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IRI Climate Digest
August 2003
July Global Climate Summary
Climatological Background
In July, heating of the continents in the Northern Hemisphere results in strengthened monsoon systems which bring rains to West Africa, South Asia, and southwestern North America. In the Southern Hemisphere, winter has set in, with stronger north-south temperature gradients fueling active mid-latitude storm tracks.
Monthly Mean Temperature (1961-1990), data from the Climate Research
Unit, University of East Anglia
Monthly Mean Precipitation (1961-1990), data from the Climate Research
Unit, University of East Anglia
Temperatures
Highlights
A distinct global circulation pattern over the mid latitudes of the Northern Hemisphere was reflected in July's temperature departures. Warmer-than-normal temperatures continued across Europe and North Africa and in eastern Russia, whereas cooler conditions were found across central Russia and Ukraine. Unusually cool temperatures and wet conditions persisted in Japan throughout July. The western U.S. and Australia experienced warmer-than-normal temperatures.
Temperature Difference from the 1961-1990 mean, with data
from NCEP Climate Prediction Center, CAMS.
Precipitation
Highlights
Nearing the height of the monsoon season over West Africa, rainfall associated with the intertropical convergence zone (ITCZ) was shifted slightly northward of its normal position in July, bringing above-normal rainfall to much of the western Sahel and below-normal precipitation to the Guinea Coast region. Enhanced monsoon rainfall also fell in parts of western and northern India during the month, although drier conditions were found in much of southwestern India. Dry conditions were found across much of southeast Asia and southern China while above-normal rainfall continued in the North China Plain and extended eastward across the Korean Peninsula and Japan. Above-normal precipitation continued across much of the eastern and southeastern U.S., while dry conditions dominated much of western North America. Dry conditions continued in much of western Europe and Scandinavia, although above-normal precipitation fell in parts of the British Isles, the Iberian Peninsula, and eastern Europe. Dry conditions also developed in southern Brazil and Uruguay in July. In the near-equatorial Indian Ocean, above-normal rainfall continued in the west and dry conditions continued in the east, with the exception of the Bay of Bengal.
Precipitation Difference from 1961-1990 mean, with data
from NCEP Climate Prediction Center, CAMS-OPI.
Oceanic Conditions
Tropical Pacific: Sea surface temperatures (SSTs) in the Tropical Pacific continued their return towards neutral conditions in July. Equatorial waters off the South American coast warmed from their slightly below average state in June while the relatively warm waters in the western Pacific continued through July. See the latest IRI ENSO Update for a detailed summary and outlook.
Tropical Atlantic: SSTs off the central African coast and along the equator in the Gulf of Guinea increased to above-average levels while the relatively warm waters near the coasts of West Africa and northern South America persisted through July.
Indian Ocean: Overall, above-average conditions continued in the Indian Ocean though they weakened slightly as the SSTs off the Greater Horn of Africa decreased to near-normal levels.
Mid-latitudes: There were very few changes in the mid-latitudes in the Southern Hemisphere as is typically seen in the winter months. At the peak of its summer, the SSTs in the Northern Hemisphere were more dynamic. SSTs along 30°N in the Pacific decreased while those further north increased to generally above-average temperatures. Waters in the Atlantic between 30° and 50°N warmed, with the exception of those northwest of the Iberian Peninsula which exhibited slight cooling during July.
Monthly Sea Surface Temperature Difference from the 1971-2000 mean,
with data from the Environmental Modeling Center, NCEP/NOAA.
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