Mission Plan :

Fly TDR mission into TS Kyle, which has intensified from AL93. Fly butterfly pattern, with the initial point on the southwest side. Fly 90 nm legs on the west and south side, and 105 nm legs on the north and east sides to better sample the convection. Fly at 10,000 ft for the whole pattern. Drop sondes at end points, at least once in the center. Do an informal fix at 12 UTC for NHC.

Mission Summary :

Kyle is still experiencing vertical shear, and the bulk of the precipitation remains on the east side of the low-level circulation center (Fig. 1, and Fig. 2). The shear is starting to relax, though, and is forecast to continue to weaken (Fig. 3). Satellite images show some convection developing closer to the center than previously. Upper-level winds (Fig. 4) show a pronounced jet of upper-level westerlies in the eastern Gulf of Mexico, but over Kyle winds are relatively weak.

There was a significant delay (4.5 h) in takeoff due to electrical problems on the aircraft, so the flight track had to be modified to a single figure-4 (Fig. 5a) with the initial point on the northwest side. As indicated from satellite imagery, precipitation remained displaced from the low-level circulation center. As a result, the downwind leg on the east side of the storm was extended to better sample the precipitation. On the inbound leg from the northeast to southwest, encountered both stratiform and convective precipitation. Indications from the flight-level, dropsonde (Fig. 6), and SFMR data are that the surface data was displaced to the southeast of the flight-level center. The surface center was never sampled. Peak SFMR winds were 50-55 kt on the northeast side, near hurricane strength. There were some areas at flight level with 60-65 kt winds.

The flight had many challenges, beginning with the 4.5 h delay in takeoff, which limited what could be done with the pattern. Mission could have been cancelled, but it looked like system was getting better organized and we wanted to be there for that organizational stage. The significant displacement of precipitation from the center, along with limited time available in pattern and erroneous estimate of low-level circulation center and no radar signature on lower fuselage imagery, combined to limit the effectiveness of the radar sampling. It is not clear how much this radar data can help to document structure and evolution of a slowly-intensifying vortex in westerly shear. Five drops were released. Takeoff was at 1320 UTC September 26.

Problems :

Other than the 4.5 h delay, there were no problems.

Robert Rogers

Mission Data :