666  
FXCA20 KWBC 191818  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
217 PM EDT THU OCT 19 2017  
 
TROPICAL DISCUSSION FROM OCT 19/12 UTC: STRONG POLAR EXITING THE  
EAST COAST OF THE UNITED STATES IS INTERACTING WITH A SURFACE  
FRONT THAT LIES ACROSS THE BAHAMAS. THE UPPER TROUGH IS STARTING  
TO UNDULATE A SURFACE LOW NEAR 30N 70W...AND TO PUSH THE FRONT  
SOUTHWARD. ALTHOUGH THERE IS NO STRONG BAROCLINICITY WITH THIS  
SYSTEM...THE FRONT IS FORECAST TO ENHANCE CONVECTION AS IT  
PROPAGATES TO THE SOUTH. BY THURSDAY EVENING...THE FRONT IS  
FORECAST TO MEANDER JUST TO THE NORTH OF GRAND BAHAMA TO THEN  
BECOME STATIONARY. A POOL OF MOISTURE WITH PRECIPITABLE WATER  
VALUES EXCEEDING 50MM IS FAVORING SCATTERED CONVECTION. THIS  
ACTIVITY WILL AFFECT THE BAHAMAS DURING THE NEXT THREE DAYS.  
RAINFALL ACCUMULATIONS ARE FORECAST TO GRADUALLY DECREASE FROM  
10-15MM/DAY AND MAXIMA OF 20-35MM ON THURSDAY TO 05-10MM/DAY AND  
MAXIMA OF 15MM BY SATURDAY.  
 
TO THE WEST...WANING NORTHERLY WIND SURGE IN THE GULF OF  
MEXICO/GULF OF HONDURAS IS STILL SUSTAINING ENHANCED MOISTURE  
CONVERGENCE AGAINST THE NORTHERN SLOPES OF NORTHERN CENTRAL  
AMERICA. ALTHOUGH THE SURGE CONTINUES WANING...A TROPICAL WAVE IS  
APPROACHING FROM THE EAST...AND WILL REINFORCE CURRENT MOIST  
PATTERN IN THE REGION. REGARDLESS...PRECIPITABLE WATER VALUES IN  
THE GULF OF HONDURAS ARE EXCEEDING 55MM. THIS WILL CONTINUE  
FAVORING MODERATE PRECIPITATION. THROUGH EARLY FRIDAY...LARGEST  
ACCUMULATIONS ARE TO CLUSTER BETWEEN SOUTHERN VERACRUZ TO SOUTHERN  
BELIZE/NORTHERN GUATEMALA...WHERE EXPECTING 10-15MM/DAY AND MAXIMA  
OF 20-40MM. BY FRIDAY-SATURDAY...AS A MOIST PLUME ARRIVES FROM THE  
EAST...EXPECTING AN INCREASE IN ACCUMULATIONS IN SOUTHERN  
BELIZE/EASTERN GUATEMALA AND NORTHERN HONDURAS/NORTHEASTERN  
NICARAGUA TO 15-20MM/DAY AND MAXIMA OF 30-60MM. BY  
SATURDAY-SUNDAY...UNDER THE INFLUENCE OF THE TROPICAL  
WAVE...EXPECTING SIMILAR AMOUNTS EXPANDING INTO ALL OF BELIZE AND  
EASTERN GUATEMALA. ALSO UNDER THE INFLUENCE OF THE TROPICAL  
WAVE...EXPECTING SOME CONVECTION TO DEVELOP IN THE PACIFIC BASIN  
TO PRODUCE 10-15MM/DAY AND MAXIMA OF 20-40MM BETWEEN THE GULF OF  
FONSECA/NORTHWESTERN NICARAGUA AND SOUTHERN GUATEMALA.  
 
IN SOUTHERN CENTRAL AMERICA...ACTIVE CONVECTION IS TO PERSIST  
THROUGH THE CYCLE UNDER THE INFLUENCE OF A MOISTURE POOL THAT  
EXCEEDS 60MM...AND A MODERATELY ORGANIZED PANAMANIAN LOW.  
FURTHERMORE...ADDITIONAL ENHANCEMENT IS EXPECTED WITH THE  
APPROACHING TROPICAL WAVE. IN COSTA RICA...EXPECTING 10-15MM/DAY  
AND MAXIMA OF 20-40MM IN A DAILY BASIS...WHEREAS IN  
PANAMA...EXPECTING A PEAK ON FRIDAY-SATURDAY WHERE AMOUNTS ARE TO  
INCREASE FROM 05-10MM/DAY AND MAXIMA OF 15-20MM TO 10-15MM/DAY AND  
MAXIMA OF 20-45MM.  
 
