All six hazards below were profiled in the 2020 plan and are carried into this update. Flooding, thunderstorms, tornadoes, and tropical cyclones are also rated medium or high risk in the state plan. Thunderstorm hail, lightning, and wind are scored separately but share one hazard profile. Select a hazard to open its profile.

Additionally, the National Risk Index developed by FEMA was utilized to determine the composite risk to 18 natural hazards, including avalanche, coastal flooding, cold wave, drought, earthquake, hail, heat wave, hurricane, ice storm, landslide, lightning, riverine flooding, strong wind, tornado, tsunami, volcanic activity, wildfire, and winter weather.

FEMA rates St. Bernard Parish’s overall risk as Relatively Moderate, with a risk index score of 86.61 out of 100 compared with the rest of the United States and 65.60 compared with Louisiana. The hazards that contribute most to the score are flooding, thunderstorms, and tropical cyclones. The parish’s Expected Annual Loss rating is Relatively Moderate (85.11 nationally, 64.10 statewide), with lightning rated Relatively High. Social Vulnerability is rated Very High (86.66 nationally, 73.40 statewide), and Community Resilience is rated Very High (91.79 nationally, 87.50 statewide).

Coastal erosion is a significant hazard in Louisiana's coastal zone and a major contributor to long-term land loss. It results from a combination of natural and human-influenced processes, including wave action, storm surge, relative sea level rise, subsidence, reduced sediment supply, changing currents, and alterations such as dredging and canal construction. Some of the most severe episodes in recent decades were tied to tropical cyclones; Hurricanes Katrina, Rita, Gustav, Ike, Laura, Delta, and Ida generated storm surge and wave action that stripped sediment and vegetation and damaged barrier islands and coastal wetlands.

Erosion is usually gradual, but severe storms can cause substantial shoreline retreat and wetland loss in a short period of time. The loss of wetlands, shorelines, and barrier islands reduces natural protection from storm surge, flooding, and wave action; increases the exposure of communities, infrastructure, and economic assets; and degrades the coastal habitats that support fisheries, wildlife, water quality, and recreation.

Subsidence is the gradual lowering of the land surface caused by natural geologic processes and human activities. Across southern Louisiana, young sediments deposited by the Mississippi River and its distributaries compact as they age, while deeper geologic adjustment, fault movement, the decomposition of organic soils, and the withdrawal of oil, gas, and groundwater also lower the surface. Wetland drainage, canal construction, and reduced sediment delivery from river management can intensify the effect.

Subsidence develops continuously rather than as a discrete event, and rates can vary considerably over short distances. Even small annual rates add up to meaningful elevation loss over decades, compounding coastal flooding, storm surge, relative sea level rise, and erosion, and undermining the accuracy of the survey benchmarks used for levee heights and base flood elevations.

Historic areas of coastal land loss and gain have been quantified for the parish using data from the U.S. Geological Survey (USGS) and the Louisiana Coastal Protection and Restoration Authority (CPRA). Since 1932, the average annual land loss in Louisiana is 35 square miles, while the average annual land gain has been 3 square miles, for a net loss of 32 square miles per year. Land loss is occurring throughout the entire area of the parish.

Subsidence is also occurring throughout the parish, further exacerbating land loss. The southwestern portion of the parish can expect subsidence rates of approximately 35 mm annually, while the remainder of the parish can expect rates of approximately 10 mm annually. The map below can show any combination of two layers: the historical pattern of land loss and gain between 1932 and 2010, and the subsidence rate zones that cover the parish.

The extent of coastal land loss is measured by the amount of shoreline, wetland, beach, or other coastal land that is lost over a specified period of time. It is commonly quantified using shoreline change rates, land loss rates, wetland conversion rates, and changes in coastal elevation, expressed as feet per year of shoreline retreat or acres or square miles of land lost over time. The USGS, NOAA, and CPRA monitor these changes with aerial photography, satellite imagery, GIS, LiDAR elevation data, and field surveys.

The extent of subsidence is measured by the amount and rate of vertical land surface movement over time. It is commonly expressed in millimeters or inches per year and evaluated over longer periods to determine cumulative change in ground elevation. Because subsidence is gradual, small annual rates can produce meaningful elevation loss when sustained for several decades.

Subsidence rates vary across St. Bernard Parish. The southwestern portion of the parish can expect rates of approximately 35 mm annually, while the remainder can expect approximately 10 mm annually. If those rates held constant, the land surface would lower by roughly 350 mm (about 14 inches) and 100 mm (about 4 inches) respectively over ten years.

