Seasonal climate summary southern hemisphere (winter 2006): El Niño develops late but Australian drought already severe

Climatic conditions are summarised for the winter season of 2006 with emphasis on the state of the tropical Pacific region as well as rainfall and temperature over the Australian continent. The Southern Oscillation Index (SOI) had fallen sharply from high positive to negative values during April and May 2006, and the negative values were sustained and increased in magnitude during the winter. Other indicators pointed to the possible development of an El Niño event by the end of the season, but most had only just exceeded the normal thresholds. Sea-surface temperatures (SSTs) across the tropical Pacific Ocean increased in June and westerly wind burstsinduced warming of the subsurface waters. Although the warming halted in July, SSTs increased in August so that NINO3 and NINO4 indices were just above +0.8 at the end of the month. Westerly wind anomalies developed across the tropical Pacific in August; the subsurface warmed but no strong coupling formed between ocean and atmosphere in the Pacific. SST anomalies in the tropical Indian Ocean developed to resemble a positive Indian Ocean Dipole event. Reflecting the negative SOI, surface pressures across Australia were above average, particularly over the south.As a result, rainfalls in June and August were very low across the south of the country. Minimum temperatures were also very much below average. For Australia as a whole, 2006 had the second lowest June mean minimum temperatures on record (since 1950) and August 2006 was the driest since records began in 1900.