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Top 5 Most Vulnerable U.S. Cities to Hurricanes

The 2012 Atlantic Hurricane Season is officially underway, and while Hurricane Katrina has tended to fade from memory, New Orleans isn’t the only major U.S. city at risk, although it remains extremely vulnerable. As Hurricane Irene demonstrated in 2011, weaker hurricanes can also do significant damage in places that are not used to experiencing such storms. Many American coastal cities are essentially sitting ducks to hurricanes, with millions of Americans living at water’s edge, exposed to high winds and flooding.

Some of these communities, like New Orleans and Houston, have experienced powerful storms during the past decade. Others, like Miami and Tampa, have been spared the brunt of landfalling storms during recent hurricane seasons.

TOP 5 MOST
VULNERABLE CITIES


No. 1-  Tampa/St. Petersburg, Fla.
No. 2-  Miami, Fla.
No. 3-  New Orleans, La.
No. 4-  Norfolk/Virginia Beach, Va.
No. 5-  Houston/Galveston, Texas

With that as a background, the following is a look at the Top 5 most vulnerable cities to a landfalling hurricane. We take into account storm frequency and typical storm tracks, as well as the population living at or below the elevation of a potential storm surge. It’s not an all-inclusive or entirely objective list, since pretty much any location along the Gulf and East Coasts are fair game for hurricanes to strike. However, it represents a list of some of the top hurricane targets that keep weather forecasters up at night.

A key issue facing many East Coast cities, in particular, is that sea level rise due to global warming and land elevation changes is already making it easier for damaging storm surge flooding to take place, even during weaker hurricanes. That was also taken into account when preparing this list.

1. Tampa-St. Petersburg, Fla.

The Tampa-St. Petersburg area, on the west coast of Florida, is extremely vulnerable to storm surge flooding, and has been fortunate to escape a direct hit from a strong hurricane for many years. Climate Central calculates the 100-year flood height in this area is 6.5 feet above the high tide line. Using Climate Central’s Surging Seas sea level rise mapping tool — it becomes clear that there are about 125,000 people currently living below this flood level. In St. Petersburg alone, there are more than 45,000 homes that lie below 6 feet in elevation, and would likely be vulnerable to a storm surge of that magnitude or greater.

Click image to enlarge. Radar image of Hurricane Charley as it swept ashore south of Tampa in 2004. Credit: National Hurricane Center.

According to Climate Central’s research, sea level rise is escalating the threat of damaging storm surge flooding in the Tampa area. The odds that a flood exceeding 6.5 feet would occur in Tampa before 2030 are about 14 percent without global warming, but these odds increase to 20 percent with the effects of global warming-related sea level rise factored in.

Tampa is no stranger to hurricanes, including storms that came very close to the city but avoided a worst-case scenario track during the past decade. According to the Hurricane City website, tropical storms and hurricanes have passed within 60 miles of Tampa on 68 occasions since 1871. These included Hurricanes Frances and Jeanne, both of which struck during 2004. However, Tampa has not suffered a direct hit by a strong hurricane since way back in 1921, when a storm surge of 10.5 feet occurred in Tampa Bay.

Hurricane Charley in 2004 was initially forecasted to strike Tampa-St. Petersburg as a Category 2 storm, but shortly before landfall it intensified rapidly into a Category 4 storm, and turned eastward sooner than expected, inflicting its worst damage on the Port Charlotte area, south of Tampa. Charley caused $16 billion in damage.

2. Miami, Fla.

Miami is no stranger to hurricanes, but it has enjoyed a lengthy lucky streak. This year is the 20th anniversary of Hurricane Andrew, a Category 5 storm that flattened southern portions of Miami, including the communities of Homestead and Florida City, in August, 1992. Had that storm tracked about 30 miles farther north, downtown Miami and Miami Beach would have seen the most intense winds and storm surge.

The scene in South Beach, Miami after the Great Miami Hurricane of 1926.Click on image for a larger version. Credit: Florida Memory Project of the Florida Photographic Collection.

Miami residents have not experienced a major hurricane since Andrew, and population growth in coastal areas plus sea level rise is increasing the threat of storm surge-related coastal flooding.

Climate Central computes the 100-year flood height in Miami and Miami Beach is 3 feet above high tide. According to Climate Central’s Surging Seas sea level rise mapping tool, about 56,000 people live below this elevation in Miami Beach, along with 23,000 people in Miami.

According to the Hurricane City website, the center of a tropical storm or hurricane has passed within 60 miles of Miami 71 times since 1871. According to a National Hurricane Center report, a hurricane typically passes within 50 miles of Miami every five to seven years. However, the last major hurricane to make landfall in the Miami area was Hurricane Andrew.

The most infamous storm in Miami’s history is the Great Hurricane of 1926, a Category 4 storm that killed 372 people and injured several thousand. According to the National Weather Service, the Atlantic Ocean advanced all the way across Miami Beach and Biscayne Bay into the city of Miami. The storm caused $167 billion in damage in 2010 dollars, which would put it ahead of Hurricane Katrina as the costliest hurricane in U.S. history.

