[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 200231
TCDAT4
TROPICAL STORM DANIELLE DISCUSSION NUMBER  27
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT THU AUG 19 2004

EVENING SATELLITE IMAGERY SHOWS THAT THE PERSISTENT CONVECTION
EARLIER ASSOCIATED WITH DANIELLE HAS SHEARED AWAY TO THE NORTHEAST.
A FEW NEW THUNDERSTORMS HAVE SINCE DEVELOPED IN THE NORTHERN
QUADRANT.  A QUIKSCAT OVERPASS AT 2010Z SHOWED AT LEAST 30 KT WINDS
ASSOCIATED WITH THE CYCLONE...AND AN SSM/I OVERPASS AT 2316Z
SUGGESTED THERE MAY STILL BE 35 KT WINDS IN THE REMAINS OF THE
CONVECTION.  BASED ON THIS...THE INITIAL INTENSITY WILL BE HELD AT
35 KT ONE MORE TIME.

THE INITIAL MOTION IS 100/3.  DANIELLE IS CURRENTLY EMBEDDED IN THE
SUBTROPICAL RIDGE AND ISOLATED FROM MOST STEERING INFLUENCES.
LARGE-SCALE MODELS SUGGEST THIS WILL CONTINUE UNTIL ABOUT 72 HR...
WHEN A DEEP LAYER RIDGE DEVELOPS NEAR THE AZORES.  THIS SHOULD MOVE
DANIELL GENERALLY NORTHWESTWARD FROM THAT TIME...WITH ERRATIC
MOTION UNTIL THEN.  THE TRACK GUIDANCE GENERALLY AGREES WITH THIS
SCENARIO...ALTHOUGH THERE IS A SIGNIFICANT SPREAD ON JUST WHERE THE
STORM COULD WIND UP BEFORE THE 72 HR POINT.  THE OFFICIAL FORECAST
IS A BLEND OF THE CURRENT MOTION AND THE PREVIOUS FORECAST UNTIL 72
HR...AND THEN FOLLOWS THE GFDL...GUNS...AND GUNA MODELS AFTER THAT.
THE FIRST 72 HR IS A VERY LOW CONFIDENCE FORECAST...AND THERE IS A
CHANCE DANIELLE COULD BE FURTHER EAST IF THE UKMET AND NHC98
VERIFY.

WATER VAPOR IMAGERY SHOWS THE UPPER-LEVEL LOW THAT WAS WEST OF
DANIELLE LAST NIGHT IS MOVING EASTWARD ACROSS THE SYSTEM...WHICH
HAS RESULTED IN SIGNIFICANT SHEARING.  LARGE-SCALE MODELS SUGGEST
THE VERTICAL SHEAR SHOULD REMAIN MODERATE TO STRONG FOR 72 HR.
DESPITE THIS...THE GFDL AND SHIPS HOLD ON TO THE SYSTEM UNTIL 120
HR...AND SO WILL THE INTENSITY FORECAST.  THERE ARE TWO ALTERNATIVE
SCENARIOS.  THE FIRST IS THAT DANIELLE COULD DISSIPATE BEFORE 72 HR
DUE TO THE SHEAR.  THE SECOND IS THAT LARGE-SCALE MODELS FORECAST
THE SHEAR TO DIMINISH SOME AFTER 72 HR...WHICH COULD ALLOW SOME
RE-INTENSIFICATION IF DANIELLE SURVIVES THAT LONG.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL      20/0300Z 29.7N  36.7W    35 KT
 12HR VT     20/1200Z 29.9N  36.1W    30 KT
 24HR VT     21/0000Z 30.5N  35.9W    25 KT
 36HR VT     21/1200Z 31.1N  35.9W    25 KT
 48HR VT     22/0000Z 31.7N  36.1W    25 KT
 72HR VT     23/0000Z 32.5N  36.5W    25 KT
 96HR VT     24/0000Z 33.0N  37.0W    25 KT
120HR VT     25/0000Z 34.5N  39.0W    25 KT


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