242  
FXCA20 KWBC 271944  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
243 PM EST WED DEC 27 2017  
 
TROPICAL DISCUSSION FROM DEC 27/12 UTC: AT 250 HPA...A LOW  
AMPLITUDE RIDGE EXTENDS FROM NORTHERN SOUTH AMERICA INTO THE  
CARIBBEAN. A SUBTROPICAL JET MAXIMA EXTENDS ALONG THE NORTHERN  
FRINGES OF THIS RIDGE...WITH AXIS ACROSS THE GREATER  
ANTILLES/NORTHERN CARIBBEAN...WITH PATTERN FORECAST TO GENERALLY  
HOLD DURING THE NEXT FEW DAYS. A WANING TUTT TO THE WEST EXTENDS  
NORTH-TO-SOUTH ACROSS THE SOUTHERN STATES OF MEXICO TO THE EASTERN  
PACIFIC. AT 500 HPA IT REFLECTS AS AN INVERTED TROUGH OFF THE  
SOUTH COAST OF MEXICO. THE SHORT WAVE TROUGH IS TO SLOWLY LIFT  
OVER THE RIDGE TO THE EAST...PULLING ACROSS GUATEMALA-THE YUCATAN  
LATER ON THURSDAY. THE SHORT WAVE TROUGH...AS IT MEANDER OVER  
NORTHERN CENTRAL AMERICA...IS TO VENT CONVECTIVE DEVELOPMENT. AT  
LOW LEVELS...BRISK NORTHEASTERLY TRADES ARE TO CONVERGE ALONG A  
SHEAR LINE OVER THE WESTERN CARIBBEAN. THIS WILL ENHANCE LOW LEVEL  
MOISTURE CONVERGENCE ACROSS THE GULF OF HONDURAS-NORTHEAST  
GUATEMALA AND BELIZE. EARLY IN THE CYCLE EXPECTING RAINFALL  
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM. ON THURSDAY THIS  
INCREASES TO 15-20MM/DAY AND MAXIMA OF 35-70MM. AS THE TROUGH  
PULLS AWAY ON FRIDAY...THIS WILL THEN DECREASE TO 05-10MM/DAY AND  
MAXIMA OF 15-20MM. THE TROUGH IS TO ALSO ENHANCE CONVECTION ACROSS  
NORTHERN CHIAPAS AND SOUTHERN VERACRUZ. EARLY IN THE PERIOD  
EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM. ON  
THURSDAY THE MAXIMA INCREASES TO 15-20MM.  
 
AT 500 HPA...THE NORTHERN CARIBBEAN/GREATER ANTILLES REMAIN UNDER  
THE INFLUENCE OF A MID LEVEL RIDGE THAT EXTENDS WEST-TO-EAST FROM  
THE GULF OF MEXICO TO THE WESTERN ATLANTIC. EARLY IN THE CYCLE  
THIS IS TO CENTER ON TWO CLOSED HIGHS...WITH ONE OVER WESTERN CUBA  
AND THE OTHER TO THE NORTH OF PUERTO RICO. THROUGH THURSDAY THESE  
ARE TO COMBINE INTO A SINGLE HIGH TO THE NORTH OF THE DOMINICAN  
REPUBLIC. MEANWHILE... THIS IS TO FAVOR AN ELEVATED  
INVERSION...WITH THE GOES 16 AIR MASS PRODUCT SHOWING A VERY DRY  
AIR MASS OVER THE NORTHEAST CARIBBEAN. A POLAR TROUGH LIES TO THE  
NORTH OF THIS RIDGE...DOMINATING THE FLOW ACROSS THE EASTERN  
USA-WESTERN ATLANTIC WHILE BOTTOMING OUT AROUND 30N. UNDER  
PRESSURE FROM POLAR TROUGH TO THE NORTH...MID LEVEL RIDGE PATTERN  
IS TO GRADUALLY WEAKEN FROM THE WEST...AND IT IS TO NEARLY  
COLLAPSE BY THE END OF THE WEEK. THE UPPER LEVEL  
INVERSION...HOWEVER...IS TO GENERALLY HOLD ACROSS THE NORTHEAST  
CARIBBEAN ISLES THROUGH THE WEEKEND/EARLY NEXT WEEK.  
 
