729  
WTNT42 KNHC 122037  
TCDAT2  
 
HURRICANE OPHELIA DISCUSSION NUMBER 15  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL172017  
500 PM AST THU OCT 12 2017  
 
OPHELIA'S STRUCTURE HAS CONTINUED TO IMPROVE DURING THE AFTERNOON.  
THE EYE OF THE HURRICANE HAS CLEARED AND IS SURROUNDED BY A RING OF  
CLOUD TOPS COLDER THAN -55 DEG C. DVORAK CLASSIFICATIONS FROM TAFB  
AND THE UW-CIMSS ADT HAVE INCREASED ACCORDINGLY, AND ON THAT BASIS  
THE INITIAL INTENSITY HAS BEEN INCREASED TO 85 KT. OPHELIA IS  
NEARLY STATIONARY, WHICH COULD CAUSE THE HURRICANE TO STOP  
STRENGTHENING, OR EVEN WEAKEN SLIGHTLY DURING THE NEXT 12 TO 24  
HOURS DUE TO UPWELLING EFFECTS. THAT SAID, THE INTENSITY GUIDANCE  
IS IN GOOD AGREEMENT THAT OPHELIA WILL REMAIN AT HURRICANE STRENGTH  
FOR THE NEXT 48 H WHILE IT REMAINS IN A FAIRLY UNSTABLE, LOW-SHEAR  
ENVIRONMENT. BEYOND THAT TIME, EXTRATROPICAL TRANSITION WILL BEGIN,  
THOUGH BAROCLINIC FORCING WILL LIKELY KEEP POST-TROPICAL OPHELIA  
NEAR HURRICANE STRENGTH AS IT APPROACHES IRELAND AND THE UK. THE  
NEW INTENSITY FORECAST IS VERY SIMILAR TO THE PREVIOUS ADVISORY, AND  
IS GENERALLY CLOSE TO THE MULTI-MODEL INTENSITY CONSENSUS.  
 
ALTHOUGH OPHELIA IS CURRENTLY STATIONARY, A MID-LATITUDE TROUGH  
SHOULD CAUSE IT TO BEGIN MOVING TOWARD THE EAST-NORTHEAST WITHIN  
ABOUT 24 HOURS. THE CYCLONE WILL THEN ACCELERATE ON THAT HEADING IN  
THE FASTER MID-LATITUDE WESTERLY FLOW AHEAD OF THE TROUGH, BEFORE  
TURNING TOWARD THE NORTHEAST AROUND DAY 3 AS EXTRATROPICAL  
TRANSITION OCCURS AND THE HURRICANE BECOMES ENTANGLED WITH THE  
SOUTHERN EXTENT OF THE TROUGH. CONFIDENCE IN THE TRACK FORECAST IS  
FAIRLY HIGH FOR THE FIRST 72 H, AND ALL OF THE DYNAMICAL GUIDANCE IS  
TIGHTLY CLUSTERED THROUGH THIS PERIOD. THE MODEL SPREAD INCREASES  
SUBSTANTIALLY AT 96 H AND BEYOND. AS A POST-TROPICAL CYCLONE,  
OPHELIA WILL CONTINUE TO INTERACT WITH THE SOUTHERN EXTENT OF THE  
TROUGH, AND SHOULD TURN TOWARD THE NORTHEAST AS A RESULT OF THIS  
INTERACTION. HOWEVER, THE DETAILS OF THIS TURN VARY GREATLY FROM  
MODEL TO MODEL. THE NEW NHC FORECAST HAS BEEN NUDGED SLIGHTLY  
TOWARD THE EAST AT THIS TIME RANGE, CLOSER TO THE UKMET AND ECMWF  
MODELS, AS WELL AS THE CORRECTED CONSENSUS AIDS HCCA AND FSSE.  
 
WHILE THE TRACK GUIDANCE KEEPS THE CENTER OF OPHELIA SOUTH AND EAST  
OF THE AZORES, TROPICAL-STORM-FORCE WINDS ARE POSSIBLE THROUGHOUT  
THE AZORES BY SUNDAY DUE TO AN APPROACHING FRONT. IN ADDITION, THE  
WIND FIELD OF OPHELIA WILL LIKELY EXPAND AS THE CYCLONE BEGINS  
EXTRATROPICAL TRANSITION, AND 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.  
 
KEY MESSAGES:  
 
1. OPHELIA IS EXPECTED TO TRANSITION TO A HURRICANE-FORCE POST-  
TROPICAL CYCLONE BY MONDAY WHEN IT MOVES NEAR IRELAND AND THE  
UNITED KINGDOM. WHILE POST-TROPICAL OPHELIA WILL LIKELY BRING SOME  
DIRECT IMPACTS FROM WIND AND HEAVY RAIN TO PORTIONS OF THESE AREAS,  
AS WELL AS DANGEROUS MARINE CONDITIONS, GIVEN THE FORECAST  
UNCERTAINTY AT THESE TIME RANGES IT IS TOO SOON TO DETERMINE THE  
EXACT MAGNITUDE, TIMING AND LOCATION OF THE IMPACTS. RESIDENTS IN  
IRELAND AND THE UNITED KINGDOM SHOULD MONITOR THE PROGRESS OF  
OPHELIA FOR THE NEXT SEVERAL DAYS. FOR MORE INFORMATION ON LOCAL  
IMPACTS, RESIDENTS OF 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 12/2100Z 30.4N 35.5W 85 KT 100 MPH  
12H 13/0600Z 31.0N 34.6W 85 KT 100 MPH  
24H 13/1800Z 31.9N 32.6W 80 KT 90 MPH  
36H 14/0600Z 33.2N 29.6W 75 KT 85 MPH  
48H 14/1800Z 35.0N 25.6W 75 KT 85 MPH  
72H 15/1800Z 42.6N 17.1W 75 KT 85 MPH  
96H 16/1800Z 53.0N 10.0W 65 KT 75 MPH...POST-TROP/EXTRATROP  
120H 17/1800Z 62.5N 2.0W 55 KT 65 MPH...POST-TROP/EXTRATROP  
 

 
FORECASTER ZELINSKY  
 
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