601  
FXCA20 KWBC 171944  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
244 PM EST WED JAN 17 2018  
 
TROPICAL DISCUSSION FROM JAN 17/12 UTC: AT UPPER LEVELS...THE  
SUBEQUATORIAL RIDGE EXTENDS FROM NORTHERN SOUTH AMERICA INTO THE  
CENTRAL AND EASTERN CARIBBEAN. THE NORTHERN FRINGES OF THIS RIDGE  
EXTEND INTO JAMAICA...SOUTHEASTERN CUBA...THE TURKS AND CAICOS AND  
THE SOUTHEASTERN BAHAMAS. AT MID-LEVELS...A RIDGE CENTERS ON A  
HIGH JUST TO THE NORTH OF THE MONA PASSAGE/PUERTO RICO...AND  
EXTENDS AN AXIS TO THE WEST SOUTHWEST INTO JAMAICA-EASTERN GULF OF  
HONDURAS. THESE MID AND UPPER RIDGES ARE LIMITING THE INCURSION OF  
POLAR TROUGHS INTO THE CARIBBEAN BASIN. AS GLOBAL MODELS AGREE ON  
THE RIDGES GENERALLY HOLDING THROUGH THE CYCLE...RAIN-PRODUCING  
PERTURBATIONS ARE TO LIMIT TO AREAS TO THE WEST AND NORTH OF THE  
UPPER RIDGES...AND ALONG ITS PERIPHERY. THIS INCLUDES EASTERN  
CENTRAL AMERICA...THE GULF OF HONDURAS...JAMAICA...CAYMAN  
ISLANDS...CUBA AND THE BAHAMAS.  
 
TO THE NORTH OF THE RIDGE...IN THE WESTERLIES...A STRONG UPPER  
TROUGH IS CROSSING THE MISSISSIPPI VALLEY INTO THE EASTERN UNITED  
STATES. THIS TROUGH IS SUSTAINING A PROGRESSIVE SURFACE COLD FRONT  
THAT IS PROPAGATING ACROSS THE GULF OF MEXICO. BY WEDNESDAY  
EVENING...THE POLAR FRONT IS FORECAST TO EXTEND ACROSS SOUTHERN  
FLORIDA...THE SOUTHEASTERN GULF...INTO THE EXTREME NORTHERN  
YUCATAN PENINSULA. SIMULTANEOUSLY...AN ILL DEFINED OLD FRONT WILL  
EXTEND TO ITS SOUTH ACROSS THE CENTRAL BAHAMAS......CENTRAL  
CUBA...AND INTO CAYMAN ISLANDS...WHERE THE BOUNDARY WILL BE  
ILL-DEFINED. THE LATTER WILL ALSO SUSTAIN A SHEAR LINE THAT...BY  
WEDNESDAY EVENING IS FORECAST TO EXTEND ACROSS SOUTHEASTERN  
CUBA...WESTERN JAMAICA...SAN ANDRES/NUEVA PROVIDENCIA...COSTA  
RICA. THE FRONTS ARE TO MERGE DURING THURSDAY...AND BY THURSDAY  
EVENING THE BOUNDARY WILL EXTEND ACROSS THE SOUTHEASTERN  
BAHAMAS/TURKS AND CAICOS...SOUTHEASTERN CUBA...CAYMAN ISLANDS AND  
NORTHERN HONDURAS/SOUTHERN BELIZE. ALSO BY THURSDAY EVENING...THE  
SHEAR LINE WILL EXTEND ACROSS NORTHERN HAITI...INTO SOUTHERN  
NICARAGUA. BY FRIDAY EVENING THE FRONT WILL EXTEND ACROSS THE  
SOUTHEASTERN BAHAMAS...CENTRAL CUBA...INTO THE GULF OF HONDURAS.  
THE SHEAR LINE WILL START LOSING DEFINITION TO EXTEND ACROSS  
EASTERN HISPANIOLA...INTO THE HAITIAN PENINSULA...JUST TO THE  
SOUTH OF JAMAICA. BY SATURDAY...THE FRONT WILL RETROGRESS  
NORTHWARD TO EXTEND ACROSS THE CENTRAL BAHAMAS AND CUBA WHILE  
LOSING DEFINITION.  
 
