IRI Climate Information Digest - May 1999
Highlights La Niña remains a significant factor in the global climate even though the magnitude diminished somewhat in May. Computer models and statistical indicators suggest that this cold episode will continue to diminish slightly, or hold steady, over the next two or three months. These same forecast tools further suggest that La Niña will regain some of its strength in the Northern Hemisphere autumn and that cold conditions will remain until early in 2000. Other ocean basins also showed significant temperature departures not necessarily associated with La Niña. The south Atlantic Ocean experienced above average temperatures over most of the basin for the second consecutive month. Ocean surface temperatures were more than 1oC above average just to the south of the Gulf of Guinea. The Indian Ocean was characterized by a pattern of warmer waters near Australia and relatively cooler waters surrounding the Indian sub-continent.
Precipitation Patterns La Niña conditions dominated the western Pacific rainfall pattern during May 1999 continuing a pattern of generally wet conditions west of 140 E longitude and dry conditions to the east in equatorial regions. There appeared to be very little La Niña related rainfall departures outside of this core region except, perhaps, the enhanced rainfall in southern Africa. Enhanced rainfall along India's west coast was mainly due to the effects of a tropical storm. Drier conditions in many of the African countries along the Gulf of Guinea were likely related to the warmer than average ocean temperatures and southern displacement of the inter-tropical convergence zone. The same sea surface temperature pattern may also be related to enhanced rainfall in the eastern Amazon basin. Dry conditions continued along the eastern North America from Nova Scotia through the Gulf of Mexico.
Temperature Above average temperatures were evident in Western Europe, all of Africa, the Mid-East and Australia. Cooler than average temperatures were recorded from the Scandinavian countries eastward through much of European Russia. In contrast, much of Russia to the east of the Ural mountains experienced above average temperatures. Western North America experienced below average temperatures partially in response to below average sea surface temperatures which stretched from the western Pacific La Niña regions northeastward to the west coast of the continent. In South America the eastern Amazon recorded below average temperatures near the regions of enhanced rainfall.