October 2025 Climate Forecast Discussion
October 2025 Climate Forecast Discussion for the period Nov-Jan through Feb-Apr 2026
**Note: ** The IRI seasonal forecasts of precipitation and temperature issued this month are based on an objective calibration procedure that combines four models NCEP-CFSv2, CanSIPS-IC4, COLA-RSMAS-CESM1, and NASA-GEOSS2S models. The climatological base period for normal is 1991-2020. The SST anomalies cited below refer to the OISST.v2.1 SST data set. Starting from June 2024, the observed climatology used to compute the dry mask was updated to 1991-2020, and the criterion modified to mask points where 10% of the training sample (i.e. 3 or more years) received less than or equal to 1 mm over a 3-month season.
During September 2025, sea surface temperature (SST) anomalies remained within the ENSO-neutral range over the central-eastern equatorial Pacific Ocean, with the monthly Niño 3.4 anomaly index at -0.44 °C. Weekly-averaged SST anomalies in the Niño 3.4 region were -0.3 °C for the week centered on October 8, 2025, indicating the persistence of cooler sea surface temperatures still within the ENSO-neutral range. The early October CPC ENSO forecast, issued a “La Nina Advisory”. According to the statement, La Niña conditions are present and are favored to persist through December 2025 – February 2026, with a 55% chance of transitioning to ENSO-neutral conditions during January–March 2026. The Indian Ocean Dipole (IOD) index is negative and is expected to remain so over the next couple of months. Meanwhile, the North Atlantic Ocean continues to exhibit slightly warm SST anomalies, although they have decreased substantially. Additionally, the Pacific Decadal Oscillation (PDO) Index recorded a value of -2.38 in September, following a stronger negative value of -3.23 in August and a record-breaking low of -4.12 in July 2025.
The IRI Multi-Model Probability Precipitation Forecast for November–January (NDJ) 2026 indicates increased likelihoods of above-normal precipitation (green/blue shading) across parts of Southeast Asia, Indonesia, and northern Australia, and of below-normal precipitation (yellow to brown shading) over Mexico, the southern United States, the Mediterranean, eastern China, and portions of northern South America. Large areas of central Africa lie in the dry season (no forecast). These general patterns persist through DJF and JFM 2026, with some slight weakening of the above-normal signal over Southeast Asia and northern Australia, and expansion of below-normal signals into western Europe and northern Africa. Central Africa remains in its dry season, with forecasts withheld. By FMA 2026, the increased likelihood of above-normal precipitation weakens but remains present in northern Australia, Southeast Asia, and emerges in northern Europe and eastern Asia. Slightly enhanced probabilities of below-normal precipitation continue to be forecast across Mexico, the southern U.S., northern Africa, and western Europe, reflecting persistent dry signals into early 2026.
The temperature forecasts indicate that above-normal temperatures (red shading) are highly probable in nearly all seasons across much of North America, northern and central Eurasia, the Middle East, and large portions of Africa and South America. Regions with gray shading, notably portions of South America (including the Amazon basin and southern South America), Central Africa, and southeastern Australia, reflect areas where the probability of the normal temperature category is dominant, indicating outcomes close to the climatological median. In contrast, the multi-model forecasts for the Northern Hemisphere cold season of 2026 (NDJ, DJF, JFM) highlight increased probabilities of below-normal temperatures (blue shading) across western Canada and Alaska. Additionally, enhanced probabilities for below-normal temperatures appear in parts of northern Eurasia—especially segments of Siberia and far-northeastern Russia—during upcoming winter of 2026.