This behavior is well-known to be honest. There's this myth that white-tail activity increases if it rains (the deer seeks shelter). However, the truth is that this doesn't really affect the daily routine. The animal just takes it as something what happens from time to time.
As you may already know the two main sense of a deer is its ability to smell and to hear. Both of these senses are nearly blocked while it rains. This is just getting worse if the rain intensifies.
The reaction of the deer is easy: compensate this loss with another sense. This, in fact, means, that they want to see. Where do they see? Not in the dark forest but rather in the open fields.
I've found a good article regarding this topic:
It’s no secret deer rely on their senses of smell and hearing as top
lines of defense. Rain can influence both. Swirling clouds of
molecules, scent, both good and bad, can be rain-washed from the air,
making it difficult for deer to smell that which the nose would have
otherwise known. Too, the steady pitter-patter of rain on the leaves
fills a deer’s ears with aural clutter — potentially
Deer recognize these situations, and will often attempt to compensate
by increasing the emphasis placed upon the third sense, sight. How?
Heightened visual awareness, something the animal can accomplish
easily by frequenting areas which offer extended fields of vision.
Hidden meadows, field edges, or powerline right-of-ways are three
examples. Simply put, go to where deer can see, and you’ll see deer.
And yes of course, you can use this as an advantage to hunt. If you are willing to go out in the rain, it's even a commonly used practice.
Notice the last sentence in the quote above:
- Simply put, go to where deer can see, and you’ll see deer.