On 15th May IMD announced the onset window for this year’s Monsoon Onset over Kerala. The statistical model forecast gave 26th May with +/- error of 4 days for MOK. A day later we saw onset of Southwest Monsoon over parts of Andaman & Nicobar islands. Monsoon dynamics effectively confirms the start of the Westerly wind regime. This also means Chennai’s home grown hero Sea Breeze now has a battle on hands. A battle against the stiff westerlies for the next 5 months or so.
The convex coastline near Chennai in way plays a key role in how weather is shaped. It makes sea breeze more pronounced around Chennai coastline. But it also means when land breeze is strong the temperature spike is more pronounced as well. Weather models indicate lower level winds are now from the West completely. The daily mean wind plot from today over North Coastal TN is from WSW confirming the Westerly wind regime.
Using ECMWF forecast an hourly plot of wind direction and humidity now shows sea breeze may now start to arrive after 2 PM on a regular basis. During late April this would have possibly happened around noon mitigating heat increase. With winds from land blowing well into the afternoon temperatures may peak around 2 or 3 PM from now on. Certain days when offshore winds are strong then we may see the peak get pushed to even as late as 4 PM.
What will possibly aggravate weather watchers more is how thunderstorms may tease over the next couple of weeks. With westerly winds we may slowly start seeing thunderstorms move West to East from interiors. The convex coastline around Chennai means our steering improves only after monsoon onset completes over Peninsular India. Until then we may see places around 50 – 100 kms away from Chennai come under thunderstorms. Occasionally we may also see suburbs like Tiruvallur / Avadi also come under rains but city areas may miss out.
Staying on thunderstorms over the next few days thunderstorms may continue over many places in Peninsular India. In particular AP / TN / KA Tri Junction will be the hotspot. This effectively means for the next few days evening commute in Bengaluru may become a game of cat and mouse with rains. Peninsular West Coast may continue to see daily rains. With stiff westerlies Kanyakumari district in South TN is effectively now under monsoon dynamics.