Passengers wait in line at the Southwest Airlines ticket counter on Sept. 6, 2017 at Tampa International Airport. Many passengers were leaving Tampa on Wednesday ahead of Hurricane Irma which is threatening the Florida peninsula. (Chris Urso/Tampa Bay Times via AP)

The rush to get out of Florida is intensifying as Hurricane Irma gets closer, and following allegations of price gouging more airlines have joined JetBlue in announcing they will discount some one-way fares out of the state.

American and Delta were the first to follow JetBlue and say they are discounting fares for people trying to leave. Later Thursday, United also joined its fellow carriers as forecasters continued to warn that Irma could cause catastrophic damage when it makes landfall sometime this weekend.

The National Hurricane Center on Thursday issued a hurricane watch for the southernmost part of Florida, the first that Irma has prompted in the United States. A storm surge watch, which warned of potentially life-threatening levels of water, was also issued for the southern part of the state, an area that includes the Florida Keys, where evacuations began Wednesday.

Delta said Thursday it will cap fares in all cabins at $399 for flights to and from South Florida through Sept. 13. In addition, the airline will waive all baggage and pet-in-cabin fees for customers traveling to or from selected cities. Delta officials also said they are adding more than 2,000 seats to scheduled flights, including 1,100 in Fort Lauderdale and 400 in Miami.

American said it will cap one-way fares at $99 each way for the main cabin and $199 for the premium cabin on direct, single-leg flights to cities covered under their travel alert, which is now in place for more than 40 airports.  The fares will apply to flights out of the affected area through Sept. 17 and returning to the affected area between Sept. 10 and Sept. 17.

United also said it would cap fares at $399, but offered no details beyond that.

American added 3,600 seats to help folks get out of the state.  The airline added 16 extra flights from its hub in Miami: 12 to Dallas-Fort Worth; one to Philadelphia and three to New York’s Kennedy Airport. United said it added six new flights to the region.

JetBlue was the first to announce that it would offer a limited number of $99 one-way tickets for travelers trying to flee Irma through Sept. 13. But according to a note on the airline’s website many of those seats have already been booked.

Officials at Delta said they have been “examining and adjusting” Florida fares since early this week when Irma’s path became clearer. They tapped Henry Harteveldt, a San Francisco-based industry analyst to explain how demand impacts pricing.

“There’s only so much airline capacity to any destination,” he said. “When bad weather hits, there’s typically a surge of last-minute demand. Normally, these last-minute fares may be expensive. When bad weather may affect a city or region, an airline can make more last-minute, lower-fare seats available to help people who need to travel find and get an affordable fare.”

Delta officials said that Miami, Fort Lauderdale and West Palm Beach airports are expected to close Friday night, as the first signs of Irma begin to approach South Florida. Delta is canceling operations Saturday and possibly Sunday, but that will depend on weather conditions. The airline has also expanded its weather waiver to include airports along the Georgia and South Carolina coast.

They noted that St. Thomas and St. Martaaen airports remain closed.

At Key West International Airport, all air carrier operations will be suspended after the last air carrier flights depart Thursday, Don DeGraw, airport director, said in a Facebook post. He said the Delta and American flights will be the last to leave. General aviation traffic will be allowed to operate until the runway is closed late Friday or early Saturday, he said. Already some car rental services at the airport are closed, but a few remained open Thursday with just about about 10 cars remaining.

American said Wednesday that it will begin winding down its Florida operations in Miami, Fort Lauderdale, Fort Meyers and West Palm Beach Friday evening. The airline has canceled flights from those airports for Saturday and Sunday, in addition to several international flights that were scheduled to land in Miami on Friday. The airline’s last Miami departure is scheduled to be Flight 2213, departing at 3:49 p.m. Eastern Time and headed to Dallas/Fort Worth, Texas. At Orlando, the airline will wind down operations Saturday afternoon at 2 p.m. ET. and Sunday flights are canceled.

United said it will halt operations in South Florida starting Friday afternoon and extending through the weekend.

Meanwhile, Transportation Security Administration officials said they are deploying 250 people at airports in the southeast who will then travel to Florida to assist with airport security after Hurricane Irma moves through the region. Many of the workers are volunteers — from as far away as San Jose, Calif. and Detroit, will fill in for colleagues who live in the storm’s path.

Mandatory evacuations in Miami are expected to affect at least 200 TSA employees — and officials said that number could expand depending on the path of the storm.

“My thoughts and prayers are with all those impacted by the storms,” said TSA Administrator David Pekoske, who visited Houston on Wednesday. “We are actively engaged in preparing for Hurricane Irma and its impact. We have begun to move TSA personnel into that area of the country so that we will have people in place to provide security screening when the airlines and airports are ready to resume service after the storm passes.

“Currently, we have nearly 1,000 TSA employees who are participating in recovery efforts related to both hurricanes,” he added. “I am proud of and humbled by the spirit and dedication to service exhibited by the TSA workforce during this difficult time.”