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ENSO Quick
Look IRI ENSO Update / Forecast Technical ENSO Update IRI Probabilistic ENSO Forecast ENSO Prediction Plume Monthly archive ENSO Update20 June 2007SummaryAs of mid-June the cooling trend suggestive of La Nina development has slowed, and eastern Pacific SST anomalies have retracted since the beginning of June. However, current equatorial sea surface temperatures (SSTs) are much below average in the far eastern Pacific and along the coast of Peru. Based on the latest observations and forecasts, there is a 55% probability of developing La Nina conditions over the coming season.General DiscussionThe pattern of SST anomalies in the equatorial Pacific has weakened relative to those in May. In particular, the cold anomalies have retracted toward South America. Colder than average waters still dominate in the far eastern Pacific, but with the below-average temperatures extending only to approximately 130W. Coolest SST anomalies remain situated near the South American coast. Slightly warmer than average waters are situated in the western Pacific, west of the dateline.The anomalies in the subsurface ocean structure have also weakened since last month, although the upper ocean mixed layer remains shallower than normal throughout the central equatorial Pacific. This appears as cold temperature anomalies at the thermocline depth along the equator. Weakening of the subsurface anomalies resulted from westerly wind anomalies extending across much of the equatorial Pacific in late May. These westerly wind anomalies also transported warm surface waters from the western Pacific into the central/eastern Pacific, and are largely responsible for the retraction of cold SST anomalies toward the east. Since early June, however, enhanced easterly Trade Winds have been observed. These are contributing to, and reinforcing, the shallow thermocline anomalies. Continuation of the enhanced Trade Winds will be important for further evolution toward La Nina conditions in the coming seasons. Out of a large set of dynamical and statistical forecast models, they are approximately split between ENSO-neutral and La Niña conditions through the end of 2007. However, dynamical models that incorporate information about sub-surface ocean conditions give a stonger indication of the development of La Nina. Overall, based on model forecasts and current observations of the ocean surface and subsurface, the probability of a La Niña is estimated at 55% from the coming Jun-Jul-Aug season through Sep-Oct-Nov 2007. The probability of El Niño conditions re-emerging during the forecast period remains at or below 5% throughout the forecast period. The probability of maintaining ENSO-neutral conditions is below 50% probability, until late-2007. Note 1 - Only models that produce a new ENSO forecast every month are included in the above statement.
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