Information on the Florida Keys

Miami to Key West

(1) This chapter describes the Florida Keys and the various passages that lead through it from the Straits of Florida and Hawk Channel to Florida Bay and the Gulf of Mexico. Also discussed are Key West Harbor and the small-craft basins at Key West, Boot Key Harbor, Safe Harbor, and several other small-craft harbors along the Florida Keys.

(2) Strangers using Hawk Channel and the various passages through the Florida Keys can obtain the services of fishing boat captains and other qualified charter-boat captains at Miami or Key West who will act as pilots or guides.

COLREGS Demarcation Lines
(3) The lines established for this part of the coast are described in 80.735 and 80.740, chapter 2.

Weather
(4) Tropical cyclones are the greatest weather hazard to navigation in this area. While they can form in any month they are most likely during August, September and October. Some of the greatest hurricanes on record have moved through this area. Often considered the most devastating, was the Labor Day Hurricane that struck the Florida Keys in 1935. Winds were calculated to be 175 to 215 knots. Near Lower Matecumbe Key (Craig) a pressure of 892.3mb was measured; the lowest ever in a North Atlantic hurricane. Storm tides were estimated to have exceeded 18 feet (5.5 m) above mean sea level. Donna (1960) and Betsy (1965) were other severe hurricanes that wreaked havoc in the Keys. For more detail see Key West.

(5) This area lies close to the northern boundary of the trade winds in winter but in the heart of this system in summer. Therefore easterlies and northeasterlies are persistent throughout the year. They are occasionally interrupted by winter cold fronts, easterly waves and tropical cyclones. Local effects also come into play near the Keys. The trades usually blow at 10 to 20 knots but can strengthen at times. While gales are infrequent, winds of 22 knots or more blow about 7 to 12 percent of the time from October through March. In the Straits of Florida, October and November trade winds are persistent and intense, averaging around 15 knots. From fall through spring, waves of 10 feet (3 m) or more are reported 1 to 3 percent of the time.

(6) The nearness of the Gulf Stream and the tempering effects of the Gulf of Mexico produce a tropical maritime climate in which average winter temperatures are only 12° to 15°F (6.7° to 8.4°C) cooler than summer averages. Cold fronts are usually modified even if they reach the Keys. Just south of Miami there are about 10 to 12 days on the average when minimums drop below 40°F (4.4°C). June through October is generally considered the rainy season and most of this falls as showers and thunderstorms. Particularly heavy amounts fall in conjunction with easterly waves or more organized tropical cyclones. In winter, cold fronts may bring rain. Visibilities are usually good but may be reduced briefly in showers.

Chart 11460

(7) The Florida Keys consist of a remarkable chain of low islands, beginning with Virginia Key and extending in a circular sweep to Loggerhead Key, a distance of about 192 miles. For some 100 miles of that distance they skirt the southeast coast of the Florida Peninsula, from which they are separated by shallow bodies of water known as Biscayne Bay, Card Sound, Barnes Sound, Blackwater Sound, and Florida Bay. Biscayne Bay has depths of 9 to 10 feet for most of its length, and the other bodies of water are shallow, containing small keys and shoals, and of no commercial importance except as a cruising ground for small boats. Westward of Florida Bay the Florida Keys separate the Straits of Florida from the Gulf of Mexico.

(8) The keys are mostly of coral formation, low, and generally covered with dense mangrove growth, though some are wooded with pine, and on a few are groves of coconut trees. Most of the keys that are connected by U.S. Highway 1 to Key West are inhabited. Key West is the most important of the keys. Florida Keys National Marine Sanctuary, a Marine Protected Area (MPA), surrounds the keys from Biscayne Bay to Dry Tortugas. (See Appendix C for additional information.)

(9) The openings under the viaduct and bridges are indicated on the charts. Drawbridges are over Channel Five, Jewfish Creek, and Moser Channel. Overhead power cables run parallel to U.S. Highway 1 from Tavernier to Big Coppitt Key. All clearances are greater than those of the adjacent fixed bridges. Cables are submerged at the movable spans of drawbridges. Small craft with local knowledge use these channels to go from the Straits of Florida to Florida Bay and the Gulf of Mexico. Strangers should not attempt passage without a pilot or guide.

(10) The tidal currents are strong through the openings between the keys. Wind effects may at times be expected to modify the velocities shown in the tidal current tables.

(11) The Florida Keys are skirted on the side next to the straits throughout their extent by the Florida Reefs, a chain of dangerous reefs and shoals lying at an average distance of about 5 miles from the line of keys. The reefs are hazardous because they are not marked by breakers in smooth weather and only a few show above the water. On the outer edge of and between the reefs the water shoals abruptly.

(12) In the seaward approach to the reefs, warning of their proximity usually will be given by the difference in color of the water, from deep blue to light green, or by the Bank Blink, described in chapter 3. Too much reliance in these warnings, however, may lead to trouble. In clear weather the lights and daybeacons make navigation along the reefs easy, but in thick weather soundings should be relied upon for safety. Fifty-fathom soundings indicate a distance of 2 to 3 miles from the reefs, and great caution should be used in approaching them closer. Fog is not frequent in this locality.

(13) The water always becomes milky following windy weather. The usual color of the water on the reefs is bluish green, and the shoal patches show dark, shading through brown to yellow as they approach the surface. The shoal sand patches show as a bright green. At depths of 10 to 15 feet grass patches on the bottom look quite similar to rocks. When piloting in this area choose a time so that the Sun will be astern, conning the vessel from aloft or from an elevated position forward, for then the line of demarcation between deep water and edges of the shoal will be indicated with surprising clarity.