« AnteriorContinuar »
Fog.—The percentage of fog is highest from March to June, reaching a maximum of 30 per cent of days with fog near the mouth of Chesapeake Bay in June. This percentage decreases to 10 at Hatteras, but fog can be expected as far south as Florida.
Prevailing winds. The winds are westerly north of the thirty-fifth parallel, except in September and October when they are northeasterly along the entire coast. The westerly winds extend to the thirtieth parallel from December to April, inclusive. Easterly winds prevail along the Florida coast. At Key West they are northeasterly, except during the summer months, when they are southeasterly.
Northers. In the winter months heavy northers occur in the vicinity of the Straits of Florida. They blow generally from northwest to north, hauling, as a rule, northward and eastward, and rarely backing. Their approach is nearly always heralded by a heavy bank of clouds in the northwest, preceded by light airs from the contrary direction, and accompanied by a falling barometer; they commence with a violent squall, gradually settling to a fresh gale. Vessels caught in the narrower parts of the straits in these gales are subject to a most trying sea.
Southeast gales also occur at intervals during the winter months in the vicinity of the Straits of Florida. They usually commence to blow at about ENE., freshening rapidly with a falling barometer and rising thermometer, and hauling southward and eastward, obtain their greatest force at about southeast.
Storm warnings are displayed by the United States Weather Bureau on the coasts of the United States and the Great Lakes.
The small craft warning.-A red pennant indicates that moderately strong winds that will interfere with the safe operation of small craft are expected. No night display of small craft warnings is made.
The northeast storm warning. -A red pennant above a square red flag with black center displayed by day, or two red lanterns, one above the other, displayed by night, indicate the approach of a storm of marked violence with winds beginning from the northeast. The southeast storm warning.
A red pennant below a square red flag with black center displayed by day, or one red lantern displayed by night, indicates the approach of a storm of marked violence with winds beginning from the southeast.
The southwest storm warning.--A white pennant below a square red flag with black center displayed by day, or a white lantern below a red lantern displayed by night, indicates the approach of a storm of marked violence with winds beginning from the southwest.
The northwest storm warning.-A white pennant above a square red flag with black center displayed by day, or a white lantern above a red lantern displayed by night, indicates the approach of a storm of marked violence with winds beginning
from the northwest. Hurricane, or whole gale warning.-Two square flags, red with black centers, one above the other, displayed by day, or two red lanterns, with a white lantern between, displayed by night, indicate the approach of a tropical hurricane, or one of the extremely severe and dangerous storms which occasionally move across the Great Lakes and Atlantic coast.
These warnings are displayed at all stations on the Atlantic and Gulf coasts of the United States and on the following islands in the Atlantic: Jamaica, Turks Island, Bermuda, Haiti, Curacao, Porto Rico, Virgin Islands of the United States, St. Kitts, Dominica, Barbados, Trinidad, St. Lucia, St. Vincent, Grenada, Swan Island, and Cuba.
The following are the storm warning display stations within the limits covered by this volume: VIRGINIA :
Georgia-Continued. *Cape Henry.
St. Simon Island.
Alligator Reef Lighthouse.
American Shoal Lighthouse.
Carysfort Shoal Lighthouse.
Fowey Rocks Lighthouse.
Key West, corner Caroline and Washington.
Elizabeth Streets. *Wilmington,
Key West, No. 611 Front Street. SOUTH CAROLINA:
Sombrero Key Lighthouse.
*West Palm Beach. *Savannah. Note.-The Weather Bureau - stations at Cape Henry, Va., and Sand Key, Fla., are equipped for day and night communication with passing vessels. The International Code is used by day and the
*At these stations barometers will be compared with standards.
Morse Code, flash-light, by night. Messages to or from vessels will be forwarded to destination. At lighthouses and light vessels warnings are not displayed at night.
WEST INDIA HURRICANES.
These are cyclonic storms with a center of lowest barometer, around which the wind blows in a more or less circular course (spirally) in a direction contrary to the hands of a watch. At the same time the storm field advances on a straight or curved track, sometimes with great velocity, and sometimes not more than a few miles an hour, occasionally appearing to come to a pause in its onward movements. The estimated velocity on the Atlantic coast between Hatteras and the island of Cuba is 5 to 15 miles per hour. They cover simultaneously an approximately circular area from 150 to 500 miles in diameter. At the center, the area of lowest barometer, which is from 10 to 20 miles in diameter, comparative calm prevails; the seas within this center are violent and confused, and combined with the sudden shifts of wind which are encountered as the vessel passes through the center make this the most dangerous part of the hurricane and the one to be avoided.
Hurricanes form eastward of the Winward Islands or in the Caribbean Sea, and take a westerly or northwesterly course. Some curve gradually northward, passing north of the island of Cuba and northeasterly along and east ward of the Atlantic coast of the United States. Others pass over or southward of Cuba and enter the Gulf of Mexico, and while in the Gulf usually curve northward or northeastward so as to strike the coast somewhere between Tampa, Fla., and the Rio Grande. Tracks of hurricanes are shown on pilot charts of the North Atlantic Ocean, published monthly by the Hydrographic Office.
The months during which hurricanes are usually encountered are June to November; the months of their greatest frequency are August, September, and October. During these months mariners should be on the watch for indications of a hurricane, and should frequently and carefully observe and record the barometer.
Signs of approach.–First, a long heavy swell, a slight rise followed by a continuous fall of the barometer; second, a strong, gusty wind from some northerly point (northeast, north, or northwest), blowing with increasing force; and third, a rough, increasing sea. If one or more of these signs be wanting there is little cause for anticipating a hurricane.
