299  
FXCA20 KWBC 121917  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
217 PM EST FRI JAN 12 2018  
 
TROPICAL DISCUSSION FROM JAN 12/12 UTC: DIGGING MID/UPPER LEVEL  
TROUGH REMAINS THE SYSTEM OF CONCERN ACROSS WESTERN HALF OF THE  
FORECAST DOMAIN. LATER TODAY THE TROUGH IS TO ENVELOP MOST OF  
NORTH AMERICA WHILE EXTENDING INTO THE WESTERN CARIBBEAN TO  
NORTHERN CENTRAL AMERICA. THE HIGH AMPLITUDE LONG WAVE PATTERN IS  
TO THEN PERSIST DURING THE NEXT THREE DAYS. AT LOW LEVELS...UNDER  
THE INFLUENCE OF STRONG FRONTAL NORTHERLIES ACROSS THE GULF OF  
MEXICO...EXPECTING A TEHUANTEPECER JET OF 50KT OVER THE NEXT FEW  
DAYS. THESE ARE TO ALSO DISPLACE THE ASSOCIATED FRONT ACROSS  
FLORIDA-WESTERN CUBA TO BELIZE/GUATEMALA LATER THIS AFTERNOON.  
EARLY ON SATURDAY MORNING THE FRONT WILL THEN MOVE TO THE  
NORTHWEST BAHAMAS-WESTERN/CENTRAL CUBA INTO THE WESTERN  
CARIBBEAN/NORTHERN CENTRAL AMERICA...WITH FRONTAL NORTHERLIES OF  
20-30KT ACROSS THE ISLAS DE LA BAHIA TO NORTHERN HONDURAS. LATER  
ON SATURDAY THE FRONT MOVES OVER THE CENTRAL BAHAMAS-CENTRAL  
CUBA-THE CAYMAN ISLES WHILE TRAILING TO NORTHERN CENTRAL  
AMERICA...AND ON SUNDAY IT BECOMES STATIONARY OVER THE SOUTHEAST  
BAHAMAS-EASTERN CUBA-WESTERN JAMAICA WHILE TRAILING TO NORTHERN  
CENTRAL AMERICA. AHEAD OF THIS FRONT...A PREFRONTAL SHEAR LINE  
FORMS OVER THE WESTERN CARIBBEAN-NORTHWEST NICARAGUA LATER THIS  
AFTERNOON. ON SATURDAY THROUGH SUNDAY THIS MOVES ACROSS CUBA TO  
THE CENTRAL CARIBBEAN-COSTA RICA/WESTERN PANAMA...WITH 850 HPA  
WINDS OVER NICARAGUA-EASTERN PACIFIC FORECAST TO PEAK AROUND  
40-50KT...WHILE THE BOUNDARY LAYER WINDS ARE EXPECTED TO PEAK AT  
30-35KT. ACROSS PANAMA THE 850 HPA WIND ARE TO INTENSIFY ON  
SUNDAY...PEAKING AT 20-25KT ACROSS THE ISTHMUS INTO THE EASTERN  
PACIFIC.  
 
