702  
FXCA20 KWBC 281928  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
228 PM EST THU DEC 28 2017  
 
TROPICAL DISCUSSION FROM DEC 28/12 UTC: AT 250 HPA...BROAD UPPER  
LEVEL RIDGE DOMINATES THE FLOW ACROSS THE CARIBBEAN BASIN. AN  
ANTICYCLONICALLY CURVED SUBTROPICAL JET BOUNDS THE NORTHERN  
FRINGES OF THIS RIDGE WHILE EXTENDING OVER THE GREATER ANTILLES.  
UPPER LEVEL RIDGE IS TO HOLD ITS GROUNDS AS POLAR TROUGH OVER THE  
EASTERN USA-WESTERN ATLANTIC STRENGTHENS DURING THE NEXT FEW DAYS.  
THIS IS TO TIGHTEN THE GRADIENT FAVORING GRADUAL INTENSIFICATION  
OF JET FLOW ACROSS THE BAHAMAS INTO THE ATLANTIC NORTH OF THE  
GREATER ANTILLES. A WANING TUTT TO THE WEST EXTENDS NORTH-TO-SOUTH  
ACROSS THE CAMPECHE SOUND-THE SOUTHERN STATES OF MEXICO TO THE  
EASTERN PACIFIC. THE UPPER LEVEL SHORT WAVE TROUGH IS TO SLOWLY  
LIFT OVER THE RIDGE TO THE EAST...PULLING ACROSS GUATEMALA-THE  
YUCATAN LATER THIS EVENING. IT IS TO THEN RAPIDLY WEAKEN WHILE  
SHEARING ACROSS CUBA-THE BAHAMAS ON FRIDAY. EARLY IN THE  
CYCLE...AS IT MEANDER OVER SOUTHERN MEXICO/NORTHERN CENTRAL  
AMERICA...THE TROUGH IS TO VENT CONVECTIVE DEVELOPMENT. AT LOW  
LEVELS...BRISK NORTHEASTERLY TRADES CONTINUE TO CONVERGE ALONG A  
SHEAR LINE THAT IS TO MEANDER OVER THE WESTERN CARIBBEAN. THIS  
WILL ENHANCE LOW LEVEL MOISTURE CONVERGENCE ACROSS THE ISLAS DE LA  
BAHIA/GULF OF HONDURAS-NORTHEAST GUATEMALA AND BELIZE. DURING THE  
DAY TODAY EXPECTING RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF  
35-70MM. AS THE TROUGH WEAKENS THIS DECREASES TO 10-15MM/DAY AND  
MAXIMA OF 20-40MM WHILE SPREADING NORTH ALONG THE COAST OF BELIZE  
TO QUINTANA ROO OVER SOUTHERN MEXICO. ON SATURDAY THIS IS TO THEN  
FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. THE  
UPPER TROUGH IS TO ALSO ENHANCE CONVECTION ACROSS NORTHERN  
CHIAPAS-SOUTHERN VERACRUZ AND NORTHERN GUATEMALA...WITH RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM THROUGH FRIDAY  
MORNING.  
 
AT MID LEVELS...A WEST-TO-EAST RIDGE EXTENDS FROM THE GULF OF  
MEXICO ACROSS THE NORTHERN CARIBBEAN ISLES...WHERE IT SUSTAINS AN  
ELEVATED CAP INVERSION. UNDER PRESSURE FROM DEEPENING POLAR TROUGH  
TO THE WEST AND NORTH...THE RIDGE IS TO GRADUALLY WEAKEN FROM THE  
WEST. IN THIS PROCESS THE RIDGE AXIS IS FORECAST TO COLLAPSE BY  
MIDDAY ON SATURDAY. ALTHOUGH THE RIDGE WEAKENS...THE TRADE WINDS  
CAP OVER THE NORTHERN CARIBBEAN TENDS TO HOLD THROUGHOUT THE  
WEEKEND. HOWEVER...ON SATURDAY...IT IS EXPECTED TO WEAKEN ENOUGH  
TO ALLOW FOR DEEPER MOISTURE TO POOL ACROSS THE NORTHEAST  
CARIBBEAN ISLES. EARLY NEXT WEEK THE RIDGE TRIES TO BOUNCE BACK  
WHILE SLOWLY BUILDING FROM THE WEST. BUT IT IS GOING TO HAVE A  
HARD TIME OVERCOMING INFLUENCE OF BROAD POLAR TROUGH PATTERN  
ESTABLISHING OVER THE WESTERN ATLANTIC.  
 
