September 2021 Climate Forecast Discussion

Sep 2021 Climate Forecast Discussion for Oct-Dec through Jan-Mar

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

The sea surface temperature (SST) and most atmospheric indicators in the tropical Pacific are currently neutral. However the SST forecasts of the models used in this seasonal climate forecast predict a re-emergence of cool SST anomalies and enhanced likelihood of a second La Niña event (5 consecutive overlapping seasons, according to NOAA’s definition). The La Niña forecasted in the coming seasons does impact the associated seasonal climate forecast. The strongest Atlantic Niño event ever observed has weakened, as has the negative Indian Ocean Dipole, and these two potential drivers are predicted to return to the neutral state in the coming seasons.

For temperature, the Oct-Dec and Nov-Jan forecasts favor above-normal temperatures over most land areas, with particularly enhanced probabilities over Maritime Continent, South Asia, large parts of African continent, much of North America, eastern Canada, and southern South America. For the last two seasons (Dec-Feb and Jan-Mar), the temperature forecast over most of these regions show weakened likelihood for above-average conditions, as confidence typically decreases with forecast lead time. In Oct-Dec, enhanced probabilities of below-normal temperatures are forecasted for much of Australia except its northern coasts, and some parts of central Brazil, tending to diminish in the subsequent seasons.