485 
 WTPZ43 KNHC 081446
 TCDEP3
 TROPICAL STORM LOWELL DISCUSSION NUMBER   7
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP132008
 800 AM PDT MON SEP 08 2008
  
 MORNING VISIBLE SATELLITE IMAGERY AND A RECENT TRMM MICROWAVE
 OVERPASS SHOW THAT THE CENTER OF LOWELL REMAINS EXPOSED TO THE
 NORTHEAST OF A CONVECTIVE BURST.  ANALYSES FROM CIMSS AT THE
 UNIVERSITY OF WISCONSIN INDICATE THAT THE STORM IS UNDERGOING ABOUT
 20 KT OF EASTERLY VERTICAL WIND SHEAR.  SATELLITE INTENSITY
 ESTIMATES FROM TAFB AND SAB ARE 35 AND 45 KT RESPECTIVELY.  IN
 ADDITION...JUST-RECEIVED QUIKSCAT DATA SHOW 40 KT WINDS...AND THERE
 WAS AN AMSU INTENSITY ESTIMATES OF 43 KT AT 0926Z.  BASED ON THE
 ABOVE...THE INITIAL INTENSITY IS REDUCED TO 45 KT.
 
 THE INITIAL MOTION IS 305/8.  LOWELL IS CURRENTLY BEING STEERED BY A
 MID-LEVEL RIDGE OVER NORTHERN MEXICO.  ALL OF THE DYNAMICAL MODELS
 FORECAST A MID/UPPER-LEVEL TROUGH TO AMPLIFY SOUTHWARD ALONG THE
 WEST COAST OF THE UNITED STATES DURING THE NEXT COUPLE OF
 DAYS...WHICH SHOULD TURN LOWELL TOWARD THE NORTH AND EVENTUALLY
 NORTHEAST.  WHILE THE GUIDANCE AGREES ON THIS SCENARIO...THERE IS
 MAJOR DISAGREEMENT ON HOW FAST LOWELL WILL MOVE AFTER RECURVATURE. 
 THE HWRF...BAMD...AND LBAR ALL MOVE THE THE STORM VERY RAPIDLY...
 WITH 120 HR POSITIONS OVER THE CENTRAL UNITED STATES.  ON THE OTHER
 HAND...THE GFS...UKMET...AND BAMS KEEP THE LOW-LEVEL CENTER WEST
 AND SOUTHWEST OF BAJA CALIFORNIA THROUGH 120 HR.  THE DIFFERENCE
 BETWEEN THE BAMS AND BAMD MODELS IS STRIKING AND SUGGESTS THE
 POSSIBILITY THAT LOWELL COULD SHEAR APART AFTER 48 HR.  THE NEW
 FORECAST TRACK IS A LITTLE FASTER THAN THE SLOWEST MODELS...CALLING
 FOR LOWELL TO REACH BAJA CALIFORNIA IN ABOUT 4 DAYS AND THEN MOVE
 INTO THE GULF OF CALIFORNIA.  IT IS A LITTLE TO THE RIGHT OF THE
 PREVIOUS TRACK BASED ON THE INITIAL POSITION AND MOTION...AND IT IS
 IN THE BEST AGREEMENT WITH THE GFDL AND ECMWF.
 
 THE DYNAMICAL MODELS FORECAST THE CURRENT SHEAR TO DIMINISH IN ABOUT
 24 HOUR.  HOWEVER...LOWELL IS FORECAST TO MOVE TOWARD COOLER SEA
 SURFACE TEMPERATURES DURING THE NEXT 48 HR...AND THIS SHOULD REDUCE
 THE CHANCE OF INTENSIFICATION EVEN WHEN THE SHEAR DECREASES.  AFTER
 RECURVATURE...LOWELL MAY FIND WARMER WATER...BUT IS ALSO EXPECTED
 TO ENCOUNTER INCREASING SOUTHWESTERLY SHEAR..  THE INTENSITY
 GUIDANCE IS IN GOOD AGREEMENT ON A SLOW WEAKENING DURING THE
 FORECAST PERIOD.  THUS...THE NEW INTENSITY FORECAST ALSO CALLS FOR
 A GRADUAL WEAKENING...WITH THE NEW INTENSITIES A LITTLE ABOVE ALL
 THE GUIDANCE.  AN ALTERNATIVE SCENARIO WOULD BE FOR LOWELL TO SHEAR
 APART AFTER 48 HR...WHICH WOULD LEAD TO DISSIPATION BEFORE THE END
 OF THE FORECAST PERIOD.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      08/1500Z 19.0N 111.2W    45 KT
  12HR VT     09/0000Z 19.8N 112.0W    45 KT
  24HR VT     09/1200Z 20.7N 113.0W    45 KT
  36HR VT     10/0000Z 21.5N 113.5W    40 KT
  48HR VT     10/1200Z 22.4N 113.5W    40 KT
  72HR VT     11/1200Z 23.5N 112.5W    35 KT
  96HR VT     12/1200Z 25.0N 111.0W    30 KT...INLAND
 120HR VT     13/1200Z 26.0N 110.0W    30 KT
  
 $$
 FORECASTER BEVEN