578  
FXCA20 KWBC 261058  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
657 AM EDT THU OCT 26 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM OCT 26/06  
UTC: MEANDERING TUTT LIES SOUTH OF THE FORECAST AREA WHILE  
CENTERING ON A CLOSED LOW NORTH OF ISLA DE MARGARITA. AS THE TUTT  
MEANDERS TO THE SOUTH...THE FORECAST AREA WILL REMAIN UNDER  
INFLUENCE OF A MID LEVEL CAP INVERSION. ON FRIDAY...PROGRESSIVE  
SHORT WAVE TROUGH IS TO STREAM ACROSS THE WESTERN ATLANTIC TO THE  
NORTHEAST CARIBBEAN ISLES...BRIEFLY PHASING WITH THE TUTT TO THE  
SOUTH. THIS WILL BE STRONG ENOUGH TO BREACH THE TRADE WINDS  
CAP...WITH DEEPER LAYER CONVECTIVE INSTABILITY TO ENVELOP THE  
ENTIRE FORECAST AREA DURING THE EARLY MORNING HOURS ON FRIDAY. THE  
AREA OF INSTABILITY THIS IS TO QUICKLY EXPAND ACROSS PUERTO RICO  
DURING THE MID-LATE MORNING HOURS. AT LOW LEVELS...AN EASTERLY  
WAVE/TUTT INDUCED PERTURBATION ENTERS THE ISLAND CHAIN EARLY THIS  
MORNING. THE WAVE THEN CONTINUES ACROSS THE VIRGIN ISLES BY FIRST  
LIGHT ON FRIDAY...TO THEN MEANDER EAST ACROSS PUERTO RICO DURING  
THE DAY...REACHING THE MONA PASSAGE EARLY ON SATURDAY MORNING.  
MODELS AGREE ON DEEP PLUME OF TROPICAL MOISTURE TO ACCOMPANY THIS  
FEATURE...WITH PWAT CONTENT OF TWO INCHES. AS ENVIRONMENTAL  
CONDITIONS BECOME MORE FAVORABLE AND CONDUCIVE FOR ORGANIZED  
CONVECTION TO DEVELOP...WE ARE NOW CONSIDERING POSSIBILITY OF AN  
MCS FORMING ACROSS THE VIRGIN ISLES/EASTERN PUERTO RICO-SAN JUAN  
METRO AREA DURING THE MORNING HOURS ON FRIDAY...TO SUSTAIN HEAVY  
RAINFALL AMOUNTS. DURING THAT PERIOD MOST ACTIVE IS LIKELY TO  
CLUSTER ACROSS THE NORTHERN VI. A SECOND ROUND OF CONVECTION IS TO  
THEN ENVELOP CENTRAL-WESTERN PUERTO RICO DURING THE EARLY  
AFTERNOON HOURS AS ENHANCED BY DIURNAL HEATING...WITH POTENTIAL  
FOR HEAVY RAINFALL AMOUNTS ACROSS THE GUAJATACA RIVER BASIN.  
 
A MID/UPPER LEVEL RIDGE IS TO THEN GRADUALLY BUILD FROM THE  
WEST...BRANCHING ACROSS THE NORTHEAST CARIBBEAN ISLES ON  
SUNDAY-MONDAY. THE BUILDING RIDGE WILL THEN STEER THE TUTT TO THE  
EAST-SOUTHEAST...MEANDERING ALONG THE COAST OF SOUTH AMERICA TO  
THE CENTRAL CARIBBEAN. AS THE RIDGE ESTABLISHES ACROSS THE  
FORECAST AREA...THIS IS TO RESULT IN THE GRADUAL EROSION OF  
AVAILABLE MOISTURE...WITH A MORE STABLE AIR MASS TO GRADUALLY  
ESTABLISH ACROSS THE FORECAST AREA EARLY NEXT WEEK. MEANWHILE...  
SCATTERED DIURNAL CONVECTION IS TO CONTINUE TO PESTER THE FORECAST  
AREA. IN A DEEP LAYER WESTERLY FLOW EXPECTING EARLY MORNING  
SHOWERS ACROSS THE VIRGIN ISLES TO EASTERN PUERTO RICO...TO FAVOR  
LIGHT TO MODERATE RAINFALL AMOUNTS ACROSS EL YUNQUE  
RAINFOREST/LUQUILLO. LATER ON SATURDAY...AS THE STEERING WINDS  
VEER TO THE SOUTHEAST...THE FOCUS OF THE DIURNAL CONVECTION WILL  
SHIFT TO NORTHWEST PORTIONS OF PUERTO RICO WHERE WE EXPECT  
MODERATE RAINFALL AMOUNTS. THROUGH SUNDAY-MONDAY MODELS TREND IN  
FAVOR OF LESSER RAINFALL AMOUNTS AS THE UPPER SUPPORT TO THE  
CONVECTION WANES.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON...WPC (USA)  

 
 
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