So, what is special about Ockhi?
Mostly, the area in which it developed. Cyclones are known to originate in both the Bay of Bengal and the Arabian Sea sides of the northern Indian Ocean; there is much more frequency on the Bay of Bengal side though, especially of the stronger cyclones — in fact, the Bay of Bengal side witnesses four times more cyclones than the Arabian Sea side on average.
But Ockhi originated near the south-western coast of Sri Lanka, and travelled very near the southern-most tip of the Indian mainland, along the coasts of Tamil Nadu and Kerala, towards the Lakshadweep islands, where it was at its most powerful. It weakened considerably after that and continued further, taking a north-easterly turn towards the Maharashtra and Gujarat coastlines —cyclones in this area are not a common phenomenon.
Why does the Bay of Bengal have more cyclones than the Arabian Sea?
Meteorologists say the relatively colder waters of the Arabian Sea are not conducive to the formation and intensification of cyclones. Additionally, the eastern coast of India receives cyclones that form not just in the Bay of Bengal, mostly around the Andaman Sea near the Andaman and Nicobar Islands, but also those travelling from the Pacific Ocean, where the frequency of ‘typhoons’, as these are called there, is quite high. Most of these cyclones weaken considerably after encountering a big landmass. Therefore, these do not travel to the Arabian Sea side. The western coast of India thus witnesses only those cyclones that originate locally or the ones, like Ockhi, that travel from the Indian Ocean near Sri Lanka.
How powerful was Ockhi?
Ockhi was described as a ‘very severe cyclonic storm’, the third strongest category according to the definitions used by the India Meteorological Department (IMD). Cyclones are categorised by the maximum wind speed they generate. On Saturday, at its most powerful, Ockhi had wind speeds between 155 and 165 km per hour, touching the upper border for ‘very severe cyclonic storm’.
Cyclones with wind speeds between 165 and 220 km per hour are classified as ‘extremely severe cyclonic storm’. Those with even higher wind speeds are called ‘super-cyclones’. The most famous instance of a ‘super-cyclone’ was the one that hit the coast of Odisha in October 1999. It was the strongest-ever cyclone recorded in that area, with wind speeds touching 260 km per hour. It was also the most devastating cyclone to have hit India.
The 2013 Phailin cyclone very nearly got categorised as a super-cyclone. It had maximum wind speeds of around 220 km per hour.
Cyclone forecasts by the IMD in the recent past have been made five to six days in advance, thereby minimising the damage caused — was the IMD late in issuing a warning for Ockhi?
How early the forecast is depends on how far we are from the place where the cyclone is emerging. Many of the big cyclones in recent years, like Phailin in 2013, Hudhud in 2014 or Vardah in 2016, developed near the Andaman Sea. From there, it took those cyclones about five to six days to hit the Andhra Pradesh or Odisha coasts.
These forecasts can be made only after an emerging depression is detected to have the properties of a cyclonic storm. This was true in the case of Ockhi as well. But the origin of Ockhi was much closer home. The cyclone formation was detected during the morning of Wednesday, November 29. An alert was issued around noon. But many areas in Tamil Nadu and on the Kerala coast started feeling the impact from Thursday itself. A day later, the Lakshadweep islands bore the brunt of the cyclone. Because it developed nearby, the lead time for the forecast was much less than in other recent cyclone cases.