I've always wanted to enter, but have trouble remembering to check the topic

Is there a weekly email announcing the Derby topic?

No. The next week’s derby topic is previewed on the current derby page. Here is the one for the derby that starts on Thursday, 11/30/17… Next week’s Derby preview: Circle Shirts - Next week’s derby is all about circles! Your art for this derby needs to be contained within a circle. That circle will go on a shirt. And then we have a Circle Shirt! One more rule: no cream tees.