Hurricane coastal impacts

Storm impacts on coasts

As powerful hurricanes approach the coast, they generate elevated water levels and dangerous wave conditions that can cause extensive flooding, significant landscape changes, and destruction of property. The National Oceanographic Partnership Program (NOPP) Hurricane Coastal Impacts (NHCI) project aims to document the height, extent, and timing of storm surge and waves as they evolve in the nearshore environment and dissipate across natural and man-made landscapes. The work, which includes observations and models, is critical for improving hurricane coastal impact modeling, which helps communities better assess the risks associated with hurricanes.

This story map provides descriptions of key aspects of the NHCI project and how they contribute to advancing scientists' ability to predict storm impacts.

Observing the coastline from above

NHCI uses remote sensing techniques and airborne and shipborne measurements to:

• Map coastal regions and underwater terrain
• Track changes in water levels along the coast and inland before, during, and after hurricanes
• Collect data about atmospheric conditions, including winds

Why observe the coastline from above?

The shape and configuration of landforms on the coast (topography) and underwater terrain (bathymetry) control physical processes in the coastal environment, including flooding and storm surge from hurricanes. Scientists use remote sensing techniques and surveys to collect information about water levels and features on land and underwater. This data feeds into models tasked with simulating flooding in coastal regions.

Wind speed and direction also impact where and how water moves onto land during storms. Scientists use satellites to track how winds change as a hurricane progresses. This data will help improve predictions about where high surf and damaging storm surge might occur.

How do we get these observations?

Scientists use remote sensing techniques, including satellites and lidar, and instruments aboard airplanes and ships to collect information about coastal landforms, underwater terrain, water levels, and atmospheric conditions. The NHCI team uses this information to build detailed maps of coastal regions and to test and improve models that simulate storm surge and flooding.

How do we use the data?

Digital elevation models (DEMs)

Coastal digital elevation models (DEMs), which capture the topography on land and the bathymetry underwater, are essential for accurate coastal flood modeling. NHCI partners use measurements from airborne remote sensing campaigns and shipborne hydrographic surveys to create and maintain "topobathymetric" DEMs. The DEMs are the foundations of models that simulate coastal flooding or "inundation."

Scientists use data collected from instruments on ships, airplanes, and satellites to build digital elevation models (DEMs) that display land elevations and underwater bathymetry. Coastal inundation models use information about land elevation and underwater bathymetry to simulate flooding during a storm event.

Where the water meets the land

Topographic maps

NHCI remote sensing teams at the University of Miami, the University of Massachusetts at Amherst, Airbus Defence & Space, and Capella Space develop and evaluate advanced techniques for rapid assessment of changes to land surface and coastlines during and after a hurricane landfall. To do this, the teams create land surface or topographic maps using stereo radargrammetry, which extracts geometric information about surfaces and objects from radar images. Modelers can then incorporate these maps into flood models to improve predictions.

Wind direction and speed

The University of Miami team uses satellite imagery to calculate wind direction and speed prior to, during, and after hurricane landfall. In the future, this data can be used to improve model predictions of storm impacts.

Observing the coastline from the ground

NHCI collects measurements from the nearshore environment to the farthest extent of inland flooding to capture changes in waves and water levels as a hurricane progresses.

Why observe the coastline from the ground?

When a hurricane makes landfall, water can surge past the high-tide line and flood low-lying areas. Measurements of waves, including direction and height, and storm surge are vital for understanding risk to coastal communities. But these measurements are notoriously difficult to capture due to the extreme conditions during storms.

How do we get these observations?

NHCI teams aim to collect water level and wave height measurements along two shore-perpendicular transects — one on the right side of hurricane landfall, where winds and waves tend to be stronger, and one on the left side of hurricane landfall, where impacts tend to be less severe. These measurements allow scientists to link conditions at the shoreline and the dynamic surf zone to deep water conditions and subsequent impacts inland.

To measure water levels and waves, NHCI teams use Geolux non-contact oceanographic radar sensors, which can transmit raw data via a cellular connection. The sensors allow scientists to collect real-time data and access sensor data without the need to retrieve the instrument in case of equipment loss. The sensors are non-intrusively attached to pier railings to measure over the dynamic outer and inner surf zones where traditional bottom-mounted instruments may be destroyed and are nearly impossible to install during dangerous storm conditions.

In 2022, NHCI rapidly deployed sensor transects at a pier in Clearwater Beach, Florida just before Hurricane Ian made landfall. The site, which was on the left side of Ian's landfall, experienced weaker impacts due to the direction of offshore winds and lower water levels.

An NHCI team repeated the process in 2023 for Hurricane Idalia, which made landfall north of the pier. The site, which was on the right side of Idalia's landfall, suffered significant beach erosion due to elevated waves and water levels.

How do we use this data?