Sea level rise adds to the effect. The plan’s loss model applies a linear global sea level rise rate of 3.1 mm per year over a ten-year period, an increase of about 0.1 foot, together with the 20th-percentile subsidence value for each subsidence zone.

Coastal land loss is an ongoing process that includes both discrete processes (hurricanes) and continuous processes (subsidence, sea level rise). While historic flood loss data undoubtedly include the effects of coastal land loss, specific previous occurrences have not been identified as a source of direct disaster damage in Louisiana. Rather, the effects of the underlying flood or hurricane storm surge hazard are recorded.

Land loss is nonetheless a significant hazard, and the plan quantifies the added flood impacts it causes in its Estimated Impact analysis. Subsidence has continued at approximately 35 mm annually in the southwestern portion of the parish and approximately 10 mm annually in the remainder.

Subsidence, sea level rise, and coastal land loss are ongoing hazards. Unlike discrete hazards such as hurricanes or tornadoes, they do not occur as a series of individual events that can be used to calculate a traditional return interval.

Based on historical subsidence rates and land loss and gain trends, the probability of future land loss in the parish is 100% certain. The actual rates of subsidence and land loss vary along the coast based on meteorological, geological, and human-influenced dynamics such as water and resource extraction, canal dredging, saltwater intrusion, and marsh restoration projects.

Flooding results from a combination of natural and human-influenced conditions. Precipitation, topography, vegetation, soils, drainage patterns, and seasonality interact with development, impervious surfaces, land use change, and flood-control structures to determine how water moves across the landscape. Heavy rainfall from frontal systems, thunderstorms, tropical storms, and hurricanes is one of the primary causes of flooding in Louisiana, and slow-moving weather systems can produce prolonged rainfall that drives riverine flooding.

Several types of flooding may affect the parish: riverine flooding, when waterways exceed their capacity; flash flooding, when intense rainfall produces rapidly rising water; ponding, when water collects in low or poorly drained areas; backwater flooding, when elevated downstream water levels restrict drainage; urban flooding, when rainfall exceeds the capacity of stormwater systems in developed areas; and coastal flooding, typically caused by storm surge or gradual sea level rise. A single rainfall event can produce more than one type depending on local drainage, topography, waterways, and development patterns.

St. Bernard Parish has experienced significant flooding in its history and can expect more in the future. Stormwater excesses caused by large amounts of rainfall in a short period of time occur frequently in the parish. Topography, poor drainage, and an extensive levee system mean that stormwater cannot flow out of many areas. Generally, the most damaging stormwater events are a function of a tropical storm or hurricane.

Stormwater excesses and riverine flooding primarily affect the low-lying areas of the parish. Elevations range from below sea level to approximately 35 feet (NAVD88), with the highest ground along the Mississippi River.

The extent of flooding can be characterized by the depth, duration, velocity, geographic area of inundation, and probability of occurrence of a flood. Flood probability is commonly expressed as an annual chance: a 10% annual chance flood has a 10% probability of occurring in any given year, a 1% annual chance flood a 1% probability, and a 0.2% annual chance flood a 0.2% probability. These events have historically been called the 10-year, 100-year, and 500-year floods. The terms do not mean that a flood of a given magnitude will occur only once in that many years; they describe a statistical probability for any given year.

The 1% annual chance flood, commonly called the 100-year flood or base flood, remains an important regulatory benchmark under the National Flood Insurance Program. The area it would inundate is identified as the Special Flood Hazard Area on Flood Insurance Rate Maps, and federally backed lenders generally require flood insurance for buildings in the SFHA of participating communities.

Flood severity along rivers and streams may also be described using National Weather Service flood categories, which are set for individual river forecast points. Flood impacts generally increase from minor through moderate and major to record flooding.

The National Weather Service issues a Flood Watch when conditions are favorable for flooding but flooding is neither certain nor imminent, and a Flood Warning when flooding is imminent or occurring.

The parish experienced 24 recorded flooding events between 1996 and 2024. Since the last plan update, there have been eight recorded flooding events within the boundaries of the parish. These events resulted in approximately $100,000 in reported property damage, no fatalities, and no injuries. Select an event in the table below to read its narrative.

The NCEI Storm Events Database records one additional flooding event in 2025, after the 1996–2024 period the plan analyzed. It is shown here for reference and is not included in the plan’s counts or probabilities.

The annual return rate (frequency) for periods of flooding in the parish is 0.83, or an 83% annual probability, based on the 24 flooding events recorded between 1996 and 2024. That is approximately one flood occurrence every one to two years.

The average interval between events is the inverse of the annual return rate, about 1.2 years over the long term. This interval represents a historical average and should not be interpreted to mean that flooding events will occur on a predictable cycle.

