Heat wave need not be considered till maximum temperature of a station reaches at least 40º C for Plains, 30º C for Hilly regions and 37º or more for coastal region.
a) When normal maximum temperature of a station is less than or equal to 40º C
Heat Wave Departure from normal is 5º C to 6º C & Severe Heat Wave Departure from normal is 7º C or more.
b) When normal maximum temperature of a station is more than 40º C
Heat Wave Departure from normal is 4º C to 5º C & Severe Heat Wave Departure from normal is 6º C or more
c) When actual maximum temperature remains 45ºC or more irrespective of normal maximum temperature, heat wave should be declared.
To declare Heat Wave, the above criteria should be met at least in two station in a meteorological sub-division for at least two consecutive days and it will be declared on the second days.
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