In recent years names like Vardah, Thane, Ockhi are etched in the memory of people from Tamil Nadu. These have one more thing in common apart from impacting Tamil Nadu. All of these are late season cyclones that formed during La Nina years. Old timers may remember the Dhanushkodi Cyclone, one of the strongest to hit Tamil Nadu, from the year 1964. That was another La Nina year which saw a late season cyclone impact the coast of Tamil Nadu.
Over the past couple of days ensembles are showing a possible disturbance developing over Equatorial Bay in the coming week. More than 2 weeks back when a Monsoon Revival update was written last week of November was mentioned as a period to watch out for. The consistency of ensembles for a long period of time indicate a high probability of this event happening.
In this context today’s post is an attempt to identify the peak Cyclone season for Tamil Nadu. Most of us know by now Northeast Monsoon season coincides with peak cyclone season of North Indian Ocean Basin. The performance of Northeast Monsoon has a close association with these disturbances. Favourable genesis and tracks bring better seasonal rainfall for Tamil Nadu
The IMD Cyclone E-Atlas throws up a few things if we break down the Northeast Monsoon season into parts.
- The probability of a cyclone making landfall over Tamil Nadu is the highest during the 2nd fortnight of November. Effectively 2 in 5 cyclones that formed during the 2nd fortnight of November headed towards Tamil Nadu coast.
- 2nd fortnight of November has seen highest number of cyclones impacting Tamil Nadu coast. Of the 61 cyclones that made landfall over Tamil Nadu during NEM season 19 formed during the 2nd fortnight of November.
- If one were to expand the landfall horizon slightly during the 2nd half of Northeast Monsoon season every other cyclone that formed in Bay of Bengal has impacted either Tamil Nadu or East Sri Lanka. A East Sri Lanka landfall will bring a fair bit of rains over Delta districts and South TN after landfall.
- 2nd fortnight of November and December sees a more WNW / NW track among Bay Cyclones. As a result of this there is an increased impact over Tamil Nadu coast.
- First fortnight of November sees the highest instance of disturbances intensifying into Cyclones.
- Crucially during 2nd half of NEM season 3 out 4 disturbances that impact Tamil Nadu intensify into cyclones.
With the arrival of MJO into Indian Ocean basin we are about to enter a highly favourable period for North Indian Ocean basin. This also coincides with the peak period of cyclone impact for Tamil Nadu as well. This favourable climatology gets reflected in more ensemble members picking up a WNW track for the upcoming disturbance. It is essential to point out here the probability of WNW remains high at this time of the year. But there is always a chance for northward movement as Phethai showed during 2018.
This post does not aim to create panic about a potential cyclone for Tamil Nadu. This post is an attempt to create an awareness about why 2nd fortnight of November and 1st fortnight of December is vulnerable historically for coastal TN. Disaster Preparedess always revolves around Risk awareness. Cyclones are a risk not only from wind damage but rainfall too. There will be more clarity as we get to closer to the event from weather models. More clarity in terms of impact areas, impact potential, rainfall potential etc.
The upcoming week see rains remain around Delta and South TN while North TN sees a break. As things churn over Equatorial Bay there is a fair confidence overall Northeast Monsoon season will end in the positive for not only TN but also Chennai.