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FXCA20 KWBC 231423
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
922 AM EST THU JAN 23 2025
WEEKLY DISCUSSION FOR PUERTO RICO AND THE USVI JAN 23 14 UTC:
UPPER LEVEL HIGH PRESSURE ENE OF THE LEEWARDS CURRENTLY HAS A
WEAKNESS ON THE SW QUADRANT WHICH IS ALLOWING FOR SOME WEAK
TROUGHINESS TODAY...BUT IT WILL FLATTEN BY FRIDAY...AND
THEN...UPPER LEVEL CONFLUENCE WILL BE OBSERVED OVER THE EASTERN
CARIBBEAN INTO THE TROPICAL WESTERN ATLANTIC AS THE UPPER HIGH
PRESSURE INTERACTS WITH AN APPROACHING UPPER TROUGH FROM THE
NORTHWEST. THIS UPPER TROUGH WILL FLATTEN WELL TO THE NORTH OF THE
LOCAL ISLANDS...BUT A SHORTWAVE UPPER TROUGH WILL APPROACH
HISPANIOLA ON MONDAY THEN PR/USVI BY EARLY TUESDAY MORNING. AN
UPPER RIDGE WILL ONCE AGAIN MOVE OVER THE GREATER ANTILLES BY
WEDNESDAY.
THE MID LEVELS ALSO HAS A HIGH PRESSURE TO THE NE OF THE
LEEWARDS...BUT THE HIGH PRESSURE SYSTEM IN THE MID LEVELS EXTENDS
FROM NORTHEAST OF THE LEEWARDS THROUGH THE GREATER ANTILLES...AND
NO REAL WEAKNESS IN THE RIDGE IS OBSERVED TO THE SW OF
IT...CONTRARY TO WHAT IS FORECAST IN THE UPPER LEVELS.
THEREFORE...THE WEAK TROUGHINESS THAT THE MODELS ARE SUGGESTING IN
THE UPPER LEVELS FOR TODAY WILL LIKELY NOT BE A MAJOR CONTRIBUTOR
OF INSTABILITY IN THE LOWER LEVELS AS THE MID LEVEL HIGH PRESSURE
WOULD BE DOMINATING. THE MID LEVEL WINDS WILL WEAKEN THIS
WEEKEND...THEN BY TUESDAY A WEAK MID LEVEL TROUGH COULD MOVE
THROUGH HISPANIOLA AND PR/USVI. THAT SAID...THE MODEL GUIDANCE IS
SUGGESTING THIS TROUGH TO BE VERY WEAK AND ANY SHIFT IN LOCATION
MAY ACTUALLY PLACE THE LOCAL ISLANDS IN A MID LEVEL COL...AS
ANOTHER MID LEVEL HIGH PRESSURE MOVING IN RIGHT BEHIND IT FROM THE
WEST.
IN THE LOWER LEVELS...HIGH PRESSURE IN THE CENTRAL ATLANTIC WILL
DOMINATE THE TROPICAL REGION...CAUSING EASTERLY WINDS TO PERSIST
OVER THE LOCAL ISLANDS. EVEN THOUGH THE MID LEVELS WILL BE
RELATIVELY STABLE...AND THERE WILL BE A TRADE WIND INVERSION OVER
THE AREA FOR THE NEXT FEW DAYS...WHICH WILL KEEP THE AVAILABLE
MOISTURE IN THE LOWER LEVELS...THERE WILL BE A SERIES OF SHORTWAVE
TROUGHS THAT WILL MOVE THROUGH WITH PATCHES OF MOISTURE THAT COULD
ENHANCE THE CHANCES FOR BRIEF SHOWERS ACROSS THE LOCAL AREA.
HOWEVER...THE TRADE WIND INVERSION DOES WEAKEN SOMEWHAT ON SUNDAY
INTO MONDAY...CAUSING MOISTURE TO REACH THE MID LEVELS AT
TIMES...WITH THE FLUCTUATION IN MOISTURE WITH THE TRADES. THE
TRADE WIND INVERSION WILL WEAKEN ONCE AGAIN LATE TUESDAY INTO
WEDNESDAY...AS THE MID LEVEL TROUGHINESS OR COL MOVES OVER THE
LOCAL ISLANDS.
OVERALL...THIS SYNOPTIC PATTERN AND FLUCTUATIONS IN MOISTURE WILL
FAVOR BRIEF SHOWER ACTIVITY ACROSS THE EASTERN SECTIONS OF PR AND
ACROSS THE USVI...ESPECIALLY INTO THE WEEKEND. THERE IS A CHANCE
OF AFTERNOON CONVECTION ACROSS WESTERN PR AS WELL...BUT THE
AMOUNTS WOULD BE MODEST AND THE BETTER CHANCES ARE FROM SUNDAY
ONWARD WHEN THE TRADE WIND INVERSION STARTS TO DETERIORATE. THE
OVERALL MOISTURE WOULD BE HIGHEST TODAY WITH A SFC TROUGH THAT IS
MOVING THROUGH...BUT THEREAFTER THE MOISTURE WILL GO UP AND DOWN
IN PATCHES...FAVORING THE SHOWER ACTIVITY IN THE OVERNIGHT AND
MORNING HOURS. THE 5-DAY RAINFALL FORECAST IS FOR UP TO 2 INCHES
TO BE OBSERVED ACROSS THE EASTERN THIRD OF PR.
ELSEWHERE...INCLUDING THE USVI...UP TO AN INCH OF RAIN IS
FORECAST...THE CENTRAL INTERIOR INTO SOUTH CENTRAL AND SOUTHWEST
PR IS EXPECTED TO HAVE THE LOWEST RAINFALL ACCUMULATIONS OVER THE
NEXT 5 DAYS...PERHAPS UP TO A HALF AN INCH OF RAIN...IF THAT.
ALAMO...WPC(USA)
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