286  
WTNT42 KNHC 130851  
TCDAT2  
 
HURRICANE OPHELIA DISCUSSION NUMBER 17  
NWS NATIONAL HURRICANE CENTER MIAMI FL AL172017  
500 AM AST FRI OCT 13 2017  
 
OPHELIA'S EYE HAS BECOME CLOUD FILLED DURING THE PAST SEVERAL HOURS,  
AND AN 0330 UTC GCOM MICROWAVE PASS INDICATED THAT THE HURRICANE  
ONLY HAD ABOUT HALF AN EYEWALL, WITH NEARLY ALL OF THE DEEP  
CONVECTION LOCATED OVER THE EASTERN PART OF THE CIRCULATION.  
HOWEVER, THE INITIAL INTENSITY REMAINS 90 KT BASED ON DVORAK CI  
NUMBERS OF 5.0 FROM TAFB AND SAB.  
 
THE INITIAL MOTION ESTIMATE IS A LITTLE FASTER TOWARD THE  
EAST-NORTHEAST, OR 070/7 KT, WITH OPHELIA EMBEDDED IN THE FLOW AHEAD  
OF A LARGE MID-LATITUDE TROUGH PUSHING EAST OF ATLANTIC CANADA. AS  
THIS TROUGH SWINGS EASTWARD OVER THE NORTH ATLANTIC, OPHELIA IS  
EXPECTED TO CONTINUE ACCELERATING AND TURN NORTHEASTWARD BY DAY 3  
AND NORTH-NORTHEASTWARD BY DAY 4. THERE IS HIGH CONFIDENCE IN  
THE TRACK FORECAST FOR THE FIRST 48 HOURS WHILE OPHELIA REMAINS A  
TROPICAL CYCLONE. ALTHOUGH THERE IS SOME MODEL DIVERGENCE AFTER 48  
HOURS ONCE OPHELIA BECOMES EXTRATROPICAL, THE GLOBAL MODELS REMAIN  
RELATIVELY TIGHTLY CLUSTERED THROUGH DAY 4, AND THEY ALL AGREE THAT  
OPHELIA WILL TRACK VERY CLOSE TO THE WESTERN SHORES OF THE BRITISH  
ISLES ON DAYS 3 AND 4. AS SUCH, VERY LITTLE CHANGE WAS MADE TO THE  
NHC OFFICIAL FORECAST COMPARED WITH THE PREVIOUS ADVISORY. THERE  
IS SIGNIFICANTLY MORE SPREAD IN OPHELIA'S TRACK BY DAY 5, WITH THE  
GFS MOVING OPHELIA OVER THE NORTH SEA WHILE THE ECMWF AND UKMET  
TURN THE CYCLONE EASTWARD OVER NORWAY. HOWEVER, NHC'S GRAPHICAL  
PRODUCT SUITE CANNOT HANDLE FORECAST POINTS EAST OF THE PRIME  
MERIDIAN, SO THE OFFICIAL FORECAST NOW CUTS OFF AFTER DAY 4.  
 
VERTICAL SHEAR OVER OPHELIA MAY DECREASE A BIT OVER THE NEXT 24  
HOURS, AND THE HURRICANE WILL REMAIN OVER MARGINALLY WARM WATERS  
FOR THE NEXT DAY OR TWO. HENCE, ONLY SLIGHT WEAKENING IS  
ANTICIPATED THROUGH 48 HOURS, AND OPHELIA IS FORECAST TO REMAIN A  
TROPICAL CYCLONE DURING THAT PERIOD. OPHELIA IS THEN EXPECTED TO  
MERGE WITH AN APPROACHING COLD FRONT AND DEVELOP INTO A WARM  
SECLUSION BY DAY 3 TO THE SOUTHWEST OF IRELAND, WITH BAROCLINIC  
FORCING LIKELY HELPING TO MAINTAIN THE CYCLONE'S INTENSITY FOR  
ABOUT A DAY. SOME WEAKENING IS ANTICIPATED AFTER DAY 3 WHILE  
OPHELIA MOVES NEAR THE BRITISH ISLES, BUT STRONG WINDS ARE BECOMING  
INCREASINGLY LIKELY OVER PORTIONS OF IRELAND AND UNITED KINGDOM  
REGARDLESS OF THE CYCLONE'S EXACT INTENSITY.  
 
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 BY SATURDAY NIGHT 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 BEFORE 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 13/0900Z 31.1N 33.9W 90 KT 105 MPH  
12H 13/1800Z 31.8N 32.5W 85 KT 100 MPH  
24H 14/0600Z 33.1N 29.7W 85 KT 100 MPH  
36H 14/1800Z 35.0N 25.5W 80 KT 90 MPH  
48H 15/0600Z 37.9N 20.8W 80 KT 90 MPH  
72H 16/0600Z 47.9N 13.7W 75 KT 85 MPH...POST-TROP/EXTRATROP  
96H 17/0600Z 57.5N 6.0W 50 KT 60 MPH...POST-TROP/EXTRATROP  
120H 18/0600Z...EAST OF THE PRIME MERIDIAN  
 

 
FORECASTER BERG  
 
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