To err on the side of the caution is always the guiding principle for disaster communicators. The cone of uncertainty in cyclone forecasts is a classic example of probability in weather. A small change in dynamics could effectively change path of a cyclone. This could catch out people who may be unprepared if only a very narrow landfall path is given. Similar rationale is adopted when water is released from lakes for flood cushion. The release is in anticipation of expected rains when the reservoirs are near FRL is based on well established protocols. As we look at the struggling LPA over South Bay minds get refreshed to Cyclone Phethai in 2018.
For every Cyclone Phethai there is always a Cyclone Michaung. A matter of 100 kms difference in the tracks altered the impact drastically. In 2018 Chennai saw cloudy skies with drizzles as Cyclone Phethai passed 200 kms to our East moving North. In 2023 Michaung came as close as 50 kms to the East of Chennai devastating the city with floods. This struggling LPA will resemble Cyclone Phethai than Cyclone Michaung in its influence as things stand.
A combination of hostile environment, poor overall support meant the struggling LPA was fighting battle right through its life cycle. Compared to model forecasts 48 hours in advance the LPA has not only remained weaker but also stayed in a lower latitude. This effectively has changed the equations in terms of rainfall prospect for Coastal TN. The wind convergence has effectively stayed off the coast thanks to the location of circulation being further south and further East than expectations.
Additionally the constant struggles have meant a proper structure which could bring a CDO never happened. A proper Central Dense Overcast is very essential for widespread rains. The third important factor always in the equation was the Westerly Trough. The delay in consolidation and movement has meant the window for rains has now shrunk. What could have been a 60 hour rainfall window is now effectively 24 hours. Even this 24 hours will depend a lot on further NW movement of the circulation which could bring the convection over North Coastal TN and South AP.
As things stand Chennai and most of North Coastal TN can expect cloudy skies, gusty conditions for the next couple of days. On and off light to moderate rains may happen as the LPA comes closer to the coast, but the probability for rains is fading fast with the Westerly Trough expected to come in to picture later tomorrow. With the window for rains narrowing down the risk for heavy rainfall over places like Chennai in North Coastal TN is also reducing. The estimated ensemble rainfall chart also indicates reducing rains for most places of TN except North Coastal TN.
It is routine work for every one, keep a tab on radar for on and off spells of rains during the next couple of days. Chance for heavy / very heavy rains reducing with every passing hour for Chennai and rest of Coastal TN.