Synopsis: El Niño will likely peak during the Southern Hemisphere summer 2015-16, with a transition to ENSO-neutral anticipated during the late autumn or early winter 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 autumn or early winter. 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 Southern Hemisphere summer 2015-16, with a transition to ENSO-neutral anticipated during the late autumn or early winter 2016.
Much of the North Island will be close to normal for temperatures with the Waikato north slightly above normal and the Manawatu and to the south and east near normal to slightly cooler than normal.
Almost all of the North island should be slightly to moderately above normal
From Northland to Wellington and across to Taranaki and east to East Cape it should be near normal to slightly drier than normal. Only the east coast from Gisborne through Hawkes Bay and eastern wellington should be near normal to in isolated places slightly wetter than normal.
The upper part of the North island should be slightly to moderately wetter than normal with much of the central part of the island near normal and the east coast slightly to moderately wetter than normal.
Much of the South Island will be close to normal for temperatures with the West Coast slightly cooler than normal and the rest of the island near normal.
Almost all of the South Island should be slightly to moderately above normal.
Most of the island should be slightly to moderately drier than normal except for the Canterbury Plains and North Canterbury that should be near normal.
The east coast should be slightly to in some isolates places moderately drier than normal and the West Coast and Southland should be near normal.