Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 281910
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
310 PM AST WED JAN 28 2015

.SYNOPSIS...A JET MAX OF OVER 85 KNOTS WILL PASS OVER THE LOCAL
AREA ON THURSDAY AS AN UPPER LEVEL TROUGH MOVES THROUGH THE
WESTERN ATLANTIC AND THE RIDGE OVER THE WINDWARD ISLANDS THAT
EXTENDS INTO THE CENTRAL ATLANTIC CONTINUES TO MOVE EAST. HIGH
PRESSURE WILL BUILD BACK INTO THE WESTERN AND CENTRAL CARIBBEAN
OVER THE WEEKEND AND BACK OVER THE LOCAL AREA BY LATE NEXT WEEK.

AT MID LEVELS...AFTER THE TROUGH PASSAGE IN THE WESTERN ATLANTIC
LATE THIS WEEK HIGH PRESSURE WILL DEVELOP OVER THE GREATER
ANITLLES. MOISTURE WILL INCREASE TO VERY MODEST LEVELS ON FRIDAY
AND THEN SLOWLY DIMINISH AFTER WEDNESDAY.

AT LOWER LEVELS...A COLD FRONT SHEAR-LINE COMBINATION SITTING OVER
HISPANIOLA WILL BECOME MORE EAST WEST AROUND 20 DEGREES NORTH LATE
THIS WEEK WITH SOME CONVERGENCE AHEAD OF THE BOUNDARY OVER THE
LOCAL AREA. AREAS OF MOISTURE WILL PASS THROUGH THE AREA ON FRIDAY
AND MONDAY ON TRADE WIND FLOW...DIMINISHING ON THURSDAY OF NEXT WEEK.


&&

.DISCUSSION...THIS MORNING`S SOUNDING AT 28/12Z CAME IN WITH ONLY
1.02 INCHES OF PRECIPITABLE WATER AND LESS THAN 10 PERCENT
RELATIVE HUMIDITY AT 700 MB. CLOUDS THAT DID DEVELOP DURING THE
LATE MORNING AND EARLY AFTERNOON FOUND THIS LAYER NEARLY
IMPENETRABLE SO THAT VERY FEW SHOWERS DEVELOPED AS OF LATE THIS
AFTERNOON. BUT COUNTING FROM MIDNIGHT...SCATTERED SHOWERS WERE
OBSERVED OVER THE CARIBBEAN...INCLUDING THE WESTERN TIP OF SAINT
CROIX...UNTIL 11 AM AST. A PATCH OF MOISTURE WAS OBSERVED IN THE
SATELLITE IMAGERY JUST EAST OF SAINT MARTIN AND IT IS EXPECTED TO
MOVE ACROSS THE U.S.VIRGIN ISLANDS AND INTO PUERTO RICO THURSDAY
AROUND 08-10Z. SINCE MID LEVELS REMAIN MOSTLY DRY...THIS IS ONLY
EXPECTED TO YIELD LIGHT AMOUNTS...AND MAINLY IN THE EASTERN
PORTION OF PUERTO RICO. BY THURSDAY LOW LEVEL WINDS WILL HAVE
TURNED TO THE NORTHEAST...THEN AS HEATING CONTINUES DURING THE
DAY...A THUNDERSTORM OR TWO IN INTERIOR FROM NORTHEAST TO
SOUTHWEST PUERTO RICO CANNOT BE RULED OUT IN THE LIKELY SHOWERS.
SCATTERED SHOWERS WILL CONTINUE OVERNIGHT THURSDAY AND INTO FRIDAY...
FIRST ON THE NORTHERN COASTS DURING THE MORNING AND THEN IN MUCH
THE SAME PATTERN ACROSS THE INTERIOR OF PUERTO RICO DURING THE
AFTERNOON...BEFORE SOME DRYING OCCURS OVER THE WEEKEND. CURRENTLY
THE GFS IS INDICATING ANOTHER SURGE IN MOISTURE ON MONDAY...BUT
AGAIN SHOWERS WILL BE LIMITED BY LESS THAN FAVORABLE MOISTURE AT
MID LEVELS.

&&

.AVIATION...MOSTLY VFR CONDITIONS WILL PREVAIL ACROSS THE FORECAST
AREA DURING THE FORECAST PERIOD. ISOLATED -SHRA STILL POSSIBLE IN
AND AROUND TJBQ AND TJMZ UNTIL 28/22Z CAUSING AT LEAST VCSH. ESE WINDS
AT 5 TO 15 KNOTS WILL CONTINUE THROUGH 29/12Z.

&&

.MARINE...SWELL OF 10 FEET HAVE BEEN NOTED AT BUOY 41046 TO OUR
NORTHWEST...AND THIS IS SOME 2-3 FEET HIGHER THAN THE WAVE WATCH
WAS FORECASTING. THEREFORE AM EXPECTING AT LEAST 6 FOOT SEAS
TONIGHT IN OUR ATLANTIC WATERS AND POSSIBLY 7 FEET BY TOMORROW AT
BUOY 41043 WHICH HAS SHOWN A RAPID RISE TO 6.4 FEET IN THE LAST 6
HOURS. MARINERS SHOULD CONSIDER THE POSSIBILITY THAT 7 FOOT SEAS
COULD ENTER THE FORECAST AREA`S ATLANTIC WATERS TOMORROW IF SWELL
CROSSING THROUGH BUOY 41046 TO THE NORTHWEST ARRIVES HERE. WILL
ADVISE NEXT SHIFT TO BE ALERT TO UPDATING FORECAST IF NECESSARY.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  75  87  75  86 /  40  40  50  50
STT  77  84  77  83 /  40  40  50  50

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
COASTAL WATERS...NONE.
&&

$$

13/12






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