578  
FXCA20 KWBC 291751  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1251 PM EST FRI DEC 29 2017  
 
TROPICAL DISCUSSION FROM DEC 29/12 UTC: A BROAD UPPER LEVEL RIDGE  
REMAINS THE DOMINANT FEATURE ACROSS THE CARIBBEAN  
BASIN....DOMINATING THE FLOW ACROSS NORTHERN SOUTH AMERICA-CENTRAL  
AMERICA-NORTHERN CARIBBEAN ISLES. AN ANTICYCLONICALLY CURVED  
SUBTROPICAL JET LIES ALONG THE NORTHERN FRINGES OF THIS RIDGE...AS  
IT EXTENDS OVER THE SOUTHWEST ATLANTIC/THE GREATER ANTILLES. POLAR  
TROUGH OVER THE USA-WESTERN ATLANTIC WILL PRESS AGAINST THIS  
RIDGE. AS THE GRADIENT TIGHTENS...THE JET IS TO GRADUALLY  
INTENSIFY AS IT MEANDERS OVER THE BAHAMAS-NORTH OF THE ISLANDS. A  
WANING TUTT OVER THE YUCATAN IS TO RAPIDLY LIFT OVER THIS RIDGE TO  
CUBA DURING THE DAY TODAY. EARLY IN THE CYCLE THIS IS TO ENHANCE  
CONVECTIVE DEVELOPMENT ACROSS THE NORTHWEST CARIBBEAN...WHERE  
UNDER THE INFLUENCE OF A PREFRONTAL SHEAR LINE EXPECTING RAINFALL  
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM TO CLUSTER ACROSS  
BELIZE-QUINTANA ROO-NORTHWEST HONDURAS AND EASTERN GUATEMALA. ON  
SATURDAY-SUNDAY...AS THE TUTT WEAKENS...THIS WILL DECREASE TO  
05-10MM/DAY AND MAXIMA OF 15-20MM. THE UPPER TROUGH IS TO ALSO  
ENHANCE CONVECTION ACROSS NORTHERN CHIAPAS-SOUTHERN VERACRUZ AND  
NORTHERN GUATEMALA EARLY IN THE CYCLE...WITH RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15MM THROUGH SATURDAY MORNING.  
 
AS THE POLAR TROUGH DEEPENS ACROSS THE WESTERN ATLANTIC...IT IS TO  
PRESS AGAINST A MID LEVEL RIDGE OVER THE NORTHERN  
CARIBBEAN/GREATER ANTILLES. UNDER PRESSURE FROM THIS TROUGH THE  
RIDGE IS TO GRADUALLY ERODE FROM THE WEST...AND LATER ON SATURDAY  
IT IS TO COMPLETELY COLLAPSE. ALTHOUGH MID LEVEL RIDGE PATTERN  
WEAKENS...UNDER INFLUENCE OF UPPER LEVEL RIDGE AND JET MAXIMA TO  
THE NORTH...AN ELEVATED SUBSIDENCE CAP IS TO PERSIST ACROSS THE  
NORTHERN CARIBBEAN. THIS INVERSION WILL BE STRONG ENOUGH TO  
INHIBIT ORGANIZED DEEP CONVECTION...BUT NOT STRONG ENOUGH TO  
SUPPRESS SHALLOW CONVECTIVE DEVELOPMENT. AT LOW LEVELS SHALLOW  
CLOUD CLUSTERS ARE TO ADVECT ACROSS THE NORTHEAST CARIBBEAN IN  
ASSOCIATION WITH TUTT INDUCED EASTERLY WAVES STREAMING FROM THE  
TROPICAL ATLANTIC TO THE EASTERN/CENTRAL CARIBBEAN. THIS PATTERN  
PERSISTS THROUGH SUNDAY MORNING WHEN A DRYER AIR MASS ENTRAINS  
FROM THE EAST ACROSS THE LEEWARD ISLES TO THE VIRGIN ISLES-PUERTO  
RICO-DOMINICAN REPUBLIC. DEEPER MOISTURE...HOWEVER...IS TO  
CONVERGE TO THE SOUTH ACROSS THE ABC ISLANDS-NORTHERN VENEZUELA TO  
TRINIDAD/THE GRENADINES-NORTHERN GUYANA DURING THE NEXT FEW DAYS.  
 
