[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 252052
TCDAT4

HURRICANE IRENE DISCUSSION NUMBER  22
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 PM EDT THU AUG 25 2011

THE EYE OF IRENE MOVED OVER ABACO ISLAND EARLIER THIS AFTERNOON. AN
AUTOMATED WEATHER STATION ON THE ISLAND MEASURED A MINIMUM PRESSURE
OF 950.4 MB AROUND 1700 UTC. THE AIR FORCE RESERVE HURRICANE HUNTER
AIRCRAFT INVESTIGATING IRENE THIS AFTERNOON HAS REPORTED A 700 MB
PEAK-FLIGHT WIND OF 99 KT. ALTHOUGH RECENT AIRCRAFT DATA DO NOT
QUITE SUPPORT THE 100-KT ADVISORY INTENSITY...WE WILL HOLD THE
INTENSITY FOR A LITTLE LONGER TO SEE IF THE AIRCRAFT FINDS HIGHER
WINDS.

IRENE CONTINUES MOVING NORTH-NORTHWESTWARD AT ABOUT 12 KT. THERE HAS
BEEN NO CHANGE TO THE TRACK FORECAST REASONING. IRENE IS FORECAST
TO TURN NORTHWARD BY EARLY FRIDAY AS IT MOVES THROUGH A BREAK IN
THE SUBTROPICAL RIDGE. AFTER 24 HOURS...THE HURRICANE IS EXPECTED
TO MOVE ON A HEADING BETWEEN NORTH AND NORTH-NORTHEAST AS A TROUGH
BYPASSES THE CYCLONE TO THE NORTH. THIS WILL LEAVE THE IRENE IN A
STEERING PATTERN THAT SHOULD KEEP THE HURRICANE ON THAT GENERAL
HEADING AS IT MOVES VERY NEAR OR OVER MID-ATLANTIC COAST. THE TRACK
GUIDANCE HAS COME INTO BETTER AGREEMENT ON THIS SOLUTION...AND THE
CONFIDENCE IN THE TRACK FORECAST IS INCREASING. THE NEW TRACK HAS
BEEN NUDGED WESTWARD AND IS CLOSE TO THE CENTER OF THE GUIDANCE
ENVELOPE. IT IS ALSO IN GOOD AGREEMENT WITH THE 1200 UTC GFS. SINCE
IRENE IS A LARGE TROPICAL CYCLONE...ONE SHOULD NOT FOCUS ON THE
EXACT TRACK OF IRENE...AS SIGNIFICANT IMPACTS WILL BE FELT WELL
AWAY FROM THE CENTER.

THERE IS STILL SOME TIME FOR IRENE TO STRENGTHEN AS IT WILL BE
MOVING OVER WARM WATER AND THE SHEAR REMAINS LOW.  HOWEVER...THE
UPDATED FORECAST CALLS FOR A LITTLE LOWER INTENSITY OVER
THE FIRST 24-36 HOURS.  IN ABOUT 48 HOURS...SOUTHWESTERLY SHEAR IS
FORECAST TO INCREASE...WHICH SHOULD START A WEAKENING PROCESS.
HOWEVER...SINCE IRENE HAS SUCH A LARGE AND INTENSE CIRCULATION...
IT WILL PROBABLY BE SLOW TO WEAKEN.


FORECAST POSITIONS AND MAX WINDS

INIT  25/2100Z 27.0N  77.3W  100 KT 115 MPH
 12H  26/0600Z 28.7N  77.8W  100 KT 115 MPH
 24H  26/1800Z 30.6N  77.8W  105 KT 120 MPH
 36H  27/0600Z 32.5N  77.4W  100 KT 115 MPH
 48H  27/1800Z 34.5N  76.9W   95 KT 110 MPH
 72H  28/1800Z 39.8N  74.6W   75 KT  85 MPH...INLAND
 96H  29/1800Z 48.5N  68.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  30/1800Z 56.0N  54.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
FORECASTER BROWN


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