When storms are in your area it is important to disconnect from the internet and turn your computer off. To completely protect your computer, it is advised to completely unplug your computers power cables from the wall outlet.
Also it is advisable to unplug the telephone line from the wall jack as well if you computer connects to the internet via your telephone line. Most users forget this step and their modem is damaged by a lightning strike.
Once your computer is completely unplugged it should be relatively safe from potential power surges across the power lines and telephone lines in your home.
After the storm has passed you can then plug your computer's power and telephone line again and use your computer as normal.