Steve,
I'm a PADI Instructor/Dive Guide in Saipan and I'm also a former midwest diver, originally from Iowa. Brrr...
Here the water is 80-84F, a lot of us 'locals' dive in swim trunks and a rashguard or t-shirt. tourists tend to wear wetsuits...but it's really not necessary. You can rent a shorty here for $4 a day.
I have a blog and a website that list a lot of info about diving here. The blog has a lot of photos of what you can expect here.
Blog -->
www.scubablues.blogspot.com
Website -->
www.saipanscuba.com
I was first certified in rock quarries (cold waters) in Iowa, even dove the Mississippi once (0 visibility). Here the waters are warm, you see 100+ feet on a good day...and almost always find a turtle or an eagle ray if you know where to look.
Send me an email and I'd be happy to answer any other questions you might have. The diving here is awesome. You won't be disappointed.
Brad