234  
WTNT42 KNHC 112031  
TCDAT2  
 
HURRICANE OPHELIA DISCUSSION NUMBER 11  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL172017  
500 PM AST WED OCT 11 2017  
 
INTENSITY ESTIMATES FOR OPHELIA STILL RANGE WILDLY. DVORAK  
ESTIMATES, BOTH SUBJECTIVE AND OBJECTIVE, CONTINUE TO SUPPORT A MUCH  
HIGHER INTENSITY THAN OTHER SATELLITE-DERIVED MAXIMUM WIND  
ESTIMATES. ADDING TO THE UNCERTAINTY, SUBJECTIVE DVORAK  
CLASSIFICATIONS AT 1800 UTC WERE HIGHER THAN 6 HOURS PRIOR, BUT  
SINCE THAT TIME, THE RAGGED EYE HAS BECOME OBSCURED IN IR IMAGERY.  
HOWEVER, A RECENT SSMIS PASS AT 1813 UTC INDICATED THAT THE  
CONVECTIVE STRUCTURE OF THE CYCLONE HAS IMPROVED DURING THE DAY, SO  
IT WOULDN'T BE SURPRISING IF THE EYE BECAME APPARENT AGAIN SHORTLY.  
IN AN ATTEMPT TO BLEND ALL AVAILABLE DATA, THE INITIAL INTENSITY HAS  
BEEN INCREASED TO 65 KT, MAKING OPHELIA A HURRICANE. HOWEVER, IT  
SHOULD BE STRESSED THAT THE UNCERTAINTY OF THE INITIAL INTENSITY IS  
HIGHER THAN NORMAL.  
 
THE HURRICANE IS MOVING SLOWLY TOWARD THE EAST AND THE INITIAL  
MOTION ESTIMATE IS 090/3 KT. THE HURRICANE IS EMBEDDED WITHIN WEAK  
STEERING FLOW, AND ONLY A SLOW NORTHEASTWARD DRIFT IS EXPECTED FOR  
THE NEXT 24 H. AFTER THAT TIME, AN APPROACHING DEEP-LAYER TROUGH  
SHOULD FORCE OPHELIA TO ACCELERATE TOWARD THE NORTHEAST. ALL OF THE  
DETERMINISTIC MODELS ARE IN FAIRLY GOOD AGREEMENT ON THE SPEED AND  
TRACK OF OPHELIA, HOWEVER THE VARIOUS MODEL ENSEMBLES SUGGEST THAT  
THE UNCERTAINTY IS MUCH HIGHER, ESPECIALLY REGARDING THE FORWARD  
SPEED OF OPHELIA BEYOND 48 H. THE OFFICIAL TRACK FORECAST FAVORS  
THE DETERMINISTIC MODEL SOLUTIONS, IN PART TO MAINTAIN CONTINUITY  
WITH THE PREVIOUS ADVISORY. THE TRACK FORECAST IS THEREFORE CLOSE  
TO THE MULTI-MODEL CONSENSUS, BUT MUCH FASTER THAN THE VARIOUS  
ENSEMBLE MEAN AIDS.  
 
SINCE IT ISN'T CLEAR EXACTLY HOW STRONG OPHELIA IS, THE INTENSITY  
FORECAST IS LOW CONFIDENCE. ALL OF THE INTENSITY GUIDANCE INDICATES  
THAT STRENGTHENING IS LIKELY FOR THE NEXT 24 TO 36 HOURS, HOWEVER  
THE NEAR STATIONARY MOTION OF THE HURRICANE COULD INDUCE SOME  
UPWELLING AND LIMIT THE EXTENT TO WHICH THE HURRICANE MAY  
STRENGTHEN. AROUND 72 HOURS, THE SHEAR SHOULD BEGIN TO INCREASE  
SUBSTANTIALLY AS OPHELIA BEGINS TO INTERACT WITH THE APPROACHING  
TROUGH, AND EXTRATROPICAL TRANSITION WILL LIKELY BEGIN, ACCOMPANIED  
BY A BROADENING OF THE WIND FIELD AND A GRADUAL DECREASE OF THE  
MAXIMUM WINDS. THE GLOBAL MODELS INDICATE THAT THIS PROCESS WILL  
COMPLETE BY 96 H. THE NEW NHC INTENSITY FORECAST IS SLIGHTLY HIGHER  
THAN THE PREVIOUS FORECAST, BUT LIES ON THE LOWER END OF THE  
INTENSITY GUIDANCE FOR THE FIRST 72 H. IT IS NEAR THE CONSENSUS  
AIDS THEREAFTER.  
 
FORECAST POSITIONS AND MAX WINDS  
 
INIT 11/2100Z 30.0N 36.1W 65 KT 75 MPH  
12H 12/0600Z 30.3N 35.7W 70 KT 80 MPH  
24H 12/1800Z 30.7N 35.2W 75 KT 85 MPH  
36H 13/0600Z 31.4N 34.1W 75 KT 85 MPH  
48H 13/1800Z 32.3N 31.9W 70 KT 80 MPH  
72H 14/1800Z 35.5N 24.5W 70 KT 80 MPH  
96H 15/1800Z 43.0N 16.0W 65 KT 75 MPH...POST-TROP/EXTRATROP  
120H 16/1800Z 53.5N 10.5W 60 KT 70 MPH...POST-TROP/EXTRATROP  
 

 
FORECASTER ZELINSKY  
 
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