THE COOL-SEASON TROPICAL DISTURBANCES OF SOUTHEAST ASIA

Abstract

During the cool season (November through April), two types of tropical disturbance occasionally bring rain to a normally dry part of southeast Asia. The area, enclosed approximately between 15°N and 25°N, and 95°E and 120°E, includes south China and the northern portions of Indo-China and Thailand. In early winter, tropical storms or easterly waves, moving westward to the south of the subtropical ridge, may cause sufficient convergence north of the ridge to give rain. In late winter and spring, tropical troughs in the high-level (above 400 mb) southwesterlies cross southern India. Moving eastward, they link in the region of Burma with the low-latitude polar westerlies further north, then intensify and become stationary over the Thailand-Indo-China region. East of the trough line, disturbances with extensive rain areas develop on the China Sea polar front.