700  
FXCA20 KWBC 201925  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
224 PM EST MON NOV 20 2017  
 
TROPICAL DISCUSSION FROM NOV 20/12 UTC: A MID/UPPER LEVEL RIDGE  
OVER NORTHWESTERN MEXICO/SOUTHWEST USA IS STEERING A SHORT WAVE  
TROUGH ACROSS TEXAS TO THE WESTERN GULF. AS IT CLEARS THE FRINGES  
OF THE MID LEVEL RIDGE THE TROUGH IS TO THEN DEEPEN ACROSS THE  
GULF TO THE CAMPECHE SOUND LATER THIS AFTERNOON. THIS SETS THE  
STAGE FOR A SECONDARY PERTURBATION TO FOLLOW...WITH MID LEVEL  
VORTEX MOVING ACROSS TEXAS TO THE NORTHWEST GULF EARLY ON  
WEDNESDAY MORNING. THIS IS TO THEN DEEPEN OVER THE GULF OF MEXICO  
TO THE YUCATAN PENINSULA/CENTRAL GUATEMALA-BELIZE ON WEDNESDAY  
EVENING. AT LOW LEVELS AN ELONGATED FRONT STRETCHES ACROSS THE  
NORTHWEST BAHAMAS-SOUTHERN FLORIDA TO THE NORTHEAST STATES OF  
MEXICO. LATER TODAY/EARLY ON TUESDAY MORNING THE FRONT IS TO  
RETROGRESS ACROSS CENTRAL FLORIDA TO THE NORTHERN GULF. ON  
WEDNESDAY...AS THE MID LEVEL TROUGH DEEPENS ACROSS THE GULF...IT  
IS TO INDUCE A FRONTAL LOW ALONG THE MEANDERING BOUNDARY OVER THE  
GULF. THE LOW IS TO GRADUALLY DEEPEN AS IT LIFTS ACROSS FLORIDA  
LATER IN THE WEEK. THIS WILL TIGHTEN THE GRADIENT AND IT IS TO  
SUSTAIN A NORTHERLY LOW LEVEL FLOW OF 25-30KT ACROSS THE WESTERN  
GULF ON WEDNESDAY THAT DISPLACES THE FRONT SOUTH TO TAMAULIPAS IN  
NORTHEAST MEXICO LATER IN THE DAY. ON THURSDAY MORNING THE FRONT  
SURGES ACROSS VERACRUZ-OAXACA...AND ON THURSDAY EVENING IT REACHES  
THE NORTHERN YUCATAN PENINSULA/SOUTHERN STATES OF MEXICO. 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...BRISK 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...WHILE OVER  
CAMPECHE/YUCATAN EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND  
MAXIMA OF 10MM.  
 
AS THE POLAR TROUGH DEEPENS TO THE WEST...A MID LEVEL CELL OF THE  
SUBEQUATORIAL RIDGE IS TO THEN AMPLIFY ACROSS THE ISLAND CHAIN TO  
THE EASTERN CARIBBEAN LATER THIS EVENING. AS THE PATTERN  
EVOLVES...SHORT WAVE TROUGH OVER THE WESTERN CARIBBEAN IS TO  
FINALLY FILL WHILE SHEARING SHORT WAVE ENERGY ACROSS  
HISPANIOLA-WESTERN PUERTO RICO EARLY IN THE PERIOD. ON  
WEDNESDAY-THURSDAY THE MID LEVEL RIDGE IS TO THEN CENTER ON A  
CLOSED HIGH OVER PUERTO RICO. THE BUILDING MID LEVEL RIDGE IS TO  
SUSTAIN A STRONG TRADE WINDS CAP ACROSS THE EASTERN CARIBBEAN  
ISLES LATER THIS EVENING. THIS EXPANDS ACROSS THE VIRGIN ISLES TO  
PUERTO RICO LATER THIS EVENING...TO REMAIN STRONG AND WELL  
ENTRENCHED THROUGH AT LEAST THURSDAY MORNING. THIS WILL BE  
ACCOMPANIED BY A SHARP DROP IN AVAILABLE WATER ACROSS PUERTO  
RICO-VIRGIN ISLES LATER TODAY. MEANWHILE...ACROSS PUERTO RICO  
EXPECTING RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF  
25-50MM...WHILE ACROSS THE VIRGIN ISLES EXPECTING RAINFALL AMOUNTS  
OF 00-05MM/DAY AND MAXIMA OF 10MM. FAIR WEATHER CONDITIONS WILL  
THEN PREVAIL THROUGH THURSDAY MORNING.  
 
AT LOW LEVELS...AN ILL ORGANIZED LOW SOUTH-SOUTHWEST OF HAITI  
EXTENDS A SHORT WAVE TROUGH TO NORTHERN COLOMBIA. THE LOW/TROUGH  
IS ENHANCING LOW LEVEL MOISTURE CONVERGENCE ACROSS THE CENTRAL  
CARIBBEAN...WITH PLUME OF TROPICAL MOISTURE LIFTING ALONG THE  
WESTERN FRINGES OF THE SUBEQUATORIAL RIDGE TO PUERTO RICO AND THE  
DOMINICAN REPUBLIC. AS PREVIOUSLY INDICATED BUILDING MID LEVEL  
RIDGE IS TO SUSTAIN RAPID EROSION OF AVAILABLE WATER ACROSS PUERTO  
RICO LATER THIS EVENING...AND ACROSS HISPANIOLA LATER IN THE  
MORNING ON TUESDAY. OVER SOUTHERN HISPANIOLA EXPECTING RAINFALL  
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM THROUGH THIS  
EVENING...WHILE ACROSS NORTHERN HALF OF THE ISLAND EXPECT  
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-20MM. ON  
TUESDAY...LIGHT TO MODERATE CONVECTION ACROSS THE HAITIAN  
PENINSULA WILL RESULT IN ADDITIONAL RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15MM.  
 
