HURRICANE IKE DISCUSSION NUMBER 21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092008
500 AM EDT SAT SEP 06 2008

AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT RECORDED A MAXIMUM FLIGHT
LEVEL WIND OF 104 KT OVER THE NORTHWEST QUADRANT AND AN SFMR PEAK
WIND OF 96 KT OVER THE NORTHEASTERN PORTION OF THE CYCLONE. BASED
ON THESE DATA...THE INITIAL INTENSITY IS HELD AT 100 KT. THE
AIRCRAFT METEOROLOGIST ALSO INDICATED THAT IKE HAS A CLOSED 24 NM
DIAMETER EYE. A DROPSONDE WITHIN THE EYE MEASURED 983 MB BUT THAT
WAS WITH A SURFACE WIND OF 16 KT. AS A COMPROMISE...THE CENTRAL
PRESSURE IS ADJUSTED SLIGHTLY TO 982 MB. ALTHOUGH NORTHERLY SHEAR
SEEMS TO BE PERSISTING OVER THE CYCLONE...IT DOES NOT APPEAR TO BE
AFFECTING THE INNER CORE CONVECTION AS MUCH AS IT WAS PREVIOUSLY.
INTENSITY MODELS CONTINUE TO INDICATE THAT THE SHEAR WILL DECREASE
IN ABOUT 24 HOURS...WHICH SHOULD ALLOW FOR SOME STRENGTHENING
BEFORE IKE MOVES NEAR OR OVER THE NORTHERN COAST OF CUBA. THE
INTENSITY FORECAST IS VERY SIMILAR TO THE PREVIOUS PACKAGE BUT NOW
DEPICTS SOME WEAKENING AS IKE TRAVERSES THE CUBAN COAST. OF
COURSE...ANY SLIGHT DEVIATION NORTH OR SOUTH OF THE FORECAST WILL
EITHER ALLOW FOR STRENGTHENING OVER WATER OR A LONGER PERIOD OF
WEAKENING OVER LAND. LATER ON...CONDITIONS APPEAR RATHER CONDUCIVE
FOR STRENGTHENING OVER THE GULF OF MEXICO.

INITIAL MOTION IS ESTIMATED AT 255/14...WITHIN THE DEEP-LAYER FLOW
OF A STRONG RIDGE DIGGING SOUTHWESTWARD OVER THE BAHAMAS...THROUGH
THE STRAITS OF FLORIDA...AND INTO THE SOUTHEASTERN GULF OF MEXICO.
DYNAMICAL MODELS SUGGEST THAT THE RIDGE WILL SHIFT TO A MORE ZONAL
PATTERN DURING THE NEXT 24 TO 36 HOURS WHICH WILL CAUSE IKE TO MOVE
IN A MORE WESTWARD FASHION. AFTERWARD...GUIDANCE INDICATES THAT
THE SOUTHWEST RIDGE EXTENSION OVER THE SOUTHEASTERN GULF/STRAITS OF
FLORIDA WILL ERODE JUST ENOUGH TO INDUCE A GRADUAL TURN TOWARD THE
NORTHWEST BY THE END OF THE FORECAST PERIOD. THERE IS MUCH
UNCERTAINTY IN THE MODELS AS TO HOW CLOSE IKE WILL APPROACH THE
NORTHERN COAST OF CUBA. IN FACT...THE TWO HURRICANE MODELS
ACTUALLY BRING THE CYCLONE OVER THE ISLAND IN 36 HOURS. WITHOUT
QUESTION...THE PARTICULAR TRACK THAT THE GFDL AND HWRF ARE
SUGGESTING COULD HAVE A SIGNIFICANT IMPACT ON IKE'S INTENSITY.
THE OFFICIAL FORECAST IS WEIGHED HEAVILY ON THE MODEL CONSENSUS AND
IS ADJUSTED JUST TO THE LEFT OF THE PREVIOUS ADVISORY TO COMPENSATE
FOR THE WESTWARD-SHIFTING MODEL TREND.

FORECAST POSITIONS AND MAX WINDS

INITIAL 06/0900Z 22.4N 67.1W 100 KT
12HR VT 06/1800Z 22.1N 69.0W 100 KT
24HR VT 07/0600Z 21.8N 71.6W 100 KT
36HR VT 07/1800Z 21.6N 74.1W 105 KT
48HR VT 08/0600Z 21.8N 76.6W 115 KT
72HR VT 09/0600Z 23.0N 80.5W 90 KT...NEAR COAST OF CUBA
96HR VT 10/0600Z 24.5N 83.5W 105 KT
120HR VT 11/0600Z 26.0N 85.5W 110 KT

$$
FORECASTER ROBERTS/KNABB

TROPICAL DEPRESSION JOSEPHINE DISCUSSION NUMBER 17...CORRECTED
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL102008
500 AM EDT SAT SEP 06 2008

...CORRECTED FOR HEADER...

JOSEPHINE HAS FINALLY SUCCUMBED TO THE EFFECTS OF THE SUBSTANTIAL
SOUTHERLY VERTICAL SHEAR COUPLED WITH MARGINAL SEA SURFACE
TEMPERATURES. WITH ONLY A COUPLE OF THUNDERSTORMS FLARING UP IN
THE NORTHERN SEMI-CIRCLE...THE SYSTEM NO LONGER CAN BE CONSIDERED A
TROPICAL CYCLONE.

THE REMNANT LOW OF JOSEPHINE IS MOVING AT 295 DEGREES AT 8 KT SOUTH
OF A DEEP LAYER RIDGE. THE SYSTEM SHOULD CONTINUE MOVING TOWARD
THE WEST-NORTHWEST AT A SLIGHTLY FASTER FORWARD SPEED AS IT ADVECTS
ALONG IN THE LOWER TROPOSPHERIC FLOW. THE TRACK IS JUST NORTH OF
THE MODEL CONSENSUS AND CLOSEST TO BAM-SHALLOW.

WITH THE STRONG SHEAR EXPECTED TO CONTINUE DURING THE NEXT TWO DAYS
BECAUSE OF AN UPPER CLOSED LOW NORTHWEST OF JOSEPHINE...
REGENERATION OF THE SYSTEM BACK INTO A TROPICAL CYCLONE IS NOT
LIKELY. HOWEVER...AT DAYS 3 AND 4 ALL GLOBAL MODELS DO SHOW THE
SHEAR RELAXING AS THE UPPER LOW MOVES AWAY FROM JOSEPHINE'S
REMNANTS. DESPITE THIS...NONE OF THE DYNAMICAL MODELS SUGGEST ANY
REGENERATION OF THE CYCLONE AT THE LONGER RANGE. THE OFFICIAL
FORECAST AGREES WITH THE DYNAMICAL GUIDANCE AND KEEPS JOSEPHINE
DISSIPATED.

FORECAST POSITIONS AND MAX WINDS

INITIAL 06/0900Z 16.8N 36.9W 25 KT...REMNANT LOW
12HR VT 06/1800Z 17.5N 38.3W 25 KT...REMNANT LOW
24HR VT 07/0600Z 18.5N 40.3W 25 KT...REMNANT LOW
36HR VT 07/1800Z 19.7N 42.4W 20 KT...REMNANT LOW
48HR VT 08/0600Z 20.9N 44.6W 20 KT...REMNANT LOW
72HR VT 09/0600Z 23.5N 48.5W 20 KT...REMNANT LOW
96HR VT 10/0600Z...DISSIPATED

$$
FORECASTER LANDSEA/KNABB