013  
FXCA20 KWBC 051917  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
216 PM EST TUE DEC 05 2017  
 
TROPICAL DISCUSSION FROM DEC 05/12 UTC: THE SYSTEM OF CONCERN IS A  
DEEPENING MID/UPPER LEVEL TROUGH OVER NORTH AMERICA. THROUGH  
THURSDAY AFTERNOON THE HIGH AMPLITUDE TROUGH IS TO DEEPEN ACROSS  
THE CENTRAL USA WHILE TRAILING ACROSS TEXAS TO THE NORTHERN STATES  
OF MEXICO. AT LOW LEVELS...THE POLAR TROUGH SUSTAINS A SURFACE  
FRONT THAT IS TO MOVE ACROSS TEXAS TO COAHUILA IN NORTHERN MEXICO  
BY MIDDAY TODAY. ON WEDNESDAY MORNING THE FRONT MOVES TO THE  
NORTHWEST GULF WHILE TRAILING ACROSS THE NORTHERN STATES OF  
MEXICO. A 30-35KT NORTHERLY WIND SURGE ACROSS THE WESTERN GULF 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. LATER ON FRIDAY THE FRONT MOVES OVER THE  
YUCATAN WHILE TRAILING TO THE SOUTHERN STATES OF MEXICO. 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 20-35MM. NOTE THAT DURING THAT PERIOD  
THERE IS A CHANCE FOR SCATTERED SNOW SHOWERS TO AFFECT HIGHER  
ELEVATIONS OF CHIHUAHUA AND COAHUILA. ON THURSDAY SOLID  
PRECIPITATION WILL PREVAIL...WITH SNOWFALL AMOUNTS OF 15-20CM AND  
MAXIMA OF 25-50CM. 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 20-35MM/DAY ON WEDNESDAY THROUGH FRIDAY. OVER THE  
NORTHWEST BAHAMAS...PREFRONTAL CONVECTION ON FRIDAY IS TO TRIGGER  
RAINFALL AMOUNTS 10-15MM/DAY AND MAXIMA OF 20-35MMM...WHILE OVER  
WESTERN CUBA EXPECTING ACCUMULATION OF 15-20MM/DAY AND MAXIMA OF  
25-50MM. THIS AFFECTS THE CAYMAN ISLES EARLY ON SATURDAY  
MORNING...WITH ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF 20-35MM.  
 
THE DEEPENING POLAR TROUGH OVER THE USA IT IS TO THEN INDUCE THE  
NORTHWARD AMPLIFICATION OF A MID/UPPER LEVEL RIDGE FROM THE  
CARIBBEAN NORTHWARD TO THE WESTERN ATLANTIC ON WEDNESDAY-THURSDAY.  
AS THE RIDGE BUILDS ACROSS THE WESTERN ATLANTIC IT IS TO DISPLACE  
A TROUGH THAT LIES OVER THE CENTRAL-WESTERN ATLANTIC...WITH TROUGH  
AXIS TO CONFINE TO THE CENTRAL ATLANTIC LATER ON THURSDAY.  
MEANWHILE...A SHORT WAVE TROUGH EAST OF THE BAHAMAS EARLY THIS  
MORNING IS TO MOVE NORTH OF HISPANIOLA/PUERTO RICO LATER  
TODAY...TO THEN MERGE INTO BROAD TROUGH PATTERN TO THE EAST. AT  
250 HPA THE SHORT WAVE PERTURBATION WILL SUSTAIN RAPID  
INTENSIFICATION OF A SUBTROPICAL JET MAXIMA NORTH OF THE ISLANDS.  
THIS IS TO SUSTAIN A DIVERGENT PATTERN ACROSS THE NORTHEAST  
CARIBBEAN THROUGH THURSDAY MORNING.  
 
THE TROUGH ALOFT SUSTAINS A MEANDERING FRONT THAT LIES OVER THE  
WESTERN ATLANTIC JUST NORTH OF PUERTO RICO-HISPANIOLA TO THE  
SOUTHEAST BAHAMAS-CUBA. A RIDGE TO THE NORTH OF THIS BOUNDARY  
FAVORS A TIGHT GRADIENT ACROSS THE BASIN...WITH BOUNDARY LAYER  
WINDS OF 18-21KT EXPECTED TO DOMINATE THE NORTHERN CARIBBEAN ISLES  
LATER TODAY...WHILE ACROSS THE CENTRAL CARIBBEAN THE WINDS ARE TO  
PEAK AT 25-30KT. THIS ALSO FAVORS A PREFRONTAL SHEAR LINE OVER THE  
VIRGIN ISLES-PUERTO RICO EARLY THIS MORNING...MOVING ACROSS THE  
LEEWARD ISLES LATER TODAY. THE SHEAR LINE RAPIDLY MOVES ACROSS THE  
WINDWARD ISLES EARLY ON WEDNESDAY...REACHING GUYANA ON WEDNESDAY  
AFTERNOON. SIMULTANEOUSLY...THE BRISK EASTERLY TRADES ARE TO  
SUSTAIN A COLD ADVECTIVE PATTERN...WITH SURFACE FRONT SAGGING  
ACROSS THE VIRGIN ISLES TO EASTERN PUERTO RICO ON WEDNESDAY. THE  
FRONT IS TO REMAIN NEARLY STATIONARY WHILE GRADUALLY WEAKENING  
LATER IN THE WEEK. AS MOISTURE CONVERGES ALONG THIS  
BOUNDARY...EXPECTING PWAT CONTENT OF 40-45MM TO PERSIST OVER THE  
NEXT THREE DAYS. LATER IN THE WEEK A DRYER AIR MASS IS TO ENTRAIN  
ACROSS THE NORTHEAST CARIBBEAN FROM THE EAST.  
 
