337  
FXCA20 KWBC 261908  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
308 PM EDT THU OCT 26 2017  
 
TROPICAL DISCUSSION FROM OCT 26/12 UTC: A HIGH AMPLITUDE TROUGH  
EXTENDS AN AXIS ACROSS THE EASTERN USA INTO WESTERN CUBA...AND IS  
FORECAST TO LIFT TO THE NORTH OF A RIDGE THAT CENTERS TO THE  
NORTHEAST OF PUERTO RICO. THE ASSOCIATED FRONT IS FORECAST TO  
EXTEND ACROSS THE SOUTHEASTERN BAHAMAS-SOUTHEASTERN CUBA-CAYMAN  
ISLANDS INTO BELIZE ON THURSDAY EVENING...WHERE IT IS TO MEANDER  
THROUGH LATE FRIDAY. THIS WILL SUSTAIN HEAVY RAINFALL THROUGH THE  
CYCLE ACROSS THE NORTHWESTERN CARIBBEAN...WHERE A DEEP MOISTURE  
POOL WITH PRECIPITABLE WATER VALUES EXCEEDING 60MM LINGERS. ON  
THURSDAY-FRIDAY...THIS WILL LEAD TO LARGEST ACCUMULATIONS BETWEEN  
EXTREME NORTHERN HONDURAS INTO THE CAYMAN ISLANDS AND EXTREME  
WESTERN JAMAICA...WHERE EXPECTING 25-50MM/DAY AND MAXIMA OF  
75-125MM. ACROSS EASTERN JAMAICA INTO SOUTHEASTERN CUBA EXPECTING  
10-15MM/DAY AND MAXIMA OF 20-40MM. IN EASTERN CUBA AND THE  
SOUTHEASTERN BAHAMAS...EXPECTING 05-10MM/DAY AND MAXIMA OF  
15-25MM. BY FRIDAY-SATURDAY...ACTIVITY WILL CONTINUE PEAKING IN  
THE CAYMAN ISLANDS AND WILL EXTEND INTO WESTERN CUBA. THIS WILL  
SUSTAIN AMOUNTS OF 25-50MM/DAY AND MAXIMA OF 75-125MM. TO THE  
EAST...ACROSS JAMAICA AND EASTERN CUBA EXPECTING 05-10MM/DAY AND  
MAXIMA OF 15MM. AS THE EASTERLIES RETURN IN BELIZE AND THE EASTERN  
YUCATAN PENINSULA...EXPECTING AMOUNTS OF 15-20MM/DAY AND MAXIMA OF  
30-60MM WHILE THE DEEP MOISTURE POOL REMAINS SITTING IN THE GULF  
OF HONDURAS. THE FRONT IS FORECAST TO WEAKEN AFTER.  
YET...LINGERING ACTIVITY WILL MEANDER TO THE NORTH ACROSS WESTERN  
CUBA INTO THE NORTHERN BAHAMAS. AS A LARGE NEW UPPER TROUGH  
APPROACHES FROM THE UNITED STATES AND PRESSES AGAINST THE UPPER  
RIDGE CENTERING OVER JAMAICA...AN UPPER DIVERGENT PATTERN IS TO  
SET UP IN THE REGION. THIS WILL CONTINUE SUSTAINING HEAVY  
RAINFALL. LARGEST ACCUMULATIONS DURING SATURDAY-SUNDAY ARE  
EXPECTED IN THE NORTHERN BAHAMAS WHERE AMOUNTS WILL REACH  
25-50MM/DAY AND MAXIMA OF 75-125MM. IN WESTERN AND CENTRAL CUBA  
AND THE CAYMAN ISLANDS EXPECTING 15-30MM/DAY AND MAXIMA OF 40-80MM.  
 
