MIAMI — Dangerous tropical weather brewed Saturday in the Atlantic Ocean with Humberto intensifying into a powerful Category 4 hurricane and a separate weather system taking aim at the Southeast U.S.

The mayor of South Carolina’s port city Charleston declared a state of emergency ahead of the system that’s forecast to reach the southeastern U.S. coastline as a hurricane early next week.

“Today’s action is about readiness,” Charleston Mayor William Cogswell said in a news release. “Our teams are clearing drains, staging pumps and barricades, and adjusting staffing so we can respond quickly if conditions worsen.”

Gov. Henry McMaster, who declared a state of emergency for all of South Carolina on Friday, advised residents to pay close attention to the storm.

“While the storm’s arrival, speed, and intensity remain hard to predict, we do know that it will bring significant wind, heavy rainfall, and flooding across the entire state of South Carolina. We have seen this before,” McMaster said.

Hurricane Humberto had maximum sustained winds of 145 mph (230 kph) Saturday, according to the Miami-based National Hurricane Center’s latest advisory. The storm was located about 365 miles (587 kilometers) northeast of the northern Leeward Islands. It was moving west at 8 mph (13 kph).

Humberto could produce life-threatening surf and rip currents for the northern Leeward Islands, the Virgin Islands, Puerto Rico and Bermuda over the weekend, forecasters said.

The National Weather Service in Puerto Rico issued a small craft advisory, urging people to stay ashore and avoid unnecessary trips, with Saturday’s swells from Humberto expected to reach about 7 feet (2 meters) in Atlantic waters. They also advised residents to heed the beach warning flag system due to the high risk of rip currents.

Coastal and urban areas of the island were also under an extreme heat warning.

Meanwhile, a weather system likely to develop into a tropical storm over the weekend was threatening parts of the Bahamas and Cuba with heavy rainfall and flash flooding. Parts of the Bahamas were under a tropical storm warning on Saturday.

The Bahamas’ Department of Meteorology urged residents in the northwest and central islands, which include New Providence, Andros Island, San Salvador and Long Island, to “make final preparations” for possible tropical storm conditions to begin late Saturday or early Sunday. They noted rainfall in the central and southeast Bahamas could reach between 4 and 8 inches (10 and 20 centimeters) with some isolated areas seeing up to 10 inches (25 centimeters).

“Residents in low-lying areas should take actions to mitigate property damages due to flooding,” the department warned in a statement.

Gradual strengthening into a tropical storm is expected by Sunday as the system runs parallel offshore of Florida’s Atlantic coastline.

Officials across South Florida, which has been saturated by rain throughout September, continued keeping an eye on the system. A tropical storm watch was issued Saturday for parts of the Florida coastline north of West Palm Beach to an area north of Daytona Beach.

In Homestead, Florida, which was devastated by Hurricane Andrew in 1992, Emergency Manager Jaime Hernandez worried about complacency among residents.

“Too many South Floridians who may have experienced limited impacts from storms that came close in recent years, such as Hurricane Irma in 2017, have come away from these events mistakenly believing they have ‘been through the big one,’” Hernandez said.

He notes that Homestead is one of only four communities in the continental U.S. to experience the catastrophic impacts of a Category 5 hurricane. “We know all too well the importance of having an emergency plan and remaining informed,” Hernandez said.

The tropical disturbance brought heavy rains in the Dominican Republic on Friday, leading authorities to evacuate hundreds of people and declare a red alert in five provinces.

Flooding in the southwestern province of Azua displaced at least 774 people, and 26 were being sheltered due to the overflowing of the Tábara River, Civil Defense spokesman Jensen Sánchez told The Associated Press.

In the eastern Atlantic, the center of post-tropical cyclone Gabrielle moved away from the Azores. A hurricane warning for the entire Portuguese archipelago was discontinued.

Gabrielle was expected to approach the Portugal’s coast by early Sunday. Swells expected to produce life-threatening surf and rip currents were expected to reach Portugal, northwestern Spain and northern Morocco on Saturday.

In the Pacific Ocean, Hurricane Narda was churning about 1,025 miles (1,650 kilometers) west-southwest of the southern tip of Baja California and heading west-northwest at 12 mph (19 kph). The Category 1 storm was expected to maintain its strength on Friday before weakening over the weekend.

Swells generated by Narda were affecting coastal Mexico and Baja California Sur, forecasters said. The swells that could bring life-threatening surf and rip current conditions were expected to reach southern California over the weekend.

Associated Press reporter Regina Garcia Cano reported from Caracas, Venezuela.

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