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StEER: Hurricane Helene Preliminary Virtual Reconnaissance Report (PVRR)
StEER - Structural Engineering Extreme Event Reconnaissance
12/2024
Abstract
StEER activated a Level 1 response to conduct building performance assessments following this event, initiating a Virtual Assessment Structural Team (VAST) on September 29, 2024, based on the event having the strong potential to generate new knowledge. The VAST was charged with the production of the primary product of StEER’s Level 1 response: this Preliminary Virtual Reconnaissance Report (PVRR), intended to:
provide an overview of Hurricane Helene, particularly relating to coastal impacts, inland flooding, and wind damage impact on the built environment,
overview the regulatory environment and construction practices in the landfall area and other areas affected by the storm,
synthesize preliminary performance assessment reports for buildings and a range of infrastructure classes across multiple states,
provide recommendations for continued study on (1) Non-Stationary Hurricane Risk, (2) Drivers of Catastrophic Loss in North Carolina, (3) Housing Vulnerability, and (4) Future Reconnaissance Needs.
Note that this hurricane was geographically expansive and its impacts wide ranging, well beyond what could be documented through the volunteer efforts of a VAST. Moreover, since the VAST data collection initiated immediately following Hurricane Helene, at a time when access was limited to many areas and impacts were not fully known or reported, the observations herein may not capture the full scope of the impacts as now understood.
Hurricane Helene made landfall as a Category 4 in the Big Bend region of Florida, near Perry, FL at approximately 0310 UTC September 27, 2024. The storm’s intensity and northeastern track across the Gulf of Mexico produced coastal flooding along a large portion of Florida’s Gulf Coast from Apalachee Bay to the north in the Big Bend, extending to just south of Naples. The most significant coastal flooding occurred in Florida’s “Nature Coast” between Clearwater Beach and Apalachee Bay, and because much of this coastline is less developed than other parts of Florida’s coast, potentially high economic losses were minimized there to some extent. Hurricane Helene’s wind field was notably extensive, with hurricane force winds extending outward up to 60 miles but wind velocities at landfall were substantially lower than Category 4 strength and well below the design wind speed in this region.
Like Hurricane Harvey, Helene generated a series of cascading hazards as it moved inland, with a wide range of impacts across several other states as it moved through the Southeastern United States and into Appalachia. Beyond spawning tornadoes across Georgia, South Carolina and North Carolina, Helene produced rainfall values exceeding 35 cm (14 in) in parts of Florida, Georgia, and South Carolina, with at least one location in North Carolina exceeding 78 cm. North Carolina, despite being hundreds of miles north of Hurricane Helene’s landfall site, arguably experienced the most severe impacts. The extreme precipitation in the western part of North Carolina resulted in unprecedented flooding. As a result, Hurricane Helene will be one of the deadliest and costliest natural disasters in US history with over 230 reported fatalities and damage and economic losses possibly surpassing 160B USD, though estimates are still quite fluid, with expected sizable gaps between total losses and insured losses.
While storm surge in excess of 10 feet caused significant damage to structures with insufficient freeboard, there were no significant wind losses in Helene. Instead, the vast majority of notable structural failures occurred well inland, emanating from an unprecedented intensity of rainfall, exacerbating a prior condition of heavily saturated soils and rivers at or near flood stage, leading to flash flooding, high-velocity flows, large debris fields, and widespread geotechnical failures that destroyed buildings, claimed lives, and cut entire regions of North Carolina off for extended periods of time. While there may be limited ability to engineer individual structures to resist such demands, it is important to document and learn from a disaster of this scale.
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Details
- Title
- StEER: Hurricane Helene Preliminary Virtual Reconnaissance Report (PVRR)
- Resource Type
- Report
- Publisher
- StEER - Structural Engineering Extreme Event Reconnaissance; NSF NHERI DesignSafe Data Depot Repository
- Format
- link
- Identifiers
- 99381900686206600
- Academic Unit
- Civil Engineering and Construction Management; Hal Marcus College of Science and Engineering
- Language
- English