510  
FXCA20 KWBC 041909  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
209 PM EST MON DEC 04 2017  
 
TROPICAL DISCUSSION FROM DEC 04/12 UTC: AMPLIFYING MID/UPPER LEVEL  
TROUGH OVER THE USA IS TO PRESS AGAINST A SHORT WAVE RIDGE  
EXTENDING OVER MEXICO-NORTHERN CENTRAL AMERICA. UNDER PRESSURE THE  
RIDGE IS FORECAST TO GRADUALLY WEAKEN THROUGH WEDNESDAY EVENING.  
AT LOW LEVELS...THE POLAR TROUGH SUSTAINS A SURFACE FRONT THAT IS  
TO MOVE ACROSS TEXAS TO COAHUILA IN NORTHERN MEXICO BY MIDDAY ON  
TUESDAY. ON WEDNESDAY MORNING THE FRONT MOVES TO THE NORTHWEST  
GULF WHILE TRAILING ACROSS THE NORTHERN STATES OF MEXICO. A  
30-35KT NORTHERLY WIND SURGE IS TO THEN DISPLACE THIS BOUNDARY  
SOUTH ACROSS THE FLORIDA PENINSULA ON WEDNESDAY-THURSDAY...WHILE  
TRAILING ACROSS THE GULF OF MEXICO TO THE STATE OF VERACRUZ. THE  
STRONG NORTHERLY WINDS ACROSS THE WESTERN GULF OF MEXICO ARE TO  
PERSIST THROUGH THE END OF THE WEEK...MEANWHILE FAVORING A  
TEHUANTEPECER JET OF 35-45KT. AS IT MEANDERS INTO THE NORTHERN  
STATES OF MEXICO THE FRONT IS TO INITIALLY FAVOR LIGHT TO MODERATE  
CONVECTION...WITH ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15MM.  
ON WEDNESDAY THIS IS TO BECOME BETTER ORGANIZED...WITH CONVECTION  
ACROSS NORTHERN CHIHUAHUA-COAHUILA TO TRIGGER RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-30MM. NOTE THAT DURING THAT PERIOD  
THERE IS A CHANCE FOR SCATTERED SNOW SHOWERS TO AFFECT HIGHER  
ELEVATIONS OF CHIHUAHUA AND COAHUILA. ACROSS THE STATE OF VERACRUZ  
MOST ACTIVE IS EXPECTED TO THE SOUTH...TO ALSO AFFECT NORTHERN  
PORTIONS OF CHIAPAS WHERE IT IS TO FAVOR RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-30MM.  
 
AS THE POLAR TROUGH DEEPENS ACROSS THE USA IT IS TO INDUCE THE  
NORTHWARD AMPLIFICATION OF A MID/UPPER LEVEL RIDGE ACROSS THE  
EASTERN USA/WESTERN ATLANTIC. THIS IS TO SLOWLY YIELD TO THE POLAR  
TROUGH...SETTLING OVER THE ATLANTIC TO THE WEST OF 60W AND NORTH  
OF 20N LATER ON TUESDAY/WEDNESDAY MORNING. DOWNSTREAM FROM THE  
RIDGE...A TROUGH TO THE EAST DOMINATES THE FLOW NORTH OF THE  
GREATER ANTILLES. CONSISTENT WITH PREVIOUS FORECASTS...A 500/250  
HPA SHORT WAVE TROUGH ON THE SOUTHERN STREAM EXITS FLORIDA LATER  
THIS AFTERNOON. EARLY ON TUESDAY THIS IS TO QUICKLY MOVE NORTH OF  
HISPANIOLA/PUERTO RICO WHILE GRADUALLY MERGING INTO BROAD TROUGH  
PATTERN TO THE EAST. AS THEY MERGE...THIS IS TO SUSTAIN THE  
GRADUAL INTENSIFICATION OF A SUBTROPICAL JET MAXIMA TO THE NORTH  
OF PUERTO RICO/VIRGIN ISLES. DIVERGENCE ON ITS RIGHT ENTRANCE  
REGION IS TO THEN VENT CONVECTIVE DEVELOPMENT OVER THE NORTHEAST  
CARIBBEAN ON TUESDAY-THURSDAY.  
 
