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IRI Climate Information Digest - August 1999

Issued 13 September 1999

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NOAA NCEP Sea Surface Temperature Anomaly
Highlights The equatorial Pacific saw a resurgence of La Niña  during August as below-average sea surface temperatures (SSTs) strengthened to the east of the dateline.  Weak above-average SSTs persisted in the western tropical Pacific. Elsewhere, warmer than average conditions eased in the Gulf of Guinea, the North Atlantic and the Indian Ocean while below average SSTs slackened in the eastern North Pacific.  A healthy west African monsoon  produced widespread rains throughout the Sahel  while the Asian monsoon circulation weakened in intensity.  Dry conditions persisted in portions of the North China Plain and the North American monsoon became irregular during the month. Lower temperatures and increased rainfall eased the heat wave/drought conditions over much of the eastern US.  And although slow to develop, the tropical cyclone season in the North Atlantic became well established during August with the naming of  four systems and three hurricanes which is close to average for the region and the month.

Precipitation La Niña conditions were evident in rainfall patterns in the tropical Pacific with reduced precipitation over central and eastern sections and enhanced rainfall over the southern Philippines and nearby islands.  Tropical storms brought heavy rainfall to the Korean peninsula but did little to alleviate drought in the North China Plain. Heavy rains associated with the west African Monsoon were observed in the Sahel while precipitation was noticeably absent along coastal sections near the Gulf of Guinea.   The Indian monsoon circulation weakened in August with precipitation over the subcontinent below-average  and noticeable rainfall deficits in northwestern India into Pakistan.  Much of the eastern US received beneficial rains to ease drought conditions while dry conditions developed over the southern states.  Dry conditions also prevailed over central South America.

Temperature Above-average temperatures were observed throughout southern Europe, the Middle East and southwest Asia.  In the eastern US cooler conditions developed while cool conditions persisted along the west coast.  Above-average temperatures were observed in the southern US and northern Mexico while cooler than average conditions prevailed in central South America from Bolivia into Paraguay and western Brazil.

Forecasts - Seasonal Temperature and Precipitation
Impacts - On Health, Agriculture, Hazards, Water Resources and Fisheries.

Material for the IRI Climate Information Digest has been extracted from the IRI Climate Data Library, the IRI Experimental Forecast Division, the NOAA NCEP Climate Prediction Center, the Climate Diagnostic Center, and the NOAA ERL Pacific Marine Environmental Laboratories. Additional information has been obtained from the Bureau of Meteorology, Australia, and INPE, Brazil.