Passengers due to fly into the path of Tropical Storm Dorian may be able to reschedule their flights for free.

Several US airlines are offering travel waivers to customers with scheduled flights to the eastern Caribbean as the storm travels through the Caribbean Sea.

The National Hurricane Center issued a tropical storm warning and a hurricane watch for Puerto Rico on Tuesday morning. It's expected to strengthen when it makes landfall in the US territory Wednesday, CNN meteorologist Dave Hennen said.

Delta

Delta customers with flights scheduled until August 29 to parts of the Dominican Republic, Puerto Rico, Haiti and Saint Lucia can change out their flight, free of charge, before September 5. Passengers who cancel their trip can use the value toward a future flight, the airline said.

Southwest

Customers flying Southwest to Turks and Caicos, the Dominican Republic and Puerto Rico between today and August 30 may rebook a flight. They must rebook within 14 days of their original travel date and can reschedule their travel plans online, too, if they booked on Southwest.com.

American

American Airlines will waive the fee to change flights scheduled until August 29 if they're canceled. Trips to Barbados, Haiti, Martinique, the Dominican Republic, Puerto Rico and Saint Lucia are subject to cancellation.

JetBlue

Passengers flying to or from several cities in Puerto Rico and the Dominican Republic on August 28 and 29 can reschedule their flights without a cancellation fee, JetBlue said. What's more, JetBlue will waive fare differences, too, as long as customers rebook through September 1.

Spirit

Spirit will waive the fee to change flights for passengers with flights between August 27 and 30 to Puerto Rico, Haiti or the Dominican Republic. Customers must rebook no later than September 5.

Frontier

Frontier allows customers with flights booked to Puerto Rico and the Dominican Republic until August 30 to make one change to their itinerary free of charge.