Forecasters are predicting rain showers for the shuttle Endeavour's first Florida landing opportunity Monday and possible thunderstorms for the second, one orbit later. If the forecast holds up - and the outlook is nearly as bad Tuesday - the returning Expedition 4 space station crew will extend their U.S. endurance record from 194 days to at least 195 and possibly 196.

NASA managers want to get the shuttle back on the ground in Florida if at all possible to have any chance at all of holding an October launch date for Endeavour's next space station assembly mission.

Endeavour has enough on-board supplies to remain in orbit until Thursday. With good weather expected all week at the shuttle's alternate landing site in California, NASA managers could wait until Wednesday, if it comes to that, before bringing the shuttle home on one coast or the other.

"The program really wants to get into Florida," entry flight director John Shannon said in a telephone interview.

But it is the weather that will tell the tale.

Endeavour has two chances to land in Florida Monday, at 12:59:06 p.m. and one orbit later, at 2:36:10 p.m. The forecast is decidely bleak, with rain showers expected within 20 nautical miles for the first opportunity - a violation of NASA flight rules - and possible thunderstorms in the area by the time the second opportunity rolls around.

NASA is not staffing Edwards Monday and Shannon said the agency might not staff the Mojave Desert landing site Tuesday, depending on the Florida forecast for Tuesday and Wednesday. If Endeavour hasn't gotten down by Tuesday, however, Shannon said he would recommend bringing Endeavour down one way or the other on Wednesday.

For most shuttle crews, the prospect of an extra day in space is not necessarily a bad thing. But for the space station's returning Expedition 4 crew - commander Yuri Onufrienko, Daniel Bursch and Carl Walz - every additional day in space is one more day away from family and friends.

They were launched to the space station Dec. 5. On June 11, Walz and Bursch set a new U.S. space endurance record, beating the old mark of 188 days set by astronaut Shannon Lucid in 1996 aboard the Russian Mir space station. A landing Monday would cap a record 194-day stay in space.

"Well, we have more film to shoot so you know, we'll just keep shooting film up here," Walz joked today when asked about the prospect of a landing delay. "Of course, we're hoping to be able to get back home tomorrow. But if we have to wait a day, we'll wait a day and we'll land in Florida on Tuesday."

Maybe.

Endeavour is scheduled for its next launch Oct. 6. The goal of mission STS-113 is to carry up the third section of the station's huge solar array truss. The shuttle must get off the ground by Oct. 11 to ensure a landing by Oct. 20. That's important because the next Russian Soyuz taxi flight is scheduled for launch Oct. 22 and there is a flight rule requiring a two-day separation between shuttle landings and Soyuz launches.

The Soyuz, in turn, must launch by Oct. 22 to ensure a full-duration mission and a landing by Nov. 1. Starting Nov. 2, landing opportunities would occur after dark, an option the Russians will not entertain.

Because of Endeavour's weeklong launch delay, some NASA managers believe they have already lost any chance of launching the shuttle in October. Others hold out hope the shuttle's prime contractor, United Space Alliance, can refine the processing schedule to bring in at least a few opportunities between Oct. 6 and 11.

But to have any chance at all of making October, Endeavour must get back to Florida this week. A diversion to California would all but guarantee a slip into November.

"We've got to land at the Cape to have any shot at all," said one NASA manager.

Weather aside, Endeavour came through a round of pre-entry systems checks today in good condition and Shannon said the orbiter is ready for landing.

"Today was a very good day," he said. "I'm happy to say Endeavour is in really good shape. We had a flawless checkout of all the entry systems and we had good comm checks with our landing site in Florida and our landing site in California."

While Edwards will not be staffed Monday, Shannon said NASA managers have not ruled out the possibility of bringing it up Tuesday.

"What I think will happen, if we can't land tomorrow we'll look at what Kennedy looks like on Tuesday, what it looks like on Wednesday and decide if Edwards should be brought up on Tuesday. ... The long-range forecast for Florida, Tuesday is not a great deal better ... so it'll be rain again. Wednesday looks much better, but it's pretty far away and I'm not sure the models have a good handle on it yet.

"If I had a pretty good feeling the Kennedy Space Center was going to be available to us Wednesday, and I continued to have the good feeling that Edwards would be good on Wednesday and Thursday, I would try for Kennedy Space Center tomorrow, Tuesday and make Wednesday what we call our 'pick 'em day' where we bring up two sites and pick the best of the two sites. I don't want to go down to the last day. I can if I have to, but I'd like to have that in my back pocket when we land."