The answer to both of your questions is no. Remember, in the wild duckweed will be growing in a pond which likely will have a build-up of silt and so will be dark and shallow. With regards to the rainstorm, the problem could be that it would float out of your pond as the water rises. In the photo, you'll see a low cost (virtually free) method of creating an overflow system so the water flows out and the duckweed stays in the pond.
Where we live, it is 87°F (30°C) year-round and we get a UV index of 11 which is in the extreme range. We also have a constant wind for several months. What I would suggest is find a duckweed that grows local to you, and then you'll know that it will survive in your conditions.