BUILDING RIDGE OVER THE WESTERN NORTH ATLANTIC ON  
MONDAY-TO-TUESDAY IS TO THEN FAVOR A BRISK EASTERLY FLOW ACROSS  
THE ISLAND CHAIN-EASTERN/CENTRAL CARIBBEAN. THE SURFACE LOW SOUTH  
OF HAITI WILL WEAKEN TO AN OPEN TROUGH THAT RELOCATES ACROSS  
JAMAICA DURING EARLY MORNING HOURS ON TUESDAY...NEARING 80W LATER  
IN THE DAY...WHERE IT IS TO THEN REMAIN THROUGH THURSDAY MORNING.  
AS IT MEANDERS ACROSS JAMAICA/EASTERN CUBA-THE TURKS AND CAICOS  
THIS WILL FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF  
20-35MM...WITH MAXIMA OF 20-40MM ACROSS EASTERN CUBA/JAMAICA ON  
WEDNESDAY.  
 
AS THE LOW LEVEL TROUGH RELOCATES ACROSS THE CENTRAL CARIBBEAN IT  
IS TO ALSO FAVOR AN INCREASE IN DIURNAL CONVECTION OVER SOUTHERN  
CENTRAL AMERICA. ACROSS COSTA RICA/SOUTHERN NICARAGUA-PANAMA  
INITIALLY EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15-20MM. THROUGH WEDNESDAY THIS INCREASES TO 10-15MM/DAY AND  
MAXIMA OF 20-30MM. OVER WESTERN COLOMBIA/ANDEAN REGION EXPECTING  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-30MM. ON  
WEDNESDAY...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. ACROSS VENEZUELA  
EXPECT RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15-20MM...WITH MOST INTENSE OVER AMAZONIA TO THE SOUTH.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE  
SOF  
42W 44W 46W 49W 52W 54W 57W 60W EW  
16N  
47W 48W 50W 52W 54W 56W 58W 60W TUTT-INDCD  
28N  
55W 58W 60W 63W 65W 67W 69W 71W EW  
12N  
73W 74W 75W 77W 78W DISSIPATES EW  
18N  
 
AN EASTERLY WAVE IS INITIALIZED ALONG 42W. THE ECMWF IS DOING  
SLIGHTLY BETTER THAN THE GFS WITH THE FORECAST OF THIS FEATURE.  
EXPECTING THE WAVE TO REACH FRENCH GUIANA EARLY ON WEDNESDAY  
MORNING...TO FAVOR LIGHT RAINFALL AMOUNTS IN ISOLATED CONVECTION.  
THIS QUICKLY SPREADS ACROSS SURINAME DURING THE MORNING. ACROSS  
GUYANA/NORTHEAST VENEZUELA AND TRINIDAD/TOBAGO THIS IS TO THEN  
SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM.  
 
TUTT INDUCED PERTURBATION IN THE EASTERLY TRADES EXTENDS ALONG 42W  
AND NORTH OF 20N. THIS REACHES THE NORTHEAST CARIBBEAN LATER ON  
THURSDAY. THIS...HOWEVER...IS GOING TO HAVE A HARD TIME OVERCOMING  
NEGATIVE INFLUENCE OF MID LEVEL RIDGE OVER THE NORTHEAST  
CARIBBEAN. AS A RESULT...ONLY EXPECTING LIGHT ISOLATED CONVECTION  
IN ASSOCIATION WITH THIS FEATURE.  
 
AN EASTERLY WAVE ALONG 55W AND SOUTH OF 12N MOVE TO  
GUYANA/SOUTHERN WINDWARD ISLES-NORTHEAST VENEZUELA LATER THIS  
EVENING...TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15-20MM. EARLY ON TUESDAY THIS INCREASES TO 10-15MM/DAY AND MAXIMA  
OF 20-35MM. ACROSS VENEZUELA THIS IS TO THEN FAVOR RAINFALL  
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM ACROSS AMAZONIA TO  
THE SOUTH.  
 
AN ILL ORGANIZED EASTERLY WAVE ALONG 73W IS PHASING WITH  
MEANDERING TROUGH OVER THE CENTRAL CARIBBEAN. MOST ACTIVE  
CONVECTION WITH THIS FEATURE IS EXPECTED OVER WATER ACROSS THE  
CENTRAL CARIBBEAN. EARLY ON TUESDAY MORNING IT IS TO ENHANCE  
CONVECTION ACROSS JAMAICA-EASTERN CUBA TO FAVOR RAINFALL AMOUNTS  
OF 10-15MM/DAY AND MAXIMA OF 20-35MM...WHILE OVER NORTHERN  
COLOMBIA EXPECTING ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF  
15-20MM.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  
 

 
 
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