Climatological Analysis of Passage-type Tropical Cyclones from the Western North Pacific into the South China Sea

  • Author(s): Jau-Ming Chen, Pei-Hua Tan, Liang Wu, Jin-Shuen Liu, and Hui-Shan Chen
  • DOI: 10.3319/TAO.2016.10.04.02
  • Keywords: Tropical cyclone, Western North Pacific, South China Sea
  • Chances for WNP TCs into the SCS decrease when TCs form more northerly
  • An intensified subtropical high favors TC passages into SCS during Aug.-Sep
  • An enhanced monsoon trough facilitates TC passages during Jun.-Jul. and Oct.-Nov
Abstract

Climatological characteristics of tropical cyclones (TCs) with passages from the Western North Pacific (WNP) into the South China Sea (SCS) during the June-November season are analyzed in this study. These TCs tend to form in the WNP west of 150oE, and on average westward by 7o-12o in longitude of TCs that do not track into the SCS. Their formation locations migrate with the monsoon trough, moving northward from June to August, and southward from September to November. The probability of a WNP TC moving into the SCS varies seasonally, only 12-18 % of the WNP TCs do so during August-September due to more northern TC formation; however, this probability rises to 25-26 % in June-July and 25-32 % in October-November with more southern TC formation. The passage-type TCs generally form in the eastern part of an elongated lower-level cyclonic anomaly of the 10-day low-pass filtered environmental circulation in the 10o-20oN zone, which is paired with an anticyclonic anomaly to the north. Between this circulation pair, anomalous easterly flows steer these TCs westward, giving them a westward track into the SCS. The formation of these passage-type TCs is associated with a southward displacement of the monsoon trough and a westward intensification of the Pacific subtropical high in August and September. During June-July (October-November), the associated features appear as a southeastward (meridional) expansion of the monsoon trough and a northward displacement of the Pacific subtropical high.

 

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