AccuWeather.com
Rachel will maintain enough tropical moisture and integrity to bring much-needed rain to many areas, but at the cost of dangerous and damaging flash flooding, mudslides and other debris flows over a large part of the southwestern United States from Saturday night to Monday. Some areas will also experience strong wind gusts associated with squalls and severe thunderstorm activity.
It is conceivable that rain from Rachel could approach or exceed the entire annual rainfall for some desert locations.
Once a Category 1 on the Saffir-Simpson Hurricane Wind Scale, Rachel is maintaining tropical storm intensity on Saturday and is likely to make landfall as a tropical storm in the northwestern corner of Mexico late Saturday night. The storm will take a rare path into part of Southern California early Sunday morning.
Even though Rachel will lose wind intensity soon after landfall, AccuWeather will categorize it as a tropical wind and rainstorm over most of its time in the western United States since it will still bring significant, dangerous and costly impacts to the region.
Due to flooding rainfall and gusty winds, Rachel is a 1 on the AccuWeather RealImpact™ Scale for Hurricanes in the United States.
The RealImpact™ Scale for Hurricanes is a six-point scale, with ratings of less than one and 1 to 5, that accounts for not only wind speed, but also flooding rain, storm surge and economic damage and loss.
“The fast speed of Rachel will allow strong wind gusts to occur well inland over the U.S. from Sunday to Sunday night,” AccuWeather Chief Meteorologist Jon Porter said.
Thunderstorm activity will drag down strong winds from aloft as Rachel moves along, which can bring damaging gusts well into southeastern California, southern Nevada, Arizona and even Utah. There is the potential for a handful of tornadoes to be spawned in a small number of thunderstorms. Strong gusts can lead to sporadic power outages.
By far, the most dramatic impact from Rachel in the U.S. will be due to its rain.
These impacts will range from disrupting outdoor plans, travel delays and minor street flooding to drought relief. Motorists from Los Angeles and San Diego to Palm Springs, Las Vegas, Phoenix and even Salt Lake City should be prepared for flash urban flooding.
However, much more serious conditions are likely to unfold in some areas, where torrential rainfall leads to life-threatening flash flooding, mudslides and other debris flows.
The variance of conditions will extend from Southern California to Arizona, northward to much of Nevada and Utah and into parts of Idaho, Wyoming, Colorado and New Mexico.
“Locations most prone to flash flooding, such as canyons, arroyos and near dry streams, will be at greatest risk for dangerous conditions,” AccuWeather Meteorologist Brandon Buckingham said. Debris, such as tree trunks, lumber and boulders, can become damaging projectiles when driven by the force of the water.
Road and rail washouts will be possible in hilly terrain with sudden rockslides also being a threat to passing vehicles.
The storm will deposit a tremendous amount of rain on the region with much of that falling on the drought-stricken Colorado River basin.
Runoff will eventually work its way into Lake Powell and Lake Mead, where water levels dipped to historic lows this past summer. Rising water levels may force new adjustments on marinas that were moved due to receding lake levels.
A large area will exist where 1-4 inches of rain is likely to fall from Rachel over the interior Southwest. However, drenching downpours will reach the coast of Southern California for a time. Pockets of 4-8 inches of rain are likely to occur over the mountainous terrain in Utah, Arizona, Nevada and Southern California. In these areas, the AccuWeather Local StormMax™ rainfall is 12 inches.
Where rain soaks the autumn landscape, the wildfire threat will be significantly reduced and may remain suppressed for at least several weeks due to lower evaporation rates from October to November as temperatures trend downward.
“As tropical moisture from Rachel joins up with a non-tropical storm, jet stream energy and colder air over the interior Northwest and the northern part of the Rockies, tremendous snowfall rates may unfold in parts of Montana, Idaho and perhaps northwestern Wyoming later this weekend to early next week,” Buckingham said.
The same jet stream and non-tropical storm will send showers to coastal areas of California, Oregon and Washington through the weekend and into early next week. Since Rachel was the primary producer of swells offshore in the Pacific, as the tropical wind and rainstorm pushes well inland, seas and coastal flooding should subside from Sunday to Monday along the Southern California coast.
Toward the middle of the week, a new storm may form that gathers some of Rachel’s and Simon’s moisture over the middle of the nation.
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