India, Oct. 27 -- India's 2026 southwest monsoon ended 12.6% below normal, the weakest season since 2015. Behind the shortfall is a warming of the equatorial Pacific Ocean, thousands of kilometres away, and an Indian Ocean pattern that came too late to help this time.

What El Nino is

El Nino is the warm phase of a natural climate cycle in the tropical Pacific. Every few years, surface waters in the central and eastern Pacific become unusually warm, and that changes where the heaviest rain-bearing clouds form. For India, the shift usually means a weaker monsoon.

Scientists track it through the Nino-3.4 region, a band of the central equatorial Pacific. On October 8, sea-surface temperatures there were 2.1degC above normal - in the "stron...