The National Oceanic and Atmospheric Administration (NOAA) says El Nino is likely to develop this month and persist through December or February 2012-13.
"Possible signs of El Nino development in the atmosphere included upper-level easterly wind anomalies and a slightly negative Southern Oscillation Index. Despite these indicators, key aspects of the tropical atmosphere did not support the development of El Nino conditions during the month," states NOAA. "In particular, low-level trade winds were near average along the equator, and the pattern of tropical convection from Indonesia to the central equatorial Pacific was inconsistent with El Nino with the typical regions of both enhanced and suppressed convection shifted too far west. Because of the lack of clear atmospheric anomaly patterns, ENSO-neutral conditions persisted during August. However, there are ongoing signs of a possibly imminent transition towards El Niño in the atmosphere as well as the ocean."
NOAA says most of the dynamical models, along with roughly one-half of the statistical models, now predict the onset of El Niño beginning in August-October 2012, persisting through the remainder of the year. "The consensus of dynamical models indicates a borderline moderate strength event (Niño 3.4 index near +1.0°C), while the statistical model consensus indicates a borderline weak El Niño (+0.4° to +0.5°C). Supported by the model forecasts and the continued warmth across the Pacific Ocean, the official forecast calls for the development of most likely a weak El Nino during September 2012, persisting through December-February 2012-13," states NOAA.