895  
FXCA20 KWBC 221751  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1251 PM EST FRI DEC 22 2017  
 
TROPICAL DISCUSSION FROM DEC 22/12 UTC: A HIGH AMPLITUDE POLAR  
TROUGH WILL EXTEND ACROSS THE WESTERN USA-NORTHWEST MEXICO TO THE  
EASTERN PACIFIC LATER THIS AFTERNOON. ON SATURDAY-SUNDAY...WHILE  
PRESSING AGAINST A RIDGE TO THE EAST...THE BASE OF THE TROUGH IS  
TO PULL AS IT CROSSES THE CENTRAL-EASTERN USA. AT LOW LEVELS...THE  
ASSOCIATED SURFACE FRONT SURGES ACROSS FLORIDA TO COAHUILA IN  
NORTHERN MEXICO LATER TODAY/EARLY SATURDAY MORNING. LATER ON  
SATURDAY THE FRONT WILL MOVE ACROSS THE SOUTHEAST USA WHILE  
TRAILING ACROSS THE NORTHERN GULF TO NORTHEAST MEXICO. THE FRONT  
IS TO THEN REMAIN NEARLY STATIONARY THROUGH MIDDAY ON  
SUNDAY...WHEN A BUILDING POLAR RIDGE DRIVES A SECONDARY FRONT THAT  
MERGES WITH/REINFORCES THE OLD BOUNDARY TO THE SOUTH. EARLY ON  
MONDAY MORNING THE FRONT WILL THEN MOVE TO CENTRAL FLORIDA...AND  
LATER IN THE DAY IT WILL ENTER THE NORTHWEST BAHAMAS...MEANWHILE  
TRAILING ACROSS THE NORTHERN GULF TO NORTHEAST MEXICO. A  
PREFRONTAL SHEAR LINE IS TO THEN FORM AHEAD OF THIS BOUNDARY EARLY  
ON MONDAY MORNING...TO EXTEND ACROSS WESTERN CUBA TO THE GULF OF  
HONDURAS. LATER ON MONDAY THIS WILL MOVE TO CENTRAL  
BAHAMAS-CENTRAL CUBA WHILE TRAILING ACROSS THE ISLAS DE LA BAHIA  
TO NORTHERN HONDURAS. ON SATURDAY THIS IS TO TRIGGER SCATTERED  
CONVECTION ACROSS SOUTHERN TAMAULIPAS/NORTHERN VERACRUZ...TO  
SUSTAIN RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM. OVER  
SOUTHERN VERACRUZ-NORTHERN CHIAPAS THE FRONTAL NORTHERLIES ARE TO  
THEN FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM  
ON SATURDAY-SUNDAY. OVER CUBA THE SHEAR LINE WILL RESULT IN  
RAINFALL AMOUNTS OF 00-05MM/DAY AND WIDELY ISOLATED MAXIMA OF  
10MM. HIGHER AMOUNTS ARE EXPECTED ACROSS NORTHERN HONDURAS...WITH  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM EARLY ON  
MONDAY MORNING. ON MONDAY TO TUESDAY IT INCREASES TO 15-20MM/DAY  
AND MAXIMA OF 25-50MM WHILE BUILDING EAST ALONG THE COAST TO LA  
CEIBA.  
 
BROAD RIDGE EXTENDS OVER THE GULF OF MEXICO-SOUTHEAST USA TO THE  
CARIBBEAN BASIN...WITH AXIS TO ANCHOR AT 500 HPA ON A CLOSED HIGH  
OVER SOUTH FLORIDA LATER THIS AFTERNOON. UNDER PRESSURE FROM  
AMPLIFYING POLAR TROUGH OVER NORTH AMERICA THE RIDGE IS TO  
GRADUALLY FLATTEN FROM THE WEST...AND IT IS TO NEARLY COLLAPSE ON  
MONDAY-TUESDAY. EARLY IN THE CYCLE THIS WILL FAVOR STRONG TRADE  
WINDS CAP ACROSS MEXICO-CENTRAL AMERICA-CUBA AND THE BAHAMAS. BUT  
AS THE RIDGE WEAKENS...THE CAP WILL GRADUALLY LIFT...ALLOWING  
DEEPER MOISTURE TO POOL ACROSS THE WESTERN CARIBBEAN/NORTHERN  
CENTRAL AMERICA. THIS WILL THEN FEED THE AFOREMENTIONED CONVECTION  
IN ASSOCIATION WITH THE PREFRONTAL SHEAR LINE ENTERING THE WESTERN  
CARIBBEAN EARLY NEXT WEEK. A STRONGER CAP INVERSION IS TO HOLD  
ACROSS JAMAICA-HISPANIOLA-PUERTO RICO-ISLAND CHAIN. IN THIS AREA  
THE STRONG CAP INVERSION IS TO CONTINUE INHIBITING ORGANIZED DEEP  
CONVECTION.  
 
