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FXCA20 KWBC 091217
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
816 AM EDT WED AUG 09 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM AUG
09/12UTC: SHOWERS AND THUNDERSTORMS ARE FORECAST ACROSS THE LOCAL
ISLANDS FOR TODAY AND THURSDAY...AS MOISURE WILL REMAIN WELL ABOVE
NORMAL AND A TROPICAL WAVE APPROACHES THE AREA. THIS WILL CAUSE
PRECIPITABLE WATER TO PEAK AT AROUND 2.4 INCHES TODAY. DRIER AIR
WITH SOME SAHARAN DUST WILL MAKE ITS WAY INTO THE NORTHEAST
CARIBBEAN ON FRIDAY INTO SATURDAY...CAUSING THE AVAILABLE MOISTURE
TO DECREASE TO BELOW NORMAL LEVELS AND PRECIPITABLE WATER TO
BOTTOM OUT AT AROUND 1.4 INCHES. THE AVAILABLE MOISTURE WILL
INCREASE ONCE AGAIN LATE SATURDAY INTO SUNDAY AS ANOTHER TROPICAL
WAVE APPROACHES THE AREA...THOUGH THE INCREASE IN MOISUTRE WILL BE
UP TO THE NORMAL RANGE...PRECIPITABLE WATER RANGING BETWEEN 1.6
AND 1.9 INCHES. THE THUNDERSTORMS EXPECTED TODAY WOULD CAUSE HEAVY
DOWNPOURS OCCASIONALLY. HOWEVER...AN APPROACHING TUTT FROM THE
EAST WILL CAUSE AN INCREASE IN INSTABILITY LATE THURSDAY...WHICH
COULD CAUSE STRONGER THUNDERSTORMS. THE GR02T SEVERITY ALGORITHM
IS SUGGESTING A MARGINAL RISK OF SEVERE STORMS ON
THURSDAY...POSSIBLY BECAUSE THE 500MB TEMPS MAY STILL BE NEAR
NORMAL AT -6C BUT DECREASING RAPIDLY TO -8C BY THURSDAY EVENING.
BY LATE THURSDAY NIGHT INTO FRIDAY...THE INSTABILITY PARAMETERS
ARE SUGGESTING THE POTENTIAL OF STRONG STORMS AS THE TUTT
CONTINUES TO MOVE WEST AND OVER THE LOCAL ISLANDS. HOWEVER...THE
MOISTURE WILL BE ON A DONWARD TREND AND SAHARAN DUST WILL BE
MOVING IN. THEREFORE...IF THERE IS ANY THUNDERSTORM
DEVELOPMENT...IT COULD BE ISOLATED BUT STRONG...BASED ON THE
LATEST GUIDANCE WHICH HAS HIGH INSTABILITY WITH COLD MID LEVEL
TEMPS...LOW THICKESS AND HIGH LAPSE RATES IN THE LOW TO MID
LEVELS.
IN TERMS OF AMOUNTS OF RAIN...THE SHORT TERM RAINFALL GUIDANCE HAD
SOME DISCREPANCIES...WHICH WOULD BE EXPECTED...BUT THE ECMWF
ENSEMBLE IS VERY BULLISH WITH THE RAINFALL AMOUNTS...THOUGH NOT
NECESSARILY UNREALISTIC. THEREFORE SOME ADJUSTMENTS WERE MADE IN
THE RAINFALL FORECAST TO ACCOUNT FOR THE INCREASE IN RAINFALL
SOLUTION FROM THE ECMWF AND OTHER HI-RES MODELS. BETWEEN 1 AND 2
INCHES OF RAIN ARE FORECAST TODAY FOR EASTERN PR...AND 2 TO 3
INCHES ACROSS WESTERN TO NORTHWESTERN PR. THE USVI COULD OBSERVE
UNDER A HALF AN INCH OF RAIN TODAY. ON THURSDAY THE RAIN COULD BE
A BIT MORE GENERALIZED ACROSS PR...SUGGESTING NEAR OR OVER 1 INCH
ACROSS EASTERN AND SOUTHERN PR...WHILE 1.25 TO 1.5 INCHES EXPECTED
ACROSS NORTHWESTERN PR. FRIDAY INTO VERY EARLY SATURDAY LOOKS TO
BE THE DRIEST PERIOD OVER THE NEXT 5 DAYS WITH THE DRIER AIR AND
SAHARAN DUST MOVING IN...AND THE RAINFALL FORECAST REFLECTS
THAT...WITH MUCH LESS RAINFALL FORECAST BUT STILL NEAR 0.75 INCHES
ACROSS NORTHWESTERN PR. HOWEVER...SUNDAY INTO MONDAY THE AMOUNT OF
RAIN THAT IS FORECAST INCREASES ONCE AGAIN TO OVER 1 INCH ACROSS
EASTERN AND SOUTHWESTERN PR...WHILE THE USVI IS FORECAST OVER 0.25
INCHES.
THE 5-DAY TOTAL RAINFALL FORECAST IS FOR PORTIONS OF W/NW PR TO
RECEIVE OVER 5 INCHES OF RAIN...WHILE EASTERN AND NORTHEASTERN PR
IS FORECAST TO OBSERVE OVER 4 INCHES. THE USVI ARE FORECAST TO
HAVE AROUND 1 INCH OF RAIN OVER THE 5-DAY PERIOD.
ALAMO/GALVEZ...WPC (USA)
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