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RSMC Tokyo-Typhoon Center

Technical Review No.9  (March 2007)

  The Mechanism of the Storm Surges in the Seto Inland Sea Caused by Typhoon Chaba (0416)
   Nadao KOHNO
   Meteorological Research Institute, Japan Meteorological Agency
   Kazuo KAMAKURA, Hiroaki MINEMATSU, Yukihiro YORIOKA, Kazuhisa HISASHIGE, Eichi SHIMIZU, Yuichi SATO, Akifumi FUKUNAGA, Yoshihiko TANIWAKI, and Shigekazu TANIJO
   Takamatsu Local Observatory, Japan Meteorological Agency

  Typhoon Chaba in 2004 made landfall on the southeastern Kyushu and went through Chugoku (western part of Japan's Main Island) on 30 August, causing large storm surges in the Seto Inland Sea (SIS). The high tide records were broken at tide stations in Takamatsu and Uno Ports. We analyzed the tidal data and simulated this case with a numerical storm surge model. The storm surges moved eastward along with the passage of the typhoon, and it was favorably simulated. The results revealed that the wind set-up basically played a key role in causing the large storm surges. However, the maximum storm surge (MSS) in Takamatsu did not occur when the typhoon was the nearest to the city, but about 2 hours later. Since the time of MSS approximately corresponds to the high spring tide time, the record breaking storm tide was observed there. Moreover, we found the SIS can be divided into 6 areas according to the characteristics of sea topography and dominant wind direction by the typhoon. We also investigated the degrees of the contribution of two main factors of storm surges, i.e. inverted barometric effect and wind set-up, in each area. As a result, it turned out that the peak times of each effect were influenced by the geographical feature, as well as the wind field and the position of the typhoon, and had different characters in each area.
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   Comparative Study on Organized Convective Cloud Systems detected through Early Stage Dvorak Analysis and Tropical Cyclones in Early Developing Stage in the Western North Pacific and the South China Sea
   Kenji KISHIMOTO, Tsuguhito NISHIGAKI
   National Typhoon Center, Japan Meteorological Agency
   Shuji NISHIMURA, Yoshiyuki TERASAKA
   Meteorological Satellite Center, Japan Meteorological Agency

  The Japan Meteorological Agency (JMA) has been operating the satellite image analysis for tropical cyclones (TCs) in early developing stage such as tropical depressions (TDs) since 2001 to detect them and diagnose their possibility to develop into tropical storms (TSs). The analysis, which is based on Dvorak (1984), is referred to the early stage Dvorak analysis (EDA) in this report. Comparing organized convective cloud systems (OCCSs) detected through EDA with TCs on weather charts from 2002 to 2006, the detected OCCSs can be acknowledged as follows:
  • TDs usually have an OCCS detected through EDA, while low pressure areas (LPAs) do not.
  • OCCSs determined as the T-number of less than 1.0 have considerable possibility (about 50%) to develop into TDs with the 10-minute maximum sustained wind (MSW) of less than Beaufort Force 7. On the other hand, few (about 5%) OCCSs develop into TDs with MSW of less than Force 7 before the first detection of OCCSs.
  • OCCSs determined as the T-number of 1.0 (T1.0) have very high possibility (about 80%) to develop into TDs with MSW of Force 7 and high possibility (about 60%) to develop into TSs. Before or at the first T1.0 determination, many (about 75%) of them develop into TDs of with MSW of less than Force 7.
  • OCCSs determined as T1.5 have very high possibility (about 80%) to develop into TSs. Before or at the first T1.5 determination, many (about 80%) of them develop into TDs with MSW of Force 7.
  • Most (near 100%) of OCCSs determined as T2.0 develop into TSs.

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