TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
649 AM EDT FRI APR 20 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APR 20/06
UTC: FAIRLY STRONG TRADE WINDS CAP PERSISTS ACROSS THE NORTHEAST
CARIBBEAN...WITH SATELLITE DERIVED ANALYSIS SHOWING A PWAT MINIMA
ENVELOPING THE FORECAST AREA. AT LOW LEVELS BRISK EASTERLY TRADES
RETURNED...WITH 850 HPA WINDS PEAKING AT 15-20KT. THIS REMAINS
STRONG ENOUGH TO FAVOR GENERATION OF STREAMERS ACROSS THE VIRGIN
ISLES-VIEQUES AND CULEBRA DURING THE DAYTIME HOURS. UPSTREAM FROM
THE ISLANDS...EMBEDDED IN THE PREVAILING EASTERLY FLOW...A PLUME
OF MOISTURE IS ADVECTING ACROSS THE LEEWARD ISLES. THE PLUME WILL
MOVE ACROSS THE VIRGIN ISLES TO EASTERN PUERTO RICO EARLY ON
SATURDAY MORNING. THIS WILL COINCIDE WITH WEAKENING OF THE TRADE
WINDS CAP...WITH INVERSION LIFTING TO AROUND 650/600 HPA BY MID
AFTERNOON ON SATURDAY. THE DEEPER MOISTURE WILL SUSTAIN AN
INCREASE IN DIURNAL CONVECTION...BUT LACKING MID/UPPER LEVEL
FORCING ONLY EXPECTING MODERATE RAINFALL AMOUNTS. MOST ACTIVE IS
TO CLUSTER ACROSS INTERIOR PORTIONS OF PUERTO RICO. ON SUNDAY A
DRYER AIR MASS ENTRAINS FROM THE EAST...LEADING TO A LULL IN
ACTIVITY WITH FEW SHOWERS TO BUILD ACROSS INTERIOR PORTIONS OF THE
ISLAND.

SIMULTANEOUSLY...AN UPPER LEVEL TROUGH IS TO AMPLIFY ACROSS THE
CENTRAL CARIBBEAN EARLY IN THE CYCLE. A SUBTROPICAL JET MAXIMA
ROUNDING THE BASE OF THE TROUGH IS TO THEN LIFT ACROSS THE
NORTHEAST CARIBBEAN ISLES EARLY NEXT WEEK...WITH DIVERGENCE ON ITS
LEFT EXIT REGION (INDIRECT CIRCULATION) TO ENVELOP THE FORECAST
AREA. AS IT PULLS AWAY...THE JET IS TO THEN DRAW THE MID/UPPER
LEVEL TROUGH ACROSS THE FORECAST AREA ON MONDAY-TUESDAY. AT LOW
LEVELS...TRADES ARE EXPECTED TO SLACKEN...ALLOWING THE DIURNAL
HEAT CYCLE/SEA BREEZE DRIVEN CONVECTION TO PREVAIL. IN
SOUTHWESTERLY UPPER LEVEL SHEAR...EXPECTING MOST ACTIVE TO AFFECT
NORTHEAST PUERTO RICO/SAN JUAN METRO AREA IN MID TO LATE AFTERNOON
CONVECTION. AS A RESULT...ON MONDAY TO TUESDAY  EXPECTING MODERATE
TO HEAVY RAINFALL AMOUNTS.

DAVISON/GALVEZ...WPC (USA)