Synopsis: El Niño is expected to remain strong through the Northern Hemisphere winter 2015-16, with a transition to ENSO-neutral anticipated during late spring or early summer 2016.
A strong El Niño continued during November as indicated by well above-average sea surface temperatures (SSTs) across the central and eastern equatorial Pacific Ocean. The Niño-4, Niño-3.4 and Niño-3 indices rose to their highest levels so far during this event, while the Niño-1+2 index remained approximately steady. The subsurface temperatures in the central and eastern Pacific, while still well above average, decreased slightly due to the eastward push of the upwelling phase of an equatorial oceanic Kelvin wave. Low-level westerly wind anomalies and upper-level easterly wind anomalies continued over the most of the tropical Pacific. The traditional and equatorial Southern Oscillation Index (SOI) values remained negative. These conditions are associated with enhanced convection over the central tropical Pacific and suppressed convection over Indonesia. Collectively, these atmospheric and oceanic anomalies reflect a strong El Niño episode that has matured.
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 from last month, with the expectation that this El Niño will rank among the three strongest episodes as measured by the 3-month SST departures in the Niño 3.4 region dating back to 1950. El Niño is expected to remain strong through 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 and is expected to affect temperature and precipitation patterns across the United States during the upcoming months. Seasonal outlooks indicate an increased likelihood of above-median precipitation across the southern tier of the United States, and below-median precipitation over the northern tier of the United States. Above-average temperatures are favored in the West and northern half of the country with below-average favored in the southern Plains and along the Gulf Coast.
Much of the west and intermountain region should be slightly cooler than normal while the Great Plains should be moderately colder than normal. From Wisconsin, Illinois and Missouri south and eastward temperatures should be slightly to moderately warmer than normal.
Oregon, Washington and across the northern plains states should be only slightly drier than normal. California and much of Nevada and the Mississippi Valley and Gulf states should be slightly wetter than normal. The eastern seaboard should be slightly to moderately drier than normal. Florida should be near normal in the north and slightly drier than normal in the south.
Much of the west and intermountain region should be from slightly warmer to slightly cooler than normal than normal while the Great Plains east and including Wisconsin, Illinois and Missouri and most of Michigan and Indiana should be moderately colder than normal while the Northeast, Eastern Seaboard and Southwest remain 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 eastern seaboard all way to Florida should be slightly to moderately drier than normal.