The rainy season in Mexico usually ends in late September - early October. Even in the season, precipitation is short-lived - from half an hour to an hour. After the rain, it's usually sunny and beautiful weather. Less often are tropical storms, but they are more typical for the rainy season, which means that the rain can go all day, but the next day the weather is wonderful. Certainly, it is impossible to guarantee the absence or presence of precipitation, but I can say that you have chosen a wonderful time for the trip.

For more information, see the "Weather in Mexico" page.