Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 281921
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
321 PM AST THU MAY 28 2015

.SYNOPSIS...AT UPPER LEVELS...LOW PRESSURE NORTH OF THE AREA WILL
WEAKEN AND DRIFT NORTH NORTHEAST THROUGH THE WEEKEND. A BRANCH OF
THE SUBTROPICAL JET WILL CROSS OVER THE AREA FRIDAY MORNING AND
CONTINUE MOVING NORTH AS HIGH PRESSURE BUILDS OVER THE EASTERN
CARIBBEAN. HIGH PRESSURE WILL SPREAD INTO THE WESTERN CARIBBEAN
AND INTENSIFY THROUGH THURSDAY WITH A STRONG RIDGE EXTENDING
NORTH.

AT MID LEVELS...LOW PRESSURE NORTH OF THE AREA WILL DRIFT NORTH AS
HIGH PRESSURE EXTENDS WESTWARD OVER THE CARIBBEAN SEA THROUGH MID
WEEK. HIGH PRESSURE DOMINATES THE CARIBBEAN SEA THROUGH THE
REMAINDER OF NEXT WEEK. MOISTURE WILL INCREASE SIGNIFICANTLY
BEGINNING ON FRIDAY.

AT LOWER LEVELS...LOW PRESSURE EAST OF THE BAHAMAS NORTH OF THE
AREA WILL DRIFT EAST AND WEAKEN LEAVING MODERATELY STRONG HIGH
PRESSURE OVER THE CENTRAL ATLANTIC AND MODERATE TO FRESH EAST
SOUTHEAST TRADE WINDS OVER THE LOCAL AREA BY SUNDAY. DURING THE
WEEK THE HIGH WILL PULL NORTHEAST AND GRADIENTS WILL
WEAKEN...ALLOWING WINDS TO DIMINISH AND TURN TO THE SOUTHEAST.
MUCH BETTER MOISTURE WILL MOVE INTO THE AREA ON FRIDAY FROM THE
SOUTHEAST AND CONTINUE AT HIGHER LEVELS THROUGH THE ENTIRE WEEK
AHEAD.

&&

.DISCUSSION...MOISTURE THIS MORNING AT 12Z WAS SIMILAR TO THAT
YESTERDAY AT 27/12Z...BUT WINDS BELOW 7500 FEET TURNED
DEFINITIVELY TO THE SOUTHEAST AND CONVECTION WAS NOT QUITE AS
QUICK TO FORM. SOME THUNDERSHOWERS WITH HEAVY RAIN DID APPEAR FROM
ANASCO TO VEGA ALTA. VEGA BAJA REPORTED ABOUT 6 TENTHS OF AN INCH
OF RAIN WITH SOME SMALL HAIL WITH HIGHER AMOUNTS POSSIBLE TO THE
NORTH. MOISTURE CAUSED CLOUDY SKIES IN THE BARBADOS THIS MORNING
AND SKIES CLOUDED UP IN SANTA LUCIA AND GUADELOUPE DURING THE DAY
WITH SHOWERS IN THE AREA...CONFIRMING WHAT MIMIC AND THE MODELS
ALREADY TOLD US...THAT DEEP MOISTURE IS HEADED TOWARD THE AREA.
THE GFS SUGGESTS THAT THE DRIEST AIR WILL PASS OVERHEAD AROUND
29/06Z FOLLOWED ABRUPTLY BY AIR WITH COLUMNAR MOISTURE OF OVER 1.8
INCHES ARRIVING BY 28/12Z. ALTHOUGH THE MODEL SENDS THE BEST
MOISTURE INTO THE DOMINICAN REPUBLIC AND OVER THE LOCAL OUTER
CARIBBEAN WATERS...THERE STILL APPEARS TO BE PLENTY OF MOISTURE
FOR SHOWER AND THUNDERSTORM DEVELOPMENT DURING THE DAY FRIDAY FOR
PUERTO RICO AND THE U.S. VIRGIN ISLANDS. THESE SHOWERS AND SOME
THUNDERSTORMS WILL LINGER WELL INTO THE NIGHT WITH GENERAL AMOUNTS
IN THE NEXT 24 TO 29 HOURS RANGING FROM 1 TO 3 INCHES IN THE
WETTER AREAS. SOME AREAS MAY RECEIVE LESS THAN ONE HALF INCH
DURING THE SAME TIME PERIOD. THEN ON SATURDAY MOISTURE WILL
INCREASE AND BETTER RAINFALL IS EXPECTED OVER A WIDER AREA.

A DECISION ON WHETHER TO ISSUE A WATCH WILL BE MADE NO LATER THAN
FRIDAY MORNING...IF NEEDED...AND CURRENT FORECASTS SUGGEST THAT
FLASH FLOODING ON SMALL RIVERS AND URBAN AND SMALL STREAM FLOODING
ARE LIKELY IN A FEW SPOTS AND POSSIBLE IN MORE THAN JUST A FEW
AREAS. CURRENTLY MODELS SUGGEST THAT THE U.S. VIRGIN ISLANDS WILL
HAVE A SIGNIFICANT AMOUNT OF RAINFALL WILL OCCUR THERE FRIDAY
THROUGH SUNDAY. SHOWERS WILL CONTINUE THROUGH AT LEAST
MONDAY...ALTHOUGH THE BEST MOISTURE APPEARS TO OCCUR SATURDAY
EVENING OVER THE FORECAST AREA AND SUBSIDES SLOWLY OVER THE
FORECAST AREA THROUGH WEDNESDAY. MOISTURE WILL INCREASE SOMEWHAT
THURSDAY NIGHT THROUGH FRIDAY NEXT WEEK.

&&

.AVIATION...BETWEEN 28/17Z AND 28/23Z...MVFR PSBL...MAINLY ACROSS
TJBQ AND TJMZ DUE TO AFTERNOON CONVECTION AND MOUNTAIN OBSC ACROSS
THE INTERIOR...WEST AND NW QUADRANT OF PR. SFC WINDS FROM THE
E-ESE AT 10 TO 15 KT WITH HIGHER GUSTS AND SEA BREEZE VARIATIONS
THROUGH 28/23Z... FOLLOWED BY LIGHT SFC WINDS AT AROUND 5KT
THEREAFTER. INCREASING SHOWERS AND THUNDERSTORMS BEGINNING NOW IN
TNCM AND TKPK AND SPREADING THROUGH 28/14Z TO PR AND USVI.
WIDESPREAD OBSCURATIONS OF HIGHER TERRAIN AFT 28/16Z.

&&

.MARINE...WINDS AND SEAS INCREASE FRIDAY NIGHT THROUGH SATURDAY
NIGHT WITH SHOWERS AND THUNDERSTORMS INCREASING OVER THE AREA.
CONDITIONS ARE NOT EXPECTED TO REACH SMALL CRAFT ADVISORY
LEVELS...BUT LOCAL GUSTY WINDS IN EXCESS OF 30 KNOTS COULD BE
ENCOUNTERED IN THUNDERSTORMS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  89  78  87  75 /  20  20  70  60
STT  86  77  84  77 /  20  40  70  70

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
AM...NONE.
&&

$$

27/12


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