AT LOW LEVELS THE UPPER LEVEL TROUGH SUSTAINS AN ELONGATED FRONT  
ACROSS THE WESTERN NORTH ATLANTIC TO CENTRAL FLORIDA-GULF OF  
MEXICO TO THE RIO BRAVO/NORTHEAST MEXICO. FRONTAL BOUNDARY IS TO  
REMAIN NEARLY STATIONARY DURING THE NEXT COUPLE OF DAYS...THEN  
MEANDER SOUTH INTO THE NORTHWEST BAHAMAS ON FRIDAY AS A FRONTAL  
LOW FORMS OFF THE SOUTHEAST COAST OF THE USA. THE FRONT IS TO ALSO  
FAVOR GENERATION OF A PREFRONTAL SHEAR LINE ACROSS THE CENTRAL  
BAHAMAS-CENTRAL CUBA TO NORTHWEST HONDURAS EARLY IN THE CYCLE.  
ACROSS THE BAHAMAS-CUBA THE SHEAR LINE IS TO FAVOR RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM...WHILE OVER THE  
CAYMAN ISLANDS EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND  
MAXIMA OF 10MM. ON THURSDAY...SHEAR LINE CONVERGENCE OVER THE  
TURKS-EASTERN CUBA WILL SUSTAIN RAINFALL AMOUNTS 10-15MM/DAY AND  
MAXIMA OF 20-30MM...WHILE OVER JAMAICA EXPECTING RAINFALL AMOUNTS  
OF 00-05MM/DAY AND MAXIMA OF 10MM. AS THE TRAILING END OF THE  
FRONT MEANDERS OVER NORTHEAST MEXICO IT IS TO FAVOR LIGHT RAINFALL  
AMOUNTS OF 00-05MM/DAY...WHILE ACROSS NORTHERN VERACRUZ EXPECTING  
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-25MM.  
 
FARTHER EAST...A TUTT LOW OVER THE TROPICAL ATLANTIC EXTENDS A  
TROUGH TO THE WEST-SOUTHWEST ACROSS THE FRENCH ISLES TO THE  
SOUTHEAST CARIBBEAN. UNDER INFLUENCE OF MID LEVEL RIDGE TO THE  
NORTH THE TROUGH IS TO SPREAD WEST INTO THE CENTRAL CARIBBEAN  
LATER TODAY. BUT AS THE RIDGE TO THE WEST WEAKENS...THE TUTT IS TO  
RAPIDLY PULL TO THE EAST-NORTHEAST LATER IN THE WEEK. REMAINING  
SEGMENT OVER THE CARIBBEAN IS TO THEN EVOLVE INTO A NARROW SHEAR  
AXIS ACROSS THE CENTRAL-EASTERN CARIBBEAN ON THURSDAY-FRIDAY.  
MEANWHILE...THE MID/UPPER LEVEL TROUGH IS TO FAVOR GENERATION OF  
SHORT WAVE PERTURBATIONS IN THE LOW/MID LEVEL EASTERLY TRADES THAT  
ARE TO STREAM ACROSS THE NORTHEAST-CENTRAL CARIBBEAN DURING THE  
NEXT FEW DAYS (SEE BELOW FOR DETAILS). AT LOW LEVEL BRISK EASTERLY  
TRADES ARE TO DOMINATE THE BASIN...WITH WINDS OF 15-20KT OVER THE  
NORTHERN CARIBBEAN WHILE TO THE SOUTH EXPECTED TO PEAK AT 20-30KT.  
AS LOW/MID LEVEL RIDGE WEAKENS LATER IN THE WEEK...WINDS ARE TO  
DROP TO 10-15KT ACROSS MOST OF THE CARIBBEAN BASIN. AT 700 HPA AN  
ILL ORGANIZED TROUGH IS TO THEN FORM OVER THE FRENCH/SOUTHERN  
LEEWARD ISLES LATER ON FRIDAY. OVER THE FRENCH ISLANDS EXPECTING  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM THROUGH  
THURSDAY EVENING. OVER PUERTO RICO AND HISPANIOLA MOST ACTIVE IS  
EXPECTED ON THURSDAY WITH RAINFALL AMOUNTS OF 10-15MM/DAY AND  
MAXIMA OF 20-30MM. ACROSS CENTRAL AMERICA MOST ACTIVE CONVECTION  
WITH THE TRADES IS EXPECTED OVER EASTERN NICARAGUA AND CARIBBEAN  
COASTAL PLAINS OF COSTA RICA...WITH RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-35MM/DAY ON WEDNESDAY AND  
THURSDAY...WHILE ON FRIDAY IT DECREASES TO 05-10MM/DAY AND MAXIMA  
OF 15-20MM.  
 
