117  
FXCA20 KWBC 201823  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
222 PM EDT FRI OCT 20 2017  
 
TROPICAL DISCUSSION FROM OCT 20/12 UTC: THE GFS...CFS AND  
EMPIRICAL WAVE PROPAGATION MODELS OF CPC ARE SUGGESTING THAT THE  
UPPER DIVERGENT PHASE OF THE MADDEN-JULIAN OSCILLATION WILL  
ESTABLISH OVER THE AMERICA SURING THE WEEKEND INTO EARLY NEXT  
WEEK. THIS WILL ENHANCE ANY CONVECTIVE ACTIVITY AND PRECIPITATION  
THAT DEVELOPS IN THE REGION DURING THE LAST 10 DAYS OF OCTOBER.  
 
STRONG POLAR EXITING THE EAST COAST OF THE UNITED STATES CONTINUES  
INTERACTING WITH A SURFACE FRONT THAT IS FORECAST TO LIGER TO THE  
NORTH OF THE BAHAMAS THROUGH THE CYCLE...AS WELL AS WITH A SURFACE  
TROUGH THAT IS TO MEANDER AHEAD OF THE FRONT IN THE BAHAMAS. THE  
DYNAMICAL ENHANCEMENT OF ASCENT IN ASSOCIATION WITH THE  
APPROACHING UPPER TROUGH IS TO PEAK ON FRIDAY...TO THEN MOVE  
SOUTHEASTWARD. THIS WILL LEAD TO A PEAK IN ACCUMULATIONS ON  
FRIDAY-SATURDAY...WHEN EXPECTING 05-10MM/DAY AND ISOLATED MAXIMA  
OF 15-25MM IN THE CENTRAL BAHAMAS...DECREASING TO 00-05MM/DAY AND  
MAXIMA OF 10MM AFTER.  
 
OTHER FEATURE OF INTEREST IS A TRADE WIND SURGE THAT IS  
PROPAGATING ACROSS THE CENTRAL CARIBBEAN. THIS SURGE IS  
ACCOMPANIED BY A SUBSIDENCE CAP THAT SITS AT 900 HPA...BY TRADE  
WINDS IN THE 20-30KT RANGE...AND BY VERY DRY MID-LEVELS.  
ACCORDINGLY...ONCE THE TRADE WIND SURGE CROSSES A  
LOCATION...EXPECTING A SHARP DECREASE IN RAINFALL ACCUMULATIONS.  
ON FRIDAY EVENING THE SURGE EDGE WILL EXTEND ACROSS HAITI...BY  
SATURDAY EVENING JUST WEST OF JAMAICA...AND BY SUNDAY EVENING JUST  
TO THE WEST OF THE CAYMAN ISLANDS. BY THIS TIME THE SURGE WILL  
START LOSING DEFINITION. AHEAD OF THE SURGE...PRECIPITATION IS  
BEING STIMULATED BY ENHANCED TRADE WIND CONVERGENCE...BUT ALSO BY  
A TROPICAL WAVE. THIS WILL INITIALLY LEAD TO 10-15MM/DAY AND  
MAXIMA OF 20-35MM IN JAMAICA...ALTHOUGH STRONGEST ACTIVITY IS  
FORECAST TO REMAIN OFFSHORE. BY SATURDAY-SUNDAY...TROPICAL WAVE  
CONVECTION WILL ENHANCE ACTIVITY IN NORTHEASTERN HONDURAS AND  
EASTERN NICARAGUA. NOTE THAT MOISTURE CONVERGENCE WILL BE  
REINFORCED BY THE CONVERGENCE IN THE MOUTH OF A LOW-LEVEL JET.  
THIS WILL SUSTAIN ACCUMULATIONS OF 15-30MM/DAY AND MAXIMA OF  
40-80MM...THAT ARE TO EXTEND INTO NORTHERN HONDURAS/EASTERN  
GUATEMALA AND SOUTHERN BELIZE. BY SUNDAY-MONDAY...LARGEST  
ACCUMULATIONS ARE EXPECTED IN BELIZE/NORTHERN GUATEMALA AND  
SOUTHERN MEXICO. DURING THIS PERIOD...THE TROPICAL WAVE WILL  
INTERACT WITH A DEVELOPING NORTHERLY SURGE AND A SHEAR LINE IN THE  
GULF OF MEXICO. THIS WILL LEAD TO 25-50MM/DAY AND MAXIMA OF  
75-125MM. LARGER ACCUMULATIONS ARE EXPECTED ON MONDAY-TUESDAY IN  
SOUTHERN MEXICO/NORTHERN GUATEMALA.  
 
REGARDING THE SURGE IN THE GULF OF MEXICO BY THE LATE  
WEEKEND...THE ASSOCIATED SURFACE FRONT IS FORECAST TO EXTEND INTO  
SOUTHERN TEXAS BY SUNDAY EVENING...AND INTO CENTRAL  
VERACRUZ-MEXICO BY MONDAY EVENING. THE SHEAR LINE WILL FORM ON  
SUNDAY...AND BY SUNDAY EVENING IT WILL EXTEND FROM SOUTHERN  
LOUISIANA INTO THE GULF OF CAMPECHE...AND BY MONDAY EVENING THE  
SHEAR LINE WILL EXTEND ACROSS THE YUCATAN CHANNEL INTO WESTERN  
BELIZE/CENTRAL GUATEMALA. THIS WILL REINFORCE THE AFOREMENTIONED  
WET SPELL IN THE REGION...TO SUSTAIN LARGEST ACCUMULATIONS BETWEEN  
SUNDAY AND TUESDAY.  
 
