The U.S. National Hurricane Center in Miami said Monday evening that Air Force Reserve hurricane hunter planes found that Maria had strengthened into a storm with 260 km/h winds.
The hurricane is about 25 kilometres east-southeast of Dominica and moving west-northwest at 15 km/h.
The storm was on a path that would take it near Dominica and the Leeward Islands later on Monday, and then on toward Puerto Rico and the Dominican Republic on Tuesday and Wednesday.
"This storm promises to be catastrophic for our island," said Ernesto Morales of the U.S. National Weather Service in San Juan. "All of Puerto Rico will experience hurricane force winds."
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