Modi's swearing-in ceremony will be an open air event at the forecourt of Rashtrapati Bhavan.
The minimum temperature settled six notches below average at 21.4 degrees Celsius.
"The skies will turn partly cloudy with thundershower and possibility of rain," said the India Meteorological Department (IMD) official.
Overnight rains brought down the soaring temperatures.
The city has so far recorded 12.6 mm of rainfall.
Sunday's maximum temperature was recorded at 39.3 degrees Celsius, one notch below the season's average, while the minimum temperature was recorded two notches below the season's average at 24.2 degrees Celsius.