Do you know, how does the India Meteorological Department (IMD) forecast monsoon?

IMD has divided India into 36 meteorological subdivisions for the purpose of issuing of weather forecasts. Also, there are a number of regional offices and national level offices that coordinate with these subdivisions and run forecasting models.

“In order to maintain the required standards and to bring about uniformity among all forecasting offices, various procedures have been formulated by IMD. These procedures also facilitate the meteorological research community to assess various actions adopted by IMD in an objective manner. These procedures include various criteria for onset and withdrawal of Indian Summer Monsoon, description of spatio-temporal distribution of rainfall during the season, formats for issuance of intensity and activity of weather forecasts and warnings, etc.,” as per the Monsoon Monograph.

The arrival of South-West (SW) monsoon currents over the Andaman Seas, its onset over the main Indian landmass and the further advance is monitored closely. Bulletins are issued regularly by regional monitoring centres and also by the Weather Central, Pune, of course, with prior consultation to avoid sending out contradictory messages.

IMD starts by tracking the SW monsoon from May 10th onwards each year. Remember in part 2 of this series we saw when and how is monsoon onset declared over Kerala?

Next step is to monitor and forecast rainfall owing to further advance that is based “on the occurrence of rainfall over parts / sectors of the sub-division and maintaining the spatial continuity of the northern limit of monsoon.

And then, IMD also monitors and tells us when the SW monsoon starts withdrawing and when the withdrawal is complete, before it starts monitoring onset and withdrawal of NE monsoon.

Image: IMD’s 36 meteorological subdivisions.

---- to be continued