Delhi's maximum temperature on Wednesday reached 43.4 degrees Celsius, three notches above the season's average, and remained in the 'Yellow' alert zone, according to the India Meteorological Department (IMD).
There is a very high likelihood of developing heat-related illnesses and heat stroke in people of all ages, and a significant health concern for vulnerable individuals, such as infants, the elderly, and those with chronic diseases, the weather office said.
"Avoid heat exposure and keep cool. Avoid dehydration," the IMD advised, adding that people should drink sufficient water and use ORS or homemade drinks like lassi, torani (rice water), lemon water and buttermilk to stay hydrated.
According to the IMD, the city will be on orange alert on Thursday.
It predicted mainly clear skies with heatwave conditions at a few places, accompanied by strong surface winds at speeds of 25-35 kmph on Thursday.
In a seven-day forecast, the weather office issued a red alert from Thursday to Saturday and urged "extreme care for vulnerable people" due to the heatwave.
Delhi's relative humidity oscillated between 59 and 37 per cent during the day.
The threshold for a heatwave is met when the maximum temperature of a weather station reaches at least 40 degrees Celsius in the plains, 37 degrees in the coastal areas, and 30 degrees in the hilly regions, and the departure from normal is at least 4.5 notches. A severe heatwave is declared if the departure from normal exceeds 6.4 notches.
The weather department has four colour-coded warnings -- green (no action needed), yellow (watch and stay updated), orange (be prepared) and red (take action).
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