Observations of water levels and waves are used to validate the model predictions of storm-induced flooding and wave impacts.

• Sensors installed along the coast provide information about the spatial variability in the storm impacts, including differences in the timing, duration, and magnitude of storm surge and waves.
• Sensors deployed in shore-perpendicular transects provide detailed information about the transformation of waves and water levels across the nearshore region and over land. They are also useful in examining and validating the physical processes that are being modeled as part of the forecasts.
• Together, onshore and offshore measurements can be compared and used to evaluate differences in storm properties and impacts on either side of the storm.

All of these measurements are important for capturing the unique characteristics of each hurricane, to improve our understanding and document extreme conditions to help us better prepare coastal communities for future storm events.

Observing the ocean

NHCI teams are developing various technologies to make new observations of ocean properties in hurricanes and other strong storms. Sensors that measure directional wave energy, sea surface temperature, sea level pressure, and more are attached to buoys. The measurements can be used to evaluate and improve models.

Why observe the ocean offshore?

Hurricanes form over the open ocean. To predict what happens at the coastlines, scientists first need to understand the evolution of storms offshore.

How do we get these observations?

Hurricanes evolve rapidly and their forecasts change quickly as they approach land. Collecting measurements across these storms requires NHCI teams to stage buoys ahead of time in collaboration with partners at the Navy’s VXS-1 airborne squadron. NHCI works with forecasters to make decisions on when and where to drop buoys.

To track Hurricane Idalia in 2023, NHCI used forecasts to select an initial set of locations for aerial drops of buoys five days ahead of the predicted landfall. The team refined those locations with each forecast update.

A scientist drops a buoy into the ocean before hurricane landfall during testing of new buoy systems.

As Hurricane Idalia made landfall, buoys measured the waves underneath the storm, including on the right side where wave energy was high and coastal impacts were greatest.

How do we use this data?

Data from the wave buoys help scientists better understand the underlying physics of extreme waves during hurricanes. Wave data from buoys can be compared to wave and inundation models to determine where the models may be misrepresenting or inaccurately simulating wave energy and direction.

Simulating tropical cyclones

Models of the atmosphere that simulate changes through time are the cornerstone of weather forecasting. The Coupled Ocean-Atmosphere Mesoscale Prediction System – Tropical Cyclone (COAMPS-TC), developed by the U.S. Naval Research Laboratory, simulates tropical storm conditions, including wind, temperature, and pressure. Every 6 hours, the COAMPS-TC model makes predictions of all storms worldwide with a lead time of five days. Scientists at the National Hurricane Center use this model to build their official hurricane forecasts.

GIF showing model-simulated radar reflectivity and wind vectors over coastal North Carolina.

Simulating the coast, ocean, and inundation during storms

NHCI innovates new modeling tools to improve predictions of hurricane impacts.

The NHCI team from Deltares USA is focused on forecasting the hazards of flooding and erosion, including the impacts on buildings and roads, using a suite of innovative models.

These models are managed by the Coastal Storm Modeling System (CoSMoS). The Deltare USA team uses information about land elevation, vegetation, and real-time predictions of wind, air pressure, and rainfall to build a storm forecast. They then feed their forecast into CoSMoS to predict hazards and impacts along the coast.

NHCI's work covered 4 hurricane seasons (1 June - 1 November) from 2021 to 2024. The forecast models were able to accurately predict changes along the coast, in the ocean, and on land. Modeled wave heights closely match the observations made with drifter buoys and modeled water levels for Hurricane Idalia (2023) closely match the observations at NOAA tide gauges.

Quantifying structural damage and economic impacts

NHCI has developed BuiLD-FORCE(Building-Level Damage Forecasting of Regional Coastal Events), a machine learning model to predict the damages on residential buildings. BuiLD-FORCE extracts building information from StreetView and satellite images, integrates geospatial and socio-economic data from various sources, and uses forecasted COAMPS-TC winds and COAWST water levels to predict the probability of varying degrees of damage.

NHCI scientists continually retrain BuiLD-FORCE by incorporating new datasets, including updated information on hurricane impacts. BuiLD-FORCE is dynamic and can incorporate new information, making it well-suited to adapt to changing urban, socio-economic, and climate conditions.

NHCI partners

Government partners: US Geological Survey, US Naval Research Laboratory, NOAA/NWS/NCEP, and NGIA

Industry partners: SOFAR Ocean, Deltares USA and Deltares, Capella Space, Seahorse Coastal Consulting, Fathom Science, The Water Institute of the Gulf, and Airbus

Academic Partners: IHE Delft, Louisiana State University, North Carolina State University, Oregon State University, Scripps Institution of Oceanography, University of Colorado Boulder, University of Florida, University of Georgia, University of Massachusetts Amherst, University of Miami, University of North Carolina Chapel Hill, University of Rhode Island, University of Washington, and Woods Hole Oceanographic Institution