October 2024 Climate Forecast Discussion
Oct 2024 Climate Forecast Discussion for the period Nov-Jan through Feb-Apr 2025
**Notes: ** The IRI seasonal forecasts of precipitation and temperature issued this month are based on an objective calibration procedure that combines the NCEP-CFSv2, CanSIPS-IC4, COLA-RSMAS-CESM1, GFDL-SPEAR, 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.
In September 2024, slightly negative sea surface temperature (SST) anomalies emerged over the central-eastern equatorial Pacific Ocean, resulting in a NINO3.4 anomaly index value of -0.15 °C, whereas the SST anomalies from June to September 2024 were -0.0 °C. This suggests the continuation of the ENSO-neutral state in the equatorial Pacific Ocean. According to the early-October CPC ENSO forecast, La Niña is favored to emerge in September-November (60% chance) and is expected to persist through January-March 2025. The Indian Ocean Dipole (IOD) index is currently in a neutral state. The North Atlantic Ocean continues to exhibit persistent warm SST anomalies, which are expected to persist for the next few months. Forecasts suggest that the Indian Ocean Dipole will remain neutral or potentially develop into a weak negative IOD event.
The IRI's seasonal precipitation forecasts issued in October 2024 suggest an increased likelihood of above-normal rainfall in northern North America, Central America, northern South America, the Caribbean, Southeast Asia, the Maritime Continent, and Australia throughout the forecast period. There is a heightened probability of below-normal precipitation for most of the Southern U.S. and Mexico during much of the forecast period. A weak probability of below-normal precipitation is also anticipated over northeastern South America for Nov-Jan 2025, while the remainder of the forecast period shows climatological odds over most of South America. During Nov-Jan and Dec-Feb 2025, forecasts indicate a shift towards below-normal precipitation in East Africa, the Arabian Peninsula, and central Southwest Asia; however, this probability diminishes in the final two seasons (Jan-Mar and Feb-Apr 2025). Many of these precipitation patterns align with historical La Niña events and are consistent with the forecasted onset of La Niña in boreal autumn and its persistence through boreal winter. It is noteworthy that the uncertainty regarding the onset of La Niña has increased compared to previous months, potentially indicating reduced influence from the tropical Pacific in the current forecasts.
Regarding temperature, the forecasts indicate a strong likelihood of above-normal temperatures across most land areas throughout the forecast period. There are elevated, though weak, probabilities of below-normal temperatures over parts of western Canada, the central U.S., and Alaska extending into Jan-Mar and Feb-Apr 2025. Additionally, forecasts suggest that temperatures in northern South America, Southeast Asia, and northwestern Australia are expected to remain near normal (gray shading) during Jan-Mar and Feb-Apr 2025.