369  
WTNT42 KNHC 120840  
TCDAT2  
 
HURRICANE OPHELIA DISCUSSION NUMBER 13  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL172017  
500 AM AST THU OCT 12 2017  
 
SATELLITE IMAGERY INDICATES THAT OPHELIA CONTINUES TO GRADUALLY  
BECOME BETTER ORGANIZED, WITH THE HURRICANE MAINTAINING A  
WELL-DEFINED EYE AND THE CLOUD TOPS IN THE EYEWALL GRADUALLY  
COOLING. THE VARIOUS SUBJECTIVE AND OBJECTIVE SATELLITE INTENSITY  
ESTIMATES RANGE BETWEEN 75-90 KT, AND BASED ON THE PREVIOUS TREND OF  
THE INTENSITY BEING NEAR THE LOWER END OF THE ESTIMATES, THE INITIAL  
INTENSITY IS KEPT AT A POSSIBLY CONSERVATIVE 75 KT.  
 
THE INITIAL MOTION IS 040/3. OPHELIA IS CURRENTLY IN AN AREA OF  
LIGHT STEERING CURRENTS TO THE SOUTH OF THE MID-LATITUDE  
WESTERLIES. THE LARGE-SCALE MODELS FORECAST A DEEP-LAYER TROUGH TO  
AMPLIFY OVER THE CENTRAL AND NORTHEASTERN ATLANTIC DURING THE  
FORECAST PERIOD, WHICH SHOULD STEER OPHELIA NORTHEASTWARD OR  
EAST-NORTHEASTWARD AT AN INCREASING FORWARD SPEED FOR THE NEXT FEW  
DAYS. THE TRACK GUIDANCE HAS CHANGED LITTLE SINCE THE LAST  
ADVISORY, AND THE NEW FORECAST TRACK, WHICH LEANS TOWARD THE HFIP  
CORRECTED CONSENSUS AND THE FLORIDA STATE SUPERENSEMBLE, IS AN  
UPDATE OF THE PREVIOUS FORECAST.  
 
OPHELIA IS FORECAST TO REMAIN IN A LIGHT TO MODERATE SHEAR  
ENVIRONMENT AND OVER MARGINAL SEA SURFACE TEMPERATURES FOR THE NEXT  
24-36 H, AND THE INTENSITY FORECAST SHOWS SOME STRENGTHENING DURING  
THIS TIME IN AGREEMENT WITH THE GUIDANCE. AFTER THAT, THE HURRICANE  
IS EXPECTED TO MOVE OVER COOLER WATER. AS THAT HAPPENS, THOUGH,  
INTERACTION WITH THE ABOVE-MENTIONED WESTERLY TROUGH SHOULD HELP  
OPHELIA KEEP ITS INTENSITY. EXTRATROPICAL TRANSITION SHOULD BEGIN  
BY 72 H, WITH OPHELIA LIKELY TO BECOME A HURRICANE-FORCE BAROCLINIC  
LOW BY 96 H. THE GUIDANCE IS IN GOOD AGREEMENT THAT OPHELIA SHOULD  
AFFECT IRELAND, NORTHERN IRELAND AND GREAT BRITAIN BETWEEN 96-120 H  
AS A POWERFUL EXTRATROPICAL LOW.  
 
ALTHOUGH THE TRACK GUIDANCE KEEPS THE CENTER OFFSHORE OF THE  
AZORES, A TROPICAL STORM WATCH OR WARNING COULD BE NEEDED FOR THE  
EASTERN AZORES ON THURSDAY BECAUSE OF THE FORECASTED INCREASE IN  
WIND RADII IN THE NORTHWESTERN QUADRANT OF THE CYCLONE.  
 
FORECAST POSITIONS AND MAX WINDS  
 
INIT 12/0900Z 30.3N 35.6W 75 KT 85 MPH  
12H 12/1800Z 30.7N 35.2W 80 KT 90 MPH  
24H 13/0600Z 31.3N 34.0W 80 KT 90 MPH  
36H 13/1800Z 32.2N 32.0W 75 KT 85 MPH  
48H 14/0600Z 33.7N 28.6W 75 KT 85 MPH  
72H 15/0600Z 38.5N 20.5W 75 KT 85 MPH  
96H 16/0600Z 49.0N 13.5W 70 KT 80 MPH...POST-TROP/EXTRATROP  
120H 17/0600Z 59.0N 7.0W 55 KT 65 MPH...POST-TROP/EXTRATROP  
 

 
FORECASTER BEVEN  
 
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