Fiona strengthened into a hurricane on Sunday as it barreled down on the US island territory of Puerto Rico, which has been devastated by previous storms, the National Hurricane Center said.
Packing winds of 80 miles (130 kilometers) per hour, Fiona is forecast to strengthen further in the next 48 hours as it moves toward Puerto Rico and the Dominican Republic before heading for the Atlantic Ocean.
"Fiona becomes a hurricane," the NHC said in an advisory, warning that "torrential rains and mudslides (are) expected across Puerto Rico and the Dominican Republic."
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"Additional strengthening is forecast during the next 48 hours while Fiona moves near Puerto Rico, the Dominican Republic and over the southwestern Atlantic," it said.
Puerto Rico and part of the Dominican Republic -- an island nation located to its northwest -- are under a hurricane warning.
This means "hurricane conditions are expected somewhere within the warning area, in this case within the next 24 hours," NHC said.
Puerto Rico -- which has suffered from major infrastructure problems for years -- was hit by hurricanes Irma and Maria in 2017, devastating the island and its electrical grid.
The grid was privatized in June 2021 in an effort to resolve the problem of blackouts, but the issue has persisted, and the entire island lost power earlier this year.
The former Spanish colony became a US territory in the late 19th century before gaining the status of associated free state in 1950.
After years of financial woes and recession, in 2017 the island declared the largest bankruptcy ever by a local US administration.