All but one of the weather stations in the national capital recorded maximum temperatures above 44 degrees Celsius on Sunday, as hot and dry westerlies swept across northwest India.
The Safdarjung Observatory, Delhi's base station, recorded a maximum temperature of 43.9 degrees Celsius, four notches above normal.
The maximum temperature settled at 46.7 degrees Celsius at the Sports Complex automatic weather station near the Akshardham temple, making it the hottest place in the city.
Najafgarh, Mungeshpur, Pitampura, and Ridge stations recorded a high of 46.4 degrees Celsius, 46.2 degrees Celsius, 45.8 degrees Celsius and 45.8 degrees Celsius, respectively.
The India Meteorological Department (IMD) has issued a yellow alert, warning of a heatwave in parts of Delhi on Monday.
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).
Weather experts have attributed the heatwave spell to the lack of strong western disturbances and incessant hot and dry westerly winds.
They said a major respite from the scorching heat is likely from June 15-16.
Thundershowers, cloudy sky, gusty winds and light rainfall are predicted on the coming weekend. The maximum temperature at the Safdarjung Observatory may dip to 38 degrees Celsius by Saturday.
Mahesh Palawat, vice-president (climate change and meteorology), Skymet Weather said the monsoon is likely to arrive in Delhi around the normal date -- June 27. There is no system in sight which could stall its progress. A clear picture will emerge in a week or so.
Last year, the IMD had forecast that the monsoon would arrive in Delhi nearly two weeks before its usual date. However, it reached the capital only on July 13, making it the most delayed in 19 years.
The monsoon had entered a "break" phase and there was virtually no progress from June 20 to July 8, Palawat recalled.
A heatwave is declared when the maximum temperature is over 40 degrees Celsius and at least 4.5 notches above normal. A severe heatwave is declared if the departure from normal temperature is more than 6.4 notches, according to the IMD.
Based on the absolute recorded temperatures, a heatwave is declared when an area logs a maximum temperature of 45 degrees Celsius. A severe heatwave is declared if the maximum temperature goes beyond 47 degrees Celsius.