Remnants of Tropical Depression Sixteen-E Bring Flash Floods to Phoenix, Albuquerque and Omaha Metro Areas

Heavy rainfall stemming from former Tropical Depression Sixteen-E caused flash flooding in at least three states and killed at least one person. Moisture from the depression made it all the way into the Upper Midwest Wednesday after drenching the Desert Southwest on Monday and Tuesday.

Local television station KOB-TV says one person died in Albuquerque, New Mexico, after driving into a flooded arroyo on Tuesday, Sept. 22. Flash flooding also occurred Tuesday evening near the eastern edge of the Phoenix metropolitan area, where roads were flooded by heavy rain from an intense but isolated thunderstorm near Apache Junction, Arizona.

On Wednesday morning, Sept. 23, extremely heavy rain broke out in parts of Nebraska and Iowa, including the Omaha metropolitan area. Rainfall rates from 3 to 4 inches per hour triggered flash flooding across the river from Omaha in Council Bluffs, Iowa.

Local media reported water over many city streets, up to vehicle bumpers in some areas. At least one vehicle stalled in flood waters, requiring a water rescue. Council Bluffs closed its public school system for the day due to extensive flooding of the city's flat western half.

A CoCoRaHS observer on the north side of Council Bluffs reported 8.00 inches of rain Tuesday through early Thursday. WOWT-TV reported 5,000 customers were without power in the Council Bluffs/Omaha area early Wednesday morning.

Omaha's Eppley Airfield reported 5.22 inches between midnight and noon Wednesday, making it the city's sixth wettest calendar day rainfall on record with half the day still to go. The final total for Wednesday was 5.74 inches of rainfall, making it the fourth-wettest day on record in Omaha and the second-wettest on record in the month of September.

Heavy rain fell across a swath of eastern South Dakota, northern and eastern Nebraska, and western Iowa, with several areas receiving 4 to 6 inches of rain. Despite the widespread heavy rainfall, only minor rises on area rivers occurred. It appears much of the rain soaked into the ground.

The Setup: A Tropical Tap

The floods in the Southwest and Midwest were fueled by moisture associated with the remnants of Tropical Depression Sixteen-E.

The combination of upper-atmospheric low pressure near the northern Baja California coast and upper-level high pressure centered over the Rio Grande Valley of Texas acted like an atmospheric egg-beater, piping an air mass chock-full of moisture northward into the Desert Southwest.

These summer surges of moisture in the wet phase of the North American monsoon are typical in the Desert Southwest. But deep moisture alone doesn't guarantee heavy rainfall. 

In this setup's case, the upper-level low along with the remnants of Tropical Depression Sixteen-E tracked across Southern California and the Desert Southwest early this week, providing added instability and lift in the atmosphere for clusters of thunderstorms.

Trajectory models clearly indicated that moist air some 30,000 feet above ground over the Omaha area Wednesday morning had originated from the tropical eastern Pacific Ocean. However, Wednesday's thunderstorms also wrung out moisture from lower levels of the atmosphere, which were also humid but contained moisture from other regions, including the Gulf of Mexico.

So while the depression's moisture contributed to Wednesday's flooding in the Midwest, the depression was not the sole cause of it.

By Thursday morning, Sept. 25, there was still a clearly identifiable center of low pressure aloft, marking the remnants of Tropical Depression Sixteen-E, over northeast Nebraska. Rain continued to fall across parts of the central and northern Plains, but was no longer heavy enough to cause significant flooding.

(MORE: Weather Underground Expert Blog on T.D. 16-E)

Storm History and Reports

Tropical Depression Sixteen-E originated in the eastern Pacific Ocean and quickly moved onshore, crossing Baja California and the Gulf of California before making its second and final landfall in northwestern Mexico Monday morning, about 160 miles south-southwest of the bend in the Arizona-Mexico border. Tropical Depression Sixteen-E then dissipated Monday afternoon over northwestern Mexico.

Even before the depression formed, moisture associated with its preceding disturbance contributed to thunderstorms with very heavy rainfall in northwestern Mexico. Mazatlan reported 122.5 millimeters (just under 5 inches) of rain in a 24-hour period Wednesday into Thursday morning, Sept. 16-17, and noroeste.com reported flooding of some neighborhoods in Culiacán.

Rain moved into southern Arizona early Monday morning (Sept. 21) and spread across much of Arizona and New Mexico Monday. Additional rain fell in those states Tuesday, Sept. 22, but more in the form of scattered but intense downpours.

(MORE: Utah Deadly Flood | Strange Southern California September Rain)

Rainfall totals from southern Arizona included:

• Dan Saddle, northeast of Tucson, recorded 4.61 inches through 7 p.m. Monday.
• Park Tank, near Redington Pass, reported 3.94 inches through 7 p.m. Monday
• White Tail, near Palisades, measured 2.87 inches through 7 p.m. Monday.
• Nogales, along the Mexican border, reported 1.89 inches of rain as of 6:54 p.m. MST Monday. 
• Davis-Monthan Air Force Base in Tucson measured just over one inch of rain through 7 p.m. Monday.

(MORE: Your Vehicle is Dangerous In a Flash Flood)

Tuesday brought 1.05 inches of rain to the Albuquerque International Sunport in New Mexico's largest city, tying for the sixth-wettest September day on record there.

Midwest rainfall totals Tuesday through early Thursday included:

• 8.00 inches in Council Bluffs, Iowa (north side)
• 6.60 inches in Coleridge, Nebraska
• 6.23 inches in Omaha, Nebraska (54-hour total at Eppley Airfield as of 1 p.m. Thursday)
• 6.00 inches in Glenwood, Iowa
• 5.95 inches in Reliance, South Dakota
• 5.32 inches in Audubon, Iowa

MORE ON WEATHER.COM: Deadly Utah Flooding