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Hurricane IRWIN


ZCZC MIATCDEP1 ALL
TTAA00 KNHC DDHHMM
 
HURRICANE IRWIN DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
800 AM PDT SAT OCT 08 2011
 
THE MODERATE EASTERLY VERTICAL SHEAR PARTIALLY BEING INDUCED BY
NEARBY TROPICAL STORM JOVA IS TAKING ITS TOLL ON IRWIN. THE
LOW-LEVEL CENTER HAS EMERGED ON THE EAST SIDE OF THE DEEP
CONVECTION AS SEEN IN THE FIRST GEOSTATIONARY VISIBLE IMAGERY. BOTH
SUBJECTIVE AND ADVANCED DVORAK INTENSITY ESTIMATES HAVE DROPPED
CONSIDERABLY WITH TAFB...SAB...AND CIMSS ADT INDICATING
CURRENT-INTENSITY NUMBERS OF 4.5...4.0...AND 4.1...RESPECTIVELY.
CIMSS AMSU EVEN SUGGESTS WELL-BELOW HURRICANE INTENSITY. THE
INITIAL INTENSITY IS ESTIMATED TO BE 65 KT...WITH CONSIDERABLE
UNCERTAINTY.  

THE HURRICANE IS CURRENTLY EMBEDDED IN A VERY WEAK STEERING FLOW AND
INITIAL MOTION IS SET AT 345 DEGREES AT 2 KT.  THE CYCLONE SHOULD
START MOVING OFF TOWARD THE EAST WITH INCREASING FORWARD SPEED OVER
THE NEXT FEW DAYS AS IT RESPONDS TO A SHORT-WAVE TROUGH DIGGING
DOWN OVER THE SW UNITED STATES AND NE MEXICO.  THE INFLUENCE ON THE
STEERING BY NEARBY TROPICAL STORM JOVA IS MINIMAL CURRENTLY...
THOUGH THE ECMWF MODEL SUGGESTS SOME FUIJIWHARA INTERACTION AFTER
DAY TWO WITH IRWIN PUSHED TO A SOUTH-OF-EAST TRACK IN A MUTUAL
COUNTER-CLOCKWISE ROTATION OF THE TWO VORTICES.  THE FORECAST
TRACK IS SIMILAR TO THE MULTI-MODEL CONSENSUS.  THE FORECAST IS
ALSO SLIGHTLY SOUTH THE PREVIOUS ADVISORY BECAUSE OF A MODEST
RELOCATION OF THE VORTEX AT THE INITIAL TIME.

THE INTENSITY FORECAST OF IRWIN IS QUITE DIFFICULT. THE EASY PART IS
THAT THE SEA SURFACE TEMPERATURES UNDER THE TRACK OF THE CYCLONE
SHOULD REMAIN A VERY WARM 28C. ALSO...THE VERTICAL SHEAR CURRENTLY
PLAGUING THE CYCLONE SHOULD SOMEWHAT ABATE DURING THE NEXT DAY OR
TWO...ALLOWING A MODERATE REBOUND IN THE INTENSITY TO OCCUR.
HOWEVER...BY DAY THREE THE SHEAR MAY AGAIN INCREASE AT THE SAME
TIME THAT THE ATMOSPHERE BECOMES MORE STABLE TO DEEP CONVECTION.
UNFORTUNATELY...THE INTENSITY GUIDANCE SHOWS A VERY LARGE
VARIABILITY AT THE EXTENDED RANGE...ANYWHERE FROM A WEAK TROPICAL
STORM TO A CATEGORY 2 HURRICANE. THE INTENSITY FORECAST IS BETWEEN
THE MULTI-MODEL CONSENSUS ON THE LOW SIDE AND THE PREVIOUS ADVISORY
ON THE HIGH SIDE...AND HAS EVEN MORE UNCERTAINTY THAN USUAL.
  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  08/1500Z 14.3N 121.0W   65 KT  75 MPH
 12H  09/0000Z 14.6N 120.8W   65 KT  75 MPH
 24H  09/1200Z 14.8N 120.3W   70 KT  80 MPH
 36H  10/0000Z 15.0N 119.4W   75 KT  85 MPH
 48H  10/1200Z 15.1N 118.0W   70 KT  80 MPH
 72H  11/1200Z 15.0N 114.5W   65 KT  75 MPH
 96H  12/1200Z 16.0N 110.5W   60 KT  70 MPH
120H  13/1200Z 19.0N 107.0W   55 KT  65 MPH
 
$$
FORECASTER LANDSEA/STEWART
 
NNNN


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Page last modified: Tuesday, 17-Jul-2012 13:44:20 UTC