IMD Criteria for Confirming Southwest Monsoon Arrival in Kerala
The arrival of rain at the end of May is often considered the onset of the Southwest monsoon (Edavapathi), but the Indian Meteorological Department (IMD) disagrees with this assumption. The internet is currently abuzz with memes and speculation about whether the monsoon has truly arrived. The reason for this contradiction lies in the IMD’s specific criteria for confirming the monsoon’s onset.
The IMD uses three main criteria to confirm the onset of the monsoon:
Rainfall: Nine out of 14 designated rain gauges in Kerala, Karnataka, and Lakshadweep must record 2.5 mm or more of rain for two consecutive days. These locations include Thiruvananthapuram, Punalur, Kollam, Alappuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kasaragod, Mangalore, Minicoy, and Amini.
Wind Field: Even with adequate rainfall, the monsoon cannot be confirmed if the west wind is not strong. The west wind should extend up to 4.5 km high between 10 degrees latitude and 55-80 degrees longitude in the Arabian Sea.
Outgoing Longwave Radiation (OLR): The heat radiation from the ground should be less than 200 watts per square meter, indicating sufficient cloud cover. Higher radiation levels suggest less cloud cover, preventing confirmation of the monsoon.
