SEA SURFACE TEMPERATURE (SST)

By the end of September 2006, the waters of the equatorial Pacific had sufficiently warmed to meet NOAA’s definition of El Niño. From mid-September to mid-December, ocean surface temperatures remained greater than 0.5ºC above average across the equatorial Pacific between 155ºE and the South American coast, with departures exceeding +1ºC between 165ºE and 145ºE and also between 85ºW and 125ºW. After peaking in mid-December, SST anomalies have begun to decrease in all NIÑO regions. The latest ocean surface temperature anomalies remain between +0.9ºC and +1.1ºC in all of the Niño regions except the Niño 1+2 region (+0.5ºC), indicating weak-to-moderate El Niño conditions. During November - December 2006, positive subsurface temperature anomolies were observed throughout the equatorial Pacific. Since early October, upper ocean heat content has been increasing in the central and east-central equatorial Pacific, and decreasing in the western equatorial Pacific. The most recent analysis shows positive anomolies between the surface and 200m depth across most of the equatorial Pacific, particularly near the Date Line where sub-surface temperatures are up to 4ºC above normal.

Low-level easterly wind anomolies have been observed across portions of the central and western equatorial Pacific since mid-December. As a response to the stronger-than-average easterly winds, SST anomolies have decreased in the region. Most statistical and coupled models estimate that El Niño conditions will weaken during the next 2-3 months, with a return of ENSO-neutral conditions sometime during the boreal spring (March - May 2007). With all these aforementioned factors in place, it seems likely that weak-to-moderate El Niño conditions will continue through March-May.