Synopsis: El Niño will likely peak during the Northern Hemisphere winter 2015-16, with a transition to ENSO-neutral anticipated during the late spring or early summer 2016.
A strong El Niño continued during October as indicated by well above-average sea surface temperatures (SSTs) across the central and eastern equatorial Pacific Ocean. Most Niño indices increased during the month, although the far eastern Niño-1+2 index decreased, accentuating the maximum in anomalous SST farther west. The subsurface temperature anomalies also increased in the central and eastern Pacific, in association with another downwelling equatorial oceanic Kelvin wave. Low-level westerly wind anomalies and upper-level easterly wind anomalies continued over the western to east-central tropical Pacific. Also, the traditional and equatorial Southern Oscillation Index (SOI) values remained negative. These conditions are associated with enhanced convection over the central and eastern tropical Pacific and with suppressed convection over Indonesia. Collectively, these atmospheric and oceanic anomalies reflect a strong and mature El Niño episode.
Most models indicate that a strong El Niño will continue through the Northern Hemisphere winter 2015-16, followed by weakening and a transition to ENSO-neutral during the late spring or early summer. The forecaster consensus remains nearly unchanged, with the expectation that this El Niño could rank among the top three strongest episodes as measured by the 3-month SST departures in the Niño 3.4 region going back to 1950. El Niño will likely peak during the Northern Hemisphere winter 2015-16, with a transition to ENSO-neutral anticipated during the late spring or early summer 2016.
El Niño has already produced significant global impacts. El Niño is expected to affect temperature and precipitation patterns across the United States during the upcoming months. Seasonal outlooks generally favor below-average temperatures and above-median precipitation across the southern tier of the United States, and above-average temperatures and below-median precipitation over the northern tier of the United States.
Much of the continental USA should be warmer than normal for the month with the south and southeast up to the Ohio Valley and up to the Northeast should be moderately warmer than normal. Only California and some isolated areas in the western plains and intermountain areas should be slightly cooler than normal.
From Washington state to northern California and across to Wisconsin and through the western plain states precipitation should be slightly to in the case of the norther plain moderately drier than normal. Central and Southern California through Nevada and Arizona should experience slightly to moderately wetter than normal conditions as well and the eastern plains and Mississippi and Ohio valleys with near normal precipitation in the eastern seaboard through the Carolinas and Florida.
Much of the west and intermountain region should be slightly warmer than normal while the Great Plains should be slightly to moderately colder than normal. From Wisconsin, Illinois and Missouri south and eastward temperatures should be slightly to moderately warmer than normal.
Parts of central Washington state and Oregon and north Idaho and western Wyoming along with Southern California and the Central Valley and Arizona and western New Mexico should be slightly to moderately wetter than normal. Much of the western plans from Montana through west Texas should be moderately to severely drier than normal. The Mississippi and Ohio valleys should be near normal to slightly wetter than normal. The Carolinas should be slightly direr than normal as well as eastern Florida.