033  
FXCA20 KWBC 151209  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
709 AM EST WED NOV 15 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM NOV 15/06  
UTC: THE MODELS HAVE GOOD CONTINUITY FROM PREVIOUS CYCLE...WITH  
PERSISTENT MID/UPPER LEVEL RIDGE OVER MEXICO STEERING SUCCESSIVE  
SHORT WAVE PERTURBATIONS ACROSS THE SOUTHEAST USA/GULF OF MEXICO.  
THESE THEN COMBINE IN SUPPORT OF A DEEPENING LONG WAVE TROUGH OVER  
THE WESTERN ATLANTIC-WESTERN CARIBBEAN/NORTHERN CENTRAL AMERICA.  
UNDER PRESSURE FROM DEEPENING MID/UPPER LEVEL TROUGH...RIDGE OVER  
THE EASTERN CARIBBEAN IS TO WEAKEN ENOUGH TO ALLOW FOR DEEPER  
INSTABILITY TO ENVELOP PUERTO RICO AND THE VIRGIN ISLES LATER THIS  
MORNING. AS THE SHORT WAVE PERTURBATIONS ROUND THE BASE OF THE  
LONG WAVE AXIS THESE ARE TO THEN LIFT ACROSS HISPANIOLA-MONA  
PASSAGE/NORTHWEST PUERTO RICO...WITH A STRONG VORTEX EXPECTED  
LATER THIS EVENING. A SECOND ONE WILL FOLLOW BY MIDAFTERNOON ON  
FRIDAY. LATER DURING THE WEEKEND...MID/UPPER LEVEL TROUGH IS TO  
SPLIT IN TWO...WITH HALF TO THE NORTH LIFTING ACROSS THE CENTRAL  
ATLANTIC WHILE THE SOUTHERN HALF MEANDERS ACROSS EASTERN  
CUBA-JAMAICA/CENTRAL CARIBBEAN. AS THE TROUGH WEAKENS...MID/UPPER  
LEVEL RIDGE PATTERN IS TO GRADUALLY BUILD FROM THE EAST. THIS IS  
TO ONCE AGAIN FAVOR A TRADE WINDS CAP ACROSS THE NORTHEAST  
CARIBBEAN THAT IS TO STRENGTHEN THROUGH MONDAY EVENING.  
 
AT LOW LEVELS...FRONTAL TROUGH EXTENDS OVER THE WESTERN ATLANTIC  
TO THE BAHAMAS... WITH ASSOCIATED FRONT FORECAST TO BOTTOM OUT FAR  
TO THE NORTH. THIS IS IN PHASE WITH A SECONDARY TROUGH TO THE  
SOUTH OVER THE CENTRAL CARIBBEAN. AS ENHANCED BY UPPER LEVEL  
TROUGH...THE ONE OVER THE CARIBBEAN IS TO BECOME BETTER ORGANIZED  
EARLY IN THE CYCLE. UNDER INFLUENCE OF THIS TROUGH THE LOW-MID  
LEVEL WINDS OVER THE EASTERN CARIBBEAN ARE TO VEER TO THE  
SOUTH-SOUTHWEST BY NOONTIME TODAY. WINDS WILL THEN RETAIN A  
SOUTHWESTERLY COMPONENT THROUGH SATURDAY EVENING/EARLY SUNDAY  
MORNING. THIS IS TO FAVOR A MOIST ADVECTIVE PATTERN...WITH PWAT  
CONTENT INCREASING TO AROUND TWO INCHES EARLY THIS AFTERNOON. THE  
HIGH MOISTURE CONTENT AND FAVORABLE UPPER LEVEL DYNAMICS WILL BE  
CONDUCIVE TO GENERATION OF MESO SCALE CONVECTIVE SYSTEMS ACROSS  
THE NORTH-CENTRAL CARIBBEAN...WITH CONVECTION ACROSS HAITI AND THE  
DOMINICAN REPUBLIC GRADUALLY BECOMING BETTER ORGANIZED DURING THE  
DAY TODAY INTO EARLY MORNING HOURS ON THURSDAY. THE INTENSE  
CONVECTION TO THE WEST WILL RESULT IN DENSE HIGH CLOUDS SPREADING  
ACROSS PUERTO RICO-VIRGIN ISLES. THIS WILL BLOCK DAYTIME HEATING  
AND IT IS LIKELY TO DELAY THE ONSET OF DAYTIME CONVECTION ACROSS  
PUERTO RICO. OVERALL...EXPECTING MODERATE RAINFALL AMOUNTS DURING  
THE NEXT FEW DAYS...WITH MOST INTENSE EXPECTED AROUND  
MIDAFTERNOON. HOWEVER...IF CONVECTION ACROSS HISPANIOLA IS AS  
ACTIVE AS THE ECMWF AND UKMET SUGGEST...ACTIVITY ACROSS PUERTO  
RICO WILL GENERALLY PEAK AT LESS THAN ONE INCH.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  
 

 
 
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