SEA SURFACE TEMPERATURE (SST)

During the early months (JFM) of 2006, negative equatorial SST anomalies were observed at most locations between 180ºW and 90ºW, and negative SST departures were observed in all of the Niño regions, except for Niño 1+2 (along the equatorial Pacific coast of South America). By March, these persistent cool SSTs came very close to the La Niña threshold. During April through June, however, the equatorial strip had warmed somewhat, and by June positive SST anomalies expanded eastward, with SST anomalies greater than +0.5C observed in most of the equatorial Pacific between 130ºE and 140ºW. From mid-July through mid-August, SSTs were greater than .5 C between 165ºE and 150ºW and between 80ºW and 105ºW.. In the subsurface waters there has been a gradual warming that began in February, and by June, anomalies of up to + 2° C were observed at thermocline depth (150-200m below the surface).

Most statistical and coupled models predict slightly positive SST anomalies (ENSO-neutral to weak El Niño) in the Niño 3.4 region through the end of 2006. These forecasts are consistent with the recent increase in SST and build-up in upper-ocean heat content along the equator. Since the low-level easterlies have been near average, it seems likely that ENSO-neutral conditions will continue at least for the next three months. At this time, all measures of the Pacific climate are within the neutral range, and there are no indications of a major shift.