.

&&

.PREV DISCUSSION... /issued 436 AM AST Tue Jan 16 2018/

SYNOPSIS...A mid to upper level ridge will gradually build from
the west and hold through the end of the week. Broad surface high
pressure across the north central Atlantic will continue to
slowly weaken and move over the Azores on Wednesday. A weak
surface high build across the western Atlantic during the weekend.
Moderate trades will continue for the next several days.

SHORT TERM...Today through Thursday...Cloudiness with showers were
noted across the local coastal waters and the eastern half of Puerto
Rico, and the U.S. Virgin Islands. A patch of low level moisture
embedded in the trade winds was affecting the region early this
morning. This area of moisture will continue to move west and will
produce isolated to scattered showers across most of the area this
morning and into this afternoon. For Wednesday, this weather pattern
will continue as more patches of low level moisture moves across the
islands.

High pressure system across the central Atlantic will continue to
dominate the local area through at least Thursday. Although a slot
of drier air is anticipated for Thursday, moisture content will
remain steady through the forecast period, with precipitable water
values remaining between 1.5 to 1.6 inches. Surface winds will
continue mainly east to east northeast at times.

LONG TERM...Friday through Tuesday...

No major change from previous forecasts, as trade wind showers
will continue through the forecast period. Each afternoon, the
limited available moisture content and the local effects will
result in the development of showers over portions of the
west/western interior sections of Puerto Rico. Across the USVI
and eastern PR, streamers are expected to develop early in the
afternoon hours and continue to leave mainly minor rainfall
amounts over land areas. As a surface high pressure moves into the
western Atlantic, winds will shift more from the east- northeast
and passing trade wind showers will focus across the local
Atlantic waters and over the north/northeast sections of PR and
the northern USVI.

AVIATION...Mainly VFR conditions expected throughout most of the
forecast period. However, trade wind showers could move in across
the Leeward/USVI/eastern PR terminals at times. Afternoon SHRA
development is expected over the western PR terminals with MVFR
conditions possible briefly. Low level winds will continue mainly
from the east between 10-20 kts.

MARINE...Northeast swell will continue to result in hazardous
seas across the Atlantic waters and across portions of the local
passages and the offshore Caribbean waters. Moderate easterly
winds will continue through the end of the week between 5-15 kts.
A high risk of rip currents will continue through at least
Wednesday afternoon across the Atlantic beaches of Puerto Rico,
Culebra and St. Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  82  74  84  74 /  30  40  50  40
STT  84  74  84  74 /  50  40  40  20

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Wednesday afternoon for North
     Central-Northeast-Northwest-San Juan and Vicinity-Southeast-
     Western Interior.

     High Rip Current Risk until 6 PM AST this evening for Culebra.

VI...High Rip Current Risk through Wednesday afternoon for St Croix.

     Small Craft Advisory until 2 AM AST Wednesday for
     St.Thomas...St. John...and Adjacent Islands.

AM...Small Craft Advisory until 2 AM AST Wednesday for Caribbean
     Waters of Puerto Rico from 10 NM to 17N-Coastal Waters of
     Northern USVI and Culebra out 10 NM-Coastal Waters of
     Southern USVI Vieques and Eastern Puerto Rico out 10 NM.

     Small Craft Advisory until 2 PM AST Wednesday for 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-Mona Passage Southward to 17N.

&&

$$

SHORT TERM...JA
LONG TERM....99


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