A Technique for Predicting South China Sea Tropical Cyclones.

The low-level cyclonic shear zone in the South China Sea is investigated as a possible precursor of tropical storm activity within the South China Sea. For tropical storm genesis in this area, it is shown that the strength of the cyclonic shear zone reaches a critical intensity approximately 24 to 48 hours before cyclogenesis takes place. Also, if the cyclonic shear zone is not present and there is either a large-scale ridge or easterly flow across the South China Sea, then tropical storm genesis does not take place for at least a week. With respect to tropical storms approaching the South China Sea from the Philippine Sea, the presence of a cyclonic shear zone is a good indication that the tropical storm will move into the area. On the other hand, when a large-scale low-level ridge is present over the area, these storm recurve northward and will not enter the South China Sea. Author