What causes a storm surge?

A storm surge is primarily caused by a combination of high winds and a drop in atmospheric pressure. When a hurricane or severe storm approaches land, its powerful winds push water toward the shore, creating higher water levels. This effect is amplified by a decrease in atmospheric pressure at the storm's center, which allows the sea surface to rise further. As the intense winds blow over the ocean surface, they effectively "pile up" water against the coastline, leading to significant increases in water levels known as storm surges.

The other answers indicate aspects that might contribute to flooding or coastal impact but do not directly explain the specific mechanism of storm surge formation. For instance, a sudden drop in atmospheric pressure alone would not be sufficient to create a storm surge without the accompanying high winds. Extreme rainfall can lead to flooding but primarily affects freshwater systems and is not a direct cause of storm surge. Lastly, increased ocean temperatures might contribute to storm intensity, but they do not directly cause storm surges themselves. Thus, the correct choice clearly identifies the combined effects of both high winds and surface pressure drop as the fundamental factors in the development of storm surges.