The other day I had a wasps nest outside my office window. (They are
gone now.) The thing is, there was a really bad storm with very heavy
rain. The wasps kept flying from their nest in the roof to a tree
about 50 yards away even in the heaviest part of the storm.
My question is.... How do wasps fly in heavy rain????!!!

It's probably due to their small size. During a rainfall, there's some
average distance between raindrops. An object the size of a human, for
example, has dimensions on a scale much larger than the dry regions
between drops, therefore a person out in the rain is certain to get
soaked. Something the size of an insect is much smaller than the
typical space between drops (it has a small "cross section"), and has
a pretty respectable probability of traversing a short distance
without ever getting wet.

They use their wings, like always.

They carrry tiny umbrellas

My guess is that they do a bit of ducking and diving.

You also have to think about the force of the rain on the wasp, if
rain hits us we do not fall over. The force of the rain is not strong
enough to knock them down.

Give them some big hail and see what happens then.

usrhlp