Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 251507
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1107 AM AST Tue Sep 25 2018

.UPDATE...Tutt low and associated mid to upper level trough will
continue to retrograde and cross the region through the end of the
work week. A Tropical wave/remnants of old tropical depression eleven
will continue to cross the forecast area today through Wednesday. The
combination of these two features along with good low level moisture
and speed convergence will maintain a moist and unstable environment
today through Wednesday. Therefore no changes made to the inherited
short term forecast package and reasoning as periods of showers and
isolated thunderstorm activity is expected to affect the coastal waters
and most of the islands. For the rest of the day, the moderate to strong
easterlies will continue to steer and spread developing afternoon convection
across the interior and west sections of Puerto Rico. The U.S. Virgin
islands will also continue to see periods of passing showers and isolated
thunderstorms with brief gusty winds during the rest of the day around
the islands and over the coastal waters.

&&

.AVIATION UPDATE...No change to previous AVN discussion. SCT OCNL
BKN LYS nr FL025...FL040 WITH SHRA/ISOLD TSRA over and en route
btw islands as tropical wave will contd to move across the region
today. Brief MVFR conds due to low clds and SHRA/TSRA activity
psbl at most terminals at least til 25/23z.

&&

.MARINE UPDATE...Showers and thunderstorms associated with a tropical
wave moving across the regional waters today will continue to create
locally higher seas and gusty winds. In addition the northerly swell
will maintain seas between 4-6 feet across the regional waters and
passages, except in the offshore Atlantic where seas will be up to
7 feet today through Wednesday. Small craft advisory will therefore
remain in effect for the offshore Atlantic waters. Small craft operators
should exercise caution elsewhere due to the choppy wind driven seas.

.PREV DISCUSSION... /issued 515 AM AST Tue Sep 25 2018/

SYNOPSIS...Upper level low over the forecast area will linger
over and to the west of the region through Wednesday. The remnants
of Tropical Depression 11 will interact with the upper low and
result in scattered to numerous showers and thunderstorms today.
Trough pattern aloft persists through the weekend and moisture
associated to the remnants of Tropical Storm Kirk increases
between Friday and Saturday.

SHORT TERM...Today through Thursday...

Variably to mostly cloudy skies expected throughout the period. As
the remnants of Tropical Depression (TD) 11 continues to move across
the forecast area and an upper level trough meanders westward over
the northeastern Caribbean Sea, the risk for deep convection remains
high until Wednesday due to high moisture content and favorable
upper level conditions across the region. Streamer-like showers and
thunderstorms will move across the local waters into portions of
eastern Puerto Rico and the U.S. Virgin Islands each night. Then,
local effects and diurnal heating will enhance afternoon convection
over the entire forecast area, particularly over portions of the
interior and western Puerto Rico. Although the bulk of the moisture
associated to TD 11 is expected to depart late Wednesday night,
lingering moisture and favorable upper level conditions will create
a similar weather pattern on Thursday. Given that this activity is
expected to result in total rainfall accumulations between 1 and 2
inches with isolated higher amounts, the threat of urban and small
stream flooding, mudslides near steep terrain and rapid rises along
river and its tributaries will continue at least until Thursday.

LONG TERM...Friday through Wednesday...

An upper level trough pattern will persist over and north of the
region through the long term period. This will enhance the
potential for shower and thunderstorm development each afternoon,
mainly over the interior and western sections of PR as well across
the San Juan metro area. Shower and thunderstorm activity as well
as breezy conditions are expected between Friday and Saturday in
association to what was Tropical Storm Kirk. A tropical wave is
forecast to move across the eastern Caribbean by midweek,
increasing shower and thunderstorm activity once again over the
forecast area.

AVIATION...As the remnants of TD eleven continues to approach the
forecast area from the east, VCTS/VCSH possible with brief MVFR
conditions until early morning at most terminals, except
TJPS/TJMZ/TJBQ. Then, VCTS/VCSH expected across all terminals during
the day, with MVFR conditions possible during the afternoon at
TJSJ/TJMZ/TJBQ. Surface winds from the east between 10-15 knots with
higher gusts. MVFR conditions posible over the coastal waters and en
route between the islands.

MARINE...Showers and thunderstorms across the regional waters
will create locally higher seas and gusty winds through the day.
Northerly swell will cause a high risk of rip currents along the
north facing beAches of the islands. Seas will range between 4-6
feet across the regional waters, except in the offshore Atlantic
where seas up to 7 feet are expected today and a small craft
advisory is in effect. A larger long period northerly swell is
forecast to move across the regional waters during the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  87  78  87  78 /  60  50  40  40
STT  88  78  90  79 /  70  70  40  40

&&

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

VI...High Rip Current Risk through late tonight for St Croix-
     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 PM AST Wednesday for Atlantic
     Waters of Puerto Rico and USVI from 10 NM to 19.5N.

&&

$$

SHORT TERM...RAM
LONG TERM....RAM


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