[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 132100
TCDAT4
TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT FRI AUG 13 2004

CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY CONTINUE TO INDICATE
THAT TROPICAL DEPRESSION FIVE IS GETTING BETTER ORGANIZED. THE
CYCLONE COULD POSSIBLY BE A TROPICAL STORM ALREADY...BUT THE
INITIAL INTENSITY WAS HELD AT 30 KT BASED ON A BLEND OF DVORAK
SATELLITE INTENSITY ESTIMATES OF T2.5...OR 35 KT...FROM TAFB AND
T2.0...OR 30 KT...FROM SAB. HOWEVER...IT WOULD NOT TAKE MUCH MORE
BANDING OR DEEP CONVECTION TO DEVELOP NEAR THE CENTER FOR THIS
SYSTEM TO BECOME A TROPICAL STORM.

THE INITIAL MOTION ESTIMATE REMAINS 280/13. THERE IS NO SIGNIFICANT
CHANGE TO THE PREVIOUS TRACK REASONING. THE TRACK WAS SHIFTED A
LITTLE TO RIGHT BASED ON THE CENTER BECOMING BETTER DEFINED A
LITTLE FARTHER NORTH.  BY 48 HOURS...ALL THE GLOBAL MODELS STILL
AGREE ON A MID-LEVEL TROUGH DIGGING SOUTHEASTWARD AND THEN SOUTH
AND SOUTHWESTWARD BETWEEN 35-40W LONGITUDE...WHICH SHOULD WEAKEN
THE SUBTROPICAL RIDGE. THE QUESTION IS HOW MUCH WEAKENING OF THE
RIDGE WILL OCCUR. SEVERAL OF THE NHC MODELS INDICATE A NORTHWARD
MOTION AFTER 96 HOURS...BUT A SMALL POLEWARD STAIR-STEP IN THE
TRACK...WITH A RETURN TO A WEST-NORTHWESTWARD MOTION...COULD OCCUR
INSTEAD. THE OFFICIAL TRACK IS A COMPROMISE OF THOSE TWO SCENARIOS
UNTIL MORE CONSISTENT MODEL GUIDANCE BECOMES AVAILABLE.

ONLY SLOW INTENSIFICATION IS FORECAST GIVEN THE HIGH LATITUDE OF THE
CYCLONE AND THE RELATIVELY COOL WATER...26-27C SSTS...THAT THE
CYCLONE WILL BE PASSING OVER...EVEN THOUGH THE VERTICAL SHEAR IS
EXPECTED TO REMAIN BELOW 10 KT THROUGH 48 HOURS. THE OFFICIAL
INTENSITY FORECAST IS CLOSE TO THE SHIPS INTENSITY MODEL. HOWEVER
...IF THE CYCLONE TAKES A MORE SOUTHERLY TRACK AND STAYS OVER
WARMER WATER...THEN IT COULD BECOME A HURRICANE BY 72 HOURS.

FORECASTER STEWART


FORECAST POSITIONS AND MAX WINDS

INITIAL      13/2100Z 12.5N  24.0W    30 KT
 12HR VT     14/0600Z 12.8N  25.9W    35 KT
 24HR VT     14/1800Z 13.3N  28.3W    40 KT
 36HR VT     15/0600Z 14.0N  30.9W    50 KT
 48HR VT     15/1800Z 15.2N  34.1W    55 KT
 72HR VT     16/1800Z 16.5N  38.0W    55 KT
 96HR VT     17/1800Z 17.5N  42.0W    60 KT
120HR VT     18/1800Z 19.0N  45.5W    60 KT


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