Maritime Flags

If you've never been or lived in coastal areas or even near the North Shore, you probably haven't had to think about nautical weather and warnings.
The US Coast Guard uses flags displayed on masts. flagpoles and yardarms to warn of impending maritime weather.

Here's a guide to the uninitiated.

Tropical Storm Watch

A tropical storm watch (TRA) is issued when tropical storm conditions, including winds from 39 to 73 mph (35 to 64 knots, 63 to 117 km/h) pose a possible threat to a specified coastal area within 48 hours (was 36 hours prior to 2010 hurricane season). Maritime flags indicate this with a single square red flag.

Tropical Storm Warning

A tropical storm warning (TRW) is issued when tropical storm conditions (as above) are expected in a specified coastal area within 36 hours or less (was 24 hours or less prior to 2010 hurricane season). Maritime flags indicate this with two square red flags.

Hurricanes

Hurricane Watch

A hurricane watch (HWA) is issued for a specified area for which a hurricane or a hurricane-related hazard is a possible threat within 48 hours (was 36 hours prior to 2010 hurricane season). Maritime flags indicate this with a single square red flag with a black square in the middle.

The purpose of a hurricane watch is to inform families to obtain supplies, secure your home, and be prepared to evacuate.

Hurricane Warning

A hurricane warning (HWW) is issued when a hurricane with sustained winds of 74 mph (65 knots, 118 km/h) or higher is expected in a specified coastal area in 36 hours or less (was 24 hours or less prior to 2010 hurricane season). Maritime flags indicate this with two square red flags with a black square in the middle of each.

A hurricane warning can remain in effect when dangerously high water or a combination of dangerously high water and exceptionally high waves continues, even though the winds may have subsided below hurricane intensity.

Where the intensity or track of a forecast cyclone are uncertain (such as a tropical storm bordering hurricane intensity or on the edge of a track), a Tropical Storm Warning and a Hurricane Watch are often in effect at the same time on parts of the coast. Maritime flags indicate this with two square red flags with a black square in the middle on only one of them.