Hurricane Erin, first of Atlantic season, weakens slightly to Category 4. Maps show its path and forecast.

Erin rapidly strengthened into a Category 5 hurricane over the Atlantic Ocean Saturday before weakening slightly to a Category 4 status, but it remained a “formidable” storm while it underwent a process known as an “eyewall replacement cycle,” the National Hurricane Center said. 

“Some fluctuations in intensity are expected over the next couple of days due to inner-core structural changes,” the Miami-based hurricane center said. 

A Category 4 hurricane is defined as having maximum sustained winds of 130 mph or higher.       

The center of Erin was skirting to the north of the northern Leeward Islands, which includes the Virgin Islands. It was forecast to move away from the Virgin Islands and Puerto Rico on Sunday, and then pass to the east of Turks and Caicos Islands and the southeastern Bahamas Sunday night and Monday. The hurricane center warned that heavy rain in some areas could trigger flash flooding, landslides and mudslides.

Tropical storm watches were in place for Turks and Caicos Islands. 

Erin, which grew from a tropical storm into a hurricane on Friday, is the first hurricane of the 2025 Atlantic season.

Forecasters urged people in the Caribbean islands to monitor Erin’s progress, warning of the potential for heavy rainfall and life-threatening surf and rip current conditions.

Erin is not currently forecast to impact the United States, but meteorologists continue to watch it closely.

What is an eyewall replacement cycle?

The hurricane center disclosed Saturday night that Erin was undergoing an “eyewall replacement cycle,” which, according to CBS News meteorologist Nikki Nolan, is when the storm has become so significantly powerful that its eyewall, its strongest part, reaches maximum strength.

When this happens, Nolan said, the eyewall itself becomes so intense from intaking the available energy from its environment that a new eyewall will begin to build on the outside of the existing, inner eyewall. Once the new eyewall is created, it cuts off the fuel to the original eyewall. 

Furthermore, as the new eyewall gains strength to keep up with the power of the storm, the radius of the eye itself will become much larger than it originally was, Nolan said.

This process may cause the storm to weaken temporarily, and its wind speeds may slow as it regains strength.

According to Nolan, however, after this process, the storm could emerge even stronger than it was before. 

Maps show Hurricane Erin’s forecast path

Erin’s path continued to curve northward, with the center of the hurricane passing just to the north of the northern Leeward Islands and Puerto Rico. 

The northern Leewards stretch from the Virgin Islands to Guadeloupe and include St. Martin, St. Barts and other islands. Officials  had issued tropical storm watches for several islands, alerting people of the possibility of winds ranging between 39 mph and 73 mph. 

A “spaghetti map” of the forecast models shows the storm skirting the Caribbean islands and remaining well offshore of the U.S. East Coast as it moves north.

A high-pressure system in the Atlantic was expected to steer Erin away from the Eastern Seaboard while a cold front was also forecast to push the hurricane offshore, CBS News Bay Area meteorologist Jessica Burch reported.

On the U.S. Virgin Islands, officials with the National Park Service announced that sites on the island of St. Croix would be closed starting late Friday afternoon until after the storm passes.

First hurricane of the Atlantic season

Erin formed as a tropical storm on Monday west of the island nation of Cabo Verde, a few hundred miles off Africa’s western coast. It is the fifth named storm of the 2025 Atlantic hurricane season, which started in June and runs through November. 

So far this year, Tropical Storm Chantal is the only one to have made landfall in the U.S., bringing deadly flooding to North Carolina in early July. In June, Barry made landfall as a tropical depression on Mexico’s eastern coast.

Erin’s increased strength comes as the Atlantic hurricane season approaches its peak in September. According to the hurricane center, most of the season’s activity typically happens between mid-August and mid-October. In the eastern Pacific Ocean, hurricane season starts on May 15 with a peak in activity typically seen in late August.

The U.S. National Oceanic and Atmospheric Administration, or NOAA, forecast an above-normal season for the Atlantic this year, expecting between 13 and 18 named storms.

Tropical storms have maximum sustained winds of at least 39 mph. Forecasters with NOAA anticipated that between five and nine of the storms this year could become hurricanes, which have sustained winds of at least 74 mph. Hurricanes are rated on a scale based on their wind speeds, ranging from Category 1, the weakest, to Category 5, the most severe rating.

NOAA forecasters predicted there could be between two and five major hurricanes in the Atlantic this season.

Nikki Nolan

contributed to this report.

• Atlantic Hurricane Season
• Hurricane
• National Hurricane Center