After remaining dry for almost ten days, Chennai finally observed some good rain. In a span of 24 hours from 8.30 am on Sunday, the city experienced 89.3 mm of heavy rain. This spell has taken the total rainfall figure to 186.6 mm against the monthly average of 140 mm. And with some more rain expected in the next two days this figure is likely to go up.
Such spells of heavy rain are not very common in Chennai during this time. There has been only two occasions in the last ten years when over 100 mm of rain has been recorded in the city in 24 hours. On 25th August 2011 the city had witnessed the heaviest 24 hour spell by recording 156 mm of rain. The second spell of heavy rain 100 mm on 20th August 2008.
Tamil Nadu is a rain shadow area as less rain is observed in the region during the Southwest Monsoon season. During the active Monsoon phase, rainfall in the region is not adequate as the Western Ghats block the flow of Monsoon air, giving all the rain to Kerala. On the contrary, we see enhanced rainfall activity along coastal Tamil Nadu during the weak Monsoon phase. This is because of the westerly winds getting weak and giving rise to sea breeze along the coast during afternoon and evening hours.
Also, during the weak and break Monsoon conditions, Monsoon systems have a tendency to appear in the lower latitudes in the Bay of Bengal off Tamil Nadu and Andhra Pradesh coast.
The weather in Chennai is also governed by these factors. The highest amount of rain received in the month of August in last ten years in Chennai is 368.9 mm, recorded in 2011. The lowest has been 47.1 mm, observed in 2004.
