The weather system that became Cyclone Arnab followed a familiar Bay of Bengal script, and forecasters have tracked each step of it in public. The India Meteorological Department said on Monday that a deep depression in the Bay of Bengal was moving west northwestwards and was currently closest to Gopalpur, Odisha. The storm was intensifying and was expected to transform into Cyclone Arnab by midnight, then intensify further into a severe cyclonic storm over the west central Bay of Bengal by midnight on October 26, and into a very severe cyclonic storm over the same region on October 27.
Why the Bay of Bengal breeds strong storms
The Bay of Bengal is one of the world’s most active regions for tropical cyclones, for reasons that are partly geographic and partly seasonal. Warm surface waters feed a developing system with heat and moisture, while the shape of the bay funnels storm surge toward low lying coasts in India and Bangladesh. In October, as the monsoon withdraws, the conditions for cyclogenesis, the birth of a cyclone from a depression, are often at their most favourable, with warm water, moist air and weak wind shear allowing a disorganised cluster of thunderstorms to organise into a rotating system. Once that rotation tightens, the storm can intensify rapidly, which is why a depression on Monday can be forecast as a very severe cyclonic storm by Tuesday, and why forecasters update their bulletins several times a day as new observations arrive.
What the forecast can and cannot tell you
The forecast for Arnab puts landfall between Bapatla and Visakhapatnam on October 28, with sustained winds of 115 to 125 kilometres per hour and gusts up to 140 kilometres per hour, along with heavy to very heavy rainfall for coastal Andhra Pradesh, Yanam and parts of Odisha. Those numbers are the best estimate from current observations, but forecast tracks can change, and the difference between a landfall at Bapatla and one at Visakhapatnam matters enormously for which districts receive the worst wind, rain and surge. That is why residents are urged to check the latest official bulletins rather than treating any single forecast as final, and why officials in both Andhra Pradesh and Odisha have prepared for a range of tracks, not only the central one. Science can tell you a storm is coming, how strong it is likely to be, and roughly where it will land. It cannot tell you, days in advance, which street will flood, and that gap is where preparation, not prediction, saves lives.
