August 2025 Climate Forecast Discussion for the period Sep-Nov through Dec-Feb2025/2026
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 July 2025, sea surface temperature (SST) anomalies remained in the ENSO-neutral range over the central-eastern equatorial Pacific Ocean, with the monthly NINO3.4 anomaly index value at -0.06 °C. The weekly-averaged SST anomalies in the NINO3.4 region were -0.3 °C for the week centered on August 6, 2025. This indicates persistence of the ENSO-neutral state, which is expected to continue through the rest of the summer. However, according to the early August CPC ENSO forecast, a “La Nina Watch” was issued. As per the statement, beginning in fall and continuing into early winter 2025, La Niña conditions are expected to develop, although their likelihood remains low and similar to that of ENSO-neutral conditions. The Indian Ocean Dipole (IOD) index is negative and expected to remain so for the next couple of months, while the North Atlantic Ocean exhibits slightly warm SST anomalies that have decreased substantially.
The IRI Multi-Model Probability Forecasts issued in August 2025 provide a global outlook for precipitation probabilities across four overlapping seasons: September–November (SON), October–December (OND) 2025, November 2025–January (NDJ), and December 2025–February (DJF) 2026. Across the 2025–2026 forecast periods (September, 2025 to February, 2026), the strongest above-normal precipitation probabilities (green to blue shading, often above 60%) are concentrated over the Maritime Continent region—including Indonesia, Papua New Guinea, and northern and eastern Australia—particularly during the SON and OND seasons. During NDJ and continuing into DJF, the signal for above-normal rainfall over this region remains, but is noticeably weaker, with probabilities dropping mostly into the low 40s and 50s. In contrast, as the season progresses into NDJ and DJF, there is a gradual increase in probabilities for above-normal precipitation over southern Africa (especially southeastern areas), parts of Central America, and the northern areas of South America; these regions transition from mostly near-normal conditions towards slightly elevated chances (mostly 40–50%) for wetter than average weather during the heart of the austral summer. Most other regions on the maps exhibit weak or near-climatological signals, with only localized and moderate below-normal probabilities persisting in Central Asia, the Middle East, the Southern US, the Greater Horn of Africa, and southeastern South America (Uruguay).This evolving pattern broadly matches the general La Niña influence expected for 2025–2026, with maritime Southeast Asia and eastern Australia seeing their wettest signals early in the forecast, and southern Africa, Central America, and northern South America turning wetter later on.
The IRI Multi-Model Probability Forecasts for temperature show a widespread and persistent likelihood of above normal temperatures globally from September 2025 through February 2026, with the strongest warming signals (dark red, 70%+ probability) prevailing across most land areas. However, below-normal temperatures are favored over Australia in SON and OND (blue colors), shifting to mostly normal odds during NDJ and DJF, and over Indochina in NDJ and DJF. For North America and South Africa in NDJ and DJF, forecasts indicate climatological odds or slightly below-normal probabilities—meaning no strong signal for either warmer or colder than average during these seasons. Most other regions show a strong tilt toward above-normal temperatures throughout.