Miami was also struck by intense hurricanes in 1945, 1947, and 1964.

3. New Orleans, La.

Click image to enlarge. Estimated return period in years for hurricanes passing within 50 nautical miles of various locations on the U.S. Coast. Credit: National Hurricane Center.

After New Orleans was devastated by Hurricane Katrina eight years ago, one might think that the city had paid its hurricane dues, and would not see a storm for a long time to come. Unfortunately, Mother Nature doesn’t work that way, as several close calls with storms such as Gustav and Ike have since demonstrated. On average, the Weather Service says that a hurricane should make landfall within 50 miles of New Orleans about once every seven to 11 years.

Despite upgrades to its flood protection systems since Katrina, low-lying New Orleans remains highly vulnerable to hurricanes, particularly major storms of Category 3 or greater. The continued loss of wetlands in southeastern Louisiana is providing the Big Easy with less protection from a storm surge with each passing year.

About half of New Orleans lies below sea level, and 340,000 people — nearly 100 percent of New Orleanians — live below the 100-year reference flood of 9.2 feet above high tide.

4. Norfolk/Virginia Beach, Va.

Norfolk and nearby Virginia Beach are vulnerable to hurricanes that move up the Eastern Seaboard, and were affected by Hurricane Irene in 2011. While these communities tend to miss the most intense storms, they are home to expensive infrastructure that is vulnerable to storm surge-related impacts, such as the U.S. Navy’s largest base, which is located on low-lying land in Norfolk.

According to Climate Central’s research, Virginia’s Chesapeake area has one of the fastest rates of sea level rise in the country, due to a combination of manmade global warming and the natural sinking of land in this region.

Area of Norfolk, Va. like will likely flood from 5 feet of sea level rise. Credit: Surging Seas.

In Norfolk, Climate Central calculates that about 19,000 people live below the 100-year flood level of 5.4 feet above high tide. Sea level rise is dramatically raising the odds of storm surge flooding at or above this height. This means that future hurricanes are likely to have greater storm surge-related impacts than past storms.

In Virginia Beach, the 100-year flood level is 4.8 feet above high tide, and there are about 40,000 people who live below this elevation. Here too, sea level rise is boosting the odds that such a flood will be exceeded by 2030.

Since 1871, the centers of tropical storms or hurricanes have passed within 60 miles of Norfolk on 57 occasions. This list includes noteworthy storms such as Hurricane Floyd in 1999, and Hurricane Isabel in 2003.

According to the National Weather Service, the highest recorded wind speed at Norfolk Airport was recorded during Hurricane Hazel in 1954, when the wind gusted to 100 mph. Nearby Hampton, Va., recorded a wind gust of 130 mph during the same storm.

Hurricanes come close enough to produce hurricane force winds within 50 miles of the Norfolk/Virginia Beach area about once ever seven to 11 years. With warmer than average water temperatures off the East Coast right now, perhaps this year will see another Virginia storm?

5. Houston/Galveston, Texas

The sprawling Houston metropolitan area, with a population of 6.1 million and vital oil and gas infrastructure located on low-lying land, is vulnerable to hurricanes that traverse the Gulf of Mexico. Hurricane Ike heavily impacted Houston and the nearby city of Galveston in 2008, causing $27.8 billion in damage, and killing 20. The communities of Crystal Beach, Gilchrest, and High Island experienced “near total destruction of property,” according to the Weather Service.

One of the few homes left standing after Ike's storm surge swept across the Texas community of Gilchrest. Click on image for a larger version. Credit: FEMA.

Typically, hurricanes will strike the Texas coast once every nine to 16 years, while tropical storms are more common than that. While Ike was a powerful Category 2 storm at landfall, it was a large storm, and it drove a storm surge onshore that was more typical of a Category 4 storm.

Parts of Jefferson County, Texas, and Cameron Parish, La., experienced a storm surge of up to 17 feet. The highest storm surge as measured by a National Ocean Service tide gauge was 12.79 feet at Sabine Pass North, Texas, as Ike was coming ashore at Galveston. A report from the National Hurricane Center states that the highest storm surge occurred on the Bolivar Peninsula and parts of Chambers County, Texas, and was between 15 to 20 feet.

Galveston was the site of America’s worst-recorded hurricane disaster, when a storm struck in 1900, sending a massive storm surge across the island, killing at least 8,000 people. Despite the continued risk of coastal flooding in that community, about 40,000 people live below the 100-year flood level there.

Tropical storms and hurricanes in Texas are also known for being heavy rain producers as well as wind and storm surge threats. This can be beneficial, since tropical weather systems can alleviate drought conditions, but too much rain can be devastating. For example, Tropical Storm Allison in 2001 dumped as much as 35 to 40 inches of rain on southeast Texas, killing 41 people and causing $9 billion in damage.