000 WTPZ42 KNHC 201452 TCDEP2 HURRICANE IVO DISCUSSION NUMBER 9 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP122007 800 AM PDT THU SEP 20 2007 A TRMM PASS AT O9Z SHOWED WELL-DEFINED BUT SLIGHTLY DISPLACED EYEWALL FEATURES IN THE LOW AND MID LEVELS. ALTHOUGH SUBJECTIVE DVORAK INTENSITY ESTIMATES INCREASED TO 77 KT AT 12Z...OBJECTIVE ADT ESTIMATES FROM CIMSS ACTUALLY HAVE FALLEN AND ARE BELOW HURRICANE STRENGTH. THE PRESENTATION IN IR IMAGERY IS RELATIVELY INDISTINCT. GIVEN THE MIXED SIGNALS...THE ADVISORY INTENSITY ESTIMATE WILL REMAIN 65 KT. BASED ON THE TRMM FIX THE INITIAL MOTION ESTIMATE REMAINS 330/6. A WEAK MID-LEVEL RIDGE EXTENDS WESTWARD FROM THE SOUTHERN BAJA PENINSULA...WITH A LARGE DEEP-LAYER CUTOFF LOW OFF THE CALIFORNIA COAST. IVO IS EXPECTED TO ROUND THIS RIDGE OVER THE NEXT 24 HOURS...BUT AFTER THAT THE FORECAST IS HIGHLY UNCERTAIN. ON ONE EXTREME IS THE UKMET...WHICH MAINTAINS IVO AS A STRONG SYSTEM AND CARRIES IT TOWARD SOUTHERN BAJA CALIFORNIA IN THE SOUTHWESTERLY FLOW ASSOCIATED WITH THE CUTOFF LOW. THE ECMWF REPRESENTS THE OPPOSITE EXTREME...WEAKENING IVO ABRUPTLY AND BOUNCING IT SOUTHWESTWARD IN THE LOW-LEVEL FLOW. MOST OF THE DYNAMICAL MODELS...INCLUDING THE GFS...GFDL...AND HWRF...ARE IN BETWEEN THESE EXTREMES. THIS GROUP SLOWLY WEAKENS THE HURRICANE AND HAS ONLY A MODERATE INTERACTION WITH THE SOUTHWESTERLIES...TAKING IVO ON A TRACK THAT IS SLOWER AND MORE NORTHERLY THAN THE UKMET SOLUTION. THE OFFICIAL SOLUTION IS ADJUSTED WESTWARD TO BE IN BETTER AGREEMENT WITH THIS INTERMEDIATE SOLUTION. THE ENVIRONMENT WOULD SEEM TO FAVOR SOME INTENSIFICATION...AT LEAST UNTIL IVO ROUNDS THE RIDGE. THE WATER IS WARM AND THE SHEAR IS LOW..ALTHOUGH THERE IS A STABLE AIR MASS NOT FAR TO THE NORTHWEST OF IVO. THE INTENSITY FORECAST BEYOND 24 HOURS IS VERY UNCERTAIN...AS A TRACK TO THE NORTH OF THE OFFICIAL FORECAST WOULD BRING IVO UNDER INCREASED SHEAR AND INTO A MORE STABLE ENVIRONMENT. THE OFFICIAL FORECAST IS LOWERED SLIGHTLY FROM THE PREVIOUS ADVISORY BUT IS STILL ABOVE THE OBJECTIVE GUIDANCE MODELS. INTERESTS IN SOUTHERN BAJA CALIFORNIA SHOULD CLOSELY MONITOR THE PROGRESS OF IVO DURING THE NEXT FEW DAYS...AND KEEP IN MIND THAT THERE IS GREAT UNCERTAINTY IN DAY 4 TO 5 FORECASTS. FORECAST POSITIONS AND MAX WINDS INITIAL 20/1500Z 17.1N 112.8W 65 KT 12HR VT 21/0000Z 17.8N 113.2W 70 KT 24HR VT 21/1200Z 18.8N 113.3W 75 KT 36HR VT 22/0000Z 19.8N 113.1W 70 KT 48HR VT 22/1200Z 20.8N 112.6W 65 KT 72HR VT 23/1200Z 22.5N 111.5W 60 KT 96HR VT 24/1200Z 24.0N 111.0W 50 KT 120HR VT 25/1200Z 25.5N 110.5W 30 KT $$ FORECASTER FRANKLIN