000 WTPZ42 KNHC 210831 TCDEP2 HURRICANE IVO DISCUSSION NUMBER 12 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP122007 200 AM PDT FRI SEP 21 2007 THE EYE OF IVO MADE AN APPEARANCE IN INFRARED IMAGERY AROUND 0600 UTC...AND THEN VERY QUICKLY DISAPPEARED. SINCE THEN...THE OVERALL SATELLITE APPEARANCE HAS BECOME RAGGED...WITH EVIDENCE OF WESTERLY VERTICAL WIND SHEAR UNDERCUTTING THE OUTFLOW ON THE WEST SIDE. SATELLITE INTENSITY ESTIMATES REMAIN 77 KT FROM TAFB AND SAB...AND THE INITIAL INTENSITY REMAINS 70 KT. IVO HAS SLOWED ITS FORWARD SPEED OVER THE PAST FEW HOURS WITH THE MOTION ESTIMATED AT 340/7. WATER VAPOR IMAGERY INDICATES A LARGE UPPER-LEVEL LOW JUST WEST OF THE COAST OF SOUTHERN CALIFORNIA... WITH WHAT IS BECOMING A NORTH-SOUTH ORIENTED RIDGE EAST OF IVO. THE LARGE-SCALE MODELS AGREE THAT THE LOW SHOULD BEGIN MOVING NORTHEASTWARD IN 24-36 HR. HOWEVER...THAT IS ABOUT ALL THEY AGREE ON...AS THEY HAVE A WIDE VARIETY OF SOLUTIONS FOR THE TRACK OF IVO. THE ECMWF CONTINUES TO FORECAST IVO TO REACH 20N...THEN MOVE SOUTHWARD AND DISSIPATE. THE GFS AND GFDL FORECAST IVO TO MOVE SLOWLY NORTHWARD AND STALL BEFORE REACHING BAJA CALIFORNIA. THE UKMET...HWRF...AND NOGAPS...MOVE IVO NORTHWARD ACROSS BAJA...WITH THE UKMET CALLING FOR LANDFALL IN LESS THAN 48 HR. GIVEN THE UNCERTAINTY...THE NEW FORECAST TRACK IS ESSENTIALLY AN UPDATE OF THE PREVIOUS TRACK...CALLING FOR THE CENTER OF IVO TO REACH BAJA IN 72-96 HR. HOPEFULLY SUBSEQUENT MODEL RUNS WILL COME INTO BETTER AGREEMENT ON THE FORECAST FORWARD SPEED. WATER VAPOR IMAGERY SUGGESTS THERE IS MORE WESTERLY SHEAR AFFECTING IVO THAN CURRENTLY ANALYZED BY THE LARGE-SCALE MODELS OR SHIPS MODEL. THE IMAGERY ALSO SHOWS DRY AIR WEST OF THE HURRICANE THAT THE SHEAR MAY ADVECT INTO THE SYSTEM AS IT MOVES NORTHWARD OVER COOLER WATERS. THE GFS AND UKMET FORECAST FAVORABLE UPPER-LEVEL WINDS ALONG THE FORECAST TRACK...WITH THE ECMWF AND NOGAPS SHOWING A MORE HOSTILE ENVIRONMENT. THE SHIPS MODEL FORECASTS A SLOW WEAKENING AFTER 24 HR...WHILE THE HWRF AND THE GFDL SHOW A STRONGER SYSTEM WITH NO APPRECIABLE WEAKENING UNTIL AFTER 60 HR. GIVEN THE CURRENT SHEAR...THE INTENSITY FORECAST WILL GO WITH THE SLOW DECAY FROM THE SHIPS MODEL AND IS SIMILAR TO THE PREVIOUS FORECAST. GIVEN THE EXTREME UNCERTAINTY PRESENT IN THE OFFICIAL FORECAST AT THIS TIME...INTERESTS IN SOUTHERN BAJA CALIFORNIA SHOULD CLOSELY MONITOR THE PROGRESS OF IVO. FORECAST POSITIONS AND MAX WINDS INITIAL 21/0900Z 19.0N 113.5W 70 KT 12HR VT 21/1800Z 19.9N 113.5W 70 KT 24HR VT 22/0600Z 20.8N 113.2W 70 KT 36HR VT 22/1800Z 21.5N 112.9W 65 KT 48HR VT 23/0600Z 22.3N 112.5W 60 KT 72HR VT 24/0600Z 24.0N 112.0W 55 KT 96HR VT 25/0600Z 25.5N 111.5W 40 KT...INLAND 120HR VT 26/0600Z 27.0N 111.5W 30 KT...OVER WATER $$ FORECASTER BEVEN