The national capital on Tuesday recorded a minimum temperature of 33.8 degrees Celsius, six notches above the season's average.
The weather department has predicted mainly clear sky and heatwave to severe heatwave conditions and strong surface winds.
The humidity was 61 per cent at 8.30 am. The maximum temperature is likely to settle around 45 degree Celsius, it stated.
The threshold for a heat wave is met when the maximum temperature of a weather station reaches at least 40 degrees Celsius in the plains, 37 degrees in coastal areas, and 30 degrees in hilly regions, and the departure from normal is at least 4.5 notches.
A severe heat wave is declared if the departure from normal exceeds 6.4 notches.
The India Meteorological Department (IMD) has issued a red alert for Delhi. The IMD uses four colour codes for weather warnings -- green (no action needed), yellow (watch and stay updated), orange (be prepared) and red (take action).
According to the IMD's seven-day forecast, the national capital will experience slight relief from Wednesday.
The city is expected to be on yellow alert on Wednesday and Thursday while it will be put on green alert on Friday and Saturday.
After Wednesday, a fresh western disturbance will approach northwest India, also affecting the national capital and bringing relief, according to the weather office.
The Air Quality Index (AQI) of the national capital was recorded in the moderate category with a reading of 178 at 9 am, according to the Central Pollution Control Board.
An AQI between zero and 50 is considered good, 51 and 100 satisfactory, 101 and 200 moderate, 201 and 300 poor, 301 and 400 very poor, and 401 and 500 severe.