Southwest Monsoon 2021 is traversing like military punctuality, knocking before time and with a steady pace. The first stop South Andaman Sea and Car Nicobar was a day ahead of schedule on 21st May and uniform progress thereafter. Monsoon has reached the doorsteps and is merely an arms distance from Indian mainland Kerala.
Southwest Monsoon 2021 has already reached Maldives, Comorin Sea, Sri Lanka, and large parts of South and East Bay of Bengal. There have been 2 back to back cyclones in the Indian Seas, one on either side of the coastline. Cyclone Tauktae over the Arabian Sea and Yaas in the Bay of Bengal formed 'just in time' to expedite the advance of the monsoon stream.
The onset of monsoon has to essentially fulfill a criterion of Rain, Clouds and winds over the equatorial part of the Arabian Sea, Lakshadweep Islands and mainland Kerala. While at least 60% of the designated 14 stations in Kerala, Lakshadweep and Coastal Karnataka have to have 2 consecutive rainy days (rainfall >/= 2.5mm), the outgoing longwave radiation (OLR) over the equatorial Indian Ocean in the proximity of Sri Lanka and Kerala has to drop below 200w/m2 associated with dense clouds. Also, the westerly stream of winds needs to pick up speed and also prevail in depth beyond 12,000 feet over the extreme southern parts of the Arabian Sea next to the equator. Simultaneous fulfillment of all these conditions suffices to announce the arrival of southwest monsoon over Kerala.
Pre-monsoon showers over Kerala have been rather heavy for the last 3 days. Towards the fag end, it becomes difficult to distinguish between the continuation of pre-monsoon and the arrival of monsoon. Invariably, it becomes an overlapping event. Other meteorological conditions are also building up to facilitate the arrival of the monsoon around 30th May. The onset phase of the monsoon over the South Peninsula and along the West Coast for the first 10 days of June looks promising. Monsoon may also find simultaneous timely advance over Northeast India.
