If you’re going to be around water, it’s not a bad idea to carry a portable lightning detector with you. Expensive? Heavy? Awkward? Nope. A cheap, battery-powered AM radio will do the job.
Say you’re out on the boat and you see some clouds rolling in. Turn the radio to a station with weak reception and any sudden, loud crackling noises you hear will likely have been caused by lightning. Distant strikes will sound muffled; close strikes will be louder and more crisp.
If you actually see lightning, the sound on the AM radio will occur at the same time as the flash. This is because, unlike the sound of thunder which travels about 1/5 of a mile per second, radio waves travel at the same speed as the light from the strike…instantaneously…or 186,000 miles per second.
Because the sound of thunder is so slow compared to the speed of light, you can tell how far the strike was from you by counting the seconds between the flash or AM crackle and hearing the thunder; then divide by 5 to get an approximation of the distance in miles.
Suggestion: Don’t take chances with a lightning storm, If it’s coming your way…get out of its way. NOAA says even if the lightning’s source is 5-10 miles away, it can reach out and zap you.
This site has good information on what to do in case of lightning: NOAA