July 2024 Climate Forecast Discussion for the period Aug-Oct 2024 through Nov-Jan 2025
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, 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. 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.
This month (July 2024), CanSIPS-IC4 (from ECCC, Canada) has become operational, leading the IRI-Seasonal Forecasts to switch from CanSIPS-IC3 to CanSIPS-IC4. Further details can be found here: https://iridl.ldeo.columbia.edu/SOURCES/.Models/.NMME/.CanSIPS-IC4/
During June 2024, there was a further weakening in the positive sea surface temperature (SST) anomalies over the central-eastern equatorial Pacific Ocean compared to the preceding month, leading to a NINO3.4 anomaly index value of +0.24 °C. The weekly-averaged SST anomalies in the NINO3.4 region were +0.30 °C for the week centered on July 03, 2024. This shows that the ENSO-neutral state is ongoing in the equatorial Pacific Ocean. According to the early-July CPC ENSO forecast, ENSO-neutral is expected to continue for the next several months, along with an onset of La Niña during Aug-Oct, 2024 (70% chances), which will persist thereafter. The Indian Ocean Dipole (IOD) index is currently neutral. The North Atlantic Ocean continues to exhibit persistent warm SST anomalies. Forecasts indicate that the warming in the North Atlantic Ocean will continue for the next couple of months while the Indian Ocean Dipole is forecasted to remain in the neutral state.
IRI’s seasonal precipitation forecasts issued in July 2024 show elevated probabilities of above-normal precipitation in Central America and Caribbean regions, Southwestern parts of the Arabian Peninsula, South Asia, the Maritime Continent regions, parts of China and Australia during the three forecasts seasons (Aug-Oct, Sep-Nov, and Oct-Dec, 2024). Over the Sahel region, the forecasts indicate elevated probabilities of above-normal precipitation in Aug-Oct 2024. However, these probabilities diminish in Sep-Nov 2024 and are no longer present in the subsequent (Oct-Dec, and Nov-Jan) forecast periods. The forecast shows elevated probabilities of below-normal precipitation over different parts of South America (e.g., northeast South America, over and around Uruguay, and southern Chile) during the forecasts period. The forecast also shows increasing probability of below-normal precipitation over the western and central parts of the U.S., and most of Mexico in Aug-Oct, and Sep-Nov 2024, while during Oct-Dec, and Nov-Jan, most of the southern U.S. and northern Mexico show a strong shift towards below-normal signal. There is a gradual shift towards below-normal signal over the Middle East starting from Aug-Oct 2024, to the end of the forecast period. Many, while not all, of these precipitation patterns align with historical La Niña events, in line with the forecasted onset of La Niña in next couple of months.
Regarding temperature, strongly enhanced probabilities for above-normal temperature are forecasted across most land areas throughout the forecast period. The forecast shows elevated probabilities (though weak) of below-normal temperatures over scattered parts of Sahel in Aug-Sep, 2024. The forecasts also show probability shift towards below-normal temperatures over southern Alaska, and different parts of central southwest Asia in Sep-Nov, Oct-Dec, and Nov-Jan, 2025.
