000 WTPZ41 KNHC 110847 TCDEP1 TROPICAL DEPRESSION IRWIN DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 200 AM PDT TUE OCT 11 2011 SATELLITE IMAGERY INDICATES SOME RECENT DEEP CONVECTION HAS BEGUN TO DEVELOP OVER THE SOUTHEAST PORTION OF THE CYCLONE. THUNDERSTORM ACTIVITY OVER THE REMAINING QUADRANTS...HOWEVER...CONTINUES TO BE QUITE LIMITED. DVORAK SATELLITE INTENSITY ESTIMATES ARE 35 KT FROM TAFB...AND 30 KT FROM SAB. IT WOULD NOT TAKE MUCH MORE BANDING DEVELOPMENT FOR IRWIN TO RETURN TO TROPICAL STORM STRENGTH...BUT I HAVE ELECTED TO KEEP THE SYSTEM AS A DEPRESSION FOR THIS ADVISORY BASED ON THE POSSIBILITY THAT THE NEW CONVECTION COULD BE SHORT-LIVED AS HAS OCCURED OVER THE PAST COUPLE OF DAYS. THE SHIPS MODEL AND UW-CIMSS SHEAR PRODUCT INDICATES FAVORABLE LIGHT 850-200 MB SHEAR OVER THE CYCLONE. THE CIRA AMSU AREA-AVERAGED WIND SHEARS PRODUCT...HOWEVER...INDICATES AN INCREASE IN MID-LEVEL VERTICAL SHEAR...POSSIBLY UNDERCUTTING THE OUTFLOW ALOFT. THIS ALONG WITH A DRY/STABLE SURROUNDING ENVIRONMENT APPEARS TO BE INHIBITING SIGNIFICANT DEVELOPMENT. FURTHERMORE...STATISTICAL AND DYNAMICAL MODELS INDICATE AN INCREASE IN NORTHEASTERLY SHEAR TOWARD THE END OF THE FORECAST PERIOD. THE INTENSITY FORECAST IS AN UPDATE OF THE PREVIOUS ONE...BUT NOW INDICATES IRWIN AS A REMNANT LOW AT DAY 5...CONSISTENT WITH THE MODEL GUIDANCE. THE INITIAL MOTION IS 080/7. IRWIN REMAINS EMBEDDED WITHIN THE DEEP WESTERLY FLOW ASSOCIATED WITH A MAJOR SHORTWAVE TROUGH SITUATED TO THE NORTHWEST OF THE CYCLONE. THE DEPRESSION IS EXPECTED TO CONTINUE ON A GENERAL EASTWARD TRACK DURING THE NEXT 24 HOURS. FROM 36-72 HR...THE LARGE-SCALE MODELS SHOW A CUT-OFF LOW DEVELOPING AT THE BASE OF THE SHORTWAVE TROUGH. THIS MID- TO UPPER-LEVEL FEATURE SHOULD INDUCE A NORTHEASTWARD TURN OF THE CYCLONE. FOR THE REMAINDER OF THE PERIOD...THE DYNAMICAL MODELS GENERALLY AGREE WITH A GRADUAL TURN BACK TO THE EAST OR EAST-SOUTHEAST AS THE VERTICALLY SHALLOW SYSTEM BEGINS TO TRACK WITHIN THE STRENGTHENING NORTHWESTERLY LOW-LEVEL FLOW. THE OFFICIAL NHC FORECAST IS SIMILAR TO THE PREVIOUS ONE AND IS NUDGED TO THE LEFT TO COINCIDE WITH NOGAPS AND THE TV15 HFIP CONSENSUS MODEL WHICH ALSO INCLUDES THE GFS...ECMWF...AND UKMET GLOBAL MODELS. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 15.2N 115.5W 30 KT 35 MPH 12H 11/1800Z 15.2N 114.3W 30 KT 35 MPH 24H 12/0600Z 15.6N 112.3W 30 KT 35 MPH 36H 12/1800Z 16.4N 110.0W 30 KT 35 MPH 48H 13/0600Z 17.1N 107.9W 30 KT 35 MPH 72H 14/0600Z 17.5N 105.1W 30 KT 35 MPH 96H 15/0600Z 16.5N 103.5W 30 KT 35 MPH 120H 16/0600Z 16.0N 103.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER ROBERTS/BROWN