October 2021 Climate Forecast Discussion

Oct 2021 Climate Forecast Discussion for Nov-Jan through Feb-Apr

Note: The IRI seasonal forecasts issued this month are based on the NCEP-CFSv2, CanSIPsv2, and COLA-RSMAS-CCSM4, and GFDL-SPEAR models. This month’s forecasts also use the new climatological normal period 1991-2020.

The oceanic and atmospheric patterns in the tropical Pacific during September are consistent with La Niña. The early October CPC/IRI sea surface temperature (SST) forecast in the eastern equatorial Pacific indicates high probabilities of La Niña developing during the upcoming winter, and a La Niña advisory has been issued accordingly. Unanimously, models used in this seasonal climate forecast predict cooler than average SST anomalies and an enhanced likelihood of a second-year La Niña event (5 consecutive overlapping seasons, according to NOAA’s definition), which does impact the associated seasonal forecasts of precipitation and temperature. The strongest Atlantic Niño event ever observed is waning gradually, as has the negative Indian Ocean Dipole and these two additional drivers are predicted to return to the neutral state in the coming seasons.

For temperature, high probabilities of above-normal temperatures are predicted over most land areas, with particularly high and consistent probabilities over Maritime Continent, parts of South Asia, the Middle East, large parts of African continent, much of North America, eastern Canada, and southern South America. Enhanced probabilities of below-normal temperatures are forecasted for northwestern regions of US and Canada in Nov-Jan, and later forecast periods. In addition, Dec-Feb, Jan-Mar, and Feb-Apr forecast shows near- or slightly below- normal temperature probabilities over northern South America, southern tropical belt of African landmass, and some parts of western Australia.