909  
FXCA20 KWBC 141842  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
141 PM EST THU DEC 14 2017  
 
TROPICAL DISCUSSION FROM DEC 14/12 UTC: FAIR CONDITIONS ARE  
ESTABLISHING ACROSS MOST OF THE CARIBBEAN/CENTRAL AMERICAN BASIN.  
A ROBUST UPPER RIDGE CENTERS OVER MOST OF THE CARIBBEAN...AND HAS  
ALSO A REFLECTION INTO THE MID-LEVELS. AS RIDGE PATTERN  
STRENGTHENS THROUGH THE FORECAST CYCLE...EXPECTING A STRENGTHENING  
OF THE TRADE WIND CAP ACROSS THE CARIBBEAN...WHICH WILL RESULT IN  
A GENERAL DECREASING TREND IN ACCUMULATIONS.  
 
IN MEXICO...A LARGE POLAR MID-UPPER TROUGH IS DIGGING FROM THE  
NORTH TO EXTEND ACROSS BAJA CALIFORNIA AND SONORA BY THURSDAY  
EVENING...ACROSS WEST TEXAS-CHIHUAHUA-SOUTHERN SONORA-BAJA  
CALIFORNIA BY FRIDAY EVENING...TO THEN START LIFTING TO THE  
NORTHEAST AND EXTEND ACROSS WEST TEXAS-COAHUILA-EASTERN DURANGO BY  
SATURDAY EVENING. THE UPPER TROUGH IS INTERACTING WITH A  
SUBTROPICAL MOISTURE PLUME/ATMOSPHERIC RIVER THAT ORIGINATES IN  
THE TROPICAL PACIFIC. THIS WILL LEAD TO UNUSUALLY HEAVY  
PRECIPITATION IN PARTS OF NORTHERN MEXICO...ESPECIALLY DURING  
FRIDAY-EARLY SATURDAY...WHEN ENHANCEMENT WILL BE PROVIDED BY THE  
DIVERGENT ENTRANCE OF AN UPPER JET. THROUGH EARLY  
FRIDAY...EXPECTING LARGEST RAINFALL ACCUMULATIONS IN  
SINALOA/NAYARIT WITH AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM.  
INLAND INTO ZACATECAS/SAN LUIS POTOSI EXPECTING 05-10MM/DAY AND  
MAXIMA OF 15-20MM. IN CHIHUAHUA/COAHUILA EXPECTING 00-05MM/DAY AND  
MAXIMA OF 10MM. BY FRIDAY SATURDAY...RAINFALL IS TO PEAK TO  
PRODUCE ACCUMULATIONS OF 15-20MM/DAY AND MAXIMA OF 25-50MM FROM  
SINALOA/NAYARIT NORTH INTO COAHUILA AND SAN LUIS POTOSI. BY  
SATURDAY-SUNDAY EXPECTING A DECREASE IN ACCUMULATIONS...TO  
10-15MM/DAY AND MAXIMA OF 20-35MM ACROSS NAYARIT/JALISCO...AND  
05-10MM/DAY AND MAXIMA OF 15-20MM IN COAHUILA/SAN LUIS POTOSI.  
 
IN THE MEANTIME...A SURFACE FRONT WILL MAKE IT INTO THE  
NORTHWESTERN GULF OF MEXICO ON THURSDAY. BY THURSDAY EVENING IT  
WILL EXTEND ACROSS THE RIO BRAVO...WHILE ON FRIDAY EVENING IT WILL  
EXTEND INTO SOUTHERN VERACRUZ...TO THEN RETREAT TO THE NORTH. THIS  
WILL LEAD TO RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM ON  
FRIDAY-SATURDAY.  
 
