Hmmm...i think ylou will find the coast hot and sticky at that time of year, or any time of year for that matter. On my world tour I rode south from Puerta Vallarta for only a day or two. Then i headed inland (north, briefly, since Mexico by this time has become and east/west country) to the mountains inland; the "Sierra Meridionale" if I recall. Not only is the scenery more spectacular, it is cooler since the roads are up 1000 to 2000 feet.
Geologically they are interesting mountains, too: they are the end of the north american continent and the boundary with the 'true' central america (being on the caribbean tectonic plate).
I followed the mountains over to Puebla and then turned south. I rarely was on the ocean in this par of the world.
If ya want some real detail I can dig up a map and find my route in detail.