The great thing about visiting Puerto Vallarta on vacation is that the weather is very predictable. A five day forecast usually delivers what it predicts and depending on the time of year, you will more or less know what kind of weather you are going to experience.
Sun Weather
Classified as tropical savanna, Puerto Vallarta, is warm and sunny throughout the year, with over 300 guaranteed days of sunshine – perfect for a beach vacation. It would be very unusual for visitors on a week vacation to have bad weather for their entire stay. You can pretty much enjoy the beach any day during any season. Puerto Vallarta also benefits from its southern location closer to the equator, as the length of the day does not fluctuate greatly so that even in winter you get around 11 hours of sunlight. Many people escaping the Northern Hemisphere winters will appreciated still having daylight after 4pm.
Warm Temperatures
Puerto Vallarta boasts stable warm temperatures and you will not need to bring any socks even in winter. In summer, temperatures can reach around 91ºF (33ºC) with lows of 77ºF (25ºC), making the nighttime balmy and air-conditioning a welcome plus in your accommodation. Winter on the other hand, offers very pleasant temperatures. During the day you can expect up to 82ºF (28ºC) while temperatures drop at night to no less than 61ºF (16ºC).
Rain
Rain is inevitable if you visit from June to October, however, it is also very predictable. Once the season has got into a pattern, you will find it easy to organize your vacation around the rain showers, which are usually in the afternoon or at night. Rarely will you experience rain all day and all night for more than a couple of days. The heaviest rain is during August and September but that is also the time when you will experience fabulous electrical storms over the ocean. Puerto Vallarta offers some spectacular natural light shows!
The great thing about the rainy season in Puerto Vallarta is that you will still enjoy sunshine between showers. Head for the beach in the morning and when you see the clouds forming in the distance you know it will be time for an hour or two in a restaurant or bar!
Hurricane Season
Puerto Vallarta can be affected by hurricanes that form along the Pacific coast from June to November but are seldom a significant problem. What usually happens is that the destination experiences heavy rains and the hurricane swings round towards the north.
Reference: http://weatherspark.com/averages/32587/Puerto-Vallarta-Jalisco-Mexico