May 2023 Climate Forecast Discussion

May 2023 Climate Forecast Discussion for Jun-Aug through Sep-Nov 2023

**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 April 2023, equatorial sea surface temperatures (SSTs) in the central-eastern equatorial Pacific Ocean remained at an ENSO-neutral level (the NINO3.4 index value in April 2023 was +0.19 °C). The current SST anomalies in the region have reached the El Niño threshold on a weekly basis (as of the week of 10 May, the NINO3.4 index was 0.5 °C). Based on the early-May CPC ENSO forecast, the tropical Pacific is expected to shift from an ENSO-neutral state to El Niño over the next couple of months, with a very high likelihood (greater than 90%) of El Niño persisting until boreal winter. An El Niño watch remains in effect. Both observations and model forecasts indicate the presence of mild warm SST anomalies in the Atlantic Ocean, while the forecasts also suggest the emergence of a positive Indian Ocean Dipole during the boreal summer.

The multi-model precipitation forecasts indicate gradually increasing probabilities of above-normal precipitation over the southeast South America, the African Sahel and Greater Horn of Africa, Madagascar, and over the Middle East during the forecast period. Increased probabilities of below-normal precipitation are forecasted over northern South America, Central America and parts of the Caribbean, parts of the Maritime Continent, South Asia, and most of Australia. Many, though not all, of these precipitation patterns are consistent with historical El Niño events.

For temperature, enhanced probabilities for above-normal temperature are forecasted over most land areas throughout the forecast period. Weakly enhanced probabilities of below-normal temperatures are forecast in Jun-Aug 2023 for some parts of northern South America, parts of Madagascar, northwest South Asia, and southeastern Australian regions. The forecasts continue to show slightly enhanced probability of below-normal temperatures at those locations for the remainder of the forecast period, although the probability values and effective areas tend to decrease.