I have been in PV on 4th of July several times and it was never celebrated, just the usual fireworks over the bay that take place every night.
As far as the clouds go, every weather site shows clouds over PV almost daily all year long. Just remember you are going during the rainy season and the clouds do build up in the afternoon. It typically will rain in the late afternoon/early evening for anywhere from an hour to all night long, depending on if there are tropical storms in the area, as there are right now. The rain cools things down and the sun comes out the next day until afternoon when the cycle starts all over again. You will also see some of the most fantastic lightening shows over the bay. It will be hot and humid so make sure you drink lots of water and use lots of sunscreen. PV is closer to the equator so the sun is much stronger and you will burn a lot easier.
As far as the clouds go, every weather site shows clouds over PV almost daily all year long. Just remember you are going during the rainy season and the clouds do build up in the afternoon. It typically will rain in the late afternoon/early evening for anywhere from an hour to all night long, depending on if there are tropical storms in the area, as there are right now. The rain cools things down and the sun comes out the next day until afternoon when the cycle starts all over again. You will also see some of the most fantastic lightening shows over the bay. It will be hot and humid so make sure you drink lots of water and use lots of sunscreen. PV is closer to the equator so the sun is much stronger and you will burn a lot easier.