000
WTPZ42 KNHC 190226
TCDEP2
TROPICAL STORM IVO DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
800 PM PDT TUE SEP 18 2007
 
THE SATELLITE PRESENTATION HAS IMPROVED MARKEDLY DURING THE PAST FEW
HOURS. THE CLOUD PATTERN HAS BECOME MORE SYMMETRIC WITH A
WELL-DEFINED CURVED CONVECTIVE BAND AND EXCELLENT OUTFLOW IN ALL
QUADRANTS. T-NUMBERS FROM TAFB AND SAB HAVE INCREASED TO 2.5 AND
3.0 RESPECTIVELY ON THE DVORAK SCALE. BASED ON THESE DATA..THE
DEPRESSION HAS BEEN UPGRADED TO TROPICAL STORM STATUS WITH AN
INITIAL INTENSITY OF 40 KNOTS. IVO IS EXPECTED TO STRENGTHEN DURING
THE NEXT 2 TO 3 DAYS WHILE MOVING OVER WARM WATER AND WITHIN AN
ENVIRONMENT OF LIGHT SHEAR. THEREAFTER...STRONG SHEAR IS FORECAST
TO DEVELOP NEAR THE CYCLONE AND WEAKENING SHOULD BEGIN.
 
IVO IS MOVING TOWARD THE WEST-NORTHWEST OR 300 DEGREES AT 11 KNOTS
AROUND THE SOUTHWESTERN EDGE OF A SUBTROPICAL RIDGE EXTENDING FROM
MEXICO WESTWARD. A GRADUAL TURN TO THE NORTHWEST SHOULD BEGIN IN
ABOUT 36 TO 48 HOURS AS IVO REACHES THE WESTERN PERIPHERY OF THE
RIDGE. BY THEN...A STRONG MID-LATITUDE TROUGH IS FORECAST TO DIG
SOUTHWARD AND THIS PATTERN SHOULD FORCE THE CYCLONE ON A SLOW NORTH
AND NORTH-NORTHEASTWARD TRACK. SINCE STEERING CURRENTS ARE EXPECTED
TO BE LIGHT...IVO IS FORECAST TO SLOW DOWN SIGNIFICANTLY BEYOND 3
DAYS.
 
THE TRACK GUIDANCE DIVERGES IN ABOUT 72 HOURS AND THE FORECAST
BECOMES HIGHLY UNCERTAIN. SOME MODELS DO NOT KEEP THE
CYCLONE...OTHERS TURN IVO TOWARD THE NORTHEAST AND THE GFS MOVE IT
TOWARD THE WEST. HOWEVER..THEY ALL AGREE IN FORECASTING WEAKENING
AFTER 3 DAYS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      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 KT
120HR VT     24/0000Z 21.5N 113.5W    40 KT
 
$$

FORECASTER AVILA