By using Dynamic Lighting, we are able to simulate Lightning. By setting up a script, we can toggle a flashing light to blink on and then off for a short time. Then we add in the thunder noise, and then "WaitForRandomTime" tag to randomize the bursts of thunder.
Finally we add rain, the droplet effect on the water and we got ourselves a cool Environment. All that's left is to add the HUD drops to simulate rain on the visor.