IMD has indicated Monsoon is likely to make onset over Nicobar Islands today. The Southwest Monsoon is one of the most prominent monsoons of the world. In simpler terms it is a large scale replica of land and sea breeze. The summer heat over the Indian Sub continent creates a thermal low which triggers a gush of winds from the High Pressure over Southern Hemisphere. While travelling through the equatorial region and over the Arabian Sea it picks up moisture. This in turn brings the rains over the West Coast where the Ghats play a crucial role.
Interestingly it is the Nicobar Islands not Kerala where Monsoon checks in first in India. The Bay arm develops much earlier compared to the Arabian Sea arm. IMD opts for one date covering most of the A&N Islands setting 22nd May as the normal date. This does not take into account the staggered onset that happens over the Islands. For example last year Nicobar Islands and the adjoining Bay saw monsoon onset on 19th May. Taking 15th May as the normal date for onset over the southern parts of the Island this year Southwest Monsoon is hitting a couple of days early.
The British may have coined the phrase Southwest Monsoon. But the Indian Monsoon has been present for many centuries. According to one theory the phrase Monsoon has its origin from the Arabian word “mausim” which means seasonal winds. Closer home the Chola empire’s Maritime conquests was possible by their understanding of monsoon winds. Not only the Cholas but the Kalinga of present day Odisha were also masters of Monsoon. The close connect Kalinga had with Sri Lanka and places like Bali is an example of their understanding of monsoons.
On the weather front for Tamil Nadu the strengthening westerlies is expected to bring scorching afternoons over most parts of the state for the next couple of days. A developing cyclonic circulation in Bay is likely to bring some respite after that. Wind convergence created by this developing circulation is likely to trigger thunderstorms. This spell of thunderstorms over the next few days is likely to be the last spell of pre monsoon thunderstorms. Weather models indicate monsoon dynamics will strengthen over Peninsular India from next week. There is a high possibility of Monsoon Onset over Kerala (MOK) during the 4th week of May between 20th and 23rd May.
Today and tomorrow most interior places of Tamil Nadu may see day time temperatures hit 39 / 40°C. Chennai and suburbs may also see 39 / 40°C with few of the west and southwest suburbs likely to see 41°C today. Stay Indoors during the afternoon if possible. Stay Hydrated. Depending on the strength of sea breeze intrusion few places about 25 – 50 kms from the coastline may see convective thunderstorms during the evening hours.