Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 180053
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
853 PM AST Sun Dec 17 2017

.UPDATE...No major changes to forecast package at this time. Surge
of moisture in the strong northeasterly trades continued to cross
the region this afternoon and evening bringing periods of moderate
to locally heavy showers across the local waters and parts of the
islands. While no significant flood problems are expected to occur,
periods of light to moderate rains and brief gusty winds will remain
possible during most of the overnight hours. Breezy conditions expected
to persist on Monday, however a gradual diminishing of the low to mid
level cloudiness is expected by late morning and during rest of the
day. The northeast winds area also expected to slightly diminish on
Tuesday, however periods of passing low level clouds and trade winds
showers will remain possible but should be less frequent.

&&

.AVIATION UPDATE...No chg to previous AVN discussion. SFC wnds
contd btwn 12-20 kts with ocnl higher gusts mainly w/passing SHRA
and along the coastal areas. SCT-BKN cld lyr nr FL022...FL040...FL080.
SHRA en route btw PR and the northern Leeward Islands,Few tops nr
FL120. VFR at local terminals...except for passing VCSH til 18/14z.
Mtn top obscr ovr Ern PR vcnty of EL YUNQUE due to SHRA/LOW CLDS.Low
lvl wnds fm NE 20-30 kts blo FL250 and incr w/ht.

&&

.MARINE UPDATE...No change to previous marine discussion. Choppy
and hazardous wind driven seas expected to persist across the regional
waters through Monday. A northerly swell will also arrive across local
waters on Monday and Tuesday.

&&

.PREV DISCUSSION... /issued 431 PM AST Sun Dec 17 2017/

SYNOPSIS...The weather conditions across the region will
continue to be dominate by a mid-upper level ridge over the region
in combination with a strong surface high pressure just to the
north of Puerto Rico through at least mid-week. Small surges of
moisture embedded in the northeasterly trades will move across the
islands bringing periods of clouds and brief showers at times
each day.

SHORT TERM...Tonight through Wednesday...
A mid to upper level ridge over the region in combination with a
strong surface high pressure across the Atlantic just to the north
of Puerto Rico will remain as the main weather features across
the forecast area Tonight and through at least Wednesday. These
features will maintain a relatively stable and dry weather pattern
across Puerto Rico, the U.S. Virgin Islands as well as across the
local coastal waters. The surface high pressure is expected to
maintain a northeast wind flow across the local islands for the
next several days. Surges of low level moisture embedded in the
northeasterly trades will move across the U.S. Virgin Islands,
Vieques, Culebra as well as over the eastern and northern sections
of Puerto Rico from time to time, resulting in mostly isolated to
scattered shower activity. However, the showers will move rapidly
southwestward producing minimal rainfall accumulations. By late
Wednesday, the mid to upper level ridge will begin to erode ahead
of a cut-off low that will dive southward into the forecast area.

LONG TERM...Thursday through Wednesday...
By Thursday and during the upcoming weekend, the ridge pattern
aloft is forecast to erode rapidly, as a polar trough amplified
from the northeast and sink southward into the northeastern
Caribbean specially during the upcoming weekend. This upper
trough is expected to create a moist and unsettled environment
across the local islands and surrounding waters during the Christmas
Eve weekend, Christmas Day and possible beyond.

AVIATION...Trade wind showers will continue to affect the USVI/PR
terminals through Monday morning. Tempo -SHRA and BKN cigs are
possible at times. Breezy NE winds will continue around 14-18 kts
with higher gusts.

MARINE...A fresh to strong northeasterly wind flow will continue
to result in choppy and rough seas across most of the regional
waters. Small craft advisories are in effect for most of the local
waters. Mariners can expect seas at 5 to 7 feet with occasional
seas up to 9 feet and winds up to 20 knots. For the beach goers,
a high risk of rip currents is in effect for the northwest to
northeast facing beaches Puerto Rico and for St Croix in the USVI.
Elsewhere a moderate to low risk of rip currents is expected.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  76  83  77  85 /  30  40  30  30
STT  76  86  75  85 /  50  50  30  30

&&

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

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

     Small Craft Advisory until 2 PM AST Monday for St.Thomas...St.
     John...and Adjacent Islands.

AM...Small Craft Advisory until 2 PM AST Monday for Atlantic Waters
     of Puerto Rico and USVI from 10 NM to 19.5N-Caribbean
     Waters of Puerto Rico from 10 NM to 17N-Coastal Waters of
     Northern USVI and Culebra out 10 NM-Mona Passage Southward
     to 17N.

     Small Craft Advisory until 2 AM AST Monday for Anegada Passage
     Southward to 17N-Coastal Waters of Southern USVI Vieques
     and Eastern Puerto Rico out 10 NM.

&&

$$

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



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