A High Surf Advisory (HSA) is a formal announcement issued by governmental weather authorities to alert the public to impending hazardous wave conditions along coastal areas. These alerts communicate a threat level that requires caution from beachgoers and mariners. High surf conditions result from large ocean swells, often generated by distant storms or powerful wind systems far out at sea, which travel toward the shore. The issuance of an advisory is intended to protect life and property by informing people that the ocean environment is significantly more dangerous than usual.
Defining the High Surf Advisory
The National Weather Service (NWS) is the agency responsible for issuing these meteorological alerts for United States coastlines. An Advisory represents a lower level of hazard severity compared to a Warning, but it still signifies a significant threat to safety. A High Surf Advisory is issued when breaking wave action is expected to pose a threat to life and property.
The NWS uses a tiered system for communicating coastal hazards. A High Surf Watch is the first alert, issued when conditions are possible, typically 12 to 48 hours in advance, but the timing or location is still uncertain. The Advisory is issued when the hazardous conditions are imminent or occurring, meaning caution is advised and the threat is confirmed.
A High Surf Warning represents the highest level of threat, reserved for conditions that present an especially heightened danger to life and property. The step from an Advisory to a Warning signifies that the surf event is expected to be more destructive, potentially causing widespread damage or extreme risk of injury.
Conditions That Trigger an Advisory
The precise criteria required to trigger a High Surf Advisory are not universal and are determined locally by individual weather forecast offices. This geographical variation accounts for the different coastal environments. What constitutes a dangerous wave height in one area may be considered normal in another, making local knowledge paramount for setting the thresholds.
Advisories are generally issued when breaking wave heights are forecast to reach a certain threshold, often falling within the range of 8 to 15 feet in most areas. The wave height alone is not the only factor considered in the decision to issue an alert.
Forecasters also analyze the wave period, which is the time interval between successive wave crests. A longer wave period, even with a moderate wave height, indicates that the wave carries significantly more energy, leading to a much more powerful and dangerous impact at the shoreline. Furthermore, the expected duration of the high surf event is factored in, as prolonged periods of large waves increase the risk of coastal erosion and infrastructure damage. The conditions that meet advisory criteria are hazardous to anyone entering the water, but they are not typically life-threatening to the general beachgoer who remains safely away from the surf line.
Public Safety During High Surf
High surf creates secondary hazards that can quickly overwhelm an unprepared individual.
Rip Currents
High surf greatly intensifies the formation and strength of rip currents, which are narrow channels of fast-moving water flowing rapidly away from the shore. These currents can pull even strong swimmers away from the beach, and escaping them requires swimming parallel to the shore until the current dissipates, rather than struggling against it.
Shore Break
Another significant hazard is dangerous shore break, a condition where waves peak and break suddenly and violently directly onto the beach in shallow water. Shore break can lead to serious injuries, including spinal and neck trauma, when swimmers or waders are slammed head-first into the sandy bottom by the force of the crashing wave. This danger exists even with waves that do not meet the full criteria for a High Surf Advisory.
Sneaker Waves and General Safety
The unpredictable nature of the ocean during these events means that unusually large waves, sometimes called “sneaker waves,” can run significantly higher up the beach than preceding waves. These unexpected surges pose a threat to those walking along the sand, sweeping people, children, or pets off their feet and into the turbulent water. It is highly recommended to stay off structures like jetties, piers, and rock outcroppings, as these areas are frequently hit by powerful, unpredictable wash-over. Never turn your back to the ocean, as awareness of incoming waves allows for quick movement to higher ground if a large wave approaches.