New Delhi, June 16 -- This May, India has seen an unprecedentedly early and rapid monsoon. The India Meteorological Department (IMD) officially reported Kerala's monsoon onset on May 24-a full week earlier than the usual June 1. Mizoram experienced rainfall on the same day, roughly 12 days earlier than normal. By May 26, the monsoon had reached Mumbai (its earliest arrival in 25 years) and was sweeping across Maharashtra, Karnataka, Telangana and even parts of Northeast India. Normally it takes 10-11 days for the monsoon to progress from Kerala to Mumbai, but this year that journey took barely two days.

Even before the calendar monsoon began, India saw torrential, unseasonal rain in May. An unusually high incidence of Western Disturbance...