Hurricane Lili
Hurricane Lili Reconnaissance

(961018H2 Aircraft 42RF -- single aircraft)

Scientific crew
Chief Scientist Michael Black/Peter Dodge
Radar Scientist Chris Landsea/Mike Black/Peter Dodge
Cloud Physics Scientist Chris Landsea/Mike Black
Pilots Capt. Gerry McKim/Lt. Brian Taggart
Flight Director Jack Parrish
Navigator Lt. Tom Strong
Flight Engineer Butch Moore
Systems Engineers Terry Lynch/Jim Barr
Data Technicians Juan Pradas-Bergnes/Dale

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

Mission Briefing

Because Hurricane Lili was forecast to be quite near the northern Cuban coast at 0000 UTC, 19 October, NOAA's Aircraft Operations Center (AOC) was tasked for reconnaissance in the storm for the 0Z, 3Z and 6Z fixes. HRD scientists Mike Black, Bob Black and Chris Landsea were already in Tampa, resting from the reconnaissance flight the night before. Bob decided to return to Miami and Peter Dodge went to Tampa to assist in planning for a possible flight pattern over Florida Bay. To support Powell and Houston's study of surface wind fields in the Bay, the plan was to drop several GPS sondes near surface stations in the Keys and the north end of Florida Bay. The criterion for flying a windfield pattern was that the winds had to be at least gale force. Another possibility was to gather radar and microphysical data to support the Florida Bay rainfall study of Marks, Willis, and Churchill. If there was stratiform precipitation over the Ocean Acoustics Division disdrometer in the Everglades, we would request an ascent to 14000' upwind of the gauge and then a slow spiral descent, at 8-9 m/s, to look at changes in the drop-size distributions. Of course, these plans depended on winds and rain over the southeastern tip of Florida, and the ability of AOC to break off from the reconnaissance pattern.

By 0500 EDT, when AOC flight director Jack Parrish was briefing the flight crew, it was apparent that the Florida Bay options could not be flown. The Key West WSR-88D radar display indicated that Florida Bay would probably be free of precipitation by the time we got there, and Lili had moved far enough east by then that it was doubtful whether there would be gale-force winds over the Keys either.

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Mission Synopsis

We took off from MacDill at 2217 UTC, and crossed Big Pine Key at 2302. At 2313 we descended in a spiral in light rain to 1500' and headed southeast to the center. Jack fixed the center at 23d 02m N, 78d 22m W, at 2358 UTC, with a minimum sea level pressure estimated at 975 mb. The center was ~80 km NNE of Punta Alegre, Cuba. The eastern eyewall had a sharp gradient of reflectivity and Jack didn't like the looks of it, so we ascended to 5000', where we remained for the rest of the flight. Jack selected flight legs to maximize the mapping of the winds in the forward quadrants of the storm. Because we did not want to fly over Cuba, legs that were not oriented northwest or southeast involved turns in the eye. We fixed the center six times, and the pressure dropped to 967 mb during the flight. The last fix was at 0558, at 23d 31m N, 76d 20m W, about 40 km west of Exuma, Bahamas.

The most interesting part of the flight, and the most bumpy, was in the convective line ~ 100 nmi east of the center. After our first pass through the eye we flew NW outside the line from 0036 to 101 UTC. There were lots of lightning flashes, and we passed close to a cell with 30 dBZ extending to 12 km altitude. We crossed the line again at 330, and noted some interesting structures including elevated dBZ maxima and an echo-free vault at 336. During our final pass through this area, from 450 to 507 UTC, we bounced around a lot as the pilots maneuvered the aircraft between the thunder-storms. At 456 we were very near an impressive cell with an apparent bounded weak-echo region and Mike called out a 15 m/s downdraft. By this time the whole NE region of the storm seemed to be filled with strong cells, like a prairie full of thunderstorms. The satellite images for this period suggest that the hurricane may have interacted with another feature in this region.

With the exception of the last leg, the tail radar scanned perpendicular to the track in all radial passes, and in Forward/Aft Scanning mode (F/AST) during downwind legs. For the last leg, a SE to NW pass, we ran the radar in F/AST mode, to try doing EVTD later ( an idea of Frank and Wen-Chau).

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Mission Evaluation and Problems

The flight went well. The flight-level data were incorporated in surface wind analyses supplied to forecasters at the Tropical Prediction Center. We collected radar data that can be used in Mike's continuing vertical incidence study, and to test F/AST EVTD. The F/AST data could also be used to describe the possibly complex wind patterns near the strong thunderstorms in the convective rain band NE of the center.

Although we brought along GPS sondes, we did not drop any. Maybe we were too conservative. I do not know if an eye drop from 5000' would have been valuable (certainly there was no interest expressed before Dodge left for Tampa), but drops on either side of the rainband might have been interesting. Should we always drop a sonde in the eye, or on either side of the eyewall?

The radar system froze up twice, from 0152 to 0203, and from 0316 to 0323.

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