AL97 Begins to Fall Apart

As expected, it was an interesting day for AL97 and plans for us to fly this system. While the G-IV did fly its mission this evening, leaving MacDill AFB at 1:30 pm and still out there even though it's after 9:00 pm. The flights on the P-3 scheduled to begin at 4:00 am in the morning and continue every 12 hours for at least two days were, however, cancelled because the system weakened during the day for several reasons (shear, dry air entrainment, Saharan dust, etc.). The G-IV is still on the schedule for a second flight tomorrow, but I suspect it too will be cancelled in the morning.

So what did the flight today accomplish? As explained in my last posting it flew a mission to the east and southeast of Florida. The track is shown in that posting. I spoke of the plane and the dropsonde, but a visual is more explanatory, so I'm showing both here. The plane is shown to the right in the margin. The dropsonde is shown in a cut-away view and in a drawing suspended

from its parachute. As I have indicated before, the sonde is launched from the aircraft, falls towards the surface on its drogue chute at a speed of about 3,000 ft. per minute, all the while transmitting data back to the aircraft. The sample rate is two times a second (2 Hz) for temperature, humidity and pressure, and 4 times a second (4 Hz) for wind speed and direction. From 45,000 ft. it takes about 15 minutes for the sonde to reach the surface.

These data are processed onboard the aircraft and transmitted via high-speed satellite communications back to the NOAA computing center in Camp Springs, MD where they are assimilated (big word) into the model runs done every six hour. The data from this flight will go into the 00Z (8:00 pm) forecast run this evening.

As you can see from the forecast tracks issued at 18Z (2:00 pm) this afternoon where there were no dropsonde data, quite a spread has developed in the various track forecasts. The forecast with the dropsonde data in it will be published

later this evening, and we'll see what impact this flight had. Hopefully it will bring many of those lines into more agreement with each other. I'll let you know in the morning. Please bear in mind, though. Forecasting is not an exact science, and when the flapping of a butterfly's wings in China can ultimately affect the weather in Miami, FL, one has to find that elusive butterfly in order to do a better job. We'll be sure to be out with our nets for the next couple of days.

Well, here's a piece of luck. The forecast runs done at 8:00 pm have already been published and are shown at the right. These have the dropsonde data from the G-IV in them. Please note that the tracks are in much better agreement with each other than those shown in the 2:00 pm runs which did not contain any sonde data - again proving the value of this aircraft and its role in hurricane forecasting. Guess we caught a couple of butterflies.

The bad news is that the tracks are carrying whatever happens to AL97 into the Gulf and across the Deepwater Horizon oil spill area. Most of the models continue to weaken the system, but we'll have to wait a few days to see what it does when it gets to the Gulf. Keep your fingers crossed.