Synopsis: A transition from ENSO-neutral to La Niña conditions is possible within the next 2-3 months.
The pattern of anomalous sea surface temperatures (SSTs) during April 2007 was consistent with ENSO-neutral conditions in the tropical Pacific, with average to slightly below-average SSTs extending from the date line to the west coast of South America (Fig. 1). The latest weekly SST departures in the Niño regions are -1.2ºC in Niño 1+2, -0.3ºC in the Niño 3, zero in Niño 3.4, and +0.1ºC in Niño 4 (Fig. 2).
The upper-ocean heat content (average temperature departures in the upper 300 m of the ocean) remained below average across the central and east-central equatorial Pacific (Fig. 3), with temperatures at thermocline depth generally 2o-5oC below average (Fig. 4). Consistent with the surface and sub-surface ocean temperature patterns, stronger than-average low-level easterly winds persisted over the central equatorial Pacific. Also, convection was enhanced over the western equatorial Pacific and suppressed east of the date line. Collectively, these atmospheric and oceanic conditions continue to indicate the possibility that La Niña conditions will develop over the next 2-3 months.
Most of the statistical and coupled model forecasts, including those from the NCEP Climate Forecast System (CFS) (Fig. 5), indicate below-average SSTs during the next several months. Some forecast models, especially the CFS, predict a rapid transition to La Niña during May-July 2007. However, for the past few months the CFS forecasts have been predicting a stronger and more rapid cooling than has actually occurred. Historically, the next couple of months are a critical time period for the possible emergence of La Niña.
This discussion is a consolidated effort of NOAA and its
funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web
site (El Niño/La Niña Current
Conditions and Expert Discussions). 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 June 2007. To receive
an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message
to: ncep.list.enso-update@noaa.gov.
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