So this is one of those things that I've grown so accustomed to that I've not really put any effort or thought into looking for a solution. I've just "dealt with it" to the point of ignoring it for so long now.
Almost all rain jackets provide an adjustable cuff via velcro or other means to cinch up around the wrist, but this barely impedes the invasion of moisture at that point. What is a method or piece of gear that will prevent water from dripping down the hands and wrist into the cuffs of a rain jacket when hands are horizontal or reaching above? Gloves are a quick thought but they will capture water when your hands are down and are unlikely to be worn in warm weather.
Just to head this one off: please no "buy a new rain jacket" answers. Even the best rain jackets will have this problem.