Showers and thunderstorms are likely to develop in Florida around the time of this week\'s planned final launch of the space shuttle, NASA\'s weather officer said on Tuesday. \"We have a 60 percent chance of KSC (Kennedy Space Center) weather prohibiting launch,\" shuttle weather officer Kathy Winters told reporters, ahead of Friday\'s planned liftoff. \"Our primary concern for launch would be showers and thunderstorms within 20 nautical miles,\" said Winters. She added that the turbulent weather and clouds were likely to move in \"near the end of the countdown, right around that 11 am time period.\" Atlantis is set for liftoff July 8 at 11:26 am (1526 GMT) from Kennedy Space Center for a 12-day mission the International Space Station with four US astronauts on board. The flight will be the last by a US shuttle, ending the 30-year program and leaving a gap in US human spaceflight. Until a new crew vehicle can be built, the world\'s astronauts will have to rely on Russia\'s space capsules. If weather forces a delay in Friday\'s liftoff, other opportunities will arise on Saturday and Sunday. The weather improves to a 40 percent chance of weather prohibiting launch on Saturday, and a 30 percent chance on Sunday.