THE TUTT ALOFT IS TO ALSO VENT CONVECTIVE DEVELOPMENT ACROSS THE  
NORTHERN GUIANAS AS ENHANCED BY TRADE WIND CONVERGENCE ALONG THE  
COAST. OVER FRENCH GUIANA AND SURINAME EXPECTING RAINFALL AMOUNTS  
OF 05-10MM/DAY AND MAXIMA OF 15-25MM. ACROSS NORTHERN GUYANA TO  
NORTHEAST VENEZUELA AND PORTIONS OF TRINIDAD EXPECT RAINFALL  
AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 25-50MM. ON THURSDAY THIS  
INCREASES TO MAXIMA OF 35-70MM...WHILE ON FRIDAY THE MAXIMA PEAKS  
AT 30-60MM.  
 
THE BRISK EASTERLIES ACROSS CENTRAL AMERICA ALSO FAVOR A FAIRLY  
STRONG CELL OF THE PANAMANIAN LOW OVER THE EASTERN PACIFIC THAT IS  
TO MEANDER OFF THE CENTRAL COAST OF COLOMBIA. THIS TROUGH WILL  
ENHANCE COASTAL CONVERGENCE BETWEEN THE CAUCA VALLEY TO THE  
SOUTHWEST AND THE EJE CAFETERO TO THE NORTHWEST...TO RESULT IN  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM. THROUGH  
FRIDAY THE MAXIMA IN THIS AREA DECREASES TO 20-30MM. ON THE ANDEAN  
REGION OF COLOMBIA... MEANWHILE...EXPECTING RAINFALL AMOUNTS OF  
00-05MM/DAY AND MAXIMA OF 10MM...INCREASING TO 05-10MM/DAY AND  
MAXIMA OF 15MM ON FRIDAY.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE  
SOF  
57W 61W 64W 67W 71W 74W 76W 78W TUTT INDCD  
24N  
67W 69W 72W 75W 77W 79W 80W DISSIPATES TUTT INDCD  
22N  
74W 76W 78W 80W 81W 82W DISSIPATES EW  
18N  
 
A TUTT INDUCED PERTURBATION ALONG 57W AND SOUTH OF 24N MOVES  
ACROSS THE LEEWARD ISLES EARLY IN THE CYCLE...WITH SHALLOW PLUME  
OF TROPICAL MOISTURE TO ACCOMPANY THIS FEATURE AS IT MOVES ACROSS  
THE ISLAND CHAIN...TO TRIGGER RAINFALL AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15-25MM. IT REACHES PUERTO RICO BY MIDDAY ON THURSDAY TO  
SUSTAIN RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF  
20-30MM...WITH SIMILAR AMOUTNS ACROSS THE DOMINICAN REPUBLIC. OVER  
THE ABC ISLES/NORTHERN VENEZUELA THIS IS TO TRIGGER RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM.  
 
A TUTT INDUCED PERTURBATION ALONG 67W AND SOUTH OF 22N MOVES  
ACROSS HISPANIOLA EARLY IN THE PERIOD TO TRIGGER RAINFALL AMOUNTS  
OF 05-10MM/DAY AND MAXIMA OF 15-20MM. OVER THE ABC  
ISLANDS/NORTHERN VENEZUELA IT IS TO TRIGGER RAINFALL AMOUNTS OF  
00-05MM/DAY AND MAXIMA OF 10MM. OVER NORTHERN COLOMBIA THIS SI TO  
ALSO FAVOR RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM ON  
THURSDAY-FRIDAY.  
 
AN EASTERLY WAVE ALONG 74W AND SOUTH OF 18N TENDS TO DISSIPATE AS  
IT PROPAGATES ACROSS THE CENTRAL CARIBBEAN. MEANWHILE...OVER  
JAMAICA THIS IS TO SUSTAIN RAINFALL AMOUNTS OF 00-05MM/DAY AND  
MAXIMA OF 10MM EARLY IN THE CYCLE. ON THURSDAY-FRIDAY IT MOVES TO  
EASTERN NICARAGUA WHERE IT WILL FAVOR RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-35MM.  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON...WPC (USA)  
 

 
 
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