203  
FXCA20 KWBC 171849  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
148 PM EST FRI NOV 17 2017  
 
TROPICAL DISCUSSION FROM NOV 17/12 UTC: MID/UPPER LEVEL RIDGE  
ACROSS WESTERN PORTIONS OF THE DOMAIN DOMINATES THE FLOW ACROSS  
NORTHERN/CENTRAL MEXICO AND THE SOUTHERN USA WHILE CENTERING ON A  
CLOSED HIGH OVER MEXICO NEAR 22N 101W. CONSISTENT WITH PREVIOUS  
FORECAST THE BROAD UPPER RIDGE PATTERN IS TO PERSIST THROUGH  
SATURDAY MORNING. LATER IN THE DAY...IT WILL START TO CRUMBLE  
UNDER PRESSURE FROM AMPLIFYING POLAR TROUGH OVER THE USA. AS THE  
RIDGE COLLAPSES...ASSOCIATED CAP INVERSION ACROSS MEXICO IS TO  
GRADUALLY WEAKEN. BROAD POLAR TROUGH IS TO THEN DOMINATE THE FLOW  
ACROSS THE USA-GULF OF MEXICO LATER DURING THE WEEKEND. AT LOW  
LEVELS THE TROUGH ALOFT IS TO SUSTAIN A PROGRESSIVE FRONT THAT  
MOVES TO NORTHERN FLORIDA/NORTHERN GULF OF MEXICO-TAMAULIPAS EARLY  
ON SUNDAY MORNING. THE FRONT SLIDES ACROSS THE FLORIDA PENINSULA  
TO THE NORTHWEST BAHAMAS EARLY ON MONDAY MORNING...WHILE TRAILING  
END MEANDERS OVER THE GULF TO NORTHEAST STATES OF MEXICO. OVER  
SOUTHERN TAMAULIPAS/NORTHERN VERACRUZ THIS WILL SUSTAIN RAINFALL  
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM....WHILE ACROSS  
SOUTHERN VERACRUZ-CHIAPAS THE FRONTAL NORTHERLIES WILL FAVOR  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM.  
 
THE FRONT IS TO ALSO FAVOR A PREFRONTAL SHEAR LINE THAT MOVES OVER  
THE CENTRAL BAHAMAS-CENTRAL CUBA-CAYMAN ISLES LATER ON SUNDAY. ON  
MONDAY MORNING IT MOVES TO THE SOUTHEAST BAHAMAS-TURKS AND  
CAICOS/JAMAICA WHILE TRAILING TO NORTHEAST NICARAGUA. ACROSS THE  
CENTRAL BAHAMAS-CENTRAL CUBA THIS WILL TRIGGER RAINFALL AMOUNTS OF  
00-05MM/DAY AND MAXIMA OF 10MM. OVER THE CAYMAN ISLES ALSO  
EXPECTING ACCUMULATION OF 00-05MM/DAY AND MAXIMA OF 10MM. ON  
MONDAY...IT IS TO THEN TRIGGER SCATTERED CONVECTION ACROSS THE  
SOUTHEAST BAHAMAS-TURKS AND CAICOS...WITH ACCUMULATION OF  
00-05MM/DAY AND MAXIMA OF 10MM. ACROSS JAMAICA EXPECTING RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM...WHILE OVER NORTHEAST  
HONDURAS/ NICARAGUA EXPECTING ACCUMULATION OF 05-10MM/DAY AND  
MAXIMA OF 15-20MM.  
 
A LONG WAVE TROUGH TO THE EAST FLANKS THE EASTERN FRINGES OF THE  
CONTINENTAL RIDGE...WITH MID/UPPER LEVEL AXIS EXTENDING FROM THE  
WESTERN ATLANTIC...ACROSS CUBA TO THE WESTERN CARIBBEAN/NORTHERN  
CENTRAL AMERICA. BUT AS THE RIDGE TO THE WEST COLLAPSES...THE  
TROUGH WILL THEN BEGIN TO PULL TO THE EAST-NORTHEAST. OVER THE  
CENTRAL/WESTERN CARIBBEAN THIS WILL THEN WEAKEN TO A SHEAR AXIS  
LATER DURING THE WEEKEND...WHILE TO THE NORTH IT GRADUALLY PULLS  
AWAY. AS THE TROUGH OVER THE CARIBBEAN WEAKENS IT WILL MAKE WAY  
FOR A CELL OF THE SUBEQUATORIAL RIDGE TO BUILD ACROSS THE ISLAND  
CHAIN TO THE EASTERN CARIBBEAN LATER ON SUNDAY/MONDAY. THE  
BUILDING RIDGE IS TO THEN FAVOR A TRADE WINDS CAP. ON  
SUNDAY-MONDAY THE INVERSION IS TO LINGER AROUND 500/600  
HPA...WHILE LATER ON MONDAY-TUESDAY IT DROPS TO AROUND 700 HPA.  
 
AT LOW LEVELS...WANING FRONT EXTENDS ACROSS THE CENTRAL/SOUTHEAST  
BAHAMAS AS ANOTHER BOUNDARY SURGES ACROSS FLORIDA TO THE ISLANDS.  
EARLY ON SATURDAY MORNING THIS MOVES TO THE CENTRAL  
BAHAMAS-CENTRAL CUBA. LATER ON SATURDAY IT IS TO MEANDER NORTH TO  
THE NORTHWEST BAHAMAS...TO DISSIPATE EARLY ON SUNDAY MORNING. AS  
IT ENTERS THE BAHAMAS THIS SUSTAINS A PREFRONTAL SHEAR LINE OVER  
THE ISLANDS TO CUBA. LATER TODAY THIS MOVES ACROSS THE TURKS TO  
NORTHERN HISPANIOLA...WHERE IT IS TO FAVOR RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-35MM. ON SATURDAY THIS BOUNDARY  
BECOMES ILL DEFINED.  
 
