Uniqueness of March winds over Chennai coast

Residents may often complain of sultry, humid weather at night and wonder if summer is already upon us. 

In fact, Chennai is still experiencing winter winds, which will continue until third week of April. Normally in March the wind blows from the east, and what we are experiencing are the easterlies. What happens is that due to the easterlies, the wind speed will strengthen during the day, but begin to slow down towards evening hours. As the night progresses, the wind speed drops to about a nautical mile, and westerly winds begin to blow from around 2. 30 am. The westerlies will continue to blow until 7.30 am. 

Interestingly, the sea surface temperature ranges 27 degrees, while the land temperature will vary between 23 and 24 degrees. This results in the land getting colder than the sea, causing flow of land from land to sea. When the land breeze sets in, the easterlies weaken. Wind will be very sluggish until 7 am or so and that is the reason many people wake up complaining of sweat and humid weather. However, when the land warms rapidly due to the bright, strong sun, land breeze will fall gradually and pave the way for sea breeze to set in. Surface winds of easterlies can touch 10 nautical miles comfortably during the daytime in Chennai. Those residing close to the Days will continue to be cool and windy, unlike night time until the third week of April. 

From mid-April through the summer months and until September, the day temperature would be determined by the onset of sea breeze on a given day. However, everything depends upon location, and alignment to the coast. Sea breeze will be effective in areas like Mylapore, Besant Nagar, Thiruvanmiyur and Tiruvottiyur. In areas like Avadi, the sea breeze will not even brush past, so the surface temperature there would have no relief from winds, for the simple reason that wind is a localised condition. For example, while a commuter may experience a breezy morning in Chennai due to the easterlies, he may not catch the wind in Vellore, which has no coast to speak of. 

Immigrants often say Chennai has no winter as such and the city ranges between hot and hottest. As a matter of fact, that is not correct. Around December 23, the radiation (heat) is lowest and it slowly increases, until third week of March when the equinox takes place. This year, March equinox falls on March 20. Two things happen with the March equinox. First, the length of the day will increase. Secondly, the rays of the sun will fall more sharply, and day temperatures will rise. Cities like Madurai and Tiruchy will soon start experiencing hotter days, with the mercury likely to touch 35 degrees. Due to its proximity to the coast, temperature in Chennai will be comparatively better.