906
FXCA20 KWBC 261131
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
731 AM EDT WED APR 26 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APR
26/12UTC: ZONAL WESTERLY FLOW CONTINUES IN THE MID AND UPPER
TROPOSPHERE OVER THE ESTERN CARIBBEAN...AS THE REGION LIES UNDER
THE INFLUENCE OF THE SUBEQUATORIAL UPPER RIDGE. THE SAN JUAN
SOUNDING SHOWS WESTERLY FLOW ABOVE 800 HPA INTO THE TROPOPAUSE. IN
THE LOW-LEVELS...THE TRADES CONTINUE WEAK AND DISORGANIZED. THE
TRADE WIND CAP HAS LOWERED WITH RESPECT TO PREVIOUS DAYS...ANS
SITS NEAR 700 HPA ON WEDNESDAY MORNING. THE CAP IS NOT TOO
STRONG...BUT THERE IS PLENTY OF DRY AIR ABOVE IT. THIS FAVORS
ENTRAINMENT OF DRY AIR INTO THE MIXED LAYER...WHICH IS CONSISTENT
WITH VERY LITTLE CLOUDINESS OBSERVED IN THE AREA THIS MORNING.
TOTAL PRECIPITABLE WATER CONTINUES LOW. THE MIMIC-TPW ANALYSIS
SHOWS VALUES RANGING NEAR 30MM IN PUERTO RICO. YET...A MOIST PLUME
WITH VALUES OF 40-45MM LIES TO THE SOUTH OF THE ISLANDS NEAR
16N...AND IS FORECAST TO GRADUALLY MEANDER NORTH TO APPROACH THE
ISLANDS IN THURSDAY.
THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST. ZONAL WESTERLY
FLOW IS EXPECTED TO CONTINUE THROUGH THURSDAY EVENING. THEN A
BROAD TROUGH OVER THE NORTH ATLANTIC ON THURSDAY DEEPENS INTO THE
NORTHEAST CARIBBEAN BY THURSDAY EVENING. THIS WILL PROVIDE SOME
ENHANCEMENT TO AFTERNOON/EVENING CONVECTION ON THURSDAY. THE AXIS
OF THE TROUGH CROSSES FROM WEST TO EAST BETWEEN 00-06 UTC ON
FRIDAY...FAVORING AN GRADUAL INCREASE IN UPPER CONVERGENCE AND
SUBSIDENCE BY FRIDAY INTO THE WEEKEND. THIS IS CONSISTENT WITH THE
EVOLUTION OF THE MID-LEVELS...WHICH SHOWS A MID-LEVEL RIDGE MOVING
IN FROM THE SOUTHEAST ON FRIDAY...AND ESTABLISHING OVER THE
NORTHEAST CARIBBEAN ON SATURDAY TO PERSIST THROUGH MONDAY. MODELS
ARE CONSISTENT WITH A WEAK TRADE WIND CAP PERSISTING THROUGH THE
CYCLE...ONLY STRENGTHENING SOME BY THE WEEKEND. THIS WILL CONTINUE
TO FAVOR AFTERNOON CONVECTION ON A DAILY BASIS...LIKELY TO CLUSTER
ALONG AND JUST TO THE NORTH OF THE CORDILLERA FAVORED BY THE
CONVERGENCE OF DIURNAL BREEZES. WEAK SOUTHWESTERLY FLOW IN 700 HPA
STILL POSES A THREAT FOR SOME OF THE AFTERNOON CONVECTION TO
DEVELOP OR MOVE INTO THE SAN JUAN METRO ON WEDNESDAY AND THURSDAY.
BUT THE RETURN OF SOUTHEASTERLIES AFTERWARDS WILL FAVOR A
RELOCATION OF AFTERNOON CONVECTION TO NORTH-CENTRAL PUERTO RICO ON
FRIDAY...AND TO NORTHWEST PUERTO RICO BY SATURDAY AND
SUNDAY...FOLLOWING A MORE CLIMATOLOGICAL DISTRIBUTION FOR LATE
APRIL.
IN TERMS OF AMOUNTS...EXPECT LOCALIZED MAXIMA OF 1-1.5 INCHES ON
WEDNESDAY AND THURSDAY...PRIMARILY IN AREAS IMMEDIATELY NORTH OF
THE CORDILLERA. THIS INCLUDES THE SAN JUAN METRO WHERE EXPECT
MAXIMA OF 0.25-0.75 INCHES...PRIMARILY IN SOUTHERN PORTIONS. ON
FRIDAY...EXPECT MAXIMA DECREASING TO 0.5-1 INCH CLUSTERING IN
NORTH-CENTRAL PUERTO RICO...WHILE ON SATURDAY AND SUNDAY EXPECT
MAXIMA OF 0.5-0.75 INCHES IN INTERIOR PORTIONS OF NORTHWEST PUERTO
RICO.
GALVEZ/ACOSTA...WPC (USA)
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