Synopsis: ENSO-neutral conditions are expected during the northern summer and fall (June-November) 2005.

Sea surface temperature (SST) anomalies decreased by more than 2°C in the eastern equatorial Pacific during May (Fig. 1, bottom). By the end of the month, negative equatorial SST anomalies were observed in most areas between 120°W and the South American coast (Fig. 1, top). The decrease in SST anomalies in the eastern equatorial Pacific during May was reflected by a decrease in the SST anomalies in the Niño 3 and Niño 1+2 regions (Fig. 2) and by a decrease in the upper-ocean heat content in the eastern half of the equatorial Pacific (Fig. 3). These features were associated with the upwelling phase of an eastward-propagating Kelvin wave. No additional Kelvin wave activity is expected, since the MJO has weakened during the last few weeks (Fig. 4) and the overall patterns of tropical convection, low-level winds and upper-level winds are near average.

A majority of the statistical and coupled model forecasts (Fig. 5) indicate that ENSO-neutral conditions will prevail during the northern summer (June-August) and fall (September-November). The spread in the forecasts indicates increasing uncertainty during the last half of 2005.

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 7 July 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.