THE STRONGER TRADES ARE TO FAVOR GENERATION OF STREAMERS ACROSS  
THE LEEWARD/VIRGIN ISLES THAT ARE TO AFFECT EASTERN PUERTO RICO  
FROM TIME-TO-TIME. COLD ADVECTION OVER THE WARMER WATERS TO THE  
NORTH OF THE ISLANDS WILL ALSO FAVOR CONVECTIVE INSTABILITY AND  
GENERATION OF TRADE WIND SHOWERS. ADD FRONTAL CONVERGENCE TO THE  
MIX AND MODERATE TO HEAVY RAINS ARE TO AFFECT THE NORTHEAST  
CARIBBEAN ISLES DURING THE NEXT THREE DAYS. EARLY IN THE  
CYCLE...AS THE FRONT MEANDERS OVER THE BAHAMAS/TURKS-EASTERN  
CUBA...IT IS TO FAVOR RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA  
OF 10MM. THROUGH THURSDAY THIS INCREASES TO 05-10MM/DAY AND MAXIMA  
OF 15-25MM. ACROSS THE DOMINICAN REPUBLIC-PUERTO RICO AND THE  
VIRGIN ISLES EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA  
OF 20-35MM. THROUGH THURSDAY THIS DECREASES TO 05-10MM/DAY AND  
MAXIMA OF 15-25MM. OVER THE LEEWARD AND FRENCH ISLES...SHEAR LINE  
CONVERGENCE IS TO SUSTAIN RAINFALL AMOUNTS OF 10-15MM/DAY AND  
MAXIMA OF 20-40MM EARLY IN THE CYCLE. ON WEDNESDAY THIS DECREASES  
TO 05-10MM/DAY AND MAXIMA OF 15-20MM. ACROSS EASTERN VENEZUELA TO  
NORTHERN GUYANA THE SHEAR LINE WILL THEN SUSTAIN RAINFALL AMOUNTS  
OF 10-15MM/DAY AND MAXIMA OF 20-35MM ON WEDNESDAY...WITH SIMILAR  
AMOUNTS OVER SURINAME TO FRENCH GUIANA ON THURSDAY-FRIDAY.  
 
AT 250 HPA...A MEANDERING TUTT EXTENDS ACROSS GUATEMALA TO A LOW  
OVER THE TROPICAL PACIFIC NEAR 02N 100W. TUTT PATTERN ALOFT TENDS  
TO INTENSIFY LATER IN THE WEEK. AS IT MEANDERS OVER THE EASTERN  
PACIFIC THE TUTT WILL DRAW 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 05-0MM/DAY AND MAXIMA OF 15-25M. ON  
WEDNESDAY THIS INCREASES ACROSS THE CAUCA VALLEY TO THE SOUTHWEST  
TO 10-15MM/DAY AND MAXIMA OF 20-35MM. ON THE ANDEAN REGION AND  
ACROSS EASTERN COLOMBIA/AMAZONIA EXPECTING RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-20MM.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
57W 59W 62W 65W 68W 70W 72W 74W EW 11N  
76W 78W 81W 83W 85W 87W 90W 92W EW 17N  
 
AN EASTERLY WAVE ALONG 57W AND SOUTH OF 11N IN INTERACTION WITH  
THE ITCZ IS TO TRIGGER SCATTERED CONVECTION ACROSS NORTHERN  
GUYANA-NORTHEAST VENEZUELA-TRINIDAD/TOBAGO...WITH RAINFALL AMOUNTS  
OF 10-15MM/DAY AND MAXIMA OF 20-35MM THROUGH WEDNESDAY MORNING.  
ACROSS EASTERN-CENTRAL VENEZUELA THIS IS TO THEN SUSTAIN RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM...WITH MOST INTENSE  
ACROSS AMAZONIA TO THE SOUTH. ACROSS COLOMBIA THIS IS TO ALSO  
SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM ON  
THURSDAY-FRIDAY.  
 
AN EASTERLY WAVE ALONG 76W AND SOUTH OF 17N WILL SUSTAIN SCATTERED  
CONVECTION ACROSS 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. ON THURSDAY-FRIDAY THIS INCREASES TO  
15-20MM/DAY AND MAXIMA OF 25-50MM.  
 
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  
 

 
 
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