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FXCA20 KWBC 251137
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
736 AM EDT THU APR 25 2024

WEEKLY DISCUSSION FOR PUERTO RICO AND THE USVI APR 25/12UTC: THE
ANALYSIS OF THE CURRENT CONDITIONS SHOWS A CELL OF THE
SUBEQUATORIAL RIDGE CENTERING JUST TO THE NORTH OF FRENCH GUIANA
WHILE EXTENDING ACROSS THE ENTIRE EASTERN CARIBBEAN UPPER LEVELS.
IN THE MID-LEVELS A RIDGE IS STRENGTHENING ACROSS THE EASTERN
CARIBBEAN AS WELL...WHILE CENTERING ON A HIGH OVER THE LEEWARD
ISLANDS. THESE SYSTEMS ARE CURRENTLY LIMITING THE EASTWARD
PROGRESSION OF A MID-UPPER TROUGH LOCATED IN THE NORTHWEST
CARIBBEAN. CURRENTLY...THE TROUGH HAS AN AXIS THAT EXTENDS ACROSS
THE NORTHWEST BAHAMAS...WEST CUBA INTO NORTHEAST HONDURAS. OVER
PUERTO RICO...THIS INTERACTION OF FACTORS IS LEADING TO
WEST-SOUTHWESTERLY FLOW ABOVE 500 HPA. MADDEN-JULIAN CONDITIONS
REMAIN GENERALLY UPPER CONVERGENT/DRY...YET THE MJO IS NOT VERY
WELL ORGANIZED AT THE CURRENT TIME...WHICH LIMITS ITS
APPLICABILITY INTO MEDIUM-RANGE FORECASTING.

IN THE MID AND LOWER TROPOSPHERE...A FRONT IS SITTING AS A
STATIONARY BOUNDARY ALONG 29N 62W...TURKS AND CAICOS...INTO
CENTRAL CUBA. ANOTHER FRONT/FRONTAL SHEAR LINE IS PROPAGATING
SOUTHWESTWARD ACROSS THE LESSER ANTILLES. THE MID-LEVEL RIDGE
LOCATED OVER THE LEEWARD ISLANDS IS LIMITING THE DEVELOPMENT OF
CONVECTION WITH THE LATTER SYSTEM. NOTE...HOWEVER...THAT
PRECIPITABLE WATER VALUES ARE IN THE 44-48MM RANGE WITH THIS
SYSTEM...WHICH REPRESENT ABOVE-AVERAGE VALUES FOR THIS TIME OF THE
YEAR AS IT MOVES TOWARDS PUERTO RICO ON THURSDAY. LARGER VALUES OF
AVAILABLE MOISTURE ARE CLUSTERING IN WESTERN PUERTO RICO AND
EASTERN HISPANIOLA ALONG A PREFRONTAL TROUGH STRUCTURE...WHICH IS
A CONCERN FOR HISPANIOLA LATER TODAY.

FORECAST: THE MID- AND UPPER RIDGES IN THE EASTERN/SOUTHEASTERN
CARIBBEAN ARE EXPECTED TO HOLD THROUGH LATE FRIDAY...LIMITING THE
EASTWARD PROGRESSION OF THE UPPER TROUGH IN THE NORTHWEST
CARIBBEAN. HOWEVER...A POTENT UPPER TROUGH EXITING THE EAST COAST
OF THE USA ON FRIDAY IS EXPECTED TO BUILD A POLAR HIGH AND PUSH
THE SURFACE FRONT LOCATED IN THE SOUTHEAST BAHAMAS/TURKS AND
CAICOS. AS THE SURFACE FRONT PROPAGATES TO THE SOUTHEAST...THE
MOIST PLUME BUILDING IN THE WARM SIDE OF THE FRONT IS FORECAST TO
ARRIVE IN PUERTO RICO LATE ON FRIDAY EVENING ACCOMPANIED BY A
CHANGE IN TRADE WIND DIRECTION TO EAST-NORTHEASTERLY. THIS WILL
LIKELY FAVOR A PEAK IN PRECIPITATION ON SATURDAY...WHEN THE
LARGEST ACCUMULATIONS ARE LIKELY TO CLUSTER IN THE SOUTHWEST
CORDILLERA. AFTER THIS PERIOD...CONTINUED NORTHEASTERLY LOW-LEVEL
WINDS ARE FORECAST TO TRANSPORT THE MOIST PLUME SOUTHWARD AWAY
FROM THE ISLANDS. AS THE PLUME EXITS...A DRIER AIR MASS IS
EXPECTED TO MOVE IN FROM THE NORTH...TO PERSIST AT LEAST INTO
TUESDAY. THIS WILL LIKELY INCLUDE A REESTABLISHMENT OF THE TRADE
WIND CAP...WHICH IS FORECAST TO GRADUALLY STRENGTHEN THROUGH
TUESDAY NEXT WEEK. THIS EVOLUTION IMPLIES ACTIVE DIURNAL
CONVECTION THROUGH SATURDAY EVENING...FOLLOWED BY DRIER CONDITIONS
ON SUNDAY...MONDAY AND TUESDAY.

AT THIS TIME...UNCERTAINTY EXITS ON (1) HOW FAR TO THE SOUTHEAST
MIGHT THE MOIST PLUME BE DISPLACED AND (2) WHEN MIGHT THE MOIST
PLUME RETURN TO PUERTO RICO AS EAST-SOUTHEASTERLY TRADES ARE
REESTABLISHED. THE ECMWF ENSEMBLES SHOW A DRIER SOLUTION AND THE
MOIST PLUME MEANDERING AS FAR AS GUADELOUPE/DOMINICA BY
TUESDAY...TO THEN START MEANDERING BACK TOWARDS PUERTO RICO/VI.
THE GFS SHOWS A WETTER SOLUTION...AS IT MAINTAINS HIGHER
PRECIPITABLE VALUES IN THE VI AND EASTERN PUERTO RICO THROUGH
TUESDAY...AND SHOWS A RAPID INCREASE IN PRECIPITABLE WATER BY
WEDNESDAY. FOR A DAY SIX/SEVEN...AND GIVEN THE CURRENT
EVOLUTION...THERE IS NOT ENOUGH CONFIDENCE TO DETERMINE WHICH
SOLUTION MIGHT APPROACH REALITY SO WE ARE LEANING EQUALLY TOWARDS
THE DIFFERENT GUIDANCE SOLUTION.

GALVEZ/ALAMO/ACOSTA...WPC (USA)


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