Evolution of large‐scale factors influencing extreme rainfall over south western coast of India

Abstract The life cycle and the large‐scale factors driving extreme heavy rainfall events over the south west coast of India are studied. The extreme rainfall events are linked to the development of monsoon depressions and the associated large‐scale dynamics. Strengthening of these parameters intensifies the monsoon low‐level circulation over the Arabian Sea and the west coast via steepened meridional pressure gradient. The intensification of the low‐level jet stream speed and its extension in the vertical causes an increase in the humidity flux in the lower and midtroposphere. The consequent ascending motion is from the midtroposphere to the upper troposphere, resulting in the formation of deep convective cloud clusters over the west coast and eastern parts of the Arabian Sea. This results in the incidence of extreme heavy rainfall over the south west coast of India. It is observed that during days of extreme rainfall, the direction of wind in the lower troposphere tends to be almost perpendicular to the Western Ghats favouring a strong orographic lift. The extreme rainfall events over the south west coast do not necessarily occur during the active cycle of monsoon intraseasonal oscillation, but are linked to the north westwards propagating monsoon depressions. We show that the signatures of extreme rainfall can be observed in several meteorological variables developing over different parts of the monsoon region. A synergistic analysis of these variables may help in the accurate and timely prediction of these events.