[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT44 KNHC 060844
TCDAT4
TROPICAL DEPRESSION NINE DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SAT AUG 06 2005

TD-9 REMAINS A LARGE AND WELL-DEFINED CIRCULATION...AND THE INNER
CORE WIND FIELD HAS ACTUALLY IMPROVED CONSIDERABLY SINCE THIS TIME
YESTERDAY WITH NO MULTIPLE CIRCULATIONS APPARENT IN NIGHTIME
VISIBLE IMAGERY. THE INTENSITY IS BEING INCREASED TO 30 KT BASED ON
THE TIGHTER INNER CIRCULATION...TWO CONSECUTIVE QUIKSCAT OVERPASSES
INDICATING NUMEROUS 30-KT UNFLAGGED WIND VECTORS IN THE NORTHEAST
QUADRANT...AND A CIMSS AMSU PRESSURE ESTIMATE OF 1006.5MB ...EQUAL
TO ABOUT 33 KT. CONVECTION HAS BEEN RECENTLY BEEN TRYING TO DEVELOP
INTO A CURVED BAND IN THE EASTERN SEMICIRCLE ABOUT 120 NMI AWAY
FROM THE CENTER...WHICH FURTHER SUGGEST IMPROVED ORGANIZATION.

THE INITIAL MOTION IS 285/13. THE DEPRESSION HAS SLOWED AND TURNED
MORE WESTWARD NOW THAT THE CYCLONE HAS MOVED WEST OF AN UPPER-LEVEL
TROUGH LOCATED TO THE NORTH. THE FORECAST TRACK IS PROBLEMATIC IN
THAT IT IS DIRECTLY RELATED TO THE INTENSITY...AND THEREFORE...THE
VERTICAL DEPTH OF CYCLONE. UPPER-LEVEL WESTERLY WINDS ARE EXPECTED
TO CONTINUE ACROSS THE SYSTEM FOR AT LEAST THE NEXT 36-48 HOURS.
THESE UNFAVORABLE SHEAR CONDITIONS COMBINED WITH AN ABUNDANCE OF
MID-LEVEL DRY AIR SHOULD KEEP CONVECTIVE ORGANIZATION AND VERTICAL
DEVELOPMENT OF THE CYCLONE TO A MINIMUM DURING THAT TIME. THIS
SHOULD ALLOW THE SYSTEM TO BE STEERED MORE WESTWARD BY THE
LOW-LEVEL FLOW. BY 72 HOURS...THE CYCLONE WILL BE OVER WARMER WATER
AND MORE STEADY INTENSIFICATION AND DEEPENING OF THE VERTICAL
CIRCULATION SHOULD OCCUR...WHICH SHOULD ALLOW THE CYCLONE TO BE
STEERED SLOWLY NORTHWESTWARD BY THE DEEP-LAYER FLOW TOWARD AN
EXPECTED WEAKNESS IN THE SUBTROPICAL RIDGE BETWEEN 55W-60W
LONGITUDE. HOWEVER...IF THE STORM MOVES MORE WESTWARD AND STAYS
BELOW 20N LATITUDE THROUGH 72 HOURS...THEN IT MAY NEVER FEEL THE
WEAKNESS IN THE RIDGE AND NOT TURN NORTHWESTWARD. SINCE THE GLOBAL
MODELS ARE ALREADY TOO FAR TO THE NORTH OR RIGHT OF THE CURRENT
POSITION AND MOTION...THE OFFICIAL TRACK WAS SHIFTED TO THE LEFT OF
THE PREVIOUS FORECAST TRACK AND IS CLOSE TO THE NHC MODEL CONSENSUS
THROUGH 72 HOURS AND THEN A LITTLE LEFT OF THE CONSENSUS AFTER
THAT...BUT NOT NEARLY AS FAR LEFT OR SOUTH AS THE UKMET MODEL.

THE PREVIOUSLY MENTIONED INHIBITING FACTORS ARE NOT EXPECTED TO
ABATE FOR AT LEAST 48 HOURS. THE OFFICIAL INTENSITY FORECAST IS
SIMILAR TO THE SHIPS MODEL THROUGH 72 HOURS AND THEN SLIGHTLY
HIGHER AFTER THAT SINCE THE FORECAST TRACK IS FARTHER SOUTH IN A
LOWER SHEAR ENVIRONMENT THAN WHAT THE SHIPS MODEL USED. HOWEVER...
IF THE ACTUAL FORECAST ENDS UP BEING FARTHER SOUTH...THEN WARMER
WATER AND EVEN LESS VERTICAL SHEAR WOULD ALLOW FOR MORE
STRENGTHENING THAN CURRENTLY INDICATED.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      06/0900Z 17.7N  41.7W    30 KT
 12HR VT     06/1800Z 18.2N  43.8W    30 KT
 24HR VT     07/0600Z 18.8N  46.4W    35 KT
 36HR VT     07/1800Z 19.4N  48.6W    35 KT
 48HR VT     08/0600Z 20.1N  51.0W    40 KT
 72HR VT     09/0600Z 21.3N  54.0W    40 KT
 96HR VT     10/0600Z 23.0N  57.0W    45 KT
120HR VT     11/0600Z 25.5N  59.5W    55 KT

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