251
FXCA20 KWBC 201230
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
830 AM EDT THU JUL 20 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JUL
20/12UTC: SAHARAN DUST WILL CONTINUE OVER PR/USVI THROUGH SUNDAY.
THE AVAILABLE MOISTURE WILL BE BELOW NORMAL THROUGH
SATURDAY...INCREASING INTO THE NORMAL LEVELS ON SUNDAY...BRIEFLY
GOING DOWN TO BELOW NORMAL ON MONDAY...BEFORE INCREASING AGAIN
LATE MONDAY INTO TUESDAY AS A TROPICAL WAVE APPROACHES. THE
PRECIPITABLE WATER WILL BOTTOM OUT AT AROUND 1.2 INCHES ON THIS
AFTERNOON AND FRIDAY AFTERNOON...WHICH IS NEAR 2 STANDARD
DEVIATIONS BELOW NORMAL. FAIR WEATHER IS TO BE EXPECTED THROUGH
SATURDAY WITH HAZY SKIES. THAT SAID...THERE IS A SLIGHT CHANCE OF
BRIEF SHOWERS THAT COULD AFFECT EASTERN PR/USVI IN THE MORNINGS
AND OVERNIGHT...WITH WESTERN PR PERHAPS HAVING VERY LIMITED
AFTERNOON CONVECTION. SINCE THE MOISTURE IS EXPECTED TO INCREASE
SLIGHTLY ON SUNDAY INTO MONDAY...AND THE SAHARAN DUST
CONCENTRATION IS EXPECTED TO DECREASE LATE SUNDAY...THE RAINFALL
FORECAST SUGGESTS SLIGHTLY HIGHER RAINFALL ACCUMULATIONS FOR THE
SUNDAY TO MONDAY MORNING FORECAST PERIOD. THERE WILL BE A TROPICAL
WAVE THAT COULD MOVE IN ON MONDAY INTO TUESDAY...WHICH COULD CAUSE
EVEN MORE RAINFALL...BUT THE GUIDANCE HAS THE WAVE MOVING
QUICKLY...WHICH WOULD LIMIT THE TIME WINDOW. THAT SAID...THE
LATEST MODEL GUIDANCE SUGGESTS PRECIPITABLE WATER INCREASING TO
OVER 2 INCHES FOR TUESDAY...WHICH IS SIGNIFICANT.
EASTERLY WINDS ARE EXPECTED FOR THE NEXT SEVERAL DAYS. A MID LEVEL
HIGH PRESSURE IS FORECAST TO MOVE INTO THE WESTERN ATLANTIC FRIDAY
INTO SATURDAY...THEN A WEAK MID LEVEL TROUGH WILL MOVE INTO THE
SOUTHWESTERN ATLANTIC THIS WEEKEND. AN UPPER LOW AND ASSOCIATED
TILTED TROUGH DIGS SOUTH AND HAS AN AXIS BETWEEN PR AND
HISPANIOLA. THE TROUGH AXIS WILL MOVE EAST TODAY AND WILL BE OVER
EASTERN PR AND THE USVI BY LATE TONIGHT/EARLY FRIDAY. HOWEVER...AN
UPPER LOW WILL THEN DEVELOP OVER THE CARIBBEAN...SOUTH OF
HISPANIOLA...CAUSING WEAK WINDS ALOFT. THE LATEST GUIDANCE
CONTINUES TO SUGGEST A TRADE WIND INVERSION AT AROUND 850HPA
THROUGH LATE FRIDAY...WEAKENING SLIGHTLY IN THE WEEKEND.
OVERALL...WE STILL EXPECT A DRIER THAN NORMAL AIR MASS...WITH
SAHARAN DUST AND A TRADE WIND INVERSION TO CAUSE MOSTLY RAIN FREE
CONDITIONS OVER PR/USVI THROUGH AT LEAST SATURDAY. ALTHOUGH THERE
IS A SLIGHT CHANCE OF BRIEF SHOWERS...THERE WOULD BE MINIMAL IF
ANY RAINFALL ACCUMULATIONS. SUNDAY COULD HAVE BETTER RAINFALL
CHANCES...BUT NOT MUCH ACCUMULATION IS EXPECTED EITHER. MONDAY
INTO TUESDAY COULD HAVE AN EVEN BETTER CHANCE OF RAIN AS A
TROPICAL WAVE IS FORECAST TO APPROACH THE LOCAL AREA...LATE MONDAY
INTO TUESDAY HAVING THE BEST POTENTIAL FOR RAIN. THE 5-DAY
RAINFALL ACCUMULATION FORECAST HAS MAX VALUES BETWEEN 0.75 AND 1
INCH ACROSS NORTHEASTERN AND NORTHWESTER PR...WHILE AROUND A
QUARTER OF AN INCH OR SO IS FORECAST FOR THE USVI.
ALAMO/ACOSTA...WPC (USA)
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