Photo: NOAA
Forecasters at the National Oceanic and Atmospheric Administration (NOAA) first released data back in February indicating the El Niñ0 conditions that had dominated 2023 would be fading away and La Niña would develop right on its heels. At the time, they gave a 55 percent chance that La Niña would develop during the summer months. By March, those odds were bumped up to 62 percent during that same time period and an almost overwhelming 82 percent chance La Niña would emerge by October.
La Niña is a periodic cooling of the ocean’s surface in the central and east-central equatorial Pacific. It’s the cooling phase of the El Nino/Southern Oscillation (ENSO) cycle, and conditions have remained neutral since El Niño ended earlier this year (neither El Niño or La Niña conditions over the equatorial Pacific). While probabilities of a La Niña emerging evolve month-to-month, NOAA forecasters have generally upgraded the odds and even intensity of such events whenever they release monthly updates. This month, however, that trend shifted.
NOAA stated in its October monthly update, “the team still favors a weak event, but has lowered the chances of La Niña. A weaker La Niña implies that it would be less likely to result in conventional winter impacts, though predictable signals could still influence the forecast guidance.”
La Niña is favored to emerge in September-November (60% chance) and is expected to persist through January-March 2025. A #LaNina Watch remains in effect. #ENSO https://t.co/5zlzaZ1aZx pic.twitter.com/SwlYIgkki0
— NWS Climate Prediction Center (@NWSCPC) October 10, 2024
For reference, last month’s forecast highlighted just over 70 percent odds that La Niña would form by the end of November.
So, why are we suddenly stuck in ENSO neutral conditions after a quick flip from El Niño to La Niña was first predicted for 2024? Only four La Niña events have formed this late in the year, according to NOAA, but forecasters still anticipate this weaker-than-expected event to emerge and sustain into 2025.
“Short-term fluctuations, such as the weaker equatorial trade winds that occurred during September, can’t be predicted more than a couple of weeks (at best) in advance,” wrote Emily Becker in NOAA’s ENSO blog. “They tend to have a disproportionate impact during borderline, more marginal situations when we are hovering near our ENSO thresholds. These small fluctuations can tip the scales one way or the other. In this case, they’ve added up to a slower and weaker La Niña development. That said, many of our models are holding steady for La Niña to develop shortly.”