IN ASSOCIATION WITH THE NEW UPPER TROUGH EXITING INTO THE GULF OF  
MEXICO FROM THE CENTRAL UNITED STATES ON SATURDAY...A NEW SURFACE  
COLD FRONT WILL STREAM ACROSS THE GULF OF MEXICO. BY FRIDAY  
EVENING...THE FRONT WILL EXTEND ACROSS LOUISIANA INTO TAMAULIPAS.  
BY SATURDAY EVENING...THE FRONT WILL EXTEND ACROSS THE CENTRAL  
GULF INTO SOUTHERN VERACRUZ. THIS WILL LEAD TO THE DEVELOPMENT OF  
A TEHUANTEPECER JET ON SUNDAY. IN TERMS OF RAINFALL  
AMOUNTS...CONVECTION WILL START INCREASING IN SOUTHERN  
MEXICO/NORTHERN GUATEMALA ON SATURDAY...TO SUSTAIN ACCUMULATIONS  
OF 10-15MM/DAY AND MAXIMA OF 20-40MM. LARGER AMOUNTS ARE EXPECTED  
ON SUNDAY.  
 
THE PERSISTENCE OF UPPER TROUGHS DEEPENING OVER THE GULF OF MEXICO  
HAS LEAD TO A NORTHWARD UNDULATIONS OF THE ITCZ. EMBEDDED IN  
THIS...TWO SURFACE LOWS HAVE FORMED. ONE EXTENDS OFF THE COASTS OF  
NICARAGUA IN THE PACIFIC...AND ANOTHER IN THE CARIBBEAN EAST OF  
NICARAGUA. SOUTHWESTERLY WINDS AT LOW-LEVELS ARE ENHANCING  
ACTIVITY IN THE PACIFIC BASIN OF CENTRAL AMERICA. THIS  
PATTERN...FAVORABLE FOR HEAVY RAINFALL...IS TO CONTINUE THROUGH  
THE WEEKEND. YET...NOTE THAT AS THE CIRCULATION TIGHTENS AROUND  
THE SURFACE LOWS...THE OROGRAPHIC FORCING ALONG THE PACIFIC BASIN  
SLOPES WILL DECREASE. THUS THIS IS REFLECTED IN THE FORECAST.  
STILL...LOCALLY HEAVY RAINS ARE EXPECTED. THROUGH EARLY  
FRIDAY...LARGEST AMOUNTS ARE EXPECTED IN WESTERN COSTA RICA AND  
WESTERN NICARAGUA WHERE EXPECTING 20-30MM/DAY AND MAXIMA OF  
50-100MM. IN EASTERN NICARAGUA AND THE CARIBBEAN ISLANDS EXPECTING  
15-20MM/DAY AND MAXIMA OF 25-50MM. BY FRIDAY-SATURDAY...LARGEST  
AMOUNTS ARE EXPECTED IN EL SALVADOR/SOUTHERN GUATEMALA/SOUTHERN  
HONDURAS...WHERE EXPECTING 15-20MM/DAY AND MAXIMA OF 35-70MM. BY  
SATURDAY-SUNDAY...LARGEST ACCUMULATIONS ARE EXPECTED FROM WESTERN  
EL SALVADOR INTO SOUTHERN CHIAPAS...WHERE EXPECTING 15-30MM/DAY  
AND MAXIMA OF 40-80MM. AS THE ITCZ MEANDERS TO THE  
NORTH...EXPECTING A GRADUAL DECREASE IN ACCUMULATIONS IN NICARAGUA  
AND COSTA RICA THROUGH SATURDAY.  
 
FARTHER EAST OVER THE CARIBBEAN...A TUTT LOW WEST OF THE WINDWARD  
ISLANDS EXTENDS A SHORT WAVE TROUGH TO EASTERN VENEZUELA. THIS IS  
TO REMAIN NEARLY STATIONARY THROUGH FRIDAY...TO START MEANDERING  
WESTWARD ON LATE FRIDAY-SATURDAY. THIS TUTT IS INTERACTING WITH A  
TROPICAL WAVE...AND SUSTAINING LOCALLY STRONG CONVECTION IN  
VENEZUELA. YET...DEEP-LAYER MOISTURE IS NOT IN PLACE TO SUSTAIN  
EXCESSIVE RAINS. THROUGH EARLY FRIDAY...EXPECTING 10-15MM/DAY AND  
ISOLATED MAXIMA OF 20-40MM IN WESTERN VENEZUELA/SANTANDERES IN  
COLOMBIA. ACCUMULATIONS ARE TO DECREASE GRADUALLY AFTER IN  
VENEZUELA. IN COLOMBIA...HOWEVER...AS TROPICAL WAVE  
APPROACHES...EXPECTING A REORGANIZATION OF THE PANAMANIAN LOW.  
CONVECTIVE INSTABILITY AND VENTILATION IN THE UPPER LEVELS ARE TO  
REMAIN FAVORABLE TO SUSTAIN SEASONALLY MODERATE RAINFALL AMOUNTS  
STARTING ON FRIDAY. BY FRIDAY-SATURDAY EXPECTING 15-20MM/DAY AND  
MAXIMA OF 30-60MM. BY SATURDAY-SUNDAY...EXPECTING SIMILAR AMOUNTS  
IN WESTERN COLOMBIA...WHILE ACCUMULATIONS IN NORTHERN COLOMBIA  
DECREASE TO 10-15MM/DAY AND MAXIMA OF 20-35MM.  
 
