Posted on 09/21/2002 3:05:23 PM PDT by newsperson999
Statement as of 5:00 PM EDT on September 21, 2002
Air Force recon data indicate major Hurricane Isidore has continued to rapidly strengthen and the central pressure has dropped 21 mb in the past 13 hours. A pressure of 946 mb generally corresponds to a maximum wind of about 117 kt. However...the eye is open to the west and there may be a lag in the wind field. Also...dropsonde data indicated about 105 kt surface winds...but winds just a few hundred above the surface have been as high as 130 kt. The three satellite agencies reported a Dvorak satellite intensity estimate of t6.0...or 115 kt...while the 3-hour objective Dvorak T-number was also t6.0. Based on this information...the initial intensity was increased to 110 kt.
The initial motion estimate is 270/3. Recon fix positons since about 12z indicate Isidore has actually remained nearly stationary the past 6 hours...but right over some of the hottest water in the Atlantic Basin. Steering currents remain weak and are forecast by all of the global to remain weak or even get weaker. Isidore remains caught between a mid- to upper-level low east of Florida and one to the west over the Bay of Campeche. A weak and narrow low- to mid-level ridge extends across the northern Gulf of Mexico coast from Florida westward to Texas. Given the relative weakness of this ridge...only 5880 meters at 500 mb...it would not take much of a shortwave trough to erode it and allow Isidore to drift slowly poleward. All of the NHC model guidance...except LBAR...keeps Isidore moving on a slow west or west-southwest track through the forecast period. The AVN and GFDL are very similar in hooking Isidore to the southwest around the western Yucatan Peninsula in 36 to 48 hours. This may be some artifact of terrain interaction which I have ignored for this advisory package since all of the global models show no significant ridging north of isiodre to push the system to southwest. The forecast calls for a slow...less than 6 kt...motion throughout the forecast period with a slight west-northwestward motion after 48 hours as a strong shortwave trough drops down the west side of the broad longwave trough...which is expected to erode the weak ridge over Texas and the northwest Gulf of Mexico and allow Isidore to gain some latitude. However... the slower Isidore moves during the next 36 to 48 hours will determine just how far north and the cyclone will move in the longer time periods beyond 72 hours. The good news is that it appears that Isidore is not going to go anywhere fast. The bad news is that it will remain over very hot water.
The central pressure has dropped 21 mb in the past 13 hours. A typical rapid intensification period. This trend would normally continue for another 12 hours or so...but radar and recon data indicate that the eye is open to the west and that an eyewall replacement cycle may be starting. As such...the official intensity forecast is held below the ships intensity model which brings Isidore to 135 kt in 36 hours and 140 kt in 60 hours. This type of intensification is certainly possible given the low shear...less than 6 kt...and high SSTs...about 30c/86f. However...predicting internal convective changes is nealry impossible so there could be flucuations by as much 10 kt either way from the offical intensity forecast. Some coastal upwelling may weaken the hurricane slightly as it moves west of 88w longitude...but then some restrengtnening is forecast after 48 hours when Isidore is forecast to move back over warmer water.
Forecaster Stewart
forecast positions and Max winds
initial 21/2100z 21.9n 86.2w 110 kts
12hr VT 22/0600z 21.9n 87.0w 120 kts
24hr VT 22/1800z 21.9n 88.0w 125 kts
36hr VT 23/0600z 21.9n 89.2w 125 kts
48hr VT 23/1800z 22.0n 90.3w 125 kts
72hr VT 24/1800z 22.5n 92.5w 130 kts
EARLIER TODAY...A RECON PLANE OBSERVED A SMALLER EYE AND A DOUBLE MAX WIND BAND STRUCTURE. BOTH THE CANCUN RADAR AND SATELLITE DATA SHOWED AN OUTER CONVECTIVE RING SURROUNDING THE EYE. THEN...THE MINIMUM PRESSURE LEVELED OFF AROUND 946 MB. THIS SUGGESTS THAT ISIDORE WAS GOING THROUGH AN EYEWALL CYCLE OR REPLACEMENT. THIS IS PROBABLY THE REASON THAT THE RAPID DEEPENING OBSERVED EARLIER HAS TEMPORARILY ENDED.
SINCE THE PLANE LEFT THE AREA THE EYE HAS BECOME VERY DISTINCT ON IR IMAGES AND DVORAK T-NUMBERS FROM TAFB...SAB AND GLOBAL ARE 6.0 CORRESPONDING TO WINDS OF 115 KNOTS. MOST RECENT SATELLITE IMAGES INDICATE THAT ISIDORE MAY BE STRONGER. HOWEVER...THE INITIAL INTENSITY IS KEPT AT 110 KNOTS UNTIL POTENTIALLY HIGHER WINDS ARE CONFIRMED BY RECON.
THE UPPER-LEVEL ENVIRONMENT CONTINUES TO BE FAVORABLE FOR INTENSIFICATION AND THE ONLY NEGATIVE EFFECTS ARE THE YUCATAN PENINSULA AND ITS SURROUNDING SHALLOW COOL WATERS. ONCE ISIDORE MOVES AWAY FROM YUCATAN INTO THE WEST-CENTRAL GULF OF MEXICO WHERE THE OCEAN HEAT CONTENT IS HIGHER...THERE COULD BE ANOTHER CYCLE OF INTENSIFICATION.
ISIDORE HAS BEEN DRIFTING WESTWARD DURING THE PAST FEW HOURS. STEERING CURRENT ARE EXPECTED TO REMAIN WEAK AND ISIDORE IS FORECAST TO DRIFT WEST-OR WEST-SOUTHWEST FOR THE NEXT DAY OR TWO ON A TRACK VERY CLOSE TO THE NORTH COAST OF YUCATAN. THIS SLOW MOTION WOULD GIVE ENOUGH TIME FOR A MID-LEVEL RIDGE TO BUILD OVER THE WESTERN ATLANTIC THAT WOULD STEER THE HURRICANE ON A MORE NORTHWESTERLY TRACK OVER THE GULF OF MEXICO. THE OFFICIAL FORECAST IS VERY CLOSE TO THE NCEP GLOBAL MODEL OR GFS...PREVIOUSLY CALLED AVN...ALTHOUGH MOST OF THE OTHER MODELS ARE ALSO INDICATING THE SAME NORTHWESTWARD TREND.
IF THE HURRICANE MOVES TOO FAR SOUTH INTO THE BAY OF CAMPECHE...I DOUBT IT WILL EVER MOVE NORTHWARD. IT IS NECESSARY TO HAVE VERY STRONG STEERING FLOW FROM THE SOUTH TO PULL HURRICANES OUT OF THAT AREA.
FORECASTER AVILA
FORECAST POSITIONS AND MAX WINDS
INITIAL 22/0300Z 22.2N 86.7W 110 KTS
12HR VT 22/1200Z 22.1N 87.7W 115 KTS
24HR VT 23/0000Z 22.0N 89.0W 120 KTS
36HR VT 23/1200Z 21.8N 90.5W 120 KTS
48HR VT 24/0000Z 22.0N 91.5W 125 KTS
72HR VT 25/0000Z 23.0N 92.5W 125 KTS
LOL - I'll never die happy knowing Askel is quicker at the draw than I am.
Ya think it's a coincidence that the barometer sinks whenever these vicious harpies come near?
Trust me - the posters at FR pays me top dollar to do that.
Sending you a couple of my hurricane magnets. Would you drop them there for me?
Tomorrow would be an excellent day for Gulf Coast residents to make sure they have working flashlights, plywood, screws, and toe tags.
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