Mlssion Summary
Hurricane Georges

Mission Briefing:

At 3 am EDT, 28 September 1998, we briefed the AOC flight crew for a Tropical Cyclone Windfields at Landfall research flight in Hurricane Earl, which at that time was forecast to make landfall between Mobile, Alabama, and New Orleans, Louisiana. 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 possible storm surge in Lake Ponchatrain and Mobile Bay. Ed Walsh and Wayne Wright were there to collect Scanning Radar Altimeter (SRA) data to map out the wave heights and storm surge. Our plan was to pass along the Gulf Coast, followed by a figure 4 through the storm, all at 7,000' altitude. Then we would climb to 14 000', if necessary, and fly radials between Mobile and New Orleans WSR-88D radars. There was also an option to fly along the principal rainband east of the center, similar to the pattern we flew in Hurricane Earl a few weeks before.

Several University groups sent surface observing systems to catch Georges' landfall; their locations near Slidell and Gulfport are shown in Figure 1. The University Of Oklahoma sent two mobile Doppler radars (DOWs), an instrumented 1 10m tower, and two portable observing systems mounted on cars. Clemson University and Texas Tech University erected instrumented towers, and the University of Alabama/Huntsville deployed a profiler. Flight patterns for this flight (and the previous flight, NOAA 42) were designed to overfly these sites if possible and to drop GPS sondes nearby.

Mission Synopsis:

We left MacDill Air Force Base at 0907 UTC, and reached our mission altitude of 7000' by 1005. Figure 1 shows most of our flight track, and Figure 2 shows the surface data from most of our GPS sondes. The core of Hurricane Georges was mainly stratiform, so we maintained our altitude at 7 000' until we finished our pattern at 1712 and climbed out to return home. The experiment is conveniently described in three parts:

1. Initial coastal survey and figure 4, 1005-1326 UTC:
   After dropping two sondes near buoys 42036 and 42039, the aircraft descended to 7,000' and headed for C-Man station CSBF1 (Figure 3a), where we dropped another sonde. We then turned NW and then W, to map the winds and waves east of the center, deviating slightly to avoid the nastier cells in a strong rainband between Panama City and Fort Walton Beach ( the rainband was right over the Eglin Air Force 88D at this time). At 1028 we were ~110 nmi from the center and Ed Walsh reported 10-15' wave heights.

   After the 5th sonde drop at 1032, the aircraft turned to move closer along the coast on our first pass through the center. Sondes were deployed near C-Man station DPIA1, in the east eyewall, in the center at 1057, and then in the west eyewall and along the coast, finishing with our 10th sonde in the center of Lake Ponchatrain. During this initial pass the radar was in F/AST mode. We turned and headed back east to fly a figure 4 pattern in continuous mode, so that we could construct an EVTD analysis and send a horizontal windfield image back to TPC. But two errors rendered the second pass through the storm unsuitable for EVTD: the radar operator forgot to switch out of F/AST until we were in the center and the workstation operator (me!) had forgotten to start the radar capture. It had been a long week, and fatigue was starting to play tricks on us. But no problem, we just added another east-west leg, which ended at 1326 over Lake Ponchatrain. One image of the EVTD winds at 1 km was transmitted back to TPC. During the figure 4 several GPS sondes were dropped in Georges to define the eyewall winds. Sondes 7,11 -13 and 18 were dropped near the Gulfport-Biloxi area where the surface teams were deployed. We also flew over that region three times in this part of the flight.

2. Second coastal pass and WSR-88D triangle, 1326-1632:
   From Lake Ponchatrain we flew south to the GDIL1 C-Man station to drop sonde #20 (Figure 3b), followed by a drop at BURL1. This was the first time we got out of the rain and clouds and could see the Gulf of Mexico and bayous. Then we turned northeast and flew towards KEVX, releasing a sonde at buoy 42040 on the way. At 1427 we turned at the coast, dropped another sonde and headed back along the coast. We followed the coast line more closely, to measure the wave heights close to the shore. We passed through the center for the 5th time at 1504 and then followed the coast to Lake Borgne where we turned south east, heading for 42040. From 42040 we flew North up into Mobile Bay, where we dropped the 25th GPS sonde. We had intended to repeat the KMOB-KLIX-42040 triangle, but time was running short so Mike suggested we pass through the center, turn and go back to the center again. Then we would turn in the center to head southeast towards the inflow region of the main rainband, which was now just east of Mobile Bay. By doing this we were able to release sondes 26 and 27 quite near the shore on each side of the center to get a pair of onshore and offshore soundings in higher winds.

3. rainband module, 1632-1712:
   The strong rainband was shaped similarly to the line-echo wave pattern seen occasionally in mid western squall lines, and the only weakness in the high reflectivity was at the kink. After dropping a sonde in the inflow region, we flew up the outside edge until we reached to the weak spot, dropped sonde # 30 as we crossed the band and continued along the inside edge until we were about 25 km inland, above Fairhope, Alabama. We turned south and stayed on the inside edge of the band. At 1704 there was a great view of the the disturbed ocean as we came off the coast. A sonde was launched there, (# 31), and probably landed on the beach. Our last sonde was dropped in the band at 1707. After we crossed back through the rainband at 1712 the pattern was finished and we climbed out to return home.

NOAA 43 landed at MacDill at 1823 UTC.

Evaluation:

The flight went very well. The sondes, Doppler radar and SRA data provide good coverage of a destructive hurricane. GPS sonde data and F/AST Doppler radar data were collected near every one of the deployed profilers, instrumented towers and DOW radars, so there will be a lot of joint effort required to analyze all of the data collected.

Acknowledgements:

The AOC crew were great. Jack Parrish and the flight crew agreed to every change in the flight patterns that we requested, and Dave Tennesen and Brian Taggart moved us through some bumpy flying with a minimum of surprises. Terry Lynch kept the radar running, and Jeff Smith and Chris Hornbrook managed to keep with our evolving plans for GPS sonde drops.

Mike Black acted as co-LPS on this mission; he called most of the sonde drops, and also helped design the patterns. James Franklin processed and transmitted the GPS sonde data. Frank Marks and Pete Black helped plan the flight . Mark Powell and Jerry Straka (University of Oklahoma) coordinated the mobile teams' deployment on the ground.

Problems:

There was a brief problem with the ASDL system at the beginning of the flight. The radar system was down from 1002 to 1014 UTC, and the tail radar froze from 1106 to 1115.

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