Hurricane Polo, an extremely powerful Category 4 storm, swirls off Mexico's Pacific coast. See its path.

Hurricane Polo, an extremely powerful Category 4 storm, continued to swirl off Mexico's southwestern coast early Wednesday but was only expected to skirt the Pacific shoreline over the next few days, not make landfall, as it continues along its path.

The U.S. National Hurricane Center said Polo's maximum sustained winds — which had rapidly intensified Tuesday, reaching as high as a 180 mph — decreased somewhat to 150 mph, not far beneath the 157 mph threshold which would make it a Category 5, the strongest on the hurricane scale.

The storm is expected to fluctuate in intensity over the next few days, forecasters said, but remain a "very powerful major hurricane."

Maps show Hurricane Polo's path

As of early Wednesday, Polo was located about 165 miles off the coast of Zihuatanejo, a coastal resort city in the Mexican state of Guerrero. Polo's outer rain bands were starting to reach the coast, the hurricane center said.

It hurled hurricane-force winds outward up to 40 miles from its center and tropical storm-force winds some 105 miles out, but was roughly stationary, crawling northward at 2 mph.

Polo was forecast to bring tropical storm conditions to parts of the coastline starting Wednesday. In some areas, heavy rainfall "may produce life-threatening flooding and mudslides, especially in areas of steep terrain," the hurricane center warned.

The storm remains far south of Mexico's Baja California peninsula, but the longer-term forecast indicates it could turn in that direction early next week.

The Mexican government issued a tropical storm warning for a stretch of the Mexican coast from Tecpan de Galeana, in Guerrero, to Punta San Telmo, in Michoacán. A tropical storm watch was in effect from Punta San Telmo to Playa Perula, in the state of Jalisco. Tropical storm warnings are issued when forecasts indicate tropical storm conditions will develop in a particular area, while tropical storm watches are issued when those conditions are possible, but not imminent. 

In this case, the hurricane center said people under a tropical storm warning should expect those conditions to take shape on Wednesday. For those in the watch area, such conditions could develop by Thursday.

Parts of Guerrero and Michoacán may receive between 3 and 6 inches of rainfall as Polo barrels past, with up to 8 inches possible in certain spots, through Thursday. Between 2 and 4 inches of rain could also fall in coastal parts of the states of Oaxaca, Colima and Jalisco through Thursday, forecasters said. 

Along with rain, Polo was also expected to cause life-threatening surf conditions, including rip currents, along the southwestern Mexican coast. The surf conditions could also contribute to flooding.

Polo is the second-strongest hurricane on record in terms of its central pressure in the Eastern Pacific (behind Patricia in 2015) and tied for third-strongest in terms of wind speed (along with Rick in 2009).

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.