000
WTPZ42 KNHC 220848
TCDEP2
TROPICAL STORM IVO DISCUSSION NUMBER  16
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
200 AM PDT SAT SEP 22 2007
 
AFTER SEVERAL HOURS WITHOUT CONVECTION...A SMALL CONVECTIVE CLUSTER
HAS FORMED TO THE NORTH OF THE CENTER OF IVO.  HOWEVER...WESTERLY
SHEAR CONTINUES TO AFFECT THE SYSTEM...WITH SATELLITE CLOUD
MOTIONS INDICATING 20-25 KT OF UPPER-LEVEL WESTERLY FLOW IMPINGING
ON THE SYSTEM.  SATELLITE INTENSITY ESTIMATES ARE 65 KT FROM TAFB
AND 55 KT FROM SAB.  BASED ON ON THE DECAY OF THE CLOUD PATTERN AND
CONTINUITY FROM THE PREVIOUS ADVISORY...THE INITIAL INTENSITY IS
DECREASED TO 50 KT...AND THIS COULD BE GENEROUS.

THE INITIAL MOTION REMAINS 030/5.  WATER VAPOR IMAGERY INDICATES A
LARGE MID/UPPER-LEVEL LOW CENTERED JUST WEST OF SOUTHERN
CALIFORNIA...AND AN EAST-WEST UPPER-LEVEL RIDGE ALONG 15N SOUTH OF
IVO.  THE LARGE-SCALE MODELS FORECAST THE LOW TO MOVE NORTHEASTWARD
DURING THE NEXT 24 HOURS...WITH A MID-LEVEL RIDGE BUILDING NEAR OR
JUST SOUTH OF IVO.  MODEL GUIDANCE REMAINS VERY SPREAD.  THE ECMWF
TURNS IVO SOUTHWARD AND DISSIPATES IT.  THE GFS STALLS IVO NEAR ITS
CURRENT LOCATION AND DISSIPATES IT.  THE GFDL AND HWRF FORECAST A
SLOW MOTION TO THE SOUTHERN BAJA CALIFORNIA PENINSULA IN 2-3 DAYS...
WHILE THE UKMET AND NOGAPS MOVE THE SYSTEM ACROSS BAJA AND INTO THE
GULF OF CALIFORNIA.  GIVEN THE CURRENT SLOW MOTION AND SHEAR...THE
FORECAST TRACK AGAIN CALLS FOR A SLOW NORTHEASTWARD MOTION...
REACHING BAJA IN 2-3 DAYS.  THE NEW FORECAST TRACK IS AN UPDATE OF
THE PREVIOUS PACKAGE.
 
THE LARGE-SCALE MODELS APPARENTLY ARE UNDERFORECASTING THE AMOUNT OF
SHEAR AFFECTING IVO...WHICH MAKES THE INTENSITY FORECAST A LITTLE
PROBLEMATIC AS NONE OF THEM ARE FORECASTING SHEAR STRONG ENOUGH TO
CAUSE SIGNIFICANT WEAKENING.  THE GFDL AND HWRF MAINTAIN IVO AS A
TROPICAL STORM UNTIL IT REACHES BAJA...WHILE SHIPS WEAKENS IT TO A
DEPRESSION IN 48 HR.  THE INTENSITY FORECAST CALLS FOR WEAKENING IN
AGREEMENT WITH THE SHIPS MODEL...AND IF THE CONVECTION DOES NOT
MAKE A COMEBACK TODAY IVO COULD WEAKEN FASTER THAN CURRENTLY
FORECAST.
 
ALTHOUGH IVO IS EXPECTED TO WEAKEN AS IT APPROACHES SOUTHERN BAJA
CALIFORNIA...TROPICAL STORM WATCHES MAY BE REQUIRED LATER TODAY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      22/0900Z 20.9N 112.9W    50 KT
 12HR VT     22/1800Z 21.6N 112.5W    45 KT
 24HR VT     23/0600Z 22.3N 112.0W    40 KT
 36HR VT     23/1800Z 22.8N 111.5W    35 KT
 48HR VT     24/0600Z 23.3N 110.9W    30 KT
 72HR VT     25/0600Z 24.0N 110.0W    25 KT...INLAND
 96HR VT     26/0600Z 24.5N 109.5W    20 KT...REMNANT LOW
120HR VT     27/0600Z 25.5N 109.5W    20 KT...REMNANT LOW
 
$$
FORECASTER BEVEN