Delhi witnessed maximum temperatures below 40 degrees between May 5th and 10th. However, on May 8 and 9 temperatures reached 40 Degrees. Maximum of Delhi and NCR increased significantly between May 10 and 22nd. Parts of Delhi and NCR recorded more than 49 degrees on May 15th, which was the highest temperature ever recorded over Delhi during May.
The reason for the drop in temperature over Northwest India including Delhi can be attributed to the heavy downpour on May 22nd and 23rd over Delhi and NCR. Many parts of Punjab, Haryana, North Rajasthan, and western parts of Uttar Pradesh also witnessed good rain and thundershower activities along with isolated hailstorms. Easterly winds from the Bay of Bengal continued over Indo Gangetic plains and did not allow temperatures to increase much.
Winds have changed direction from easterly to westerly since May 28. Dry and hot westerly winds have increased the temperatures over many parts of Northwest India including Delhi. We expect temperatures to increase further, but it will not reach the threshold value of heat wave. Therefore, we can say despite an increase in temperature heat wave is not going to make a comeback anytime soon over northern plains including Delhi and NCR.