000 WTPZ41 KNHC 110236 TCDEP1 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