| Feature Article East Pacific hurricanes bring rain to Southwest By Melanie Lenart the time frame 1966–1984, according to an earlier analysis by Walter Smith of Pacific hurricanes and tropical cyclones the National Oceanic and Atmospheric can have a profound influence even on Administration (NOAA) that was pub- the landlocked Southwest—and, argu- lished in 1986 as a NOAA Technical ably, their impact may increase as the Memorandum. oceans warm. However, it’s unlikely the studies by “It turns out that there’s quite a lot of Ritchie and Walter are directly compa- tropical cyclone activity that actually rable. Detecting remnants of tropical impacts the Southwest,” explained Eliza- cyclones remains more of an art than beth Ritchie, a climatologist who joined a science, researchers noted, as official The University of Arizona faculty this long-term tracking data ends when wind summer. September is the peak month speeds fall below tropical storm status. Figure 5. Satellite image of hurricane Javier for this activity, which has resulted in on September 13, 2004 approximately 610 some serious floods in years past. From 1974 through 2004, the number miles southeast of Cabo San Lucas, Mexico. of intense East Pacific hurricanes in- Source: Jesse Allen, NASA Earth Observatory, An average of 2.2 remnants from East creased by about a third, according to a data from the MODIS Rapid Response team Pacific hurricanes and named tropical study by Peter Webster of the Georgia cyclones ventured into the Southwest Institute of Technology and several Tropical storms generally must encoun- each year between 1992 and 2004, colleagues. Intense hurricanes have ter sea surface temperatures (SSTs) of 83 representing 15 percent of the region’s sustained winds above 130 mph. Web- degrees Fahrenheit or more to attain the named storms, Ritchie found in an ster and his colleagues compared data sustained 111 mph wind speeds of ma- analysis she conducted with a colleague. based on satellite imagery and found 49 jor hurricanes, based on a study of 270 A tropical cyclone must reach sustained intense hurricanes forming from 1990 Atlantic hurricanes and corresponding wind speeds of 39 miles per hour (mph) through 2004 compared to 36 forming SSTs by Patrick Michaels and colleagues to qualify for a name, and 74 mph to at- from 1974 through 1989. from the University of Virginia (Geo- tain hurricane status. physical Research Letters, May 2006). Their finding and its perceived link to All but two of the 29 cyclones brought global warming via rising sea surface The tropical storms that do reach the at least some rain to the Southwest. The temperatures remains controversial Southwest can provide drought relief researchers defined the Southwest as among some researchers (see June 2006 or cause floods, sometimes both. The Arizona, California, and New Mexico. Southwest Climate Outlook). Although remnants of Hurricane Javier (Figure climate experts agree rising ocean tem- 5) helped break a string of dry years in “The main story is Albuquerque re- peratures strengthen individual hur- September 2004, ushering in a wet win- ally does the best out of all these sites,” ricanes, they disagree on whether past ter by gently soaking parts of drought- Ritchie noted, adding, “Tucson is not data is reliable enough to reveal a trend parched Arizona and New Mexico. far behind.” directly connected to global warming. Too much of a good thing led to flood- During this 13-year time frame, Albu- More intense East Pacific hurricanes ing in the autumn of 1983, when four querque received a total of 20 inches of won’t directly translate into more rain- cyclone remnants visited the Southwest. rainfall from tropical cyclone remnants, fall in the Southwest, at any rate, as The storm from former Hurricane Oc- while Tucson received 12 inches and David Gutzler, a climatologist at the tave created the most havoc, causing Phoenix collected 4 inches. Compared University of New Mexico, pointed out. $500 million in flooding damage to Ari- to the annual average rainfalls for these That’s because storms are more likely zona with its days-long rains. three cities, the values amount to half a to become intense when contacting the year’s worth for Phoenix, a year’s worth warm waters of the open sea, he noted, Melanie Lenart is a postdoctoral research for Tucson, and more than two years’ while those heading into the Southwest associate with the Climate Assessment for the Southwest (CLIMAS). The SWCO feature worth for Albuquerque. must swing toward cooler coastal waters. article archive can be accessed at the fol- The current from Alaska typically keeps lowing link: http://www.ispe.arizona.edu/ About 1.3 tropical cyclone remnants af- U.S. coastal sea surface temperatures in climas/forecasts/swarticles.html fected the Southwest each year during the 70s and below even in August. http://www.ispe.arizona.edu/climas/forecasts/swarticles.html Southwest Climate Outlook, August 2006