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TROPICAL STORM CHRIS DISCUSSION NUMBER   4
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT FRI AUG 18 2000
 
DEEP CONVECTION OVERNIGHT HAS WRAPPED AROUND THE SYSTEM CENTER...AND
SATELLITE INTENSITY ESTIMATES OF 35 KT WERE GIVEN BY TAFB...SAB...
AND KGWC. EVEN THOUGH CLOUD TOPS HAVE WARMED DURING THE PAST FEW
HOURS...THE INTENSITY HAS BEEN INCREASED TO 35 KT AND TROPICAL
DEPRESSION SIX IS NOW TROPICAL STORM CHRIS. OUTFLOW IS FAIR TO GOOD
TO THE NORTH...FAIR TO THE SOUTHEAST...AND POOR ELSEWHERE. AN AIR
FORCE RESERVE RECON AIRCRAFT WILL BE IN THE SYSTEM LATER THIS
AFTERNOON AND WILL GIVE US MORE ACCURATE POSITION AND INTENSITY
INFORMATION.
 
THE INITIAL MOTION IS 295/11.  ALTHOUGH THE GENERAL MOTION HAS BEEN
TO THE NORTHWEST THE PAST 6 HOURS...OUR FEELING IS THAT THE
NORTHWARD JUMP IN THE CENTER POSITION IS DUE TO THE CONVECTIVE 
RE-ORGANIZATION. THERE IS GOOD CLUSTERING OF THE DYNAMIC MODELS
AROUND THE PREVIOUS FORECAST TRACK...WHILE THE STATISTICAL-BASED
MODELS HAVE A MORE NORTHWESTERLY TRACK. THE GFDL HAS BEEN FLIP-
FLOPPING BACK AND FORTH EITHER SIDE OF THE PREVIOUS TRACKS...WHEREAS
THE UKMET HAS CONSISTENTLY KEPT THE SYSTEM WELL NORTH OF THE LEEWARD
AND PUERTO RICO. ALL OF THE GLOBAL MODELS AGREE ON BUILDING AT LEAST
A 592 DM 500 MB HIGH WESTWARD TO THE NORTHEAST OR NORTH OF CHRIS.
GIVEN THE SMALL SIZE OF THE CYCLONE...IT WILL NOT TAKE MUCH RIDGING
TO THE NORTH TO KEEP CHRIS MOVING ON A GENERAL WEST-NORTHWEST TRACK.
BY 72 HOURS...THE STRENGTH OF THE SUBTROPICAL RIDGE IS UNCERTAIN.
THE GLOBAL MODELS WEAKEN THE 500 MB RIDGE...BUT KEEP THE SURFACE TO
700 MB RIDGE INTACT. THE RESULT MAY BE A DECREASE IN FORWARD SPEED
MORE THAN WE ARE INDICATING AS THE STEERING FLOW WEAKENS.

ALL OF THE GLOBAL MODELS SUGGEST THAT CHRIS WILL REMAIN UNDER AT
LEAST WEAK SOUTHWESTERLY UPPER-LEVEL SHEAR THROUGH 48 TO 60 HOURS.
HOWEVER...THE MODELS ALSO AGREE THAT THE UPPER-LEVEL FLOW IN THE
NORTHERN SEMICIRCLE WILL ALSO ANTICYCLONICALLY CURVED AND WITH A 30
TO 40 KT OUTFLOW JET PRESENT TO THE NORTHEAST. AT THE LEAST...SOME
SLOW INTENSIFICATION SHOULD OCCUR AND THE SHIPS INTENSITY MODEL
TAKES CHRIS TO NEAR HURRICANE INTENSITY IN 72 HOURS. HOWEVER...IF
CHRIS SLOWS DOWN AFTER 48 HOURS AND ALLOWS THE 200 MB RIDGE AXIS TO
THE SOUTHEAST TO BUILD ACROSS THE SYSTEM...THEN MORE STRENGTHENING
COULD OCCUR THAN IS INDICATED BY THE OFFICIAL FORECAST.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     18/1500Z 16.7N  55.5W    35 KTS
12HR VT     19/0000Z 17.5N  57.1W    40 KTS
24HR VT     19/1200Z 18.4N  59.2W    45 KTS
36HR VT     20/0000Z 19.4N  61.4W    50 KTS
48HR VT     20/1200Z 20.3N  63.6W    55 KTS
72HR VT     21/1200Z 22.3N  67.9W    60 KTS
 
 
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