Yesterday afternoon saw once again parts of Chennai receive a quick batch of thunderstorms that brushed past places like Nungambakkam, Anna Nagar, Madhavarm & Puzhal etc. While the city observatory in Nungambakkam recorded 15 mm the Airport observatory in Meenambakkam did not record anything. Later in the evening Tiruvannamalai, Kanchipuram and delta districts recorded moderate rains in a few places.
Southwest Monsoon is going through its worst phase of the season with yesterday being the 13th straight day of below average daily mean rainfall. As of yesterday the deficit is at -2.5% which is the lowest for the season and is expected to now drop further with suppressed conditions likely to prevail for the next week to 10 days over most parts of the core monsoon zone.
While the active areas of Southwest Monsoon is seeing below average conditions things are getting set for the next active phase of the thunderstorm season over Tamil Nadu. As a precursor we are already seeing a bit of wind instability just North of Chennai latitude at mid tropospheric levels which could create the necessary unstable conditions in the atmosphere for thunderstorms to thrive.
Sea Breeze the other key trigger in this overall convective equation is expected to be stay strong for this phase with Westerlies gradually weakening. This Weakening westerlies are likely to aid the development of mature thunderstorms that are likely to move slowly giving rains to wider areas and for longer time.
Today things are once again looking good for the stretch between Pondicherry and SHAR to see some moderate to heavy thunderstorms in one or two places. Depending on how wind pattern works out these lucky places could end up getting a good spell of heavy rains at times. While models indicate south of Chennai to be hotspot once again for the rains the genesis location of the thunderstorms will decide the eventual beneficiary. With areas to the W/NW of Chennai likely to be unstable Chennai also has a fair chance for the evening batch of thunderstorms to give a decent spell of rains.