These estimates come from the Hazus Flood Model’s 100-year flood scenario, a flood with a 1% chance of occurring in any given year, as analyzed for the 2025 plan update.

Sinkholes commonly form in karst terrain, where soluble materials such as limestone, carbonate rock, gypsum, or salt lie beneath the ground surface. As groundwater moves through soluble rock it gradually enlarges fractures and voids, and overlying soil and sediment may migrate into those openings, creating surface depressions or, in some cases, sudden ground collapse. Cover subsidence sinkholes form slowly as soil settles into openings in the rock, while cover collapse sinkholes occur when a bridge of stronger surface soil over a developing void gives way, often with little warning.

Both natural processes and human activities can contribute to sinkhole development, including groundwater withdrawal, mining, drilling, leaking water or sewer lines, irrigation, and drainage changes. In Louisiana, sinkhole hazards are particularly associated with subsurface salt formations and solution-mined caverns. Collapse of salt-related voids can develop gradually or occur suddenly and may affect large areas with limited warning, which makes salt-related sinkholes a distinct concern where salt domes and cavern development are present.

Currently, there is one identifiable salt dome location in the parish. It is located in the western portion of the parish. The specific area that could be affected by a future sinkhole would depend on the location, size, and mechanism of any subsurface failure.

The map below shows the mapped salt dome with a two-mile buffer zone around it. Sinkhole formation above or near salt domes is uncommon in Louisiana, and no sinkhole or salt dome collapse has been recorded in the parish.

There is no standard intensity scale for sinkholes in the plan. Extent is described by the size and depth of the depression that forms, which can range from a few square feet to hundreds of acres and from about one foot to more than 100 feet deep, and by whether it forms gradually (cover subsidence) or suddenly (cover collapse).

For the parish, the plan describes extent by exposure: the buildings, people, houses, and critical infrastructure located within two miles of the center of the mapped salt dome. These figures are shown on the Estimated Impact tab.

There have been no recorded incidents of sinkholes or salt dome collapses in the parish to date. The NCEI Storm Events Database also reports no fatalities or injuries as a result of sinkholes.

Sinkholes are relatively rare events, and their timing is difficult to predict because formation may result from a combination of geologic, hydrologic, and human-influenced conditions. Unlike recurring weather hazards, sinkhole formation does not occur with sufficient frequency to establish a reliable return interval from historical occurrences alone.

Based on historical data for the past 29 years, there has been no incident of sinkhole formation or salt dome collapse in St. Bernard Parish. The annual chance of occurrence is calculated at less than 1%. Although the overall probability is low, susceptibility may be greater in the area around the mapped salt dome.

Tornadoes are violently rotating columns of air that extend from thunderstorms to the ground and produce some of the most intense localized winds associated with severe weather. They generally form within strong thunderstorms when warm, moist air near the surface meets cooler air aloft in the presence of wind shear, which can create horizontal rotation that strong updrafts tilt vertically. Tornadoes can develop rapidly and last from a few minutes to more than an hour. Their paths are typically narrow, but they can occur as isolated events or as part of larger outbreaks, and they may also form in association with tropical cyclones.

The National Weather Service issues a Tornado Watch when conditions are favorable for tornadoes and a Tornado Warning when a tornado has been observed or indicated by radar and poses an immediate threat. Warning times may be limited. Tornado activity in Louisiana peaks in spring, with about half of the state’s tornadoes, including many of the strongest, occurring between March and June, though activity is more evenly distributed through the year than farther north. The major health hazard is injury from flying debris or collapsing buildings.

Tornadoes occur sporadically throughout the parish, and the occurrence of a tornado in the parish is highly unpredictable, making it impossible to forecast the exact time and location of a touchdown or the path it will take. Because of this, the entire planning area is considered equally at risk, and no portion of the parish is geographically exempt.

Documented tornado touchdown locations provide context for where tornadoes have occurred, but areas with more recorded events should not necessarily be interpreted as inherently more susceptible, since tornado occurrence is highly localized and the record represents only past events. The map below shows recorded touchdown locations in and near the parish.

Tornado intensity is classified using the Enhanced Fujita (EF) Scale, which the National Weather Service has used since February 1, 2007. The EF Scale evaluates observed damage to structures, vegetation, and other objects and uses it to estimate wind speeds, from EF0 (generally lighter damage) to EF5 (the most extreme damage, with estimated winds greater than 200 mph). Before the EF Scale, tornadoes were classified using the original Fujita (F) Scale, so historical records may contain both. The table compares the two scales and summarizes typical damage.

