Synopsis: ENSO-neutral or weak La Niña conditions are likely during the next 6-9 months.

By the end of October, equatorial SST anomalies greater than +0.5ºC were found between Indonesia and 175ºW, while negative anomalies less than –0.5ºC were observed at most locations between 130ºW and the South American coast (Fig. 1). The SST departures in the Niño 3, Niño 3.4, and Niño 1+2 regions were negative, while weak positive departures were observed in the Niño 4 region (Fig. 2). During the last three months surface and subsurface temperature anomalies decreased, especially in the eastern equatorial Pacific, and the Southern Oscillation Index (SOI) increased. During the same period persistent stronger-than-average low-level equatorial easterly winds were observed over the central Pacific (Fig. 3), while near-average patterns of convection and sea level pressure occurred over most of the tropical Pacific. Collectively, the present oceanic and atmospheric anomalies are consistent with ENSO-neutral conditions in the tropical Pacific.

The spread of the most recent statistical and coupled model forecasts (weak La Niña to weak El Niño) indicates some uncertainty in the outlooks (Fig. 4). However, current conditions (stronger-than-average easterly winds over the central equatorial Pacific) and recent observed trends (decreasing SST anomalies throughout the central and eastern equatorial Pacific) do not support the development of El Niño. Rather, they support either a continuation of ENSO-neutral conditions or the development of weak La Niña conditions during the next 6-9 months.

This discussion is a consolidated effort of NOAA and its funded institutions. Weekly updates for SST, 850-hPa wind, OLR and features of the equatorial subsurface thermal structure are available on the Climate Prediction Center web page at http://www.cpc.ncep.noaa.gov (Weekly Update). Forecasts for the evolution of El Niño/La Niña are updated monthly in the Forecast Forum section of CPC's Climate Diagnostics Bulletin. The next ENSO Diagnostics Discussion is scheduled for 8 December 2005. To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message: ncep.list.enso-update@noaa.gov.