Prognostic Meteorological Discussion
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FXCA20 KWBC 241059
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
658 AM EDT MON APR 24 2017

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APRIL
24/06 UTC: POLAR TROUGH OVER THE EASTERN USA/GULF OF MEXICO IS
SLOWLY PRESSING AGAINST A RIDGE TO THE EAST. THE MID/UPPER LEVEL
TROUGH IS FORECAST TO GRADUALLY LIFT OVER THIS AXIS OVER THE NEXT
DAY OR SO. AS IT STREAMS ACROSS THE FORECAST AREA...THIS IS TO
SUSTAIN DEEP LAYER CONVECTIVE INSTABILITY AND MESO-SYNOPTIC
FORCING. A JET MAXIMA EXITS JUST SOUTH OF PONCE ON TUESDAY. THIS
WILL FAVOR A DIVERGENT PATTERN ALOFT THAT IS TO VENT DEEP
CONVECTION DURING THE DAY. AT LOW LEVELS...ASSOCIATED FRONT
MEANDERS OVER THE WESTERN ATLANTIC...WHILE A RIDGE TO THE EAST
SETTLES OVER THE CENTRAL ATLANTIC. THE RIDGE SUSTAINS A MOIST
SOUTHEASTERLY FLOW ACROSS THE LESSER ANTILLES...WITH MOISTURE
CONVERGING OVER PUERTO RICO/VIRGIN ISLES. THE GLOBAL MODEL
GUIDANCE DIVERGE ON WHAT IMPACT THIS IS GOING TO HAVE ACROSS THE
FORECAST AREA...WITH THE ECMWF FAVORING MOST ACTIVE JUST NORTH OF
THE ISLANDS...WHILE THE UKMET AND GFS SHOW MORE WIDESPREAD
CONVECTION ACROSS THE FORECAST AREA.

CONSIDERING HIGH MOISTURE CONTENT...WITH PWAT OF NEARLY TWO
INCHES...WE ARE LEANING TOWARDS THE WETTER MODELS. DURING THE DAY
TODAY THIS IS TO FAVOR SCATTERED CONVECTION...WITH GRADUAL
INCREASE EXPECTED ON TUESDAY AS UPPER JET DYNAMICS BECOME MORE
FAVORABLE. OVER THE NEXT COUPLE OF DAYS...IN A SOUTHEASTERLY
STEERING FLOW...THE MOST INTENSE IS LIKELY TO CLUSTER ACROSS
NORTHWEST PUERTO RICO BY MIDDAY/EARLY AFTERNOON...WITH SECONDARY
MAXIMA ACROSS THE VIRGIN ISLES/EASTERN PUERTO RICO DURING THE
AFTERNOON HOURS. STREAMERS FORMING OVER SAINT CROIX ARE LIKELY TO
AFFECT SOUTHEAST PORTIONS OF PUERTO RICO. RAINFALL MAXIMA WILL
LIKELY PEAK AROUND AN INCH FOR THE DAY TODAY...AND UNDER STRONGER
FORCING ON TUESDAY EXPECTING LOCALIZED MAXIMA OF 3-4 INCHES.

PREVAILING EASTERLY TRADES RETURN TO THE FORECAST AREA ON
WEDNESDAY AS THE POLAR TROUGH/FRONT LIFT TO THE NORTH-NORTHEAST
AND THE RIDGE BUILDS WEST ACROSS THE ATLANTIC. THIS IS TO
GRADUALLY STRENGTHEN THE TRADE WINDS CAP...SUSTAINING EROSION OF
AVAILABLE MOISTURE. DURING THAT PERIOD LIGHT COASTAL CONVECTION IS
TO AFFECT EASTERN PORTIONS OF PUERTO RICO...WHILE MEASURABLE
AMOUNTS CONFINE TO WESTERN INTERIOR PORTIONS OF THE ISLAND.

GAJADHAR...SLMS (SAINT LUCIA)
SUBRATH-ALI...TTMS (TRINIDAD AND TOBAGO)
DAVISON/GALVEZ...WPC (USA)
$$




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