Abstract
On the afternoon of 27 June 1991, the Okayama area in the western part of Japan was hit by strong gusty winds and a heavy precipitation of rain and hail associated with severe thunderstorms. The synoptic condition was that the area was located to the south of the Baiu-front with the northern edge of the Pacific Subtropical Anticyclone (PSA) prevailing. At one location in the area, a gusty wind blew down 18 utility poles that were built to withstand winds of 51m/s.
The present work was derived from this incident. Virtually all available data from various sources were collected and analyzed. These sources include weather surveillance radars, meteorological observatories, densely deployed surface anemometers for air pollution monitoring, commercial aircraft, videotaped imageries and a damage survey. The result of the analysis reveals that at least four wet downbursts (either microbursts or macrobursts) occurred in the area and that one of them, which was associated with hail precipitation, blew down the 18 utility poles. Furthermore, the environmental conditions are found to be similar to those identified as favorable for the development of wet microbursts in northern Alabama by Atkins and Wakimoto (1991). The potential risk of downburst on the northern edge of the PSA is also suggested.
