It's kind of like saying will there be snow in our part of Ontaio in December? Historically there is but some years there isn't.
If you are expecting high humidity you won't be disappointed. It should be VERY hot and humid. Don't pack much in the way of clothing you won't need it. No pants, capris or shirts with any kind of sleeves. Sleeveless tops and light weight everything, sandals, extra bathing suits (things don't dry well in the humidity). If you have the right clothing and don't over dress you will be able to tolerate it. First day is the hardest. Don't pre-plan alot of things requiring physical exertion, wait until you get there to see what this year will be like and take it from there.
August is during the rainy season which will amount to maybe 10 minutes of rain and a thunder and lightning show usually in the evening or at night. If it rains more than that you will appreciate it.
The good thing is the A/C is usually great at the RDC and they have several pools. The ocean is right there. It is low season and a fab time to be in the PV/Neuvo/Bucerias area. A different cultural experience compared to high season. Personally I love it!!