The approach of a hurricane is usually indicated by a long, heavy swell, propagated to a great distance two or three days in advance, where there is no intervening land to interrupt it, and which comes from the direction in which the storm is approaching.
One of the earliest signs of a hurricane are high cirrus clouds which converge toward a point on the horizon that indicates the direction of the center of the storm. The snow-white fibrous mare's tails appear when the center of the storm is about 300 or 400 miles distant.
As the storm center approaches, the barometer continues to fall, the velocity of the wind increases and blows in heavy squalls, and
the changes in its direction become more rapid. Rain in showers accompanies the squalls, and when closer to the center the rain is continuous and attended by furious gusts of wind; the air is frequently thick with rain and spume drift, making objects invisible at a short distance. A vessel on a line of the hurricane's advance will experience the above disturbances, except that as the center approaches, the wind will rernain from the same direction, or nearly so, until the vessel is close to or in the center.
Distance from center.—The distance from the center of a hurricane can only be estimated from a consideration of the height of the barometer and the rapidity of its fall and the velocity of the wind and rapidity of its change in direction. If the barometer falls slowly and the wind increases gradually, it may be reasonably supposed that the center is distant; with a rapidly falling barometer and increasing winds the center may be supposed to be approaching dangerously near.
Practical rules.—When there are indications of a hurricane, vessels should remain in port or seek one if possible, carefully observing and recording the changes in barometer and wind and taking every precaution to avert damage by striking light spars, strengthening moorings, and if a steamer preparing steam to assist the moorings. In the ports of the Southern States hurricanes are generally accompanied by very high tides, and vessels may be endangered by overriding the wharf where lying if the position is at all exposed.
Vessels in the Straits of Florida may not have the sea room to maneuver so as to avoid the storm track, and should use every endeavor to make a harbor or stand out of the straits to obtain sea room. Vessels unable to reach port and having sea room to maneuver should observe the following rules:
When there are indications of a hurricane near, sailing vessels should heave to on the starboard tack and steamers remain stationary and carefully observe and record the changes in wind and barometer so as to find the bearing of the center and ascertain by the shift of wind in which semicircle the vessel is situated. Much will often depend on heaving to in time.
Facing the wind the storm center will be 8 to 12 points to the right; when the storm is distant it will be from 10 to 12 points, and when the barometer has fallen five or six tenths it will be about 8 points.
A line drawn through the center of a hurricane in the direction in which it is moving is called the axis or line of progression, and looking in the direction in which it is traveling the semicircle on either side of the axis is called, respectively, the right-hand, or dangerous, semicircle, and the left-hand, or navigable, semicircle.
To find in which semicircle the vessel is situated: If the wind shifts to the right, the vessel will be in the right-hand, or dangerous, semicircle, with regard to the direction in which the storm is traveling, in which case the vessel should be kept on the starboard tack and increase her distance from the center.
If the wind shifts to the left, the vessel will be in the left, or safe, semicircle. The helm should be put up and the vessel run with the wind on the starboard quarter, preserving the compass course, if possible, until the barometer rises, when the vessel may be hove to on
the port tack. Or if there is not sea room to run, the vessel can be put on the port tack at once.
Should the wind remain steady and the barometer continue to fall, the vessel is in the path of the storm and should run with the wind on the starboard quarter into the safe semicircle.
It all cases act so as to increase as soon as possible the distance from the center, bearing in mind that the whole storm field is advancing.
In receding from the center of a hurricane the barometer will rise and the wind and sea subside.
The following special signals for surveying vessels of the United States employed in hydrographic surveying have been prescribed :
A surveying vessel of the United States, under way or at anchor in a fairway and employed in hydrographic surveying, may carry where they can best be seen, but in any case well above the rigging lights prescribed by law for preventing collisions, three lights in a vertical line one over the other and not less than 6 feet apart. The highest and lowest of these lights shall be green, and the middle light shall be white, and they shall be of such a character as to be visible all around the horizon at a distance of at least 2 miles.
In the case of a small vessel the distance between the lights of such private code may be reduced to 3 feet if necessary.
By day such surveying vessel may carry in a vertical line, not less than 6 feet apart, where they can best be seen, three shapes of not less than 2 feet in diameter, of which the highest and lowest shall be globular in shape and green in color, and the middle one diamond in shape and white.
Lighthouse tenders when working on buoys in channels or other frequented waters may display a red flag (international signal-code letter B) and a black ball at the fore as a warning to other vessels to slow down in passing.
The wire drags, some of which are over 2 miles long, used by the Coast and Geodetic Survey in sweeping for dangers to navigation, may be crossed by vessels without danger of fouling at any point except between the towing launches and the large buoys near them, where the towline approaches the surface of the water. Steamers passing over the drag are requested not to pass close to the towing launch; also to change course so as to cross the drag approximately at right angles, as a diagonal course may cause the propeller to foul the supporting buoys and attached wires.
Radio compass bearings.- The Naval Communication Service will furnish radio bearings to mariners of all vessels equipped with radiotelegraph transmitters.
While the use of these bearings should not lead a mariner to neglect other precautions, such as the use of the lead, etc., during a fog, these bearings will greatly reduce the dangers to navigation for mariners who are compelled for any reason to proceed during foggy or misty weather.
These radio compass stations are provided primarily to assist the mariner in closing the land during fog or poor visibility, but they