The defending champion Miami Heat are on top of SB Nation's first set of weekly NBA power rankings from Seth Rosenthal. With the season not yet started, these rankings are based off last season's records and offseason activity.

It's no surprise to see Miami atop these rankings, as they actually improved this offseason after winning the NBA championship. Rosenthal on the Heat:

Despite limited funds and the devastating loss of Eddy Curry, Miami managed to grow slightly more terrifying this summer by reuniting Ray Allen and Rashard Lewis. Meanwhile, Josh Harrellson is living, breathing frontcourt depth for a team that could use it. Man knows how to sport a jort, too.

Allen should be a perfect fit in Miami, as he can simply spot up and get open looks off drives from LeBron James and Dwyane Wade. Lewis could do some of the same, although his game has declined in recent years.

Miami's chief competition in the Eastern Conference, the Boston Celtics, are fourth in the rankings. The Celtics replaced Allen with Jason Terry and also added Courtney Lee to the mix.

Over in the Western Conference, Miami's opponent from last year's NBA Finals, the Oklahoma City Thunder, are still at No. 3 despite the shocking James Harden trade. The Los Angeles Lakers come in at No. 2.

Miami opens their 2012-13 season on Tuesday night against Boston.