971  
FXCA20 KWBC 061847  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
146 PM EST TUE FEB 06 2018  
 
TROPICAL DISCUSSION FROM FEB 06/12 UTC: AT UPPER LEVELS...THE  
SUBEQUATORIAL RIDGE EXTENDS OVER NORTHERN SOUTH AMERICA INTO THE  
SOUTHERN AND EASTERN CARIBBEAN. AT MID-LEVELS...A ROBUST RIDGE  
EXTENDS AN AXIS FROM THE SOUTHERN GULF OF MEXICO/NORTHERN CENTRAL  
AMERICA INTO CUBA...THE BAHAMAS...TO A CLOSED HIGH LOCATED AT 32N  
70W. MODELS CONTINUE FORECASTING THE UPPER RIDGE STRENGTHENING AND  
BUILDING TO THE NORTHWEST...TO EXTEND INTO CUBA/THE BAHAMAS AND  
THE GULF OF MEXICO BY THURSDAY. THE MID-LEVEL RIDGE IS FORECAST TO  
HOLD THROUGH THE CYCLE WHILE ITS CENTER MEANDERS  
EAST-NORTHEASTWARD ACROSS THE FLORIDA STRAIGHT ON WEDNESDAY...TO  
ANDROS ISLAND BY THURSDAY...AND TO 27N 68W BY FRIDAY. GIVEN THE  
INFLUENCE OF THE MID-AND UPPER RIDGES IN LATITUDES TO THE NORTH OF  
20N...SURFACE FRONTS THAT ARRIVE FROM THE UNITED STATES ARE  
FORECAST TO LIMIT THEIR INFLUENCE TO AREAS TO THE NORTH OF THE  
CENTRAL GULF OF MEXICO AND THE FLORIDA STRAIT/NORTHWESTERN BAHAMAS.  
 
ON TUESDAY...AN ILL-DEFINED FRONTAL BOUNDARY IS WEAKENING ACROSS  
THE NORTHWESTERN BAHAMAS WHERE IT WILL STILL PRODUCE TRACE  
RAINFALL ACCUMULATIONS. THE FRONT WILL FINISH DISSIPATING DURING  
TUESDAY. THE NEXT COLD FRONT TO ENTER THE BASIN IS FORECAST TO  
ARRIVE INTO THE EXTREME NORTHWESTERN GULF OF MEXICO BY WEDNESDAY  
EVENING...WHEN THE WESTERN TAIL OF THE FRONT WILL EXTEND INTO  
NORTHERN TAMAULIPAS IN MEXICO. BY THURSDAY EVENING...THE BOUNDARY  
WILL EXTEND ACROSS CENTRAL FLORIDA...INTO THE CENTRAL GULF OF  
MEXICO...WHILE TAIL STARTS TO BECOME ILL-DEFINED ACROSS THE GULF.  
A SHEAR LINE WILL ORGANIZE BY THIS PERIOD TO EXTEND ACROSS THE  
NORTHWEST BAHAMAS...INTO THE FLORIDA STRAIT AND JUST TO THE NORTH  
OF THE YUCATAN PENINSULA.  
 
