August 2026 Climate Forecast Discussion for the period September-November 2026 through December-February2026-2027
Note: The CCSR/IRI seasonal forecasts of precipitation and temperature issued this month are based on an objective calibration procedure that combines the output from four models: NCEP-CFSv2, CanSIPS-IC4, COLA-RSMAS-CESM1, and NASA-GEOSS2S-2. 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 2026, sea surface temperature (SST) anomalies increased further across the central and eastern equatorial Pacific Ocean. The monthly Niño 3.4 index reached +2.03 °C, marking the transition of the ongoing El Niño event into the very strong category. The most recent weekly Niño 3.4 index value (centered on 05 August 2026) reached +2.6 °C, indicating that El Niño has continued to intensify and confirming the presence of strong El Niño conditions across the tropical Pacific. The IOD is near the positive threshold and trending upward, with the latest weekly value of +0.41°C on 9 August 2026. The North Atlantic registered a value of +0.37 °C in July 2026. The Pacific Decadal Oscillation (PDO) index recorded a value of -1.29 °C in July 2026.
The CCSR/IRI Objective Multi-Model Probability Precipitation Forecast for September–October (SON) 2026 indicates substantially increased probabilities of below-normal precipitation (yellow to brown shading) across northern South America, Central America and the Caribbean, the Indian Peninsula, parts of Australia, and the Maritime Continent. These dry signals persist through the forecast period (OND to DJF) across northern South America, Central America, the western seaboard of South America (including Chile), and the Maritime Continent. The probability of below-normal precipitation also becomes high across southern Africa and Madagascar during the SON–DJF period. In contrast, from SON through DJF, the southwestern United States and adjacent Southern Plains, the southeastern United States, Uruguay and surrounding areas, northeastern Africa, the Middle East, and parts of Eurasia show high probabilities of above-normal precipitation. Many of these dry and wet precipitation patterns are broadly consistent with the expected evolution of El Niño conditions in the central and eastern tropical Pacific, which are forecast to strengthen and peak during fall 2026. However, not all regional precipitation anomalies can be directly attributed to ENSO. Other modes of climate variability, particularly the developing positive Indian Ocean Dipole (IOD), along with regional processes, may also influence these patterns.
The temperature forecasts indicate a high likelihood of above-normal temperatures (red shading) across much of the globe throughout the forecast period. Of particular interest are the regions showing increased probabilities of below-normal temperatures (blue shading), including the southern United States and southeastern South America, particularly Argentina and Uruguay, although the probabilities remain moderate. In the southern United States, this signal becomes more pronounced during NDJ and DJF, while over southeastern South America, the below-normal temperature signal persists across all forecast seasons.
