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FXCA20 KWBC 051255
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
855 AM EDT WED APR 05 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APR
05/12UTC: TODAY...THURSDAY...AND FRIDAY COULD BE A PERIOD WITH
OCCASIONAL HEAVY RAIN AND STRONG THUNDERSTORMS. THERE ARE SEVERAL
FACTORS THAT WILL PLAY A ROLE...INCREASED MOISTURE TO SLIGHTLY
ABOVE NORMAL LEVELS FOR THE TIME OF YEAR...A MID LEVEL LOW...AND A
TUTT OVER THE AREA. AT THE SURFACE WE HAVE A HIGH PRESSURE ACROSS
THE EASTERN ATLANTIC AND ANOTHER SURFACE HIGH PRESSURE MOVING INTO
THE WESTERN ATLANTIC...WHICH WILL KEEP A GENERALLY EASTERLY WIND
FLOW OVER THE NEXT SEVERAL DAYS ACROSS PR/USVI. IN THE MID
LEVELS...THERE IS A TROUGH THAT IS STRENGTHENING AND WILL BE A LOW
PRESSURE CENTERED JUST NORTHEAST OF PR/USVI BY THIS
EVENING...WHICH WILL MEANDER OVER THE AREA UNTIL SATURDAY. AND IN
THE UPPER LEVELS...THE AFOREMENTIONED TUTT WILL STRENGTHEN AND
WILL BE CENTERED TO THE NORTHWEST OF PR BY THIS EVENING...THEN
MOVING SLIGHTLY SOUTH AND CENTERING OVER THE MONA PASSAGE BY
FRIDAY EVENING BEFORE WEAKENING ON SATURDAY AND FLATTENING ON
SUNDAY. THIS STRONG TUTT WILL CAUSE A SURFACE INDUCED TROUGH FOR
THE MID TO LATTER PART OF THE WORKWEEK AS WELL. THIS GENERAL
PATTERN WILL CAUSE A SIGNIFICANT INCREASE IN INSTABILITY OVER THE
LOCAL AREA. THE 500MB TEMPERATURES ARE FORECAST TO DECREASE BY
THIS AFTERNOON INTO FRIDAY TO AN IMPRESSIVE -12C ACCORDING TO THE
ECMWF MODEL...WHILE THE GFS IS SUGGESTING AN EVEN COLDER -13C BY
THIS EVENING. THE 700-500MB RELATIVE HUMIDITY WILL INCREASE TO
OVER 2 STANDARD DEVIATIONS ABOVE NORMAL THROUGH FRIDAY...AND THE
700-500MB LAPSE RATES WILL BE ALSO ABOVE NORMAL TODAY AND
THURSDAY...THOUGH DECREASING TO NEAR NORMAL ON FRIDAY. BECAUSE OF
ALL THIS...THE LATEST ENHANCED GALVEZ-DAVISON INDEX (EGDI) IS
SUGGESTING THE CHANCE OF ISOLATED TO SCATTERED THUNDERSTORMS THIS
AFTERNOON ACROSS WESTERN PR...ISOLATED ACROSS THE USVI.
HOWEVER...THIS EVENING AND OVERNIGHT...THE EGDI INCREASES
SIGNIFICANTLY OVER THE USVI INTO EASTERN PR...WHICH WOULD SUGGEST
A HIGH RISK OF SCATTERED THUNDERSTORMS OVERNIGHT IN AND AROUND THE
USVI...VIEQUES...CULEBRA...AND THE EASTERN MUNICIPALITIES OF PR.
THE EGDI ALGORITHM SUGGESTS ISOLATED THUNDERSTORMS ON
THURSDAY...BUT THEN ON FRIDAY IT INCREASES ONCE AGAIN TO SCATTERED
THUNDERSTORMS ACROSS THE EASTERN HALF OF PR INTO THE USVI.
IN TERMS OF FORECAST AMOUNTS...TODAY AND THURSDAY INTO EARLY
FRIDAY...DUE TO THE EXPECTED THUNDERSTORM ACTIVITY...MODELS DID
BACK OFF A BIT IN THE RAINFALL AMOUNTS COMPARED TO THE MODEL RUNS
FROM YESTERDAY...BUT CONTINUE TO BE IN GOOD AGREEMENT THAT
RAINFALL MAXIMA OF OVER AN INCH ARE TO BE EXPECTED ACROSS
NORTHEAST AND WEST SOUTHWEST PR TODAY AND THURSDAY...THOUGH
ISOLATED HIGHER AMOUNTS ARE EXPECTED. OVER ONE INCH OF RAIN IS
EXPECTED ACROSS WEST SOUTHWEST PR ON FRIDAY AS WELL...BUT THE
INCREASE IN SHOWER AND THUNDERSTORMS ACROSS THE EASTERN SECTIONS
OF PR INTO THE USVI COULD PRODUCE OVER 2 INCHES OF RAIN ACROSS THE
EXTREME NORTHEAST OF PR. THAT BEING SAID...THE AMOUNT OF
INSTABILITY THAT SEEMS TO BE POSSIBLE...IT SHOULD NOT BE
SURPRISING TO SEE UP TO 3 INCHES OF RAIN ACROSS ISOLATED AREAS AT
SOME POINT FROM THIS AFTERNOON THROUGH FRIDAY. A DECREASING
THUNDERSTORM TREND IS STILL EXPECTED STARTING ON FRIDAY EVENING.
HOWEVER...SHOWERS AND THUNDERSTORMS ARE STILL FORECAST FOR THE
WEEKEND...BUT MUCH MUCH LESS RAINFALL ACCUMULATION. ACROSS WESTERN
PR...THE 5-DAY TOTALS ARE FORECAST TO EXCEED 4 INCHES...AND
POSSIBLY OVER 5 INCHES ACROSS NORTHEAST PR. THE USVI COULD SEE
BETWEEN 1 AND 4 INCHES OF RAIN OVER THE NEXT 5 DAYS..WITH THE
NORTHERN USVI BEING ON THE UPPER END OF THAT RANGE.
ALAMO/ACOSTA...WPC (USA)
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