703  
FXCA20 KWBC 241100  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
700 AM EDT TUE OCT 24 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM OCT 24/06  
UTC: FORECAST AREA REMAINS ON THE CONVERGENT SIDE OF AN UPPER  
LEVEL TUTT THAT EXTENDS SOUTH ACROSS THE EASTERN CARIBBEAN TO  
EASTERN VENEZUELA...WHILE CENTERING ON A CLOSED LOW TO THE NORTH  
OF THE FORECAST AREA. AS A RESULT...A PWAT MINIMA PERSISTS ACROSS  
THE FORECAST AREA. AT LOW LEVELS...THE TUTT ALOFT SUSTAINS AN  
INDUCED PERTURBATION IN THE EASTERLY TRADES THAT IS ENHANCING  
CONVECTIVE DEVELOPMENT ACROSS THE FRENCH ISLES EARLY THIS MORNING.  
FARTHER SOUTH...A TROPICAL WAVE IS STREAMING ACROSS  
TRINIDAD/TOBAGO TO EASTERN VENEZUELA. HOWEVER...THIS WAVE IS TO  
GENERALLY CONFINE TO SOUTH OF 12N AND IT IS NOT TO HAVE A  
SIGNIFICANT IMPACT ON LOCAL WEATHER CONDITIONS.  
 
LATEST RUN OF THE GFS SHOWING CORRECTIONS TO TUTT PATTERN  
ALOFT...WITH MODEL NOW FORECASTING THE LOW NORTH OF THE ISLANDS TO  
FILL TO AN OPEN TROUGH EARLY IN THE CYCLE. A NEW LOW IS TO THEN  
FORM ALONG THE BASE OF THE TROUGH OVER THE SOUTHEAST CARIBBEAN  
LATER THIS EVENING/EARLY WEDNESDAY MORNING. THE LOW/SHORT WAVE  
TROUGH IS TO THEN REMAIN SOUTH OF THE FORECAST AREA THROUGH THE  
END OF THE WEEK. ALTHOUGH PATTERN EVOLVES...MODELS FORECAST THE  
MID LEVEL CAP TO GENERALLY HOLD THROUGH AT LEAST FRIDAY  
MORNING...WITH THE GFS AND ECMWF GDI FORECASTS SHOWING A  
CONVECTIVELY STABLE AIR MASS TO GENERALLY PREVAIL THROUGH FRIDAY  
MORNING. AT LOW LEVELS...THE TUTT INDUCED PERTURBATION PULLS  
ACROSS THE FORECAST AREA EARLY ON WEDNESDAY...WITH LOW/MID LEVEL  
WINDS VEERING FROM THE EAST TO THE SOUTHEAST AS THE WAVE LIFTS  
NORTH OF THE FORECAST AREA. UNABLE TO OVERCOME THE TRADE WINDS  
CAP...THIS WAVE IS TO ONLY FAVOR A SLIGHT INCREASE IN SHALLOW  
CONVECTION AS IT STREAMS ACROSS THE NORTHEAST CARIBBEAN ISLES.  
PREVAILING EASTERLY TRADES RETURN TO THE FORECAST AREA ON  
THURSDAY.  
 
UNDER INFLUENCE OF UPPER LEVEL TROUGH...EXPECTING SOME ENHANCEMENT  
OF DIURNAL CONVECTION ACROSS WESTERN INTERIOR PORTIONS OF PUERTO  
RICO DURING THE DAY TODAY. BUT THIS IS TO GENERALLY FAVOR LIGHT TO  
MODERATE RAINFALL AMOUNTS WITH MOST ACTIVE ON THE GUAJATACA BASIN.  
UNDER THE INFLUENCE OF THE TUTT INDUCED PERTURBATION A SLIGHT  
INCREASE IN CONVECTION IS PROBABLE ON WEDNESDAY...BUT IN A  
SOUTHEASTERLY STEERING FLOW THE MOST ACTIVE IS EXPECTED ACROSS  
NORTHWEST PUERTO RICO TO THE WEST OF MANATI/BARCELONETA. LESSER  
AMOUNTS ARE EXPECTED ON THURSDAY AS THE PREVAILING EASTERLY TRADES  
RETURN TO THE FORECAST AREA AND THE TRADE WINDS CAP CONTINUES TO  
HOLD.  
 
DURING THE MEDIUM RANGE PERIOD...THE GLOBAL MODEL GUIDANCE IS  
TRENDING TOWARDS A MORE UNSTABLE AIR MASS LATER IN THE WEEK AS A  
STRONGER TROPICAL WAVE ENTERS THE EASTERN CARIBBEAN.  
HOWEVER...MODELS DIVERGE ON THE TIMING OF THIS FEATURE...WITH THE  
ECMWF FAVORING A FASTER SOLUTION THAN WHAT THE GFS SUGGESTS. AT  
THIS TIME WE ARE GOING WITH A COMPROMISE SOLUTION...NOT AS FAST AS  
THE EUROPEAN AND SLIGHTLY FASTER THAN THE GFS. INTERESTINGLY THE  
NAM SUPPORTS A FASTER EVOLUTION THAN THE GFS.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON...WPC (USA)  

 
 
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