“Some persons attribute influence to the moon in respect of weather, and say a change may be expected within a few days of the moon’s phases. But the interval between one and another phase of the moon is but seven days, and ‘a few’ of these days must be a time near one phase or another. Accidental coincidences are generally allowed to influence the wind, because, when they occur, they mark any event more particularly. Similar to these are the prejudices against sailing on Friday, which used to be so general.”
Continued comparisons of changes of weather or wind during many consecutive years, in various parts of the world, have proved decidedly that there is no regular correspondence between the lunar phases and atmospherical changes.
The following are a few of the more marked signs of weather:-
“Weather, clear or cloudy, a rosy sky at sunset presages fine weather; a red sky in the morning, bad weather, or much wind (if not rain); a gray sky in the morning, fine weather; a high dawn, wind; a low dawn, fair weather.”
[A high dawn is when the first streaks of morning light appear over a bank of cloud, instead of near the horizon, as is usual when there are no heavy clouds.]
“Soft-looking, or delicate clouds, foretell fine weather, with moderate or light breezes; hard edged, oily-looking clouds, wind. A dark, gloomy blue sky is windy; but a light, bright blue sky indicates fine weather. Generally, the softer clouds look, the less wind (but perhaps more rain) may be expected; and the harder, more ‘greasy,’ rolled, tufted, or ragged, the stronger the coming wind will prove. Also a bright yellow sky at sunset presages wind; a pale yellow, wet; and thus, by the prevalence of red, yellow, or gray tints, the coming weather may be foretold very nearly; indeed, if aided by instruments, almost exactly.
“Small inky clouds foretell rain; a light scud, driving across heavy clouds, wind and rain; but if alone, wind only.
“High upper clouds crossing the sun, moon, or stars, in a direction different from that of the lower clouds or wind then blowing, foretell a change of wind (beyond tropical latitudes).”After fine, clear weather, the first signs (in the sky) of change, are usually small, curly, streaked, or spotty clouds, followed by an overcasting of vapor that grows into cloudiness. This murky appearance, more or less oily or watery, as wind or rain will prevail, is a sure sign. The higher and more distant the clouds seem to be, the more gradual, but extensive, the coming change of weather will prove.
“Generally speaking, natural, quiet, delicate tints or colors, with soft, undefined forms of clouds, foretell fine weather; but gaudy, or unusual hues, with hard, definite outlines, presage rain and wind.”
RECORD OF WEATHER.
In keeping the Journal, for the sake of brevity, the force of the wind and state of the weather are expressed thus:
0. Calm. 1. Light air; just perceptible. 2. Light breeze; ship going from one to two knots. 3. Gentle breeze, from two to four. 4. Moderate; from four to six. 5. Fresh; when royals can be carried. 6. Strong breeze; first reef and topgallant sails.
7. Moderate gale; double reefed topsails. 8. Fresh gales; treble reefed topsails and reefed courses. 9. Strong gale; close reefs. 10. Whole gale; close reefed main topsail. 11. Storm; storm staysails. 12. Hurricane; no canvas.
b. Blue sky. c. Cloudy. d. Drizzling rain. f. Foggy. g. Gloomy weather. h. Hail. l. Lightning. m. Misty. o. Overcast.
p. Passing showers. q. Squalls. r. Rainy. s. Snow. t. Thunder. u. Ugly threatening weather. v. Visibility of objects. w. Wet dew. z. Hazy.
A star (*) under any letter denotes a great degree.
“Cirrus” expresses a cloud, like a lock of hair, consisting of streaks, wisps, and fibres, vulgarly called “mares’ tails.” “Cumulus,” a cloud in dense convex heaps in rounded forms definitely terminated above, indicating saturation in the region of air, and rising supply of vapor from below. “Stratus” is a continuous extended level sheet, but must not be confounded with the flat base of the Cumulus. “Cumulo-stratus,” or anvil-shaped cloud, is said to forerun
heavy gales. “Nimbus,” a dense cloud spreading out into a crown of “Cirrus” above, and passing beneath into a shower.The amount of clear sky is expressed in all log-books, in tenths, zero denoting a sky completely overcast, and 10 a clear sky.
TABLE SHOWING THE FORCE AND VELOCITY OF THE WIND.
BY SIR W. SNOW HARRIS.
Pressure in lbs. per square foot
Vel’city in miles per hour
Popular Descriptions, and Corresponding Numbers.
