| ||
|
ENSO Quick
Look IRI ENSO Update / Forecast Technical ENSO Update IRI Probabilistic ENSO Forecast ENSO Prediction Plume Monthly archive ENSO Update19 April 2007SummaryAs of mid-April the possibility exists for La Nina conditions to develop. Currently equatorial sea surface temperatures (SSTs) are much below average in the eastern Pacific and along the coast of Peru. Based on the latest observations and forecasts, there is a 50% probability of developing La Nina conditions by mid-2007.General DiscussionThe pattern of SST anomalies in the equatorial Pacific is beginning to resemble that of La Nina conditions, with colder than average waters in the far eastern Pacific and slightly warmer than average waters in the western Pacific. Below average SSTs extend along the equatorial Pacific from the coast of South America to appoximately 130W. Between mid-February and mid-March, considerable cooling has occured east of 120W and all along the South American coast, although the strength of the cold anomalies has weakened slightly in the last week or so.The subsurface ocean structure shows a shallower than average 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 cold SST anomalies in the eastern Pacific may have dampened slightly 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. However, the realized impact of the sub-surface anomalies on surface conditions will depend on strengthening Trade Winds to pull them to the surface. 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 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 increases from 45% in the coming April-May-June season to 50% by mid-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 most likely at the beginning of the forecast period, with over 50% probability, dropping to 45% likely by mid-2007. Note 1 - Only models that produce a new ENSO forecast every month are included in the above statement.
|
