814  
WTNT42 KNHC 131440  
TCDAT2  
 
HURRICANE OPHELIA DISCUSSION NUMBER 18  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL172017  
1100 AM AST FRI OCT 13 2017  
 
THE EYE OF OPHELIA HAS BECOME A BIT MORE APPARENT IN VISIBLE AND  
INFRARED IMAGERY DURING THE PAST COUPLE OF HOURS, BUT THE CLOUD TOPS  
AROUND THE EYE HAVE ALSO WARMED RECENTLY. THE INITIAL INTENSITY IS  
SET TO 85 KT BASED ON A BLEND OF THE LATEST SUBJECTIVE AND OBJECTIVE  
DVORAK CI AND FINAL-T NUMBERS. THE HURRICANE WILL REMAIN IN AN  
ENVIRONMENT OF MARGINAL SSTS AND LIGHT TO MODERATE SHEAR FOR THE  
NEXT DAY OR SO, WHICH SUGGESTS LITTLE CHANGE IN INTENSITY DURING  
THAT TIME. BY 36 HOURS, THE SHEAR WILL BEGIN TO INCREASE AS A  
POWERFUL UPPER-LEVEL TROUGH APPROACHES FROM THE WEST, BUT OPHELIA  
SHOULD REMAIN AT HURRICANE FORCE DURING EXTRATROPICAL TRANSITION AS  
IT UNDERGOES A FAVORABLE INTERACTION WITH THE AFOREMENTIONED TROUGH  
AND TAKES ON A WARM SECLUSION STRUCTURE. THE TRANSITION PROCESS  
IS EXPECTED TO BE COMPLETE BY 72 HOURS, AND POST-TROPICAL OPHELIA  
SHOULD GRADUALLY WEAKEN AS THE CYCLONE OCCLUDES BENEATH THE UPPER  
TROUGH. THE LOW-LEVEL CIRCULATION OF OPHELIA IS EXPECTED TO  
DISSIPATE OVER SCANDINAVIA BY DAY 5.  
 
THE INITIAL MOTION ESTIMATE IS 060/10. THE TRACK FORECAST REASONING  
REMAINS UNCHANGED FROM THE PREVIOUS ADVISORY. OPHELIA SHOULD MOVE  
EAST-NORTHEASTWARD AHEAD OF THE APPROACHING UPPER-LEVEL TROUGH WITH  
A STEADY INCREASE IN FORWARD SPEED THROUGH THE NEXT 24 HOURS. THE  
HURRICANE SHOULD TURN NORTHEASTWARD BY 48 HOURS FOLLOWED BY A  
NORTH-NORTHEASTWARD MOTION AT DAYS 3 AND 4. THE TRACK MODEL GUIDANCE  
IS IN GOOD AGREEMENT ON THIS OVERALL SCENARIO, BUT THERE ARE SOME  
DIFFERENCES IN FORWARD SPEED BEYOND 48 HOURS. THE NEW NHC TRACK  
IS SIMILAR TO THE PREVIOUS ONE AND LIES BETWEEN THE LATEST TVCA  
MULTI-MODEL CONSENSUS AND THE HCCA CORRECTED CONSENSUS AID THROUGH  
THE FORECAST PERIOD. ON THIS TRACK, THE CENTER OF OPHELIA IS  
EXPECTED TO MOVE SOUTHEAST OF THE AZORES DURING THE NEXT 36 HOURS  
AND THEN MOVE NEAR OR OVER IRELAND AND THE WESTERN PART OF THE UK IN  
3 TO 4 DAYS. GIVEN THE EXPECTED INCREASE IN THE SIZE OF OPHELIA'S  
WIND FIELD DURING EXTRATROPICAL TRANSITION, IMPACTS FROM STRONG  
WINDS AND RAIN ARE BECOMING INCREASINGLY LIKELY OVER PORTIONS OF THE  
BRITISH ISLES REGARDLESS OF THE EXACT TRACK OF THE CENTER.  
 
WHILE THE NHC TRACK CONTINUES TO KEEP THE CENTER OF OPHELIA SOUTH  
AND EAST OF THE AZORES, TROPICAL-STORM-FORCE WINDS ARE POSSIBLE  
THROUGHOUT THE AZORES BEGINNING LATE SATURDAY OR SATURDAY NIGHT DUE  
TO AN APPROACHING COLD FRONT. ANY DEVIATION TO THE LEFT OF THE  
FORECAST TRACK COULD BRING STRONGER WINDS TO THE ISLANDS. INTERESTS  
IN THE AZORES SHOULD REFER TO PRODUCTS ISSUED BY THE AZORES WEATHER  
FORECAST AND WATCH CENTER.  
 
A 1242 UTC ASCAT-B PASS WAS HELPFUL IN ANALYZING THE 34-KT WIND  
RADII AROUND OPHELIA.  
 
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 BECOMING MORE 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 13/1500Z 31.8N 32.9W 85 KT 100 MPH  
12H 14/0000Z 32.6N 30.9W 85 KT 100 MPH  
24H 14/1200Z 34.1N 27.3W 85 KT 100 MPH  
36H 15/0000Z 36.5N 22.6W 80 KT 90 MPH  
48H 15/1200Z 40.7N 17.9W 80 KT 90 MPH  
72H 16/1200Z 51.0N 11.5W 70 KT 80 MPH...POST-TROP/EXTRATROP  
96H 17/1200Z 60.0N 4.0W 50 KT 60 MPH...POST-TROP/EXTRATROP  
120H 18/1200Z...DISSIPATED  
 

 
FORECASTER BRENNAN  
 
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