The parish experienced nine recorded tornado events between 1996 and 2024. Since the last plan update, there have been three recorded tornado events within the boundaries of the parish. They resulted in approximately $80,000,000 in reported property damage, no crop damage, one fatality, and six injuries. Across all nine events since 1996, the NCEI Storm Events Database reports one fatality and 11 injuries, with approximately $80,245,000 in total property damage. Select an event in the table below to read its narrative.

Based on the nine tornado events recorded between 1996 and 2024, the annual return rate, or average annual frequency, for tornadoes in the St. Bernard Parish planning area is approximately 0.31 events per year, or a 31% annual probability. That is approximately one tornado occurrence every three to four years.

The average interval between events is calculated as the inverse of the annual return rate, about 3.2 years. This interval represents a historical average and should not be interpreted to mean that tornado events will occur on a predictable cycle.

Tropical cyclones are organized low-pressure systems that develop over warm tropical or subtropical waters, with rotating winds and thunderstorms surrounding a defined circulation. Their main energy source is the heat released as water vapor condenses over a deep layer of warm water. A system becomes a tropical storm, and is named, when sustained winds reach 39 mph, and a hurricane when they reach 74 mph. The Atlantic hurricane season runs from June 1 through November 30 and peaks in late summer and early fall. Track, intensity, forward speed, size, and angle of approach vary considerably from storm to storm, producing very different conditions across the same area.

Tropical cyclones produce several hazards at once, including damaging winds, heavy rainfall, inland and coastal flooding, tornadoes, storm surge, and large waves. Storm surge, water pushed toward shore by strong onshore winds and low pressure, is the greatest natural threat to property and life in Louisiana, and nine out of ten hurricane deaths are caused by surge flooding. Major hurricanes (Category 3 to 5) make up only about 20% of U.S. landfalls but cause over 70% of the damage. High winds damage buildings through direct wind force, flying debris, and pressure, and once debris breaks the building envelope, wind pressure can act on every surface.

Tropical cyclones typically impact multiple regions rather than one specific jurisdiction, so the entire St. Bernard Parish planning area is susceptible to their effects and no portion of the parish is considered geographically exempt. Tropical cyclones are the single biggest threat to all of South Louisiana, and any single event has the potential to devastate multiple parishes at once.

Hurricane Katrina in 2005 produced the highest modern-day storm surge levels in Louisiana, reaching up to 18.7 feet near Alluvial City in St. Bernard Parish. The map below shows the wind zones, in miles per hour, that affect the parish in relation to critical facilities.

The intensity of hurricanes is classified using the Saffir-Simpson Hurricane Wind Scale, which categorizes hurricanes from Category 1 through Category 5 based on maximum sustained wind speed. Hurricanes of Category 3, 4, or 5 are considered major hurricanes. Tropical depressions and tropical storms fall below hurricane strength and are not assigned a category.

Storm surge is not incorporated into the Saffir-Simpson classification and should be evaluated separately. Surge height and inland penetration depend on storm intensity, size, forward speed, track, angle of approach, coastal topography, and bathymetry, so a lower-category hurricane can produce significant surge under favorable conditions while a stronger hurricane may produce a different surge profile depending on its size and path.

The parish experienced 24 recorded tropical cyclone events between 2002 and 2024. Since the last plan update, there have been five recorded events within the boundaries of the parish, with approximately $35,053,000 in reported property damage, no crop damage, and no reported fatalities or injuries in the parish. Select a storm in the table below to read its narrative, because impacts can vary considerably from one storm to another.

Based on the 24 tropical cyclone events recorded between 2002 and 2024, the annual return rate, or average annual frequency, for tropical cyclones in the parish is approximately 1.04 events per year. The plan expresses this as a 100% annual probability, or approximately one tropical cyclone occurrence every year.

The average interval between events is calculated as the inverse of the annual return rate. This interval represents a historical average and should not be interpreted to mean that tropical cyclone events will occur on a predictable cycle.

A thunderstorm is any precipitation event in which thunder is heard or lightning is seen, often accompanied by heavy rain and strong winds and occasionally by hail. Thunderstorms form when heated, humid air becomes unstable and rises, and they are classified as single-cell, multi-cell, squall line, or supercell, with supercells the longest-lived and most severe. NOAA characterizes a thunderstorm as severe when it produces hail of one inch in diameter or larger, wind gusts of 58 mph or greater, or a tornado. Because tornadoes and flooding are profiled separately, this page covers the thunderstorm sub-hazards of hail, lightning, and thunderstorm wind. Severe thunderstorms occur most often in late spring and early summer and again in late summer and early fall.

