South India is sweating and swearing under the sweltering sun.
With the day-time temperatures escalating in all southern states, the India Meteorological Department (IMD) has advised caution and issued a heat wave alert for coastal Andhra Pradesh on Thursday, 18 May.
What is a heat wave?
A heat wave is a weather condition where the air temperature reaches levels that can be dangerous to the human body when exposed.
The IMD defines heat waves qualitatively and quantitatively. Qualitatively, it is based on temperature thresholds over a region — either in terms of actual temperature or its departure from normal.
In some countries, it may also be defined based on the heat index, which considers temperature and humidity, or extreme percentiles of temperatures.
The criteria for declaring a heat wave varies based on the region:
Based on Departure from Normal Heat Wave:
- Heat Wave: When the departure from normal is between 4.5°C and 6.4°C.
- Severe Heat Wave: When the departure from normal is greater than 6.4°C.
Based on Actual Maximum Temperature Heat Wave:
- Heat Wave: When the actual maximum temperature reaches or exceeds 45°C.
- Severe Heat Wave: When the actual maximum temperature reaches or exceeds 47°C.
For declaration, the above criteria should be met in at least two stations within a meteorological sub-division for a minimum of two consecutive days, with the declaration being made on the second day.
For coastal stations, the criteria for describing a heat wave is when the maximum temperature departure from normal is 4.5°C or more, and the actual maximum temperature is 37°C or higher.
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Heat wave in Andhra Pradesh
The Andhra Pradesh State Disaster Management Authority (APSDMA) issued a heat wave forecast for eight mandals in the state on Thursday.
Komarada mandal in Parvathipuram Manyam district and seven mandals in Kadapa district, namely Chapadu, Veerapunayunipalle, Kamalapuram, Valluru, Muddanur, Yerraguntla, and Proddatur, are expected to experience heat waves.
APSDMA Managing Director, Dr BR Ambedkar, mentioned in a press note that the scorching conditions are also anticipated in other areas.
According to Ambedkar, several districts, including Vizianagaram, Parvathipuram Manyam, Alluri Sitharamaraju, Eluru, Krishna, NTR, Guntur, Bapatla, Palnadu, Prakasam, Nellore, Kadapa, and Tirupati may see maximum temperatures ranging from 43°C to 44°C.
On Wednesday, Venkatachalam mandal in Nellore district and Yerpedu in Tirupati recorded a maximum temperature of 46°C each, while Narasaraopeta in Palnadu registered 45.9°C.
Ambedkar advised people to take necessary precautions and be cautious of the scorching weather.
“For the next two days, there will be a heat wave. There are troughs extending from coastal Andhra Pradesh to Tamil Nadu, which will bring some thundershowers, but will not be helpful enough to give respite from the heat. The temperature will remain high,” vice-president of the private forecaster Skymet, Mahesh Palawat told South First.
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Telangana on the boil
As the mercury continues to soar in various parts of South India, the scorching heat has also enveloped the state of Telangana — and notching up the hottest day of the summer season.
The Telangana State Development Planning Society (TSDPS) reported that Julurpad in the Bhadradri Kothagudem district recorded the highest maximum temperature of 46.4°C.
On Wednesday, several locations across the state experienced high temperatures, with many areas reaching 45°C. Julurpad, Garimellapadu and Khanapur PS in Khammam recorded 45.4°C; Bayyaram in Mahabubabad recorded 45.4°C; and Mamillagudem in Suryapet recorded 45.3°C.
In the state capital of Hyderabad, Khairatabad registered the highest maximum temperature of 41.6°C. Serilingampally, Kukatpally, Quthbullapur, Secunderabad, and Musheerabad also recorded temperatures exceeding 40°C.
According to the IMD in Hyderabad, the weather is expected to remain dry for the next two days. The IMD forecasts that maximum temperatures in the northern, eastern, and northeastern districts of Telangana will hover around 41°C for the next five days. With the rising temperatures, heatwaves are anticipated in the upcoming days.
However, starting from 20 May, there may be some relief as isolated places in Telangana are likely to experience light-to-moderate rain or thundershowers, providing respite from the scorching heat.
Related: Kerala searches for cool options as it wilts in summer sun
Tamil Nadu: Mercury rising
Following Chennai experiencing record-breaking temperatures, with Meenambakkam reaching a scorching 42.7°C and Nungambakkam at 41.8°C, the city found some relief from the heat on Wednesday. The early onset of the sea breeze prevented the temperature from escalating further.
On Wednesday, the Meenambakkam station of the Regional Meteorological Centre (RMC) recorded a temperature of 39.4°C, while Nungambakkam logged 37.1°C.
The IMD stated that a trough line had formed, stretching from Andhra Pradesh to southern Tamil Nadu, approximately 0.9 km above mean sea level. The state is expected to witness thunderstorms and lightning activity in isolated areas.
“These activities will be in the interior areas, the coastal areas will be dry with temperature ranging between 37°C to 40°C. However, there will be respite as thunderstorms may help the temperature go down,” said Skymet’s Mahesh Palawat.
The RMC has predicted light-to-moderate rain in a few places across Tamil Nadu, Puducherry, and Karaikal until Sunday. In Chennai, the skies are expected to be partly cloudy, with a maximum temperature of around 39.4°C.
Related: Find out all about why it ‘feels-like’ 54°C in Kerala
Kerala sees a ‘yellow alert’
The IMD has issued a yellow alert for Kerala, indicating the likelihood of very high temperatures. The yellow warning signifies that the maximum temperatures are expected to be 2 to 4°C above normal.
According to the latest weather forecast, several districts in Kerala, including Kollam, Kottayam, Alappuzha, Kozhikode, and Palakkad, may witness maximum temperatures reaching up to 37°C. However, with the high humidity factor, the “feels-like” temperature is in the high 40s.
In Kannur, Thrissur, and Thiruvananthapuram districts, the maximum temperature is predicted to hover around 36°C. Similarly, in Malappuram, the anticipated temperature is around 35°C. These districts are expected to experience relatively high temperatures.
The IMD is expecting a slight delay in the onset of the southwest monsoon over Kerala. The rains are expected on 4 June. However, scientists stated that the delay is unlikely to have any impact on the Kharif sowing (summer crop planting) or the overall rainfall across the country.
Typically, the southwest monsoon sets in over the Kerala coast on 1 June, with a standard deviation of around seven days. Private forecasting agency Skymet Weather, on the other hand, forecast that the monsoon is likely to reach Kerala on 7 June, with a margin of error of three days.
It also mentioned that the monsoon’s progression over peninsular India might be slightly sluggish and that hot weather is expected to persist well into June over the central and northern parts of the country. It expressed concern that the sluggish monsoon progress could hurt Kharif sowing.
In previous years, the monsoon arrived in Kerala on 29 May (2022), 3 June (2021), 1 June (2020), 8 June (2019), and 29 May (2018).
The Indian monsoon is driven by temperature and pressure differences between the Indian landmass and the Indian Ocean. During the summer months, the landmass heats up, creating a low-pressure zone that draws in moist air from the ocean, resulting in rainfall.