July Climate Briefing: La Niña Watch Issued
Read our ENSO Essentials & Impacts pages for more about El Niño and La Niña.
In mid-July, the sea-surface temperatures were slightly below average but in the ENSO-neutral range, and some atmospheric indicators showed neutral conditions while others leaned slightly toward La Niña. A new set of model runs predicts that cool-neutral or weak La Niña conditions are most likely from late Northern Hemisphere summer through early winter, with a 50-55% probability for weak La Niña for the August-October through October-December seasons. This outlook calls for just slightly lower chances for La Niña from late summer to early winter as the official ENSO forecast issued July 9, which used both models and human judgment, and which now carries a La Niña watch.
Weston Anderson provides the briefing summary:
See below for tweets summarizing the current El Niño situation.
To predict ENSO conditions, computers model the SSTs in the Niño3.4 region over the next several months. The plume graph below shows the outputs of these models, some of which use equations based on our physical understanding of the system (called dynamical models), and some of which use statistics, based on the long record of historical observations.
The La Niña odds are lower in the official probabilistic forecast issued by the U.S. Climate Prediction Center (CPC) and IRI in early July than in the mid-month IRI/CPC forecast. The earlier forecast uses human judgement in addition to model output, while the mid-month forecast relies solely on model output. More on the difference between these forecasts in this IRI Medium post.
ENSO in context: Resource page on climate variability
IRI’s Global Seasonal Forecasts
Each month, IRI issues seasonal climate forecasts for the entire globe. These forecasts take into account the latest model outputs and indicate which areas are more likely to see above- or below-normal temperatures and precipitation.
All forecast maps, including temperature in addition to precipitation, and also including a description of the methodologies, are available on our seasonal forecast page. Additional forecast formats, such as our flexible forecast maproom, are available in the IRI Data Library.