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 (Fig. 6). 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.
Warmer than normal across the eastern half of the four state region with temperatures at close to 1 degree C (1.8 degree F) above normal. The western parts of Washington, Oregon and California should be close to normal to slightly cooler than normal especially in the coastal zone.
Cooler than normal across nearly the entire four state region with only Central Washington and southern Nevada and southeastern California near normal to slightly and in the case of Central Washington moderately warmer than normal.
Much of the southern two thirds of California and southern half of Nevada should be slightly wetter. The rest of the region including all of Washington and Oregon should be slightly to moderately drier than normal.
In California, the southern half of the State and the Central Valley to the border with Oregon should be slightly drier than normal along with southern Nevada. The northwest coastal ranges and northern Sierra should be slightly drier than normal while much of the northern half of Nevada should be slightly to moderately drier than normal. The coastal ranges of Oregon should be slightly drier than normal along with eastern Oregon while central Oregon should be near normal to slightly wetter than normal. Most of Washington State should be near normal to only slightly wetter than normal in the central regions.