Mexico is enjoyable year-round, but October to May is generally the most pleasant time to visit. The May-September period can be hot and humid, particularly in the south, and inland temperatures can approach freezing during December-February. Facilities are often heavily booked during Semana Santa (the week before Easter) and Christmas/New Year, the peak domestic travel periods.
Mexico's climate has something for everyone: it's hot and humid along the coastal plains, and drier and more temperate at higher elevations inland (Guadalajara or Mexico City, for example). Try to avoid the southern coast between July and September - the resorts are decidedly soggy and jam-packed.
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