Global setting: August 2019

The NINO3.4 Index anomaly (in the central Pacific) for the month of August (to the 25th) was +0.20˚C, suggesting that oceanic ENSO neutral conditions have arrived. Warmth was steadfast in the NINO4 region (west-central Pacific) with a monthly value of +0.75˚C.

Upper-oceanic heat content anomalies continued to decrease, but remained slightly above average in the west-central equatorial Pacific. In the eastern part of the basin, heat content was below normal for the time of year. Overall, this distribution of heat content across the Pacific reflects ENSO neutral conditions, but with a slight lean toward El Niño-Modoki.

During August, above normal rainfall occurred from the eastern Maritime Continent into the western Pacific, with below normal rainfall just north of the equator in the central Pacific. This remained broadly consistent with El Niño Modoki conditions.

Trade winds were slightly weaker than normal in the eastern Pacific and slightly stronger than normal in the west-central Pacific. During September, reduced trades are forecast to west of the International Dateline, which may help to sustain the warm pool of water in the NINO4 region.

On the other hand, stronger than normal trade winds are expected in the east-central tropical Pacific, which may lead to additional cooling of SSTs.

According to the consensus from international models, oceanic ENSO-neutral conditions are most likely at 59% chance for the September – November period with El Niño at 33% chance. For the December 2019 – February 2020 period, the probability for neutral conditions is 49% with the chance for El Niño increasing to 41%. For the March – May 2020 period, the probability for neutral conditions and El Niño is 55% and 43%, respectively.

Sea Surface Temperatures

New Zealand’s coastal water temperatures for August 2019 cooled compared to July for all regions except the east of the North Island, where a slight increase occurred. The east of the South Island remains the most anomalously warm coastal region with the rest of New Zealand experiencing near or slightly above average coastal SSTs. Elsewhere, SSTs in the Southwest Pacific remain above average for the time of year and near or above average in the Tasman Sea.

In other words, the warm seas that helped to modify sub-Antarctic air masses earlier in the season have now cooled.

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: August SOI -0.2; June-August average -0.6.
Differences from average August surface temperatures in the seas around New Zealand