October 2023 Climate Forecast Discussion

Oct 2023 Climate Forecast Discussion for the period Nov-Jan 2024 through Feb-Apr 2024

Note: The IRI seasonal forecasts of precipitation and temperature issued this month are based on an objective calibration procedure that combines the NCEP-CFSv2, CanSIPS-IC3, COLA-RSMAS-CCSM4, and 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.

In September 2023, sea surface temperatures (SSTs) in the central-eastern equatorial Pacific Ocean were well above the El Niño threshold (the NINO3.4 index value in September 2023 was +1.53 °C), while the weekly-averaged SST anomalies in the NINO3.4 region was +1.5 °C during the week centered on 04 Oct 2023. According to the early-October CPC ENSO forecast, the tropical Pacific is experiencing El Niño conditions and an El Niño Advisory remains in place. The observational data reveals a notable warming in the North Atlantic Ocean alongside a significantly positive Indian Ocean Dipole. Forecasts indicate that the warming in the North Atlantic Ocean and the positive Indian Ocean Dipole are expected to persist over the next two seasons (Nov-Jan, and Dec-Feb, 2024), both gradually weakening towards the end of the forecast period (Jan-Mar, and Feb-Apr, 2024).

Moderately enhanced probabilities for below-normal precipitation are predicted for most of northeastern South America, the Maritime Continent, South Africa, Southern Madagascar, and some parts of Australia during much of the forecast period. A strong tilt of the odds toward above-normal precipitation is predicted over and around the Greater Horn of Africa, the Middle East, and central and South Asia during the forecast period. Moderately enhanced probabilities for above-normal precipitation are also forecasted over and around Uruguay, southern and southeast US, and northern and eastern China during the forecast period, though values decrease gradually by the end of the forecast period. Many, though not all, of these precipitation patterns are consistent with historical El Niño as well as positive Indian Ocean Dipole events.

Regarding temperature, strongly enhanced probabilities for above-normal temperature are forecasted across most land areas throughout the forecast period. A few local instances of enhanced probabilities for below-normal temperature do appear locally, most notably over southern half of Madagascar throughout the forecast period. The forecast indicates near equal chances of the three temperature tercile categories for much of the United States during the forecast period.