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Tropical Depression IRWIN (Text)

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TROPICAL DEPRESSION IRWIN DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112011
800 PM PDT MON OCT 10 2011
 
IRWIN CONTINUES TO WEAKEN. ONLY A COUPLE OF PATCHES OF DEEP
CONVECTION REMAIN AND THESE ARE CONFINED TO LOOSELY ORGANIZED
CURVED BANDS. IN ADDITION...THE LATEST MICROWAVE DATA INDICATE THAT
THE LOW-LEVEL CENTER OF IRWIN HAS BECOME ELONGATED DURING THE PAST
FEW HOURS. DVORAK CLASSIFICATIONS AT 0000 UTC WERE 30 AND 35 KT
FROM TAFB AND SAB...RESPECTIVELY. GIVEN THE DECREASE IN THE
CONVECTIVE ORGANIZATION SINCE THAT TIME AND THE DEGRADED APPEARANCE
IN MICROWAVE IMAGES...THE INITIAL WIND SPEED IS SET AT THE LOWER
ESTIMATE...MAKING IRWIN A TROPICAL DEPRESSION.

THE DEPRESSION CONTINUES TO MOVE EASTWARD AT ABOUT 6 KT. THE GLOBAL
MODELS SHOW A MID-LEVEL CUTOFF LOW DEVELOPING TO THE WEST OF THE
TROPICAL CYCLONE IN ABOUT 24 HOURS. ALTHOUGH THE MODELS ARE IN
AGREEMENT IN THE EVOLUTION OF THE SYNOPTIC PATTERN...THEY DIFFER ON
HOW MUCH IRWIN INTERACTS WITH THE MID-LEVEL LOW. THE GFS MODEL
SHOWS LESS INTERACTION...AND THEREFORE KEEPS IRWIN ON A GENERAL
EASTWARD TRACK FOR THE NEXT FEW DAYS. CONVERSELY...THE ECMWF MODEL
SHOWS IRWIN MOVING CYCLONICALLY AROUND THE EAST SIDE OF THE
MID-LEVEL LOW...RESULTING IN A TRACK CONSIDERABLY NORTH OF THE GFS.
REGARDLESS...BY THE END OF THE FORECAST PERIOD ALL OF THE MODELS
SHOW A SLOW DOWN AND TURN TO THE SOUTHEAST AS IRWIN IS EXPECTED TO
BECOME EMBEDDED IN LOW TO MID-LEVEL NORTHWESTERLY FLOW BY THAT
TIME. THE OFFICIAL FORECAST LIES BETWEEN THE GFS AND ECMWF MODELS
AND IS NEAR THE HFIP MODEL CONSENSUS.

ALTHOUGH IRWIN IS EXPECTED TO BE MOVING INTO A MORE MOIST
ENVIRONMENT DURING THE NEXT FEW DAYS...AN INCREASE IN SOUTHWESTERLY
MID-LEVEL FLOW IS EXPECTED AS THE AFOREMENTIONED LOW DEVELOPS.
THEREFORE...THE OFFICIAL FORECAST SHOWS NO CHANGE IN STRENGTH
THROUGHOUT THE PERIOD. HOWEVER...IT IS POSSIBLE THAT IRWIN COULD
DEGENERATE INTO A REMNANT LOW AT SOME POINT DURING THE NEXT FEW
DAYS.

FORECAST POSITIONS AND MAX WINDS
 
INIT  11/0300Z 15.0N 116.3W   30 KT  35 MPH
 12H  11/1200Z 15.0N 115.2W   30 KT  35 MPH
 24H  12/0000Z 15.1N 113.4W   30 KT  35 MPH
 36H  12/1200Z 15.7N 111.1W   30 KT  35 MPH
 48H  13/0000Z 16.5N 108.9W   30 KT  35 MPH
 72H  14/0000Z 17.4N 105.3W   30 KT  35 MPH
 96H  15/0000Z 16.5N 103.5W   30 KT  35 MPH
120H  16/0000Z 16.0N 103.0W   30 KT  35 MPH
 
$$
FORECASTER CANGIALOSI
 
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