Prognostic Meteorological Discussion
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
649 AM EDT MON MAR 27 2017

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM MARCH
27/06 UTC: MID LEVEL LOW OVER THE BAHAMAS ANCHORS A SHORT WAVE
TROUGH THAT EXTENDS OVER THE GREATER ANTILLES TO THE NORTHERN
CARIBBEAN. AT LOW LEVELS THE TROUGH ALOFT SUSTAINS A CLOSED LOW TO
THE NORTH OF THE DOMINICAN REPUBLIC. THIS FAVORS A MOIST SOUTHERLY
FLOW ACROSS THE FORECAST AREA...WITH BEST MOISTURE CONVERGENCE
CURRENTLY TAKING PLACE JUST NORTH OF THE FORECAST AREA. AT 700 HPA
IT FAVORS A SOUTHWESTERLY STEERING FLOW...THAT WOULD LIKELY FOCUS
DIURNAL CONVECTION ACROSS THE SAN JUAN METRO AREA THIS AFTERNOON.

MODELS CONSISTENTLY FORECAST THE MID LEVEL LOW/TROUGH TO LIFT TO
THE EAST-NORTHEAST ON TUESDAY AS ANOTHER TROUGH EXITS THE EASTERN
USA. THE LATTER WILL TAKE A BEELINE ACROSS THE WESTERN
ATLANTIC...REACHING THE FORECAST AREA LATER ON WEDNESDAY. THIS
WILL THEN YIELD TO A BUILDING RIDGE. THE RIDGE IS TO QUICKLY
STRENGTHEN THE TRADE WINDS CAP...SUSTAINING EROSION OF AVAILABLE
MOISTURE. AT LOW LEVELS...IN RESPONSE TO EVOLVING MID/UPPER LEVEL
PATTERN...THE SURFACE LOW IS TO ALSO LIFT TO THE EAST-NORTHEAST.
MEANWHILE...SOUTHERLY WINDS ARE TO PERSIST THROUGH TUESDAY
EVENING...WHEN WINDS SHIFT TO THE NORTH-NORTHEAST. THIS WILL HELP
SUSTAIN THE AFOREMENTIONED DRYING TREND WHILE ADVECTING A COOLER
AIR MASS. AT 700 HPA...SOUTHWESTERLY STEERING FLOW IS TO PERSIST
THROUGH LATE AFTERNOON ON TUESDAY...WITH WINDS TO THEN SHIFT TO
THE WEST EARLY ON WEDNESDAY.

THE LOW LEVEL SOUTHERLY WINDS ARE TO INITIALLY FAVOR CONVECTIVE
DEVELOPMENT ALONG THE CORDILLERA OVER PUERTO RICO. THROUGH THE
EARLY AFTERNOON HOURS...UNDER INFLUENCE OF SOUTHWESTERLY WINDS
ALONG...THE FOCUS SHIFTS TO NORTHEAST PUERTO RICO/SAN JUAN METRO
AREA. THIS PATTERN WILL PERSIST DURING THE NEXT COUPLE OF
DAYS...WITH HIGHER RESOLUTION MODEL GUIDANCE SHOWING MOST ACTIVE
ON TUESDAY UNDER INFLUENCE OF MID LEVEL CYCLONIC VORTICITY.
ALTHOUGH MODEL GUIDANCE ONLY SHOW ISOLATED DEEP CONVECTION ACROSS
PUERTO RICO...WEAK VERTICAL SHEAR WOULD LIKELY FAVOR LONGER
LASTING CONVECTION THAN YOUR TYPICAL AIR MASS THUNDERSTORM. SO
THERE IS AN ENHANCED RISK OF HEAVIER RAINFALL AMOUNTS ON TUESDAY.
CONVECTIVE CELLS FORMING OVER SAINT CROIX IN THE MORNING WILL ALSO
LIFT ACROSS THE NORTHERN VI IN THE AFTERNOON...WITH POTENTIAL FOR
MODERATE RAINFALL AMOUNTS. A GRADUAL DECREASE IN ACTIVITY IS
EXPECTED ON WEDNESDAY AND ONWARD...WITH FAIR WEATHER CONDITIONS
LIKELY TO PREVAIL BY THE END OF THE WEEK/WEEKEND.

JIMENEZ...IMN (COSTA RICA)
SUBRATH-ALI...TTMS (TRINIDAD AND TOBAGO)
DAVISON/GALVEZ...WPC (USA)

$$





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