Global Seasonal Climate Update

WMO has been issuing El Niño/La Niña Updates on a quasi-regular basis over the past 25 years, providing useful real-time information based on expert assessments underpinned by WMO’s role as the UN System’s authoritative voice on weather, climate and water. While these have been well‐received worldwide due to the significant implications of El Niño/La Niña occurrence for regional climate impacts, there has been a persistent and widely expressed need to expand on these products to include more comprehensive information on the seasonal climate, particularly in terms of precipitation and temperature patterns. To complement the WMO El Niño/La Niña Updates, the Sixteenth World Meteorological Congress decided to develop a Global Seasonal Climate Update (GSCU). The GSCU provides information on regional climate anomalies associated with El Niño, La Niña and other climate drivers." The GSCU provides the international community with a global‐scale expert assessment of the ongoing and upcoming seasonal climate along with information on robustness of the available forecast signals.

The GSCU has been designed to be used primarily by WMO Regional Climate Centres (RCCs), Regional Climate Outlook Forums (RCOFs) and National Meteorological and Hydrological Services (NMHSs) as an important global input into their operational activities to elaborate on the ongoing and upcoming seasonal climate on regional and national scales. Additionally, it also caters to the global user needs such as those of the United Nations agencies, humanitarian agencies, the Early Warning Early Action Reports of the Inter Agency Standing Committee (IASC), etc. The Updates are regularly issued a few days ahead of each of the standard seasons (DJF/MAM/JJA/SON). In addition, a simplified version of the GSCU is also being provided every month as an interim update. The coordinators of WMO LC LRFMME, NOAA and KMA have integrated the regular production of GSCU into their operational schedule and have made concerted efforts to ensure its timely provision and dissemination.

The GSCU has a long history over more than a  decade in its making, involving consultations with a wide range of stakeholders,  a trial run, a peer-review process and a pre-operational phase under the  guidance of the World Meteorological Congress, WMO Executive Council and WMO  Technical Commissions.  The GSCU is  currently guided by the WMO Services Commission and Infrastructure Commission. The  key milestones in its development are briefly outlined here.

GSCU for March-April-May 2023

During November 2022-January 2023, all four Pacific Niño sea-surface temperature (SST) indices in the central and eastern Pacific were below-normal. The observed SST conditions in the equatorial Pacific were characterized by a weak La Niña state. The Indian Ocean Dipole (IOD) over the observed period was near zero. The North Tropical Atlantic (NTA) SST index was near zero while the South Tropical Atlantic (STA) SST index was slightly positive.

Near-normal sea-surface temperature anomalies in the Niño 3.4 and Niño 3 regions are predicted during the March-May (MAM) 2023 season indicating a return to the near-normal ENSO conditions. The IOD is also predicted to be nearnormal in MAM 2023. In the equatorial Atlantic, SSTs are predicted to be near-normal in both the northern (NTA) and the southern (STA) areas during the season.

Figure 1: Probabilistic forecasts of surface air temperature and precipitation for the season March-May 2023.
The tercile category with the highest forecast probability is indicated by shaded areas. The most likely category for below-normal, above-normal and near-normal is depicted in blue, red and grey shadings respectively for temperature, and orange, green and grey shadings respectively for precipitation.
White areas indicate equal chances for all categories in both cases. The baseline period is 1993–2009.

Although a tendency towards a return to near-normal ENSO conditions is predicted for the equatorial central and eastern Pacific, warmer-than-average sea-surface temperatures are generally predicted over other oceanic regions and contribute to widespread prediction of above-normal temperatures over land areas. Positive temperature anomalies are expected over most of the land areas in the Northern Hemisphere except for north-western North America and southeast Asia. The largest increase in probabilities for above-normal temperatures are along the northern parts of central America, south-eastern North America, the Caribbean, eastern Maritime Continent, New Zealand, and islands off the coast of northern east Asia. There are also small areas of strong probabilities for abovenormal temperature over the eastern part of South Asia, and southern Europe. There are enhanced probabilities for above-normal temperatures over most of Asia, Europe, Africa north of 15°S, southern South America, and southern and eastern North America. However, over most land areas, the probabilities for above-normal temperature are only weakly or moderately increased. Strongly enhanced probabilities for above-normal temperatures are predicted in a band from north of Australia, extending to the south-eastern South Pacific, and in an arc extending over New Zealand to the vicinity of Tasmania. Many of the southwest Pacific islands lie within this band of above-normal temperatures. From the Maritime Continent east of 120°E, this area with the likelihood of above-normal temperature also extends into the central North Pacific, and at about 40°N stretches almost continuously from the west coast of North America to the east coast of Asia. Near-normal temperatures are expected over eastern coastal regions of Australia, and northeast South America.

Predictions for rainfall are similar to some of the canonical rainfall impacts of La Niña, although ENSO neutral conditions are predicted for MAM 2022-2023. Probabilities for above-normal rainfall are enhanced over an area extending from north of Australia, primarily below the equator, into the Southwest Pacific to an area east of New Zealand, extending to about 120°W. There is an additional narrow band of high probabilities for above-normal rainfall stretching continuously across the Pacific to about 150°W. The likelihood of above-normal rainfall is enhanced over north Asia and northern regions of the Indonesian Archipelago. Much of southern Africa and north-eastern South America extending into the Atlantic below the equator have increased probabilities of above-normal rainfall. A likelihood for anomalously dry is predicted over an area in the equatorial Pacific from the date line to 150°E and extending south of the equator to 100°W. Enhanced probabilities for below-normal rainfall are predicted over the entire Indian Ocean, and in the equatorial western Atlantic extending into the Gulf of Mexico to southwestern North America and into the eastern Pacific adjacent to Central America. The likelihood of near-normal rainfall is enhanced in the equatorial Pacific east of the dateline and in the eastern Atlantic off the coast of western Africa.

Since May 2019 the GSCU is being produced on a regular basis as a pre-operational product and disseminated widely to WMO Members, as well as regional and international partners and United Nations organizations. The GSCU current and past releases are accessible in real time through a dedicated web page of LC-LRFMME website.