Cancun-Palenque-Oaxaca(?)-Mexico City. Do I need a warm/waterproof jacket? Will I use my swimsuit? Do I need warm stuff to sleep in?
Any experienced comments appreciated.

Doesn't anybody know?

Just got back from Mexico...Mexico City was smoggy (as usual) and it rained lightly, quite cool, as a matter of fact. The interior (Merida, Palenque) were hot and humid, but not unbearably so, and Cancun, were we finished our trip had finished a very rainy season (thunderous rain in the afternoon) but the weather seemed to be getting better just as we left. Not too hot, and quite pleasant. By all means, take your swim suit. If you are staying in hotels, they all have AC, so you won't need heavy sleep gear. It's a good time to go. If you go to Morelia or thereabouts, it can be cold. We were there last winter (Nov) and it was pretty cold at night but sunny in the days. Guess it all depends on where you go. by the way, you might as well plan to ski Oaxaca, they are still having a 'rumble' there and we opted not too go...a US travel advisory was in effct then...don't know about now.

www.wunderground.com
enter the city/airport.
They have a forecast, and scrolling down, a history/archive function for any date going back many years.
M

In OAX over the years I have seen a variety of weather conditions from 80 + in the daytime to very chilly at night. A few years back I was there in January when it was getting into the 40's at night and there was not much going on. Having clothing you can layer has always made me comfortable. The way things are in OAX right now I might pass on going there this year. Normally its wonderful in Jan.

Yep, for January, expect hot and humid in Cancun and Palenque (probably be able to use that swimsuit), but bring a jacket for Mexico City, since it will likely get cool in the evenings. As others have said, this is a good time (unfortunately) to avoid Oaxaca (the city, anyway --- I'd still do its beaches, like Huatulco...)

Have fun!
Mark
www.tiogringo.com