213  
FXCA20 KWBC 211914  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
213 PM EST TUE NOV 21 2017  
 
TROPICAL DISCUSSION FROM NOV 21/12 UTC: AT MID/UPPER  
LEVELS...BROAD CELL O THE SUBTROPICAL RIDGE TO THE WEST OF THE  
BAJA PENINSULA IS STEERING SHORT WAVE TROUGHS ACROSS TEXAS INTO  
THE WESTERN GULF OF MEXICO...WHERE THEY FEED INTO A HIGH AMPLITUDE  
LONG WAVE TROUGH EXTENDING OVER THE GULF-SOUTHERN MEXICO/NORTHERN  
CENTRAL AMERICA. THE SLOW TO EVOLVE PATTERN IS TO HOLD DURING THE  
NEXT FEW DAYS. AS IT HOLDS...AT 250 HPA...A SUBTROPICAL JET MAXIMA  
IS TO ROUND THE BASE OF THE TROUGH. THIS JET MAXIMA IS TO  
GENERALLY FAVOR A DIVERGENT PATTERN ALOFT ACROSS THE CENTRAL  
CARIBBEAN AND SOUTHERN PORTIONS OF CENTRAL AMERICA. AT LOW  
LEVELS...AN ELONGATED FRONT STRETCHES ACROSS CENTRAL FLORIDA TO  
THE NORTHERN GULF/SOUTH TEXAS...WHERE IT IS TO REMAIN DURING THE  
NEXT DAY OR SO. LATER ON WEDNESDAY...A LOW FORMS OVER THE EASTERN  
GULF OF MEXICO. THIS IS NOW TO MEANDER OFF THE WEST COAST OF  
FLORIDA THROUGH THURSDAY MORNING...MOVING INLAND LATER IN THE DAY.  
THE LOW...AS IT DEEPENS...IS TO FAVOR A STRONG NORTHERLY FLOW  
ACROSS THE WESTERN GULF...WITH BOUNDARY LAYER WINDS OF 25-30KT  
EXPECTED ON WEDNESDAY...INCREASING TO 30-35KT ON THURSDAY MORNING.  
THIS IS TO THEN SUSTAIN A TEHUANTEPECER JET OF 40-45KT. THE  
SURFACE FRONT INITIALLY MOVES ACROSS VERACRUZ MEXICO ON WEDNESDAY  
EVENING/EARLY THURSDAY MORNING...SURGING ACROSS THE  
YUCATAN-SOUTHERN SATES OF MEXICO ON THURSDAY AFTERNOON. AS IT  
SURGES ACROSS THE GULF OF MEXICO THIS IS TO INITIALLY FAVOR LIGHT  
CONVECTION BETWEEN SOUTHERN TAMAULIPAS-NORTHERN VERACRUZ...WITH  
ACCUMULATION OF 00-05MM/DAY AND MAXIMA OF 10MM. ON  
WEDNESDAY-THURSDAY...THE FRONTAL NORTHERLIES OVER THE CAMPECHE  
SOUND ARE TO ENHANCE LOW LEVEL MOISTURE CONVERGENCE ACROSS  
SOUTHERN VERACRUZ-NORTHERN CHIAPAS...WHERE WE EXPECT RAINFALL  
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-30MM. ON THURSDAY THIS  
DECREASES TO 00-05MM/DAY AND MAXIMA OF 10MM. OVER  
CAMPECHE/YUCATAN EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND  
MAXIMA OF 10MM ON WEDNESDAY...INCREASING TO 05-10MM/DAY AND MAXIMA  
OF 15MM ON THURSDAY.  
 
IN RESPONSE TO THE HIGH AMPLITUDE LONG WAVE TROUGH TO THE  
WEST...AT MID/UPPER LEVELS...CELL OF THE SUBEQUATORIAL RIDGE  
BUILDS ACROSS THE EASTERN CARIBBEAN TO THE WESTERN ATLANTIC. LATER  
ON WEDNESDAY THIS IS TO THEN ANCHOR AT 500 HPA ON A CLOSED HIGH  
OVER PUERTO RICO...WHERE IT IS TO MEANDER DURING THE NEXT FEW  
DAYS. THE BUILDING MID LEVEL RIDGE SUSTAINS A STRONG TRADE WINDS  
CAP ACROSS THE EASTERN CARIBBEAN ISLES-VIRGIN ISLANDS-PUERTO RICO.  
THIS EXPANDS TO INCLUDE MOST OF HISPANIOLA LATER TODAY. STRONG  
TRADE WINDS CAP IS TO GENERALLY PERSIST DURING THE NEXT FEW DAYS.  
AT LOW LEVELS...BROAD RIDGE DOMINATES THE FLOW ACROSS THE WESTERN  
ATLANTIC TO THE NORTHERN CARIBBEAN. THIS FAVORS A BRISK EASTERLY  
FLOW ACROSS THE ISLAND CHAIN TO THE CENTRAL CARIBBEAN...WITH 850  
HPA WINDS PEAKING AT 15-20KT. POLAR FRONTS EXITING THE EASTERN USA  
ARE TO PRESS AGAINST THIS RIDGE...WITH AXIS TO WEAKEN WHILE  
RELOCATING TO THE CENTRAL ATLANTIC LATER ON WEDNESDAY/EARLY  
THURSDAY MORNING. ALTHOUGH EASTERLY TRADES PERSIST ACROSS THE  
BASIN...WINDS DROP TO 05-10KT. IN THIS PATTERN MEASURABLE RAINFALL  
AMOUNTS WILL LIMIT TO TRINIDAD/TOBAGO-THE GRENADINES-ORINOCO DELTA  
REGION IN NORTHEAST VENEZUELA...WITH RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-35MM. THIS DECREASES TO 05-10MM/DAY  
AND MAXIMA OF 15-20MM ON WEDNESDAY-THURSDAY. LIGHT TO MODERATE  
CONVECTION ACROSS THE HAITIAN PENINSULA WILL RESULT IN RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM...WHILE ON THE DOMINICAN  
REPUBLIC SIDE OF THE ISLAND EXPECTING ACCUMULATION OF 00-05MM/DAY  
AND MAXIMA OF 10MM EARLY IN THE CYCLE.  
 