IN THE CARIBBEAN...A TRADE WIND SURGE CONTINUES PROPAGATING  
WESTWARD WHILE LEADING TO WINDY AND DRY CONDITIONS BEHIND THE  
LEADING EDGE. THIS SURGE IS ASSOCIATED WITH WINDS OF 20-35KT...A  
SUBSIDENCE CAP THAT SITS NEAR 900 HPA...AND VERY DRY MID-LEVELS.  
BY LATE THURSDAY...THE SURGE EDGE WILL EXTEND ACROSS THE EASTERN  
DOMINICAN REPUBLIC...BY FRIDAY EVENING IT WILL EXTEND ACROSS  
WESTERN HAITI...AND BY SATURDAY EVENING IT WILL EXTEND WEST OF  
JAMAICA AND CLOSE TO THE CAYMAN ISLANDS. AHEAD OF THE  
SURGE...ENHANCED MOISTURE CONVERGENCE WILL CONTINUE SUSTAINING  
ACTIVE CONVECTION. THIS IS REINFORCED BY THE INFLUENCE OF A  
TROPICAL WAVE. BY EARLY FRIDAY...LARGEST RAINFALL ACCUMULATIONS  
ARE EXPECTED IN THE DOMINICAN REPUBLIC AND EASTERN JAMAICA WHERE  
EXPECTING 10-15MM/DAY AND MAXIMA OF 20-35MM. SIMILAR AMOUNTS ARE  
EXPECTED IN JAMAICA ON FRIDAY-EARLY SATURDAY...AND A SHARP  
DECREASE IS EXPECTED AFTER.  
 
ALSO IN THE CARIBBEAN...AS THE TRADE WIND SURGE PROPAGATES ACROSS  
THE NORTHERN TIER...THE ITCZ IS TO CONFINE TO THE WINDWARD  
ISLANDS/SOUTHERN CARIBBEAN...ENTERING THE BASIN THROUGH TRINIDAD  
AND TOBAGO. NOTE THAT TRADE WINDS WILL ALSO REMAIN FAST...BETWEEN  
15-30KT...YET UNDER THE INFLUENCE OF THE MOIST PLUME...EXPECTED  
MODERATE RAINFALL AMOUNTS. LARGEST ACCUMULATIONS ARE EXPECTED IN  
THE SOUTHERN WINDWARD ISLANDS/NORTHEASTERN VENEZUELA...WHERE  
AMOUNTS ARE TO GRADUALLY DECREASE FROM 15-20MM/DAY AND MAXIMA OF  
25-50MM ON THURSDAY...TO 10-15MM/DAY AND MAXIMA OF 20-40MM BY  
SATURDAY. IN THE ABC ISLANDS AND NORTHERN VENEZUELA...EXPECTING A  
GRADUAL INCREASE FROM 05-10MM/DAY AND MAXIMA OF 15-25MM ON  
THURSDAY...TO 10-15MM/DAY AND MAXIMA OF 20-35MM ON SATURDAY.  
 
IN NORTHERN SOUTH AMERICA...LARGEST ACCUMULATIONS WILL CLUSTER IN  
COLOMBIA...WHERE ENHANCED CONVECTIVE INSTABILITY AND WESTERLIES  
ACROSS THE PACIFIC BASIN WILL CONTINUE TO SUSTAIN THE CURRENT  
SEASONALLY ACTIVE PATTERN OF CONVECTION. EXPECTING AMOUNTS OF  
15-20MM/DAY AND MAXIMA OF 25-50MM THROUGH EARLY  
SATURDAY...INCREASING TO 15-20MM/DAY AND MAXIMA OF 35-70MM BY  
SATURDAY-SUNDAY.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
36W 40W 43W 46W 49W 52W 55W 58W TW 20N  
72W 74W 77W 80W 82W 84W 87W 89W TW 18N  
90W 92W 94W 96W DISSIPATES TW 24N  
 
A TROPICAL WAVE IS INITIALIZED AT 36W. THIS WAVE APPROACHES THE  
BASIN ON SUNDAY TO START ENHANCING ACTIVITY IN THE GUIANAS.  
 
TROPICAL WAVE INITIALIZED AT 72W WILL CONTINUE STIMULATING  
CONVECTION AS IT PROPAGATES WEST ACROSS THE CARIBBEAN BASIN. ON  
THURSDAY/FRIDAY...THE WAVE WILL ENHANCE ACCUMULATIONS IN JAMAICA  
TO PRODUCE 10-15MM/DAY AND MAXIMA OF 20-35MM. ALSO DURING THIS  
PERIOD...THIS WILL SUSTAIN AMOUNTS OF 15-20MM/DAY AND MAXIMA OF  
25-50MM IN COLOMBIA. IN PANAMA AND COSTA RICA...THE WAVE WILL  
ENHANCE ACTIVITY TO SUSTAIN AMOUNTS OF 10-15MM/DAY AND MAXIMA OF  
20-45MM ON FRIDAY-SATURDAY. BY SATURDAY-SUNDAY...ENHANCEMENT WILL  
CONCENTRATE IN CENTRAL AMERICA. LARGEST ACCUMULATIONS ARE EXPECTED  
IN THE GULF OF HONDURAS...WHERE THE WAVE IN INTERACTION WITH A  
LOW-LEVEL JET WILL FAVOR AMOUNTS OF 15-20MM/DAY AND MAXIMA OF  
30-60MM. NOTE THAT THERE IS A CHANGE FOR ISOLATED HIGHER AMOUNTS  
IN REGION OF OROGRAPHIC FORCING.  
 
A TROPICAL WAVE INITIALIZED AT 90W CONTINUES TO BE ILL-DEFINED AND  
HAS LIMITED EFFECT ON THE PRECIPITATION IN CONTINENTAL REGIONS.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
GALVEZ...WPC (USA)  

 
 
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