Seasonal climate summary southern hemisphere (winter 1999): a return to near-normal conditions in the tropical Pacific

Circulation patterns and associated anomalies for the austral winter season 1999 are reviewed, with emphasis given to the tropical Pacific and Australian regions. As a whole, surface ocean and atmospheric indicators of the El Niño - Southern Oscillation displayed near neutral values during the winter of 1999, suggesting the moderate La Niña event whose intensity had peaked during the previous summer season had effectively ended. In the ocean subsurface, however, residual cool anomalies persisted through the season, and showed signs of strengthening and expansion in August, forewarning the reestablishment of Pacific cool conditions which was to occur later in the year. In contrast to the near neutral phase of the El Niño - Southern Oscillation in the Pacific, winter 1999 was far from normal in the Australian region. The season as a whole was very anticyclonic, with seasonal pressure anomalies widely greater than +2 hPa, and approaching +5 hPa near Victoria. The positive pressure departures took the form of an anomalously strong and poleward shifted subtropical ridge, and were reflected in the lowlevel circulation as east to northeast wind anomalies over Australia. Seasonal rainfall totals and cloud amounts were widely below normal, particularly over southern parts, reflecting the prevalence of high pressure systems and a relative absence of substantial frontal passages. Seasonal mean maximum temperatures were mostly higher than normal with the Australia-wide value a near record, while the seasonal mean minimum temperature anomalies were mixed and of modest amplitude.