Mission Summary
Hurricane Earl

Mission Briefing:

At 1 pm EDT, 2 September 1998, we briefed the AOC flight crew for a Tropical Cyclone Windfields at Landfall research flight in Tropical Storm Earl, which at that time was forecast to reach hurricane strength and make landfall between Mobile, Alabama, and Panama City Florida. The goal of the flight was to collect flight-level, radar and GPS dropsonde data to capture the structure of the windfield in a landfalling hurricane. We were especially interested in the onshore flow because of the possibile storm s urge in the Florida Panhandle.

Pete Black started the briefing by cautioning the flight crew that there could be severe weather associated with Earl, because of the higher wind shear and the interaction with the coast . I explained our initial pattern, a figure 4 through the storm to be followed by some radial legs toward the Eglin Air Force Base WSR-88D (KEVX). Then we planned, tentatively, to fly a saw-tooth pattern through the main rainabnd east of the center and then to descend to 8000' to fly along the coast, to measure the storm surge in Apalachee Bay with Ed Walsh's surface radar. We planned to drop numerous GPS Sondes and Airborne Expendable BathyThermographs (AXBT's) to map out the onshore and offshore flow, the eye, and the main rainband and/or wind maximum. The AOC crew agreed to this flexible plan. It helped that both Stan Czyzyk and Jerry McKim had been on the Fran and Danny landfall missions in previous years.

Mission Synopsis:

We left MacDill at 1925 UTC, and reached our initial altitude of 14,000' by 1945. This flight was seperated into three modules:

1. The initial paffern: By 2007 we had reached the wind max in the main rainband, ~200 km east of the center of the storm. Sondes and AXBT's were deployed in the band and at buoy 42039. At 2037 Stan fixed the center at 29°04.7'N, 87°09.1'W, and we proceeded west to buoy 42040 where we also dropped sonde and AXBT at 2050. We passed through the center for the second time at 2110 and headed NE to KEVX. This leg was bouncy as we flew through rainbands near the coast. John Gamache reset the LF color scale so we could more easily pick out the 50 dBZ cores; there were several and we managed to avoid them all. At 2129 we turned at the coast dropped some more sondes and AXBT's and passed through the center again at 2150, where we dropped a center sonde. As we headed the south the bouncing subsided and we were in clearer air for a while.
2. The rainband sawtooth: After we had finished the outbound leg from KEVX at 2200 UTC, Mike and Rob designed a sawtooth pattern to measure the inflow into the main convection of the storm. The goal was to drop sondes on either side of the band, as well as in the middle. We had succesful sonde + BT drops at 2240, 2254 and 2305.
3. The coastal survey: We began our descent to 8000' at 2311 as we headed for Keaton Beach (KTNF1).

Evaluation:

The flight went very well. The sonde and AXBT coverage provide good coverage of a rather unusual hurricane. Jimmy Franklin noted that the sondes did nott find a surface wind > 50 kts, yet at 7000' the flight-level winds were > 70 kts for much of the latter part of the flight. Mark Powell incorporated some of that flight level data in an analysis centered at 0130 that estimated the maximum surface wind to be 79 kts, 91 nmi east of the center. A preliminary surface analysis of the GPS sonde data shows similarities to a cold front! The portion of the data set that was collected in Apalachee Bay will be supplemented by wind profiler data collected by Kevin Knupp's group from the University of Alabama-Huntsville, and the WSR-88D data collected by the Eglin AFB and Tallahassee WSR-88D radars.

We now have four data sets collected over land in weak to moderate hurricanes. l still think we must be very cautious about flying in stronger hurricanes overland. It is difficult to interpret the LF display when at 14,000' because strong echo can be caused ether by convectlion or bright band echo. The Dopplerized nose radar may help in discriminating the nasty places from the merely bumpy.

Acknowledgements:

The AOC crew were great. Stan Czyzyk and Dave Rathbun agreed to every change in the flight patterns that we requested, and Jerry McKim, Dave Tennesen, and Tim O'Mara moved us through some bumpy flying with a minimum of surprises. Jim Barr kept the radar running, and Sean McMillan and Richard McNamara managed to keep with our evolving plans for GPS sonde and AXBT drops.

Mike Black acted as co-LPS on this mission; he called most of the Sonde and AXBT drops, and also helped design the rainband and second figure-4 patterns. Rob Rogers also helped plan the rainband pattern. Jimmy Franklin processed and transmitted most of the GPS data. Bob Black collected some more big raindrop data; NASA will probably be interested in our cloud physics data because they did not fly below 14 000 '. Pete Black helped plan the flight, and reminded us to be careful on this hurricane flight after 21/2 weeks of continuous operation.Steve Feuer and Mark Powell's analyses and comments helped set up the first part of the flight for the briefing.

Problems:

I forgot to request that we record WARDS data, so the WARDS system did not collect Dopplerized Nose radar data. There was a brief probblem with the ASDL system at the beginning of the flight. There may be a problem with the way spectral width is reorded on the data system. We did not send out our LF composites until late in the flight; we should have sent them in a more timely manner. The radar tape has numerous parity errors, which may result in significant data gaps.

Mission Data: