Low Temp at Start- Any suggestions?

Take antifreeze with you to chisel out the bike!

GL&HF

I have both arm warmers and light jacket packed. I am wondering about whether to wear the arm warmers under my  wetsuit or put them on during TI-after drying off my arms. 

The last time I raced this season it was in the 50's when I entered T1.  I was worried about being cold so I slipped on my windbreaker right before getting on the bike.  Turns out I wasn't cold and probably didn't need it past a the first five minutes on the bike.  I really wished after the fact that I hadn't wasted the 30 seconds trying to get it on and zipped as that 30 seconds meant the difference between me finishing 6th woman overall and 3rd

If you have a decent cold tolerance, consider not spending any extra time adding layers in T1.

I'd go with arm warmers in case you need them.  If you roll them up, its easy to slide them on your wrists in transition and then roll them up on the bike if you decide you need them.  If not, easy to fit in a jersey pocket.

^^Yup.

This is what I would do. Roll them up inside out, then in T1 slip them over your wrists and roll them up while you pedal if you need them.

try putting on the arm warmers a few times before the race.

the arm warmers aren't much, but they take off the wind chill.

My first tri was a Sprint.  Then day before at the first timers clinic, the air temperature was a balmy 82.  The next day coming out of the hot natatorium dripping wet, it was 42.  I had a jacket, arm warmers and gloves.  The adrenalin was so high, I decided not to use any of them.  I was never cold.  BTW, I'm 110 lbs soaking wet.

Good luck on your first race.  Enjoy.  It's the only 1st tri you'll ever have.