Seasonal climate summary southern hemisphere (spring 1998): a weak, but intensifying, cold event (La Niña) in the Pacific basin

Southern hemisphere circulation patterns and anomalies for spring 1998 (September - November) are reviewed, with emphasis given to the tropical Pacific and the Australian region. Compared with winter, there was a decline in the speed with which cold event conditions were developing in the tropical Pacific. The Walker Circulation in the western Pacific continued to strengthen, and there was a gradual expansion and intensification of cooling along the central equatorial Pacific. However, substantial subsurface cooling failed to make an impact on the surface in the eastern Pacific, which was still largely characterised by warmer than normal water. The resulting weak La Niña pattern was distinctly asymmetric and non-classical. A wet spring over Australia made it two wet seasons in succession. Tropical-extratropical cloudbands and an active early northern wet season were the chief rainfall-producing mechanisms. Maximum temperatures across Australia were generally close to normal, but minima were significantly above normal over the northern half of the country.