Understanding Weather Warning Flags

Have you ever visited the coast or lake shore and noticed red flags posted along the beach or waterfront? These flags are weather warnings. Their shape and color indicate a unique weather hazard. 

The next time you visit the coast, make sure you know what each of the following flags mean:

Rectangular Red Flags

Red Warning flag on windy beach
Lyn Holly Coorg / Getty Images

A red flag means that high surf or strong currents, such as rip currents, are present.

Notice double red flags? If so, you'll have little choice but to avoid the beach altogether, since this means the water is closed to the public.

Red Pennants

Big Red Flag
David H. Lewis / Getty Images

A single red triangle (pennant) symbolizes a small craft advisory. It is flown whenever winds of up to 38 mph (33 knots) are expected to be a danger to your sailboat, yacht, or other small vessels. 

Small craft advisories are also issued when sea or lake ice exists that could be hazardous for small boats.

Double Red Pennants

Mexico, Quintana Roo, Yucatan Peninsula, Cancun, Red flag on beach
Bryan Mullennix / Getty Images

Whenever a double pennant flag is hoisted, be warned that gale-force wind (winds of 39-54 mph (34-47 knots)) are forecast.

Gale warnings often precede or accompany a hurricane watch but can be issued even when there's no threat of a tropical cyclone.

Rectangular Red and Black Flags

Tropical Storm Hanna

Logan Mock-Bunting/Getty Images 

A single red flag with a black square center signifies a tropical storm warning. Whenever this flag is raised, be on the lookout for sustained winds of 55-73 mph (48-63 knots). 

Double Rectangular Red and Black Flags

Wake Forest v Miami
Joel Auerbach / Getty Images

University of Miami sports fans will no doubt recognize this next flag. Double red-and-black-square flags indicate hurricane-force winds of 74 mph (63 knots) or higher are expected to impact your forecast area. You should take precautionary measures to protect your coastal property and your life!

Beach Warning Flags

Red flag on a beach

Matt Cardy/Getty Images 

In addition to flying weather flags, beaches follow a similar practice that makes visitors aware of water conditions and advises guests whether or not to enter the ocean based on those conditions. The color code for beach flags includes: 

  • Green flags are an "all-clear" and symbolize that the risk of hazards is low and it's safe to swim. 
  • Yellow flags indicate moderate surf. You'll typically see these when ocean conditions are rough, but not life-threatening. 
  • Purple flags are flown when dangerous marine life (jellyfish, sharks, etc.) have been spotted. They indicate you should exercise caution while in the water.
  • Red flags are the most serious of all beach flags. They signal a serious hazard.

Unlike weather flags, the shape of beach flags doesn't matter — just the color. They may be triangular in shape or in the classic rectangular shape. 

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Means, Tiffany. "Understanding Weather Warning Flags." ThoughtCo, Jul. 31, 2021, thoughtco.com/weather-warning-flags-4045449. Means, Tiffany. (2021, July 31). Understanding Weather Warning Flags. Retrieved from https://www.thoughtco.com/weather-warning-flags-4045449 Means, Tiffany. "Understanding Weather Warning Flags." ThoughtCo. https://www.thoughtco.com/weather-warning-flags-4045449 (accessed March 20, 2023).