704  
WTNT43 KNHC 281500  
TCDAT3  
 
TROPICAL DEPRESSION EIGHTEEN DISCUSSION NUMBER 4  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182017  
1100 AM EDT SAT OCT 28 2017  
 
DATA FROM AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT INDICATE  
THAT THE LOW PRESSURE SYSTEM LOCATED OVER THE NORTHWESTERN  
CARIBBEAN SEA HAS DEVELOPED A WELL-DEFINED LOW-LEVEL CIRCULATION  
CENTER. SATELLITE IMAGERY ALSO SHOWS MORE CENTRAL DEEP CONVECTION  
HAS DEVELOPED AND PERSISTED IN THE INNER-CORE REGION SINCE  
YESTERDAY. BASED ON THESE DATA, THE DISTURBANCE HAS BEEN UPGRADED  
TO TROPICAL DEPRESSION EIGHTEEN.  
 
WITH THE RECENT REDEVELOPMENT OF THE INNER-CORE REGION THIS MORNING,  
THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 020/19 KT. THE GLOBAL  
MODELS REMAIN IN EXCELLENT AGREEMENT ON AN APPROACHING FRONTAL  
SYSTEM AND DEEP MID-TROPOSPHERIC TROUGH ACCELERATING THE CYCLONE  
NORTH-NORTHEASTWARD ACROSS WEST-CENTRAL CUBA TODAY, FOLLOWED BY A  
MOTION TOWARD THE NORTHEAST TONIGHT AND SUNDAY, WITH THE SYSTEM  
PASSING ABOUT MIDWAY BETWEEN BERMUDA AND THE SOUTHEASTERN UNITED  
STATES IN 36-48 HOURS. THE NEW NHC FORECAST TRACK IS ESSENTIALLY  
JUST AN UPDATE OF THE PREVIOUS ADVISORY DUE TO THE GOOD AGREEMENT IN  
THE GLOBAL AND CONSENSUS MODELS, WHICH LIE ALONG OR JUST A TAD TO  
THE WEST OF THE OFFICIAL FORECAST TRACK.  
 
THE VERTICAL WIND SHEAR AFFECTING THE CYCLONE IS EXPECTED TO REMAIN  
SOMEWHAT FAVORABLE FOR STRENGTHENING TO OCCUR FOR THE NEXT 24 HOURS  
OR SO, WITH THE DEPRESSION EXPECTED TO BECOME A TROPICAL STORM BY  
TONIGHT. THEREAFTER, BAROCLINIC PROCESSES ASSOCIATED WITH THE  
AFOREMENTIONED FRONTAL SYSTEM ARE FORECAST TO INDUCE SOME ADDITIONAL  
STRENGTHENING BEFORE THE CYCLONE MERGES WITH THE FRONTAL SYSTEM  
AND BECOMES AN EXTRATROPICAL LOW BY 48 HOURS. DISSIPATION IS  
EXPECTED BY 72 HOURS WHEN THE SYSTEM IS LOCATED OVER THE FAR NORTH  
ATLANTIC.  
 
KEY MESSAGES:  
 
1. WHILE THE FORECAST TRACK OF THE CENTER LIES ABOUT 35 MILES  
SOUTHEAST OF THE UPPER FLORIDA KEYS AND EXTREME SOUTHEAST FLORIDA  
AND MOST OF THE WINDS ARE EXPECTED TO REMAIN EAST OF THE CENTER,  
ONLY A SLIGHT DEVIATION TO THE WEST OF THE EXPECTED TRACK OR AN  
INCREASE IN THE SIZE OF THE WIND FIELD COULD BRING TROPICAL-STORM-  
FORCE WINDS ACROSS THESE LAND AREAS. FOR THAT REASON, A TROPICAL  
STORM WATCH HAS BEEN ISSUED FOR THESE AREAS.  
 
FORECAST POSITIONS AND MAX WINDS  
 
INIT 28/1500Z 20.8N 82.9W 30 KT 35 MPH  
12H 29/0000Z 23.0N 81.8W 35 KT 40 MPH  
24H 29/1200Z 26.6N 78.5W 40 KT 45 MPH  
36H 30/0000Z 31.5N 74.0W 45 KT 50 MPH  
48H 30/1200Z 37.5N 69.5W 50 KT 60 MPH...POST-TROP/EXTRATROP  
72H 31/1200Z...DISSIPATED  
 

 
FORECASTER STEWART  
 
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