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IRI Climate Information Digest - December 1999

Issued 13 January 2000
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October-December 1999 Precipitation Percent of Average

Climatological Background

In December, the Northern Hemisphere enters the heart of winter, with strong north-south temperature differences driving the mid-latitude jet stream  and storm systems.  In the Southern Hemisphere summer is under way, with monsoon systems gaining strength  in South America, southern Africa, and Australia.

Ocean Temperatures

  • Tropics: In the tropical Pacific Ocean, La Niña (below average sea surface temperatures (SSTs) in the  equatorial Pacific) has continued to strengthen in the central part of the basin. However, most models are predicting this event to begin weaking through March.
  • Extratropics: Above average SSTs continue to persist in a broad band extending from Japan to the west-central North Pacific.  Warmer than average SSTs strengthened to the west of Australia  and along the west coast and southern tip of Africa.

Land Temperatures

  • Australia:  Colder than average temperatures occurred in Queensland and parts of Western Australia.
  • South America:  Warmer than average temperatures prevailed in the region of the Guyanas and through much of eastern Brazil with differences up to 2 degrees C above average.
  • Africa: Much of Africa reported temperatures up to 2 degrees C above average.
  • Europe and Asia:  Central Asia and the Middle East experienced above average temperatures, with differences exceeding 6 degrees C east of the Ural Mountains.
  • North America:  Most of Canada and the northern and central United States were warmer than average, with differences exceeding 6 degrees C in Saskatchewan, Alberta and Quebec.

Precipitation: October-December

  • Australia and Southeast Asia:  Above average rainfall fell in Queensland and  Western Australia marking an early start to the Australasian monsoon.  Tropical storm activity resulted in above average rainfall in Vietnam.
  • South America:  While Venezuela and the north coast received above average rainfall marked by several severe storms in December,  southeastern Brazil, Paraguay and Northern Argentina experienced drier than average conditions.
  • Africa: The rainy season in southern Africa is under way with average rainfall in the west but drier regions in the eastern Congo and Zambia for the three month period.
  • Europe and Asia:  Rainfall accumulations have been normal for the season, although Western Europe experienced violent storms in December.
  • North America:  Except for the Pacific Northwest, drier than average conditions  continued to prevail in much of the United States.
  • Middle East: Below average rainfall has persisted in the early part of the rainy season in Israel, Iraq and Syria.
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 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.For print versions of this Digest contact Sandy Vitelli .