AT LOW LEVELS...A FRONT EXTENDS ACROSS THE WESTERN NORTH ATLANTIC  
ALONG 21N/22N TO THE SOUTHEAST BAHAMAS/TURKS AND CAICOS-CUBA. OVER  
THE EASTERN CARIBBEAN...THE MEANDERING FRONT TO THE NORTH SUSTAINS  
AN INDUCED/PREFRONTAL TROUGH EAST OF THE ISLAND CHAIN. THE TROUGH  
FAVORS A MOIST SOUTHEASTERLY FLOW ACROSS THE WINDWARD ISLES TO THE  
EASTERN CARIBBEAN...WITH DEEP MOISTURE POOLING ACROSS SAINT  
CROIX/SOUTHERN PUERTO RICO. LATER TODAY A LOW LEVEL RIDGE IS TO  
ROLL ACROSS THE EASTERN USA TO THE WESTERN ATLANTIC. THIS IS TO  
THEN DOMINATE THE FLOW NORTH OF THE ISLANDS THROUGH THE END OF THE  
WEEK. AS THE PRESSURE GRADIENT TIGHTENS LATER TODAY... A  
PREFRONTAL SHEAR LINE FORMS OVER PUERTO RICO LATER THIS EVENING.  
OVERNIGHT THIS MOVES ACROSS THE ISLAND... REACHING THE NORTHERN  
VIRGIN ISLES EARLY ON TUESDAY MORNING. LATER IN THE DAY IT  
CONTINUES TO THE LEEWARD ISLES-EASTERN CARIBBEAN. ON WEDNESDAY IT  
MOVES FARTHER SOUTH INTO THE TROPICAL ATLANTIC WHILE EXTENDING TO  
NORTHEASTERN VENEZUELA. AS THE SHEAR LINE MOVES ACROSS PUERTO RICO  
THE LOW LEVEL WINDS OVER THE NORTHEAST CARIBBEAN ARE FORECAST TO  
BACK TO THE EAST WHILE INCREASING TO 15-20KT. BREEZY CONDITIONS  
ARE FORECAST TO PERSIST THROUGH THE END OF THE WORKWEEK...TO  
TRIGGER STREAMERS ACROSS THE LESSER ANTILLES THAT AFFECT THE  
VIRGIN ISLES AND PUERTO RICO FROM TIME-TO-TIME. THIS WILL ALSO  
FAVOR A COLD ADVECTIVE PATTERN...WITH WANING SURFACE FRONT SAGGING  
ACROSS THE NORTHERN VIRGIN ISLES TO EASTERN PUERTO RICO ON  
WEDNESDAY. A DRYER AIR MASS IS TO THEN ENTRAIN FROM THE EAST ON  
FRIDAY-SATURDAY. AS THE FRONT MEANDERS OVER THE  
BAHAMAS/TURKS-EASTERN CUBA IT IS TO FAVOR RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15MM. ACROSS THE DOMINICAN REPUBLIC THIS  
IS TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM IN  
PREFRONTAL CONVECTION. THROUGH WEDNESDAY THIS INCREASES TO  
10-15MM/DAY AND MAXIMA OF 20-30MM. OVER PUERTO RICO AND THE VIRGIN  
ISLANDS...UNDER INFLUENCE OF THE SHEAR LINE...INITIALLY EXPECTING  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-30MM. ON  
WEDNESDAY-THURSDAY EXPECTING SIMILAR AMOUNTS AS THE FRONT SAGS  
ACROSS THE ISLANDS. OVER THE LEEWARD ISLES...SHEAR LINE  
CONVERGENCE IS TO SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15-25MM. ACROSS EASTERN VENEZUELA TO NORTHERN GUYANA THE  
SHEAR LINE WILL THEN SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15MM ON WEDNESDAY.  
 
AT 250 HPA...A TUTT EXTENDS ACROSS HONDURAS/EL SALVADOR TO THE  
EASTERN TROPICAL PACIFIC...WITH AXIS BOTTOMING OUT ALONG THE  
EQUATOR. THIS IS DRAWING A SUBEQUATORIAL JET MAXIMA ACROSS THE  
EASTERN PACIFIC TO SOUTHERN CENTRAL AMERICA. THE JET ALOFT IS TO  
VENT ITCZ RELATED CONVECTION ACROSS PANAMA-COSTA RICA...WHERE WE  
EXPECT RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. OVER  
WESTERN COLOMBIA...UNDER INFLUENCE OF THE PANAMANIAN  
LOW/TROUGH...DEEP MOISTURE IS TO CONVERGE ALONG THE COAST...TO  
FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM. A  
LULL IN ACTIVITY IS EXPECTED ON TUESDAY...WITH ACCUMULATION OF  
05-10MM/DAY AND MAXIMA OF 15-20M...WHILE ON WEDNESDAY THE MAXIMA  
INCREASES TO 20-30MM.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
52W 54W 57W 60W 63W 65W 67W 69W EW 15N  
70W 73W 75W 77W 80W 81W 82W 83W EW 16N  
 
AN EASTERLY WAVE ALONG 52W AND SOUTH OF 15N IS TO MOVE ACROSS  
FRENCH GUIANA TO SURINAME EARLY IN THE CYCLE...TO FAVOR RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. BY MIDMORNING ON  
TUESDAY IT MOVES ACROSS GUYANA TO EASTERN VENEZUELA-TRINIDAD AND  
TOBAGO...WHERE IN INTERACTION WITH THE ATLANTIC ITCZ EXPECTING  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM. ACROSS  
EASTERN-CENTRAL VENEZUELA THIS IS TO THEN SUSTAIN RAINFALL AMOUNTS  
OF 05-10MM/DAY AND MAXIMA OF 15MM...WITH MOST INTENSE ACROSS  
AMAZONIA TO THE SOUTH.  
 
AN EASTERLY WAVE ALONG 70W AND SOUTH OF 16N WILL SUSTAIN SCATTERED  
CONVECTION ACROSS NORTHWEST VENEZUELA-NORTHERN COLOMBIA...WITH  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. OVER PANAMA  
THIS WILL THEN TRIGGER SIMILAR RAINFALL AMOUNTS. HOWEVER...OVER  
EASTERN NICARAGUA THIS WILL COMBINE WITH A TRADE WIND SURGE TO  
FAVOR MODERATE RAINFALL AMOUNTS ON WEDNESDAY...WITH ACCUMULATION  
OF 10-15MM/DAY AND MAXIMA OF 20-35MM.  
 
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  
 

 
 
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