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 731 
 WTPZ44 KNHC 241428
 TCDEP4
 TROPICAL STORM NORMA DISCUSSION NUMBER   7
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
 8 AM PDT SAT SEP 24 2005
  
 SEVERAL MICROWAVE SATELLITE IMAGES DURING THE PAST 9 HOURS INDICATE
 NORMA HAS MOVED SLOWLY NORTHWEST AND THE CENTER IS LOCATED IN THE
 NORTHEASTERN PORTION OF THE DEEP CONVECTIVE CLOUD MASS AND NOT IN
 THE CENTER NEAR THE COLDER CLOUD TOPS. THE INITIAL INTENSITY OF 50
 KT IS BASED ON A BLEND OF DVORAK CURRENT INTENSITY ESTIMATES OF 55
 KT FROM TAFB... 45 KT FROM SAB AND AFWA... AND A 24/1029Z UW-CIMSS
 AMSU INTENSITY ESTIMATE OF 994 MB AND 50 KT.
  
 BASED ON THE MICROWAVE POSITIONS... THE INITIAL MOTION IS 340/05.
 THE MID-LEVEL RIDGE TO THE NORTH AND EAST OF NORMA IS FORECAST TO
 REMAIN WEAK... SO THE RESULTANT WEAK STEERING FLOW MAY CAUSE SOME
 ERRATIC MOTION FOR THE NEXT 36 HOURS OR SO. AFTERWARDS... STEERING
 CURRENTS ARE EXPECTED TO BECOME BETTER ESTABLISHED AS A STRONG
 UPPER-LEVEL TROUGH/LOW DIGS SOUTHWARD OFF THE CALIFORNIA COAST...
 WITH ASSOCIATED DOWNSTREAM RIDGING EXPECTED TO BUILD HIGH PRESSURE
 ACROSS THE SOUTHWESTERN U.S. AND MEXICO THROUGH 72 HOURS. BY DAYS 4
 AND 5... THE FLOW IS ONCE AGAIN FORECAST TO WEAKEN AS THE FUTURE
 UPPER-LEVEL LOW OFF CALIFORNIA LIFTS OUT TO THE NORTH... WHICH
 ALLOWS WEAK RIDGING TO EXTEND WESTWARD TO THE NORTH OF NORMA. THE
 LATTER STEERING FLOW IS EXPECTED TO TURN THE CYCLONE SLOQLY
 WESTWARD AND EVENTUALLY WEST-SOUTHWESTWARD.
 
 CURRENT MODERATE EAST TO SOUTHEASTERLY VERTICAL SHEAR IS EXPECTED TO 
 CONTINUE TO AFFECT NORMA THROUGHOUT THE FORECAST PERIOD. HOWEVER...
 THE SHEAR IS NOT FORECAST TO INCREASE ABOVE THE CURRENT 20 KT
 VALUE. THEREFORE... THE INTENSITY IS FORECAST TO REMAIN STEADY
 UNTIL NORMA REACHES COOLER WATER IN 48-72 HOURS... AFTER WHICH SLOW
 WEAKENING IS EXPECTED TO OCCUR. THE OFFICIAL INTENSITY FORECAST IS
 SIMILAR TO THE GFDL MODEL... BUT HIGHER THAN THE SHIPS INTENSITY
 MODEL... ESPECIALLY AT 96 AND 120 HOURS... WHICH IS WHEN THE SHIPS
 MODEL FORECASTS NORMA TO DISSIPATE.
  
 FORECASTER STEWART
   
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      24/1500Z 16.4N 110.7W    50 KT
  12HR VT     25/0000Z 16.9N 111.0W    50 KT
  24HR VT     25/1200Z 17.6N 111.5W    50 KT
  36HR VT     26/0000Z 18.5N 112.3W    50 KT
  48HR VT     26/1200Z 19.5N 113.5W    45 KT
  72HR VT     27/1200Z 20.5N 115.5W    45 KT
  96HR VT     28/1200Z 21.0N 117.0W    40 KT
 120HR VT     29/1200Z 20.0N 119.5W    35 KT
   
 $$
 
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