ENSO Quick Look
IRI ENSO Update / Forecast
Technical ENSO Update
IRI Probabilistic ENSO Forecast
ENSO Prediction Plume
Monthly archive

ENSO Update

17 October 2007

Summary

As of mid-October La Niña conditions are fully established in the central and eastern equatorial Pacific. Below-average sea surface temperatures (SSTs) exist from the west coast of South America to the dateline. If these conditions continue to persist, they will be classified as a La Niña event. Based on the latest observations and forecasts, there is a 90% probability of maintaining La Niña conditions over the coming season.

General Discussion

Negative anomalies in the subsurface ocean structure have been observed in the east-central Pacific throughout most of 2007. Stronger than average Trade Winds in the central Pacific during Septeber contributed greatly to re-enforcing and strengthening the negative subsurface anomalies, and thus to cooling the surface tempertures further. From early to middle October, SSTs decreased by a dramatic 0.5C. SST anomalies are currently observed to reach 3C below average in the east-central Pacific, from about 140W-130W. The low-level winds continue to respond to the anomalous SSTs with strengthened Trade Winds, although not as strong as observed in September.
If cool SST anomalies persist, or strengthen, through the end of the year it would consitute a La Niña event (as distinguished from more short-lived La Niña conditions). Maintenance or amplification of La Niña conditions in the coming months will depend on continuation of enhanced Trade Winds.

Out of a large set of dynamical and statistical forecast models, most models indicate weak to moderate La Niña conditions rather than ENSO-neutral conditions through the early 2008. Most dynamical models that incorporate information about sub-surface ocean conditions give a stonger indication of strengthening of La Niña conditions. Overall, based on model forecasts and current observations of the ocean surface and subsurface, the probability of a La Niña is estimated at 90% for the Oct-Nov-Dec season in progress, and through the remainder of 2007. The probability of El Niño conditions re-emerging during the forecast period is at or below 10% until mid-2008, and the probability of returning to ENSO-neutral conditions is much below 50% until early 2008.

Note 1 - Only models that produce a new ENSO forecast every month are included in the above statement.

Top of Page