The effects of Hurricane Polo are expected to impact the southwestern United States after the powerful storm travels across Mexico, the National Hurricane Center said Tuesday. 

More than 30 million people from Arizona to Iowa could be at risk for flash floods Tuesday. Heavy rain has already flooded some roads in southern New Mexico, trapping drivers in cars until the waters receded. 

The rain will continue as Hurricane Polo crosses the region. 

Maps show Hurricane Polo’s path 

Polo is moving across Mexico’s Baja California Sur toward the northwest at about 10 miles per hour. That motion is expected to continue throughout Tuesday morning, along with significant acceleration, the NHC said. 

The core of the storm will then cross the Gulf of California and make a second landfall in Sonora, Mexico late Tuesday morning. 

The storm is expected to then move into the southwestern United States, nearing El Paso on Wednesday morning. 

The storm will likely have winds of about 35 miles per hour when it reaches El Paso. It will continue to weaken as it moves across the Southwest. 

Flash flood watches 

Flash flood watches are in effect from Phoenix, Arizona to Des Moines, Iowa. More than 14 million Americans are facing the risk of major flooding. Some areas may see up to two inches of rain per hour. 

The National Weather Service Prediction Center said that there will be a “significant flash flood threat across the Four Corners Region eastward into the Central Plains.” 

CBS News meteorologist Rob Marciano expressed a particular concern for the city of Albuquerque, New Mexico, where he said the rain may be “saturating.” The desert city is forecast to receive about two inches of rain. 

In southern Colorado and other parts of the I-35 corridor, the rain will stretch into Wednesday. Parts of Texas, including Dallas, may see rain through Thursday. Some parts of Texas may see more than seven inches of rain.  

An active Pacific region 

Hurricane Polo has been a powerful storm, at times fluctuating between Category 4 and Category 5. Part of the storm’s power is because it underwent a process called extreme rapid intensification, where wind speeds increase by 58 mph or more over the course of 24 hours. 

Polo’s intensification was particularly dramatic, with wind speeds jumping from 45 mph to 150 mph between Sept. 21 and Sept. 22. The NHC called called the change “truly remarkable.” 

The storm’s maximum sustained winds were as high as 180 mph over the weekend, tying 2009’s Hurricane Rick as the third-strongest on record for the region. Its central pressure made it the second-strongest hurricane on record in the Eastern Pacific, only behind 2015’s Hurricane Patricia. 

Another storm, Hurricane Nolo, moved past Hawaii’s Big Island and brought heavy rain and winds to the state over the weekend. 

Warmer waters, moist air and less wind shear in the region have helped enable storm formation. Unusually strong El Niño conditions have also led to increased tropical cyclone activity.