Prognostic Meteorological Discussion
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FXCA20 KWBC 221241
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
841 AM EDT FRI MAY 22 2015

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM MAY 22 AT
06UTC: AT UPPER LEVELS...THE SUBEQUATORIAL RIDGE IS STILL WELL
ESTABLISHED ON A HIGH THE CENTERS TO THE EAST OF THE GUIANAS. THIS
RIDGE EXTENDS OVER NORTHERN SOUTH AMERICA INTO CENTRAL-WESTERN
CARIBBEAN. A LOW CENTERED TO THE NORTHEAST OF THE FORECAST
AREA...JUST TO THE SOUTH OF BERMUDA...PRESSES AGAINST THIS RIDGE
RESULTING IN A JET MAXIMA WITHIN THE WESTERLY FLOW OVER AND JUST
TO THE SOUTH OF PUERTO RICO. ACTIVE CONVECTION OVER THE
SOUTHWESTERN CARIBBEAN AND HISPANIOLA...UNDER THIS FLOW
PATTERN...IS ADVECTING SCATTERED HIGH CLOUDS OVER THE REGION. A
SUBSIDENCE INVERSION BELOW 850 HPA...WHICH IS LIMITING THE
VERTICAL DEVELOPMENT OF CONVECTION. ALTHOUGH THERE IS PLENTIFUL
MOISTURE AT UPPER LEVELS...A DRY AIR MASS DOMINATES BETWEEN 925
AND 500 HPA. WINDS ARE RATHER WEAK WITH SPEEDS BELOW 15KT AND FROM
THE EAST-SOUTHEAST.
THE UPPER RIDGE IS FORECAST TO EXPAND TO THE NORTH. THIS WILL
GRADUALLY STEER THE UPPER FLOW FROM WESTERLY TO NORTHWESTERLY. JET
MAXIMA ALOFT IS EXPECTED TO GRADUALLY WEAKEN...TO DISSIPATE BY
SUNDAY. IN THE MEAN TIME...THE REGION WILL LIE IN THE UPPER
CONVERGENT SIDE OF THE JET MAXIMA. THIS WILL CONTINUE LIMITING THE
DEVELOPMENT OF DEEP CONVECTION. ALTHOUGH THE PRESENCE OF MID-HIGH
CLOUDS IS TO LIMIT THERMAL HEATING TO SOME EXTENT...THE DIURNAL
CYCLE WILL DOMINATE WITH ACTIVITY BUILDING OVER THE CORDILLERA AND
NORTHWESTERN PUERTO RICO IN THE AFTERNOON. WITH THESE ATMOSPHERIC
DYNAMICS AND STABILITY/VERTICAL DISTRIBUTION OF
MOISTURE...EXPECTING LIGHT MORNING SHOWERS OVER SOUTHEASTERN
PUERTO RICO...AND ISOLATED AND SHORT-LIVED SHOWERS AND
THUNDERSTORMS OVER THE NORTHWESTERN/WESTERN PART DURING THE
AFTERNOON AND FIRST HALF OF THE NIGHT. IN TERMS OF
ACCUMULATIONS...THE GLOBAL MODELS AND THE HIGH RESOLUTION WRF
AGREE WITH EXPECTATIONS...AS THEY ALL SUGGEST RATHER LIGHT AMOUNTS
ESPECIALLY FOR THIS TIME OF THE YEAR. SAHARAN DUST IS ALSO
ENTERING THE AREA...YET THE SAL LAYER WILL NOT BE SUFFICIENTLY
STRONG TO FULLY TAMPER CONVECTIVE DEVELOPMENT. IN TERMS OF
ACCUMULATIONS...EXPECTING AMOUNTS OF 05-10MM/DAY AND ISOLATED
MAXIMA OF 15MM. SLIGHTLY HIGHER AMOUNTS ARE POSSIBLE IN AFTERNOON
CONVECTION OVER WESTERN AND NORTHWESTERN PUERTO RICO.
NO WET PATTERN IN SIGHT. MODELS ARE SUGGESTING A SLIGHT DECREASE
IN DEEP-LAYER STABILITY INTO EARLY NEXT WEEK...BUT A SUBSIDENCE
INVERSION AND DRY AIR AT MID-LEVELS ARE LIKELY TO PERSIST...TO
SUSTAIN THE CURRENTLY UNUSUALLY DRY PATTERN FOR LATE MAY.

CRAIG...TTMS (TRINIDAD AND TOBAGO)
SAMUEL...MDS (SURINAME)
GALVEZ...WPC (USA)
$$





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