Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 150840
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
440 AM AST Fri Dec 15 2017

.SYNOPSIS...A mid to upper level ridge will hold across the
forecast area through at least midweek next week. A surface
high across the east central Atlantic will yield east northeast
winds through the weekend. Mainly fair and stable weather
conditions are expected to prevail during the next few days.

&&

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

The local weather conditions are dominated by a strong ridge
pattern, which favors a trade wind cap across the islands. GFS
forecast soundings are indicating a relative dry air mass through
the weekend, with below normal TPW values for the month of December.
Limited moisture advection will continue with light to moderate
easterly trade winds. Therefore, expect mostly sunny skies with a
few passing clouds and pleasant daytime and overnight temperatures
during the next few days. However, a few light passing showers
will remain possible during the overnight and early morning hours
followed by limited shower activity during the afternoon.

.LONG TERM...Monday through Saturday...

A mid to upper level ridge will hold across the forecast area
through at least midweek next week. The ridge pattern aloft is
then expected to erode by the end of the upcoming week as a broad
trough establishes across the central Atlantic and into the
eastern Caribbean. At lower levels, migratory surface highs north
of the area will prevail much of the forecast period, resulting in
a moderate to fresh east northeast wind flow. Under a ridge
pattern aloft, expect a fair and mainly stable weather pattern
across the local islands much of the upcoming week with a few
passing showers possible. Seasonable temperatures are also expected.
Low level moisture is then expected to increase as the ridge
aloft collapses by the end of the forecast period to result in a
better chance for shower activity across the local islands.

&&

.AVIATION...VFR conditions will prevail through the forecast period.
Brief SHRA along and to the west of the Cordillera Central could
affect the flying area of JMZ/JPS btwn 15/19-22z. Surface winds will
continue light to calm and variable but increasing between 10 and 15
kts after 15/12z.
&&

.MARINE...A northerly swell will continue to spread across the
Atlantic waters and local passages throughout the day. Seas up
to 7 feet are expected mainly across the offshore waters.Elsewhere,
seas between 3 and 6 feet. A high pressure ridge will build and
spread across the forecast area, tightening the local pressure
gradient. This will result in a moderate to fresh east to northeast
wind flow during the next several days. There is also a high risk
of rip currents along the north facing beaches of the local
islands.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  86  76  85  77 /  10  20  30  20
STT  86  76  86  75 /  10  20  30  20

&&

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

VI...High Rip Current Risk through late tonight for St.Thomas...St.
     John...and Adjacent Islands.

AM...High Rip Current Risk through late tonight for 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 8 AM AST Saturday for Atlantic Waters
     of Puerto Rico and USVI from 10 NM to 19.5N.

&&

$$

SHORT TERM...CAM
LONG TERM....OM


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