END InSight August  page  Tropical Storm Impacts on and New By Rebecca Carter areas at the headwaters of the ing across the border with south- Tonto Creek drainage. Most of the ern and most strongly Once the drama that monsoon deaths occurred as people at- impacting the western portions of storms can bring to Arizona and tempted to leave the campgrounds Arizona. New Mexico subsides toward the for home. Some rivers rose 5 to 10 end of August, it may seem like feet per hour, with Sycamore New Mexico is less likely to be af- time to breathe a sigh of relief and Creek, near Sunflower, experienc- fected by tropical storms, but may look forward to calmer autumn ing floodwaters that reached 36 still experience some minor im- weather. However, fall can also be feet above the creek bed. pacts. On rare occasions, tropical a time of dramatic and sometimes storms moving inland from the dangerous weather, due largely to The tropical storms that affect Ari- will cause heavy tropical storms. Actually, tropical zona are often the remains of hur- rains in the southwestern part of storms can feed into monsoonal ricanes that form in the eastern Pa- the state, according to the Western moisture flows and contribute to cific Ocean. Although the official Regional Climate Center. Interest- copious rainfall totals. hurricane season begins May 15 in ingly, the eastern and central parts the eastern and central Pacific ba- of the state also may be affected by Some of the most severe weather- sins, June through October are the tropical storms, but by those related events recorded in Arizona most active months for tropical spawned in the Atlantic, rather have been caused by tropical storm formation. Data from 1961- than in the eastern North Pacific. storms, more than can be attributed 2000 show that the storms peak in to either the monsoon or drought. frequency in August, with an aver- Flooding is by far the greatest threat When the National Weather age of 3.8 storms, while July and that tropical storms pose to Arizona Service’s Phoenix office put to- September each average 3.7 and New Mexico. However, high gether a listing of Arizona’s top ten storms. During a typical hurricane winds also can be a danger, al- weather/water/climate events for season, 16 named storms form in though this aspect of tropical the 20th century, flooding due to the eastern Pacific, 9 of which be- storms has been much less studied. tropical storms caused three of the come hurricanes, and 5 of those be- Although the lower elevation ten most costly weather events in come major hurricanes. winds that accompany such storms terms of impacts on people, prop- may dissipate by the time the storm erty, and the economy and also was While most tropical storms fall reaches Arizona or New Mexico, cited in four of the eleven honor- apart as they make landfall, some these gusts can still be quite well or- able mentions. do possess enough power to make ganized at higher altitudes, particu- it into Arizona and eastern New larly those over 7,000 feet. Tropical The deadliest natural disaster in Mexico. In fact, Erik Pytlak of the storms in general are likely to cause Arizona’s history was a tropical Tucson greater amounts of property dam- storm that resulted in 23 deaths. Office calculated that Arizona can age and other losses as populations According to National Weather expect a direct hit from a named grow in the Southwest. Service offices in Arizona, heavy tropical storm, including heavy rains were spawned by an influx of rainfall, every 4.5 years and that a ENSO conditions such as El Niño moisture from a dying Pacific storm will affect the state indirectly or La Niña can affect the year-to- tropical storm named Norma over every two years. That means that year levels of vertical wind shear Labor Day weekend of 1970. Dur- Arizona is more frequently af- over both the North Atlantic and ing the 24-hour period from 10 fected by tropical storms than eastern North Pacific. During an El p.m. September 4th to 10 p.m. Sep- some coastal states such as New Niño, vertical wind shear in- tember 5th, 11.4 inches of rain were Jersey! creases, which suppresses the abil- measured in the official recording ity of hurricanes to form. This ef- rain gauge at Workman Creek, Tropical storms that are likely to fect is particularly pronounced in about 60 miles east-northeast of affect Arizona are those that make the North Atlantic, where research Phoenix at an elevation of 7,000 landfall along the Pacific coast of indicates that during El Niño years feet. Of the 23 lives lost in the and travel north- the likelihood of hurricanes is de- flooding, 14 were in campground easterly into the state, often com- continued on page 4

Published by CLIMAS the Climate Assessment for the Southwest Project Institute for the Study of Planet Earth University of Arizona END InSight page 

