Hurricane Fran

Tropical Cyclone Windfields at Landfall Experiment
(960905H Aircraft 42RF -- single aircraft)

Scientific Crew

Chief Scientist -- Peter Dodge

Doppler Scientist -- John Gamache

Guru -- Pete Black

C-SCAT -- Jay Donnelly

Radiometer -- Mark Goodberlet

GPS Sondes -- Terry Hock

This document is divided into 3 sections (Each section is written by the Chief Scientist):

Mission Briefing

The primary goal of the Tropical Cyclone Windfields at Landfall experiment is to collect data that can be incorporated in real-time surface wind analyses prepared by HRD and supplied to TPC forecasters. In addition, we want to collect airborne Doppler radar data to combine with WSR-88D radar data in three-dimensional analyses to document evolution of tropical cyclones as they make landfall, and to provide corroborating data for testing WSR-88D tropical cyclone algorithms. For Hurricane Fran, forecast to make landfall near the North-South Carolina border, we planned to fly a rotated figure 4 pattern at 5000', adjusted to pass over surface marine stations, followed by several passes through the center along radials from the Wilmington, (KLTX) and Newport, NC, (KMHX) WSR-88D radars. At the flight briefing we also discussed the possibility of doing a figure 4 at 14,000' at the end of the flight. AOC agreed to give it a try, if it looked like a safe thing to do. Frankly, my briefing was vague as to what we might do after the initial 4 and radials; it all depended on how fast the storm made landfall, and its position relative to the WSR-88D radars.

Besides the HRD crew, there were two scientists from the University of Massachusetts testing microwave instruments, a scientist from NCAR testing the new GPS sondes, and three journalists. Ron Phillipsborn and Phil Kenul piloted, Dave Rathbun navigated, and Stan Czyzyk and Jack Parrish shared the Flight Director job. Jim Roles and Jim Barr kept the AOC data systems running, and another AOC technician collected water samples for the Lawrence/Gedzelman isotope study.

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Mission Synopsis

At 2012 UTC on 5 September, 1996, NOAA 42RF left MacDill Airfield to conduct research in Hurricane Fran as it moved ashore in the Carolinas. Radar recording started at 2046, and the first GPS test sonde was dropped at 2105, about 100 nmi ESE of Jacksonville. By the time we reached the IP at 2130, 280 km SE of KLTX, it was pretty obvious that Fran was going to hit well north of Myrtle Beach, which meant that we would not fly any radials relative to the Charleston WSR-88D. Our first center fix at 2209, combined with fixes from NOAA 42 and the Air Force (Teal 04), showed Fran moving North along 78° W, straight for Wilmington. We turned after passing through the northwest eyewall, and then headed south along a KLTX radial and passed right over buoy 41004. At 2239 we turned to head back towards KLTX. Then we went through the center again at 2300, and passed right over Frying Pan Shoals (FPSN7) at 2306. The NE eyewall had 107 kts.

After this the planning got very creative, and Dodge was very grateful for the suggestions of Black and Gamache, and the flexibility of Czyzyk, Parrish and Rathbun! We flew NE to fly along a KMHX radial, to map out the outer wind maximum. Then we followed a KMHX radial SW to the center, getting another fix at 0000. The minimum estimated pressure remained ~ 956 mb and the flight level winds went down to 0.4 kts on that fix. The eyewall was now on the beach. We flew a KLTX radial NW to the beach, and then did a 360° turn and tracked SE on the same radial until we ran out of scatterers, and then headed back north on a KMHX radial to investigate the stronger convective line up by Newport. On the way we hit heavy rain at 0021 and there was an impressive tilt to the cells on the tail radar display. We flew a west-east KMHX radial between two rainbands at 0029, but it took 15 minutes to move ~ 50 miles upwind. So we headed back on that radial toward KMHX. At 0055 we heard that Teal 04 was returning home, so the sky was pretty much ours. The flight crew decided we could try the overland figure 4. At 0057 we turned and headed for Cape Fear; at 0058 we had 113 kts flight level winds, highest noted during the flight. We headed SE and then at 0116 we started to climb to 14,000'.

At 0136 we crossed the coast 80 nmi SW of KLTX, turned and started the first leg of the final 4. We passed through the center at about 0200, but no fix was made, and at 0203 Phillipsborn cut the pattern short and started west. I acquiesced, but the guys in the back (especially Black and Parrish) pointed out that we wanted to the full figure 4 overland, avoiding the higher reflectivity. I'm glad that Jack and Pete stepped in. Ron agreed to try it again, so at 0201 we turned NE to hit the center once more. At 0218 we turned in the center and headed NE. Then we turned again at 0237, to start a western leg. This leg ran parallel to 90_ radials form the Raleigh WSR-88D (KRAX). The winds were 80-90 kts all along this leg. At 0300 we turned well west of Raleigh, and headed SE back to the center, which Stan fixed at 0321, with an extrapolated surface pressure of ~957 mb. By now the center was 70 km NNW of KLTX. We concluded the leg at 0348 and climbed to cruising altitude. John stopped radar recording at 0400. Terry Hock and Al Goldstein did three more GPS drops, at 0358, 0410, and 0438. ( /users/peter/thor/fran_fltrk.isl, *.ps are IslandDraw and Postscript files with a figure showing the flight track.)

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Mission Evaluation and Problems

The flight went well. The flight pattern, mostly generated on the fly with excellent guidance from Pete and John, will yield a good description of both the inner and outer wind maxima. The passes along the coast should help describe the differences in onshore and offshore flow, especially when the DOW1 and scatterometer data are tossed into the mix. Cooperation with the NWS was excellent. We should have a complete set of level II data from KLTX and KRAX, and we hope to have KHMX data up to ~0200 UTC. Mark Powell planted the seed of the overland flight, and I think the advance discussions of Pete, Hugh, Frank and Jim McFadden helped AOC go along with the figure 4 over land. However we still have to be cautious about overland flights. The mesoscale vortex that blew up at 0430 UTC, about an hour after our last leg, is a good example of the beasties that may lurk in weakening storms after landfall.

The surface analyses and drifting-buoy plots that Sam Houston and Mark faxed to us in Tampa were very useful in planning the flight. I hope that Sam can be on the plane the next plane we fly this mission, though, so he can give his input on the evolving flight tracks and their impact on the real-time analyses. For example, we did not fly over the Cape Lookout surface station (CLKN7) when we were up by KMHX, but we easily could have done so, and that would have provided another anchor for the wind adjustment.

1. The tail radar only froze up once, for 1 minute. The radar data system still writes lots of extra EOFs.

2. GPS sondes could not be dropped in turbulent parts of the storm, because extra test equipment had to be attached to the sonde workstation. This equipment could not be strapped down, so we had to wait until we were well south of the center.

3. I too easily went along with the decision to abort the figure 4. A good lesson.

4. The wide-band links at some 88D radars were cut during the storm. Evidently this stops Level II recording as well. Fortunately for our research, this happened after we had left the area. 5. Personally, I would like to see a different color scale for the LF. I believe a color table that cycles back and forth in brightness would make it easier to pick out features in storms that are mostly stratiform. The flight directors might not want to change, though.

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