Summer, from June to October, is in theory the rainy season in Mexico, but just how wet it is varies wildly from place to place. In the heart of the country you can expect a heavy but short-lived downpour virtually every afternoon; in the north hardly any rain falls, ever. Chiapas is the wettest state, with many minor roads washed out in the autumn, and in the south and low-lying coastal areas summer is stickily humid too. Along the beaches, September to mid-October is hurricane season – you’ll usually get wet weather, choppy seas and mosquitoes, if not a full-on tropical storm. Late winter is the traditional tourist season, and in the big resorts like Acapulco and Cancún, the months from December through to April are the busiest. Mountain areas, though, can get very cold then; in fact, nights in the mountains can be extremely cold at any time of year.
In effect, visitors come all year round – sticking on the whole to the highlands in summer and the coasts in winter. November is probably the ideal time to visit, with the rains over, the land still fresh and the peak season not yet begun.