Synopsis: El Niño is expected to continue through the Northern Hemisphere spring 2010 and transition to ENSO-neutral conditions by Northern Hemisphere summer 2010.
El Niño weakened to moderate strength during March 2010, with sea surface temperature (SST) anomalies decreasing slightly, but still exceeding +1oC across much of the central and eastern equatorial Pacific Ocean at the end of the month (Fig. 1 and Fig. 2). Subsurface heat content anomalies (average temperatures in the upper 300m of the ocean, Fig. 3) decreased during March in response to the eastward expansion of below-average temperature anomalies at depth (100-200m) into the east-central Pacific (Fig. 4). Anomalous tropical convection remained consistent with El Niño, with enhanced convection over the central and eastern Pacific and suppressed convection over Indonesia (Fig. 5). The equatorial low-level easterly trade winds strengthened near the Date Line, while upper-level easterly wind anomalies became confined to the eastern Pacific. Collectively, these oceanic and atmospheric anomalies reflect an ongoing, but weakening El Niño.
Nearly all models predict decreasing SST anomalies in the Niño-3.4 region through 2010, with the model spread increasing at longer lead times (Fig. 6). The majority of models predict the 3-month Niño-3.4 SST anomaly will drop below +0.5oC by May-June-July 2010, indicating a transition to ENSO-neutral conditions that will likely persist through Northern Hemisphere summer. Over the last couple months, an increasing number of models, including the latest runs from the NCEP Climate Forecast System (CFS), are predicting below-average temperatures in the Niño-3.4 region by Northern Hemisphere fall, with some forecasts meeting thresholds for La Niña. However, it should be noted that model skill is at a minimum during this time of year, and also that the majority of models continue to indicate the persistence of ENSO-neutral conditions through 2010.
Expected El Niño impacts during April-June 2010 include drier-than-average conditions over Indonesia and enhanced convection over the central and eastern equatorial Pacific Ocean. For the contiguous United States, potential El Niño impacts include above-average precipitation for the southeastern states, while above-average temperatures are most likely for the Pacific Northwest.