078  
FXCA20 KWBC 301933  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
232 PM EST TUE JAN 30 2018  
 
TROPICAL DISCUSSION FROM JAN 30/12 UTC: A LARGE POLAR TROUGH IS  
EXITING THE EASTERN COAST OF THE UNITED STATES WHILE SUSTAINING A  
SURFACE COLD FRONT. BY TUESDAY EVENING...THE FRONT IS FORECAST TO  
EXTEND ACROSS THE CENTRAL BAHAMAS...CENTRAL CUBA...BECOMING  
STATIONARY ACROSS THE CAYMAN ISLANDS INTO EXTREME SOUTHERN  
BELIZE... CENTRAL GUATEMALA AND INTO CHIAPAS. BY WEDNESDAY  
EVENING...IT WILL EXTEND ACROSS THE SOUTHERN BAHAMAS/TURKS AND  
CAICOS...SOUTHEASTERN CUBA...THE CAYMAN ISLANDS...WHILE WESTERN  
PART OF THE BOUNDARY STARTS WEAKENING ACROSS THE GULF OF  
HONDURAS...EXTREME NORTHWESTERN HONDURAS AND CENTRAL GUATEMALA. BY  
THURSDAY EVENING...THE FRONTAL BOUNDARY WILL START TO LOSE  
DEFINITION AS IT BEGINS TO RETROGRESS INTO THE CENTRAL BAHAMAS AND  
EXTREME NORTHWESTERN CUBA. THE SYSTEM IS ALSO SUSTAINING A SHEAR  
LINE...ALTHOUGH THIS IS FORECAST TO REMAIN ILL-DEFINED THROUGH THE  
CYCLE. IT IS FORECAST TO EXTEND ACROSS THE WINDWARD PASSAGE...JUST  
TO THE SOUTH OF JAMAICA...INTO NORTHEASTERN NICARAGUA ON TUESDAY  
EVENING...AND WILL RAPIDLY LOSE DEFINITION AFTER.  
 
LARGEST ACCUMULATIONS WITH THE FRONT/SHEAR LINE SYSTEM WILL  
CLUSTER ALONG NORTHERN AND EASTERN SLOPES OF SOUTHERN MEXICO AND  
NORTHERN CENTRAL AMERICA. NOTE THAT UNDER THE INFLUENCE OF  
BUILDING MID AND UPPER RIDGE OVER THE REGION...AND THE GRADUAL  
DECREASE IN THE SPEED OF THE NORTHEASTERLY TRADES...EXPECTING A  
GRADUAL DECREASE IN ACCUMULATIONS THROUGH THE FORECAST CYCLE...AND  
THE ESTABLISHMENT OF MUCH DRIER CONDITIONS BY THE END OF THE WEEK.  
THROUGH EARLY WEDNESDAY...ACTIVE CONVECTION WILL PERSIST IN  
SOUTHWESTERN PORTIONS OF THE GULF OF HONDURAS TO AFFECT  
NORTHWESTERN HONDURAS/SOUTHERN BELIZE AND EASTERN GUATEMALA.  
HERE...EXPECTING 30-60MM/DAY AND MAXIMA OF 100-150MM. ENHANCED  
MOISTURE CONVERGENCE FROM CENTRAL GUATEMALA INTO CHIAPAS WILL LEAD  
TO 15-20MM/DAY AND MAXIMA OF 25-50MM. BY  
WEDNESDAY-THURSDAY...ACTIVE CONVECTION WILL PERSIST IN NORTHERN  
HONDURAS/EXTREME EASTERN GUATEMALA/SOUTHEASTERN BELIZE...WHERE  
ENHANCED MOISTURE CONVERGENCE WILL SUSTAIN 15-20MM/DAY AND MAXIMA  
OF 30-60MM. BY THURSDAY-FRIDAY...A SHARP DECREASE IS EXPECTED.  
ACCUMULATIONS WILL LIMIT TO 05-10MM/DAY AND MAXIMA OF 15MM IN  
SHOWERS AND ISOLATED THUNDERSTORMS THAT AFFECT BELIZE AND QUINTANA  
ROO IN ASSOCIATION WITH THE RETURN OF THE MOIST EASTERLIES.  
 
