The present normal monsoon onset and withdrawal dates are based on records of only a few stations (149 stations) during the period 1901-1940.
India Meteorological Department (IMD) has now revised the normal onset and withdrawal dates based on recent data. The normal dates of onset are revised based on data during 1961-2019 and normal dates of withdrawal are revised based on data during 1971-2019.
IMD has designed new objective criteria for defining monsoon onset over the entire country based on daily gridded (1ox1o) rainfall data set. The new objective criteria used for deciding monsoon onset/progress dates are designed so as to closely simulate IMD's operational onset dates. However, the new withdrawal dates are fixed using the IMD's operational withdrawal dates during 1971-2019.
Monsoon onset over Kerala remains the same, i.e., 1 June. However, new monsoon advance dates over the states like Maharashtra, Gujarat, Madhya Pradesh, Chattisgarh, Telangana, Andhra Pradesh, Odisha, Jharkhand, Bihar and parts of Uttar Pradesh are delayed by 3-7 days compared to existing normal dates.
However, over extreme northwest India, the monsoon arrives now little earlier, on 8th July compared to the existing date of 15th July. There are however appreciable changes in the monsoon withdrawal dates, especially over Northwest and Central India.
Monsoon withdraws from NW India almost 7-14 days later from the existing dates. There is no change in the final withdrawal date over south India, i.e., 15th October.
These new dates are relevant for many applications like agriculture, water and power management etc.
Here's the full list of IMD dates for monsoon 2020;
IMD
IMD
IMD
