The all-time record for Safdarjung in May is 47.2 degrees Celsius, recorded on May 29, 1944.
Delhi recorded the hottest day in May in the last 18 years as the maximum temperature at the Safdarjung observatory rose to 46 degrees Celsius on Tuesday.
The people sweltered under a scorching heat wave as most places recorded their maximum temperatures six notches above normal and the mercury soared to 47.6 degrees Celsius in Palam area.
The Safdarjung Observatory, which provides representative figures for the city, recorded a maximum of 46 degrees Celsius.
The last time the mercury at the Safdarjung weather station touched the 46-degrees-Celsius mark was on May 19, 2002, said Kuldeep Srivastava, the head of the regional forecasting centre of the India Meteorological Department (IMD).
The all-time record for Safdarjung in May is 47.2 degrees Celsius, recorded on May 29, 1944.
The last time the Palam Observatory recorded such a high temperature in May -- 47.6 degrees Celsius -- was on May 18, 2010, Srivastava said.
The IMD said the weather stations at Lodhi Road and Aya Nagar recorded their respective maximum at 45.4 degrees and 46.8 degrees Celsius.
In large areas, a heat wave is declared when the maximum temperature is 45 degrees Celsius for two consecutive days and a severe heat wave is when the mercury touches the 47 degrees-mark for two days on the trot.
In small areas like Delhi, heat wave is declared if the temperature soars to 45 degrees Celsius even for a day, according to the IMD.
Srivastava said some respite from the stifling heat was expected on Thursday due to a fresh western disturbance and easterly winds at lower levels.
Dust storm and thunderstorm with winds gusting up to 60 kilometres per hour is likely over the National Capital Region on Friday and Saturday, the official added.