The last couple of days have seen Chennai and suburbs witness late evening thunderstorm activity. These thunderstorms intensified closer to the coast bringing sudden burst of rains accompanied by gusty winds. Since the start of Southwest Monsoon season the IMD observatory at Chennai AP has recorded 7 rainy days. The observatory at Nungabakkam also has recorded 5 rainy days. This is in a way indicative of the sub par monsoon dynamics that is currently prevailing. The monsoon progress chart over East India sums up the erratic nature of progress this year so far. Since 31st May when Sikkim saw onset monsoon progress has stalled for nearly two weeks.
On the other side Peninsular West Coast has also been seeing sub par rains since the monsoon onset. As we get closer to mid June Palakkad is the only district with a positive seasonal anomaly in Kerala. Thrissur has so far received 236.5 mm against the average of 236.5 mm. While 5 other districts are under normal category their anomalies range from -12% to -18%. Sub seasonal weather forecasts continue to indicate poor week to 10 days for core monsoon zone along the west coast. The weak progress also means most parts of North India is under a late season spike in temperatures. Heatwave conditions are likely to persist over many parts of North India for the next week to 10 days. Some reduction in temperatures is likely towards late June / early July when monsoon picks up pace.
In a way the slow progress is due to the near stationery East West Shear zone over Central Bay and adjoining areas of Peninsular India. This stall though has opened a window of thunderstorms for North Coastal TN. Compared to the past few days the EW shear zone associated instability is likely to shift slightly to the South. This could mean more places in North Coastal TN may come under late evening thunderstorms . The stretch between Chennai and Pondicherry may remain the hotspot for these late evening / night thunderstorms.
Starting from today pretty much on a daily basis North Coastal TN is likely to see thunderstorm activity until Tuesday. While it may not be widespread thunderstorms daily, as was the case around Chennai few pockets may come under intense thunderstorm activity depending on winds and local conditions. Today there is a good chance one or two places in Villupuram / Chengalpattu dts closer to the coast may see intense thunderstorms with heavy spell of rains. Possibly Monday late evening / night may bring a fairly widespread thunderstorm activity over North Coastal TN.
As far as Chennai goes until Tuesday there could be daily thunderstorm activity. But please note it may not rain in all the areas every day. With westerlies fairly strong the rainfall activity will extend for about 15 to 30 minutes as the storms quickly cross the coast.