There is double tropical trouble during the first week of meteorological fall. Two tropical cyclones are spinning simultaneously in the eastern Pacific Ocean. The remnants of one of them will raise the risk of flash flooding this weekend in the Southwest.  

Hurricanes Kiko and Lorena are churning in the Pacific, whipping up strong winds and large waves. Kiko, located well over 1000 miles southeast of the Hawaiian Islands as of Thursday morning, is by far the stronger of the two. The storm's maximum sustained winds reached 145 mph by Wednesday night. 

Lorena, now considered a tropical storm rather than a hurricane, is weaker than Kiko by comparison in terms of wind speed, but it could bring major impacts to the weather in the southwestern U.S. this weekend. Lorena's maximum sustained winds were about half the strength of Kiko's, blowing at 70 mph early Thursday. However, it isn't the wind that is cause for concern this weekend; it's the moisture from the storm that poses problems.

"The rainfall from Lorena will be very track dependent," Alex DaSilva, AccuWeather's lead hurricane forecaster, told Newsweek. "If the storm moves inland (like is currently forecast) heavy rain can spread across southern Arizona, southern New Mexico and even into western Texas. This can lead to flash flooding in some locations."

Typically, hurricanes are more associated with the Atlantic Ocean and the Caribbean Sea and Gulf of Mexico that are part of it, but hurricanes can also form within the northeastern and central Pacific Ocean even though most Pacific tropical cyclones form elsewhere and are called typhoons or cyclones. 

Lorena should lay down her heaviest rains in Baja California Sur and Sonora, Mexico, through Friday. An additional four to eight inches is expected to fall there, bringing up to 15 inches of rain to the harder hit spots in the region.

"Across the southwestern United States, 1 to 3 inches of rain, with isolated totals up to 5 inches, are expected across portions of Arizona and New Mexico through Saturday, bringing the potential for isolated to scattered flash flooding," forecasters with the National Hurricane Center cautioned in a Thursday morning advisory for Lorena.

Nearly 27 million people across portions of at least ten states, most of them in the Southwest, face a marginal to slight risk, levels one and two out of four, respectively, for excessive rainfall that could produce flash flooding Friday into Saturday morning, according to the Weather Prediction Center. Southeastern Arizona and southwestern New Mexico have the highest risk of flooding.

Sunday's WPC excessive rainfall forecast has over 29 million people across portions of at least 17 states at a marginal risk for heavy rainfall that could produce flash flooding. Like Friday's forecast, several southwestern states will be targeted for some torrential rain.

Nearly 8 million people across three states were under a flash flood watch on Thursday. Southwestern states like California and Arizona were included. 

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"Moisture will continue to push into the area through Saturday, potentially bringing periods of heavy rainfall and increased likelihood for flash flooding," meteorologists with the Tucson National Weather Service office mentioned in a forecast discussion Thursday morning.

It was the remnants of a tropical storm that contributed to deadly flooding in Texas in July. Tropical Storm Barry formed in the Bay of Campeche, in the southwestern Gulf of Mexico, during late June. The remnant moisture from Barry drifted into Texas in early July, fueling clusters of showers and thunderstorms that dumped up to a foot of rain in just a few hours. It is estimated that 100 billion gallons of water, the equivalent of the daily volume of water that flows over the Niagara Falls, fell in the Texas Hill Country.

Scientists say our overheating planet is supercharging both hurricanes and rainfall rates. According to Climate Central, a nonprofit of researchers and climate communicators studying the impacts of climate change on people's lives, our overheating planet intensified every hurricane in last year's Atlantic season. Their peer-reviewed research revealed that "human-caused global warming elevated ocean temperatures and boosted all 11 storms' intensities, increasing their highest sustained wind speeds by 9 to 28 miles per hour."

Another study conducted by Climate Central found our warming world is driving up rainfall rates. Their analysis of 126 U.S. cities showed that 88% of them have experienced a rise in hourly rainfall intensity since 1970. Hourly rainfall rates have risen by 15% in 126 locations compared to five decades ago.

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