After longest lull since 2012, year’s first cyclone forms

THe republic of india Meteorological section (IMD) said in a 4pm bulletin on fri that a late great depression in the northeast Arabian Sea had intensified into a cyclone at 11.30am, ending an unusually calm period for India’s coasts. This is the first cyclone to form in the North Indian Ocean this year — a dry spell not seen since 2012, when no cyclones were reported in either the Bay of Bengal or the Arabian Sea up to September.To be sure, this cyclone is more likely to make the seas rough than cause havoc inland. IMD’s bulletin shows that it is likely to move further away from India as it intensifies into a severe cyclonic storm.A cyclone in October is also not surprising. Historical data suggests that October-December is the busiest season of cyclones near India’s coasts. October in particular has the second highest frequency of cyclones.What is somewhat interesting is that the first cyclone of the season has formed in the Arabian Sea, which reports a lower frequency of cyclones than the Bay of Bengal.Where is Cyclone Shakhti and where will it go?According to the IMD bulletin, Shakhti had its centre at 21.7°N 66.8°E at 11.30am, a location in the Arabian Sea close to Gujarat. Its forecasted track suggests it will move north-westwards briefly before turning south-westwards, as it intensifies into a “severe cyclonic storm” by 5.30am on October 4.A severe cyclonic storm has maximum sustained wind speeds of 89-117 kilometres per hour (kmph) compared to 62-88 kmph for a “cyclonic storm”, the category at which cyclone Shakhti is currently. However, since this intensification will happen further west of India, there were no weather warnings for Gujarat for October 4; although sea conditions will be rough, as expected.What is the seasonality of cyclones in the North Indian Ocean?The Cyclone eAtlas of the IMD gives the monthly number of depressions, cyclonic storms, and severe cyclonic storms from 1891 to 2024. This shows that the post-monsoon period of October-December is the period of the highest cyclone activity near India’s coasts, although the pre-monsoon and early monsoon months of May and June are also fairly active. October in particular is the second ranked month after November in terms of monthly frequency of cyclones. This makes the formation of a cyclone in October par for the course. What is interesting this year is that no cyclone formed at all up to September, which had not happened since 2012.Cyclone formation in the Arabian Sea is increasingAnother interesting fact about Cyclone Shakhti is that the first cyclone of the year has formed in the Arabian Sea rather than the Bay of Bengal. It is in line with a known long-term trend: cyclones in the Arabian Sea are becoming more frequent. The eAtlas data also shows that while Bay of Bengal still hosts more cyclones than the Arabian Sea, the frequency of cyclones is decreasing in the former and increasing in the latter. Why is this happening? Warmer seas is the short answer. In a 2021 paper published in the journal Climate Dynamics, Medha Deshpande and other scientists have also shown an increase in duration of cyclones in the Arabian Sea. This, the scientists found, was correlated with warming surface temperatures of the sea and tropical cyclone heat potential, which measures how deep the warmth of the ocean goes.