A small island Taiwan makes a remote typhoon turn

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Koji Nakata, Mie University, Tsu, Japan
Typhoon (TC) Talas (2011), which caused Japan catastrophic disaster, landed the western part of Japan. The TC suddenly turned northwestward, and then landed on Japan. A reason for the occurrence of the disaster is that Japan Meteorological Agency (JMA) failed to predict the TC’s sudden left turn, JMA predicted that the TC would not turn northwestward but would move northeastward. The actual course was opposite to the JMA numerical weather prediction. The timing when the TC started to turn northwestward was the same as another TC, Nanmadol, crossed Taiwan Island. Here we find that whether TC Nanmadol landed Taiwan Island or not determines whether the TC Talas turned left or not. If Nanmadol had not landed on Taiwan, Talas would not have landed on Japan. A small island controls the course of a remote TC. Therefore, the presence of the Island of Taiwan is important for the determination of the course of a typhoon.

The utilization of two-way Weather Research and Forecasting (WRF) simulation with moving nesting, which allows the influence of a TC upon surrounding environmental large-scale atmospheric flow in comparison with one-way moving nesting shows that Talas remotely strengthened the subtropical high located to the east of Talas. This strengthened subtropical high somewhat blocked the eastward movement of Talas. In addition, Nanmadol remotely strengthened the high pressure system that was between Talas and Nanmadol. This strengthened high blocked westward movement of the Talas. The WRF showed that the deeper the typhoon developed, the stronger the high pressure system. When Nanmadol landed Taiwan, this remote strengthening of the high suddenly weakened because of decay of landed Nanmadol. The weakened high no longer blocked the westward movement of Talas. Therefore, Talas started to turn westward when Nanmadol landed on Taiwan. In some WRF members without landed on Taiwan, neither Nanmadol nor the high between Talas and Nanmadol did weakened. Also, Talas did not turn west. In consequence, the decay of a typhoon due to the landing on an island makes another typhoon turn. This might be a mechanism of the chain-reaction of the two typhoons, which frequently appears simultaneously over the Western Pacific.