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ENSO Quick
Look IRI ENSO Update / Forecast Technical ENSO Update IRI Probabilistic ENSO Forecast ENSO Prediction Plume Monthly archive ENSO Update19 July 2007SummaryAs of mid-July the cooling trend suggestive of La Nina development has resumed following a pause during June. Current equatorial sea surface temperatures (SSTs) are slightly below average in the east-central Pacific, and much below average in the far eastern Pacific. Based on the latest observations and forecasts, there is a 55% probability of developing La Nina conditions over the coming season.General DiscussionWhile the pattern of negative SST anomalies in the equatorial Pacific had weakened during June, it is re-strengthening and expanding westward currently in mid-July. Slightly warmer than average waters are observed in the western Pacific, from near the dateline westward.Negative anomalies in the subsurface ocean structure have also regenerated somewhat since last month, now positioned in the east-central Pacific. Thus, the mixed layer s shallower than normal throughout the east-central equatorial Pacific, and this appears as negative temperature anomalies at the thermocline depth along the equator. Weakening and strenghening of the subsurface anomalies have resulted from alternating westerly and easterly wind anomalies, respectively, extending across portions of the equatorial Pacific over the last few months. Despite the alternations of wind anomaly, an overriding tendency has been toward somewhat enhanced Trade Winds, resulting in sustained negative SST anomalies in the eastern tropical Pacific that have varied in their degree of westward extension, limited to mainly east of the dateline. Continuation of the generally enhanced Trade Winds will be important for further evolution toward La Nina conditions in the coming months. 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 Jul-Aug-Sep season through Sep-Oct-Nov 2007. The probability of El Niño conditions re-emerging during the forecast period remains at or below 10% until early 2008, while the probability of maintaining ENSO-neutral conditions is slightly below 50% through nearly all of 2007. Note 1 - Only models that produce a new ENSO forecast every month are included in the above statement.
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