ALSO AT LOW LEVELS...AN INVERTED TROUGH EXTENDS NORTH ALONG  
80W...SPANNING FROM COSTA RICA TO THE CAYMAN ISLES/JAMAICA-EASTERN  
CUBA. THIS TROUGH REMAINS ON THE DIVERGENT SIDE OF JET MAXIMA  
ROUNDING THE LONG WAVE TROUGH TO THE WEST. THIS IS TO VENT  
CONVECTIVE DEVELOPMENT...MEANWHILE ACROSS SOUTHERN NICARAGUA-COSTA  
RICA TO PANAMA INITIALLY EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY  
AND MAXIMA OF 15MM. THROUGH THURSDAY THIS INCREASES TO 10-15MM/DAY  
AND MAXIMA OF 20-40MM. OVER THE CAYMAN ISLES EXPECTING RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM THROUGH WEDNESDAY  
MORNING AND ON THURSDAY. ACROSS JAMAICA/EASTERN CUBA EXPECTING  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM. ON  
WEDNESDAY THIS INCREASES TO MAXIMA OF 20-40MM...WHILE ON THURSDAY  
THE MAXIMA IS TO PEAK AT 20-30MM.  
 
OVER WESTERN COLOMBIA/ANDEAN REGION EXPECTING RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-25MM. ON WEDNESDAY AND THURSDAY...AS  
A WESTERLY FLOW ESTABLISHES OVER THE EASTERN PACIFIC...THIS WILL  
ENHANCE COASTAL CONVERGENCE TO FAVOR RAINFALL AMOUNTS OF  
15-20MM/DAY AND MAXIMA OF 30-60MM...WITH MOST INTENSE CLUSTERING  
ACROSS THE EJE CAFETERO TO THE NORTHWEST. ACROSS VENEZUELA EXPECT  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM...WITH MOST  
INTENSE OVER AMAZONIA TO THE SOUTH. ON WEDNESDAY-THURSDAY THE  
MAXIMA PEAKS AT 20-35MM.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE  
SOF  
46W 48W 50W 52W 54W 56W 58W 60W EW  
16N  
49W 52W 54W 56W 58W 60W 62W 64W TUTT-INDCD  
26N  
60W 63W 65W 67W 69W 71W 73W 75W EW  
14N  
75W 77W 78W DISSIPATES EW  
15N  
 
AN EASTERLY WAVE IS INITIALIZED ALONG 46W. NOTE THAT THE ECMWF  
CONTINUES TO DO SLIGHTLY BETTER THAN THE GFS WITH THE FORECAST OF  
THIS FEATURE. THE WAVE REACHES FRENCH GUIANA EARLY ON WEDNESDAY  
MORNING...TO FAVOR LIGHT RAINFALL AMOUNTS IN ISOLATED CONVECTION.  
SIMILARLY ACROSS SURINAME TO GUYANA ON THURSDAY. MOST ACTIVE IS  
EXPECTED TO THE NORTH ALONG THE ITCZ.  
 
A TUTT OVER THE CENTRAL TROPICAL ATLANTIC SUSTAINS AN INDUCED  
PERTURBATION IN THE EASTERLY TRADES WITH AXIS ALONG 49W AND NORTH  
OF 20N. THIS REACHES THE NORTHEAST CARIBBEAN LATER ON  
THURSDAY...CROSSING THE VIRGIN ISLES TO EASTERN PUERTO RICO ON  
FRIDAY. MODELS SHOW A PLUME OF SHALLOW MOISTURE TO PRECEDE THIS  
PERTURBATION AS IT ENTERS THE NORTHEAST CARIBBEAN ISLES.  
HOWEVER...UNDER INFLUENCE OF MID LEVEL CELL OF THE SUBEQUATORIAL  
RIDGE...ENVIRONMENTAL CONDITIONS ARE TO REMAIN HOSTILE FOR DEEP  
CONVECTIVE DEVELOPMENT. THUS...ONLY EXPECTING LIGHT CONVECTION  
WITH THIS FEATURE AS IT STREAMS ACROSS THE NORTHEAST  
CARIBBEAN...WITH ACCUMULATION OF 00-05MM/DAY AND MAXIMA OF 10MM.  
 
AN EASTERLY WAVE ALONG 60W AND SOUTH OF 14N IS TO ENHANCE  
CONVECTION ACROSS SOUTHERN VENEZUELA OVER THE NEXT COUPLE OF  
DAYS...TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15MM. ON WEDNESDAY THIS INCREASES TO 10-15MM/DAY AND MAXIMA OF  
20-35MM. ON THURSDAY...ACROSS EASTERN COLOMBIA/WESTERN VENEZUELA  
THIS IS TO THEN FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA  
OF 15-20MM.  
 
AN ILL ORGANIZED EASTERLY WAVE ALONG 75W IS TO MERGE INTO INVERTED  
TROUGH OVER THE CENTRAL CARIBBEAN LATER ON WEDNESDAY.  
MEANWHILE...ACROSS COLOMBIA THIS IS TO SUSTAIN RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-25MM.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  
 

 
 
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