Overview

• ENSO has been neutral since March 2025 with equatorial Pacific sea surface temperatures near average, and models indicate a shift toward La Niña could begin in September.
• WMO assigns a 55% probability of La Niña for September–November and about 60% for October–December, with little chance of El Niño in that window.
• Despite La Niña’s cooling influence, forecasts point to above-normal temperatures for September–November across much of the Northern Hemisphere and large parts of the Southern Hemisphere.
• WMO cautions that regional outcomes will vary and be shaped by other climate drivers, including the North Atlantic Oscillation, Indian Ocean Dipole and Arctic Oscillation.
• The Met Office says any La Niña effect on the UK is likely to emerge gradually with little clear signal before October, noting past tendencies for either mild, wet winters or a cold start followed by a milder end.