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Tropical Discussion
 
(Latest Discussion - Issued 1130Z May 23, 2019)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
730 AM EDT THU MAY 23 2019

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM MAY 23/06
UTC: DEEP MIS-UPPER LOW PROPAGATING TO THE NORTH OF THE ISLANDS
CONTINUES TO BE THE MAIN FEATURE OF INTEREST IN THE REGION. THE
UPPER LOW CENTERS AT 25N 68W...AND EXTENDS AN ELONGATED TROUGH
AXIS TO THE SOUTHWEST ACROSS CENTRAL CUBA INTO THE YUCATAN
PENINSULA. A SHORT WAVE AXIS EXTENDS TO THE SOUTH ACROSS PUERTO
RICO AND THE VI. SATELLITE IMAGERY SHOWS SCATTERED MID-LEVEL AND
UPPER LEVEL CLOUDS STREAMING FROM THE SOUTHWEST...GIVEN CURRENT
ACTIVE CONVECTION IN THE WESTERN CARIBBEAN. THESE CLOUDS WILL
LIMIT SOMEWHAT SOLAR RADIATION DURING THE DAY ON THURSDAY...BUT
THE DYNAMIC FORCING AND INSTABILITY WILL BE SUFFICIENT TO TRIGGER
HEAVY RAIN-PRODUCING THUNDERSTORMS IN THE CORDILLERA. THE SAN JUAN
SOUNDING SHOWS A SATURATED LAYER BETWEEN 500 AND 300 HPA AND AT
LOW-LEVELS...BUT IT ALSO SHOWS A DRY LAYER BETWEEN 850 AND 700 HPA
THAT SHOULD LIMIT SOMEWHAT PRECIPITATION AMOUNTS.

THE WINDOW FOR LARGEST PRECIPITATION AMOUNTS RUNS THROUGH EARLY
HOURS OF FRIDAY. ALTHOUGH SCATTERED MID-LEVEL CLOUDS WILL LIMIT
SOLAR RADIATION DURING PERIODS OF THE DAY ON THURSDAY...MODELS ARE
CONSISTENT ON SHOWING A PEAK IN INSTABILITY FROM THE LATE MORNING
INTO EARLY MORNING HOURS ON FRIDAY. THE UPPER TROUGH TO THE NORTH
HAS INDUCED A WEAK TROUGH IN THE TRADES JUST TO THE SOUTHEAST AND
EAST OF ST. CROIX. THIS TROUGH IS FORECAST TO APPROACH THE ISLANDS
DURING THE LATE AFTERNOON ON THURSDAY AND INTERACT WITH THE UPPER
TROUGH OVER NIGHT. THIS OPENS UP A WINDOW FOR HEAVY-RAIN PRODUCING
THUNDERSTORMS IN THE VIRGIN ISLANDS AND SOUTHEAST PUERTO RICO
OVERNIGHT...WITH A MARGINAL CHANCE FOR MCS FORMATION. LARGEST
PRECIPITATION AMOUNTS...HOWEVER...ARE EXPECTED IN THE CORDILLERA
DURING AFTERNOON HOURS OF THURSDAY...FAVORED BY WEAK SOUTHEASTERLY
TRADES. EXPECTING MAXIMA OF 2-3.5 INCHES. ALSO...MODERATE
PRECIPITATION IS EXPECTED OVER AND DOWNSTREAM FROM EL YUNQUE
DURING THE MID-LATE MORNING INTO THE EARLY AFTERNOON...WHICH
INCLUDES SOUTHERN PARTS OF THE SAN JUAN METRO AREA. EXPECTING
MAXIMA OF 1-2 INCHES WITH THIS CONVECTION. NOCTURNAL CONVECTION IN
THE WESTERN VIRGIN ISLANDS AND SOUTHEAST PUERTO RICO WILL LEAD TO
ADDITIONAL MAXIMA OF 1-1.5 INCHES.

WINDS SPEED UP DURING FRIDAY AND REMAIN SOUTH EASTERLIES AT
10-15KT THROUGH LATE SATURDAY. THIS RELOCATES ONCE AGAIN THE
REGION FOR LARGEST RAINFALL AMOUNTS TO NORTHWEST PUERTO RICO ON
FRIDAY AND SATURDAY. EXPECTING MAXIMA IN THE ORDER OF 1-2 INCHES
IN MOST OF NORTHWEST PUERTO RICO ON FRIDAY...AND 1-1.5 INCHES ON
SATURDAY. ON SUNDAY...MAXIMA IS FORECAST TO DECREASE TO NEAR 1
INCH...FOCUSING ON WESTERN PUERTO RICO.

CHINCHILLA...IMN (COSTA RICA)
JIMENEZ...FAC (COLOMBIA)
PAREDES...SENAMHI (PERU)
GALVEZ...WPC (USA)