Most oceanic and atmospheric indices reflect ENSO-neutral conditions. However, there are indications that a warm episode may develop during the next several months. Since late June 2001 sea surface temperatures (SSTs) have become anomalously warm in the central equatorial Pacific, with anomalies near 1°C in the vicinity of the date line (Fig. 1). During the same period, subsurface temperature anomalies have remained positive in the central equatorial Pacific between 170°E and 120°W (Fig. 2), indicating a deeper-than-normal thermocline in that region. This pattern has been observed during the early stages of past warm episodes.

In recent months, many tropical Pacific atmospheric and oceanic variables have been modulated by intraseasonal (30-60 day) fluctuations (Fig. 3), associated with the Madden-Julian Oscillation (MJO). In the past, MJO activity has been instrumental in producing low-level wind fluctuations during both the onset and demise phases of warm episodes. During the onset phase, westerly wind bursts, associated with the convectively active phase of the MJO, initiate eastward propagating oceanic Kelvin waves that often result in subsequent oceanic warming in the eastern equatorial Pacific. This process tends to occur more often during the transition seasons (March-May and September-November) when the monsoon systems of both the Northern and Southern Hemispheres are in transition from winter to summer or vice versa. At that time the westerly wind bursts, associated with the MJO, tend to occur along the equator. Since we are currently in a transition season, special attention will be focused on the evolution of the MJO, and any effect that it has on surface and subsurface ocean temperatures. (See regular intraseasonal updates on the CPC website.)

There is no clear consensus amongst the latest statistical and coupled model predictions. However, several of these predictions indicate that positive SST anomalies will continue in the central equatorial Pacific during the remainder of 2001 and into the first half of 2002. The impacts that this warming will have on global temperature and precipitation patterns depend to a large degree on its intensity. At the moment, considering both the SST predictions, the time of year and the observed oceanic and atmospheric circulation patterns, it seems most likely that the intensity of any warming will be weak or moderate.

Weekly updates for SST, 850-hPa wind, OLR and the equatorial subsurface temperature structure are available on the Climate Prediction Center homepage at: http://www.cpc.ncep.noaa.gov (Weekly Update).  Forecasts for the evolution of El Niño/La Niña are updated monthly in CPC's Climate Diagnostics Bulletin Forecast Forum. To receive an e-mail notification when updated ENSO Diagnostic Discussions are released please send your e-mail address to