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 492 
 WTPZ42 KNHC 210831
 TCDEP2
 HURRICANE IVO DISCUSSION NUMBER  12
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
 200 AM PDT FRI SEP 21 2007
 
 THE EYE OF IVO MADE AN APPEARANCE IN INFRARED IMAGERY AROUND 0600
 UTC...AND THEN VERY QUICKLY DISAPPEARED.  SINCE THEN...THE OVERALL
 SATELLITE APPEARANCE HAS BECOME RAGGED...WITH EVIDENCE OF WESTERLY
 VERTICAL WIND SHEAR UNDERCUTTING THE OUTFLOW ON THE WEST SIDE. 
 SATELLITE INTENSITY ESTIMATES REMAIN 77 KT FROM TAFB AND SAB...AND
 THE INITIAL INTENSITY REMAINS 70 KT.
 
 IVO HAS SLOWED ITS FORWARD SPEED OVER THE PAST FEW HOURS WITH THE
 MOTION ESTIMATED AT 340/7.  WATER VAPOR IMAGERY INDICATES A LARGE
 UPPER-LEVEL LOW JUST WEST OF THE COAST OF SOUTHERN CALIFORNIA...
 WITH WHAT IS BECOMING A NORTH-SOUTH ORIENTED RIDGE EAST OF IVO. 
 THE LARGE-SCALE MODELS AGREE THAT THE LOW SHOULD BEGIN MOVING
 NORTHEASTWARD IN 24-36 HR.  HOWEVER...THAT IS ABOUT ALL THEY AGREE
 ON...AS THEY HAVE A WIDE VARIETY OF SOLUTIONS FOR THE TRACK OF IVO. 
 THE ECMWF CONTINUES TO FORECAST IVO TO REACH 20N...THEN MOVE
 SOUTHWARD AND DISSIPATE.  THE GFS AND GFDL FORECAST IVO TO MOVE
 SLOWLY NORTHWARD AND STALL BEFORE REACHING BAJA CALIFORNIA.  THE
 UKMET...HWRF...AND NOGAPS...MOVE IVO NORTHWARD ACROSS BAJA...WITH
 THE UKMET CALLING FOR LANDFALL IN LESS THAN 48 HR.  GIVEN THE
 UNCERTAINTY...THE NEW FORECAST TRACK IS ESSENTIALLY AN UPDATE OF
 THE PREVIOUS TRACK...CALLING FOR THE CENTER OF IVO TO REACH BAJA IN
 72-96 HR.  HOPEFULLY SUBSEQUENT MODEL RUNS WILL COME INTO BETTER
 AGREEMENT ON THE FORECAST FORWARD SPEED.
 
 WATER VAPOR IMAGERY SUGGESTS THERE IS MORE WESTERLY SHEAR AFFECTING
 IVO THAN CURRENTLY ANALYZED BY THE LARGE-SCALE MODELS OR SHIPS
 MODEL.  THE IMAGERY ALSO SHOWS DRY AIR WEST OF THE HURRICANE THAT
 THE SHEAR MAY ADVECT INTO THE SYSTEM AS IT MOVES NORTHWARD OVER
 COOLER WATERS.  THE GFS AND UKMET FORECAST FAVORABLE UPPER-LEVEL
 WINDS ALONG THE FORECAST TRACK...WITH THE ECMWF AND NOGAPS SHOWING
 A MORE HOSTILE ENVIRONMENT.   THE SHIPS MODEL FORECASTS A SLOW
 WEAKENING AFTER 24 HR...WHILE THE HWRF AND THE GFDL SHOW A STRONGER
 SYSTEM WITH NO APPRECIABLE WEAKENING UNTIL AFTER 60 HR.  GIVEN THE
 CURRENT SHEAR...THE INTENSITY FORECAST WILL GO WITH THE SLOW DECAY
 FROM THE SHIPS MODEL AND IS SIMILAR TO THE PREVIOUS FORECAST.
  
 GIVEN THE EXTREME UNCERTAINTY PRESENT IN THE OFFICIAL FORECAST AT
 THIS TIME...INTERESTS IN SOUTHERN BAJA CALIFORNIA SHOULD CLOSELY
 MONITOR THE PROGRESS OF IVO.
 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      21/0900Z 19.0N 113.5W    70 KT
  12HR VT     21/1800Z 19.9N 113.5W    70 KT
  24HR VT     22/0600Z 20.8N 113.2W    70 KT
  36HR VT     22/1800Z 21.5N 112.9W    65 KT
  48HR VT     23/0600Z 22.3N 112.5W    60 KT
  72HR VT     24/0600Z 24.0N 112.0W    55 KT
  96HR VT     25/0600Z 25.5N 111.5W    40 KT...INLAND
 120HR VT     26/0600Z 27.0N 111.5W    30 KT...OVER WATER
  
 $$
 FORECASTER BEVEN
  
 
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