Tropical Storm CHRIS

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TROPICAL STORM CHRIS DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032006
500 AM EDT WED AUG 02 2006
 
AIR FORCE RESERVE RECON POSITION AND WIND DATA THIS MORNING...ALONG
WITH NOAA DOPPLER RADAR DATA FROM SAN JUAN AND SATELLITE IMAGERY...
INDICATE CHRIS HAS BECOME MUCH BETTER ORGANIZED DURING THE PAST 6
HOURS. AN UPPER-LEVEL EYE FEATURE HAS BECOME APPARENT IN RADAR
IMAGERY...ALTHOUGH IT IS TILTED ABOUT 12 NMI TO THE SOUTHWEST OF
THE LOW-LEVEL CENTER. WHILE THE STRUCTURE OF CHRIS HAS IMRPOVED...
THIS HAS NOT TRANSLATED INTO AN INCREASE IN INTENSITY...YET. A PASS
THROUGH THE CENTER OF CHRIS AROUND 0745Z REVEALED AN ESTIMATED
CENTRAL PRESSURE OF 1001 MB AND AN 850 MB FLIGHT-LEVEL WIND OF 62
KT. WHILE THE PRESSURE IS DOWN 2 MB FORM EARLIER FLIGHTS...THE
FLIGHT-LEVEL WINDS STILL YIELD ONLY A 50-KT SURFACE WIND.
UPPER-LEVEL OUTFLOW HAS IMPROVED IN ALL QUADRANTS...AND THE OVERALL
CONVECTIVE STRUCTURE AS BECOME MORE SYMMETRICAL.
 
THE MOTION ESTIMATE IS 300/09 KT...ALTHOUGH THE SHORT TERM MOTION
FROM THE LAST SEVERAL RECON FIXES YIELDS A MOTION OF 310/11.
OVERALL...NO SIGNIFICANT CHANGE TO THE STRENGTH AND POSITION OF THE
BERMUDA HIGH PRESSURE RIDGE TO THE NORTH OF CHRIS IS FORECAST BY
THE GLOBAL MODELS. THE RIDGE AXIS CURRENTLY EXTENDS WESTWARD ACROSS
THE SOUTHEASTERN U.S. AND INTO THE U.S. CENTRAL PLAINS...AND IS
EXPECTED TO REMAIN IN ROUGHLY THAT POSITION THROUGHOUT THE FORECAST
PERIOD. THERE ARE SIGNIFICANT DIFFERENCES NOW IN HOW THE MODELS
HANDLE THE STRENGTH OF CHRIS. UNLIKE PREVIOUS RUNS OVER THE PAST
FEW DAYS...MOST OF THE GLOBAL MODELS...ESPECIALLY NOGAPS...NOW HANG
ONTO CHRIS AS A TROPICAL CYCLONE...ALBEIT A SMALL COMPACT ONE. THE
GFS...GFS ENSEMBLE...NOGAPS...AND UKMET MODELS HAVE MADE A
SIGNIFICANT NORTHWARD SHIFT AND ARE NOW ON THE RIGHT SIDE OF THE
MODEL GUIDANCE ENVELOPE. THE CANADIAN AND ECMWF MODELS HAVE ALSO
SHIFTED NORTHWARD AND NO LONGER TAKE CHRIS ACROSS THE GREATER
ANTILLES. THE LONE OUTLIER MODEL APPEARS TO BE THE GFDL...WHICH
ALMOST IMMEDIATELY TAKES CHRIS DUE WEST ACROSS THE NORTH COAST OF
PUERTO RICO AND INTO HISPANIOLA. THE OFFICIAL FORECAST TRACK IS A
LITTLE NORTH OF THE PREVIOUS TRACK...AND MUCH FARTHER NORTH THAN
THE MODEL CONSENSUS DUE TO THE GFDL MODEL BEING A LARGE OUTLIER. IT
SHOULD BE POINTED OUT THAT THE GFS...GFS ENSEMBLE...UKMET...AND
NOGAPS CONSENSUS FORECAST PLACES CHRIS VERY NEAR THE SOUTHERN TIP
OF FLORIDA IN 120 HOURS...AND SUBSEQUENT FORECAST TRACKS MAY HAVE
TO SHIFTED A LITTLE FARTHER NORTH IF THOSE MODEL TRENDS CONTINUE.

THE INTENSITY FORECAST REMAINS PROBLEMATIC. THE GFS-BASED SHIPS
INTENSITY MODEL INDICATES THE VERTICAL SHEAR IS EXPECTED TO WEAKEN
TO LESS THAN 5-10 KT BY 96 AND 120 HOURS...YET SHOWS LITTLE
INTENSIFICATION AND BARELY MAKES CHRIS A HURRICANE...EVEN THOUGH
THE CYCLONE WILL BE OVER 29.5C TO 30C SSTS AND BETWEEN TWO
UPPER-LEVEL LOWS THAT WILL ENHANCE THE OUTFLOW TO THE WEST AND
EAST. GIVEN THAT CHRIS IS A SMALL TROPICAL CYCLONE...WHICH MEANS IT
CAN SPIN UP QUICKLY BUT ALSO SPIN DOWN JUST AS QUICKLY...THE
INTENSITY FORECAST WILL REMAIN ON THE CONSERVATIVE SIDE AT THIS
TIME IN HE LONGER TIME PERIODS...BUT STILL ABOVE THE SHIPS MODEL.

TROPICAL STORM WARNINGS REMAIN IN EFFECT FOR PUERTO RICO AND THE
VIRGIN ISLANDS DUE TO THE POSSIBILITY OF A STRONG RAIN BAND
DEVELOPING ON THE SOUTH SIDE OF CHRIS AND MOVING OVER THOSE AREAS
LATER TODAY OR TONIGHT.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/0900Z 18.8N  62.6W    50 KT
 12HR VT     02/1800Z 19.4N  64.0W    55 KT
 24HR VT     03/0600Z 20.0N  65.8W    60 KT
 36HR VT     03/1800Z 20.6N  67.6W    65 KT
 48HR VT     04/0600Z 21.2N  69.5W    65 KT
 72HR VT     05/0600Z 22.2N  73.5W    65 KT
 96HR VT     06/0600Z 23.3N  77.5W    70 KT
120HR VT     07/0600Z 24.5N  82.5W    70 KT
 
$$
FORECASTER STEWART
 
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