940  
FXCA20 KWBC 211931  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
231 PM EST THU DEC 21 2017  
 
TROPICAL DISCUSSION FROM DEC 21/12 UTC: A 500 HPA HIGH NORTH OF  
THE YUCATAN ANCHORS A RIDGE THAT EXTENDS FROM THE GULF OF MEXICO  
ACROSS THE CARIBBEAN BASIN TO NORTHERN SOUTH AMERICA. THE RIDGE  
HOLDS ITS GROUND NEARLY UNCHANGED THROUGH FRIDAY EVENING. ON  
SATURDAY...UNDER PRESSURE FROM AN AMPLIFYING POLAR TROUGH OVER  
NORTH AMERICA...THE MID LEVEL HIGH WILL RELOCATE TO THE BAHAMAS  
WHILE THE RIDGE SLOWLY ERODES FROM THE WEST. MEANWHILE...THIS IS  
TO CONTINUE FAVORING A LARGE SCALE SUBSIDENT PATTERN ACROSS MOST  
OF THE CARIBBEAN/CENTRAL AMERICA THAT IS TO INHIBIT ORGANIZED DEEP  
CONVECTION.  
 
AT LOW LEVELS...A HIGH NORTH OF THE ISLANDS SUSTAINS A TIGHT  
PRESSURE GRADIENT AND BRISK NORTHEASTERLY TRADES ACROSS THE  
CARIBBEAN BASIN. ACROSS THE NORTHERN CARIBBEAN THE WINDS PEAK AT  
15-20KT...WHILE OVER THE SOUTHERN CARIBBEAN/CENTRAL AMERICA TO THE  
EASTERN TROPICAL PACIFIC THEY PEAK AT 30-35KT. UNDER PRESSURE FROM  
POLAR FRONT STREAMING TO THE NORTH...THE LOW LEVEL RIDGE IS TO  
COLLAPSE EARLY IN THE CYCLE. AS THE GRADIENT SLACKENS...WINDS  
ACROSS THE NORTHERN CARIBBEAN ISLES WILL DROP TO 10-15KT...WHILE  
OVER THE SOUTHERN CARIBBEAN THE WINDS WILL CONTINUE TO PEAK AT  
30-35KT. OVER PUERTO RICO AND HISPANIOLA THE LIGHTER WINDS WILL  
ALLOW FOR THE DIURNAL HEAT CYCLE TO TAKE SHAPE EARLY IN THE  
PERIOD...WITH AIR MASS CONVECTION COMBINING WITH SEA BREEZE  
CONVERGENCE. ACROSS PUERTO RICO EXPECTING RAINFALL AMOUNTS OF  
00-05MM/DAY AND MAXIMA OF 10MM. OVER THE DOMINICAN REPUBLIC THIS  
IS TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM  
OVER THE NEXT TWO DAYS...DECREASING TO 00-05MM/DAY AND MAXIMA OF  
10MM ON SATURDAY. ACROSS CENTRAL AMERICA THE BRISK EASTERLY TRADES  
WILL ENHANCE MOISTURE CONVERGENCE ACROSS NICARAGUA AND  
HONDURAS...WITH RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15MM. LESSER AMOUNTS ARE EXPECTED ON THE CARIBBEAN COASTAL PLAINS  
OF COSTA RICA AND WESTERN PANAMA. OVER COLOMBIA...AN ILL ORGANIZED  
PANAMANIAN TROUGH IS TO ENHANCE COASTAL CONVERGENCE ALONG THE WEST  
COAST...TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15-25MM. ON FRIDAY-SUNDAY IT INCREASES TO 10-15MM/DAY AND MAXIMA  
OF 20-35MM. ON THE ANDEAN REGION...MEANWHILE...EXPECTING RAINFALL  
AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM.  
 
THE DIGGING POLAR TROUGH MOVES TO THE WESTERN USA EARLY IN THE  
CYCLE...WHERE IT IS TO INTERACT/MERGE WITH A SHORT WAVE TROUGH  
THAT EXTENDS TO THE WEST OF THE BAJA PENINSULA. AS THEY  
MERGE...THE LATTER IS TO SLOWLY LIFT ACROSS THE BAJA PENINSULA TO  
THE NORTHWEST STATES OF MEXICO. MEANWHILE...THIS IS TO DRAW A  
PLUME OF SUBTROPICAL MOISTURE ACROSS SOUTHERN SONORA/NORTHERN  
SINALOA TO CHIHUAHUA WHERE IT IS TO SUSTAIN RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-20MM. ON SATURDAY THE POLAR TROUGH  
WILL RACE ACROSS THE CENTRAL TO THE EASTERN USA. AT LOW  
LEVELS...THIS IS TO SUSTAIN A SURFACE FRONT THAT MOVES ACROSS  
TEXAS TO COAHUILA IN NORTHEAST MEXICO EARLY ON SATURDAY MORNING.  
DURING THE DAY IT SWINGS ACROSS THE NORTHWEST GULF OF MEXICO TO  
TAMAULIPAS/NORTHERN VERACRUZ...MEANWHILE FAVORING STRONG BOUNDARY  
LAYER WINDS OF 30-35KT. THE FRONT IS TO CONTINUE ACROSS THE  
SOUTHERN USA WHILE TRAILING END REMAINS OVER NORTHEAST STATES OF  
MEXICO ON SATURDAY-SUNDAY. ACROSS TAMAULIPAS THIS IS TO THEN FAVOR  
RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MMM ON FRIDAY TO  
SATURDAY...WITH SIMILAR AMOUNTS OVER VERACRUZ ON SATURDAY TO  
SUNDAY.  
 
