Tropical Storm CRISTOBAL

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TROPICAL STORM CRISTOBAL DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032008
500 PM EDT SUN JUL 20 2008
 
THUNDERSTORM ACTIVITY HAS BEEN SIGNIFICANTLY INCREASING IN THE
SOUTHERN PORTION OF THE STORM.  HOWEVER...THE FLIGHT-LEVEL WINDS AT
5000 FT HAVE BEEN NO HIGHER THAN 46 KT RECENTLY...NORMALLY
CORRESPONDING TO ABOUT 35 KT AT THE SURFACE.  THE SFMR DID MEASURE
46 KT IN DEEP CONVECTION SOUTHEAST OF THE CYCLONE.  GIVEN THE LACK
OF PERSISTENCE IN THE CONVECTION DURING THE LAST DAY OR SO...WE'RE
GOING TO USE A COMPROMISE INITIAL INTENSITY ESTIMATE OF 40 KT. 
SOME INTENSIFICATION IS POSSIBLE AS THE SYSTEM FIGHTS THE DRY AIR
ALOFT AND REMAINS OVER THE WARM GULF STREAM WATERS.  THE OFFICIAL
FORECAST IS A LITTLE LOWER THAN BEFORE...BUT ABOVE MOST OF THE
GUIDANCE.  

THE INITIAL MOTION CONTINUES NORTHEASTWARD AT 7 KT...A LITTLE FASTER
THAN BEFORE.  THIS GENERAL TRACK SHOULD CONTINUE WITH AN INCREASING
FORWARD DUE TO FASTER STEERING CURRENTS BETWEEN A MID-TROPOSPHERIC
HIGH TO THE EAST AND AN APPROACHING MIDDLE-LATITUDE TROUGH. IN A
COUPLE OF DAYS...A COMBINATION OF SSTS BELOW 20C AND A LARGE
INCREASE IN VERTICAL WIND SHEAR SHOULD FACILITATE AN EXTRATROPICAL
TRANSITION OF THE STORM.  THE APPROACHING TROUGH WILL PROBABLY
ABSORB CRISTOBAL IN ABOUT THREE DAYS...THOUGH A FEW MODELS DO KEEP
IT MORE SEPARATE FROM THE TROUGH. THERE HAS BEEN LITTLE CHANGE TO
THE GUIDANCE...AND THE OFFICIAL FORECAST IS CLOSE TO THE PREVIOUS
ONE. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      20/2100Z 34.7N  75.8W    40 KT
 12HR VT     21/0600Z 35.9N  74.3W    45 KT
 24HR VT     21/1800Z 37.9N  71.6W    45 KT
 36HR VT     22/0600Z 40.8N  68.0W    45 KT
 48HR VT     22/1800Z 44.0N  63.5W    45 KT...EXTRATROPICAL
 72HR VT     23/1800Z...ABSORBED
 
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FORECASTER BLAKE/KNABB
 
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