Last night Chennai saw widespread thunderstorms with many areas in the city recording more than 4 cms in one hour. The IMD observatory at Nungambakkam recorded 67 mm while the one at Meenambakkam recorded 35 mm. Chennai AP has already crossed 30 cms for SWM season and Nungambakkam is just short at 29 cms. Over the past few years there is a clear trend of Chennai receiving more rains during June and July. Overall Southwest Monsoon has continue to see a steady increase in seasonal rainfall. Possibly this in a way is also enhancing flooding / water logging issues for Chennai during Northeast Monsoon. Higher soil moisture on account of more than ever before rains during Southwest Monsoon leads to lower flooding threshold during NEM.
Monsoon continues to remain weak over Southern parts of Peninsular India though it covered the country ahead fo schedule. The weaker than normal westerlies provide a platform for thunderstorms to develop over the leeward areas. Time to time a window of opportunity becomes available through wind convergence from developing circulations. One such opportunity is possibly coming up for Chennai to see its active phase of thunderstorms continue for the next few days.
One needs to keep in mind even though it may be active phase the rains may not happen daily as thunderstorms are a more localised phenomenon. Larger atmospheric conditions do play a role in thunderstorm development but how they move and where they move depends a lot on prevailing wind steering. But overall things do look good for the next few days for possibly 2 / 3 days of widespread thunderstorms over North TN & South AP.
Sub seasonal ensemble weather outlooks indicate above average rainfall possibility for Coastal AP and adjoining areas of North TN. The moderate probability of anomalously high rains around this region in the EFI is also an indicator towards active phase. As we mention often the convex coast of Chennai does play favourably as far as thunderstorm development goes. Also the role of sea breeze front waiting in the shadows for incoming thunderstorms should not be forgotten. It is surely a game changer for Chennai coast. Sea breeze is one of the reasons Chennai sees more intense thunderstorms during SWM compared to rest of TN coast.
The last post was summarised with a mention of Chennai likely to receive its July average by the 1st week. There is increasing confidence based on weather model forecasts this could indeed happen. Post this active phase we may see a lull in thunderstorms for leeward areas from later next week. This may coincide with some much needed momentum for Monsoon over southern Peninsular India. July end may be the time to look forward once again for another active phase of thunderstorms.