The IMD has forecast heavy rain, thunderstorms and strong winds across around 13 states on September 21, with winds of 40 to 50 kmph gusting to 60 kmph, a yellow alert for parts of Kerala, and stronger winds of 45 to 55 kmph gusting to 65 kmph over the Bay of Bengal.
An alert bundles three different kinds of information, and they deserve different responses. The colour tells you how severe the rain is expected to be. The wind figures tell you about risk to structures, trees and boats. The place names tell you whether any of it applies to you.
The yellow alert for Kerala is a useful example. It corresponds to heavy rainfall of 64.5 mm to 115.5 mm, which is enough to cause waterlogging in low-lying areas but is a step below the orange and red categories that call for evacuation-level preparation.
The wind numbers matter most for the sea. Winds of 45 to 55 kmph gusting to 65 kmph over the Bay of Bengal are the reason fishermen are told to stay ashore, since small boats face real danger in those conditions.
The practical habit is to look up your own district in the bulletin and follow the specific advice, rather than reacting to the total number of states on the list.
Over the east-central and adjoining north-east Bay of Bengal, winds of 45 to 55 kmph, gusting to 65 kmph, are expected.
Kerala could receive heavy showers over the next few days, and a yellow alert has been issued in parts of the state.
A yellow alert for Kerala indicates the possibility of heavy rainfall in the range of 64.5 mm to 115.5 mm.
Heavy rain is forecast at isolated places over the Andaman and Nicobar Islands and coastal Odisha, and isolated heavy rainfall is forecast over Chhattisgarh.
Monsoon clouds in Bengal, India (representative image), Wikimedia Commons, CC BY 2.0