SURFACE FRONT EXTENDING ACROSS THE GREATER ANTILLES IS STARTING TO  
RETREAT AS A WARM FRONT TO THE NORTHWEST...WHILE IT BECOMES  
ILL-DEFINED. BY THURSDAY EVENING IT WILL EXTEND ACROSS THE TURKS  
AND CAICOS/SOUTHEASTERN BAHAMAS INTO THE CAYMAN ISLANDS...AND BY  
FRIDAY EVENING...THE ILL-DEFINED BOUNDARY WILL EXTEND ACROSS THE  
CENTRAL BAHAMAS AND CENTRAL CUBA. AS THE FRONT WEAKENS...AND UNDER  
THE INFLUENCE OF THE BUILDING MID-LEVEL RIDGE AND ASSOCIATED  
SUBSIDENCE CAP...EXPECTING A RAPID DECREASE IN RAINFALL  
ACCUMULATIONS. THROUGH EARLY FRIDAY...EXPECTING 05-10MM/DAY AND  
MAXIMA OF 15MM IN NORTHERN HISPANIOLA/SOUTHEASTERN CUBA AND THE  
SOUTHEASTERN BAHAMAS. LIGHTER AMOUNTS ARE EXPECTED IN JAMAICA AND  
THE CAYMAN ISLANDS. ACTIVITY WILL BECOME MORE ISOLATED FROM FRIDAY  
AND ON.  
 
IN CENTRAL AMERICA...AS THE FRONT WEAKENS TO THE EAST...EASTERLY  
TRADE WINDS ARE TO RETURN DURING THURSDAY. THIS WILL BRING BACK  
THE MOISTURE LINGERING OVER OPEN WATERS OF THE SOUTHERN CARIBBEAN.  
AS MOISTURE RETURNS...EXPECTING RAINFALL ACCUMULATIONS OF  
05-10MM/DAY AND MAXIMA OF 15MM ACROSS COSTA  
RICA/NICARAGUA/NORTHERN HONDURAS ON THURSDAY-FRIDAY. DURING  
FRIDAY-SATURDAY...EXPECTING 05-10MM/DAY AND MAXIMA OF 15-20MM  
SPREADING INTO BELIZE/SOUTHERN GUATEMALA AND THE EASTERN YUCATAN  
PENINSULA. SIMILAR AMOUNTS ARE EXPECTED IN EASTERN  
HONDURAS/EASTERN NICARAGUA AND COSTA RIGA DURING THIS PERIOD IN  
ASSOCIATION WITH AN ARRIVING EASTERLY WAVE (SEE BELOW)  
 
QUIET PATTERN IS ESTABLISHING IN NORTHERN SOUTH AMERICA. ACTIVITY  
IS ORGANIZED WITH AN EASTERLY WAVE THAT IS PROPAGATING FROM THE  
VENEZUELA COAST ON LATE THURSDAY TO WESTERN CENTRAL AMERICA BY  
LATE SATURDAY. THIS WILL LEAD TO A TRANSIENT ENHANCEMENT OF  
SHALLOW CONVECTION INITIALLY...AND WILL ALLOW FOR THE DEVELOPMENT  
OF A FEW THUNDERSTORMS ONCE IT ARRIVES IN CENTRAL AMERICA ON  
FRIDAY. ELSEWHERE IN SOUTH AMERICA...DIURNAL CONVECTION IN WESTERN  
COLOMBIA WILL LEAD TO MAXIMA OF 15MM/DAY...WHILE IN THE  
GUIANAS...ACTIVE CONVECTION WILL CLUSTER MOSTLY IN FRENCH GUIANA  
UNDER THE INFLUENCE OF ITCZ CONVERGENCE.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
72W 76W 80W 84W 88W 93W 97W 101W EW 15N  
 
AN EASTERLY WAVE IS INITIALIZED AT 72W. THIS WAVE WILL ENHANCE  
SHALLOW CONVECTION IN THE ABC AND NORTHWESTERN VENEZUELA ON  
THURSDAY. ON FRIDAY-SATURDAY IT WILL STIMULATE CONVECTION IN THE  
FAR SOUTHWESTERN CARIBBEAN AND ALONG THE COASTS OF NICARAGUA AND  
HONDURAS...WHERE IT WILL LEAD TO ACCUMULATIONS OF 05-10MM/DAY AND  
ISOLATED MAXIMA OF 15-25MM. BY SATURDAY-SUNDAY THE WAVE WILL  
STIMULATE CONVECTION LONG NORTHERN HONDURAS AND SOUTHERN  
BELIZE/SOUTHERN GUATEMALA...WHERE EXPECTING SIMILAR RAINFALL  
AMOUNTS. IN THE NORTHERN YUCATAN PENINSULA EXPECTING 05-10MM/DAY  
AND MAXIMA OF 15-20MM.  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
GALVEZ/DAVISON...WPC (USA)  
 

 
 
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