Hoist the Flag!

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Warnings of impending hazardous marine weather were among the first pieces of information conveyed by the fledgling 19th Century Weather Bureau, the forerunner organization to today’s National Weather Service. Indeed, the tremendous loss of lives and cargo in maritime shipping disasters over the Great Lakes was the impetus for the formation of a national weather service under the aegis of the U.S. Army Signal Corps in 1870. The practice of weather forecasting was in its infancy during the 1870s, driven primarily by the sharing of surface observations through telegraph. Radio communications, the detailed sampling of the upper atmosphere by radiosonde balloons, radar, television, supercomputers, satellite, and smartphones were still decades into the future back in 1870. These advances in technology would revolutionize weather forecasting and the communication of weather information during the 20th century. However, the primary means of communicating hazardous weather information to a vulnerable public during the last years of the 19th century were postcards, light signals and display flags. Warning display flags were first displayed systematically in various ports, harbors and Weather Bureau stations in the Great Lakes states and along the U.S. Atlantic and Gulf coasts to warn of hurricanes, gales and strong marine wind events. Such flags were displayed routinely at the Port of Key West and the Weather Bureau stations at Key West and Sand Key Lighthouse. Mariners would catch sight of one of these flags either departing or returning from a voyage, and immediately know its meaning – hurricane warning, storm warning, gale warning or small craft warning. Over the years the Weather Service expanded the program to the U.S. Coast Guard, yacht clubs and marinas. However, by 1989, advances in communication technologies led to retirement of the “Coastal Warning Display Program”. Nevertheless, many port departments and private marinas along the coast have continued to “hoist the flag” to this day. The Florida Keys National Weather Service moved into a new hurricane-hardened facility on White Street in Key West in September of 2005. We decided during the move to resurrect the coastal warning display program to acknowledge both the nautical heritage of the Florida Keys and the long history of government weather service in Key West (dating back to 1870) while providing an alternative means of dissemination of hazardous marine weather information at a highly visible location. Hurricane Wilma brought high winds and a destructive storm surge to the Keys about a month after the move on Monday, October 24th. This photograph shows hurricane warning flags being displayed prominently at the NOAA White Street facility on the Sunday prior to Wilma’s landfall in south Florida. Selected U.S. Coast Guard stations joined in the resurrection of the coastal warning display program in 2007, including Coast Guard Stations Key West, Marathon and Islamorada. The primary marine weather warnings and advisories today are similar to what they were in years past and are tied mainly to wind and wave thresholds. In Florida Keys marine weather, as in the restaurant business, the three most important factors are location, location and location! For example, a prevailing southeast wind of 20 knots likely will result in 7-foot seas at a location like the Vandenberg wreck south of Key West, whereas a shallow water location in the lee of a mangrove island over the Gulf flats just north of the lower Keys may result in just a moderate chop with an occasional gust to 20 knots. Shift the wind direction to the northeast instead of the southeast, and the situation is altogether different. Numerous other examples abound up and down the Keys for various wind speed and direction pairings. This is why it is important to heed the advice of experienced local skippers. Such captains typically are plugged into NOAA Weather sources several times per day and often can make determinations regarding the safest location to operate their vessels, or in some cases, to cancel when the situation warrants. The most frequent marine weather advisory in the Florida Keys for which display flags are flown is the “Small Craft Advisory”, issued for sustained winds or frequent gusts of 20 to 33 knots and/or seas of seven feet or greater expected in a particular zone. A single red pennant will be hoisted for such an event, most common in the Florida Keys from late autumn to early spring. Less common is the “Gale Warning”, issued for sustained winds or frequent gusts of 34 to 47 knots. Two red pennants will be hoisted for a gale warning, an event which may occur only a few times per year in the Florida Keys. A “Tropical Storm Warning” is issued for the threat of sustained winds or frequent gusts of 34 to 63 knots associated with a tropical storm. A square red flag with an embedded black square will be hoisted for an imminent tropical storm, an event which almost always occurs during the hurricane season, between June 1st and November 30th. The rarest of them all is the “Hurricane Warning”, issued for sustained winds or frequent gusts exceeding 63 knots. Two square red flags with embedded black squares will be hoisted for a hurricane warning. Years may go by without a hurricane warning as has been the case in the Florida Keys since Wilma of 2005. Or, several hurricane warnings may be issued in the course of a season such as during the hyperactive hurricane seasons of 2004 and 2005. Fortunately, Hurricane Season 2011 was able to pass without the hoisting of any hurricane warning flags over the Florida Keys. In any case, remember to be weather-ready, and stay safe!