In 1979,the water vapor transport field over monsoon Asia underwent significant changes with the onset of the Indian summer monsoon. Strong water vapor transport extended from the Arabian Sea, across Southern India, the Bay of Bengal,the South ChinaSea(10°-15°N),then northward into Southern China and Japan. There was heavy rain with intense convergence of vertically integrated water vapor flux (Q₂).Over the Bay of Bengal and the South China Sea,the Q₂ convergence increased rapidly between June 16 and 20. During the same period, in the Bay of Bengal, the South China Sea, and the Philippines, the outgoing longwave radiation (OLR) decreased sharply and the index of convection (I_e). increased suddenly. These changes indicate that the onset date is nearly the same over India, the Bay of Bengal, the South China Sea and the Philippines.Over East Asia, the strong water vapor transport, which is controlled by the West Pacific high, developed south of Japan around June 5. Concurrently, Q₂ convergence intensified, OLR decreased and I_c increased. These changes imply that the rainy season in Japan begins approximately two weeks before the monsoon onset in India.The Q₂ differences between the pre- and post-onset periods clearly indicate the existence of two channels of water vapor transport. One is related to the South Asia monsoon and the other to the East Asia monsoon. Analysis of Q₂, OER, and I_c data indicates that in 1979, the East Asia monsoon and South Asia monsoon were relatively independent of each Other.