AT LOW LEVELS THE UPPER LEVEL TROUGH SUSTAINS A MEANDERING FRONT  
ACROSS FLORIDA-GULF TO THE RIO BRAVO BASIN IN NORTHEAST MEXICO. ON  
FRIDAY-SATURDAY...AS A LOW FORMS OFF THE COAST OF FLORIDA...THE  
FRONT IS TO MEANDER ACROSS THE NORTHEAST BAHAMAS-SOUTH  
FLORIDA/FLORIDA KEYS TO THE GULF OF MEXICO...WHERE IT IS TO REMAIN  
THROUGHOUT THE WEEKEND/EARLY NEXT WEEK. ALSO AT LOW LEVELS...THE  
MEANDERING FRONT IS TO SUSTAIN A PREFRONTAL SHEAR LINE THAT MOVES  
ACROSS THE TURKS AND CAICOS-WINDWARD PASSAGE TO JAMAICA LATER  
TODAY. THIS WEAKENS EARLY ON FRIDAY MORNING AS A NEW ONE FORMS  
OVER THE SOUTHEAST BAHAMAS-EASTERN CUBA-CAYMAN ISLES LATER IN THE  
DAY. EARLY IN THE PERIOD THIS IS TO FAVOR MODERATE RAINFALL  
AMOUNTS ACROSS THE TURKS AND CAICOS-EASTERN PORTIONS OF CUBA WITH  
ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF 20-30MM. ACROSS JAMAICA  
IT IS TO ONLY FAVOR RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF  
10MM. ON FRIDAY ACTIVITY ACROSS THE SOUTHEAST BAHAMAS-EASTERN CUBA  
WILL RESULT IN RAINFALL ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF  
15MM...WHILE OVER THE CAYMAN ISLES EXPECTING MAXIMA OF 15-20MM.  
OVER NORTHEAST MEXICO...ALONG THE TRAILING END OF THE SURFACE  
FRONT...ONLY EXPECTING LIGHT CONVECTION WITH ACCUMULATION OF  
00-05MM/DAY...WHILE ACROSS NORTHERN VERACRUZ/SOUTHERN TAMAULIPAS  
EXPECTING ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15MM.  
 
EAST OF THE MID LEVEL RIDGE...A TUTT LOW NEAR 25N 37W IS TO EXTEND  
A TROUGH TO THE WEST-SOUTHWEST ACROSS THE WINDWARD ISLES TO THE  
SOUTHEAST CARIBBEAN/NORTHERN VENEZUELA LATER TODAY. AS THE RIDGE  
OVER THE NORTHERN CARIBBEAN COLLAPSES...THE TUTT IS TO THEN  
GRADUALLY LIFT TO THE EAST-NORTHEAST LATER ON FRIDAY-SATURDAY.  
MEANWHILE...AS IT MEANDERS OVER THE TROPICAL ATLANTIC...THE MID  
LEVEL TROUGH IS INDUCING EASTERLY WAVES IN THE LOW/MID LEVEL  
EASTERLY TRADES. THESE CONTINUE TO STREAM ACROSS THE LESSER  
ANTILLES/EASTERN CARIBBEAN...THEN WEAKEN AS THEY REACH THE CENTRAL  
CARIBBEAN/CENTRAL AMERICA (SEE BELOW FOR DETAILS). PATCHY CLOUD  
CLUSTERS ACCOMPANY THESE PERTURBATIONS...TRIGGERING  
MODERATE/LOCALLY HEAVY RAINFALL AMOUNTS ACROSS PUERTO RICO-THE  
DOMINICAN REPUBLIC. IN THESE ISLANDS EXPECTING RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-30MM TODAY...WHILE ON SATURDAY THE  
MAXIMA IS TO PEAK AT 20-45MM. ON FRIDAY EXPECTING LESSER AMOUNTS  
WITH ACCUMULATION OF 00-05MM/DAY AND MAXIMA OF 10MM. OVER THE  
LEEWARD ISLES THIS IS TO ALSO FAVOR RAINFALL AMOUNTS OF  
00-05MM/DAY AND ISOLATED MAXIMA OF 10MM...INCREASING TO  
05-10MM/DAY AND MAXIMA OF 15MM ON SATURDAY. HIGHER AMOUNTS ARE  
EXPECTED ACROSS THE WINDWARD ISLES-NORTHERN VENEZUELA/ABC  
ISLES...WITH ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-20MM/DAY  
OVER THE NEXT COUPLE OF DAYS. OVER TRINIDAD-ORINOCO DELTA-NORTHERN  
GUYANA EXPECTING RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF  
35-70MM. ON FRIDAY THROUGH SATURDAY THE DAILY MAXIMA IS TO THEN  
PEAK AT 30-60MM. ACROSS SURINAME TO FRENCH GUIANA EXPECTING  
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-25MM/DAY.  
 
