Dorian is expected to strengthen Wednesday as it approaches Puerto Rico, where tropical storm warnings and hurricane watches are in effect.
Though Dorian is forecast to remain a tropical storm as it passes through Puerto Rico and the Dominican Republic, the storm may near hurricane strength and hurricane conditions cannot be ruled out.
Puerto Rico could see up to 8 inches of rain as well as flash flooding, life threatening rip currents and surf conditions and possibly near hurricane-strength winds on Wednesday.
Puerto Rico Gov. Wanda Vazquez has signed an order declaring a state of emergency as she warned residents to prepare.
"Hurricane Maria was a lesson for us and nearly two years after its devastating passage, today we can say that we are better prepared," Vazquez said Monday.
More than 7,400 generators and three mega generators are already on the island, according to the governor.
At least 360 shelters will open with a capacity of holding 48,500 people.
By the end of Tuesday, radios and satellite phones will be delivered to mayors and police departments throughout the island at all municipalities, officials said.
Vazquez added that she is in communication with the White House and there is a new Federal Emergency Management Agency (FEMA) representative on the island assisting in response coordination.
"The response to Tropical Storm Dorian will be on top of a complex recovery effort," the FEMA spokesperson said. "Even a smaller and less severe storm could have significant impact."
Dorian is forecast to move in between Puerto Rico and the Dominican Republic Wednesday night into Thursday, affecting residents in the Dominican Republic.
If Dorian still has strength at that point, it may track through the Bahamas and eventually toward Florida this weekend as a tropical storm.
The East Coast of Florida might be impacted Saturday night into Sunday.
ABC News' Matthew Vann contributed to this report.