What is a storm surge, and why does it matter? NOAA has a handy guide:

STORM SURGE OVERVIEW

Contents

• Introduction
• Storm Surge vs. Storm Tide
• Factors Impacting Surge
• Notable Surge Events
• Surge Vulnerability Facts

Introduction

Along the coast, storm surge is often the greatest threat to life and property from a hurricane. In the past, large death tolls have resulted from the rise of the ocean associated with many of the major hurricanes that have made landfall. Hurricane Katrina (2005) is a prime example of the damage and devastation that can be caused by surge. At least 1500 persons lost their lives during Katrina and many of those deaths occurred directly, or indirectly, as a result of storm surge.

Storm Surge vs. Storm Tide

Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides. Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide. This rise in water level can cause extreme flooding in coastal areas particularly when storm surge coincides with normal high tide, resulting in storm tides reaching up to 20 feet or more in some cases.

Surge Vulnerability Facts

• From 1990-2008, population density increased by 32% in Gulf coastal counties, 17% in Atlantic coastal counties, and 16% in Hawaii
• Much of the United States’ densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above mean sea level
• Over half of the Nation’s economic productivity is located within coastal zones
• 72% of ports, 27% of major roads, and 9% of rail lines within the Gulf Coast region are at or below 4 ft elevation
• A storm surge of 23 ft has the ability to inundate 67% of interstates, 57% of arterials, almost half of rail miles, 29 airports, and virtually all ports in the Gulf Coast area

Read the rest at NOAA