Tropical Storm Norma (1970)

Infobox Hurricane|Name=Tropical Storm Norma
Basin=EPac
Year=1970
Type=Tropical storm
Image location=Tropical_Storm_Norma_(1970).jpg


Formed=August 31, 1970
Dissipated=September 5, 1970
1-min winds=50
Pressure=992
Damagespre=>
Da

Inflated=0
Fatalities=23 indirect
Areas=Arizona, Utah, Colorado, New Mexico
Hurricane season=1970 Pacific hurricane season

Tropical Storm Norma was the fourteenth named tropical cyclone of the 1970 Pacific hurricane season. The storm formed off the coast of Mexico and intensified rapidly, peaking as a strong tropical storm on September 3 before starting a weakening trend which saw it dissipate before making landfall on Baja California.

While the storm never made landfall, the remnants from the storm fueled the Labor Day Storm of 1970, which caused floods in Arizona that resulted in heavy damage and loss of life. The rainfall from this storm broke records, mostly for 24 hour rainfall totals. Despite not being tropical when the damages were done, Norma is considered to be the deadliest system in Arizona history.http://www.wrh.noaa.gov/psr/tropics/hurricanes.htm]

Meteorological history

A tropical disturbance was first noted in a satellite picture taken on August 30. Soon after, a weak low pressure center associated with the system formed convert|100|nmi|km|-1 southwest of Acapulco, Mexico.http://docs.lib.noaa.gov/rescue/mwr/099/mwr-099-04-0286.pdf] The system later went through rapid intensification, becoming a tropical depression on August 31 and Tropical Storm Norma later that day. Initially with a loose organization, Norma continued to organize and strengthen, reaching its peak of convert|60|mi/h|km/h|-1|abbr=on on September 2. Satellite pictures showed cirrus outflow was greater in the tops of the feeder bands than in the eyewall chimney. On September 3, Navy reconnaissance reported a 992 mbar pressure, Norma's lowest..

Shortly after the 992 mbar report, however, Norma began to weaken. The same recon that reported the convert|60|mi/h|km/h|-1|abbr=on and 992 mbar reading reported back with a mere convert|40|mi/h|km/h|-1|abbr=on some time after. Despite the sudden drop in winds, the minimum pressure remained around 994 mbar. The weakening became obvious on satellite presentation, which showed cool inflow and a sheet of stratocumulus clouds around the west semicircle extending under the storm clouds. Norma continued to weaken, degrading into a depression by September 4. At this point, the circulation forced moist and unstablemaritime air into Arizona which resulted in disastrous floods during Labor Day along with a slow moving cold front. This system would become known as the Labor Day Storm of 1970. On September 5, a cloud spiral was still visible west of Baja California, but the storm's circulation dissipated, with the remnants of the storm finally dissipating on September 6, just before making landfall on Baja California.

Impact

While Norma did not make landfall while tropical (even though it came close to making landfall on Baja California before dissipating), the circulation introduced unstable air into Arizona and Utah which, along with a cold front, resulted in record amounts of rainfall.

Arizona

The rainfall in Arizona produced deadly flash floods which caused over $1 million in damages and killed 23 people, 14 of which died when Tonto Creek, which was in the vicinity of Kohl's Ranch, became flooded. Other deaths were reported among automobile drivershttp://ci.show-low.az.us/departments/public_works/MultiHazardMitigationPlan/Appendix%20F/HistoricalHazards_Navajo.pdf#search=%22%22Labor%20Day%20Storm%20of%201970%22%22] . Total rainfall exceeded 7 inches in certain locations, with Workman's Creek receiving convert|11.92|in|mm of rain. Other amounts were recorded in Upper Parker Creek (9.09 inches), Mount Lemmon (8.74 inches), Sunflower (8.44 inches), Kitt Peak (8.08 inches), Tonto Creek Fish Hatchery (7.12 inches), and Crown King (7.02 inches). There were also reports of injuries by campers in Mogollon Rim and Scottsdale reported significant property damage. The major flooding in the state prompted a presidential disaster declaration.http://www.flagstaff.az.gov/common/modules/documentcenter2/documentview.asp?DID=1087#search=%22%22Labor%20Day%20Storm%20of%201970%22%22] .

Utah

While the storm was causing floods in Arizona, the lower cities of Utah were also experiencing heavy rainfall. The most noteworthy rainfall total was recorded in Bug Creek, which experienced an estimated convert|6|in|mm of rain in a 24 hour period. [http://www.ametsoc.org/amsedu/online/oceaninfo/samplecourse/news.html Weekly Ocean News ] ] http://www.wrcc.dri.edu/htmlfiles/state.extremes.html] . No deaths or damage was reported in connection to the storm.

Records

When convert|11.40|in|mm of rain fell at Workman's Creek in a 24-hour period, it became the highest amount of rain to fall in Arizona in a 24 hour period. The record stood until 1997, when the remnants of Hurricane Nora produced convert|11.97|in|mm of rain on the top of Harquahala Mountain.

A similar record was recorded in Utah when convert|6|in|mm of rain fell in Bug Creek in a 24 hour period. Unlike the Arizona rainfall record, this record still stands today.

When the rains of Norma caused the San Juan River to flood it's banks, a size of 1,090 m3/s was obtained, making this the largest flood of the San Juan since 1962, when the Navajo Dam was completed. The most runoff from the storm was downstream from the reservoir. [http://pubs.usgs.gov/of/2001/ofr01-314/ CHANGES IN RIPARIAN VEGETATION IN THE SOUTHWESTERN UNITED STATES: Floods and Riparian Vegetation on the San Juan River, Southeastern Utah ] ]

With 23 associated deaths in Arizona, Norma was the deadliest storm in the state's history.

Lack of Retirement

Despite the damage and loss of life in Arizona, the name Norma was not retired. The name remains in use today and was most recently used in 2005 and is set for use next in 2011.

ee also

* List of tropical cyclones
* List of Pacific hurricanes
* List of wettest tropical cyclones in Arizona
* Hurricane Nora (1997) - 1997 hurricane in the East Pacific that produced gale-force winds and heavy rainfall in the Southwestern United States.

External links

* [http://docs.lib.noaa.gov/rescue/mwr/ Monthly Weather Reports from up to 1972 (PDF files).]
* [http://ams.allenpress.com/amsonline/?request=index-html A more extensive collection of Monthly Weather Reports up to and including 2006 (PDF files.]

References