Coastal Flood Watches, Warnings, and Advisories: What’s the Difference?

Areas on the coast are particularly susceptible to hurricanes, but with so many weather terms, it can be overwhelming to stay up to date with the latest news and information. Still, the damage from typhoons, intense storms, flooding, and more is not something to take lightly. So, what exactly is the difference between a coastal flood watch, warning, and advisory? And in addition to coastal floods, what are the other types? SERVPRO^® is Here to Help^® answers these questions and more.

Definitions of Coastal Flood Advisory, Watch, and Warning

The National Oceanic and Atmospheric Administration provides the following definition of a coastal flood advisory: “Issued when minor or nuisance coastal flooding is occurring or imminent.”

Conversely, the next step up, a coastal flood watch, is: “Issued when moderate to major coastal flooding is possible. Such flooding would potentially pose a serious risk to life and property.” In other words, when a coastal flood watch is issued, sea water has spilled over dune lines, and sea walls will occur (as long as weather conditions remain favorable). People in these areas should be prepared to move to safe ground in the event of flooding or a coastal flood warning.

Finally, a coastal flood warning (the most severe) is: “Issued when moderate to major coastal flooding is occurring or imminent. This flooding will pose a serious risk to life and property.” Unlike a coastal flood watch, when this type of warning is issued, it means sea water has spilled over dune lines, and sea walls are taking place or are imminent (and should occur within the next 12 hours). People in affected areas should immediately make efforts to protect themselves and their property.

What is a Sea Wall?

A “sea wall” is an important term related to coastal flooding, and according to the UN Climate Technology Center and Network, is defined as: “…hard engineered structures with a primary function to prevent further erosion of the shoreline.” Ultimately, they are built parallel to a shoreline, and have two primary functions: 1) protection from waves and erosion reduction (holding or preventing soil sliding), and 2) coastal flood defense.

They are sometimes vertical, sometimes sloping, and are made from a variety of materials. Additionally, they are occasionally called “revetments.”

What are the Different Flood Types?

Now that you know the difference between a coastal flood advisory, watch, and warning, you may be wondering what the different types of floods are. The NOAA National Severe Storms Laboratory outlines six different types of floods: 1) river floods, 2) coastal floods, 3) storm surge, 4) inland flooding, 5) flash floods, and 6) debris flows. But what do those mean, exactly?

Let’s start with a 1) coastal flood, which is: “…the inundation of land areas along the coast,” and is “caused by higher-than-average high tide and worsened by heavy rainfall and onshore winds (i.e., wind blowing landward from the ocean).”

Additional types include:

• River Flood: This type of flood: “occurs when water levels rise over the top of riverbanks due to excessive rain from tropical systems making landfall, persistent thunderstorms over the same area for extended periods of time, combined rainfall and snowmelt, or an ice jam.”
• Storm Surge: You might be familiar with the term “storm surge.” As a quick refresher, a storm surge is: “an abnormal rise in water level in coastal areas, over and above the regular astronomical tide, caused by forces generated from a severe storm's wind, waves, and low atmospheric pressure.” Storm surges are particularly dangerous because they are capable of flooding large coastal areas. This can be especially disruptive when storm surge occurs simultaneously with high tide, and storm tides reach up to 20 feet or more. In fact, storms are often the biggest threat to life in coastal areas during a hurricane.
• Inland Flooding: This occurs: “when moderate precipitation accumulates over several days, intense precipitation falls over a short period, or a river overflows because of an ice or debris jam or dam or levee failure.”
• Flash Flood: These are: “…caused by heavy or excessive rainfall in a short period of time, generally less than six hours.” They are particularly dangerous in that they may occur after a few hours of rainfall, or as little as a few minutes. They are characterized by vicious water torrents that can run through streets, canyons, riverbeds, and other areas.
• Debris Flow: This last kind is caused by rainfall, “…that is normally absorbed by soil and vegetation,” which “can run off almost instantly, causing creeks and drainage areas to flood much earlier and with higher magnitude than normal.” Notably, if areas have been recently burned, heavy rainfall in these locations can cause sediments to shift, contributing to a potentially destructive debris flow.

Coastal Flooding Safety Steps

Whether a coastal flood advisory, watch, or warning is issued, it is always helpful to stay aware, be prepared, and take action, if necessary. Keep the following coastal flood safety tips in mind, according to the National Weather Service, if/when flooding is imminent:

• Ultimately, if/when coastal flooding occurs, act quickly.
• Do not stay near the coast if/when water starts rising.
• Protect your property in advance by securing loose objects, boarding up windows, and establishing evacuation routes.
  • SERVPRO offers board-up and roof tarping services, as well as an Emergency Ready Plan, that may be helpful.
• Move inland to avoid and escape flood waters as much as possible.
• Avoid fishing or watching the waves from exposed areas. Large waves may sweep up onto dry areas.
• If you are outside at night during potentially dangerous coastal flooding conditions, be cautious. Sometimes, it can be harder to recognize and spot threats.
• Always be prepared to evacuate the area immediately.
• If you are stranded during a coastal flood, stay indoors if possible, and go to the highest floor, making sure you have food, water, flashlight(s), and a portable radio on-hand.

After Coastal Flood Damage and Natural Disasters, SERVPRO is Here to Help

Natural disasters are serious business, and floods are no exception. Whether you live on a coast or somewhere inland, excessive rain, burst pipes, faulty dams, and more can cause extensive flooding, threatening the health and safety of yourself, your family, employees, pets, and more. But with 2270 SERVPRO locations in the United States and Canada, there is a franchise nearby, here to help with 24-hour emergency services, including storm damage cleanup and restoration.

Established in 1967, SERVPRO has grown to become the #1 choice in fire and water cleanup and restoration*. SERVPRO professionals undergo extensive training to help ensure your property is returned to pre-flood condition as soon as possible, and each office is staffed around the clock. So, no matter when a flood may strike and you need assistance—whether on a holiday, weekend, or at 3 in the morning—reach out anytime to your local SERVPRO.

To learn more about SERVPRO and the cleanup and restoration industry, please visit our FAQ and Glossary.