Prognostic Meteorological Discussion
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FXCA20 KWBC 251046
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
646 AM EDT TUE APR 25 2017

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APRIL
25/06 UTC: UPPER LEVEL TROUGH PULLING ACROSS THE BAHAMAS/CUBA IS
BECOMING NEGATIVELY TILTED AS IT LIFTS OVER A RIDGE TO THE EAST.
CONSISTENT WITH PREVIOUS FORECASTS THE TROUGH REACHES THE FORECAST
AREA EARLY THIS AFTERNOON. A SUBTROPICAL JET ROUNDING THE BASE OF
THE TROUGH IS FORECAST TO EXIT TO THE WEST-SOUTHWEST OF PUERTO
RICO...FAVORING AN UPPER DIVERGENT PATTERN THAT IS TO VENT DEEP
CONVECTION. AT LOW LEVELS...FLOW SPLITS BETWEEN A WANING POLAR
TROUGH OVER THE EASTERN USA/WESTERN ATLANTIC AND A RIDGE OVER THE
CENTRAL ATLANTIC. THE RIDGE SUSTAINS A MOIST SOUTH-SOUTHEASTERLY
FLOW ACROSS THE ISLAND CHAIN/NORTHEAST CARIBBEAN...WITH DEEP
MOISTURE CONVERGING ACROSS THE FORECAST AREA. AS THE UPPER LEVEL
TROUGH MAKES LANDFALL DURING MAX HEATING...IT IS LIKELY TO FAVOR
ORGANIZED DEEP CONVECTION. MOST ACTIVE IS TO CLUSTER BETWEEN
RINCON AND VEGA BAJA...WITH HIGHER RESOLUTION MODEL GUIDANCE
SHOWING LOCALIZED MAXIMA OF 3-5 INCHES ALONG THE COAST. BUT THIS
IS LIKELY TO MOVE FARTHER INLAND THAN WHAT THE GUIDANCE SUGGESTS.
ALSO...CONSIDERING THE TIMING OF THE UPPER LEVEL TROUGH AND WEAK
VERTICAL WIND SHEAR ACROSS THE FORECAST AREA... THERE IS A SLIGHT
RISK OF SEVERE CONVECTION THIS AFTERNOON.

ON TUESDAY...AS THE SOUTHEASTERLY FLOW PERSISTS...EXPECTING
ANOTHER ROUND OF COASTAL CONVECTION ACROSS NORTHERN PUERTO RICO.
BUT LACKING THE UPPER LEVEL SUPPORT IT SHOULD NOT BE AS STRONG AS
TODAY. LATER IN THE DAY...AS THE POLAR TROUGH WEAKENS...THE LOW
LEVEL RIDGE IS TO BUILD ACROSS THE WESTERN CARIBBEAN. THIS WILL
THEN FAVOR A LONG FETCH EASTERLY FLOW ACROSS THE ENTIRE BASIN.
THIS PATTERN WILL THEN HOLD THROUGH THE END OF THE WEEK. THIS IS
TO FAVOR LATE MORNING CONVECTION ACROSS NORTHEAST PUERTO RICO/EL
YUNQUE RAINFOREST...AND AFTERNOON CONVECTION ON WESTERN INTERIOR
PORTIONS OF THE ISLAND. DURING THIS PERIOD DAILY RAINFALL AMOUNTS
WILL RANGE BETWEEN 0.5-1.0 INCH FOR EASTERN PUERTO RICO AND 1-2
INCHES FOR WESTERN PORTIONS OF THE ISLAND.

GLOBAL MODELS THEN SHOW A DEEPENING TUTT TO DOMINATE THE FLOW
DURING THE MEDIUM RANGE PERIOD...WITH THE MID/UPPER LEVEL TROUGH
REACHING MAXIMUM AMPLITUDE ON SATURDAY-SUNDAY. THIS WILL ONCE
AGAIN FAVOR DEEP LAYER CONVECTIVE INSTABILITY...WITH GLOBAL MODEL
GUIDANCE TRENDING IN FAVOR OF A WETTER PATTERN DURING THE WEEKEND.

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





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