Multiple monsoon onset

Double monsoon onset develops when the strong convection in the Bay of Bengal is accompanied by the monsoon-like circulation and appears in the Indian Ocean in early May, that is about 3 weeks earlier than the climatological date of the onset ( June 1). The initial "bogus onset" is followed by the flow weakening or reversal and clear and dry conditions over the monsoon region. The best example of such a phenomenon is the development of the summer monsoon in 1995, when monsoon-like perturbations that appeared in middle May dissapeared by the end of the month, and were followed by a heat wave in India delaying onset of the monsoon.

We analyze the climatology of double onsets and show that they are associated with delay of the monsoon rainfall over India. Our analysis indicates that the development of bogus onsets depends on the timing of Intraseasonal Oscillation in the Indian Ocean and the propagation of convective episodes into the Western Pacific. There is evidence that an air-sea interaction in the Bay of Bengal and Western Pacific plays an important role in this phenomenon. We show that in the case of the double monsoon onset it is possible to predict hot and dry conditions in India before the real monsoon onset.