Wetsuit Necessary?

Necessary?  No.  

Helpful?  Yes.

If I was just racing for fun and not worried about cold water, I'd probably skip it.   You wouldn't be the only one.  Whenever I see someone not wearing a wetsuit I assume they are much better, tougher, swimmers than me and I think it's badass.  

Welcome back. 

What’s your tolerance for cold water?  What’s the expected water temp?  

The shorter the swim, the easier to skip the wetsuit, but make plans to recover from the cold, which might mean pulling on long sleeves, socks, gloves, etc. for the ride. 

As noted wetsuits help with buoyancy and warmth, and both depend on your tolerances and/or swim skill.  For me I'm throwing away speed if I don't wear one so I'll push the limits on water temp to wear one (up to an Oly).  If cold doesn't impact you then don't worry about it.

And welcome back - I have my first tri in 8 years next weekend!  The water is currently 60 degrees so I'll be definitely wearing one!