AT LOW LEVELS...A RIDGE IS TO GRADUALLY BUILD ACROSS THE  
WESTERN-CENTRAL ATLANTIC DURING THE WEEKEND. AS THE RIDGE BUILDS  
IT IS TO TIGHTEN THE PRESSURE GRADIENT. OVER THE NORTHERN  
CARIBBEAN ISLES THIS IS TO THEN SUSTAIN A LONG FETCH EASTERLY  
FLOW...WITH 850 HPA WINDS FORECAST TO PEAK AT 20-25KT. STRONGER  
WINDS ARE EXPECTED TO THE SOUTH ACROSS THE SOUTHERN CARIBBEAN TO  
SOUTHERN CENTRAL AMERICA/EASTERN TROPICAL PACIFIC...WHERE THE  
WINDS ARE TO PEAK AT 35-40KT. BRISK EASTERLY TRADES WILL FAVOR  
GENERATION AND TRANSPORT OF SHALLOW CLOUD CLUSTERS ACROSS THE  
CARIBBEAN BASIN. OVER THE ISLAND CHAIN-PUERTO RICO THIS WILL  
GENERALLY FAVOR RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF  
10MM...INCREASING TO 05-10MM/DAY AND MAXIMA OF 15MM ON SUNDAY.  
OVER THE DOMINICAN REPUBLIC THIS IS TO FAVOR RAINFALL AMOUNTS OF  
00-05MM/DAY AND MAXIMA OF 10MM OVER THE NEXT TWO DAYS...DECREASING  
TO 05-10MM/DAY AND MAXIMA OF 15-20MM ON SUNDAY-MONDAY. ACROSS  
JAMAICA...PASSING SHOWERS WILL CLUSTER ACROSS EASTERN/NORTHEASTERN  
PORTIONS OF THE ISLAND...TO FAVOR RAINFALL AMOUNTS OF 00-05MM/DAY  
AND MAXIMA OF 10MM. 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  
15-20MM. ON SATURDAY...ACTIVITY ACROSS NICARAGUA INCREASES TO  
10-15MM/DAY AND MAXIMA OF 20-30MM. LESSER AMOUNTS ARE EXPECTED ON  
THE CARIBBEAN COASTAL PLAINS OF COSTA RICA AND WESTERN PANAMA.  
OVER WESTERN COLOMBIA... THE MODELS FORECAST THE PANAMANIAN TROUGH  
TO BECOME BETTER ORGANIZED LATER DURING THE WEEKEND...EVOLVING  
INTO A CLOSED LOW JUST WEST OF THE EJE CAFETERO. THIS WILL FAVOR  
ORGANIZED COASTAL CONVECTION ALONG THE WEST COAST...WITH RAINFALL  
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM. ON THE ANDEAN  
REGION...MEANWHILE...EXPECTING RAINFALL AMOUNTS OF 00-05MM/DAY AND  
MAXIMA OF 10MM...WITH LOCALIZED MAXIMA OF 20-25MM.  
 
