Isidore could deliver deadly floods

Residents of Grand Isle, Louisiana, leave the barrier island on the Gulf of Mexico under a forced evacuation order Tuesday afternoon.

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VIDEO Officials in Galveston, Texas, are making contingency plans and preparing for Hurricane Isidore. KTRK's Jeff Ehling reports (September 24) PLAY VIDEO CNN's Harris Whitbeck describes the effects of Isidore after it swept over the Yucatan coast of Mexico (September 23) PLAY VIDEO CNN's Jason Bellini travels with the 'hurricane hunters.' PLAY VIDEO Tropical Storm Isidore At 8 p.m. EDT Tuesday Latitude: 23.0 degrees north Longitude: 89.7 degrees west Position: About 420 miles south of Louisiana coast. Next advisory:  11 p.m. EDT Tuesday Tropical Storm Kyle At 5 p.m. EDT Tuesday Latitude: 30.1 degrees north Longitude: 51.4 degrees west Position: 805 miles east of Bermuda Next advisory: 11 p.m. EDT Tuesday Tropical Storm Lili At 8 p.m. EDT Tuesday Latitude: 13.5 degrees north Longitude: 67.1 degrees west Position: 395 miles southeast of Santo Domingo in the Dominican Republic  Next advisory: 11 p.m. EDT Tuesday

MIAMI, Florida (CNN) -- Tropical Storm Isidore is expected to be a weak Category 1 hurricane when it hits the U.S. Gulf Coast early Thursday, but experts warn it still could be a killer storm.

"We don't want people to get lulled to sleep here. We often have loss of life even with a Category 1 hurricane," National Hurricane Center Deputy Director Max Mayfield cautioned.

"We're very concerned about not just the winds and the rainfall, but in particular, the storm surge flooding near, and to the east of, where the center crosses the coast, and in some of those shallow areas there in Louisiana," he said.

Low-lying Gulf Coast island Grand Isle as well as Morgan City and Houma -- two cities in marshlands southwest of New Orleans -- have already begun evacuations.

"People here, they know the drill," said Grand Isle Fire Chief Aubrey Chaisson of the evacuation by the island's 1,500 residents. "We're already getting flooded roads, heavy rains and tides two feet above normal."

Grand Isle Mayor David Camardelle issued the evacuation order at noon CDT (1 p.m. EDT), allowing plenty of time for residents to get on the one road and bridge connecting the island to the mainland. Grand Isle is about 60 miles south of New Orleans, and right in the middle of the projected path of the storm.

Isidore is wobbling along at near 7 mph in a northward motion, which is expected to continue over the next 24 hours as the storm gains in intensity.

Portions of the Yucatan peninsula and southeastern Mexico are expected to get more rain, with up to five inches expected Tuesday night.

Bands of heavy rain are already spreading over the northern Gulf and up to 20 inches of rain could batter the southeastern United States over the next several days, according to the NHC.

Much of the southeast coast of Texas already has been under a coastal flood warning. Parts of Louisiana, Mississippi, Alabama and the Florida Panhandle are under coastal flood watches.

Tropical storm force winds extend 345 miles outward from the center of Isidore.

The U.S. Coast Guard urged boaters to come into port immediately, said Chief Jeff Murphy, a Coast Guard spokesman. "We're also telling them to make sure they have a lifeboat and know how to use their distress signals."

Louisiana Gov. Mike Foster declared a state of emergency Monday.

Military preps under way

U.S. military installations on the Gulf coast are battening down hatches, sailing ships and flying aircraft out of harms way. As of Tuesday, a number of bases had evacuated ships and aircraft to safer locations.

Formosa said people who live closest to the coast may need to move inland when the storm arrives. "Listen to the local authorities," he said.

All Gulf residents are being urged to have at least three days of emergency supplies on hand. From New Orleans to Mobile people have been boarding up homes, buying canned food and supplies such as batteries.

Isidore was a Category 3 hurricane when it slammed Mexico's Yucatan Peninsula, forcing at least 70,000 people from their homes -- including entire villages. About 800,000 people lost phone and power lines.

The storm has been blamed for at least two deaths in Mexico.

Kyle and Lili building strength

Forecasters say Tropical Storm Lili could reach Hurricane strength on Wednesday. The storm slowed down as it traveled westward through the eastern Caribbean Sea Tuesday.

The southern coasts of the Dominican Republic and parts of Haiti -- from Punta Palenque west to Tiburon -- are under a tropical storm watch.

A tropical storm warning may be issued for Haiti late Tuesday or early Wednesday.

A carpenter boards up the Gallery Nine Forty in New Orleans, Louisiana.

Last week, Hurricane Isidore struck the western part of Cuba causing severe damage to parts of that island nation. The U.S. Naval outpost of Guantanamo Bay, Cuba, several hundreds miles east, is home to nearly 600 detainees from the war in Afghanistan.

As Lili now heads in that direction, U.S. military officials say that the new detention facilities at Camp Delta are strong enough to weather strong storms, although a severe hurricane could damage or destroy the units.

However, officials say the classified plan to move the detainees in the event of a major hurricane or storm would involve moving the detainees to a predetermined separate and secure location on the base.

Meanwhile, in the open Atlantic, Tropical Storm Kyle is also gathering strength and could become a hurricane by Wednesday as it moves in a southwest direction.

Far from land, Kyle has been described as a threat only to shipping interests and other boats in the Atlantic.

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