May 2026 Climate Forecast Discussion for the period June-Aug through Sep-Nov 2026
**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 April 2026, sea surface temperature (SST) anomalies rapidly warmed across the central-eastern equatorial Pacific Ocean, with the monthly Niño 3.4 index reaching 0.47 °C. Over the past four weekly Niño 3.4 index observations (15 April to 06 May), values ranged from +0.5 °C to +0.9 °C, indicating that short-term conditions remained consistently above the El Niño threshold. The early May CPC ENSO forecast, issued under an “El Niño Watch,” indicates that the onset of El Niño is likely during May–July with an 82% probability and is expected to persist through at least the end of 2026. (It is important to note that ENSO monitoring and prediction issued by CPC is now based on the relative Niño 3.4 index). The Indian Ocean Dipole (IOD) index is currently in a neutral state. The North Atlantic registered a value of +0.07 °C, while the South Atlantic showed gradually increasing warming, reaching +0.64 °C in April 2026. The Pacific Decadal Oscillation (PDO) index recorded a value of -1.25 °C in March 2026.
The CCSR/IRI objective Multi-Model Probability Precipitation Forecast for June–August (JJA) 2026 shows increased odds 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. This dry signal persists into July–September (JAS), August–October (ASO), and September–November (SON), though its strength and spatial extent vary by region. During JJA and JAS, increased probabilities of below-normal precipitation are also indicated over Ethiopia and the southwestern Arabian Peninsula. In ASO, a weak signal of below-normal precipitation probability appears over the southeastern United States, while by SON, parts of southern Africa also show a modest tilt toward below-normal precipitation probabilities. During ASO, the southwestern United States and Mexico show increased probabilities of above normal precipitation, with this signal extending and strengthening into the southern United States during SON. In the same period, probabilities also tilt toward above normal precipitation over Uruguay and southern Chile, as well as parts of northeast Africa, the Middle East, southern Madagascar, and Southwest Asia. While many of these precipitation signals are consistent with the developing El Niño conditions in the central eastern Pacific expected to mature during the summer and early fall of 2026, not all regional anomalies are necessarily directly linked to the evolving ENSO state.
The temperature forecasts indicate that above-normal temperatures (red shading) are highly probable across most seasons in much of North America, northern and central Eurasia, the Middle East, Asia, and large portions of Africa and South America. In June–August, areas of below-normal temperatures (blue shading) are notable in parts of southeastern Australia. During August–October and September–November, parts of central North America, including the northern United States and southern Canada, show a tendency toward below-normal temperature probabilities.