INITIALLY...RAINFALL ACCUMULATIONS WITH THE FRONT WILL CLUSTER IN  
NORTHEASTERN MEXICO. NOTE THAT DURING WEDNESDAY...ENHANCEMENT IS  
EXPECTED AS THE DIVERGENT RIGHT ENTRANCE OF AN UPPER JET ORGANIZES  
IN NORTHERN MEXICO/TEXAS. THIS WILL LEAD TO SCATTERED  
THUNDERSTORMS WITH ACCUMULATIONS OF 05-10MM/DAY AND MAXIMA OF  
15-20MM IN TAMAULIPAS AND NUEVO LEON. OROGRAPHIC ENHANCEMENT IN  
NORTHERN VERACRUZ/NORTHERN PUEBLA WILL LEAD TO 15-20MM/DAY AND  
MAXIMA OF 25-50MM. INLAND IN THE CENTRAL PLATEAU OF MEXICO...UNDER  
THE INFLUENCE OF CYCLONIC VORTICITY ADVECTION AND MID-LEVEL  
MOISTURE FROM THE WEST...EXPECTING AN INCREASE CONVECTION TO  
SUSTAIN AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM. BY  
THURSDAY-FRIDAY...ACTIVITY WITH THE FRONT WILL WANE. YET...UNDER  
INFLUENCE OF THE UPPER TROUGH TO THE WEST...EXPECTING ENHANCEMENT  
ACROSS THE CENTRAL PLATEAU WITH FORECAST RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-20MM. EAST ALONG THE GULF  
COAST...REMNANT SHOWERS ARE TO PRODUCE 00-05MM/DAY AND MAXIMA OF  
10MM. STRONGER CONVECTION WILL DEVELOP IN THE GULF OF CAMPECHE  
DURING THIS PERIOD...ASSOCIATED WITH AN EASTERLY WAVE (SEE BELOW).  
SHEAR LINE CONVECTION WILL BE VERY LIMITED...AND IS FORECAST TO  
PRODUCE TRACE RAINFALL AMOUNTS IN THE NORTHWEST BAHAMAS ON  
THURSDAY-FRIDAY.  
 
THE LOW-LEVEL JET IS GAINING SPEED IN THE CARIBBEAN AND IS  
FORECAST TO PERSIST THROUGH THE CYCLE...WHILE EXTENDING FROM THE  
LESSER ANTILLES INTO NICARAGUA AND COSTA RICA. IN THE  
MID-LEVELS...WINDS ARE FROM THE NORTH AND ARE FORECAST TO PERSIST  
THROUGH THE CYCLE. THE INCREASED SHEAR...IN COMBINATION WITH THE  
PRESENCE OF THE TRADE WIND CAP AND SEASONALLY DRY AIR ALOFT...IS  
LIMITING POTENTIAL RAINFALL ACCUMULATIONS IN THE ENTIRE BASIN.  
ALTHOUGH SOME ENHANCEMENT IN THE COVERAGE OF TRADE WIND SHOWERS IS  
EXPECTED INTO THE WEEKEND...AS THE MID-LEVELS COOL...RAINFALL  
AMOUNTS WILL BE GENERALLY UNDER 10MM/DAY. EXCEPTIONS INCLUDE  
LOCALIZED OROGRAPHIC ENHANCEMENT IN MOUNTAINOUS REGIONS OF THE  
LESSER ANTILLES...AND ACTIVITY IN ASSOCIATION WITH THE  
AFOREMENTIONED EASTERLY WAVE (SEE BELOW). TRANSIENT ENHANCEMENT IS  
ALSO EXPECTED IN HISPANIOLA ON TUESDAY...IN ASSOCIATION WITH A  
MOIST PLUME CROSSING THE REGION FROM EAST TO WEST. THIS WILL LEAD  
TO AMOUNTS OF 05-10MM/DAY AND VERY ISOLATED MAXIMA OF 15-20MM IN  
REGION OF OROGRAPHIC ENHANCEMENT.  
 
