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 066 
 WTNT41 KNHC 300844
 TCDAT1
  
 HURRICANE OPHELIA DISCUSSION NUMBER  31
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL162011
 500 AM AST FRI SEP 30 2011
  
 OPHELIA HAS BEEN RAPIDLY STRENGTHENING DURING THE PAST 12 HOURS
 BASED ON AN EYE FEATURE OCCASIONALLY APPARENT ON BOTH INFRARED AND
 NIGHT-VISIBLE SATELLITE IMAGES. MICROWAVE IMAGERY INDICATES A
 WELL-DEVELOPED AND CLOSED DEEP-LAYER EYE...ALBEIT TILTED SLIGHTLY
 TO THE NORTHEAST. A BLEND OF SATELLITE INTENSITY ESTIMATES OF
 T5.0/90 KT FROM SAB...T4.5/77 KT FROM TAFB...AND UW-CIMSS AVERAGE
 ADT OF T4.7/82 KT IS THE BASIS FOR THE 85-KT ADVISORY INTENSITY.
  
 THE INITIAL MOTION ESTIMATE IS 345/08 KT. THERE IS NO SIGNIFICANT
 CHANGE TO THE PREVIOUS FORECAST TRACK REASONING. OPHELIA IS
 CURRENTLY ROUNDING THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
 SUBTROPICAL RIDGE SITUATED ALONG 32N LATITUDE. AN UNSEASONABLY
 STRONG MID-TROPOSPHERIC TROUGH IS FORECAST TO DEEPEN AND MOVE
 EASTWARD TO THE U.S. EAST COAST BY 48 HOURS...AND WILL ACT TO
 ACCELERATE AND LIFT OPHELIA NORTHWARD OVER THE NEXT 72 HOURS. BY
 DAYS 3-4...OPHELIA IS FORECAST TO MERGE WITH A FRONTAL SYSTEM AND
 BE OVER MUCH COLDER WATER...WHICH WILL RESULT IN THE CYCLONE
 BECOMING A STRONG POST-TROPICAL WINTER-TYPE LOW PRESSURE SYSTEM
 THAT WILL TURN EASTWARD NEAR THE CANADIAN MARITIMES. THE ONLY
 NOTICEABLE CHANGE IN THE MODEL GUIDANCE IS A SOUTHWARD SHIFT IN THE
 GUIDANCE TRACKS AFTER 72 HOURS. IN FACT...THE NEW ECMWF RUN BARELY
 TAKES OPHELIA AS FAR NORTH AS 45N LATITUDE. THE OFFICIAL FORECAST
 TRACK WAS NUDGED SLIGHTLY TO THE LEFT THROUGH 72 HOURS...AND THEN
 BROUGHT FARTHER SOUTH IN LINE WITH THE CONSENSUS MODEL...TVCN...BUT
 NOT AS FAR SOUTH AS THE ECMWF MODEL TRACK.
 
 THE OUTFLOW OF OPHELIA REMAINS QUITE IMPRESSIVE...EXCEPT THAT THE
 WESTERN EDGE OF THE CIRRUS OUTFLOW HAS STARTED TO FLATTEN AND
 DISSIPATE AS WESTERLY UPPER-LEVEL WINDS ENCROACH ON THE CYCLONE.
 HOWEVER...THE LIGHT TO MODERATE WESTERLY VERTICAL WIND SHEAR THAT
 IS CURRENTLY AFFECTING THE CYCLONE IS FORECAST TO TURN MORE FROM
 SOUTH-SOUTHWEST BY 36-48 HOURS...WHICH SHOULD ALLOW FOR SOME
 ADDITIONAL STRENGTHENING TO OCCUR. ALTHOUGH FURTHER RAPID
 STRENGTHENING IS A POSSIBILITY...THE VERTICAL SHEAR IS FORECAST BY
 THE SHIPS MODEL TO FLUCTUATE BETWEEN 5 AND 15 KT DURING THE NEXT 48
 HOURS...WHICH SHOULD ACT TO KEEP THE EYE TILTED AT TIMES AND LIKELY
 DISRUPT THE RAPID INTENSIFICATION PROCESS. AS A RESULT...ONLY
 MODEST STRENGTHENING IS FORECAST UNTIL OPHELIA REACHES 22C AND
 COLDER SSTS SHORTLY AFTER THE 48-HOUR TIME PERIOD...WHICH IS ALSO
 COINCIDENT WITH AN EXPECTED SHARP INCREASE IN THE VERTICAL SHEAR.
 THE INTENSITY FORECAST IS SIMILAR TO THE INTENSITY CONSENSUS
 MODEL...ICON...THROUGH 72 HOURS...AND THEN LEANS CLOSE TO THE LGEM
 MODEL AFTER THAT. IT IS WORTH NOTING THAT SOME OF THE GLOBAL MODELS
 ARE NOW HOLDING ON TO OPHELIA AS A ROBUST EXTRATROPICAL LOW
 PRESSURE SYSTEM BEYOND 96 HOURS.
 
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  30/0900Z 22.4N  62.6W   85 KT 100 MPH
  12H  30/1800Z 24.2N  63.1W   90 KT 105 MPH
  24H  01/0600Z 27.0N  63.4W   90 KT 105 MPH
  36H  01/1800Z 30.1N  62.9W   95 KT 110 MPH
  48H  02/0600Z 34.6N  61.7W   95 KT 110 MPH
  72H  03/0600Z 44.3N  57.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
  96H  04/0600Z 51.5N  38.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 120H  05/0600Z...DISSIPATED
  
 $$
 FORECASTER STEWART
  
 
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