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ENSO Quick
Look IRI ENSO Update / Forecast Technical ENSO Update IRI Probabilistic ENSO Forecast ENSO Prediction Plume Monthly archive ENSO Update14 March 2007SummaryAs of mid-March a possibility for La Nina development exists, although currently equatorial sea surface temperatures (SSTs) are near their climatological average in the eastern and central Pacific. Based on the latest observations and forecasts, there is a 50% probability of developing La Nina conditions by mid-2007.General DiscussionThe warm SST anomalies that remained in the eastern central Pacific during January, following the 2006/07 El Niño event, declined significantly and between 140W-100W were replaced by cold anomalies in February. Temperatures declined by approximately 1.0C between January and February in the NINO3 ENSO index region (5S-5N, 150W-90W). Warm anomalies, exceeding 0.5C, are now confined west of the dateline. Since mid-February, however, the cold SST anomalies have returned to near their climatological average. This is largely the result of localized atmospheric effects on SST, rather than an indication that cold SST anomalies associated with La Nina will not develop.The subsurface ocean structure shows a shallowing of the upper ocean mixed layer across the equatorial Pacific. This appears as cold temperature anomalies at depth along the equator. The upwelling currents acting in the eastern equatorial Pacific, are thus bringing colder than average waters to the surface. Although the SSTs may have returned to normal in the recent week, the subsurface still shows cold anomalies that will not disappear so quickly. Thus the chance of developing La Nina conditions in the coming seasons is enhanced. Out of a large set of dynamical and statistical forecast models, the majority predict the maintenance of ENSO-neutral conditions through the end of 2007. However, dynamical models that incorporate information about sub-surface ocean conditions tend to indicate development of La Nina. Overall, based on model forecasts and current observations of the ocean surface and subsurface, the probability of a La Niña increases from 35% in the coming March-April-May season to 50% by mid-2007. The probability of El Niño conditions re-emerging during the forecast period remains below 15% throughout the forecast period. The probability of maintaining ENSO-neutral conditions is most likely at the beginning of the forecast period, with over 60% probability, dropping to 40% likely by mid-2007. Note 1 - Only models that produce a new ENSO forecast every month are included in the above statement.
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