ALSO WITH THE FRONT...EXPECTING PRECIPITATION ACROSS THE CAYMAN  
ISLANDS...CUBA AND THE BAHAMAS. IN CUBA...PRECIPITATION WILL  
MOSTLY CONCENTRATE ALONG THE ATLANTIC COAST...TO MEANDER FROM  
CENTRAL CUBA ON TUESDAY...TO SOUTHEASTERN CUBA ON WEDNESDAY  
THROUGH FRIDAY. LARGEST ACCUMULATIONS ARE EXPECTED ON  
WEDNESDAY...AS MOISTURE CONVERGENCE PEAKS IN ASSOCIATION WITH  
FRONTAL EASTERLIES AND THE MOUNTAINS OF SOUTHEASTERN CUBA. THIS  
WILL LEAD TO 05-10MM/DAY AND MAXIMA OF 15-25MM. THIS WILL RAPIDLY  
DECREASE AFTER. IN THE BAHAMAS...AS FRONTAL CONVECTION INTERACTS  
WITH THE UPPER TROUGHS...EXPECTING LARGEST RAINFALL AMOUNTS ON  
TUESDAY TO CONCENTRATE IN THE CENTRAL BAHAMAS...AND REACH  
05-10MM/DAY AND MAXIMA OF 15-25MM IN THUNDERSTORMS. THIS IS TO  
GRADUALLY DECREASE TO 00-05MM/DAY AND ISOLATED MAXIMA OF 10MM BY  
THURSDAY...WHILE AREA OF CONVECTION MEANDERS INTO THE SOUTHEASTERN  
BAHAMAS. IN THE CAYMAN ISLANDS...EXPECTING A PEAK ON TUESDAY WITH  
AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM.  
 
A DRYING TREND WILL CONTINUE DEVELOPING ACROSS THE EASTERN  
CARIBBEAN...AS THE MID-LEVEL RIDGE AXIS MEANDERS FROM THE  
HISPANIOLA/PUERTO RICO ON TUESDAY...TO EXTEND ZONALLY ALONG  
14N-17N ACROSS THE CARIBBEAN. ACTIVITY WILL CLUSTER ALONG  
ELONGATED CORRIDORS OF TRADE WIND CONVERGENCE...REMNANTS OF THE  
FRONT/SHEAR LINE FROM THE PAST WEEKEND. THIS WILL LEAD TO ISOLATED  
ACCUMULATIONS OF 00-05MM/DAY AND MAXIMA OF 10MM ON TUESDAY ACROSS  
THE CENTRAL LESSER ANTILLES AND THE ABC/GRENADA...DECREASING AFTER.  
 
IN NORTHERN SOUTH AMERICA...THE UPPER WESTERLY JET FROM THE  
PACIFIC CONTINUES EXTENDING INTO COLOMBIA...AND WESTERLY WINDS  
REFLECT EVEN IN THE MID-TROPOSPHERE. UNDER THIS INFLUENCE...DRY  
MID-LEVELS HAVE ESTABLISHED AND ARE SUSTAINING THE CURRENT  
SEASONALLY DRY PATTERN ACROSS ALL THE REGION. AT LOW-LEVELS...THE  
JET IN THE LLANOS CONTINUES GAINING STRENGTH...WHICH IS ALSO  
SUSTAINING DRY CONDITIONS IN EASTERN AND SOUTHEASTERN COLOMBIA AND  
VENEZUELA. CONVECTION WILL CLUSTER MOSTLY TO THE PACIFIC BASINS OF  
COLOMBIA AND ECUADOR...ESPECIALLY IN SOUTHWESTERN COLOMBIA...UNDER  
THE INFLUENCE OF THE PACIFIC ITCZ. HERE...EXPECTING 05-10MM/DAY  
AND ISOLATED MAXIMA OF 15MM THROUGH THE CYCLE. IN ANDEAN COLOMBIA  
AND ANDEAN VENEZUELA...ISOLATED DIURNAL SHOWERS WILL FAVOR MAXIMA  
UNDER 10MM ON A DAILY BASIS. DRY PATTERN IS ALSO EXPECTED IN THE  
GUIANAS AS THE ATLANTIC ITCZ HAS SHIFTED SOUTHWARD INTO BRAZIL. IN  
THE GUIANAS...EXPECTING TRACE ACCUMULATIONS ON DAILY TRADE WIND  
SHOWERS...YET A TRANSIENT INCREASE IS EXPECTED FOR FRENCH GUIANA  
AND SURINAME...AS A MOIST PLUME MOVES IN THE REGION FROM EAST TO  
WEST. THIS WILL LEAD TO 10-15MM/DAY AND MAXIMA OF 20-30MM IN  
FRENCH GUIANA ON WEDNESDAY-THURSDAY...AND 05-10MM/DAY AND MAXIMA  
OF 15-20MM IN FRENCH GUIANA AND SURINAME ON THURSDAY-FRIDAY. MUCH  
LARGER AMOUNTS ARE EXPECTED IN THE CENTRAL AND SOUTHERN AMAZON  
BASIN.  
 
PECK...MS (JAMAICA)  
GORDON...NMS (BELIZE)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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