534
FXCA20 KWBC 211452
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
952 AM EST THU NOV 21 2024
WEEKLY DISCUSSION FOR PUERTO RICO AND THE USVI NOV 21/12UTC:
ANALYSIS OF LARGE SCALE OSCILLATIONS SHOWS THE UPPER CONVERGENT
MJO CROSSING THE CARIBBEAN THROUGH THE NEXT TWO WEEKS. YET...A
TROPOSPHERIC KELVIN IS FORECAST TO CROSS THE REGION THROUGH
SATURDAY. THIS WILL LIKELY ENHANCE VENTILATION.
THE SYNOPTIC ANALYSIS SHOWS A LARGE UPPER RIDGE CENTERING JUST TO
THE NORTH OF PUERTO RICO WHILE EXTENDING OVER THE ENTIRE NORTHEAST
CARIBBEAN. IN THE MID-LEVELS...A RIDGE CENTERING OVER MEXICO IS
EXTENDING A ZONAL AXIS ACROSS THE GREATER ANTILLES. THIS RELATES
WITH A TEMPERATURE INVERSION THAT SITS NEAR 750 HPA ON THURSDAY
MORNING. SATELLITE IMAGERY SHOWS STRATIFORM LOW-LEVEL
CLOUDS...CONSISTENT WITH THE STRONG INVERSION. IN TERMS OF
LOW-LEVEL FEATURES...A WEAK STATIONARY FRONT SITS NORTH OF THE
ISLANDS ALONG 21N 56W...20N 65W. LOW-LEVEL WINDS ARE WEAK TO THE
SOUTH OF THIS BOUNDARY. THE SAN JUAN 12 UTC SOUNDING SHOWS VERY
WEAK WINDS IN THE LOW AND MID-TROPOSPHERE...INCLUDING NEARLY CALM
CONDITIONS AT THE SURFACE.
THE FORECAST OF THE UPPER LEVELS SHOWS A POTENT LARGE POLAR TROUGH
PATTERN AMPLIFYING ACROSS THE NORTHWEST CARIBBEAN AND BAHAMAS.
THIS WILL FAVOR A PERSISTENT UPPER RIDGE PATTERN IN PUERTO
RICO...WITH NO SIGNIFICANT UPPER TROUGH EXPECTED IN SITU THROUGH
THE NEXT SEVEN DAYS. IN THE MID-LEVELS...THE NORTHEAST CARIBBEAN
IS EXPECTED TO REMAIN UNDER THE DIRECT INFLUENCE OF A RIDGE
THROUGH SATURDAY. AFTER THIS PERIOD...THE RIDGE MEANDERS TO THE
NORTH AND THEN EAST...WHICH SHOULD ALLOW FOR MORE VERTICAL
DEVELOPMENT UPON SYSTEMS ARRIVING IN THE TRADES. ANALYSIS OF
AVAILABLE MOISTURE AND LOW-LEVEL FLOW SHOWS THE ARRIVAL OF LONG
FETCH SOUTHEASTERLY TRADES LATER ON THURSDAY. THIS WILL YIELD TO
AN INCREASE IN PRECIPITABLE WATER STARTING ON FRIDAY.
HOWEVER...ENHANCED SOUTHERLY FLOW WILL LIMIT THE RESIDENCE TIME OF
TRIGGERS ASSOCIATED WITH DIURNAL HEATING IN NORTHERN PUERTO
RICO...LEADING TO CONSERVATIVE RAINFALL AMOUNTS. EXPECT
HOWEVER...ENHANCED SHOWERS IN SOUTHERN PUERTO RICO ASSOCIATED WITH
THE SOUTHERLY TRADES. THE AMOUNTS OF AVAILABLE MOISTURE ARE
EXPECTED TO INCREASE SIGNIFICANTLY DURING OVERNIGHT HOURS ON
SATURDAY IN ASSOCIATION WITH A TROUGH ARRIVING IN THE EASTERLY
TRADES. NOTE TPW REACHING VALUES OVER 55MM AND PERSISTING THROUGH
MONDAY MORNING. THIS WILL FAVOR A PEAK IN PRECIPITATION ON SUNDAY.
MODELS GENERALLY AGREE IN THE LARGEST RAINFALL AMOUNTS CLUSTERING
IN THE VI AND EASTERN PUERTO RICO...WHERE EXPECT 24-HR TOTALS OF
20-40MM. ISOLATED MAXIMA EXCEEDING 50MM IS POSSIBLE.
AFTER THIS PERIOD...THE FOCUS FOR CONVECTION IS LIKELY TO CLUSTER
IN HISPANIOLA AND AREAS WEST...GIVEN THE DEEPENING OF AN UPPER
TROUGH IN THE WESTERN CARIBBEAN. HOWEVER...MODELS STILL SHOW
ENHANCED AVAILABLE MOISTURE AND INSTABILITY ACROSS PUERTO RICO AND
THE VI...WHICH WILL ALLOW TO LIGHT CONVECTION AND PRECIPITATION ON
A DAILY BASIS.
GALVEZ...WPC (USA)
JACKMAN... BMS (BARBADOS)
MATHIAS... CIAARA-MB (BRAZIL)
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