The very first time my family visited this park, we got soaked! I checked the weather ahead of our hike and there wasn't a cloud in the sky, no rain in the forecast. I should've remembered we live in New England. Out of the blue we could hear a rumble of thunder, we began our trek back to the car. As you correctly assumed, we didn't make it there before the rain got to us. Not at the cache site, but nearby there is some shelter. Whether it's to take a break from your walk, have lunch, or to get out of the rain, you'll find a bench and some cover just east of ground zero.
Please be sure to replace hide to protect it from the many muggles that use the park daily.