Strong, gusty winds and heavy rains with thunder and lightning will soon follow. Fortunately, few squalls last more than an hour. The sharper, darker and lower the front edge of the cloud, the more severe the storm. The anvil-shaped top of the storm cloud points in the direction that the storm is traveling. In summer, afternoon thunderstorms are likely to occur over water when the humidity and temperature ashore are high.
Hot air radiates upward from land surfaces heated by the sun.
Moisture from a nearby body of water is absorbed by the warm air, which rises to begin the formation of thunderheads. You can determine the distance of an approaching thunderstorm by counting the number of seconds between the lightning flash and the thunder clap, and dividing by five. That will give you the distance in miles you are from the storm. For example, if the time lapse between the lightning flash and the thunder clap is 10 seconds, divide by 5. The storm is approximately 2 miles away from you.