Some cyclones originating over the Bay of Bengal have attained the intensity of super cyclones. And they hav claimed lives and caused destruction to property on a large scale, severest among them being the Orissa super cyclone of October 29, 1999. A look at data of the last 50 years for insights into the vagaries of our cyclones.

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Even as the country braces itself to face a cataclysmic storm, data of the past half century seems to suggest that the frequency of cyclones have been on the lower side in recent years.

As many as 74 cyclonic storms occurred between 1993 and 2012, but the number is lower than the 126 seen between 1963 and 1982 .

For context consider what the India Meterological Department (IMD) says about cyclonic storms based on the available dataset stretching back to a longer period: that their average annual frequency in the north Indian Ocean (covering both the Bay of Bengal and Arabian sea) is about 5, which constitutes about 5 to 6 per cent of the global annual average. More cyclones happen in the Bay of Bengal than in the Arabian Sea; the ratio is 4:1. And the most intense cyclones occur during October-November and May-June.

Cyclonic storms are categorised as severe when the wind speed is in the 90 to 119 kmph range and very severe when in the 119-220 kmph range and a super cyclone when it exceeds 220 kmph.

The number of cyclones and severe cyclones India has faced from 1963 to 2012 every year ranges from 1 to 10 (except for the figure 9) and a total of 236 of those have been experienced during this period, based on historical IMD cyclone data covering the Bay of Bengal and Arabian sea. In 1986 there was only one cyclone as against the maximum of 10 recorded in 1976. The IMD says that as many as 10 yearly cylcones have occured only four times over the past century or so: 1893,1926,1930 and 1976.

A NASA Terra satellite image shows cyclone Phailin positioned over the Bay of Bengal on October 11. Photo: AFP/ NASA

During the 50 year period, 143 severe cyclones had occurred with as many as 7 of them being experienced a single year: 1976.

If there are numbers the weather gods seem to particularly favour, these are 3 and 4: these are the number of cyclones (including severe cyclones) recorded per year most during the past 50 years - the frequency being 10 years each.

February and March are months when a cyclone is least likely to happen - only one each have been recorded in those months between 1951 and 2012. That said, cyclones including severe ones have been witnessed in all months during this period - there has never been an instance of a particular month being skipped altogether.

It is Andhra Pradesh that is likely to be most hit by severe cyclones in terms of numbers, while Odisha experiences more cyclones overall. More cyclones occur along the East cost than on the West coast, where Gujarat is vulnerable to them.

Keywords: Phailincyclonesdatapatterns