IN TERMS OF ACCUMULATIONS...LARGEST AMOUNTS ARE EXPECTED IN THE  
GULF OF HONDURAS REGION/COSTA RICA AND PANAMA...WHERE MOISTURE  
CONVERGENCE WILL PEAK AS THE FRONT AND SHEAR LINE INTERACT WITH  
OROGRAPHY. FURTHERMORE...UPPER VENTILATION IN THE RIGHT DIVERGENT  
ENTRANCE OF AN UPPER JET TO THE NORTH WILL BE FAVORABLE FOR THE  
CONTINUED DEVELOPMENT OF HEAVY-RAIN PRODUCING THUNDERSTORMS DURING  
WEDNESDAY-THURSDAY IN AREAS OF THE GULF OF HONDURAS. IN TERMS OF  
RAINFALL AMOUNTS...THROUGH EARLY THURSDAY...EXPECTING 25-50MM/DAY  
AND MAXIMA OF 75-150MM IN NORTHERN HONDURAS. IN NORTHERN COSTA  
RICA/SOUTHEASTERN NICARAGUA EXPECTING 15-30MM/DAY AND MAXIMA OF  
40-80MM. IN EASTERN COSTA RICA/WESTERN PANAMA EXPECTING  
15-20MM/DAY AND MAXIMA OF 25-50MM WITH THE SHEAR LINE. IN THE  
NORTHERN BAHAMAS EXPECTING 10-15MM/DAY AND MAXIMA OF 20-35MM WHERE  
THUNDERSTORMS DEVELOP. IN CENTRAL CUBA...CAYMAN ISLANDS... AND  
SOUTHERN BELIZE EXPECTING 05-10MM/DAY AND ISOLATED MAXIMA OF  
15-25MM. IN JAMAICA...EXPECTING MAXIMA OF 15MM. BY THURSDAY-EARLY  
FRIDAY EXPECTING LARGEST AMOUNTS IN NORTHERN HONDURAS AND EXTREME  
SOUTHERN BELIZE/EASTERN GUATEMALA WHERE ENHANCED MOISTURE  
CONVERGENCE WILL LEAD TO 25-50MM/DAY AND MAXIMA OF 75-150MM.  
ENHANCED MOISTURE CONVERGENCE IN WESTERN PANAMA/EASTERN COSTA RICA  
WILL LEAD TO 15-20MM/DAY AND MAXIMA OF 40-80MM. FRONTAL AND  
SHEAR-LINE CONVECTION IN SOUTHEASTERN CUBA/NORTHEASTERN HISPANIOLA  
AND THE TURKS AND CAICOS AND NORTHERN JAMAICA WILL LEAD TO  
05-10MM/DAY AND MAXIMA OF 15-25MM...UNDER INTERACTION WITH  
OROGRAPHY. BY FRIDAY-SATURDAY...EXPECTING LARGEST ACCUMULATIONS ON  
EASTERN HISPANIOLA...WHERE SHEAR-LINE CONVECTION WILL LEAD TO  
15-20MM/DAY AND MAXIMA OF 25-50MM. IN CENTRAL AMERICA...SHEAR LINE  
CONVECTION WILL LEAD TO 10-15MM/DAY AND MAXIMA OF 20-45MM. ALSO IN  
CENTRAL AMERICA...AS MOISTURE CONVERGENCE PEAKS TO THE SOUTH OF  
THE CARIBBEAN LOW-LEVEL JET...EXPECTING LOCALLY HEAVY RAINFALL IN  
EASTERN COSTA RICA/WESTERN PANAMA WITH ACCUMULATIONS OF  
30-60MM/DAY AND MAXIMA OF 100-150MM. IN NORTHERN COSTA  
RICA/SOUTHEASTERN NICARAGUA EXPECTING 15-20MM/DAY AND MAXIMA OF  
30-60MM.  
 
IN THE NORTHEASTERN CARIBBEAN...MID-LEVEL RIDGE PATTERN IS TO  
PERSIST. A SUBSIDENCE CAP IS WELL DEFINED IN THE  
MID-TROPOSPHERE...YET IT IS SUFFICIENTLY ELEVATED TO ALLOW SOME  
VERTICAL DEVELOPMENT AND MODERATE AFTERNOON SHOWERS IN WESTERN  
PUERTO RICO AND HISPANIOLA. THIS WILL LEAD TO 15-20MM/DAY AND  
MAXIMA OF 25-50MM ON WEDNESDAY AND FRIDAY...AND LESSER AMOUNTS ON  
THURSDAY. ELSEWHERE ACCUMULATIONS WILL BE GENERALLY UNDER 10MM.  
 
IN NORTHERN SOUTH AMERICA...LARGEST ACCUMULATIONS ARE TO CLUSTER  
IN THE AMAZON BASIN INCLUDING SOUTHEASTERN COLOMBIA. EXPECTING  
15-20MM/DAY AND MAXIMA OF 25-50MM ON A DAILY BASIS. ISOLATED  
LARGER AMOUNTS ARE EXPECTED IN STRONGEST THUNDERSTORMS.  
ELSEWHERE...MODERATE RAINFALL AMOUNTS ARE EXPECTED WHERE THE  
ATLANTIC ITCZ CONVERGES WITH THE COAST. THIS WILL LEAD TO TOTALS  
OF 10-15MM/DAY AND MAXIMA OF 20-35MM IN THE GUIANAS ON  
WEDNESDAY...DECREASING IN COVERAGE AND INTENSITY AS THE CYCLE  
PROGRESSES...TO PRODUCE 05-10MM/DAY AND MAXIMA OF 15-20MM BY  
FRIDAY. IN COLOMBIA...DIURNAL CONVECTION WILL LEAD TO 05-10MM/DAY  
AND ISOLATED MAXIMA OF 15-20MM...WHILE IN SOUTHWESTERN  
COLOMBIA/CAUCA VALLEY AND NORTHWESTERN ECUADOR EXPECTING  
10-15MM/DAY AND MAXIMA OF 20-35MM THROUGH THURSDAY MORNING.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
NONE  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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