[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 290853
TCDAT3
TROPICAL STORM HANNA DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082008
500 AM EDT FRI AUG 29 2008

ALTHOUGH THE UPPER-LOW TO THE NORTHWEST OF HANNA HAS BEGUN TO MOVE
AWAY...IT IS STILL PRODUCING SHEAR OVER THE TROPICAL CYCLONE. ONCE
AGAIN THE CENTER HAS MOVED AWAY FROM THE DEEP CONVECTION WHICH IS
NOW CONFINED TO A CYCLONICALLY CURVED BAND IN THE EASTERN
SEMICIRCLE. DVORAK T-NUMBERS STILL SUPPORT AN INITIAL INTENSITY OF
45 KNOTS...BUT WITH THE CURRENT SHEARED PATTERN...THIS ESTIMATE
COULD BE GENEROUS. THE EVOLUTION OF THE UPPER-LEVEL LOW APPEARS TO
BE THE KEY PLAYER FOR BOTH THE INTENSITY AND TRACK OF HANNA FOR THE
NEXT 24 TO 48 HOURS. IF THE LOW WEAKENS AND MOVES AWAY AS INDICATED
BY GLOBAL MODELS...THE ENVIRONMENT BECOMES MORE FAVORABLE FOR
STRENGTHENING. THE OFFICIAL FORECAST ASSUMES A GOOD SOLUTION FROM
GLOBAL MODELS AND CALLS FOR A GRADUAL INTENSIFICATION FROM 24 TO 72
HOURS. THE FORECAST IS SIMILAR TO THE SHIPS MODEL BUT DOES NOT
SHOWS AS MUCH STRENGTHENING AS SUGGESTED BY THE GFDL AND HWRF.

HANNA HAS BEEN MOVING AROUND THE EAST SIDE OF THE UPPER-LOW AND THE
BEST ESTIMATE OF THE INITIAL MOTION IS 310 DEGREES AT 12 KNOTS. A
GENERAL NORTHWEST TO WEST-NORTHWEST MOTION IS EXPECTED DURING THE
NEXT 2 TO 3 DAYS WHILE THE CYCLONE IS EMBEDDED WITHIN THE FLOW
BETWEEN THE UPPER LOW AND THE SUBTROPICAL RIDGE. BEYOND 3
DAYS...MOST OF THE GLOBAL MODELS ARE CARVING A LARGE TROUGH OVER
THE CENTRAL ATLANTIC AND DEVELOPING A LARGE RIDGE OVER THE EASTERN
UNITED STATES. THIS PATTERN SHOULD FORCE HANNA ON A SLOW
SOUTHWESTERLY TRACK BEYOND THREE DAYS...BUT AT THE SAME TIME THE
UPPER-LEVEL WINDS SHOULD WEAKEN THE CYCLONE. THE OFFICIAL FORECAST
SHOWS A LITTLE BIT OF THE SOUTHWESTERLY MOTION BUT DOES NOT GO AS
FAR SOUTH AS SHOWN BY MOST OF THE MODELS. IN FACT...THE GFS HAS
JOINED THE REST OF THE GLOBAL MODELS IN BRINGING THE CYCLONE
SOUTHWESTWARD. I PREFER TO WAIT FOR MORE MODEL RUNS BEFORE FORECAST
SUCH A RARE BUT NOT UNIQUE TRACK TOWARD THE SOUTHWEST.


FORECAST POSITIONS AND MAX WINDS

INITIAL      29/0900Z 21.7N  62.3W    45 KT
 12HR VT     29/1800Z 22.6N  64.0W    45 KT
 24HR VT     30/0600Z 24.0N  66.0W    50 KT
 36HR VT     30/1800Z 25.3N  68.3W    60 KT
 48HR VT     31/0600Z 26.0N  70.0W    70 KT
 72HR VT     01/0600Z 26.0N  71.5W    80 KT
 96HR VT     02/0600Z 25.5N  72.2W    80 KT
120HR VT     03/0600Z 25.0N  73.0W    75 KT

$$
FORECASTER AVILA



This weather bulletin was brought to you by:
www.nashvilleweather.net