I was diving in Bocas del Toro, Panama a few years ago, and as I was ascending from the dive, I noticed that I'd be surfacing into one of Panama's typical afternoon torrential rain storms. The rain drops pelting the surface looked and sounded like a gravel truck unloading into the water. I literally thought to myself, "I don't want to get out, now. I'll get soaked!"
Before we decided to settle in Bocas del Toro my wife and I visited on numerous occasions. On our very first visit we were staying at a nice bed and breakfast and I awakened in the middle of the night seriously thinking a train was passing by our location. It turned out that it was one of those torrential downpours on the tin roof. Your description is very accurate!