Hail forms within strong thunderstorms when updrafts carry water droplets into portions of the cloud where temperatures are below freezing. The droplets freeze and may be carried repeatedly through supercooled water, adding layers of ice until the hailstone becomes too heavy for the updraft to support. Stronger and longer-lasting updrafts produce larger hailstones, and hail can vary considerably in size and intensity within the same storm.

Larger hailstones can damage roofs, windows, vehicles, crops, outdoor equipment, and other exposed property, while smaller hail may cause little or no damage. Damage to individual structures is often minor, but the cumulative cost to communities can be significant. Hail rarely causes loss of life, although large hailstones can cause bodily injury.

Lightning is an electrical discharge associated with thunderstorms and may occur within a cloud, between clouds, or between a cloud and the ground. Intra-cloud lightning is the most common type and generally poses less direct risk at the surface. Cloud-to-ground lightning presents the greatest direct threat: a strike may affect an object directly or transmit current through the ground, wiring, plumbing, or other conductive materials, and it can strike several miles away from the main rain core of a storm.

Positive cloud-to-ground lightning is less common but can be particularly intense, with higher currents and longer-duration discharges that make fire ignition more likely. Lightning can injure people, ignite fires, and damage structures, utilities, and electronic equipment, and it remains one of the top three storm-related killers in the United States according to FEMA.

High winds occur in a number of ways, with and without thunderstorms. The high winds of present concern for this hazard are thunderstorm winds and downbursts. Thunderstorm winds are a frequent hazard in Louisiana, especially in spring and summer, and can last from a few minutes to several hours; downbursts occur with medium to high frequency and last roughly 15 to 20 minutes.

Major damage directly caused by thunderstorm winds is relatively rare, while minor damage is common and pervasive, and is most noticeable when it contributes to power outages. Those outages can bring a greater tendency for traffic accidents, increased vulnerability to fire, food spoilage, and other losses.

Because hailstorms are a climatological-based occurrence that can occur anywhere, the entire planning area is at risk for hailstorms. Individual hail events may affect only a relatively small area, and the location of future hail events cannot be predicted with precision.

Because lightning strikes are a climatological-based occurrence that can occur anywhere, the entire planning area is at risk from lightning strikes. Individual lightning events are highly localized, but thunderstorms capable of producing lightning may affect any part of the parish.

Because thunderstorm winds are a climatological-based occurrence that can occur anywhere, the entire planning area is at risk from thunderstorm wind. The location and intensity of future events cannot be predicted with precision, and areas with fewer documented events may still experience damaging winds during future storms. The map below shows the thunderstorm high wind speed classes mapped for the parish.

The severity of a hailstorm is primarily characterized by hailstone size, although storm duration, wind speed, and the concentration of exposed property also influence the resulting impacts. The National Weather Service considers hail with a diameter of 1 inch or greater to meet the severe thunderstorm criteria. The TORRO Hailstorm Intensity Scale relates hailstone size and kinetic energy to potential damage, from H0 (hard hail with little or no damage) to H10 (extremely destructive hail capable of extensive structural damage and severe or fatal injuries).

The severity of lightning activity can be characterized by the frequency of lightning strikes within a defined observation area. The Lightning Activity Level (LAL) scale describes thunderstorm development and the number of lightning strikes during a 15-minute period, from Level 1 (no thunderstorms) to Level 5 (numerous thunderstorms with more than 25 strikes).

The severity of thunderstorm wind events is characterized primarily by wind speed, duration, and the resulting effects on the built and natural environment. A thunderstorm is considered severe when it produces gusts of 58 mph (50 knots) or greater. The Beaufort Wind Scale, first developed in 1805 by Sir Francis Beaufort, relates wind speed to the appearance of wind effects on land, from calm conditions at Force 0 to hurricane-force winds at Force 12.

The parish experienced eight hail events between 1996 and 2024. Since the last plan update, no hail events have been recorded within the boundaries of the parish by the NCEI Storm Events Database. The eight events produced approximately $1,000 in total reported property damage, with no reported injuries or fatalities.

The parish experienced five lightning events between 1996 and 2024. Since the last plan update, no significant lightning events have been recorded within the boundaries of the parish. The five events produced approximately $20,500 in total reported property damage, one fatality, and one injury.

The parish experienced 24 thunderstorm wind events between 1996 and 2024, with approximately $143,400 in total reported property damage and no reported fatalities or injuries. Since the last plan update, there have been five thunderstorm wind events within the boundaries of the parish, none with reported property or crop damage. Select an event in the table below to read its narrative.

The NCEI Storm Events Database records two additional thunderstorm wind events in 2025, after the 1996–2024 period the plan analyzed. They are shown here for reference and are not included in the plan’s counts or probabilities.