Tropical Storm Alberto has already delayed the Florida spaceport arrival of NASA’s next shuttle astronaut crew to rocket spaceward, though things seem on track for this week’s launch countdown rehearsal.

It promises to be a rainy week for the STS-121 crew, though this week’s two-day Terminal Countdown Demonstration Test (TCDT) is a critical milestone in the astronauts’ push towards a July 1 launch.

The crew, commanded by Steven Lindsey, was expected to arrive at NASA’s Kennedy Space Center spaceport from Houston’s Johnson Space Center at 6 p.m. EDT (2200 GMT) yesterday, though Alberto threw a wrench into those plans. They are expected to try again today.

Tropical Storm Alberto is the first named storm of the 2006 Atlantic Hurricane Season, but was expected to sweep across Florida in about 12 hours after making landfall today, according to the Weather Channel. Some folks were concerned the storm could strengthen into a Category 1 hurricane, though it is apparently weakening as its approaching landfall (encouraging since my flight leaves in just over an hour).

In any event, this week’s TCDT test is vital for the STS-121 crew and launch support personnel to run through the procedures of an actual space shot.

If Lindsey and his fellow astronauts do make it to Florida this afternoon, NASA could push ahead with its TCDT plans (which called for a crew visit to the pad Wednesday and a launch dress rehearsal on Thursday) or delay the exercise to later this week.

We’ll keep you posted with the latest from not-so-sunny Central Florida as soon as we learn more (and get there!).