659  
FXCA20 KWBC 191923  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
222 PM EST FRI JAN 19 2018  
 
TROPICAL DISCUSSION FROM JAN 19/12 UTC: THE UPPER LEVEL PATTERN  
SHOWS THE SUBEQUATORIAL RIDGE PERSISTING OVER THE EASTERN AND  
CENTRAL CARIBBEAN...WITH PROGRESSIVE TROUGHS PROPAGATING TO THE  
NORTH OF THE RIDGE. A TROUGH THAT HAS EXITED THE EASTERN COAST OF  
THE UNITED STATES HAS A SURFACE FRONT ASSOCIATED. BY FRIDAY  
EVENING...THE FRONT WILL EXTEND ACROSS THE SOUTHEASTERN  
BAHAMAS-SOUTHEASTERN CUBA INTO THE CAYMAN ISLANDS...AND EXTENDING  
AN ILL DEFINED BOUNDARY INTO NORTHEASTERN HONDURAS. A SHEAR LINE  
IS ALSO PRESENT AND BY FRIDAY EVENING IT IS FORECAST TO EXTEND  
ACROSS EASTERN HISPANIOLA...JUST TO THE SOUTH OF JAMAICA...INTO  
SOUTHEASTERN NICARAGUA. BY SATURDAY EVENING THE FRONT WILL EXTEND  
ACROSS THE SOUTHEASTERN BAHAMAS...THE TURKS AND CAICOS...INTO  
CENTRAL/CENTRAL-NORTHERN CUBA...WHERE IT WILL MEANDER INTO EARLY  
MONDAY. BY SUNDAY/MONDAY THE FRONT WILL EXTEND ZONALLY ALONG  
22-23N INTO THE CENTRAL BAHAMAS. THE SHEAR LINE WILL START LOSING  
DEFINITION EARLY ON SATURDAY...AND BY SATURDAY EVENING IT WILL  
EXTEND FROM THE NORTH ATLANTIC INTO THE LEEWARD ISLANDS.  
 
REGARDING RAINFALL ACCUMULATIONS...BY FRIDAY-SATURDAY...LARGEST  
ACCUMULATIONS ARE EXPECTED WITH THE SHEAR LINE IN SOUTHEASTERN  
NICARAGUA...WHERE TOTALS WILL REACH 30-70MM/DAY AND MAXIMA OF  
75-150MM. IN SAN ANDRES/NUEVA PROVIDENCIA AND NORTHEASTERN  
NICARAGUA EXPECTING 10-15MM/DAY AND MAXIMA OF 20-45MM. IN THE  
NORTHEASTERN DOMINICAN REPUBLIC AND NORTHEASTERN JAMAICA EXPECTING  
10-15MM/DAY AND MAXIMA OF 20-35MM. IN THE TURKS AND  
CAICOS...SOUTHEASTERN BAHAMAS AND SOUTHEASTERN CUBA EXPECTING  
05-10MM/DAY AND MAXIMA OF 15-25MM. IN THE CAYMAN  
ISLANDS...NORTHWESTERN HONDURAS AND SOUTHERN BELIZE/EASTERN  
GUATEMALA EXPECTING RAINFALL TOTALS OF 05-10MM/DAY AND MAXIMA OF  
15MM. BY SATURDAY/SUNDAY EXPECTING AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15-20MM IN EASTERN CUBA...WHERE EASTERLY TRADES IN THE  
WARM SIDE OF THE FRONT INTERACT WITH OROGRAPHY...AND MAXIMA OF  
15MM IN THE SOUTHEASTERN BAHAMAS/TURKS AND CAICOS. BY  
SUNDAY/MONDAY...AS AN UPPER TROUGH APPROACHES FROM THE  
WEST...FRONTAL CONVECTION WILL BECOME ENHANCED IN THE BAHAMAS.  
MODELS ARE IN BETTER AGREEMENT ON THIS EVOLUTION TODAY...AND WE  
FORECAST 15-20MM/DAY WITH MAXIMA OF 25-50MM IN STRONGEST  
THUNDERSTORMS. TO THE WEST...THE BASE OF THE UPPER TROUGH WILL  
INTERACT WITH THE REMNANT MOISTURE OF THE FRONT IN THE YUCATAN  
CHANNEL. MODELS ARE STRUGGLING ON REPRESENTING THIS MESOSCALE  
INTERACTION...YET MOST OF THEM SUGGEST LARGEST ACCUMULATIONS  
OFFSHORE. THE FORECAST CALLS FOR 10-15MM/DAY AND MAXIMA OF 20-35MM  
STRETCHING FROM NORTHERN QUINTANA ROO TO EXTREME WESTERN  
CUBA...INCLUDING THE ISLAND OF YOUTH.  
 