A SHORT WAVE TROUGH OVER THE WESTERN ATLANTIC...UNDER INFLUENCE OF  
THE MID/UPPER LEVEL RIDGE ENVELOPING THE CARIBBEAN BASIN...IS  
FORECAST TO GRADUALLY AMPLIFY AS IT MOVES ACROSS 50W/55W ON  
FRIDAY. DURING THE DAY ON SATURDAY THIS EVOLVES INTO A TUTT LOW TO  
THE EAST-NORTHEAST OF THE LEEWARD ISLES. AT 250 HPA THIS IS TO  
EXTEND A TROUGH TO THE WEST ACROSS THE NORTHEAST CARIBBEAN ISLES.  
A JET MAXIMA ROUNDING THE BASE OF THE UPPER LEVEL TROUGH IS TO  
THEN EXTEND OVER THE SOUTHEAST CARIBBEAN-WINDWARD ISLES INTO THE  
TROPICAL ATLANTIC. THIS IS TO THEN FAVOR AN UPPER DIVERGENT  
PATTERN ACROSS THE GUIANAS...WHILE OVER THE NORTHEAST CARIBBEAN  
ISLES THIS IS TO CONTINUE FAVORING A MID/UPPER CONVERGENT PATTERN  
THAT IS TO INHIBIT ORGANIZED DEEP CONVECTION THROUGH EARLY NEXT  
WEEK. ALTHOUGH THE TUTT STAYS TO THE EAST OF THE LESSER  
ANTILLES...IT IS TO GENERATE SHALLOW CLOUD CLUSTERS THAT ARE TO  
ADVECT ACROSS THE NORTHEAST CARIBBEAN ISLES FROM TIME-TO-TIME. BUT  
THESE ARE TO ONLY TRIGGER LIGHT RAINFALL AMOUNTS IN PASSING  
SHOWERS. MOST ACTIVE CONVECTION IS EXPECTED TO THE SOUTH AT THE  
DIGGING TUTT INTERACTS WITH THE ITCZ OVER THE GUIANAS. ACROSS THE  
GUIANAS INITIALLY EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15-25MM. ON FRIDAY TO SATURDAY...AS THE TUTT  
DEEPENS...CONVECTION OVER FRENCH GUIANA AND SURINAME IS TO  
INTENSIFY...INCREASING TO 10-15MM/DAY AND MAXIMA OF 20-45MM ON  
FRIDAY...WHILE ON SATURDAY THE MAXIMA PEAKS AT 30-60MM WHILE  
BUILDING WEST ACROSS SURINAME TO NORTHERN GUYANA.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE  
SOF  
39W 41W 44W 46W 48W 51W 54W DISSIPATES TUTT INDCD  
29N  
58W 61W 64W 66W 69W 71W 74W 76W EW  
18N  
 
A TUTT EXTENDING OVER THE CENTRAL TROPICAL ATLANTIC SUSTAINS AN  
INDUCED TROUGH IN THE EASTERLY TRADES WITH AXIS NORTH ALONG 39W TO  
29N. AS IT PROPAGATES ACROSS THE TROPICAL ATLANTIC...AND DECOUPLES  
FROM THE UPPER PERTURBATION...THE WAVE IS FORECAST TO DISSIPATE  
LATER DURING THE WEEKEND. MEANWHILE...AS IT REACHES FRENCH GUIANA  
ON SATURDAY MORNING...IN INTERACTION WITH THE ITCZ IT IS TO  
SUSTAIN RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 30-60MM.  
 
AN EASTERLY WAVE ALONG 58W AND SOUTH OF 18N ENTERS THE ISLAND  
CHAIN EARLY IN THE CYCLE TO FAVOR RAINFALL AMOUNTS OF 00-05MM/DAY  
AND MAXIMA OF 10MM. ON FRIDAY IT IS TO TRIGGER SCATTERED  
CONVECTION ACROSS THE ABC ISLES/NORTHERN VENEZUELA WITH  
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15MM. ACROSS NORTHWEST  
VENEZUELA/MARACAIBO AREA EXPECTING ACCUMULATION OF 00-05MM/DAY AND  
MAXIMA OF 10MM EARLY ON SATURDAY MORNING. ON THE ANDEAN REGION OF  
COLOMBIA THIS IS TO THEN TRIGGER RAINFALL AMOUNTS OF 00-05MM/DAY  
AND MAXIMA OF 10MM.  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON...WPC (USA)  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page