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. THIS  
WILL SUSTAIN ACCUMULATIONS OF 10-15MM/DAY AND MAXIMA OF 20-40MM IN  
COSTA RICA AND WESTERN PANAMA ON A DAILY BASIS. LESSER AMOUNTS ARE  
EXPECTED IN EASTERN PANAMA. NOTE THAT THE ITCZ IS FORECAST TO  
MEANDER IN THE SOUTHERN CARIBBEAN THROUGH THE CYCLE. A SYSTEM OF  
INTEREST IS A BROAD LOW ORGANIZING IN THE REGION DURING  
MONDAY-TUESDAY. THIS WILL SUSTAIN ENHANCED SOUTHWESTERLY WINDS  
ACROSS THE PACIFIC BASINS OF WESTERN PANAMA AND WESTERN COSTA  
RICA. THIS WILL LEAD TO EXTREME MOISTURE CONVERGENCE...WHICH WILL  
LIKELY SUSTAIN RAINFALL ACCUMULATIONS OF 100-200MM/DAY ON SOUTHERN  
COSTA RICA AND WESTERN PANAMA ON THE TUESDAY-EARLY WEDNESDAY TIME  
FRAME. NOTE THAT THE MODELS ARE DIVERGING WITH THE STRENGTH AND  
LOCATION OF THE AREAS OF STRONGEST MOISTURE CONVERGENCE AND  
RAINFALL. THE GFS IS THE MOST AGGRESSIVE...AS IT SUGGESTS MAXIMA  
OF 200-300MM/DAY...WHILE THE UKMET IS THE MOST CONSERVATIVE...AS  
IT SUGGESTS MAXIMA OF 100-150MM/DAY.  
 
IN NORTHERN SOUTH AMERICA AND THE SOUTHERN CARIBBEAN...ITCZ  
CONVERGENCE WILL CONTINUE SUSTAINING MODERATE ACCUMULATIONS IN  
TRINIDAD AND TOBAGO/NORTHEASTERN VENEZUELA...ALTHOUGH AMOUNTS ARE  
DECREASING. THROUGH EARLY SATURDAY EXPECTING 10-15MM/DAY AND  
MAXIMA OF 20-40MM. THIS IS DECREASING TO 10-15MM/DAY AND MAXIMA OF  
20-30MM AFTER. TRANSIENT WET PATTERN IS ALSO EXPECTED IN THE ABC  
ISLANDS...WHERE MOISTURE PLUME TO THE SOUTH OF THE CARIBBEAN  
LOW-LEVEL JET WILL SUSTAIN ACCUMULATIONS OF 05-10MM/DAY AND MAXIMA  
OF 15-20MM/DAY THROUGH EARLY SUNDAY...DECREASING AFTER. ANOTHER  
REGION OF INTEREST IS COLOMBIA...WHERE ACTIVE SEASONAL CONVECTION  
IS BEING REINFORCED BY ENHANCED WESTERLIES ACROSS THE PACIFIC  
BASIN. THIS WILL SUSTAIN ACCUMULATIONS OF 15-20MM/DAY AND MAXIMA  
OF 25-50MM IN WESTERN COLOMBIA ON FRIDAY...WHILE IN  
CENTRAL/NORTHERN COLOMBIA EXPECTING 10-15MM/DAY AND MAXIMA OF  
20-35MM. BY SATURDAY AND INTO MONDAY THIS INCREASES TO 15-20MM/DAY  
AND MAXIMA OF 35-70MM...WHILE IN NORTHERN COLOMBIA EXPECTING  
10-15MM/DAY AND MAXIMA OF 20-40MM.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
41W 43W 45W 48W 52W 55W 58W 61W TW 20N  
77W 80W 82W 84W 87W 89W 90W 91W TW 19N  
94W DISSIPATES TW 22N  
 
A TROPICAL WAVE INITIALIZED AT 41W WILL ARRIVE INTO THE GUIANAS ON  
EARLY MONDAY. ENHANCED TRADE WIND CONVERGENCE AHEAD OF THE WAVE  
AXIS WILL SUSTAIN AN INCREASE IN ACCUMULATIONS TO 10-15MM/DAY AND  
MAXIMA OF 20-30MM.  
 
TROPICAL WAVE INITIALIZED AT 77W WILL HAVE A SIGNIFICANT IMPACT IN  
PRECIPITATION AS IT PROPAGATES INTO CENTRAL AMERICA DURING  
SATURDAY-MONDAY (SEE ABOVE FOR ACCUMULATIONS). IN THE MEAN  
TIME...THE WAVE WILL ENHANCE AMOUNTS IN JAMAICA ON FRIDAY...WHERE  
IT WILL SUSTAIN MAXIMA OF 20-35MM...MOSTLY OFFSHORE.  
 
A TROPICAL WAVE INITIALIZED AT 94W HAS LOST DEFINITION.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
GALVEZ...WPC (USA)  

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page