Outward-moving rainbands from Typhoon Megi (2010) and their association with the onset of heavy rainfall in Amami-Oshima Island

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Hiroyuki Yamada (University of the Ryukyus)
Hironori Iwai (The Okinawa Electromagnetic Technology Center, National Institute of Information and Communications Technology)

Heavy rainfall, with 622 mm of daily amount, was occurred in Amami-Oshima Island, Japan on 20 October 2010 due to the development of precipitating cloud systems over a stationary front. Past studies focused on the airmass-transformation process and the development of a mesoscale low-pressure system during the rainfall event, although the mechanisms governing the onset of the heavy rainfall are still unclear. In the present study, we focus on rainbands that moved northeastward from Typhoon Megi (2010) and reached this island at the beginning/end of the heavy rain. Characteristics and structure of the rainbands were analyzed using satellite, Doppler radar, and wind profiler data. Results show that this rainbands formed within a cyclonic circulation in the lower troposphere, with an increase in southerly wind speed in the middle troposphere. The change in vertical wind shear associated with the rainband, in conjunction with island topography, is suggested to have been a key process to the stationary evolution of the precipitating cloud systems over the island. Results also show that these rainbands formed when Typhoon Megi rapidly weakened due to the landfall in Luzon Island, Philippines. This suggests that an outward-propagating wavy disturbance from this typhoon was associated with the northeastward movement of the rainbands.

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