970  
FXCA20 KWBC 251112  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
711 AM EDT WED OCT 25 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM OCT 25/06  
UTC: A TUTT REMAINS OVER THE EASTERN CARIBBEAN...WITH AXIS NOW  
ANCHORING ON A CLOSED LOW JUST WEST OF THE WINDWARD ISLANDS.  
PUERTO RICO AND THE USVI LIE ON THE CONVERGENT SIDE OF THE UPPER  
LEVEL CIRCULATION...WHILE THE ISLAND CHAIN REMAINS ON THE  
DIVERGENT SIDE. AT LOW LEVELS...A WANING TUTT INDUCED PERTURBATION  
IN THE EASTERLY TRADES IS LIFTING ACROSS THE VIRGIN ISLES EARLY  
THIS MORNING. BUT AS IT ENTERS THE CONVERGENT SIDE OF THE UPPER  
LEVEL CIRCULATION THIS WILL ONLY FAVOR WIDELY ISOLATED LIGHT  
CONVECTION. FARTHER EAST...A SECOND TUTT INDUCED WAVE NOW LIES  
EAST OF THE ISLANDS...TRIGGERING SCATTERED DEEP CONVECTION AS IT  
INTERACTS WITH THE ITCZ AND THE TROUGH ALOFT.  
 
TUTT LOW IS TO CUT OFF FROM THE FLOW EARLY IN THE PERIOD...TO THEN  
REMAIN OVER THE EASTERN CARIBBEAN WHILE MEANDERING JUST NORTH OF  
VENEZUELA. THIS IS TO REMAIN NEARLY STATIONARY THROUGH SUNDAY  
MORNING. THIS LOW/TROUGH...IN INTERACTION WITH A BROAD RIDGE TO  
THE WEST...IS TO INITIALLY FAVOR AN UPPER CONVERGENT PATTERN THAT  
IS TO INHIBIT ORGANIZED DEEP CONVECTION ACROSS PUERTO RICO AND THE  
VIRGIN ISLES. THROUGH MID MORNING ON FRIDAY...UNDER INFLUENCE OF A  
SHORT WAVE TROUGH STREAMING TO THE NORTH...PATTERN WILL BECOME  
MORE FAVORABLE AND CONDUCIVE FOR DEEP CONVECTION TO DEVELOP ACROSS  
THE FORECAST AREA. FAVORABLE ENVIRONMENTAL CONDITIONS WILL THEN  
PERSIST THROUGHOUT THE WEEKEND. AT LOW LEVELS...WINDS ARE TO SHIFT  
TO THE SOUTHEAST EARLY THIS MORNING AS THE TUTT INDUCED  
PERTURBATION LIFTS ACROSS THE FORECAST AREA. THIS IS TO ENHANCE  
MOISTURE CONVERGENCE ACROSS NORTHWEST PUERTO RICO...MAINLY TO THE  
WEST OF MANATI/BARCELONETA. BUT AS A MID/UPPER CONVERGENT PATTERN  
HOLDS...ONLY EXPECTING LIGHT TO MODERATE RAINFALL AMOUNTS DURING  
THE DAY TODAY. PREVAILING EASTERLY TRADES RETURN TO THE FORECAST  
AREA ON THURSDAY...FAVORING LIGHT CONVECTION ACROSS THE VIRGIN  
ISLES/EASTERN PUERTO RICO...WITH MEASURABLE AMOUNTS CONFINING TO  
WESTERN INTERIOR PORTIONS OF THE ISLAND. THIS PATTERN IS WELL  
DEPICTED BY THE NMM VERSION OF THE HRWRF.  
 
DURING THE MEDIUM RANGE PERIOD...THE GLOBAL MODELS REACHED A  
CONSENSUS ON THE TIMING OF THE NEXT TUTT INDUCED PERTURBATION...  
FORECASTING THIS WAVE TO SLOWLY LIFT ACROSS THE FRENCH/LEEWARD  
ISLANDS ON THURSDAY. THE WAVE REACHES THE VIRGIN ISLES EARLY ON  
FRIDAY MORNING...AND BY MIDDAY IT WILL MOVE TO PUERTO RICO. A  
PLUME OF DEEP TROPICAL MOISTURE WILL ACCOMPANY THIS WAVE AS IT  
ENTERS THE FORECAST AREA....WITH PWAT CONTENT OF NEARLY TWO INCHES  
EXPECTED TO LINGER THROUGH EARLY MORNING HOURS ON SUNDAY. GDI  
FORECAST FOR THE PERIOD SHOWS PEAK IN INSTABILITY BY MIDDAY/EARLY  
AFTERNOON ON FRIDAY. UNDER FAVORABLE UPPER LEVEL CONDITIONS THIS  
WAVE WILL SUSTAIN HEAVY ORGANIZED DEEP CONVECTION ACROSS THE  
ENTIRE FORECAST AREA...WITH THE NCEP ENSEMBLE MEMBERS SHOWING  
DAILY MAXIMA OF 1-2 INCHES. BUT STRONG FORCING ACROSS WESTERN  
INTERIOR PORTIONS OF PUERTO RICO/GUAJATACA BASIN WOULD LIKELY  
RESULT IN LOCALLY HIGHER AMOUNTS THAN WHAT THE MODELS SUGGEST.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON...WPC (USA)  

 
 
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