Kuldeep Srivastava, head of the regional forecasting centre of the India Meteorological Department (IMD), said monsoon clouds led to rains in parts of Delhi.
He said the onset of the monsoon will be declared on Thursday. Rainfall data from all weather stations for the last 24 hours ending 8:30 am is required to declare the onset, Srivastava added.
The Met department also predicted heavy rainfall at isolated places in the national
capital on Thursday.
Normally, the wind system reaches Delhi on June 27.
According to weather experts, the arrival of the monsoon in Delhi earlier than usual can be attributed to a cyclonic circulation, which moved towards southwest Uttar Pradesh on June 19 and June 20, helping the monsoon advance further.
With rains expected over the next three days, the mercury is likely to hover around 36 degrees Celsius.