Global setting: February 2019

The Southern Oscillation Index (SOI) decreased substantially from near 0.0 in January to a value of -1.3 in February. Over the past two months, the SOI has decreased markedly from a December value of +0.8.  The three-month (December 2018 – February 2019) SOI value is -0.2, now on the El Niño side of neutral. The notable shift over the past two months suggests that the ocean and atmosphere are becoming more connected. Consequently, a weakly coupled central Pacific El Niño is now present.

The probability for oceanic El Niño conditions, according to the consensus from international models, is 76% for the March – May period, this is an increase from 66% last month. For the winter season, the probabilities have increased to 61%, up from 48% last month.  Oceanic El Niño remains the mostly likely outcome for the spring season at 48%. This continues to suggest the potential for a ‘protracted’ event (multi-year duration).

Sea Surface Temperatures

New Zealand’s coastal waters for February 2019 were warmer than average for the North Island and eastern South Island.  However, waters have cooled to near or below average for the north and west of the South Island.  Marine heatwave conditions are possibly being reached in the east-central Tasman Sea with anomalies of 2.0 to 3.0˚C above average by the last week of the month.  For the month as a whole, the anomalies are lower those observed during the marine heatwave of summer 2017-18.

The forecast models are consistent in predicting above to well above average regional ocean temperatures over the next three-month period (March – May 2019), which are expected to have a strong influence on New Zealand’s air temperatures.

Differences from average Febraury surface temperatures in the seas around New Zealand
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: Febraury SOI -1.3; December-February average -0.2.