Abstract
The state of Kerala, located on the west coast of India, experienced a record 100-year flood that resulted in major landslides from unprecedented prolonged and extremely heavy rainfall (50-480 mm center dot day(-1)) during August 1-19, 2018, causing extensive damage and about 500 causalities. Rainfall observations indicate that the heavy rainfall occurred over two spells (August 7-10 and 14-18) in association with an offshore trough, and a depression over the Bay of Bengal (BOB). High-resolution 38-year climatology data (5 km) and the ERA-Interim reanalysis dataset show a strong low-level jet over the Arabian Sea and a depression over the BOB with a southwestward tilt during the heavy rainfall. Very high-resolution (2-km) mesoscale model simulations suggest that this high convective instability due to the strong westerly jet along with the formation of offshore vortex, the transport of mid-tropospheric moisture under the presence of conducive vertical shear of horizontal wind, and transport of mid-tropospheric moisture from the BOB are the major factors (as shown in the schematic diagram) behind the extreme heavy rainfall over Kerala.