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Arizona's Summer Monsoon Storm Season
Monsoon Storms in Southern Arizona
The word "monsoon", originally comes from the Arabic word, "mausim", meaning "a season". It was first used to describe the winds over the Arabian sea, which blow from the northeast for six months and from the southwest for another six months.
In Arizona, the monsoon, begins with the extreme dry heat of May and June, when temperatures rise to 100 degrees and above. As the atmosphere warms, the dry jet stream moves northward and the winds shift up from the south. This shift brings in humidity and moisture from the Sea of Cortez, and the Gulf of Mexico. Once the moist air arrives, the intense summer sun heats the air, creating columbous clouds, which lead to frequent afternoon and evening thunderstorms with a spectacular display of lightning.
Officially, the monsoon starts on June 15th and ends on September 30th.
Average date of monsoon storms beginning - July 7
Earliest Monsoon beginning on record - June 16, 1925
Latest monsoon beginning on record - July 25, 1987
Average date of first break in monsoon - August 16
Average total number of monsoon days - 56
Greatest number of monsoon days on record - 99 in 1984
Greatest number of consecutive monsoon days on record - 72 in 1984 (June 25 - September 5)
Least number of monsoon days on record - 27 in 1962
Wettest monsoon on record (July, Aug. and Sept. rainfall) - 9.38 inches in 1984
Driest monsoon on record (July, Aug. and Sept. rainfall) - .35 inches in 1924
Average monsoon rainfall (July, Aug. and Sept.) - 2.45 inches
Tucson Lightning Storm
Causes of floods in the Southwest
Flooding causes more deaths in the United States than any other weather-related hazard except severe heat.
In Arizona and New Mexico, floods killed 57 people between 1995 and 2006, while hundreds of others have needed swift water rescues. The economic price tag is also high, costing Arizona, New Mexico, Colorado, and Utah approximately $5 billion between 1972 and 2006.
The Dangers of Flash Flooding
Flash floods can occur within minutes after the onset of a rain storm. They can be deadly because water levels rise quickly and flow like rapids within minutes.
City streets become rivers, because with no drainage system, except for low-lying washes and arroyos the water has nowhere to go and cannot be absorbed into the ground.
Mountainous areas also experience flash floods, as the higher grounds funnel water into the canyons. One tragedy in 1981, killed eight people in the Sabino Canyon area in Tucson, Arizona. (my hometown)
Share the Monsoon Madness
- National Oceanic and Atmospheric Administration: Office of Climate, Water, and Weather Services. 2009. Weather Fatalities. http://www.weather.gov/os/hazstats.shtml (last accessed on April 21, 2009).
- Changnon S.A. 2008. Assessment of flood losses in the United States, Journal of Contemporary Water Research & Education, 138:38-44.
- House, P.K. and V.R. Baker. 2000. Paleohydrology of flash floods in small desert watersheds in western Arizona. Water Resources Research, 37:1825-1839.
- Desilets, D. and S.L. Desilets. 2006. Magnitude of flash floods on the rise in the Sabino Creek. Arizona Geophysical Union, Fall Meeting 2006, abstract with programs: H21B-1369.
- Lenart, M. 2006. East Pacific hurricanes bring rain to Southwest. In Lenart, M. (ed.) Global warming in the Southwest: Projection, observations, and impacts. University of Arizona, Climate Assessment of the Southwest, Tucson, Arizona.