TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
903 AM EDT THU APR 18 2024

WEEKLY DISCUSSION FOR PUERTO RICO AND THE USVI APR 18/13UTC: AN
UPPER TROUGH EXTENDS FROM 30N 60W ACROSS THE EASTERN DOMINICAN
REPUBLIC/MONA PASSAGE INTO NORTHWEST VENEZUELA. THIS ASSOCIATES
WITH DRY AIR IN THE MID AND UPPER TROPOSPHERE...WHICH HAS ENTERED
THE ISLANDS ON WEDNESDAY AND HAS SUSTAINED A DRYING TREND SINCE
THEN. THE UPPER TROUGH HAS ALSO INDUCED A SURFACE LOW CURRENTLY
LOCATED NEAR 26N 55W...AND IS CURRENTLY LIFTING TO THE NORTHEAST.
IN ASSOCIATION WITH THIS EVOLUTION...NORTHEASTERLY TRADES HAVE
DEVELOPED TO THE WEST OF THE SURFACE LOW...AND ARE FORECAST TO
PERSIST THROUGH THE WEEKEND TO BECOME EASTERLIES ON MONDAY.
ASSOCIATED WITH THE NORTHEASTERLY TRADES...A FEW RAIN SHOWERS ARE
OCCURRING IN NORTHERN PUERTO RICO...MOSTLY OFFSHORE...AS EVIDENCED
BY THE SAN JUAN RADAR.

IN TERMS OF THE FORECAST EVOLUTION...MODELS ARE SUGGESTING THE
CURRENT UPPER TROUGH PATTERN HOLDING THROUGH SUNDAY WHILE THE
TROUGH GRADUALLY LOSES AMPLITUDE. BOTH GFS AND ECMWF AGREE ON THE
MID-UPPER FLOW BECOMING ZONAL BY MONDAY...WITH A TREND TO
MID-UPPER RIDGING BY TUESDAY AND WEDNESDAY NEXT WEEK. ALTHOUGH
THIS TREND WILL LIKELY FAVOR A LARGE SCALE INCREASE IN
SUBSIDENCE...NOTE THAT A WEAK UPPER-DIVERGENT MJO PULSE AND A
TROPOSPHERIC KELVIN WAVE WILL BE PROPAGATING ACROSS THE EASTERN
CARIBBEAN BETWEEN SUNDAY AND MONDAY...COUNTERACTING THE EFFECTS OF
THE MID/UPPER RIDGING.

IN TERMS OF THE EVOLUTION OF LOW-LEVEL FEATURES...EXPECT A RETURN
OF THE EASTERLY/EAST-SOUTHEASTERLY TRADES SOMETIME BY MONDAY IN
RESPONSE TO CHANGES IN THE MID-UPPER FLOW. THIS WILL RESULT IN A
SHIFT OF THE LOCATION OF AFTERNOON CONVECTION FROM THE CORDILLERA
TO NORTHWEST PUERTO RICO BY EARLY NEXT WEEK. OF RELEVANCE...THE
AFOREMENTIONED SURFACE LOW ASSOCIATES WITH A SURFACE TROUGH THAT
IS ORGANIZING FROM THE NORTH ATLANTIC INTO THE EASTERN CARIBBEAN.
THIS PLUME IS FORECAST TO MEANDER FROM THE NORTH ATLANTIC INTO THE
LEEWARD ISLANDS DURING THE NEXT SEVERAL DAYS. ALTHOUGH THE BULK OF
THE PLUME IS FORECAST TO REMAIN SOUTH OF PUERTO RICO THROUGH THE
WEEKEND...CHANGES IN THE FLOW PATTERN WILL LIKELY RESULT IN THE
PLUME MEANDERING NORTHWARD BY MONDAY/TUESDAY. MODELS SUGGEST
PRECIPITABLE WATER VALUES INCREASING TO 45-50MM...WHICH IMPLY
ABOVE-AVERAGE VALUES FOR THIS TIME OF THE YEAR. ALTHOUGH THE
MID-LEVEL RIDGING MIGHT TAMPER THE POTENTIAL FOR EXCESSIVE
PRECIPITATION...THE PRESENCE OF THE MOIST PLUME AND HIGH
PRECIPITABLE WATER VALUES...AS WELL AS INFLUENCE FROM THE KELVIN
WAVE...WILL LIKELY YIELD TO AN INCREASE IN THE COVERAGE OF
PRECIPITATION CONVECTION FROM MONDAY THROUGH WEDNESDAY AND
POTENTIALLY HIGHER RAINFALL AMOUNTS BETWEEN MONDAY AND WEDNESDAY.

IN THE MEANTIME...THERE WILL BE SUFFICIENT MOISTURE AVAILABLE TO
SUSTAIN DIURNAL CONVECTION IN THE ISLAND ON A DAILY BASIS.
CONSIDERING 05-10KT NORTHEASTERLY TRADE WINDS ON THURSDAY AND
FRIDAY...EXPECT DIURNAL BREEZES TO PLAY A ROLE IN FAVORING
AFTERNOON CONVECTION MOSTLY ALONG THE CORDILLERA. TRADES ARE
EXPECTED TO ACCELERATE ON SUNDAY TO 10-15KT WHILE THEY VEER TO
EASTERLIES ON SUNDAY AND SOUTHEASTERLIES ON MONDAY...FAVORING A
SHIFT OF AFTERNOON CONVECTION TO THE WESTERN CORDILLERA AND
NORTHWEST PUERTO RICO RESPECTIVELY.

NOTE THAT MODEL CONFIDENCE DECREASES NEAR
MONDAY/TUESDAY...PARTICULARLY ON THE EVOLUTION AND TIMING OF THE
MOIST PLUME...AS IT MEANDERS NORTHWARD INTO/ACROSS THE ISLANDS.

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