Residents of Puerto Rico are scrambling for supplies in advance of the storm, while the governor has declared a state of emergency, rationing basic provisions like water and baby formula.
The storm is expected to bring up to 16 inches of rain to the U.S. and British Virgin Islands and up to 25 inches to Puerto Rico, causing life-threatening flash floods and mudslides. The islands could also see several tornadoes throughout Wednesday.
Puerto Rico Gov. Ricardo Rosselló told reporters Tuesday that Maria "promises to be much more devastating" than was Hurricane Irma, which killed at least 70 people as it plowed through the Caribbean and the Southeastern United States earlier this month.
"If you are in a flood zone, your life is in danger," Rosselló said. "If you are in a wooden house, your life is in danger."