Meteorologists have nightmares about a major hurricane heading for the Louisiana coast. This scenario appears at the top of almost all lists of potential weather disasters.
Hurricanes are dangerous no matter where they make landfall, but Louisiana’s unique terrain and position on the Gulf Coast make a strong storm heading into this part of the southern United States a particularly distressing prospect.
THE GULF OF MEXICO FEELS SOME OF THE STRONGEST STORMS POSSIBLE
The very location and shape of the northern Gulf Coast makes this region exceptionally vulnerable to an approaching hurricane.
The Gulf of Mexico contains some of the warmest ocean waters in the world. Sea surface temperatures here regularly rise to 30 ° C or more during the heat of summer. This deep reserve of hot water acts as an incubator for budding tropical cyclones.
The Gulf of Mexico is home to some of the warmest sea surface temperatures in the world during peak summer. (Map by NOAA / PSL)
Tropical systems moving across the Atlantic Ocean and Caribbean Sea can intensify rapidly once they surround themselves with moist air, calm winds, and bath-like water temperatures. commonly found in the Gulf of Mexico.
Once a storm hits the Gulf, the horseshoe shape of the shoreline surrounding the basin essentially guarantees a landing, forcing a storm through the wet waters of the basin until it finally reaches the shore. .
THE LOUISIANA IS A FREQUENT BULLSEYE FOR STORMS ENTERING THE GULF
Louisiana’s position on the northern Gulf Coast leaves the state directly in the path of many tropical storms and hurricanes that enter the Gulf of Mexico.
In the height of summer, the prevailing winds over the basin often curve around a center of high pressure in the western Atlantic commonly referred to as the Bermuda High.
This high can act as a barrier that prevents tropical systems from simply curving out to sea. The strength and position of the Bermuda High generally dictates the course of storms as they enter the Gulf and begin to curve out. Earth.
Sometimes the ridge of high pressure is strong enough to force a storm through the Gulf into Mexico or Texas. Other storms can take advantage of a weak ridge and curve to hit Florida. But the high is often in the right place to guide storms along a gentle curve directly into southern Louisiana.
THE LOW ELEVATION OF THE LOUISIANA MAKES FLOODING A MAJOR ISSUE
The vast majority of Louisiana’s coastline consists of marshes, swamps, and beaches. Many communities near the coast are at sea level or a few meters above, offering little protection against flooding caused by storm surges during a tropical storm or hurricane.
Storm surge is seawater pushed inland by the strong winds of a hurricane. The effects of storm surges depend on many variables, such as the size, strength and duration of a storm, the shape of the coastline, the terrain near the coast and whether communities have built barriers or dikes to prevent water to enter.
A satellite image of the northern Gulf Coast in March 2001 (Image courtesy of NASA MODIS / Terra, with author notations.)
Louisiana’s flat, swampy coastline offers little resistance to a storm that makes landfall. The strongest hurricanes can generate a storm surge that rises more than 4m above ground level, which can easily inundate homes and businesses both near the coast and several miles away. inland.
An extreme example of the state’s vulnerability to flooding occurred during Hurricane Laura in 2020, when forecasters warned the Category 4 storm surge could push more than 60 km inland. land through the swamps and waterways of southwest Louisiana.
Tropical showers can cause widespread flash floods far inland from the coast. Prolific rains from a tropical system can easily overwhelm Louisiana’s many waterways. Hundreds of millimeters of rain falling in a short period of time can lead to flash flooding statewide, often forcing rescue teams to perform water rescues for people trapped in vehicles and homes.
A LOT OF NEW ORLEANS LIES BELOW SEA LEVEL
Few major hurricane-prone cities struggle as much with water as New Orleans. Bounded by Lake Pontchartrain to the north and the Mississippi River to the south, much of New Orleans is at or below sea level. This low altitude forces residents to rely on a system of dikes to prevent water from entering and pumps to evacuate rainwater away from the city.
A satellite image of New Orleans, Louisiana taken by Landsat 7, showing Lake Pontchartrain to the north and the Mississippi River to the south of the city. (Image from NASA / USGS)
The city’s dike system failed under the stress of the storm surge from Hurricane Katrina in August 2005, flooding 80 percent of the city.
Officials rebuilt and strengthened New Orleans’ levee system after Katrina. The network is designed to “withstand an event roughly equivalent to a typical Category 3 hurricane,” according to the city’s website.
SOME OF THE WORST STORMS IN HISTORY HAVE REACHED LOUISIANA
Louisiana’s unique vulnerability allows each major storm that hits the region to carve out its own place in meteorological history.
Two of the most impactful storms to hit Louisiana in recent decades were Hurricane Katrina in 2005 and Hurricane Laura in 2020. Both storms were high-end disasters for the region, but for very different reasons. .
Hurricane Katrina escalated into a Category 5 hurricane when it appeared over the Gulf of Mexico in late August 2005. The raw power of the system was matched only by its incredible size. , covering hundreds of kilometers across the storm at one point. other.
Katrina lost some strength and made landfall in Louisiana and Mississippi as a Category 3 major hurricane, but impacts were blocked.
The size of the storm, combined with its intensity just hours before it landed, generated a massive storm surge that devastated communities in parts of Louisiana, Mississippi and Alabama. More than 1,800 people died during the storm and its immediate aftermath.