OVER NORTHERN CHIAPAS-TABASCO IN SOUTHERN MEXICO TO CENTRAL  
GUATEMALA...THE FRONTAL NORTHERLIES WILL FAVOR RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15MM THROUGH SATURDAY MORNING. ON  
SATURDAY-SUNDAY THIS IS TO THEN SUSTAIN RAINFALL AMOUNTS OF  
00-05MM/DAY AND MAXIMA OF 10MM. HIGHER AMOUNTS ARE EXPECTED  
BETWEEN PUERTO BARRIOS GUATEMALA AND TELA/SAN PEDRO SULA IN  
NORTHWEST HONDURAS AND THE ISLAS DE LA BAHIA TO THE NORTH. EARLY  
IN THE CYCLE EXPECT ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF  
20-35MM. ON SATURDAY INCREASES TO 15-20MM/DAY AND MAXIMA OF  
25-50MM...WHILE ON SUNDAY-MONDAY THE MAXIMA PEAKS AT 20-40MM.  
ACROSS WESTERN CUBA THE FRONT WILL TRIGGER RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-35MM THROUGH SATURDAY MORNING. DURING  
THE DAY ON SATURDAY CONVECTION SPREADS ACROSS CENTRAL-EASTERN  
PORTIONS OF THE ISLAND WITH ACCUMULATION OF 10-15MM/DAY AND MAXIMA  
OF 20-40MM. ACROSS THE BAHAMAS INITIALLY EXPECTING ACCUMULATION OF  
10-15MM/DAY AND MAXIMA OF 20-30MM. ON SATURDAY FRONTAL CONVECTION  
INCREASES TO 15-20MM/DAY AND MAXIMA OF 25-50MM. ON SUNDAY...MOST  
ACTIVE IS EXPECTED OVER THE SOUTHEAST BAHAMAS WITH ACCUMULATION OF  
10-15MM/DAY AND MAXIMA OF 20-40MM. SHEAR LINE CONFLUENCE OVER THE  
CAYMAN ISLES ON FRIDAY...AND FRONTAL CONVERGENCE ON SATURDAY...  
WILL SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15-25MM. OVER JAMAICA THE SHEAR LINE AND PREFRONTAL TROUGH WILL  
SUSTAIN RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM ON  
SATURDAY. ON SUNDAY THIS INCREASES TO 15-20MM/DAY AND MAXIMA OF  
25-50MM...WITH MOST INTENSE ACROSS WESTERN PORTIONS OF THE ISLAND.  
HEAVY CONVECTION IS EXPECTED TO THE SOUTH IN ASSOCIATION WITH THE  
SHEAR LINE MOVING OVER SOUTHERN CENTRAL AMERICA. ACROSS EASTERN  
NICARAGUA THIS WILL TRIGGER SCATTERED CONVECTION WITH ACCUMULATION  
OF 10-15MM/DAY AND MAXIMA OF 20-35MM ON SATURDAY AND SUNDAY. OVER  
COSTA RICA-WESTERN PANAMA IT IS TO TRIGGER RAINFALL AMOUNTS OF  
35-70MM/DAY AND MAXIMA OF 125-200MM/DAY TO START ON SATURDAY AND  
FORECAST TO PERSIST THROUGH MONDAY MORNING. IN THIS AREA THE STORM  
TOTAL AMOUNTS WILL RANGE BETWEEN 250-500MM.  
 
AS THE POLAR TROUGH DEEPENS OVER THE WESTERN ATLANTIC IT IS TO  
INDUCE A PREFRONTAL TROUGH OVER THE CENTRAL CARIBBEAN. THIS PHASES  
WITH THE PANAMANIAN TROUGH TO THE SOUTH TO ENHANCE MOISTURE  
CONVERGENCE ALONG THE PACIFIC COAST OF COLOMBIA. OVER SOUTHWEST  
COLOMBIA EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15-25MM...PEAKING AT 15-30MM ON SATURDAY...WHILE ON SUNDAY IT  
DECREASES TO 05-10MM/DAY AND MAXIMA OF 15MM. WHILE OVER THE EJE  
CAFETERO TO THE NORTHWEST AND ACROSS THE ANDEAN REGION TO THE  
SIERRA NEVADA DE SANTA MARTA EXPECTING ACCUMULATION OF 05-10MM/DAY  
AND MAXIMA OF 15-25MM. ON SATURDAY-SUNDAY THIS DECREASES TO  
05-10MM/DAY AND MAXIMA OF 15MM.  
 
EAST OF THE POLAR TROUGH...A 500 HPA HIGH TO THE EAST-SOUTHEAST OF  
BERMUDA EXTENDS A RIDGE TO THE SOUTHWEST ACROSS PUERTO RICO TO THE  
EASTERN CARIBBEAN. THE RIDGE IS PROVIDING THE STEERING FLOW TO A  
TROUGH OVER THE CENTRAL ATLANTIC...WITH AXIS TO PROPAGATE TO THE  
SOUTHWEST OVER THE NEXT DAY OR SO. ON SATURDAY IT APPROACHES THE  
NORTHEAST CARIBBEAN ISLES...WHERE IT IS FORECAST TO STALL WHILE  
CENTERING ON A CLOSED LOW TO THE NORTH-NORTHEAST OF THE LEEWARD  
ISLANDS. AT 250 HPA A 50-75KT JET MAXIMA IS TO ROUND THE BASE OF  
THE LOW/TROUGH...WITH DIVERGENCE ON ITS RIGHT ENTRANCE REGION TO  
BRIEFLY ENVELOP THE NORTHEAST CARIBBEAN ISLES ON SATURDAY. ON  
SUNDAY...AS THE TROUGH STALLS...THE JET WILL MOVE TO THE WINDWARD  
ISLES...WITH DIVERGENCE ON ITS RIGHT ENTRANCE REGION TO ENVELOP  
TRINIDAD-TOBAGO-THE GRENADINES AND THE SOUTHERN FRENCH ISLES.  
 
