New Delhi: Heat wave conditions scorched the national capital Thursday, with the Palam Observatory registering a high of 46.8 degrees Celsius, the maximum temperature recorded in May since 2013. The Palam Observatory had recorded a high of 47.2 degrees Celsius in May 2013.

"Delhi heats up. Palam in Delhi recorded 46.8 degree. Highest temperature in the month of May since 2013. All time high is 48.4 degree recorded on May 26 in 1998," Mahesh Palawat of the private weather forecasting agency Skymet Weather tweeted.

"The temperature in the Palam area is always one or two notches more than that at the rest of the places because it's open. Emissions due to high aviation activity also adds to the heat," India Meteorological Department's regional weather forecasting chief Kuldeep Srivastav said.

The Safdarjung Observatory recorded a maximum of 44.7 degrees Celsius, the highest for the season so far. The minimum temperature settled at 26.8 degrees Celsius, the weatherman said.

The Ridge and Ayanagar observatories recorded the mercury at 46.4 and 46 degrees Celsius.

The official said severe heat wave conditions will prevail in a few pockets of the city over the next three-four days.

A heat wave is declared when the maximum temperature is 45 degrees Celsius for two consecutive days in large areas and severe heat wave is when the mercury touches the 47-degree mark for two days on the trot.

In smaller areas, like the national capital, a heat wave is declared if the temperature soars to 45 degrees Celsius even for a day, Srivastava said.

The official said similar conditions are likely to prevail Friday. The city is likely to record a high of 45 degrees Celsius and a low of 28 degrees Celsius.