Updated 6:45pm

Arwa Gunja here, on the evening shift.

It looks pretty certain that tomorrow, Florida Gov. Charlie Crist will officially announce that he will leave the GOP to run as an independent in a race for a U.S. Senate seat. We’ll ask tomorrow what this means for the future of the GOP and if the Tea Party movement is helping or hurting Republican chances of securing elections. With the governor's announcement, the race in Florida will become a three-way contest, between Crist on the Independent ticket, the charismatic Marc Rubio on the Republican ticket and likely Democratic nominee Congressman Kendrick Meek, making this one of the most exciting races to watch for in the country.

We’ll also be talking about America’s obesity epidemic tomorrow morning, asking whether both corporations and citizens are truly willing to change food habits to make Americans healthier. We’ll talk with Marc Ambinder, who just wrote an extensive article on this for The Atlantic.

And tomorrow, co-host Celeste Headlee broadcasts from member station WDET in Detroit, Michigan. As Anna mentioned earlier, she’ll be speaking with Jeffrey Eugenides about leaving Detroit, a city that has played a critical role in his identity and writings. And we want to ask you, have you ever had to leave a city that you call home? Tell us about that experience. You can leave us a comment here on our website, or give us a call at 1-877-8-MYTAKE.

Anna Sale here on the day shift.

We're following the response to the news this morning that the Standard & Poor's has downgraded Spain's debt rating, which comes right on the heels of the same news in Greece and Portugal yesterday. We're tracking the reaction in both European political circles and in the financial markets, and asking economists to explain what this means for government bond prices, interest rates, and ultimately, the availability of credit. We also want to know, of course, what to watch to determine how worried we should be in the United States.

In our weekly conversation about tech, we'll look at the science behind the clean-up of the oil spill off the Louisana coast. As the spill nears land, our friend David Biello from Scientific America will join us to explain the role of controlled burns and robots, and how much they can contain the damage.

We are also intrigued by the cover story in The New York Times Magazine about the increasing prevalence of data-tracking applications in our lives. We'll look at the slew of apps that let you do that — from "checking in" to locations (FourSquare) to analyzing your sleep patterns (Sleep Cycle). But people have been doing this with pen and paper long before the iPhone (not to mention Weight Watchers). We're starting the conversation on this now: Do you analyze your own habits? If so, how has it helped you?

We'll also continue our focused look at Detroit tomorrow, as Celeste Headlee broadcasts from Takeaway station WDET in Detroit. Robert Bobb, the Emergency Financial Director for Detroit Public Schools, will join us to talk about the strategy, and controversy, to increase student achievement while facing a massive budget shortfall. And Detroit native Jeffery Eugenides, author of The Virgin Suicides and Middlesex, joins us to talk about the city's central role in his writing, long after he's moved away.