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IRI Climate Information Digest - July 1999

Issued 13 August 1999

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NOAA CPC precipitation percentile
The monsoon system in North America has been a significant force in the climate system in July. The northward migration of large scale moisture-carrying, onshore flows has been quite strong in the American southwest.  In Africa's Sahel region the monsoon has been more irregular, while in Asia the monsoon moisture has not yet reached into the northwestern Indian subcontinent or northern China.  In addition, warmer than average sea surface temperatures (SSTs)  span much of the North Atlantic and tropical Atlantic oceans.  The above average SSTs of the tropical Atlantic have intensified in the Gulf of Guinea.  In the tropical Pacific Ocean,  weak La Niña conditions, which are characterized by below average SSTs, continued in the central part of the basin, with relatively cold conditions in the eastern Pacific off the coast of Peru.  However, the  warmer than average conditions in the far western Pacific have been dissipating so that the east-west temperature contrast in the tropics is much smaller than it was a year ago. Much of the Indian Ocean is near normal with regions of slightly above normal temperatures, particularly near western Australia.
Scattered monsoon rainfall spread northward into the Sahel region of west Africa during July marking a slow start to the rainy season there while more abundant rainfall continued along coast of New Guinea. Although the All India Monsoon Rainfall was near average for July,  dry conditions prevailed particularly in northwestern India and Pakistan with the exception of  north central sections of India  eastward into Bangladesh where above normal rainfall was observed.  Above normal rainfall was also observed in southern China and parts of eastern Asia, but monsoon rains have failed to progress into northern China. The North American summer monsoon produced substantial rainfall over the southwestern US and provided some relief to the dry conditions in northern Mexico.  Anomalous dry conditions continued over Chile, much of the eastern US, and in a latitudinal band extending  from the UK eastward across northern Europe into northern Russia.
Extreme heat affected the eastern third of the United States.  Above average temperatures were also prevalent in Europe from the United Kindom eastward to the Ural Mountains, northeastern Asia and central and southern Africa.
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 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.