I think it's a flowering senna. There are several varieties. And you're right. They usually bloom in the fall, but my Senna Corymbosa got mixed up as a lot of plants did from last years drought and is blooming now.

Roselee - Thanks! Senna is my guess too. Any thoughts on which Senna it might be? I've looked at tons of pictures but can't decide. The leaves were glossy and bright green (no gray tones and not velvety). They were also more pointed than rounded.

A lot of Sennas are tender. After loosing a mature 12 year old no ID Senna to the 2009 winter, which wasn't even as cold as it was in 2010, I bought Senna Corymbosa on Carrie's recommendation since she said it was hardy in her Dallas area garden. So cold hardiness might give you a clue on which one it might be. Maybe when Carrie sees this she can help with an ID.