Dr. Greg Postell is a hurricane and storm specialist at the Weather Channel. He tells us why the water can be so deadly.

Laura strengthened Wednesday into a menacing Category 4 hurricane, raising fears of a 20-foot storm surge that forecasters said would be "unsurvivable” and capable of sinking entire communities.

In 2008, Hurricane Ike pummeled the Texas Gulf Coast as a Category 2 storm and generated a 15-foot storm surge in Galveston Island. This story first appeared on NBCNews.com. More from NBC News: ...

The storm had strengthened to Category 3 late Wednesday night, and by Thursday morning it was about 70 miles from Charleston, South Carolina, according to the National Hurricane Center. Its ...

During the night, Hurricane Ike shifted 12 miles west and increased to 105 MPH. The storm is predicted to be a Category 3 before landfall at around 1 a.m. Saturday morning, according to Friday ...