A severe heat wave swept the national capital on Wednesday, with the mercury soaring to 43.5 degrees Celsius, the highest recorded this year so far, the India Meteorological Department said, adding the monsoon is at least a week away.

The maximum temperature recorded at the Safdarjung Observatory, the official marker for the city, was seven notches above normal, weather officials said.

By July 7, conditions are predicted to become favourable for the monsoon to advance into the region, according to the MeT office.

Most of the monitoring stations in the capital recorded a severe heat wave, with their respective maximum temperature remaining at least 7 degrees Celsius above the average temperature.

A severe heat wave seared Lodhi Road (43.7 degrees Celsius), Ayanagar (44.2), Ridge (44), Mungeshpur (44.3), Najafgarh (44.4), Pitampura (44.3) and Narela (43.7), officials said.

The monitoring station at Pusa recorded a high of 44.3 degrees Celsius, eight notches above normal, they added.

For the plains, a "heat wave" is declared when the maximum temperature is more than 40 degrees Celsius, and at least 4.5 notches above normal.

A "severe" heat wave is declared if departure from normal temperature is more than 6.5 degrees Celsius, according to the IMD.

On Monday, Delhi recorded the first heat wave this summer with the mercury levels increasing to 43 degrees Celsius.

Another heat wave has been predicted for Thursday.

Light rainfall and dust storm on Friday are likely to bring the mercury below the 40 degrees mark.

Usually, the capital witnesses heat waves till June 20 and cooler temperatures thereafter. The increase in the maximum temperature this time can be attributed to the delay in the arrival of the monsoon, said Kuldeep Srivastava, head of IMD's regional forecasting centre.

There has been no rainfall in the last few days and warm westerly winds are blowing across a major part of northwest India, which has not been covered by the monsoon yet, he said.

After arriving two days late in Kerala, the monsoon had raced across the country, covering eastern, central and adjoining northwest India, seven to 10 days earlier.

The meteorological office had earlier predicted that the wind system may reach Delhi by June 15, which would have been 12 days early.

However, westerly winds have been blocking its advance into Delhi, parts of Uttar Pradesh, Rajasthan, Punjab and Haryana.

Normally, monsoon reaches Delhi by June 27 and covers the entire country by July 8. Last year, the wind system had reached Delhi on June 25 and covered the entire country by June 29.

The wind system is not likely to cover the remaining part of northwest India, including Delhi, Haryana, parts of west Uttar Pradesh, Punjab and west Rajasthan in the next six to seven days, the IMD said.

The last time the monsoon arrived so late in Delhi was on July 7 in 2012.