AT LOW LEVELS...BROAD RIDGE DOMINATES THE FLOW ACROSS THE ATLANTIC  
WHILE CENTERING ON A CLOSED HIGH TO THE NORTH-NORTHEAST OF  
BERMUDA. IN A TIGHT GRADIENT BRISK EAST-SOUTHEASTERLY WINDS  
ENVELOP THE ISLAND CHAIN/EASTERN-CENTRAL CARIBBEAN...WITH 850 HPA  
WINDS PEAKING AT 20-25KT. THIS FAVORS GENERATION OF STREAMERS  
ACROSS THE LEEWARD ISLES THAT ARE TO AFFECT THE VIRGIN  
ISLES/EASTERN PUERTO RICO FROM TIME-TO-TIME. LATER DURING THE  
WEEKEND...UNDER PRESSURE FROM THE POLAR TROUGH EXITING THE EASTERN  
USA AND A TUTT INDUCED PERTURBATION ALONG 60W...THE RIDGE WILL  
WEAKEN AND THE GRADIENT WILL SLACKEN. LIGHTER WINDS ARE TO THEN  
ENVELOP THE LESSER ANTILLES/EASTERN CARIBBEAN BY MIDMORNING ON  
SUNDAY THROUGH TUESDAY. OVER THE LEEWARD/VIRGIN ISLES MOST ACTIVE  
CONVECTION IS EXPECTED ON SATURDAY...WHEN WE FORECAST RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM. ACROSS PUERTO RICO  
MOST ACTIVE IS ALSO EXPECTED ON SATURDAY...WITH RAINFALL AMOUNTS  
OF 10-15MM/DAY AND MAXIMA OF 20-30MM. OVER HISPANIOLA...INITIALLY  
EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM AS  
A MOIST PLUME ADVECTS ALONG THE CARIBBEAN WATERS OF THE ISLAND.  
THROUGH SUNDAY THIS DECREASES TO 00-05MM/DAY AND MAXIMA OF 10MM.  
 
AS THE TROUGH DEEPENS...IT IS TO DRAW ITCZ MOISTURE ACROSS THE  
GUIANAS ON SATURDAY...REACHING TRINIDAD/TOBAGO-WINDWARD ISLES ON  
SATURDAY AFTERNOON. OVER FRENCH GUIANA-SURINAME EXPECTING RAINFALL  
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM. THIS SPREADS TO  
GUYANA-TRINIDAD-SOUTHERN WINDWARD ISLANDS ON SATURDAY TO FAVOR  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
75W 78W 79W DISSIPATES EW 19N  
 
AN EASTERLY WAVE ALONG 75W AND SOUTH OF 19N IS FORECAST TO  
DISSIPATE EARLY ON SATURDAY WHILE MERGING WITH AN  
INDUCED/PREFRONTAL TROUGH OVER THE CENTRAL CARIBBEAN.  
MEANWHILE...THIS WILL SUSTAIN A MOIST PLUME ACROSS SOUTHERN  
HISPANIOLA WHERE IT IS TO TRIGGER RAINFALL AMOUNTS OF 10-15MM/DAY  
AND MAXIMA OF 20-40MM. ACROSS JAMAICA THIS IS TO THEN FAVOR  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM. OVER  
AMAZONIA IN EASTERN COLOMBIA EXPECTING RAINFALL AMOUNTS OF  
15-20MM/DAY AND MAXIMA OF 25-50MM...WHILE ON THE ANDEAN REGION  
THIS IS TO TRIGGER RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15-25MM.  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON...WPC (USA)  
 

 
 
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