I would leave the umbrella at home, or in the resort room...
Umbrella's are really not a park friendly item, you can poke someone in the head or face easily, which we have had happen many times.. and they run water all over other guest... and if you are wearing a backpack, most of the time the backpack gets wet...
Either a poncho, or a hooded rain jacket... We go the hooded rain jacket route, the ones we have are Columbia, they are really light weight, and can be used as a normal wind breaker or light jacket for in the restaurants. Ours have been all over with us, and they are holding up very well, and still look brand new, even though they are about 8 years olds... With ours with a couple of good shakes and a couple of paper towels, you can dry them off and they have a zippered pack that they fold up into for easy storage...