000 WTPZ42 KNHC 192039 TCDEP2 TROPICAL STORM IVO DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP122007 200 PM PDT WED SEP 19 2007 IVO CONTINUES TO STRENGTHEN..WITH INCREASED CONVECTIVE BANDING AROUND THE CENTER AND THE POSSIBLE BEGINNING OF EYE FORMATION IN BOTH VISIBLE AND MICROWAVE IMAGERY. SATELLITE INTENSITY ESTIMATES ARE 65 KT FROM SAB AND 55 KT FROM TAFB. THE INITIAL INTENSITY IS INCREASED TO 60 KT...AND IF IVO IS NOT YET A HURRICANE IT SHOULD BECOME ONE SHORTLY. THE CIRRUS OUTFLOW IS GOOD TO THE SOUTHWEST AND NORTHEAST AND FAIR TO POOR ELSEWHERE. THE STORM HAS MOVED A LITTLE TO THE LEFT OF THE PREVIOUS TRACK... WITH AN INITIAL MOTION OF 290/9. IVO REMAINS SOUTH OF A MID-LEVEL RIDGE EXTENDING WESTWARD FROM NORTHERN MEXICO. THE LARGE-SCALE MODELS ARE IN GOOD AGREEMENT THAT A DEEP-LAYER LOW CURRENTLY MOVING SOUTHWARD INTO CALIFORNIA WILL DROP FAR ENOUGH SOUTH TO BREAK THE RIDGE NORTH OF IVO...ALLOWING THE STORM TO RECURVE TO THE NORTHEAST DURING THE NEXT 48-96 HR. HOWEVER...IT STILL APPEARS THE LOW WILL NOT COME FAR ENOUGH SOUTH TO ACCELERATE THE STORM NORTHEASTWARD... SO THE MOTION AFTER RECURVATURE IS LIKELY TO BE SLOW. ADDITIONALLY...THE MODELS ARE FORECASTING THE RIDGE TO RE-BUILD EAST OF IVO IN 96-120 HR...AND THEY RESPOND TO THIS BY SHOWING A MORE NORTHWARD MOTION BY THE END OF THE FORECAST PERIOD. THE NEW FORECAST TRACK IS SHIFTED A LITTLE TO THE LEFT DURING THE FIRST PART OF THE FORECAST DUE TO THE INITIAL POSITION AND MOTION...AND A LITTLE TO THE LEFT OF THE PREVIOUS TRACK AT THE END OF THE FORECAST DUE TO THE BUILDING RIDGE. IT IS IN BEST OVERALL AGREEMENT WITH THE CCON CONSENSUS. IT SHOULD BE NOTED THAT THE ECMWF MODEL DOES NOT FORECAST IVO TO RECURVE...AS IT TRAPS THE STORM SOUTH OF THE RE-BUILDING RIDGE. IVO IS FORECAST TO REMAIN IN A LIGHT VERTICAL WIND SHEAR ENVIRONMENT FOR THE NEXT 24-36 HR...SO CONTINUED STRENGTHENING IS FORECAST IN AGREEMENT WITH THE SHIPS MODEL. BEYOND THAT TIME...THE LARGE-SCALE MODELS CONTINUE TO DISAGREE ON HOW MUCH WIND SHEAR IVO WILL ENCOUNTER. THE GFS AND ECMWF FORECAST INCREASING SHEAR... WHILE THE UKMET AND THE NOGAPS FORECAST A MORE FAVORABLE ENVIRONMENT. BECAUSE IT IS NOT CLEAR WHICH MODEL IS ON THE RIGHT TRACK...THE INTENSITY FORECAST IS AN UPDATE OF THE PREVIOUS PACKAGE. THE TWO ALTERNATIVE SCENARIOS FROM THE PREVIOUS PACKAGE REMAIN. FIRST...THE FORECAST TRACK BRINGS IVO OVER WARMER WATER BY 120 HR...AND IF THE SHEAR IS LIGHT IVO COULD BE STRONGER THAN FORECAST AT THAT TIME. SECOND...IF IVO TRACKS NORTH OF THE FORECAST TRACK...IT WOULD LIKELY ENCOUNTER BOTH STRONGER SHEAR AND COLDER WATER...WHICH SHOULD CAUSE A FASTER WEAKENING. FORECAST POSITIONS AND MAX WINDS INITIAL 19/2100Z 15.4N 111.9W 60 KT 12HR VT 20/0600Z 16.0N 113.0W 70 KT 24HR VT 20/1800Z 16.8N 113.7W 75 KT 36HR VT 21/0600Z 17.9N 114.0W 75 KT 48HR VT 21/1800Z 18.9N 113.7W 75 KT 72HR VT 22/1800Z 21.0N 112.5W 70 KT 96HR VT 23/1800Z 22.0N 111.5W 60 KT 120HR VT 24/1800Z 23.0N 109.5W 55 KT $$ FORECASTER BEVEN