Satellite imagery can help determine the strength, size and cohesion of a storm. The stronger a storm becomes, the more likely an eye will form in the center. When the eye looks symmetrical, that often means the storm is not encountering anything to weaken it.

A tropical storm is intensifying and is expected to reach typhoon strength before hitting southern China's coast on Sunday.

Intense flooding rainfall, powerful winds and large waves impacted Hong Kong and southern China on Sunday as Typhoon Wipha crossed the region.