000WTPZ42 KNHC 190226TCDEP2TROPICAL STORM IVO DISCUSSION NUMBER 3NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP122007800 PM PDT TUE SEP 18 2007THE SATELLITE PRESENTATION HAS IMPROVED MARKEDLY DURING THE PAST FEWHOURS. THE CLOUD PATTERN HAS BECOME MORE SYMMETRIC WITH AWELL-DEFINED CURVED CONVECTIVE BAND AND EXCELLENT OUTFLOW IN ALLQUADRANTS. T-NUMBERS FROM TAFB AND SAB HAVE INCREASED TO 2.5 AND3.0 RESPECTIVELY ON THE DVORAK SCALE. BASED ON THESE DATA..THEDEPRESSION HAS BEEN UPGRADED TO TROPICAL STORM STATUS WITH ANINITIAL INTENSITY OF 40 KNOTS. IVO IS EXPECTED TO STRENGTHEN DURINGTHE NEXT 2 TO 3 DAYS WHILE MOVING OVER WARM WATER AND WITHIN ANENVIRONMENT OF LIGHT SHEAR. THEREAFTER...STRONG SHEAR IS FORECASTTO DEVELOP NEAR THE CYCLONE AND WEAKENING SHOULD BEGIN.IVO IS MOVING TOWARD THE WEST-NORTHWEST OR 300 DEGREES AT 11 KNOTSAROUND THE SOUTHWESTERN EDGE OF A SUBTROPICAL RIDGE EXTENDING FROMMEXICO WESTWARD. A GRADUAL TURN TO THE NORTHWEST SHOULD BEGIN INABOUT 36 TO 48 HOURS AS IVO REACHES THE WESTERN PERIPHERY OF THERIDGE. BY THEN...A STRONG MID-LATITUDE TROUGH IS FORECAST TO DIGSOUTHWARD AND THIS PATTERN SHOULD FORCE THE CYCLONE ON A SLOW NORTHAND NORTH-NORTHEASTWARD TRACK. SINCE STEERING CURRENTS ARE EXPECTEDTO BE LIGHT...IVO IS FORECAST TO SLOW DOWN SIGNIFICANTLY BEYOND 3DAYS.THE TRACK GUIDANCE DIVERGES IN ABOUT 72 HOURS AND THE FORECASTBECOMES HIGHLY UNCERTAIN. SOME MODELS DO NOT KEEP THECYCLONE...OTHERS TURN IVO TOWARD THE NORTHEAST AND THE GFS MOVE ITTOWARD THE WEST. HOWEVER..THEY ALL AGREE IN FORECASTING WEAKENINGAFTER 3 DAYS.FORECAST POSITIONS AND MAX WINDSINITIAL 19/0300Z 14.5N 109.3W 40 KT 12HR VT 19/1200Z 15.2N 111.0W 45 KT 24HR VT 20/0000Z 16.0N 112.7W 50 KT 36HR VT 20/1200Z 17.0N 114.0W 60 KT 48HR VT 21/0000Z 18.0N 114.5W 60 KT 72HR VT 22/0000Z 19.5N 114.5W 60 KT 96HR VT 23/0000Z 20.5N 114.0W 50 KT120HR VT 24/0000Z 21.5N 113.5W 40 KT$$FORECASTER AVILA
000WTPZ42 KNHC 192039TCDEP2TROPICAL STORM IVO DISCUSSION NUMBER 6NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP122007200 PM PDT WED SEP 19 2007IVO CONTINUES TO STRENGTHEN..WITH INCREASED CONVECTIVE BANDINGAROUND THE CENTER AND THE POSSIBLE BEGINNING OF EYE FORMATION INBOTH VISIBLE AND MICROWAVE IMAGERY. SATELLITE INTENSITY ESTIMATESARE 65 KT FROM SAB AND 55 KT FROM TAFB. THE INITIAL INTENSITY ISINCREASED TO 60 KT...AND IF IVO IS NOT YET A HURRICANE IT SHOULDBECOME ONE SHORTLY. THE CIRRUS OUTFLOW IS GOOD TO THE SOUTHWESTAND 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-LEVELRIDGE EXTENDING WESTWARD FROM NORTHERN MEXICO. THE LARGE-SCALEMODELS ARE IN GOOD AGREEMENT THAT A DEEP-LAYER LOW CURRENTLY MOVINGSOUTHWARD INTO CALIFORNIA WILL DROP FAR ENOUGH SOUTH TO BREAK THERIDGE NORTH OF IVO...ALLOWING THE STORM TO RECURVE TO THE NORTHEASTDURING THE NEXT 48-96 HR. HOWEVER...IT STILL APPEARS THE LOW WILLNOT 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-BUILDEAST OF IVO IN 96-120 HR...AND THEY RESPOND TO THIS BY SHOWING AMORE NORTHWARD MOTION BY THE END OF THE FORECAST PERIOD. THE NEWFORECAST TRACK IS SHIFTED A LITTLE TO THE LEFT DURING THE FIRSTPART OF THE FORECAST DUE TO THE INITIAL POSITION AND MOTION...AND ALITTLE TO THE LEFT OF THE PREVIOUS TRACK AT THE END OF THE FORECASTDUE TO THE BUILDING RIDGE. IT IS IN BEST OVERALL AGREEMENT WITHTHE CCON CONSENSUS. IT SHOULD BE NOTED THAT THE ECMWF MODEL DOESNOT FORECAST IVO TO RECURVE...AS IT TRAPS THE STORM SOUTH OF THERE-BUILDING RIDGE.IVO IS FORECAST TO REMAIN IN A LIGHT VERTICAL WIND SHEAR ENVIRONMENTFOR THE NEXT 24-36 HR...SO CONTINUED STRENGTHENING IS FORECASTIN AGREEMENT WITH THE SHIPS MODEL. BEYOND THAT TIME...THELARGE-SCALE MODELS CONTINUE TO DISAGREE ON HOW MUCH WIND SHEAR IVOWILL ENCOUNTER. THE GFS AND ECMWF FORECAST INCREASING SHEAR...WHILE THE UKMET AND THE NOGAPS FORECAST A MORE FAVORABLEENVIRONMENT. BECAUSE IT IS NOT CLEAR WHICH MODEL IS ON THE RIGHTTRACK...THE INTENSITY FORECAST IS AN UPDATE OF THE PREVIOUSPACKAGE. THE TWO ALTERNATIVE SCENARIOS FROM THE PREVIOUS PACKAGEREMAIN. FIRST...THE FORECAST TRACK BRINGS IVO OVER WARMER WATER BY120 HR...AND IF THE SHEAR IS LIGHT IVO COULD BE STRONGER THANFORECAST AT THAT TIME. SECOND...IF IVO TRACKS NORTH OF THEFORECAST TRACK...IT WOULD LIKELY ENCOUNTER BOTH STRONGER SHEAR ANDCOLDER WATER...WHICH SHOULD CAUSE A FASTER WEAKENING.FORECAST POSITIONS AND MAX WINDSINITIAL 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 KT120HR VT 24/1800Z 23.0N 109.5W 55 KT$$FORECASTER BEVEN