EARLY THIS MORNING...THE MID/UPPER LEVEL RIDGE STEERED A SHORT  
WAVE TROUGH ACROSS BERMUDA. AS IT CLEARS THE EASTERN FRINGES OF  
THE MID LEVEL RIDGE THE TROUGH IS FORECAST TO RAPIDLY DEEPEN. ON  
SATURDAY THE BASE OF THE TROUGH BOTTOMS OUT OVER THE NORTHEAST  
CARIBBEAN...TO GRADUALLY EVOLVE INTO A CLOSED TUTT LOW TO THE  
EAST-NORTHEAST OF THE LEEWARD ISLES LATER IN THE DAY. A JET MAXIMA  
WILL BOUND THE SOUTHERN FRINGES OF THIS TROUGH...WITH AXIS  
ORIGINATING OVER THE SOUTHEAST CARIBBEAN. THE NORTHEAST CARIBBEAN  
ISLES WILL THEN LIE ON THE CONVERGENT LEFT ENTRANCE REGION OF THIS  
JET...WHICH IS TO HELP SUSTAIN A STRONG TRADE WINDS CAP ACROSS THE  
NORTHEAST CARIBBEAN. DIVERGENCE ON ITS RIGHT ENTRANCE REGION WILL  
VENT CONVECTION FROM NORTHEAST VENEZUELA TO THE NORTHERN GUIANAS.  
LATER DURING THE WEEKEND...AS THE RIDGE TO THE WEST FLATTENS...THE  
UPPER LEVEL TUTT IS TO GRADUALLY WEAKEN AND START TO LIFT TO THE  
EAST-NORTHEAST. THE REMAINING MID LEVEL CIRCULATION IS TO THEN  
DECOUPLE FROM THE UPPER LEVEL AXIS...RETROGRESSING ACROSS THE  
LESSER ANTILLES TO THE EASTERN CARIBBEAN ON  
TUESDAY-WEDNESDAY...SHEARING SHORT WAVE VORTICES ACROSS THE  
EASTERN CARIBBEAN THAT ARE TO ENHANCE LOCAL CONVECTION LATER  
DURING THE CYCLE. MEANWHILE...AS THE TUTT LOW MEANDERS 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 AS THE DIGGING TUTT INTERACTS WITH THE ITCZ OVER THE  
GUIANAS. OVER FRENCH GUIANA THIS IS TO INITIALLY FAVOR RAINFALL  
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-30MM...WHILE OVER SURINAME  
AND GUYANA EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15-20MM. ON SATURDAY TO SUNDAY...AS THE TUTT DEEPENS...CONVECTION  
OVER FRENCH GUIANA AND SURINAME IS TO INTENSIFY...INCREASING TO  
15-20MM/DAY AND MAXIMA OF 30-60MM ON FRIDAY...WHILE ON SUNDAY IT  
WILL FAVOR RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 25-50MM.  
ACTIVITY WILL GRADUALLY BUILD WEST ACROSS NORTHERN GUYANA...WHILE  
OVER NORTHEAST VENEZUELA EXPECT RAINFALL AMOUNTS OF 05-10MM/DAY  
AND MAXIMA OF 15-25MM.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE  
SOF  
43W 45W 48W 51W 54W 57W 60W 63W TUTT INDCD  
19N  
65W 67W 69W 72W 74W 76W 78W DISSIPATES EW  
18N  
 
A TUTT INDUCED TROUGH IN THE EASTERLY TRADES NOW EXTENDS ALONG 43W  
TO 19N. THIS IS TO ENTER FRENCH GUIANA ON SATURDAY MORNING...WHERE  
IN INTERACTION WITH THE ITCZ IT IS TO SUSTAIN RAINFALL AMOUNTS OF  
15-20MM/DAY AND MAXIMA OF 30-60MM. CONVECTION WILL THEN BUILD WEST  
ACROSS NORTHERN SURINAME TO GUYANA TO RESULT IN RAINFALL AMOUNTS  
OF 15-20MM/DAY AND MAXIMA OF 25-50MM.  
 
AN EASTERLY WAVE ALONG 65W AND SOUTH OF 18N IS TO TRIGGER ISOLATED  
TO SCATTERED CONVECTION ACROSS THE ABC ISLES/NORTHERN  
VENEZUELA...TO FAVOR RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF  
10MM. 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 ALSO TRIGGER  
RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM...WHILE ON THE  
WEST COAST EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF  
20-35MM.  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON...WPC (USA)  
 

 
 
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