489  
WTNT42 KNHC 140233  
TCDAT2  
 
HURRICANE OPHELIA DISCUSSION NUMBER 20  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL172017  
1100 PM AST FRI OCT 13 2017  
 
THE EYE OF HURRICANE OPHELIA CONTINUES TO BE REMARKABLY DISTINCT ON  
SATELLITE AND REMAINS SURROUNDED BY A RING OF DEEP CONVECTION. AN  
AVERAGE OF OBJECTIVE AND SUBJECTIVE DVORAK NUMBERS STILL SUPPORT AN  
INITIAL INTENSITY OF 85 KT. THE HURRICANE HAS MANAGED TO MOVE  
THROUGH AN AREA OF RELATIVELY LOW SHEAR AND MAINTAIN ITS INTENSITY  
SO FAR. THIS IS ABOUT TO CHANGE IN A DAY OR SO WHEN A COLD FRONT  
REACHES THE CIRCULATION OF THE HURRICANE AND THE SHEAR INCREASES  
SUBSTANTIALLY. BY THEN, ANY INCREASE IN INTENSITY SHOULD BE  
TRIGGERED BY BAROCLINIC FORCES AS THE CYCLONE BECOMES EXTRATROPICAL.  
THE NHC FORECAST CALLS FOR OPHELIA TO BECOME EXTRATROPICAL IN ABOUT  
48 HOURS AND DISSIPATE OR ABSORBED BY ANOTHER LARGE LOW BEYOND 4  
DAYS.  
 
GIVEN THAT THE CYCLONE IS FORECAST TO BECOME EXTRATROPICAL, THE WIND  
FIELD SHOULD EXPAND, RESULTING IN IMPACTS OVER PORTIONS OF THE  
BRITISH ISLES REGARDLESS OF ITS EXACT LOCATION OR STRENGTH. BY 96  
HOURS, OPHELIA SHOULD HAVE WEAKENED DUE TO THE INTERACTION WITH  
LAND, CAUSING THE SURFACE CIRCULATION TO BECOME ILL-DEFINED, AND  
DISSIPATION IS EXPECTED SHORTLY THEREAFTER.  
 
NOW THAT THE CYCLONE IS WELL EMBEDDED IN THE MID-LATITUDE  
WESTERLIES, IT IS MOVING FASTER TOWARD THE EAST-NORTHEAST OR 060  
DEGREES AT 17 KT. AN ADDITIONAL INCREASE IN FORWARD SPEED IS  
ANTICIPATED AS A LARGE HIGH-LATITUDE TROUGH ACCELERATES THE WESTERLY  
FLOW. TRACK MODELS ARE IN VERY GOOD AGREEMENT AND THIS INCREASES THE  
CONFIDENCE IN THE NHC FORECAST WHICH IS IN THE MIDDLE OF THE TIGHT  
GUIDANCE ENVELOPE.  
 
ALTHOUGH THE CENTER OF OPHELIA IS NOT EXPECTED TO REACH IRELAND OR  
THE UK FOR ANOTHER 2-3 DAYS, WIND AND RAIN EFFECTS WILL ARRIVE  
WELL IN ADVANCE OF THE CYCLONE CENTER. INDIVIDUALS IN THOSE  
LOCATIONS SHOULD CONSULT PRODUCTS FROM THEIR LOCAL METEOROLOGICAL  
SERVICE FOR MORE INFORMATION ON LOCAL IMPACTS.  
 
TROPICAL-STORM-FORCE WINDS ARE POSSIBLE THROUGHOUT THE AZORES  
BEGINNING SATURDAY NIGHT PRIMARILY DUE TO AN APPROACHING COLD FRONT.  
HOWEVER, ANY TRACK DEVIATION TO THE LEFT COULD BRING STRONGER WINDS  
ASSOCIATED WITH OPHELIA'S CIRCULATION TO THE ISLANDS. INTERESTS IN  
THE AZORES SHOULD REFER TO PRODUCTS ISSUED BY THE AZORES WEATHER  
FORECAST AND WATCH CENTER.  
 
KEY MESSAGES:  
 
1. OPHELIA IS EXPECTED TO BECOME A HURRICANE-FORCE POST-TROPICAL  
CYCLONE BY MONDAY BEFORE IT MOVES NEAR IRELAND AND THE UNITED  
KINGDOM. DIRECT IMPACTS FROM WIND AND HEAVY RAIN IN PORTIONS OF  
THESE AREAS ARE LIKELY, ALONG WITH DANGEROUS MARINE CONDITIONS. FOR  
MORE DETAILS ON THE MAGNITUDE, TIMING, AND LOCATION OF IMPACTS FROM  
POST-TROPICAL OPHELIA, RESIDENTS IN IRELAND SHOULD REFER TO PRODUCTS  
ISSUED BY MET EIREANN, AND RESIDENTS IN THE UNITED KINGDOM SHOULD  
REFER TO PRODUCTS ISSUED BY THE MET OFFICE.  
 
FORECAST POSITIONS AND MAX WINDS  
 
INIT 14/0300Z 33.0N 30.6W 85 KT 100 MPH  
12H 14/1200Z 34.3N 27.9W 80 KT 90 MPH  
24H 15/0000Z 36.5N 23.2W 80 KT 90 MPH  
36H 15/1200Z 40.3N 17.7W 75 KT 85 MPH  
48H 16/0000Z 46.0N 14.0W 75 KT 85 MPH...POST-TROP/EXTRATROP  
72H 17/0000Z 56.0N 7.0W 50 KT 60 MPH...POST-TROP/EXTRATROP  
96H 18/0000Z 62.0N 1.0W 40 KT 45 MPH...POST-TROP/EXTRATROP  
120H 19/0000Z...DISSIPATED  
 

 
FORECASTER AVILA  
 
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