Cyclone Arnab crosses the Andhra coast near Yanam as the year's first very severe storm

How the IMD classes a storm

• The India Meteorological Department classes a storm by its sustained wind. A cyclonic storm blows at 62 to 88 km/h, a severe cyclonic storm at 89 to 117 km/h and a very severe cyclonic storm at 118 to 165 km/h. Arnab sat in the third class.

Why October to December

• The post monsoon months, October to December, are the second peak season for Bay of Bengal cyclones. The sea is still warm, and the strong winds high above the sea that tear a storm apart during the monsoon have gone.

• In El Niño years cyclones in the North Indian Ocean tend to form closer to the equator. Such storms are then more likely to head for Andhra Pradesh and Tamil Nadu than for Odisha and West Bengal.
• Arnab reached its peak within a day and held that intensity for about six hours after landfall, longer than a storm usually does once it leaves the sea.
• High waves reached north Chennai even though the storm crossed far to the north. Much of southern Odisha had heavy rain, with Gajapati worst hit.

Andhra Pradesh put its preliminary loss at ₹4,600 crore, with seven deaths. The figure counts the damage, from flooded crop to fallen poles, and shows the first step towards money from the National Disaster Response Fund.

• Move from wind speed warnings to impact based forecasts that tell a village what the storm will do to its homes, crops and roads. The Department has begun impact based forecasts for some hazards.
• Put coastal distribution lines underground in the worst hit districts, funded from the mitigation window of the disaster funds rather than from relief after each storm.