000 WTPZ41 KNHC 141433 TCDEP1 TROPICAL STORM IRWIN DISCUSSION NUMBER 34 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011 800 AM PDT FRI OCT 14 2011 CONVENTIONAL SATELLITE IMAGERY INDICATES THAT IRWIN IS CHARACTERIZED BY A SHAPELESS BLOB OF CONVECTION. CLOUDS TOPS ASSOCIATED WITH EARLIER BURSTS OF DEEP CONVECTION JUST TO THE SOUTHWEST OF THE CENTER HAVE WARMED AND RECENT AMSU IMAGES SHOWED JUST A FEW FRAGMENTED REMAINING BANDS. DVORAK SATELLITE INTENSITY ESTIMATES ARE 35 KT FROM TAFB AND SAB...AND THE UW-CIMSS SATCON ESTIMATE IS 33 KT. BASED ON THESE...THE INITIAL WIND SPEED IS REDUCED TO 35 KT. THE DYNAMICAL AND STATISTICAL INTENSITY MODELS SUGGEST LITTLE CHANGE THROUGH THE FIRST 48 HOURS...BUT THE OFFICIAL FORECAST WILL SHOW THE POSSIBILITY OF SOME STRENGTHENING IN THE VERY SHORT TERM. AFTER DAY 2...THE MODELS DIVERGE...EITHER SHOWING A WEAKENING TREND OR SOME STRENGTHENING. THE FORMER IS MORE REALISTIC BASED ON THE EXPECTED INCREASE IN NORTHEASTERLY SHEAR...AFFECTS FROM THE COOLER SST WAKE OF JOVA...AND THE POTENTIAL FOR DRY AND STABLE MID- TO UPPER-LEVEL AIR TO POUR INTO THE REGION FROM NORTHERN MEXICO. THEREFORE...THE OFFICIAL FORECAST CALLS FOR SLOW WEAKENING AFTER 48 HOURS WITH IRWIN BECOMING A REMNANT LOW AT DAY 5. THE INITIAL MOTION ESTIMATE IS 180/3...WITHIN THE LOW- TO MID-LEVEL FLOW PRODUCED BY A RIDGE OVER NORTHWESTERN MEXICO AND BAJA CALIFORNIA. THE GENERALLY SOUTHWARD MOTION OF THE CYCLONE IS FORECAST TO CONTINUE DURING THE NEXT 36-48 HR...WITH AN INCREASE IN FORWARD SPEED...AS THE MID-LEVEL RIDGE TEMPORARILY BUILDS TO THE NORTH. THROUGH THE REMAINDER OF THE PERIOD...IRWIN IS EXPECTED TO BECOME A RELATIVELY WEAK AND SHALLOW SYSTEM AND DRIFT GENERALLY WESTWARD WITHIN THE LOW-LEVEL FLOW AS IT BECOMES MORE INVOLVED WITH THE ITCZ. THE NHC FORECAST HAS CHANGED LITTLE FROM THE PREVIOUS ADVISORY AND IS BASED ON THE HFIP MODEL CONSENSUS... WHICH INCLUDES THE GLOBAL MODELS. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 18.6N 106.8W 35 KT 40 MPH 12H 15/0000Z 17.9N 106.8W 40 KT 45 MPH 24H 15/1200Z 16.6N 107.0W 35 KT 40 MPH 36H 16/0000Z 15.3N 107.4W 35 KT 40 MPH 48H 16/1200Z 14.8N 108.0W 35 KT 40 MPH 72H 17/1200Z 15.1N 109.2W 30 KT 35 MPH 96H 18/1200Z 15.5N 110.0W 30 KT 35 MPH 120H 19/1200Z 15.5N 110.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ FORECASTER ROBERTS/BRENNAN