Before going into analysis, lets go to the Chennai climatology for the May month. Chennai average temperature in May is 37 C, normally temp peaks at 1.30 pm and sea breeze comes to save us from scorching heat. The outskirts Chennai peaks at 2.30 to 3.30 pm as sea breeze will take time to move in. Not always we see 40-41+C in Chennai, this happens on two occasions, when a cyclone moves away from TN coast to Bengal or Odisha or Burma, thereby bringing dry winds from North West. In the 2nd case, if the offshore monsoon winds are strong during the month end when monsoon nears and Bay of Bengal branch is active. In this case, the sea breeze will struggle to come in resulting in prolonged heating and peak happening not at 1.30 pm but at 3.30 pm or 4.30 pm.
Top five hottest days in Chennai in May
The hottest days in Chennai have been always associated with Cyclones going to Burma, who can forget the heat waves in 2003 and 1998 in India and not only in Chennai.
45.0 C on 31.05.2003 – Cyclone to Burma
44.1 C on 30.05.1998
43.6 C on 23.05.1980
43.4 C on 12.05.2002
43.2 C on 04.05.1976
Unlike June, May month the humidity is less even though we are a coastal station making less sweating.
Daily May Temperature of Chennai May month in last 15 years.
I have stored the daily temperature of Chennai in last 15 years and 2021 May was so pleasant that Chennai did not even cross 37 C till 26th May and only the Cyclone yaas after moving up to Odisha triggered dry winds. There was prolonged easterlies seen till late may making the temperature of Chennai pleasant this year.
Note: Open the image in separate tab, if the data is not clear.
2021 is Coolest May for Chennai in last 15 years
In 2021, Chennai average May Temperature was 35.94 C and out of the 31 days, 22 days the temperature was below 36 C, this is the highest number of less than 36 C by a huge margin. The number of 40 C days is on par with 2020 with 3 days due to Cyclone Yaas moving away.
While 2018, 2004, 1995 saw 0 days with temperature not crossing even 40 C even 1 day the whole month.
Now we can see the Chennai rainfall is just 40mm average in May and mostly these comes from the once in 6 years Cyclone based rainfall. Chennai has got rainfall in May month in 1990, 1995, 2004, 2010 and last one in 2016. And for rains to happen in Chennai in May month, the clouds have to come from Sea side and very rarely clouds will manage to reach from west but this year for the 1st time, i have seen 2 rainy days in May month on 21st and 22nd the clouds managed to reach Chennai from west just like in June month.
And i know many will comment, that was lockdown the reason for coolest may, no it is because of the prolonged easterlies from sea.
And to me, the most horrible month is the June month than May because of delayed sea breeze and higher humidity than May and due to which sweating will be more and so will be the real feel.