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IRI Climate Information Digest - September 1999

Issued 13 October 1999

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July-September 1999 Precipitation Departure from Average

Highlights September marks the middle of the hurricane season and the end of the monsoon season in the northern hemisphere.  It is also the end of the winter season in the southern hemisphere. The tropical storm season has been active, with 8 named Atlantic storms so far this season and 6 west Pacific storms in September. The continental monsoons have met or exceeded rainfall expectations in most regions with a few exceptions (northern China and western India). The southern hemisphere winter season has been drier than average in northern Argentina and southern Brazil.
Ocean Temperatures

  • Tropical Pacific: The La Niña (colder than average sea surface temperatures)  in the tropical Pacific Ocean continued to evolve as a weak to moderate event.  Below average temperatures returned in the central Pacific in August and shifted toward the eastern Pacific in September. Models are predicting cold conditions to strengthen and persist through December with a relaxation to average conditions by April.
  • Tropical Atlantic and Indian: The warmer than average temperatures which dominated the Atlantic Ocean and the Indian Ocean have decreased to near average conditions.
  • Extratropics: Warmer than average surface temperatures continue in the northwestern Pacific and northwestern Atlantic oceans. Below average temperatures persist in the eastern North Pacific.
  • West Africa: Monsoon rainfall in West Africa and the Sahel was above average in September and, for most of the region, slightly above average for the season.
  • South Asia: Lack of rainfall in the western and southern regions of India continued in September resulting in slightly below average All-India Summer Monsoon Rainfall.
  • East Asia:  The monsoon season rainfall was above average in central and southern China and below average in the North China Plain.
  • North America: The North American summer monsoon continued to bring abundant moisture into the Southwest in September, while the eastern United States remained dry, excepting the now flooded coastal regions affected by Hurricane Floyd.
  • South America: Central and southern Chile received abundant rainfall, while southern Brazil and northern Argentina experienced a relatively dry cold season.
Unseasonably warm temperatures occurred in  northeastern North America and in central and northern Europe. Warmer than average temperatures dominated the Middle-East and southern Asia during September.   Central and southern Australia  and much of South America also experienced  above average temperatures for early spring.

Forecasts - Seasonal Temperature and Precipitation

Impacts - On Fisheries, Agriculture, Health and Hazards.

Material for the IRI Climate Information Digest has been extracted from the IRI Climate Data Library, the IRI Experimental Forecast, 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.