![]() ENSO events with a peak value above 1.5☌ (El Niño) or below -1.5☌ (La Niña) are considered strong. For La Niña events, the threshold is -0.65☌. To classify a historical El Niño event, the 3-month average Nino3.4 value must be above 0.65☌ for 5 or more consecutive months. The solid blue and yellow lines note the La Niña and El Niño thresholds used by MSS, while the dotted lines note the thresholds used by some other international centres. From June, models predict an increase in the chance of El Niño conditions, with models predicting either ENSO neutral or El Niño conditions in July and August 2023, although there is considerable uncertainty in the long-term forecasts at this time of the year.įigure 3: Forecasts of Nino3.4 index’s strength until September 2023 from various seasonal prediction models from international climate centres (grey lines). Model outlooks from Copernicus C3S (Figure 3), based on the Nino3.4 SST index, show that models predict ENSO neutral conditions are likely to continue in April and May 2023. Warm anomalies (≥ +0.65 brown) correspond to El Niño conditions while cold anomalies (≤ -0.65 blue) correspond to La Niña conditions otherwise neutral (> -0.65 and < +0.65 grey). ![]() La Niña conditions are considered to have ended when the 1-month SST anomalies are above the threshold, as well as atmospheric conditions no longer indicate La Niña conditions.įigure 2: The Nino3.4 index using the 1-month SST anomalies. La Niña conditions are considered present when the 1-month cold SST anomalies (observed or forecast) persist or are predicted to persist for at least four months below the threshold, along with supporting atmospheric observations. From the end of 2022 onwards, there has been a gradually warming of the index, returning to the ENSO-neutral range by March 2023. Looking at the Nino3.4 index in Figure 2, starting in 2021, there was a prolonged period of the 1-month Nino3.4 index being within the La Niña range. The Indian Ocean Dipole index is the difference between average SST anomalies over the western Indian Ocean (black solid box) and the eastern Indian Ocean (black dotted box). The tropical Pacific Ocean Nino3.4 Region is outlined in red. Red (blue) shades show regions of relative warming (cooling). Across the Indian Ocean, while the SSTs are cooler than average, the eastern portion is only slightly cooler than the western portion, indicating that the Indian Ocean Dipole is neutral.įigure 1: Detrended SST anomalies for March 2023 with respect to 1976-2014 climatology using ERSST v5 data. The sea surface temperatures (SSTs) over the central and eastern tropical Pacific overall represented ENSO-neutral conditions in March 2023 (Figure 1) The SSTs continued to warm in March, although still were cooler than average in the Nino3.4 region (red box). Therefore, variations between centres on the current ENSO state should be expected, especially when conditions are borderline. Each centre uses different criteria, including different SST thresholds. The centres include the Climate Prediction Center (CPC) USA, the Bureau of Meteorology (BoM) Australia, as well as information from the International Research Institute for Climate and Society (IRI) which consolidates model outputs from other centres around the world. Sub-surface temperatures in the eastern Pacific should also be warmer (colder) than average, to sustain the El Niño (La Niña) conditions.įor ENSO outlooks, information from the World Meteorological Organization (WMO) and international climate centres are assessed. There is also a decrease (increase) in the trade winds in the eastern Pacific. ![]() El Niño (La Niña) conditions also correspond to an increase (decrease) in cloudiness around or to the east of the international dateline (180°), with a decrease (increase) in cloudiness in the west. The threshold for an El Niño (La Niña) in the Nino3.4 region is above 0.65☌ (below -0.65☌). ![]() So far, there has been no noticeable background trend in the low-level winds or cloudiness.Įl Niño (La Niña) conditions are associated with warmer (colder) SSTs in the central and eastern Pacific. Therefore, this background trend is removed from the SST datasets ( Turkington, Timbal, & Rahmat, 2018), before calculating SST anomalies using the climatology period 1976-2014. As globally, SSTs have gradually warmed over the last century under the influence of climate change, the SST values over the Nino3.4 will increasingly be magnified with time, and hence appear warmer than they should be. Here, three different datasets are used: HadISST, ERSSTv5, and COBE datasets. Special attention is given to SSTs, as they are one of the key indicators used to monitor ENSO. ENSO conditions are monitored by analysing Pacific sea surface temperatures (SSTs), low level winds, cloudiness (using outgoing longwave radiation), and sub-surface temperatures.
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