Hurricane Polo is a strong Category 3 storm off Mexico. See its path.

Hurricane Polo could bring “life-threatening winds and flash floods” to parts of the Southwest U.S., Mexico’s Baja California Sur and nearby Sonora on Monday and Tuesday, forecasters said, with conditions starting to deteriorate in portions of the peninsula.

Polo, a Category 3 storm, was expected to strike Baja California Sur with near-major hurricane strength at landfall, the U.S. National Hurricane Center said. That means its maximum sustained winds would remain around 111 mph.

Map shows Hurricane Polo’s projected path

Forecasts predicted that the center of Polo would reach the coast of Baja California Sur late Monday afternoon or early evening. The storm would then proceed to move into southern Sonora late Monday night or early Tuesday and continue into the U.S. as a heavy rainmaker.

Flood watches are in effect for 11 states, including most of Arizona and New Mexico, and parts of Utah, Colorado, Kansas, Nebraska, Iowa and Texas. More than 14 million Americans are facing the risk of major flooding.

“Hurricane Polo will send a plume of moisture into the Southwest U.S., triggering a significant flash flood threat across the Four Corners Region eastward into the Central Plains,” the NWS Weather Prediction Center warned on social media, reminding people to never drive through floodwaters.

As much as 3 to 6 inches of rain could fall from Arizona to Texas and as far north as Iowa this week. Even higher amounts are possible locally. Major cities such as Phoenix, Albuquerque, Dallas, Oklahoma City and Omaha could see flash flooding for the next three days.

The hurricane center said Polo would likely weaken as it tracks inland toward mainland Mexico, but would still be powerful enough to be considered a hurricane by the time of its landfall there, with winds of at least 74 mph.

Storm watches and warnings

As of the hurricane center’s latest update Monday afternoon, the storm had maximum sustained winds of 115 mph. Hurricane-force winds were extending outward up to 40 miles from the center of the storm, while tropical storm-force winds extended outward up to 105 miles.

Polo’s intensity fluctuated over the weekend and into Monday as it swirled off Mexico’s Pacific coast.

Ahead of the storm’s imminent arrival on land, a hurricane warning was in effect for parts of Baja California Sur’s coasts and Mexico’s mainland from Bahia Kino to Huatabampito, and a hurricane watch was in effect for other parts of Baja California Sur’s coasts and mainland Mexico south of Huatabampito to Topolobampo.

A tropical storm warning is in effect for the west coast of Baja California Sur, north of Punta Abreojos to Punta Eugenia; the east coast of Baja California Sur, south of Loreto to San Evaristo; and mainland Mexico south of Huatabampito to Topolobampo.

Polo could produce 6 to 12 inches of rain across parts of Baja California Sur, 4 to 6 inches in parts of Sonora and up to 8 inches in other parts of Mexico, the hurricane center said, cautioning that the rain “may produce life-threatening flooding and mudslides, especially in areas of steep terrain.”

Mexican leaders ordered evacuations, opened shelters and deployed military troops to areas that could be affected by the storm.

Farther south, classes were suspended at schools across the city of Acapulco, along the coast of Guerrero, its municipal government announced. Shelters across the state remained open, and officials said they were coordinating with local and national authorities to prepare for additional impacts of the hurricane.

Polo’s extreme rapid intensification

Polo underwent what’s called extreme rapid intensification, in which a storm’s wind speeds increase by 58 mph or more over the course of 24 hours, between Sept. 21 and 22.

Its intensification was dramatic even by those standards, with winds that skyrocketed from 45 mph on the morning of Sept. 21 to 150 mph at around the same time the following day. The hurricane center described the storm’s transformation as “truly remarkable.”

Its maximum sustained winds climbed as high as 180 mph at one point, far exceeding the 157 mph threshold for Category 5, the strongest on the hurricane scale.

Polo’s central pressure — an indicator of its strength and potential destructiveness — made it the second-strongest hurricane on record in the Eastern Pacific, behind 2015’s Hurricane Patricia. The storm’s wind speeds tied 2009’s Hurricane Rick as the third-strongest on record for the region.

Unusually strong El Niño conditions this year have been amping up tropical cyclone activity in the Pacific, with warmer waters, moist air and less wind shear enabling storm formation.

Elsewhere in the Pacific, Hurricane Nolo moved past Hawaii’s Big Island this weekend, bringing heavy rain and winds.