Days after it knocked out Puerto Rico’s power grid, Hurricane Fiona intensified to a Category 3 storm early Tuesday as it neared the Turks and Caicos Islands and subjected parts of the Dominican Republic to heavy rains, the National Hurricane Center said.

Fiona was producing maximum sustained winds of 115 miles per hour as of 2 a.m. Eastern time on Tuesday the center said in an early morning forecast. Its maximum sustained wind speed had been about 110 m.p.h. late on Monday night.

Up to 20 inches of rain were forecast in eastern portions of the Dominican Republic, where life-threatening flash flooding was already occurring, the center said.

The storm was about 45 miles south-southeast of Grand Turk Island, home of the capital of Turks and Caicos, as it moved north northwest at about 10 m.p.h. early Tuesday. Later in the morning, it was expected to pass near the easternmost part of the islands and to bring tropical-storm conditions to parts of the southeastern Bahamas.

Forecasts did not anticipate the storm nearing the East Coast of the United States, but the hurricane center said that it could generate swells causing life-threatening surf and rip currents there.

On Monday afternoon, Fiona had moved northwestward into the Atlantic Ocean and continued to strengthen after battering the northeastern coast of the Dominican Republic through the day and knocking out power across Puerto Rico on Sunday, causing what the governor there called “catastrophic” damage.

More than 1.2 million customers in Puerto Rico were still without electricity as of Tuesday morning, according to poweroutage.us, which tracks power interruptions. Puerto Rico’s power company, LUMA, warned that full restoration could take several days.

The hurricane center said early on Tuesday that in addition to causing heavy rain across the Caribbean, Fiona would produce mudslides, landslides and catastrophic flooding in Puerto Rico.

The storm was blamed for at least one fatality in Puerto Rico, where a man died while trying to operate a generator, government officials said. The man’s wife was severely burned, but survived, the officials said. Another death was attributed to the storm in Guadeloupe, which was struck by the storm on Saturday. At least one death had been attributed to the storm in the Dominican Republic.

The storm made landfall in the Dominican Republic, meaning the eye of the storm crossed the shoreline, at 3:30 a.m. Eastern on Monday near Boca de Yuma.

The republic’s eastern provinces, home to one of the largest tourism industries in the Caribbean, took the brunt of the storm. Fiona brought 90 m.p.h. winds and heavy rain that set off mudslides, shuttered resorts and damaged highways, officials said.

Storm surge was anticipated to raise water levels by as much as 1 to 3 feet above normal tide in coastal areas hit by onshore winds in the Dominican Republic, the hurricane center said in its forecast on Tuesday.

A hurricane warning remained in effect Tuesday morning for Turks and Caicos. The eastern coast of the Dominican Republic from Cabo Caucedo to Puerto Plata was under a hurricane watch. A tropical storm warning was in effect for the southeastern Bahamas.

The Atlantic hurricane season, which usually runs roughly from June through November, had a relatively quiet start, with only three named storms before Sept. 1 and none during August, the first time that has happened since 1997. Storm activity picked up in early September with Danielle and Earl, which formed within a day of each other.

The links between hurricanes and climate change have become clearer with each passing year. Data shows that hurricanes have become stronger worldwide over the past four decades. A warming planet can expect stronger hurricanes over time and a higher incidence of the most powerful storms — though the overall number of storms may drop, because factors like stronger wind shear could keep some weaker storms from forming.

Hurricanes are also becoming wetter because there is more water vapor in the warmer atmosphere; storms like Hurricane Harvey in 2017 produced far more rain than they would have without human effects on the climate, scientists have suggested. Also, rising sea levels are contributing to higher storm surges, the most destructive elements of tropical cyclones.

In early August, scientists at the National Oceanic and Atmospheric Administration issued an updated forecast for the rest of the season, which still called for an above-normal level of activity.

In it, they predicted the season could include 14 to 20 named storms, with six to 10 turning into hurricanes that could sustain winds of at least 74 m.p.h. Three to five of those could strengthen into what the agency calls major hurricanes — Category 3 or stronger — with winds of at least 111 m.p.h.

Last year, there were 21 named storms, after a record-breaking 30 in 2020. For the past two years, meteorologists have exhausted the list of names used to identify storms during the Atlantic hurricane season, an occurrence that has happened only one other time, in 2005.

Johnny Diaz, Amanda Holpuch, Mike Ives, Anatoly Kurmanaev, Eduardo Medina, Christopher Mele, McKenna Oxenden, Vimal Patel, Hogla Enecia Pérez, Víctor Manuel Ramos, April Rubin, Edgar Sandoval, Chris Stanford, Derrick Bryson Taylor and Daniel Victor contributed reporting.