821
FXCA20 KWBC 171246
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
845 AM EDT TUE OCT 17 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI OCT 17/12UTC:
THE FORECAST TRACK AND DEVELOPMENT OF THE CURRENT INVEST 94L IS
ADDING UNCERTAINTY TO THE FORECAST OVER PR/USVI...ESPECIALLY FOR
THE WEEKEND. THIS IS BECAUSE THE GLOBAL MODEL GUIDANCE IS NOT IN
PARTICULAR AGREEMENT...WITH THE ECMWF MODEL HAVING AN OPEN WAVE
VERY CLOSE TO THE LOCAL ISLANDS BY SATURDAY...WHILE THE GFS MODEL
IS MORE AGGRESSIVE AND DEVELOPS IT INTO A TROPICAL CYCLONE BUT
KEEPS IT TO THE EAST OF THE LEEWARD ISLANDS. AT THIS TIME...THE
FORECAST BY THE NATIONAL HURRICANE CENTER HAS A CLOSED LOW NEAR
THE LEEWARD ISLANDS BY SATURDAY...BUT MOVING NNE. THIS FORECAST
TRACK WOULD BE CLOSER TO WHAT THE GFS IS SUGGESTING...THOUGH A BIT
FURTHER WEST AND CLOSER TO THE NORTHERN LEEWARDS THAN THE 00Z
GFS...STILL AWAY FROM PR/USVI HOWEVER.
OVER THE NEXT FEW DAYS...SHOWERS AND THUNDERSTORMS ARE
FORECAST...WITH THE NORTHWESTERN QUADRANT AND CENTRAL PR HAVING
THE EST CHANCE OF THUNDERSTORMS EACH DAY FOR THE REST OF THE WEEK.
THERE IS CURRENTLY A BROAD SFC HIGH PRESSURE ACROSS THE CENTRAL
ATLANTIC AND A FRONTAL BOUNDARY TO THE NORTHWEST OF
PR/USVI...CAUSING THE WINDS TO BE MAINLY SOUTHEASTERLY
TODAY...BECOMING ESE BY TONIGHT AND THEN EASTERLY BY WEDNESDAY AS
A SFC TROUGH PASSES JUST NORTH OF PR. THE EASTERLY WINDS WILL
CONTINUE THROUGH THURSDAY...THEN SOUTHEASTERLY AGAIN ON FRIDAY AND
WINDS INCREASE BRIEFLY ON FRIDAY MORNING...THEN WINDS COULD
DECREASE SIGNIFICANTLY ON SATURDAY...DEPENDING ON HOW CLOSE AND
HOW STRONG 94L IS AT THE TIME. THEREFORE...THE FORECAST FOR FRIDAY
INTO SATURDAY MAY BE INFLUENCED BY THE EVENTUAL DEVELOPMENT OF
INVEST 94L.
THE MID AND UPPER LEVELS ARE CONDUCIVE FOR ISOLATED TO SCATTERED
THUNDERSTORM DEVELOPMENT OVER THE NEXT FEW DAYS. THERE IS A MID
LEVEL HIGH PRESSURE OVER THE CENTRAL ATLANTIC THAT IS DOMINATING
THE AREA...BUT THE LATEST GUIDANCE STILL SUGGESTS A WEAKNESS IN
THE MID LEVEL RIDGE AND A SMALL MID LEVEL LOW TO MOVE INTO THE
NORTHEAST CARIBBEAN BY EARLY WEDNESDAY MORNING...BRINGING AN
INCREASE IN VORTICITY AND INCREASING INSTABILITY. IN THE UPPER
LEVELS THERE IS A LOW PRESSURE OVER THE WINDWARD ISLANDS THAT IS
SLOWLY MOVING WEST AND IS EXPECTED TO BE TO THE SOUTH OF PR/USVI
BY THURSDAY. THERE IS ALSO AN UPPER TROUGH THAT WOULD BE MOVING IN
FROM THE NORTHWEST AND THE AXIS WOULD BE OVER HISPANIOLA ON
THURSDAY AS WELL. THE EGDI ALGORITHM IS SUGGESTING ISOLATED
THUNDERSTORMS THIS AFTERNOON...THEN POSSIBLE SCATTERED
THUNDERSTORMS ON WEDNESDAY AS THE MID LEVEL VORTICITY INCREASES.
THURSDAY ONWARD...THE ALGORITHM SUGGESTS ISOLATED THUNDERSTORMS
EXCEPT SATURDAY...BUT THAT MAY BE INFLUENCED BY THE POSITION AND
INTENSITY THE MODEL HAS ON INVEST 94L.
IN GENERAL...THE 5-DAY RAINFALL TOTAL IS FORECAST TO BE OVER 6
INCHES FOR THE NORTHWESTERN QUADRANT OF PR...NEAR 2 TO 2.5 INCHES
FOR THE EAST AND NORTHEAST SECTIONS. VIEQUES..CULEBRA...AND THE
USVI ARE FORECAST TO OBSERVE BETWEEN 0.5 AND 1.25 INCHES OVER THE
5-DAY PERIOD. LOCALIZED HIGHER AMOUNTS ARE POSSIBLE WITH THE
STRONGER THUNDERSTORMS.
ALAMO...WPC (USA)
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