Tropical Storms, continued have much of El Niño and La Niña Impacts on Tropical Storm Activity an effect on creased and during La Niña years tropical storm La Niña Neither El Niño the likelihood of Atlantic hurri- activity in the Duration (# days) 6.1 / 5.0 7.1 / 6.0 canes is increased. For example, El North Atlan- 6.5 / 6.0 Niño-like conditions from 1991 to tic. Similar # Storms 15.1 / 17.0 15.2 / 16.0 15.6 / 15.0 early 1995 were accompanied by comprehen- very little Atlantic tropical storm sive forecasts # Fall Storms 4.5 / 4.0 5.4 / 5.0 6.2 / 6.0 and hurricane activity. However, for the eastern the La Niña years of 1995 and 1996 North Pacific Note: # of years – La Niña = 9; Neither =18; and El Niño = 13, showed increased tropical storm are not avail- for 1961-1990. Average values are to the left of the slash and median values are to the right of the slash. activity in the North Atlantic, but able, which re- reduced the number of storms over flects a long- the eastern North Pacific. standing lack of attention to tropi- Niño events, tropical storms tend cal storms in this area. to be longer (7.6 days) and stron- During strong El Niños, such as ger, with a slight tendency toward 1997-98, the eastern North Pacific Gregg Garfin of the END Initiative greater than average frequency recorded close to an average num- has attempted to provide some an- (16.5). In contrast, during weak El ber of storms at 17, but the storms swers to what this tropical storm Niños, such as the one currently were more intense than usual. season may bring to Arizona and occurring, Garfin found that tropi- reached unprec- New Mexico. Garfin examined cli- cal storms tend to be shorter than edented sustained winds of 185 matological records from 1961- average length (5.6 days), fewer in mph, and Hurricane Guillermo fol- 2000 and found that the overall frequency (10.2), and weaker. lowed close behind at 162 mph. number of tropical storms is not This was also the year that Hurri- any greater during El Niño years Regardless of whether or not there cane Pauline devastated Acapulco, than during other years. is a clear El Niño influence on leaving 232 dead and hundreds of tropical storms, there is no doubt thousands homeless. The National Weather Service Tuc- that these weather systems can son office also found no clear link have major impacts on drought. El Niño also may affect the usual between El Niño and tropical For example, the remnants of track of tropical storms: in 1997, storm impacts in Arizona. Fore- Tropical Storm Olivia brought 3 to was one of two casters reviewed tropical storm 5 inches of rain to southeastern storms that tracked well north of records from 1965 to the present Arizona and southwestern New their normal area. Although the and found that of the nine direct Mexico around October 11 and 12, storm did not follow its expected hits that Arizona has received, 2000, according to the U.S. path and weakened considerably three occurred during El Niño Drought Monitor archives. This upon landfall, rainfall amounts of events, three happened during La ended abnormally dry conditions three to five inches were recorded Niña conditions, and three took in the area that had begun the pre- in western Arizona. Nora caused a place during neutral years. vious December in parts of the loss to agriculture estimated at sev- states and provided these areas eral hundred million dollars and However, Garfin found that the du- with a buffer in terms of soil mois- left about 12,000 people without ration of tropical storms during El ture and water supply that some electricity in Yuma, according to the Niño years is greater than the dura- climatologists say protected the NWS Tropical Prediction Center. tion of storms during La Niña years. area for over a year from wide- He also found that the number of fall spread drought conditions. The North Atlantic, on the other storms (September-November) is hand, experienced only seven greater during El Niño years. Thus, using the past as a guide to storms in 1997, compared to its av- the future, we might reasonably ex- erage of 10; of those, three became Garfin identified four strong El pect that Arizona will see a fairly hurricanes, as opposed to an aver- Niño events, and four weak ones, quiet tropical storm season, despite age of six. This year, NOAA’s Cli- based on their intensity during the the presence of an El Niño. How- mate Prediction Center does not start of the tropical storm season. ever, as you’ve heard before, no two expect the current weak El Niño to He found that during strong El El Niños are alike—so stay tuned!

Published by CLIMAS the Climate Assessment for the Southwest Project Institute for the Study of Planet Earth University of Arizona