178
FXCA62 TJSJ 251800
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
200 PM AST WED NOV 25 2009
SYNOPSIS
SURFACE HIGH PRESSURE ACROSS THE WEST CENTRAL ATLANTIC
TO WEAKEN THROUGH THURSDAY AND RETREAT EASTWARD AS TROUGH OF LOW
PRESSURE OVER FLORIDA ADVANCES EASTWARD THROUGH THANKSGIVING DAY.
FRONTAL TROUGH TO STALL NORTHWEST OF PUERTO RICO ON SATURDAY.
DISCUSSION...UPDATED DAYTIME FORECAST DUE TO ENHANCED SCATTERED
SHOWER DEVELOPMENT OVER THE NORTH AND EAST SECTIONS OF PUERTO RICO
AND ACROSS CULEBRA AND SAINT THOMAS IN RESPONSE TO NARROW BANDS OF
CLOUDS AND SHOWERS THAT APPEARS TO BE ASSOCIATED WITH THE REMNANTS
OF LOW NEAR 38N44W.
FOR TONIGHT THE LOW LEVEL FLOW IS FORECAST TO REMAIN OUT OF THE
EAST NORTHEAST...RESULTING IN SCATTERED SHOWERS ACROSS THE USVI
AND NORTH AND EAST PUERTO RICO. THE NAM RUN THIS MORNING WAS ON
TARGET WITH THE CLOUDS AND SHOWERS COVERAGE. THE LOW LEVEL FLOW IS
FORECAST TO BECOME MORE EASTERLY ON THURSDAY AND THIS WILL ALLOW
FOR PATCHY CLOUDS AND SCATTERED SHOWERS EVIDENT ON SATELLITE EAST
OF THE LEEWARDS TO CROSS THE AREA. THE GENERAL CHARACTER OF THE
WEATHER WILL REMAIN UNDER THE INFLUENCE OF A MID TO UPPER LEVEL
HIGH WHICH SHOULD MAINTAIN SHOWERS IN THE SCATTERED OR LESS RANGE.
UPPER LEVEL WINDS WILL CHANGE LATE ON SUNDAY THROUGH MONDAY AS A
SHORT WAVE TROUGH ARRIVES AND ENHANCES MOISTURE ASSOCIATED TO THE
FRONTAL TROUGH.
AVIATION...EXPECT PREVAILING VFR CONDITIONS ACROSS THE LOCAL
ISLANDS AND AT ALL LOCAL TAF SITES REST OF THIS AFTERNOON THROUGH
TONIGHT. HOWEVER... BRIEF MVFR CONDITIONS AND LOCAL MOUNTAIN
OBSCURATIONS ARE EXPECTED IN PASSING SHRA...ESPECIALLY OVER THE
INTERIOR SECTIONS OF PUERTO RICO BETWEEN 25/18Z AND 26/01Z. PLUME
OF ASH AND STEAM FROM MONTSERRAT WAS REPORTED MOVING MOSTLY WEST
WITH A SLIGHT NORTHWEST MOTION AND EXTENDED UP TO 10 THSD FEET.
SHOULD REMAIN SOUTH OF THE LOCAL ISLANDS THROUGH THURSDAY.
MARINE...LONG PERIOD NORTHERLY SWELLS WILL BEGIN TO INVADE THE
LOCAL ATLANTIC WATERS ON THURSDAY AFTERNOON...RESULTING IN INCREASING SEAS
AND POTENTIALLY DANGEROUS SURF CONDITIONS ALONG THE NORTHERN
EXPOSED COASTLINES OF THE LOCAL ISLANDS FRIDAY AND SATURDAY.
PRELIMINARY POINT TEMPS/POPS
SJU 74 86 74 86 / 40 40 20 20
STT 76 86 76 85 / 40 40 20 20
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
02/37
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