[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 240307
TCDAT2
TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   2... CORRECTED
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT TUE AUG 23 2005

...CORRECTED TO CLARIFY CONVECTIVE BAND IN FIRST PARAGRAPH AND
POTENTIAL TIMELINE OF WATCHES AND WARNINGS IN NEXT TO LAST
PARAGRAPH...

THE RECONNAISSANCE AIRCRAFT... PRIOR TO DEPARTING THE DEPRESSION
AFTER ABOUT 2230Z... CONTINUED TO REPORT A MINIMUM CENTRAL PRESSURE
NEAR 1007 MB... AND MAXIMUM FLIGHT LEVEL WINDS DURING THIS MISSION
NEVER EXCEEDED THE 39 KT OBSERVED SHORTLY AFTER 18Z. DURING THE
PAST COUPLE OF HOURS... THE CENTER HAS BEEN NEAR GEORGETOWN ON
GREAT EXUMA ISLAND IN THE CENTRAL BAHAMAS... WHERE 1007 MB AND
NEARLY CALM WINDS HAVE RECENTLY BEEN REPORTED. LACKING ANY DATA TO
SUPPORT A STRONGER SYSTEM... THE ADVISORY INTENSITY IS MAINTAINED
AT 30 KT. HOWEVER... RECENTLY A BAND OF DEEP CONVECTION... WITH
SOME TOPS COLDER THAN -80C... HAS STRENGTHENED TO THE EAST OF THE
CIRCULATION CENTER... AND THIS BAND COULD WRAP SUFFICIENTLY AROUND
THE CENTER WITHIN THE NEXT SEVERAL HOURS TO SOON MAKE THIS SYSTEM A
TROPICAL STORM.  RADAR IMAGERY FROM GREAT EXUMA ALSO DEPICTS A
NEARLY CONTINUOUS CURVED BAND OF RAINFALL BENEATH THESE CONVECTIVE
TOPS.

THE EARLIER AIRCRAFT FIXES SUGGESTED THAT THE DEPRESSION WAS MOVING
ERRATICALLY.  BASED ON CONTINUITY AND ON SURFACE OBSERVATIONS FROM
THE BAHAMAS... THE INITIAL MOTION ESTIMATE IS 305/6 KT... A LITTLE
SLOWER THAN BEFORE.  THE WEAK STEERING CURRENTS ARE A RESULT OF
THE DEPRESSION LYING TO THE SOUTH OF A NARROW MID LEVEL RIDGE AXIS
ORIENTED EAST TO WEST BETWEEN BERMUDA AND NORTHERN FLORIDA.  SINCE
MOST OF THE DYNAMICAL MODELS DO NOT FORECAST THIS RIDGE TO
STRENGTHEN MUCH OFF THE U.S. EAST COAST DURING THE NEXT FEW DAYS...
A SLOW MOTION IS ANTICIPATED THROUGHOUT THE FORECAST PERIOD... WITH
A WESTWARD BEND BEYOND ABOUT 36 HOURS.  MOST OF THE DYNAMICAL
GUIDANCE... EXCEPT FOR THE GFS... GENERALLY AGREE WITH THIS
SCENARIO.  THE GFS CONTINUES TO BE THE SINGLE OUTLIER FORECASTING
THAT THIS SYSTEM WILL STALL OVER FLORIDA BEYOND ABOUT 48 HOURS.
THE NEW OFFICIAL FORECAST IS A LITTLE SLOWER AND TO THE RIGHT OF
THE PREVIOUS ADVISORY... TO COME INTO BETTER AGREEMENT WITH THE
MODEL CONSENSUS.

GIVEN THE SLOW TREND THIS EVENING TOWARD INCREASED ORGANIZATION...
THE DEPRESSION COULD BECOME A TROPICAL STORM EARLY ON WEDNESDAY
MORNING. BEYOND THAT TIME... THE INTENSITY FORECAST IS PROBLEMATIC
FOR MANY REASONS... NOT THE LEAST OF WHICH IS WIDELY DIFFERING
MODEL GUIDANCE. THE GFDL STILL DOES NOT EVEN FORECAST STRENGTHENING
TO A TROPICAL STORM. HOWEVER... THE SHIPS MODEL STILL INSISTS ON
HURRICANE INTENSITY BY 48 HOURS BEFORE THE SYSTEM CROSSES
FLORIDA... WITHIN AN ENVIRONMENT OF MODEST WIND SHEAR AND OVER VERY
WARM SSTS. AS MORE OF A COMPROMISE BETWEEN THESE SOLUTIONS... BUT
STILL LEANING TOWARD THE SHIPS... THE OFFICIAL FORECAST IS JUST A
LITTLE MORE CONSERVATIVE THAN THE PREVIOUS ADVISORY... BUT STILL
CALLS FOR A STRONG TROPICAL STORM TO APPROACH FLORIDA WITHIN THE
NEXT COUPLE OF DAYS.

SINCE TROPICAL STORM FORCE WINDS COULD BE VERY CLOSE TO THE
SOUTHEAST COAST OF FLORIDA AND THE NORTHERN FLORIDA KEYS IN ABOUT
36 HOURS... A TROPICAL STORM WATCH HAS BEEN ISSUED AT THIS TIME.  A
TROPICAL STORM WARNING COULD BE ISSUED FOR PORTIONS OF THE TROPICAL
STORM WATCH AREA ON WEDNESDAY... POSSIBLY INCLUDING A HURRICANE
WATCH IF THE DEPRESSION STRENGTHENS MORE RAPIDLY THAN CURRENTLY
FORECAST.

THE UNCERTAINTY IN THIS FORECAST... AND THE POTENTIAL IMPACTS OF
THIS TROPICAL CYCLONE... ARE QUANTIFIED IN AN EXPERIMENTAL NHC TEXT
PRODUCT ISSUED WITH THIS AND EVERY ADVISORY PACKAGE DURING 2005.
THIS PRODUCT PROVIDES WIND SPEED PROBABILITIES AT SPECIFIC
LOCATIONS. THE PROBABILITIES OF EXPERIENCING TROPICAL STORM FORCE
WINDS FROM THIS SYSTEM DURING THE NEXT FIVE DAYS ARE SIMILAR AT
EACH INDIVIDUAL LOCATION THROUGHOUT THE TROPICAL STORM WATCH AREA.


FORECASTER KNABB


FORECAST POSITIONS AND MAX WINDS

INITIAL      24/0300Z 23.4N  76.0W    30 KT
 12HR VT     24/1200Z 24.2N  76.7W    35 KT
 24HR VT     25/0000Z 25.1N  77.7W    40 KT
 36HR VT     25/1200Z 25.7N  78.5W    45 KT
 48HR VT     26/0000Z 26.1N  79.5W    55 KT
 72HR VT     27/0000Z 26.5N  81.5W    40 KT...INLAND
 96HR VT     28/0000Z 27.0N  83.5W    55 KT
120HR VT     29/0000Z 27.5N  85.5W    65 KT


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