436  
WTNT43 KNHC 280839  
TCDAT3  
 
POTENTIAL TROPICAL CYCLONE EIGHTEEN DISCUSSION NUMBER 3  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182017  
500 AM EDT SAT OCT 28 2017  
 
SCATTEROMETER DATA FROM SEVERAL HOURS AGO INDICATED THAT THE  
DISTURBANCE CONSISTS OF A BROAD CIRCULATION WITH A 100-150 N MI WIDE  
AREA OF LIGHT WINDS (LESS THAN 10 KT) AND AN EQUALLY AS LARGE RADIUS  
OF MAXIMUM WINDS. THE SYSTEM STILL DOES NOT APPEAR TO HAVE A  
WELL-DEFINED CENTER OF CIRCULATION, AND IN FACT, THE ASCAT DATA ALSO  
SHOWED THAT THE MAXIMUM WINDS ARE DOWN TO ABOUT 30 KT. THE  
ASSOCIATED DEEP CONVECTION IS RATHER DISORGANIZED BUT HAS BEEN  
INCREASING IN COVERAGE NEAR THE ESTIMATED CENTER DURING THE PAST  
FEW HOURS.  
 
WHILE THE EXACT CENTER IS DIFFICULT TO LOCATE, THE DISTURBANCE'S  
CIRCULATION APPEARS TO BE MOVING JUST EAST OF DUE NORTH, OR 010/9  
KT. THE DISTURBANCE IS BEGINNING TO ACCELERATE IN THE FLOW AHEAD  
OF A DEEP-LAYER TROUGH LOCATED OVER THE EASTERN THREE-QUARTERS OF  
THE UNITED STATES, AND THIS PATTERN IS EXPECTED TO CAUSE THE SYSTEM  
TO TURN NORTHEASTWARD AND ACCELERATE FURTHER DURING THE NEXT COUPLE  
OF DAYS. ALTHOUGH THE TRACK MODELS ARE IN AGREEMENT ON THIS GENERAL  
SCENARIO, THE OVERALL GUIDANCE ENVELOPE HAS SHIFTED A LITTLE  
WESTWARD, MOST LIKELY AS A RESULT OF A REPOSITIONING OF THE  
DISTURBANCE'S CURRENT LOCATION. THE NEW NHC FORECAST HAS THEREFORE  
BEEN NUDGED WESTWARD AS WELL, LYING CLOSEST TO HCCA AND TVCA MODELS  
THROUGH 36 HOURS.  
 
THE DISTURBANCE IS CURRENTLY LOCATED IN ITS BEST ENVIRONMENT  
SHEAR-WISE, BUT THE SYSTEM'S BROAD AND ELONGATED STRUCTURE IS  
LIKELY DELAYING INTENSIFICATION. ALTHOUGH THE SHEAR WILL BE  
INCREASING, IT SHOULD REMAIN LOW ENOUGH FOR THE NEXT 12-18 HOURS TO  
SUPPORT SOME STRENGTHENING IF THE CIRCULATION CAN TIGHTEN UP. IN  
ADDITION, UPPER-LEVEL DIVERGENCE IS EXPECTED TO INCREASE, WHICH  
SHOULD ALSO SUPPORT SOME STRENGTHENING. SINCE THE DISTURBANCE HAS  
SUCH A BROAD CIRCULATION, THE NHC INTENSITY FORECAST CLOSELY  
FOLLOWS THE INTENSITY TRENDS OF THE GFS AND IS NOT TOO DIFFERENT  
FROM THE PREVIOUS ADVISORY. THE SYSTEM IS NOW EXPECTED TO MERGE  
WITH A COLD FRONT AND BE EXTRATROPICAL BY 48 HOURS AND THEN  
DISSIPATE BY 72 HOURS.  
 
EVEN THOUGH THE TRACK FORECAST HAS SHIFTED A LITTLE CLOSER TO SOUTH  
FLORIDA AND THE FLORIDA KEYS, THE STRONGEST WINDS ARE EXPECTED TO  
BE WELL TO THE EAST AND SOUTHEAST OF THE CENTER OVER THE ATLANTIC  
WATERS AND THE BAHAMAS. THEREFORE, TROPICAL STORM WATCHES OR  
WARNINGS DO NOT APPEAR NECESSARY FOR FLORIDA AT THIS TIME.  
 
FORECAST POSITIONS AND MAX WINDS  
 
INIT 28/0900Z 19.6N 84.2W 30 KT 35 MPH...POTENTIAL TROP CYCLONE  
12H 28/1800Z 21.7N 82.9W 35 KT 40 MPH...TROPICAL CYCLONE  
24H 29/0600Z 24.9N 80.1W 40 KT 45 MPH  
36H 29/1800Z 28.7N 76.5W 45 KT 50 MPH  
48H 30/0600Z 34.2N 71.0W 50 KT 60 MPH...POST-TROP/EXTRATROP  
72H 31/0600Z...DISSIPATED  
 

 
FORECASTER BERG  
 
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