El Niño/La Niña Update (September 2024)

As of mid-August 2024, the tropical Pacific remains in a neutral state of the El Niño–Southern Oscillation (ENSO). The WMO Global Producing Centres of Long-Range Forecasts anticipate a possible transition to La Niña, with approximately a 55% chance in September-November, increasing to 60% during the subsequent three-month periods of October-December, November-January and December-February. The chance of ENSO neutral conditions persisting is estimated at 45% for September-November and 40% thereafter. The chance of El Niño developing during the forecast period is near zero. National Meteorological and Hydrological Services (NMHSs) will closely monitor changes in the state of ENSO over the coming months and provide updated outlooks, as needed.

ENSO-neutral conditions (i.e., neither El Niño nor La Niña), were observed over the past three months. As of mid-August 2024, the equatorial Pacific Ocean continues to experience ENSO-neutral conditions. During the week centered on 14 August 2024, sea surface temperatures across the equatorial Pacific ranged between0.3 below and 0.6 degrees Celsius above normal. Over the past few months, cold subsurface temperatures have persisted in the eastern equatorial Pacific Ocean, extending to the surface. Negative subsurface temperature anomalies continue to be present at depth in the central Pacific Ocean, while slightly above-average temperatures are observed from the surface to a depth of 50 meters in the western and central Pacific. Overall, negative subsurface temperature anomalies have weakened since early August 2024. The overlying atmospheric conditions, including surface and upper-level winds and patterns of cloudiness and rainfall, remain broadly consistent with ENSO neutral conditions. The Equatorial Southern Oscillation Index (ESOI, a measure of the standardized Equatorial Pacific (80°W-130°W; 5°N-5°S) minus Indonesia (90°E-140°E; 5°N-5°S) sea-level pressure difference) was within ENSO-neutral range for the month of July 2024. The trade winds were close to average across the tropical Pacific, and normal atmospheric convection has been observed in the central Pacific. On the whole therefore, observed oceanic and atmospheric conditions currently indicate the existence of ENSO-neutral conditions.