ALSO AT LOW LEVELS...THE UPPER LEVEL TROUGH SUSTAINS A MEANDERING  
FRONT ACROSS FLORIDA-GULF OF MEXICO 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 WHILE TRAILING ACROSS THE GULF  
OF MEXICO...WHERE IT IS TO REMAIN THROUGHOUT THE WEEKEND/EARLY  
NEXT WEEK. AS THE FRONT MEANDERS SOUTH ACROSS THE BAHAMAS IT IS TO  
SUSTAIN A PREFRONTAL SHEAR LINE ACROSS THE BAHAMAS-CUBA TO THE  
WESTERN CARIBBEAN/NORTHERN HONDURAS. SHEAR LINE CONVERGENCE ACROSS  
THE CENTRAL-SOUTHEAST BAHAMAS-EASTERN CUBA AND NORTHEAST HONDURAS  
IS TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM  
DURING THE NEXT COUPLE OF DAYS. SIMILAR AMOUNTS ARE EXPECTED OVER  
JAMAICA ON SATURDAY-SUNDAY.  
 
A TUTT LOW OVER THE EASTERN TROPICAL ATLANTIC SUSTAINS AN  
ELONGATED TROUGH THAT EXTENDS ACROSS THE WINDWARD ISLANDS TO THE  
SOUTHEAST CARIBBEAN. AS THE MID LEVEL RIDGE OVER THE CARIBBEAN  
WEAKENS...THE TUTT IS FORECAST TO PULL TO THE EAST-NORTHEAST  
DURING THE WEEKEND. EARLY IN THE CYCLE THIS IS TO ENHANCE  
CONVECTION ACROSS THE GRENADINES-TRINIDAD/TOBAGO-NORTHEAST  
VENEZUELA/NORTHERN GUYANA...WITH RAINFALL AMOUNTS OF 15-20MM/DAY  
AND MAXIMA OF 30-60MM. THROUGH SUNDAY EXPECTING DAILY MAXIMA TO  
DECREASES TO 25-50MM/DAY. OVER NORTHERN SURINAME-FRENCH GUIANA  
EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM  
DURING THE NEXT FEW DAYS.  
 
OVER THE EASTERN PACIFIC...A LOW OVER THE GULF OF PANAMA IS TO  
EXTEND A TROUGH SOUTH ALONG THE WEST COAST OF COLOMBIA TO NORTHERN  
ECUADOR. THIS PATTERN IS TO PERSIST OVER THE NEXT FEW DAYS.  
MEANWHILE...THIS IS TO ENHANCE COASTAL CONVERGENCE ACROSS WESTERN  
COLOMBIA AND ACROSS THE DARIEN IN EASTERN PANAMA...TO FAVOR  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-30MM/DAY. LESSER  
AMOUNTS ARE EXPECTED ON THE ANDEAN REGION OF COLOMBIA...WITH  
ACCUMULATION 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  
45W 47W 50W 53W 56W 59W 61W 63W TUTT INDCD 28N  
58W 61W 64W 66W 68W 71W 73W 75W TUTT INDCD 22N  
72W 74W 77W 79W 80W DISSIPATES EW 22N  
76W 79W 82W DISSIPATES EW 18N  
 
TUTT OVER THE TROPICAL ATLANTIC INDUCED A TROUGH IN THE EASTERLY  
TRADES...WITH AXIS ALONG 45W TO 28N. THIS PERTURBATION REACHES THE  
LEEWARD ISLES EARLY ON MONDAY MORNING...WHERE IT FAVORS RAINFALL  
AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM IN ISOLATED CONVECTION.  
 
A TUTT INDUCED PERTURBATION EXTENDS ALONG 58W TO 22N. THIS MOVES  
TO THE VIRGIN ISLES EARLY ON FRIDAY MORNING...CROSSING PUERTO RICO  
LATER DURING THE DAY. MOST ACTIVE CONVECTION WITH THIS FEATURE IS  
NOW EXPECTED NORTH OF THE ISLANDS. ACROSS THE VIRGIN ISLES-PUERTO  
RICO AND THE DOMINICAN REPUBLIC THIS IS TO THEN SUSTAIN RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM...WHILE ACROSS THE ABC  
ISLES-NORTHERN VENEZUELA EXPECTING ACCUMULATION OF 05-10MM/DAY AND  
MAXIMA OF 15-20MM. ON SUNDAY THIS INCREASES TO 10-15MM/DAY AND  
MAXIMA OF 20-30MM.  
 
A WANING EASTERLY WAVE ALONG 72W AND SOUTH OF 22N IS TO SUSTAIN  
LIGHT TO MODERATE CONVECTION ACROSS JAMAICA ON SATURDAY...TO FAVOR  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM. ACROSS  
NORTHERN COLOMBIA IT IS TO ALSO FAVOR RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15MM...WHILE OVER EASTERN PANAMA  
EXPECTING ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF 20-30MM.  
 
AN EASTERLY WAVE ALONG 76W AND SOUTH OF 18N DISSIPATES DURING THE  
DAY ON SATURDAY. MEANWHILE...ACROSS EASTERN PANAMA THIS IS TO  
SUSTAIN RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-30MM.  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON...WPC (USA)  
 

 
 
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