Southwest Monsoon arrived with a bang over the Andaman Sea on 16thMay, nearly a week prior to its scheduled time. Car Nicobar received a downpour of over 100mm in 2 days. Conditions are favorable for further advancement over entire Andaman Sea and more parts of South and Central Bay of Bengal. Monsoon is heading its way, to reach mainland Kerala around 26thMay, well before the normal date of 01stJune. This is likely to be the earliest onset since 2009, when it struck the Kerala coast on 23rdMay. Incidentally, year 2009 was an El Nino year and the monsoon hit hard to result severe drought over Indian Sub-Continent.
In the past, monsoon has advanced over mainland as early as 2 week before the due date. However, the monsoon has never advanced over the Andaman Sea prior to 10thMay. Weakening of easterly trade winds and strengthening of cross equatorial flow initiates arrival of monsoon. Many factors are responsible for further advancement over South Peninsula and NE India. Conditions responsible fetch as far as South China Sea and West Pacific.
Other favorable factors being any circulation pattern or a low pressure moving across Laos, Vietnam, Cambodia, Thailand and Myanmar and entering Bay of Bengal. Presently, there is no active storm anywhere across the globe , including Pacific Ocean. Accordingly, further advancement of monsoon relies upon strengthening of southwesterly winds accompanied with sturdy cross equatorial flow. Somali Jet is expected to gather pace and energy to carry the monsoon stream along the West Coast , blowing across North Equatorial Indian Ocean and South Arabian Sea.
Powerful and extensive pre – monsoon thunderstorm activity will occur over Kerala, Coastal and South Interior Karnataka and Interiors of Tamil Nadu over the next 3 days. Very heavy rainfall at some places with extremely heavy fall at few places is likely over the next 3 days. This activity will be driven by off shore vortex over Lakshadweep, drifting inland over South Peninsula. Another circulation over Arakan Coast will keep the monsoon vigorous over eastern half of Bay of Bengal. Combined influence of these systems will take the monsoon further over entire Andaman Sea and central Bay of Bengal. Northern Limit of Monsoon (NLM) will draw closer to the Island nation of Sri Lanka.
Though, early arrival of monsoon over the Andaman Sea is no assurance for before time ‘ knock’ over Kerala but it is likely this time with the surge reaching coast around 26thMay. Advancement of monsoon over various parts has no connection with its onset date over Kerala or any other region. It is purely governed by the monsoon systems emerging over sea or land.