Climate Change

Heat waves to follow in the wake of Amphan: IMD

Isolated areas in Gujarat, Rajasthan and Madhya Pradesh will suffer from heat waves between May 18 and May 22, it says

By Akshit Sangomla
Published: Tuesday 19 May 2020

The aftermath of the super cyclone Amphan might lead to an increase in day temperatures across India. This might also induce heat waves which have been absent in the country till mid-May.

“After a major cyclone like Amphan, the direction of winds over the Indian mainland become north-westerly which are warm and lack moisture,” Mrutyunjay Mohapatra, director-general of India Meteorological Department (IMD), said in an online question and answer session.

This happens because of the anti-clockwise circulation of winds in the cyclone that disrupts the local wind circulation of a region.

“This induces the rise in temperatures being observed in coastal regions of Tamil Nadu. We are also tracking a heat wave in the Vidarbha region of Maharashtra,” Mohapatra said.

India has not witnessed a single heat wave in the ongoing summer season till May 18, 2020. This is after the IMD earlier predicted a warmer-than-usual summer season this year.

Average maximum temperatures are likely to be warmer than usual by 0.5-1 degree Celsius for April-May-June according to the latest seasonal outlook for temperatures released by IMD. It had made a similar prediction about the months of March-April-May in the end of February.

The reason for the absence of heat waves was the rainier and cooler-than-usual months of March, April and early May. The major reason for the excess rainfall were the continuous western disturbances coming from the north west, that carried moisture with them.

From 2013 to 2019, there have been on an average 114 heat wave days in the country every year, according to data from the IMD. The maximum number of heat wave days were recorded last year at 157.

The heat wave last year began as early as by the end of March in some of the southern states, spreading to 22 states by June.

The sun was the most brutal to Maharashtra, where people reeled under heat wave conditions for 42 days between March 28 and June 5, 2019. Of these, the heat wave was severe on six days.

On May 18, the IMD generated a heat wave bulletin, warning of heat waves in different parts of the country beginning May 18.

After the heat wave in Vidarbha, it says that isolated areas in Gujarat, Rajasthan and Madhya Pradesh will also suffer from heat waves between May 18 and May 22.

Temperatures have also been appreciably above normal (3.1-5 °C) over Jammu and Kashmir, Ladakh, Gilgit, Mahe, Tamil Nadu, Puducherry and Karaikal.

A heat wave is considered if maximum temperature of a station reaches at least 40°C or more for the plains, 37°C or more for coastal stations and at least 30°C or more for hilly regions. The following criteria are used to declare a heat wave:

Based on Departure from Normal

  • Heat Wave: Departure from normal is 4.5°C to 6.4°C
  • Severe Heat Wave: Departure from normal is >6.4°C

Based on Actual Maximum Temperature (for plains only)

  • Heat Wave: When actual maximum temperature ≥ 45°C
  • Severe Heat Wave: When actual maximum temperature ≥47°C

To declare heat wave, the above criteria should be met at least in two stations in a meteorological sub-division for at least two consecutive days and it will be declared on the second day.

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