531  
WTNT42 KNHC 101459  
TCDAT2  
 
TROPICAL STORM OPHELIA DISCUSSION NUMBER 6  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL172017  
1100 AM AST TUE OCT 10 2017  
 
CONVECTIVE BANDING HAS CONTINUED TO BECOME BETTER DEFINED SINCE THE  
PREVIOUS ADVISORY, AND AN EYE-LIKE FEATURE HAS DEVELOPED IN THE  
CENTER OF THE CONVECTION. HOWEVER, DESPITE THE MUCH IMPROVED  
SATELLITE APPEARANCE, IT APPEARS THAT THE INCREASED CONVECTIVE  
ORGANIZATION HAS NOT YET TRANSLATED INTO AN INCREASE IN THE SURFACE  
WINDS BASED ON A 1204Z ASCAT-B OVERPASS, WHICH ONLY SHOWED WINDS OF  
30-31 KT IN THE SOUTHERN QUADRANT. SOME UNDERSAMPLING IS LIKELY DUE  
TO THE SMALL 25-NMI RADIUS OF MAXIMUM WINDS, AND TWO NEARBY SHIPS  
WERE UNDER-SAMPLED BY AT LEAST 5 KT. DVORAK INTENSITY ESTIMATES  
RANGE FROM T2.3/33 KT FROM UW-CIMSS TO T3.0/45 KT FROM TAFB TO  
T4.0/65 KT FROM SAB. FOR NOW, THE INITIAL INTENSITY WILL REMAIN AT  
45 KT, WHICH IS AN AVERAGE OF THE SCATTEROMETER WINDS AND ALL OF THE  
OTHER AVAILABLE INTENSITY ESTIMATES.  
 
OPHELIA HAS BEEN LUMBERING ALONG SLOWLY TOWARD THE SOUTHEAST DURING  
THE PAST 6 HOURS, AND THE INITIAL MOTION ESTIMATE IS NOW 130/04 KT.  
THE LATEST MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON THE  
CYCLONE MOVING SLOWLY TOWARD THE SOUTHEAST FOR NEXT 48 HOURS OR SO.  
BY 72 HOURS, OPHELIA IS EXPECTED TO TURN NORTHEASTWARD AND  
GRADUALLY ACCELERATE INTO THE WESTERLIES AHEAD OF A DEEP-LAYER  
TROUGH. SINCE THE NHC MODEL GUIDANCE IS TIGHTLY PACKED ABOUT THE  
PREVIOUS ADVISORY TRACK, ONLY MINOR ADJUSTMENTS WERE MADE FOR THIS  
ADVISORY.  
 
THE INTENSITY FORECAST ISN'T AS STRAIGHTFORWARD AS THE TRACK  
FORECAST DUE TO THE AFOREMENTIONED DIFFERENCES IN THE INTENSITY  
ESTIMATES. HOWEVER, GIVEN THAT BOTH THE GFS AND ECMWF MODELS  
ACCURATELY PREDICTED MUCH LOWER INTENSITY VALUES OF 35-40 KT FOR  
THE 1200Z INITIAL TIME PERIOD, A BLEND OF THOSE MODELS WERE USED TO  
CONSTRUCT THE INTENSITY FORECAST FOR THIS ADVISORY PACKAGE. IN  
ADDITION TO THE SLIGHTLY LOWER INTENSITY FORECAST, THE WIND RADII  
WERE ALSO DECREASED BOTH AT THE INITIAL TIME AND THROUGHOUT THE  
FORECAST PERIOD.  
 
FORECAST POSITIONS AND MAX WINDS  
 
INIT 10/1500Z 31.5N 38.3W 45 KT 50 MPH  
12H 11/0000Z 30.9N 37.9W 50 KT 60 MPH  
24H 11/1200Z 30.2N 37.4W 55 KT 65 MPH  
36H 12/0000Z 29.8N 36.9W 60 KT 70 MPH  
48H 12/1200Z 30.0N 36.2W 65 KT 75 MPH  
72H 13/1200Z 31.2N 33.8W 70 KT 80 MPH  
96H 14/1200Z 33.4N 28.5W 70 KT 80 MPH  
120H 15/1200Z 36.0N 21.5W 70 KT 80 MPH...POST-TROP/EXTRATROP  
 

 
FORECASTER STEWART  
 
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