I would have to do it on Friday so I don't have any flexibility with the weather. I would definitely dress for it, and keep a dry layer or two for the descent. When I did Bear Mountain in NY a few weeks ago I got cold on the way down, and it was a warmer day. For that matter, on Sunday I did a ride in NJ and made a quick stop. When I got back on I was damp and cold, and found that it was really downhill from where I was in NJ all the way to the West Side Greenway in Manhattan.

For Haleakala, you start at sea level on an 80+ degree morning and ascend through the clouds to where it is about 50. The downhill gets cold over the first 10 miles, but you start to warm up. I'm hoping the family meets me up at the top so I don't have to carry everything.