The late retreat of the four-month long monsoon is the 13th consecutive delayed withdrawal. It’s onset over Kerala this year happened on June 8, against the normal date of June 1. The monsoon season technically ends on September 30, but the withdrawal process normally continues till mid-October.
Although the retreat has begun, the monsoon rally continues in other parts. September has so far seen a 16% rainfall surplus in the country.
Announcing the beginning of its delayed withdrawal by eight days this year, the IMD noted that the withdrawal fulfilled all three required meteorological conditions such as no rainfall during the last five days in the region, formation of an anti-cyclonic circulation at lower tropospheric levels and dry weather conditions based on water vapour imagery.
Meanwhile, the Met department predicted sporadic light to moderate and heavy rainfall in different states till September 29 — the situation which may bring the overall monsoon closer to normal. The IMD had initially predicted a ‘normal’ monsoon this year at 96% of the long period average (LPA) with an error margin of +/- 4%.
It had, however, later indicated it to be ‘below normal’ (90-95% of the LPA) based on the huge monthly deficit of August. Monsoon rainfall between 96-104% of the LPA (average rainfall in the 1971-2020 period) is considered ‘normal’.
The monsoon, however, revived spectacularly in September, bringing the overall cumulative deficit from 11% early in the month to 5% on Monday. The revival is attributed to conditions in the Indian Ocean turning favourable (a positive Indian Ocean Dipole) and a favourable phase of Madden-Julian Oscillation (MJO) — an eastward moving pulse of cloud and rainfall near the equator — known for increasing convection in the Bay of Bengal and the Arabian Sea.
