Hurricane Polo makes landfall over Mexico. See its path.

Hurricane Polo made landfall in Baja California Sur, Mexico, bringing "damaging winds and life-threatening flash flooding," the U.S. National Hurricane Center said, and is expected hit the Southwest U.S. with heavy rain and flooding later in the week.

Polo had maximum sustained winds of 110 mph when it moved over land, making it a strong Category 2 storm on the hurricane scale. Its top winds then decreased significantly to 80 mph, making it a Category 1.

Map shows Hurricane Polo's projected path

Polo's core "will continue moving across Baja California Sur ... then move inland over southern Sonora late this morning," the Miami-based hurricane center projected.

It's expected to weaken slightly but remain a hurricane for its second landfall over mainland Mexico, then weaken further as it continues inland on Tuesday.

Mexico's Baja California Peninsula, seen below, is across the Gulf of California from the mainland Mexico state of Sonora.

Several U.S. states could feel Polo's effects

Flood watches were 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 that they should never drive through floodwaters.

Storm watches and warnings

Hurricane-force winds were extending outward up to 30 miles from Polo's center early Tuesday, while tropical storm-force winds extended outward up to 90 miles.

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 is expected to dump 6 inches to a foot of rain on Baja California Sur, and 4 to 6 inches, 8 at most, on Sonora, the hurricane center said.  

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 over the weekend, bringing heavy rain and winds.