IRI Climate Information Digest - September 1999
Issued 13 October 1999
July-September 1999 Precipitation Departure from Average
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.
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
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
Forecasts - Seasonal Temperature and Precipitation
Impacts - On Fisheries, Agriculture, Health and Hazards.