Winter '09 / '10 - ENSO Outlook - November

From The International Research Institute for
Climate and Society (IRI)

"By mid-November 2009, the NINO3.4 SST anomaly index had risen to values indicative of the moderate El Niño category. Up until recently, the event had maintainined (sic) only a weak magnitude, but strong and persistent westerly wind anomalies during September, and especially those during October, substantially increased the SST anomalies in the central and eastern equatorial Pacific.

"Those wind anomalies also had a substantial impact on the sub-surface ocean, deepening the thermocline. This could allow for further growth and will certainly provide several months of persistence to the current event. The wind anomalies in the western Pacific have become easterly since early November, suggesting that much of the rrecent (sic) wind anomalies are due to passage of a very strong MJO, or intraseasonal (sic) variability.El Niño conditions are expected to persist through the end of the calendar year and possibly a few additional months.

"Out of a large set of dynamical and statistical forecast models, nearly all indicate maintenance of El Niño conditions during the Nov-Dec-Jan season currently in progress. Overall, based on model forecasts and current observations of the ocean surface and subsurface, for the coming Dec-Jan-Feb season the probability for El Niño conditions is estimated at 96%, and for ENSO-neutral conditions approximately 3%. The estimated strength of this El Niño event now appears moderate, and the most likely period of duration is through early 2010."

Recent performance trends show the models respond too quickly (slowly) when temperature anomalies are rising (falling).