Puerto Vallarta enjoys a typical tropical climate, with near constant temperature and humidity year round and with a pronounced wet and dry seasonal variation.

The average daily high temperature is 86 °F (30 °C); average daily low temperature is 70 °F (21 °C); average daily humidity is 75%. The rainy season extends from mid June through Mid October,
with most of the rain falling between July and September. August is the city's wettest month with an average of 14 days with significant precipitation. Even during the rainy season precipitation tends to be concentrated in large rainstorms with insignificant precipitation on most days. Occasional tropical storms will bring thunderstorms to the city in November, though the month is typically dry. February, March and April are the months with the least cloud cover.

Source: http://en.wikipedia.org/wiki/Puerto_Vallarta