India, June 5 -- The India Meteorological Department (IMD) on Thursday announced the onset of the southwest monsoon over Kerala, nine days later than its forecast of May 26 and three days after the normal onset date of June 1. How usual or unusual is an onset delay of three days? Does a delay suggest that rainfall performance will be poor? Here are five charts that answer these questions:

A delay of three days in onset over Kerala is just about usual

The criteria for declaring monsoon onset over Kerala has changed somewhat over time. However, the back-series of onset dates determined using the criteria currently in use is available from 1971. This shows that a three-day delay is just about usual. 28 of 56 years have seen monsoon onset o...