A heatwave spell scorching Delhi for the last two days is predicted to worsen on Saturday, with the India Meteorological Department (IMD) issuing an 'orange' alert, warning that the mercury may soar to 46-47 degrees Celsius in parts of the city.

The maximum temperature at the Safdarjung Observatory, Delhi's base station, is predicted to settle at 44 degrees Celsius as against 42.5 degrees Celsius on Friday.

Delhi on Friday saw the mercury rise to 46.1 degrees Celsius at Najafgarh. The weather stations at Jafarpur and Mungeshpur had recorded maximum temperatures of 45.6 degrees Celsius and 45.4 degrees Celsius, respectively, six notches above normal for this time of the year.

Pitampura also reeled under heatwave conditions, recording a maximum temperature of 44.7 degrees Celsius.

A 'yellow' alert has been issued to caution people about a heatwave on Sunday.

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).

Cloudy skies and thunder may provide some relief from the intense heat next week.

This is the fifth heatwave -- one in March and three in April -- in the capital this summer season.

With scanty rains owing to feeble western disturbances, Delhi had recorded its second hottest April this year since 1951 with a monthly average maximum temperature of 40.2 degrees Celsius. A heatwave at the month-end had sent the mercury soaring to 46 and 47 degrees Celsius in several parts of the city.

The capital got a miniscule 0.3 mm of rainfall in April against a monthly average of 12.2 mm. March saw nil rainfall against a normal of 15.9 mm. The IMD had predicted above normal temperatures in May.

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 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 crosses the 47-degree Celsius mark.