600  
FXCA20 KWBC 091149  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
649 AM EST TUE JAN 09 2018  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JAN 09/06  
UTC: MID/UPPER LEVEL RIDGE REMAINS THE DOMINANT FEATURE ACROSS THE  
EASTERN CARIBBEAN. AT 250 HPA A HIGH OVER NORTHERN VENEZUELA  
ANCHORS A CELL OF THE SUBEQUATORIAL RIDGE ACROSS MOST OF THE BASIN  
INTO THE ATLANTIC...WHILE AT 500 HPA THE MID LEVEL RIDGE ANCHORS  
ON A CLOSED HIGH JUST NORTH OF PUERTO RICO. THIS FAVORS A MID  
LEVEL CONVERGENT PATTERN THAT IS INHIBITING ORGANIZED DEEP  
CONVECTION. DOWNSTREAM FROM THIS RIDGE...A TUTT LOW OVER THE  
TROPICAL ATLANTIC EXTENDS A SHORT WAVE TROUGH WEST WHILE REMAINING  
NORTH OF THE GUIANAS TO JUST EAST OF THE LESSER ANTILLES. UNDER  
INFLUENCE OF THE MID LEVEL RIDGE TO THE NORTH...THE TROUGH IS TO  
AMPLIFY ACROSS THE WINDWARD/FRENCH ISLES EARLY ON WEDNESDAY  
MORNING. THIS IS TO THEN SHEAR A SHORT WAVE VORTEX THAT SLOWLY  
MIGRATES JUST SOUTH OF PUERTO RICO ON THURSDAY. AS THE MID LEVEL  
PERTURBATION PRESSES AGAINST THE RIDGE TO THE NORTH...THE TRADE  
WINDS CAP WILL WEAKEN ENOUGH TO ALLOW A PLUME OF DEEPER MOISTURE  
TO ADVECT ACROSS THE FORECAST AREA. AT LOW LEVELS...A HIGH ROLLS  
ACROSS THE MID ATLANTIC REGION IN THE USA LATER THIS EVENING...TO  
BUILD OVER THE WESTERN ATLANTIC ON WEDNESDAY-THURSDAY. THIS IS TO  
FAVOR BRISK EASTERLY WINDS ACROSS THE EASTERN CARIBBEAN...WITH  
925-950 HPA WINDS TO PEAK AT 25-30KT ON WEDNESDAY-THURSDAY. THE  
STRONGER WINDS WILL ENHANCE SHALLOW MOISTURE TRANSPORT ACROSS THE  
FORECAST AREA...AND WILL LIKELY FAVOR GENERATION OF STREAMERS  
ACROSS THE LEEWARD/VIRGIN ISLES THAT ARE TO AFFECT EASTERN PUERTO  
RICO FROM TIME-TO-TIME.  
 
AS THE PATTERN EVOLVES DURING THE SHORT RANGE PERIOD...GLOBAL  
MODEL GUIDANCE CONTINUE TO FORESEE AN INCREASE IN CONVECTION  
ACROSS THE VIRGIN ISLES-EASTERN PUERTO RICO ON WEDNESDAY AND  
THURSDAY. THE UKMET GENERALLY FAVORS MORE WIDESPREAD CONVECTION  
THAN WHAT THE ECMWF SUGGESTS...WITH THE LATTER FAVORING MOST  
ACTIVE ACROSS EASTERN PUERTO RICO/SAN JUAN METRO AREA. THE GFS  
SEEMS TO ALSO FAVOR A SIMILAR SOLUTION TO WHAT THE ECMWF SUGGESTS.  
CONSIDERING THE INTENSITY OF THE LOW LEVEL WINDS AND LACK OF LOW  
LEVEL FORCING THE ECMWF-GFS SOLUTION LOOKS MORE PROBABLE. OVER  
WESTERN INTERIOR PORTIONS OF PUERTO RICO THE MOST ACTIVE IS  
EXPECTED ON THURSDAY...WHEN THE GFS AND ECMWF GDI FORECAST SHOWS  
POTENTIAL FOR DEEPER CONVECTION. ON FRIDAY...A LULL IN ACTIVITY IS  
EXPECTED AS THE SHORT WAVE TROUGH TO THE SOUTH MOVES AWAY AND MID  
LEVEL RIDGE BRANCHES INTO THE NORTHEAST CARIBBEAN. ALTHOUGH A  
SECONDARY PLUME OF MOISTURE ENTERS THE FORECAST AREA ON  
SATURDAY...IT WILL NOT BE AS ACTIVE AS THE FORMER.  
 
DAVISON...WPC (USA)  
 

 
 
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