[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT44 KNHC 141457
TCDAT4
HURRICANE IVAN DISCUSSION NUMBER  49
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT TUE SEP 14 2004

RECONNAISSANCE REPORTS AND SATELLITE IMAGERY INDICATE THAT IVAN HAS
WEAKENED SOMEWHAT THIS MORNING.  THE CENTRAL PRESSURE IN THE
CLOUD-FILLED EYE WAS UP TO 932 MB AND THE PEAK 700 MB WINDS HAVE
COME DOWN TO 128 KT.  BASED ON THESE OBSERVATIONS...THE ADVISORY
INTENSITY IS LOWERED TO 120 KT AND EVEN THIS ESTIMATE IS PROBABLY A
BIT HIGH.  THIS WEAKENING IS CONCURRENT WITH THE EROSION OF THE
EYEWALL REPORTED BY THE AIRCRAFT CREW AND THE DEVELOPMENT OF A NEW
EYEWALL ABOUT 40-50 NM ACROSS.

WATER VAPOR IMAGERY AND DATA FROM THE NOAA G-IV JET THIS MORNING
CONTINUE TO INDICATE RESTRICTION OF THE OUTFLOW IN THE NORTHWEST
QUADRANT OF THE HURRICANE...AS WELL AS VERY DRY AIR UNDERNEATH THE
CIRRUS CANOPY.  THIS...ALONG WITH THE CURRENT EYEWALL REPLACEMENT
CYCLE...SUGGESTS THAT IVAN MAY CONTINUE TO WEAKEN A BIT DURING THE
NEXT 12 HOURS OR SO.  AFTER THAT...GLOBAL MODELS SUGGEST A
RELAXATION OF THE WESTERLY SHEAR ABOUT THE TIME THAT IVAN IS
EXPECTED TO PASS OVER A WARM EDDY IN THE CENTRAL GULF.  THIS COULD
ALLOW IVAN TO REGAIN SOME STRENGTH BEFORE LANDFALL...AND THIS IS
REFLECTED IN THE OFFICIAL FORECAST.  THERE HAS BEEN NO CHANGE FROM
THE BASIC EXPECTATION THAT IVAN WILL BE A MAJOR HURRICANE AT
LANDFALL.

THE INITIAL MOTION IS 330/7.  IVAN IS MOVING AROUND THE PERIPHERY OF
THE ATLANTIC SUBTROPICAL RIDGE.  A SECOND MID-LEVEL HIGH IS
CENTERED OVER LOUISIANA WITH A RIDGE EXTENDING SOUTHWARD INTO THE
WESTERN GULF OF MEXICO.  12Z RAOBS AND JET DATA INDICATE THAT THIS
LATTER RIDGE IS A LITTLE STRONGER THAN FORECAST BY THE 6Z GFS RUN.
THIS MIGHT RESULT IN WEAKER STEERING AND A SLOWER MOTION TOWARD THE
COAST THAN THE GFS IS FORECASTING.  MODEL GUIDANCE IS IN PRETTY
GOOD AGREEMENT THROUGH 48 HOURS...WITH ONLY ABOUT 125 MILES
SEPARATING THE LANDFALLS OF THE ECMWF TO THE WEST OF THE OFFICIAL
FORECAST FROM THE UKMET TO ITS EAST.  THE OFFICIAL FORECAST HAS
BEEN SHIFTED SLIGHTLY WEST AND IS IN BEST AGREEMENT WITH THE FSU
SUPERENSEMBLE...WHICH HAS PERFORMED WELL WITH THIS STORM.

THERE IS CONSIDERABLE SPREAD IN THE MODEL FORECASTS AFTER
LANDFALL...AND IT IS POSSIBLE THAT THE REMNANTS OF IVAN WILL MOVE
VERY SLOWLY OR STALL NEAR OR OVER THE APPALACHIANS IN 4 OR 5
DAYS...WHICH WOULD PRODUCE A VERY SERIOUS FLOODING EVENT.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL      14/1500Z 23.4N  86.2W   120 KT
 12HR VT     15/0000Z 24.4N  86.9W   115 KT
 24HR VT     15/1200Z 26.3N  88.0W   115 KT
 36HR VT     16/0000Z 28.5N  88.5W   120 KT
 48HR VT     16/1200Z 30.5N  88.5W   110 KT...INLAND
 72HR VT     17/1200Z 34.0N  86.5W    40 KT...INLAND
 96HR VT     18/1200Z 36.0N  84.0W    20 KT...INLAND
120HR VT     19/1200Z 36.5N  83.0W    20 KT...INLAND


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