UNSEASONABLY ACTIVE PATTERN OF CONVECTION EXTENDS FROM  
NORTHWESTERN SOUTH AMERICA INTO COSTA RICA...PANAMA...AND  
NICARAGUA. THE PRECIPITABLE WATER ANALYSIS SUGGESTS VALUES  
EXCEEDING 60MM TO THE NORTH OF PANAMA INTO COSTA RICA/NICARAGUA.  
THIS IS INTERACTING WITH AN UPPER TROUGH THAT LIES BETWEEN THE  
PERIPHERY OF THE SUBEQUATORIAL JET...AND A WESTERLY UPPER JET OVER  
THE EQUATORIAL PACIFIC TO ITS SOUTH. THE POSITIVE INTERACTION WILL  
PEAK ON FRIDAY...AND GRADUALLY DECREASE THROUGH EARLY NEXT WEEK.  
ENHANCED TRADE WIND CONVERGENCE AND THE CARIBBEAN LOW-LEVEL JET  
ARE ALSO PLAYING A ROLE. ON FRIDAY/SATURDAY EXPECTING 15-20MM/DAY  
AND MAXIMA OF 30-60MM EXTENDING FROM NORTHEASTERN PANAMA INTO  
EASTERN COSTA RICA. BY SATURDAY/SUNDAY...SIMILAR AMOUNTS ARE  
EXPECTED FROM WESTERN PANAMA INTO SOUTHEASTERN NICARAGUA. BY  
SUNDAY/MONDAY AMOUNTS DECREASE TO 10-15MM/DAY AND MAXIMA OF  
20-40MM.  
 
IN THE NORTHEASTERN CARIBBEAN...THE PERSISTING MID-LEVEL RIDGE  
PATTERN WILL CONTINUE LEADING TO MOSTLY FAIR CONDITIONS AND  
ISOLATED TRADE WIND SHOWERS. MODELS CONTINUE SHOWING AN INCREASE  
IN THE SPEED OF THE TRADES...AND THE DEVELOPMENT OF A MILD  
NORTHEASTERLY COMPONENT ON SATURDAY THROUGH MONDAY. THIS SHALLOW  
COLD-ADVECTIVE PATTERN WILL ENHANCE THE FREQUENCY AND VERTICAL  
DEVELOPMENT OF LATE NIGHT/EARLY MORNING TRADE WIND SHOWERS ACROSS  
THE EASTERN CARIBBEAN ISLES...WHICH WILL SUSTAIN AN INCREASE IN  
DAILY ACCUMULATIONS TO 05-10MM/DAY AND MAXIMA OF 15MM. THIS IS  
PARTICULARLY TRUE IN EASTERN PORTIONS OF CARIBBEAN ISLANDS FROM  
SATURDAY THROUGH SUNDAY...INCLUDING THE LESSER ANTILLES.  
 
IN NORTHERN SOUTH AMERICA...A DRYING TREND IS UNDERWAY. A DRY AIR  
MASS IN THE MID-LEVELS IS APPROACHING FROM THE TROPICAL ATLANTIC.  
AS THE MID-LEVELS DRY OUT...A TRANSITION TOWARDS A MORE  
CLIMATOLOGICAL CONVECTION PATTERN IS EXPECTED. THIS WILL RESULT IN  
GENERALLY FAIR CONDITIONS...AND A FEW SHOWERS IN ASSOCIATION WITH  
TRADE WIND CONVERGENCE IN EASTERN VENEZUELA/GUYANA...AND A FEW  
SHOWERS AND THUNDERSTORMS CONSTRAINED TO WESTERN COLOMBIA. IN MOST  
OF COLOMBIA EXPECTING A DECREASE FROM 05-10MM/DAY AND MAXIMA OF  
15-20MM ON FRIDAY/SATURDAY...TO MAXIMA OF 15MM AFTER. AN EXCEPTION  
IS SOUTHWESTERN COLOMBIA...WHERE INTERACTION BETWEEN THE  
ITCZ...COAST...AND THE UPPER JET IN THE TROPICAL PACIFIC SHOULD  
FAVOR FOR A LOCALIZED INCREASE TO 10-15MM/DAY AND MAXIMA OF  
20-35MM. AMAZON CONVECTION IS DECREASING IN INTENSITY AS THE  
SUBTROPICAL HIGH IN SOUTH AMERICA WEAKENS SLIGHTLY. THIS WILL LEAD  
TO A GRADUAL DECREASE IN ACCUMULATIONS FROM 15-20MM/DAY AND MAXIMA  
OF 25-50MM ON FRIDAY...TO 10-15MM/DAY AND MAXIMA OF 20-35MM ON  
SUNDAY.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
58W 61W 64W 68W 72W 76W 80W DISSIPATES TUTT INDCD 16N  
65W 68W 72W 75W 79W 81W DISSIPATES TUTT INDCD 18N  
 
A NEW TUTT-INDUCED WAVE IS INITIALIZED AT 58W. THIS WAVE WILL  
AMPLIFY AS IT ENTERS THE BASIN...BUT ITS EFFECTS IN PRECIPITATION  
WILL BE LIMITED AS IT ASSOCIATES WITH A WEAK TRADE WIND SURGE AND  
TRAILING DRY AIR MASS AT THE MID-LEVELS.  
 
A TUTT-INDUCED WAVE IS INITIALIZED AT 65W. THIS WAVE HAS A WEAK  
SIGNATURE IN 700 HPA...AND WILL PRODUCE LIMITED EFFECTS ON  
PRECIPITATION AS IT PROPAGATES TO THE WEST ACROSS THE GREATER  
ANTILLES.  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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