Hurricane causes grid damage across Florida, Georgia, Carolinas, Tennessee, Virginia

In late September 2024 a Category 4 hurricane made landfall on the northern Gulf coast of Florida and tracked several hundred miles inland through Georgia, South Carolina, North Carolina, Tennessee and Virginia, including areas of the southern Appalachian mountains. At peak the storm caused approximately 4.7 million customer outages across these states. Reported transmission damage in one affected state exceeded 370 high voltage structures and line sections across three transmission owners. Reported distribution and substation damage included submerged substations, thousands of poles down and fallen transmission towers in mountainous terrain. One large utility reported damage to more than 8,000 poles, more than 21,000 spans of conductor (about 1,000 miles of line), more than 1,500 transformers and thousands of trees on lines. Mobile substations were trucked in to give temporary supply to communities while damaged fixed equipment was repaired or replaced, and some local networks required complete rebuild rather than repair. Customer hours lost across the affected states made 2024 the worst year for outage hours in the United States in the previous decade, and one affected state averaged nearly 53 hours of interruption per customer during 2024, mainly attributed to this storm. Restoration involved more than 50,000 utility workers from 41 states and Canada. By mid October approximately 99.4% of customers had been restored, although isolated mountain communities remained without supply more than two weeks after landfall, and distribution restoration in the worst affected areas continued for several weeks longer.

Reported by the source and subsequent public analysis: (1) the storm reached several hundred miles inland while retaining high wind speeds, and the affected mountain areas of Tennessee, North Carolina and Virginia had not generally been treated as hurricane exposed in utility planning frameworks; (2) severe flooding accompanied the wind damage, with substations submerged and access routes destroyed by floodwater and mudslides; (3) the affected networks in these states included long, dispersed distribution circuits through forested and mountainous terrain, which increased exposure to tree fall and made repair access difficult; (4) vegetation damage was reported to be widespread across whole circuits rather than the scattered tree falls assumed in local planning baselines; (5) flooded substations required extensive de-watering, drying and inspection before equipment could be re-energised, a slower process than wind damage repair; (6) reconnection in flooded areas required electrical inspection of each affected building before re-energisation, which added restoration time independent of network repair; (7) commentary in the source placed the severity of inland damage within a broader pattern of weather extremes exceeding historical planning baselines rather than treating it as a single event anomaly.

1. Inland regions historically treated as low hurricane risk can experience severe wind and flood damage, so operators should test planning baselines against current and projected weather extremes rather than historical norms alone.
2. Substation flooding is a different failure mode from wind damage and needs its own mitigation, such as elevated equipment, watertight enclosures and improved drainage at sites in flood exposed locations.
3. Dispersed distribution networks in forested, mountainous terrain are costly to maintain and slow to restore, so operators should discuss long term network options with regulators and customers, including undergrounding, local microgrids and load consolidation.
4. Large scale mutual aid arrangements provided the workforce for restoration, so operators should both contribute to and plan around such frameworks while recognising that available crews are finite during widespread events.
5. Mobile substations were a critical interim measure, so operators should hold or contract access to a fleet sized against credible disaster scenarios.
6. Reconnection in flooded areas depends on coordination between the network operator, electrical inspectors and building owners, so protocols and contracted inspection resources should be arranged before an event.
7. Microgrids installed before the storm provided local resilience only for as long as their storage lasted, so operators investing in microgrids should size storage to the credible duration of a wide area outage.

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