Global setting: July 2018

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. Waters remained 2.0°C above average between approximately 20m and 100m depth east of about 130oW.

The consensus from international models is for the tropical Pacific to transition toward El Niño over the next three-month period (55% chance over August – October 2018). The probability for El Niño conditions increases as we reach into and beyond the Southern Hemisphere summer, with a 78% chance for El Niño conditions over the February – April 2019 period. The strength and characteristics of this event – if it eventuates – remain uncertain at this point, but indications so far are that it is unlikely to be in the strong category.

Since the climate system remains ENSO-neutral, the atmospheric circulation around New Zealand for August – October 2018 is forecast to be characterized by mixed air flow patterns. The emergence of El Niño conditions, especially during the second half of the season, may influence periods of enhanced southwesterly wind flows. As a result, warmer than average conditions during the first part of the season may give way to spells of cooler conditions later on.

 

Monthly values of the Southern Oscillation Index (SOI), a measure of changes in atmospheric pressures across the Pacific, and the 3-month mean (black line). SOI mean values: July SOI 0.2; May-July average 0.0.
Differences from average July surface temperatures in the seas around New Zealand