El Niño Status and Forecast

La Niña continued to weaken over the past 30 days and is only hanging on by a thread at this point. Sea surface temperatures have warmed considerably across the equatorial Pacific Ocean and currently are only 0.6 degrees Celsius (about 1 degree Fahrenheit) below average in the eastern Pacific, where a large area of warmer-than-average water has been accumulating just below the surface. These conditions indicate that La Niña is severely diminished and neutral conditions will soon return. The International Research Institute for Climate and Society (IRI) notes that the atmosphere has not yet responded to the recent increases in sea surface temperatures and is still behaving as if a strong La Niña event were present, with above-average easterly winds along the equator and a highly positive Southern Oscillation Index (SOI) (Figure 14a). But the atmospheric response to changes in sea-surface temperatures is typically delayed. A weak La Niña event is expected to continue for the next month or two, with neutral conditions likely returning by early summer. IRI forecasts predict a greater than 50 percent chance that neutral conditions will return during the May–July period, with only a 27 percent chance that La Niña conditions will persist and a 15 percent chance that an El Niño will develop (Figure 14b). There is a slight increase in the odds for development of an El Niño later this summer. La Niña impacts on land may linger for several months, but will probably be of little consequence to Arizona and New Mexico, as May and June are historically hot and dry anyway.