April 2025 Climate Forecast Discussion for the period May-Jul through Aug-Oct 2025
**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, GFDL-SPEAR, 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.
**Note: ** NASA-GEOS2S data is unavailable due to technical issues at the time this forecast was published.
During March 2025, negative sea surface temperature (SST) anomalies weakened further over the central-eastern equatorial Pacific Ocean, leading to a monthly NINO3.4 anomaly index value of 0.10 °C. The weekly-averaged SST anomalies in the NINO3.4 region were -0.1 °C for the week centered on Apr 02, 2025. This indicates ENSO-neutral conditions. According to the early-April CPC ENSO forecast, a Final La Niña Advisory was issued with the dominance of the ENSO-neutral conditions expected during the Northern Hemisphere summer. The Indian Ocean Dipole (IOD) index is neutral, and the North Atlantic Ocean continues to exhibit persistent warm sea surface temperature (SST) anomalies.
The IRI's seasonal precipitation forecasts, issued in April 2025, forecast an increased likelihood of above-normal precipitation in several regions during May–Jul 2025. These include Alaska, western Brazil, the African Sahel, equatorial East Africa, Southwest Asia, and the Maritime Continent. Conversely, the forecasts indicate a heightened probability of below-normal precipitation in the northwestern and southwestern United States, southern Chile, central Southwest Asia, and West Africa during the same period. For the African Sahel and Southwest Asia, the enhanced probability of above-normal precipitation is expected to persist throughout their rainy seasons (Jun-Aug to Aug-Oct). The forecasts indicate gradually increasing probability of above-normal precipitation by Jul-Sep in the southern Australia which then gradually spreads across much of the continent, with probabilities exceeding 60% in some areas by Aug–Oct 2025. Meanwhile, regions with below-normal precipitation probabilities in the southern and southwestern United States are projected to shift northward and weaken over subsequent seasons. Additionally, persistent increased probabilities of below-normal precipitation are forecast for northeastern South America and western African countries near the Gulf of Guinea during Jun–Oct 2025.
In terms of temperature, most land areas are projected to have a significantly higher likelihood of experiencing above-normal temperatures throughout the forecast period. However, the forecasts also suggest a slightly increased chance of below-normal temperatures in the African and Asian Monsoon regions during Jul-Sep and Aug-Oct 2025.
