Hurricane Ernesto has cut off half of Puerto Rico's power grid and is strengthening on its way towards Bermuda

CNN

By Elizabeth Wolfe, Robert Shackelford and Mary Gilbert, CNN

(CNN) — As Hurricane Ernesto moved away from the island Wednesday afternoon, it brought torrential rain to Puerto Rico after its strong winds left hundreds of thousands of people without power there and in the Virgin Islands.

The Category 1 hurricane had sustained winds of 85 mph early Thursday. according to the National Hurricane Center.

“Strengthening is expected over the next few days, and Ernesto could become a major hurricane by Friday,” the hurricane center said. A Category 3 or higher storm is considered a major hurricane.

After passing over the Virgin Islands and bypassing Puerto Rico on Tuesday, Ernesto was located about 635 miles southwest of Bermuda at the time of the center’s 5 a.m. update.

A hurricane warning has been issued for Bermuda. The effects of Ernesto are expected to be felt Friday afternoon. In addition to hurricane-force winds, the island could experience significant coastal flooding and up to 20 centimeters of rain – and up to 30 centimeters in some areas.

Strong winds extended far beyond its center, reaching gusts of over 120 km/h – hurricane force – in Puerto Rico and the U.S. Virgin Islands.

In Puerto Rico, around half of all customers on the island were temporarily without power on Wednesday, according to LUMA Energy, the private company responsible for power transmission and distribution in Puerto Rico. By Wednesday evening, around 540,000 people were still without power.

In the U.S. Virgin Islands, nearly 28,000 customers were without power, according to PowerOutage.us, or about 55% of the island’s covered customers.

More than 6 inches of rain fell in Puerto Rico, and subsequent storm bands continued to unload Wednesday afternoon, causing flash flooding – particularly in eastern and southern Puerto Rico and the Virgin Islands.

In the mountainous town of Barranquitas, just over 10 inches of rain fell in 24 hours, according to a preliminary report from the weather service, while Villalba received about 9.5 inches of rain.

Several Flood warnings were still in effect Wednesday evening for northern parts of Puerto Rico.

Affected by water treatment systems

According to the island’s water authority, heavy rains and flooding caused several rivers in Puerto Rico to overflow their banks and disrupted water filtration processes at several water treatment plants to varying degrees.

Due to these outages, more than 120,000 water customers – about 10% of all customers – were without access to drinking water as of early Wednesday afternoon, according to the island’s emergency portal.

Ernesto has already reached the open Atlantic waters, but its power was still felt in parts of the Caribbean for most of the day.

On the east coast of Puerto Rico, a storm surge caused water levels to rise by 30 to 90 centimeters early Wednesday. Life-threatening waves and backwash could pose a threat to life for anyone in the water through the weekend.

Ahead of the storm, Puerto Rico’s governor Pedro Pierluisi mobilized the National Guard and urged people to shelter in their homes. Public schools have been closed across the island and nearly 80 shelters have been opened.

Residents have been warned to prepare for widespread power outages as the island’s fragile and aging power grid is still being repaired following its destruction by Hurricane Maria in 2017.

Power outages are a daily nuisance for Puerto Ricans, many of whom have witnessed the laborious and slow efforts to modernize an electrical grid that remains highly vulnerable to natural disasters.

LUMA Energy said it had mobilized teams across the islands to respond to power outages. And LUMA President Juan Saca urged residents to report power outages as the utility may not be aware of all outages.

“Puerto Rico’s electrical system is not sufficiently modernized to detect power outages,” Saca said Tuesday, The Associated Press reported.

Where Ernesto goes next

On Wednesday, Ernesto began to gradually move northward, moving away from the Caribbean and into the open Atlantic waters, where it is expected to continue to strengthen.

Ernesto will become a strong Category 3 hurricane later this week and could maintain that strength or become a powerful Category 2 hurricane as it passes Bermuda this weekend. How hard the storm will hit Bermuda will depend on how close it gets to the tiny island, which is one-third the size of Washington, DC.

“Rains associated with Ernesto could reach Bermuda as early as Thursday and cause flash flooding in Bermuda later this week and over the weekend,” the U.S. Hurricane Center said.

Bermuda will experience increased rain and wind impacts if the hurricane passes just west of the island as currently forecast. If Ernesto passes east of the island, the island may be spared more intense impacts.

Ernesto’s power is enhanced by very warm ocean waters – a result of global temperature increases due to fossil fuel pollution – and by minimal storm-disrupting winds aloft.

Ernesto will have widespread impacts later this week and this weekend, although its path lies somewhere over the open Atlantic.

Although the storm does not pose a direct threat to the mainland U.S., it will create dangerous beach conditions along the entire East Coast.

“The swell is expected to reach the east coast of the United States Thursday night and continue into the weekend,” the hurricane center said. “This swell is likely to create life-threatening surf and current conditions.”

Are more tropical problems ahead?

Apart from Ernesto, no tropical systems are currently expected in the Atlantic until at least early next week.

This short break in new development will not last long.

According to the Climate Prediction Center, the likelihood of another hurricane will increase again later in August and last until at least early September.

The most active time of the hurricane season is from mid-August to about mid-October, so the predicted increase in hurricanes is to be expected.

But tropical activity in the Atlantic is already faster than average. This basin usually doesn’t see its fifth named storm until late August and its third hurricane until early September.

Both have already happened, in what is expected to be a very busy season.

CNN meteorologist Taylor Ward and CNN’s Ella Nilsen and Amanda Musa contributed to this report.