Note: The CCSR/IRI seasonal forecasts of precipitation and temperature issued this month are based on an objective calibration procedure that combines forecasts from four models using the Extended Logistic Regression (ELR) method. The four NMME models are CanSIPS-IC4, CFSv2, COLA-RSMAS-CESM1, and NASA-GEOSS2S. 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 August 2026, sea surface temperature (SST) anomalies strengthened further across the central and eastern equatorial Pacific, with the monthly Niño 3.4 index reaching +2.52°C, placing the ongoing El Niño event firmly in the “very strong” category. The latest weekly Niño 3.4 index, centered on 9 September 2026, rose to +2.9°C, indicating continued strengthening of El Niño conditions across the tropical Pacific. Meanwhile, the Indian Ocean Dipole (IOD) has moved into positive territory, with the latest weekly value reaching +0.65°C for 7–13 September 2026.
The CCSR/IRI objective multi-model probability precipitation forecast for October–December (OND) 2026 indicates increased probabilities of below-normal precipitation (yellow to brown shading) across northern South America, parts of Central America, South Africa, Southeast Asia, and the Maritime Continent. These dry signals persist through the forecast period (NDJ to JFM) across several regions, although the intensity and spatial extent vary by region and forecast period. The probability of below-normal precipitation also increases across Alaska, northwestern Australia, and Madagascar during the DJF–JFM period. In contrast, the outhern United States—including the Southwest, Southeast, and adjacent Southern Plains—along with Uruguay and surrounding areas, northeastern Africa, the Middle East, and parts of Eurasia show high probabilities of above-normal precipitation during the forecast period. Many of these wet and dry precipitation patterns are broadly consistent with the ongoing El Niño conditions across 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, together with regional processes, may also influence these patterns.
The temperature forecasts indicate a high likelihood of above-normal temperature (red shading) across much of the globe throughout the forecast period. Of particular interest are regions showing increased probabilities of below-normal temperatures (blue shading), including Uruguay and surrounding areas during OND and NDJ, and the southern and southeastern United States during DJF and JFM.