OVER THE EASTERN PACIFIC...A WELL ORGANIZED CELL OF THE PANAMANIAN  
LOW IS TO MEANDER OFF THE WEST COAST OF COLOMBIA WHILE ANCHORING A  
SHORT WAVE TROUGH ALONG THE COAST. THE LOW LIFTS NORTH TO THE GULF  
OF PANAMA LATER ON FRIDAY...WHILE THE TROUGH REMAINS OFF THE  
COAST. THIS IS TO FAVOR A MOIST SOUTHERLY FLOW ACROSS WESTERN  
COLOMBIA THAT IS TO ENHANCE COASTAL CONVERGENCE. IN THIS AREA  
EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF  
20-35MM...WITH LOCALLY HIGHER AMOUNTS HIGHLY PROBABLE. OVER THE  
ANDES EXPECTING LESSER AMOUNTS...WITH ACCUMULATION OF 00-05MM/DAY  
AND MAXIMA OF 10MM. ON FRIDAY-SATURDAY THIS INCREASES TO  
05-10MM/DAY AND MAXIMA OF 15-20MM.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE  
SOF  
53W 56W 58W 61W 64W 67W 70W 73W TUTT INDCD  
26N  
65W 68W 71W 74W 77W 79W 81W 83W TUTT INDCD  
21N  
73W 75W 77W 79W 83W DISSIPATES EW  
18N  
78W 80W 81W DISSIPATES EW  
16N  
 
A TUTT INDUCED PERTURBATION IN THE EASTERLY TRADES IS INITIALIZED  
ALONG 53W TO 26N. THIS ENTERS THE LEEWARD ISLES LATER ON FRIDAY TO  
FAVOR RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM. THE WAVE  
MOVES ACROSS THE VIRGIN ISLES TO EASTERN PUERTO RICO EARLY ON  
SATURDAY MORNING TO SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15MM. AS IT ENTERS PUERTO RICO LATER IN THE MORNING THIS  
WILL COINCIDE WITH WEAKENING OF MID LEVEL RIDGE PATTERN...TO ALLOW  
FOR DEEPER MOISTURE AND A HIGHER POTENTIAL FOR SCATTERED  
CONVECTION. DURING THAT PERIOD EXPECTING RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-45MM...TO GRADUALLY BUILD WEST ACROSS  
THE DOMINICAN REPUBLIC ON SUNDAY MORNING.  
 
A TUTT INDUCED PERTURBATION ALONG 65W AND SOUTH OF 21N IS  
STREAMING ACROSS PUERTO RICO TO THE DOMINICAN REPUBLIC...WITH  
PLUME OF SHALLOW MOISTURE PROPAGATING IN TANDEM WITH THIS FEATURE.  
ACROSS PUERTO RICO THIS IS TO FAVOR RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-30MM...WITH POTENTIAL FOR LOCALLY  
HIGHER AMOUNTS ACROSS WESTERN INTERIOR PORTIONS OF THE ISLAND.  
SIMILAR AMOUNTS ARE EXPECTED ACROSS THE DOMINICAN REPUBLIC LATER  
TODAY-FRIDAY MORNING. OVER THE ABC ISLES-NORTHERN VENEZUELA THIS  
WILL SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15-20MM. ACROSS COLOMBIA TO THE DARIEN IN EASTERN PANAMA THIS IS  
TO THEN TRIGGER RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM.  
 
A WANING EASTERLY WAVE ALONG 73W AND SOUTH OF 18N IS TO FAVOR  
SCATTERED CONVECTION ACROSS NORTHERN COLOMBIA-EASTERN PANAMA EARLY  
IN THE PERIOD...WITH ACCUMULATION OF 00-05MM/DAY AND MAXIMA OF  
10MM. ACROSS JAMAICA THIS IS TO INTERACT WITH THE SHEAR LINE TO  
FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. THE  
WAVE IS TO THEN DISSIPATE EARLY ON SATURDAY MORNING.  
 
A WEAK EASTERLY WAVE ALONG 78W AND SOUTH OF 16N IS TO ALSO  
DISSIPATE EARLY IN THE CYCLE. MEANWHILE...THIS WILL FAVOR LIGHT  
CONVECTION ACROSS JAMAICA AND EASTERN PANAMA...WITH ACCUMULATION  
OF 00-05MM/DAY AND MAXIMA OF 10MM.  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON...WPC (USA)  
 

 
 
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