Seasonal Climate Outlook

The consensus from international models is for the tropical Pacific to transition toward El Niño over the next three-month period (65% chance over September – November 2018). The probability for El Niño conditions being established increases as we reach into and beyond the Southern Hemisphere summer, with a 78% chance for El Niño conditions over the March – May 2019 period. Indications are that the event – if it eventuates – will not be in the strong category. The type appears to lean toward the central Pacific event, although dynamical models indicate that warm SST anomalies may gradually transit eastward later in 2018 into early 2019.

ENSO-neutral conditions continued across the tropical Pacific during July 2018. The Southern Oscillation Index (SOI) was in the neutral range, with a preliminary value of +0.2 for July 2018. Surface ocean waters in the central and eastern equatorial Pacific continued to warm during July but remained in the neutral range. The subsurface ocean remained warmer than average in the eastern equatorial Pacific during July, but anomalies weakened slightly compared to June.

El Nino – Southern Oscillation (ENSO) neutral conditions continued across the tropical Pacific during June 2018. The Southern Oscillation Index (SOI) was slightly negative at about -0.7 during the past 30 days (on the El Niño side of neutral). The central equatorial Pacific experienced warming sea surface temperatures (SSTs) for the third consecutive month and was slightly above average for the time of year.

ENSO-neutral conditions persisted in the tropical Pacific during May 2018. The Southern Oscillation Index (SOI) was positive at about +0.3 during the past 30 days. Sea surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean warmed for the second consecutive month and are now near or slightly above average for the time of year.

Temperatures are forecast to be above average in the north of the North Island and average or above average for all remaining regions of New Zealand. Despite the prospect for average or warmer than average temperatures, frosts and cold snaps will become more common, with some cold snaps possibly quite sharp.

Weak La Niña conditions continued in the tropical Pacific during March 2018, but trends in low-level winds and in sub-surface ocean temperatures during the month indicate that the event is coming to an end.

With La Niña’s influence waning over the next three month period, New Zealand’s regional climate over March – May 2018 is expected to be driven by the warmer than average ocean waters that are present around the country.

Apart from waning La Niña conditions, New Zealand’s regional climate over the next three month period is expected to be dominated by the very warm ocean waters present around the country, in the Tasman Sea, and in the Southwest Pacific Ocean.

New Zealand’s regional climate over the next three month period is anticipated to be dominated by the very warm ocean waters present around the country and in the Tasman sea, which will influence surface air temperatures and the likelihood of significant rainfall events.

La Niña conditions are present in the tropical Pacific, as several conventional thresholds have been reached or are being approached.

The tropical Pacific is still officially in a ENSO (El Niño Southern Oscillation) neutral state, but some indicators have leaned more towards La Niña conditions during the course of October 2017.

Many atmospheric and oceanic indicators in the tropical Pacific are on the La Niña side of neutral, although not yet strong enough to reach La Niña thresholds.

ENSO (El Niño – Southern Oscillation) neutral conditions were still present in the tropical Pacific during August 2017. However, like July, several oceanic and atmospheric patterns, such as the Southern Oscillation Index (SOI) and decreasing sea surface temperatures (SSTs) in the tropical Pacific, leaned toward La Niña.

ENSO (El Niño – Southern Oscillation) neutral conditions (neither El Niño nor La Niña) continued in the tropical Pacific during July 2017, but this month mixed signals were again present. In particular some atmospheric patterns have been recently leaning more towards weak La Niña conditions.

The tropical Pacific remained in an ENSO (El Niño – Southern Oscillation) neutral state (neither El Niño nor La Niña) during June 2017, but oceanic and atmospheric anomalies were mixed, with some indicators leaning towards El Niño and others towards La Niña.

The tropical Pacific continued to exhibit an ENSO (El Niño – Southern Oscillation) neutral state (neither El Niño nor La Niña) during May 2017, although is now close to the threshold of a weak El Niño. 

The tropical Pacific overall remained in an ENSO (El Niño – Southern Oscillation) neutral state  (neither El Niño nor La Niña) during April 2017. The strong ‘coastal El Niño’ which developed along the coast of South America (southern Ecuador and northern Peru) during February and March has now weakened.

The tropical Pacific is currently in an ENSO (El Niño – Southern Oscillation) neutral state overall, but with very mixed signals.

The tropical Pacific is currently in an ENSO (El Niño – Southern Oscillation) neutral state (neither El Niño nor La Niña).

The tropical Pacific is currently in an ENSO (El Niño – Southern Oscillation) neutral state (neither El Niño nor La Niña).

The tropical Pacific continues to exhibit mainly ENSO-neutral conditions.

The tropical Pacific exhibits mainly neutral ENSO (El Niño-Southern Oscillation) conditions. Sea surface temperatures (SSTs) in the central Equatorial Pacific Ocean are marginally below average and do not exceed the threshold used by NOAA’s Climate Prediction Center to define La Niña events.

The tropical Pacific exhibits mixed ENSO (El Niño-Southern Oscillation) signals, with some indicating La Niña status and others indicating neutral conditions.

ENSO (El Niño – Southern Oscillation) neutral conditions are still present in the tropical Pacific Ocean as a whole, although some indicators are currently in the weak La Niña category.