IN NORTHERN SOUTH AMERICA...ACTIVITY IS CLUSTERING TO WESTERN  
COLOMBIA AND ECUADOR...WHILE THE REST OF THE REGION LIES UNDER THE  
INFLUENCE OF DRY MID-LEVELS...ACCELERATED NORTHWESTERLY  
TRADES/ENHANCED LOW-LEVEL SHEAR...AND FAIR WEATHER CONDITIONS. IN  
COLOMBIA/ECUADOR...ENHANCED ACTIVITY IS FAVORED BY THE PACIFIC  
ITCZ...WHICH IS ENTERING THE CONTINENT IN THE SOUTHERN COAST OF  
COLOMBIA. ALTHOUGH THERE IS AN ELEVATED SUBSIDENCE CAP IN PLACE IN  
THE REGION...LOW-LEVEL MOISTURE CONVERGENCE IS BEING ENHANCED BY  
THE NORTHERLY LOW-LEVEL JET ACROSS THE PANAMA ISTHMUS. MODELS ARE  
SUGGESTING A GRADUAL DECREASE IN THE SPEED OF THE JET AND  
ASSOCIATED MOISTURE CONVERGENCE THROUGH THE CYCLE. THIS WILL  
SUSTAIN A GRADUAL DECREASE IN ACCUMULATIONS FROM 05-10MM/DAY AND  
MAXIMA OF 15-25MM THROUGH WEDNESDAY...TO 05-10MM/DAY AND ISOLATED  
MAXIMA OF 15MM BY THURSDAY-FRIDAY.  
 
TO THE EAST...QUIET PATTERN IN THE GUIANAS IS BEING FAVORED BY THE  
ADVECTION OF A STABLE AND DRY AIR MASS FROM THE NORTH ATLANTIC. IN  
THE MEAN TIME...THE ATLANTIC ITCZ REMAINS WELL TO THE  
SOUTH...ENTERING THE CONTINENT TO THE SOUTHEAST OF THE AMAZON  
DELTA. THIS PATTERN WILL CHANGE DURING THURSDAY AS THE ITCZ  
RETURNS TO THE NORTH. THIS WILL BE ACCOMPANIED BY A MOISTURE SURGE  
WITH PRECIPITABLE WATER VALUES EXCEEDING 55MM. THE COMBINATION OF  
MOISTURE AND ENHANCED CONVERGENCE WILL RESULT IN AN INCREASE IN  
PRECIPITATION IN EASTERN AND NORTHERN FRENCH GUIANA ON  
THURSDAY-FRIDAY...WHEN ACCUMULATIONS WILL REACH 10-15MM/DAY AND  
MAXIMA OF 20-45MM. BY FRIDAY-SATURDAY ACTIVITY WILL EXPAND  
WESTWARD INTO SURINAME AND EASTERN GUIANA...YET STRONG CONVECTION  
WILL CLUSTER PRIMARILY OVER FRENCH GUIANA.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
77W 83W 88W 92W 97W 102W 105W 108W EW 17N  
 
AN EASTERLY WAVE IS INITIALIZED AT 77W AND TO THE SOUTH OF 17N.  
THIS WAVE IS MOVING RAPIDLY ACROSS THE SOUTHERN CARIBBEAN...AND IS  
FORECAST TO PRODUCE AN INCREASE IN RAINFALL ACCUMULATIONS IN SAN  
ANDRES/NUEVA PROVIDENCIA ON TUESDAY NIGHT/EARLY WEDNESDAY AND IN  
EASTERN NICARAGUA/NORTHEASTERN HONDURAS DURING WEDNESDAY MORNING.  
AN INCREASE IN CONVECTION IS EXPECTED DURING THE DAY ON  
WEDNESDAY...WHICH WILL LEAD TO AMOUNTS OF 05-10MM/DAY AND MAXIMA  
OF 15-20MM ACROSS NORTHERN HONDURAS INTO SOUTHERN BELIZE. ALTHOUGH  
THE WAVE RAPIDLY EXITS INTO THE PACIFIC...REMNANT MOISTURE WILL  
TRAIL ACROSS NORTHERN CENTRAL AMERICA INTO THE GULF OF CAMPECHE  
DURING WEDNESDAY-THURSDAY. THIS WILL REINFORCE THE TROUGH PATTERN  
IN THE GULF OF CAMPECHE ON THURSDAY...AND LEAD TO ENHANCED  
MOISTURE CONVERGENCE TO PRODUCE AMOUNTS OF 15-20MM/DAY AND MAXIMA  
OF 35-70MM.  
 
GORDON...NMS (BELIZE)  
NIXON...BDM (THE BAHAMAS)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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