SOUTH OVER THE BASIN...THE UPPER LEVEL TROUGH CONTINUES TO  
INTERACT WITH LOW LEVEL TROUGH MEANDERING OVER THE CENTRAL  
CARIBBEAN. THIS TROUGH SUSTAINS A MOIST SOUTHWESTERLY FLOW ACROSS  
THE CENTRAL CARIBBEAN...WITH DEEP TROPICAL MOISTURE CONVERGING  
ACROSS HISPANIOLA-PUERTO RICO/VIRGIN ISLES. THIS PATTERN HOLDS  
THROUGH MIDDAY ON SATURDAY...WITH WINDS BACKING TO THE  
SOUTH-SOUTHEAST LATER IN THE DAY. ON MONDAY TO TUESDAY PREVAILING  
EASTERLY TRADES RETURN TO THE EASTERN CARIBBEAN. AS THE WINDS BACK  
TO THE SOUTHEAST...IT WILL CUTOFF THE SUPPLY OF DEEP TROPICAL  
MOISTURE...WITH GLOBAL MODEL GUIDANCE AGREEING ON GRADUAL EROSION  
OF AVAILABLE WATER EARLY NEXT WEEK AS MID LEVEL RIDGE STRENGTHENS.  
THE GFS GDI FORECAST RESPONDS IN KIND...SHOWING A CONVECTIVELY  
UNSTABLE AIR MASS ENVELOPING PUERTO RICO AND THE USVI THROUGH  
MIDAFTERNOON ON SUNDAY...AND HAITI/DOMINICAN REPUBLIC THROUGH  
TUESDAY. OVER THE NEXT FEW DAYS THIS WILL LIKELY FAVOR SCATTERED  
DEEP CONVECTION...WITH MCS ACTIVITY LIKELY TO DEVELOP ON THE  
CARIBBEAN COASTAL WATERS OF HISPANIOLA/MONA PASSAGE. IN THIS AREA  
EXPECTING RAINFALL AMOUNTS OF 20-40MM/DAY AND MAXIMA OF 50-100MM  
THROUGH SATURDAY MORNING. ON SATURDAY-SUNDAY IT DECREASES TO  
15-20MM/DAY AND MAXIMA OF 30-60MM...WHILE ON SUNDAY EXPECTING  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM. ACROSS  
PUERTO RICO THIS IS TO FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND  
MAXIMA OF 20-45MM/DAY. ON SATURDAY IT INCREASES TO 15-20MM/DAY AND  
MAXIMA OF 30-60MM. ON SUNDAY...AS THE TRADE WINDS CAP STARTS TO  
STRENGTHEN...IT WILL DECREASE TO 05-10MM/DAY AND MAXIMA OF 15-20MM  
IN SHALLOW CONVECTION.  
 
SOUTH OVER THE BASIN...FOCUS OF THE HEAVY CONVECTION SHIFTS TO  
NORTHERN COLOMBIA EARLY IN THE CYCLE...TO SUSTAIN RAINFALL AMOUNTS  
OF 15-20MM/DAY AND MAXIMA OF 30-60MM. ON SATURDAY IT DECREASES TO  
10-15MM/DAY AND MAXIMA OF 20-40MM...WHILE BUILDING EAST ACROSS  
NORTHWEST VENEZUELA. ON SUNDAY...CONVERGENCE ALONG THE NEAR  
EQUATORIAL TROUGH IS TO THEN SUSTAIN RAINFALL AMOUNTS OF  
00-05MM/DAY AND MAXIMA OF 10MM. ON THE ANDEAN REGION/WESTERN  
COLOMBIA...MEANWHILE...EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY  
AND MAXIMA OF 20-30MM. OVER COSTA RICA-PANAMA EXPECT RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM. ACROSS VENEZUELA MOST  
ACTIVE IS EXPECTED OVER AMAZONIA TO THE SOUTH...WITH ACCUMULATION  
OF 05-10MM/DAY AND MAXIMA OF 15-20MM...INCREASING 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  
42W 44W 46W 49W 52W 54W 56W 57W EW 12N  
67W 68W 69W 70W 71W 72W 73W 74W EW 15N  
 
AN EASTERLY WAVE IS INITIALIZED ALONG 42W TO 12N. THIS REACHES  
FRENCH GUIANA LATER ON SATURDAY/EARLY SUNDAY MORNING WHERE IT IS  
TO FAVOR RAINFALL AMOUNTS OF 00-05MM/DAY. ACROSS SURINAME IT IS TO  
FAVOR SIMILAR RAINFALL AMOUNTS. MOST ACTIVE IS EXPECTED TO THE  
NORTH ALONG THE ITCZ.  
 
AN EASTERLY WAVE ALONG 67W AND SOUTH OF 16N IS TO SUSTAIN  
SCATTERED CONVECTION ACROSS WESTERN VENEZUELA TO EASTERN COLOMBIA  
WITH ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15MM. ACROSS  
NORTHWEST VENEZUELA TO NORTHERN COLOMBIA THIS IS TO THEN FAVOR  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-45MM ON SATURDAY  
TO SUNDAY...DECREASING TO 00-05MM/DAY AND MAXIMA OF 10MM ON SUNDAY.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  
 

 
 
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