000 WTPZ41 KNHC 090832 TCDEP1 TROPICAL STORM IRWIN DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 200 AM PDT SUN OCT 09 2011 IRWIN CONTINUES TO LACK DEEP CONVECTION NEAR THE CORE...WITH ONLY A LITTLE BIT IN A LOOSE BAND TO THE SOUTH OF THE CENTER. AN ASCAT PASS AT 0500Z SHOWED WINDS AS HIGH AS ABOUT 35 KT IN A BROAD BAND ABOUT 45 N MI FROM THE CENTER...CONSISTENT WITH THE STRUCTURE OBSERVED IN MICROWAVE IMAGERY FROM THE NRL WEB PAGE. BASED ON THESE OBSERVATIONS...THE INITIAL INTENSITY IS LOWERED TO 40 KT. THE INITIAL MOTION IS 055/4. A PAIR OF TROUGHS TO THE NORTH OF THE TROPICAL CYCLONE ARE EXPECTED TO GUIDE IRWIN GENERALLY EASTWARD OVER THE NEXT TWO TO THREE DAYS IN THE WAKE OF HURRICANE JOVA. TOWARDS THE END OF THE FORECAST PERIOD...BOTH THE GFS AND ECMWF ARE SHOWING A BINARY INTERACTION BETWEEN IRWIN AND A PIECE OF THE SECOND TROUGH...WHICH IMPARTS A TURN OF THE CYCLONE TO THE NORTHEAST. THE OFFICIAL FORECAST ATTEMPTS TO BLEND THE OUTPUT OF THESE TWO MODELS WITH THE PREVIOUS OFFICIAL TRACK...ALTHOUGH THERE IS A LARGE SPREAD AMONG THE GUIDANCE MODELS AFTER THREE DAYS AND THE LATTER PART OF THE FORECAST IS CONSIDERED TO BE OF LOW CONFIDENCE. IRWIN HAS NOT HAD THE REQUISITE ORGANIZED CONVECTION OF A TROPICAL CYCLONE FOR AT LEAST 12 HOURS...AND IT IS NOT CLEAR THAT THE NEW BAND IN THE SOUTHERN SEMICIRCLE WILL PERSIST. IN ADDITION TO EASTERLY SHEAR...IRWIN MAY BE INGESTING THE MORE STABLE AIR TO ITS NORTH. THE LARGER RMW ALSO DOES NOT FAVOR RE-INTENSIFICATION IN THE SHORT TERM. THE SHIPS AND LGEM MODELS SHOW A GRADUAL DECAY OVER THE NEXT FEW DAYS...AND THE GFDL AND HWRF HAVE BACKED OFF CONSIDERABLY FROM THEIR PREVIOUS AGGRESSIVE FORECASTS. STILL...THE UPPER WIND PATTERN IS EXPECTED TO GRADUALLY BECOME LESS HOSTILE AND IRWIN IS FORECAST TO MOVE OVER WARMER WATERS. THE OFFICIAL FORECAST ASSUMES THAT IRWIN WILL NOT DEGENERATE TO A REMNANT LOW AND SHOWS SOME RESTRENGTHENING AFTER 48 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 14.9N 120.1W 40 KT 45 MPH 12H 09/1800Z 15.3N 119.3W 35 KT 40 MPH 24H 10/0600Z 15.7N 118.2W 35 KT 40 MPH 36H 10/1800Z 15.9N 117.0W 35 KT 40 MPH 48H 11/0600Z 16.0N 115.5W 35 KT 40 MPH 72H 12/0600Z 15.5N 112.5W 40 KT 45 MPH 96H 13/0600Z 17.0N 109.0W 45 KT 50 MPH 120H 14/0600Z 19.0N 107.0W 50 KT 60 MPH $$ FORECASTER FRANKLIN