Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 220846
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
446 AM AST Wed Nov 22 2017

.SYNOPSIS...A retreating cold front and high pressure at 700 mb
north of the areas will allow some moisture to return to the area
later today through Friday. Areas of drier air will pass through
over the weekend followed by modest moisture and an increase in
clouds and showers.


&&

.SHORT TERM...Today through Saturday...
Mostly clear skies were observed across the forecast area and little
to no rain was observed over land areas. Only few light showers
were observed moving west northwestward across the surrounding
coastal waters. An upper level ridge will continue to build and
hold over the region until the upcoming weekend. The developing
upper ridge will be the main weather feature across the region
today, producing a fair and stable weather across Puerto Rico,
USVI and surrounding waters. A few isolated showers can`t be
ruled out across western PR this afternoon. Early on Thursday, a
week low level perturbation is expected to move across the region
from the east, increasing the moisture and the chances of showers
with possible isolated thunderstorms development along the
Cordillera Central as well as across the western sections of the
islands. The moisture associated with this perturbation will
remain across the region until Friday. However, due to the
presence of the upper ridge, widespread precipitation is not
expected. Temperatures will continue between the high 80s to low
90s across the lower elevations each day. A drier trend will
return to the islands beginning Saturday.

.LONG TERM...Sunday through Friday...
The high pressure at 700 mb forming north of us Thursday and
Friday will move northeast and shear out on Sunday due to an
approaching cold front. Areas of drier air will pass through on
Sunday before moisture again begins to increase Monday and Monday
night over us ahead of the front. The front will stall out
northwest of the area Tuesday through Thursday. During the
interaction of weak local troughs moving in the easterly low level
flow toward the front, moisture increases and scattered showers
begin to affect much of Puerto Rico and the U.S. Virgin Islands.
Low pressure at lower levels develops north of Hispaniola later
next week in response to a short wave that dives southeast during
the week and crosses the area on Wednesday causing a low to cut-
off north of the forecast area. This and an upper level jet around
the short wave and subsequent cut-off low will also enhance
showers in only modestly moist east to east southeast low-level
flow continuing across the area through the end of next week.

&&

.AVIATION...Mainly VFR conditions expected across the local flying
area this morning and for most of the period. Few SHRA embedded in
the trades will produce VCSH across the Leeward and USVI TAF sites
til 22/14Z. Light and variable winds until 22/13Z, becoming E-SE and
increasing to 10 to 15 knots with sea breeze variations along the
coastal areas after 22/14z. No sig wx impact expected across the
flying area attm. Maximum winds west today ranging from 30-40 kt
between FL360-450.

&&

.MARINE...Seas are rising slowly at the outer buoy and are almost
7 feet now. Seas are expected to continue to rise north of the
area and by tonight some 7 foot seas are expected in the outer
Atlantic waters that will last through Thursday. No small craft
advisories are expected after Thursday through early next week.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  88  76  88  78 /  20  30  50  50
STT  86  77  85  77 /  30  50  50  50

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Flash Flood Watch until 3 PM AST this afternoon for Northwest-
 Western Interior for the Guajataca Dam situation.

VI...None.

AM...Small Craft Advisory from 8 PM this evening to 2 PM AST Thursday
     for Atlantic Waters of Puerto Rico and USVI from 10 NM to
     19.5N.

&&

$$

SHORT TERM...JA
LONG TERM....WS



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