Seasonal climate summary for the southern hemisphere (autumn 2016): El Niño slips into neutral and a negative Indian Ocean Dipole develops

Abstract

This is a summary of the southern hemisphere atmospheric circulation patterns and meteorological indices for autumn 2016; an account of seasonal rainfall and temperature for the Australian region is also provided. While autumn began with a weak El Nino signal in the Pacific, the decay of the El Nino was evident with subsurface temperatures in the central and eastern Pacific continuing to cool. Later in the season, the Indian Ocean Dipole (IOD) transitioned to a negative phase. The negative IOD combined with warm water to Australia’s north channeled warm, moisture-laden air over the continent; unseasonable rainfall ensued, over eastern and northern Australia and New Zealand’s western coastal areas during May. Temperatures averaged over the southern hemisphere were record warm for autumn, both for land and ocean areas; separately or combined. For Australia, autumn arrived during a significant and prolonged heatwave that contributed to the warmest autumn on record for Australia. The elevated sea surface temperatures (SSTs) recorded in the Australian region earlier in the year persisted, and were warmest on record for autumn. Warm SSTs led to a global coral bleaching event affecting reefs in tropical waters; while, in extra-tropical waters, diminished kelp forests were observed. In the Australian region, reefs off the northwestern coast and, in northern areas of the Great Barrier Reef, were bleached. The most severe marine heatwave since records began was recorded in the Great Barrier Reef lagoon.