The last few days Tamil Nadu has seen a taste of what is likely to come up this Summer. Chennai AP recorded 37.7°C on Thursday which was the hottest day of the year. The IMD observatories at Karur Paramathi and Erode recorded 39°C as dry weather prevailed. South TN possibly was the only region in Peninsular India that did not see abnormally warm conditions. Additionally it also got some rains from the earlier Easterly wave. The first 3 days of March brought in 11.8 mm which is nearly 60% of the monthly rainfall quota. At a mean rainfall of 19.8 mm for TN & PDC March is the 3rd driest month.
Just as we started seeing temperatures climb up there is respite on the horizon. A fresh Easterly wave is likely to influence Peninsular India in the next 48 to 72 hours. Currently a cyclonic circulation is seen developing off Sumatra in the Equatorial waters. Weather models indicate this has a 50:50 chance to become a Low Pressure area as it moves WNW towards Sri Lanka. As it moves closer to Sri Lanka it may bring widespread rains to most parts of Tamil Nadu.
Unlike the earlier Easterly wave instance when the rains happened in Delta and South TN this time more places could see rains. A couple of favourable factors is likely to enhance the rainfall potential spatially this time around. Indian Ocean is now currently seeing favourable transit of Tropical waves. MJO is seeing transiting West to East across Indian Ocean. It is likely to reach the eastern part of Indian Ocean in the next couple of days. This is likely to enhance convection associated with the upcoming easterly wave. With Equatorial Rossby wave also transiting East to West there is a fair chance we could see heavy / very heavy rains in a few places.
Additionally the seasonal anti cyclonic circulation over Central India has moved slightly to the west. This slight nudge will allow moist Easterlies to penetrate to places in North TN as well. This is likely to increase the spatial spread of rainfall from the upcoming Easterly wave. While North TN is likely see light / moderate rains Delta and South TN may see widespread moderate to heavy rains. Rains are likely to happen between 10th and 13th March with 11th likely to see the heaviest spells.
Additionally this may also bring respite from the heat for a few days. Weather models indicate from tomorrow day time temperatures may see a reduction in TN. As far as Chennai goes we can expect some light / moderate rains on 11th March. Short duration heavy spells in a few places closer to the coast during morning hours cannot be ruled out.