TO THE NORTH OF THE TUTT LOW...A TUTT-INDUCED WAVE WILL PROPAGATE  
ACROSS THE LEEWARD ISLANDS ON THURSDAY...TO EASTERN HISPANIOLA ON  
SATURDAY. THIS WILL SUSTAIN A WET SPELL IN THE NORTHEASTERN  
CARIBBEAN THROUGH THE WEEKEND (SEE BELOW FOR ACCUMULATIONS).  
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
41W 43W 45W 47W 49W 51W 53W 55W TW 13N  
61W 64W 66W 68W 70W 72W 74W 76W TW 12N  
62W 63W 65W 67W 68W 69W 70W 71W TUTT INDCD 20N  
70W 72W 74W 76W 78W DISSIPATES TW 12N  
 
A TROPICAL WAVE IS INITIALIZED AT 41W AND TO THE SOUTH OF 13N.  
THIS WAVE WILL APPROACH THE GUIANAS ON SATURDAY WITH LITTLE  
EFFECTS IN PRECIPITATION.  
 
TROPICAL WAVE ALONG 61W AND SOUTH OF 12N...WILL ENHANCE ACTIVITY  
ACROSS NORTHERN SOUTH AMERICA IN INTERACTION WITH A TUTT. THIS  
WILL ASSOCIATE WITH AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35 IN  
SOUTHERN VENEZUELA...AND 05-10MM/DAY AND MAXIMA OF 15-25MM IN THE  
WINDWARD ISLANDS ON THURSDAY-EARLY FRIDAY...TO MAXIMA OF  
15-20MM/DAY IN CENTRAL VENEZUELA ON FRIDAY-SATURDAY...AND WITH  
MAXIMA OF 20-35MM IN NORTHERN COLOMBIA ON SATURDAY-SUNDAY.  
 
TO THE NORTH...UNDER THE INFLUENCE OF THE TUTT IN THE EASTERN  
CARIBBEAN/VENEZUELA...A TUTT-INDUCED WAVE IS INITIALIZED AT 62W  
AND TO THE SOUTH OF 20N. THIS WAVE WILL ENHANCE ACTIVITY IN THE  
LEEWARD ISLANDS ON THURSDAY...WHERE IT WILL PRODUCE 10-15MM/DAY  
AND MAXIMA OF 20-30MM. BY FRIDAY-SATURDAY EXPECTING 15-20MM/DAY  
AND MAXIMA OF 30-60MM SPREADING FROM THE LEEWARD ISLANDS INTO  
PUERTO RICO. NOTE THAT THERE IS A RISK FOR MCS FORMATION IN THE  
LEEWARD ISLANDS. AMOUNTS ARE TO DECREASE TO 10-15MM/DAY AND MAXIMA  
OF 20-30MM BY SATURDAY-SUNDAY...WHILE THEY SPREAD INTO THE EASTERN  
DOMINICAN REPUBLIC.  
 
A TROPICAL WAVE AT 70W...IS ENHANCING CONVECTION MOSTLY IN  
NORTHERN SOUTH AMERICA...AS THE SOUTHERN CARIBBEAN REMAINS UNDER  
THE INFLUENCE OF A DRY AIR MASS IN THE MID-LEVELS. THIS WILL  
SUSTAIN AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM IN WESTERN  
VENEZUELA AND NORTHERN COLOMBIA. BY FRIDAY-SATURDAY THIS WILL  
SUSTAIN 15-20MM/DAY AND MAXIMA OF 30-60MM IN COLOMBIA...TO THEN  
DISSIPATE.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON/GALVEZ...WPC (USA)  

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page