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FXCA20 KWBC 181254
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
853 AM EDT WED OCT 18 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI OCT 18/12UTC:
CURRENT INVEST 94L IS FORECAST BY THE NATIONAL HURRICANE CENTER TO
APPROACH THE NORTHERN LEEWARD ISLANDS THIS WEEKEND...ADDING
UNCERTAINTY TO THE WEEKEND FORECAST OVER PR/USVI. THE GLOBAL MODEL
GUIDANCE IS NOT IN PARTICULAR AGREEMENT...WITH THE ECMWF MODEL
HAVING 94L TRACKING VERY CLOSE TO THE NORTHERN LEEWARD ISLANDS ON
SATURDAY...WHILE THE GFS MODEL IS MORE AGGRESSIVE WITH ITS
DEVELOPMENT BUT KEEPS IT FURTHER TO THE EAST OF THE LEEWARD
ISLANDS THAN THE ECMWF MODEL. AT THIS TIME...THE FORECAST BY THE
NATIONAL HURRICANE CENTER HAS 94L NEAR THE LEEWARD ISLANDS BY
SATURDAY...WHILE IT MOVES NNE.
OVER THE NEXT FEW DAYS...SHOWERS AND THUNDERSTORMS ARE
FORECAST...ESPECIALLY ACROSS THE NORTHWESTERN QUADRANT AND CENTRAL
PR. THERE IS CURRENTLY A BROAD SFC HIGH PRESSURE ACROSS THE
CENTRAL ATLANTIC AND A STATIONARY FRONTAL BOUNDARY TO THE
NORTHWEST OF PR/USVI...CAUSING THE WINDS TO BE EASTERLY TODAY AND
THURSDAY. A SFC TROUGH IS ALSO EXPECTED TO PASS OVER THE LOCAL
ISLANDS TODAY. WINDS MAY INCREASE SLIGHTLY AND BECOME
SOUTHEASTERLY EARLY ON FRIDAY...THEN WINDS COULD DECREASE
GRADUALLY ON SATURDAY INTO SUNDAY...BUT THE WIND DIRECTION WILL
DEPEND ON THE EVENTUAL TRACK TRACK AND INTENSITY OF 94L. THAT
SAID...THE LATEST FORECAST TACK AND INTENSITY OF 94L WOULD SUGGEST
NORTHEASTERLY WINDS ON SATURDAY THEN NORTH TO NORTHWESTERLY WINDS
ON SUNDAY FOR THE LOCAL ISLANDS.
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 TODAY THROUGH THURSDAY...BRINGING AN
INCREASE IN VORTICITY AND INCREASING INSTABILITY. IN THE UPPER
LEVELS THERE IS A LOW PRESSURE OVER THE LESSER ANTILLES THAT IS
SLOWLY MOVING WEST AND IS EXPECTED TO BE TO THE SOUTH OF PR/USVI
BY THURSDAY. THERE IS ALSO A TUTT THAT WOULD BE MOVING IN FROM THE
NORTHWEST AND THE AXIS WOULD BE OVER HISPANIOLA ON THURSDAY AS
WELL. THE UPPER LOW SOUTH OF PR WILL SLOWLY MOVE NW AND WILL OPEN
INTO A TROUGH BY LATE SATURDAY INTO SUNDAY...WITH ITS AXIS JUST
WEST OF PR...WHICH NORMALLY ENHANCES THUNDERSTORM POTENTIAL ACROSS
PR...BUT AVAILABLE MOISTURE WILL DEPEND ON THE TRACK OF 94L. THE
EGDI ALGORITHM IS SUGGESTING ISOLATED TO SCATTERED THUNDERSTORMS
TODAY THROUGH FRIDAY AS THE MID LEVEL VORTICITY INCREASES. FOR
THIS WEEKEND...THE ALGORITHM SUGGESTS VERY ISOLATED
THUNDERSTORMS...BUT THAT MAY BE BECAUSE THE GFS MODEL TRACKS 94L
FURTHER EAST THAN THE OFFICIAL FORECAST.
IN GENERAL...THE 5-DAY RAINFALL TOTAL IS FORECAST TO BE OVER 4.5
INCHES FOR THE NORTHWESTERN QUADRANT OF PR...NEAR 2.5 INCHES FOR
THE EAST AND NORTHEAST SECTIONS. VIEQUES..CULEBRA...AND THE USVI
ARE FORECAST TO OBSERVE BETWEEN 1 AND 2 INCHES OVER THE 5-DAY
PERIOD. LOCALIZED HIGHER AMOUNTS ARE POSSIBLE WITH THE STRONGER
THUNDERSTORMS.
ALAMO...WPC (USA)
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