NOAA Updates its ENSO Alert on September 12, 2024 – We Remain in ENSO Neutral – Published September 14, 2024
“Synopsis: ” 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”
So we are really in ENSO Neutral but NOAA may not want to admit their forecast was wrong so they present it as waiting for La Nina. It is correct that we are in La Nina Watch but it is also correct that we currently remain in ENSO Neutral.
On the second Thursday of every month, NOAA (really their Climate Prediction Center CPC) issues its analysis of the status of ENSO. This includes determining the Alert System Status. NOAA now describes their conclusion as “ENSO Alert System Status: La Nino Watch”
The exact timing of the transition is now perhaps more clear which should increase the reliability of the Seasonal Outlook to be issued next Thursday.
We have included an ENSO Blog article by Emily Becker.
CLIMATE PREDICTION CENTER ENSO DISCUSSION (LINK)
| The second paragraph is what is important:
“The IRI plume predicts a weak and a short duration La Niña, as indicated by the Niño-3.4 index values less than -0.5°C (Fig. 6). This month, the team relies more on the latest North American Multi-Model Ensemble (NMME) guidance, which predicts La Niña to emerge in the next couple of months and continue through the Northern Hemisphere winter. The continuation of negative subsurface temperatures and enhanced low-level easterly wind anomalies supports the formation of a weak 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 (e.g., CPC’s seasonal outlooks). In summary, La Niña is favored to emerge in September-November (71% chance) and is expected to persist through January-March 2025 (Fig. 7).” Below is the middle paragraph from the discussion last month. “The IRI plume indicates that Niño-3.4 is most likely to be below La Niña thresholds for four overlapping seasons, from September-November 2024 through December 2024 – February 2025. Based on updated guidance and recent observations, the forecast team predicts nearly equal chances for ENSO-neutral and La Niña in August-October 2024, with higher odds for La Niña in September-November. Although the rate of SST cooling has been slower than previously anticipated, below-average subsurface temperatures and low-level easterly wind anomalies remain conducive to La Niña development in the coming months. In summary, ENSO-neutral is expected to continue for the next several months, with La Niña favored to emerge during September-November (66% chance) and persist through the Northern Hemisphere winter 2024-25 (74% chance during November-January). “ |
We now provide additional details.
CPC Probability Distribution
Here are the new forecast probabilities. The probabilities are for three-month periods e.g. ASO stands for August/September/October.
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Here is the forecast from last month.
| The analysis this month and last month are a bit different with again the transition to La Nina being slightly slower than thought last month. This seems to be a trend. The chart is clearer than the discussion in the summary report above. The La Nina is aa bit slower to arrive. I am not sure that we will actually have a La Nina. |