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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1155Z Nov 20, 2014)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
655 AM EST THU NOV 20 2014

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI. FORECAST AREA
REMAINS SANDWICHED BETWEEN A BROAD RIDGE TO THE WEST AND A TUTT TO
THE EAST. ALTHOUGH PUERTO RICO AND THE USVI LIE ON THE CONVERGENT
SIDE OF THE RIDGE-TUTT PAIR...THE TUTT IS INDUCING ENOUGH
INSTABILITY IN THE LOW LEVEL EASTERLY TRADES TO SUSTAIN AN
INCREASE IN SHALLOW MOISTURE SPREADING ACROSS THE FORECAST AREA.

UPPER LEVEL RIDGE IS TO BLOCK THE TUTT TO THE EAST...FORCING AXIS
TO GRADUALLY WEAKEN WHILE SLOWLY SHEARING TO THE SOUTH-SOUTHWEST.
THIS IS TO KEEP THE FORECAST AREA ON THE CONVERGENT SIDE OF THE
UPPER LEVEL RIDGE...WITH LARGE SCALE SUBSIDENCE LIKELY TO PERSIST
OVER THE NEXT FEW DAYS. BUT AS THE TROUGH ALOFT WEAKENS...IT IS TO
CONTINUE TRIGGERING SHALLOW CONVECTION ACROSS THE NORTHEAST
CARIBBEAN ISLES...TO ADVECT WEST ACROSS THE VIRGIN ISLES AND
PUERTO RICO. THUS FAR THE MODELS HAVE NOT REACHED A CONSENSUS ON
HOW THIS IS GOING TO UNFOLD...WITH THE GFS STILL SHOWING MORE
MOISTURE CLUSTERING ACROSS THE FORECAST AREA THAN WHAT THE
EUROPEAN MODELS SUGGEST. ALTHOUGH THEY DISAGREE ON HOW MUCH
MOISTURE IS GOING TO BE AVAILABLE...THEY GENERALLY AGREE ON SLOW
EROSION OF AVAILABLE WATER THROUGH SATURDAY EVENING.
MEANWHILE...EXPECTING SCATTERED SHOWERS TO ADVECT ACROSS THE
VIRGIN ISLES INTO EASTERN PORTIONS OF PUERTO RICO...WITH MODELS
SHOWING MOST ACTIVE CONVECTION BETWEEN LUQUILLO AND HUMACAO. IN
THIS AREA THE EUROPEAN MODELS SHOW RAINFALL AMOUNTS OF
05-10MM/DAY...WHILE THE GFS PEAKS AT 15-20MM. CURRENT PATTERN AND
UPPER DYNAMICS SEEMS TO FAVOR THE WEAKER EUROPEAN FORECAST. NOTE
THAT THE ARW VERSION OF THE HRWRF SEEMS TO BE DEALING WITH THIS
PATTERN A LOT BETTER THAN THE NMM VERSION OF THE MODEL.


JN BAPTISTE...MS (SAINT LUCIA)
MEDINA...ONAMET (REPUBLICA DOMINICANA)
DAVISON...WPC (USA)