Florida ? Thunderstorms are threatening to delay NASA’s planned launch tonight of space shuttle Endeavour, already running a month late.

Endeavour is back from a series of hydrogen gas leaks for a third launch attempt. But forecasters say there is a 60 percent chance that storms could force a postponement.

Launch manager Mike Moses said Friday that he’s not worrying about the weather since there’s nothing he can do about it.

Endeavour should have blasted off to the international space station in mid-June, but was grounded by potentially dangerous leaks of hydrogen gas. Repairs to a misaligned plate on the external fuel tank, which hooks up with a hydrogen vent line, solved the problem.

The shuttle and its crew are set to deliver and install the third and final piece of Japan’s $1 billion space station lab, named Kibo, Japanese for hope.