Jay has a solid rainfall/planer guide
sounds like you'll connect with wildrider. he's done some great traveling as of late.
read this book: Adventure Motorcycling Handbook, 6th: Worldwide Motorcycling Route & Planning Guide (Trailblazer Guides)
I have a blurb in there too about lessons learned traveling in Mexico.
Roughly C.A. rainy season ends oct 16 and starts again june 15th.
Most all thru riders enter into mexico aprox nov 1 and head south.
That is the ideal method to stay drier north of the equator.
Ben did that but i'd argue he missed a ton cool of incredible cities in central mexico, because he was so route focused. because the spanish were focused on the area what is now mexico, the most specular colonial cities exist in mexico. i've visted many of them. by sticking to the west coast only you miss a ton of culture & the locals. the food is also the most flavorful in mexico in all the places you'll visit. once again because of the european/spanish influence. many have said the food is downright bland in some countries as are the cities.
my point is take some extra time a explore more of mexico than just the west coast.
i'd enter mexico into baja around mexicali (get your 6mo visa and TVIP - vehicle papers) at the border! > east side hot spots and make it down to cabo pulmo (stop at the port and buy ferry tickets for a few days latter and then chill at cabo pulmo till you leave) > la paz > mazatlan > devils spine and back > sayulita. you are now in the west coast where you can travel south a bit and then head inland to colonial cities and then back down to the coast etc. the roads the connect the high elevation center of the country and the coast are always the curviest of all. the best coastal section for awesome road is michocan. places to not miss are guanajuato & san miquel de allende (hot springs there - la gruta), zacatecas (if possible), morelia & patzcuaro, bernal, xiltla & the huesteca, canyon sumidero, palenque/agua azul/san cristobal, oxaca city and coast line and so much more!