1. Gentle airs, unappr’ciable by gauge
2. Light airs, just appreciable by gauge; would fill the lightest sail of a yacht.
3. Light breezes, such as would fill the lightest sails of a large ship.
4. Moderate breezes, in which ships can carry all sail.
5. Stiff breezes ; topgallant sails and royals.
Pressure in lbs. per square foot
Vel’city in miles per hour
Popular Descriptions, and Corresponding Numbers.
6. Fresh breezes; top-gallant sails.
7. Fresh winds; reefs.
8. Moderate gales; treble reefed topsails.
9. Strong gales; close r’fed topsails and reefed courses.
10. Gales; close-r-fed topsails, and staysails.
11. Heavy gales and storms.
12. Very heavy gales; great storms, tempests.
Tornadoes; cyclones; hurricanes.
WEATHER PROVERBS COMMON AMONG SEAMEN.
” A rainbow in the morning, Sailors, take warning; A rainbow at night Is the sailor’s delight.”
Morning rainbows are always seen in the west, and indicate the advance of a rain-cloud from that quarter when it is clear in the east. The fall of rain at a time of day when the temperature should be rising is indication of a change to wet, stormy weather.On the contrary, an evening rainbow occurs when the rain-cloud passes to the east, and a clearing up ensues in the west at a time of day when the temperature has begun to fall, thus indicating a change from wet to dry weather.
Another form of the saying is:
Red sky in the morning, Sailors, take warning, &c.,
being based upon the same phenomena.
“The evening red and morning gray Are sure signs of a fine day; But the evening gray and morning red Make the sailor shake his head.””With the rain before the wind, Your topsail halliards you must mind; But when the wind’s before the rain, You may hoist your topsails up again.”
“When the sun sets in the clear, An easterly wind you need not fear.”
Relating to the Barometer:
Long foretold, long last, Short coming, soon past.and
First rise after very low, Indicates a stronger blow.
Relating to the hurricane months in the West Indies:
June, too soon; July, stand by; August, look out you must; September, remember. October, all over!
The barometer, feeling the pressure of the air, shows at once when that pressure is changing. If the pressure at one place on the earth be greater than at another, the air has a tendency to move from the place where the pressure is greater towards that where it is less, and thus wind is caused.
A change of weather comes almost always with a change of wind, and the extent of this change of weather depends on the fact of the new wind being warmer or colder, damper or drier, than that which has been blowing. Any conclusions drawn from its movements must be checked by observations of temperature, moisture of the air, present direction and force of wind, and state of the sky, before any correct opinion can be formed as to what may be expected. In general, whenever the level of the mercury continues steady, settled weather may be expected; but when it is unsteady, a change must be looked for, and perhaps a gale.A sudden rise of the barometer is very nearly as bad a sign as a sudden fall, because it shows that atmospherical equilibrium is unsteady. In an ordinary gale, the wind often blows hardest when the barometer is just beginning to rise, directly after having been very low.
Besides these rules for the instruments, there is a rule about the way in which the wind changes, which is very important. It is well known to every sailor, and is contained in the following couplet:
When the wind shifts against the sun, Trust it not, for back it will run.
The wind usually shifts with the sun, i.e., from left to right, in the northern hemisphere. A change in this direction is called veering.
Thus, an east wind shifts to west through southeast, south, southwest; and a west wind shifts to east through northwest, north, and northeast.
If the wind shifts the opposite way, viz., from west to southwest, south, and southeast, the change is called backing, and it seldom occurs unless when the weather is unsettled.
However, slight changes of wind do not follow this rule exactly; for instance, the wind often shifts from southwest to south and back again.
In the southern hemisphere, the motion with the sun is, of course, from right to left, and therefore the above rules will necessarily be reversed.
Admiral Fitzroy proposed the following words for barometer scales:
RISE. For North, N.W., N., E. Dry or less wind.Except wet from North.
FALL. For South, S.E., S., W. Wet or more wind.Except wet from North.
No reading from a mercurial barometer that is not hanging vertically should ever be relied upon.
THE ANEROID BAROMETER.
In this instrument the atmospheric pressure is measured by its effect in altering the shape of a small hermetically-sealed metallic box, from which nearly all the air has been withdrawn, and which is kept from collapsing by a spring.
When the pressure rises above the amount which was recorded when the instrument was made, the top is forced inwards, and vice versa; when the pressure falls below that amount, the top is forced outwards by the spring.
These motions are transferred by a system of levers and springs to a hand moving over a graduated dial.
The instrument is very sensitive, showing minute changes that are concealed by the “pumping” of the quicksilver, even in the best mercurial barometers, when the motion of the ship is violent. Nevertheless, the working of the aneroid should be used only for purposes of comparison and in conjunction with a good mercurial barometer.
NOTE ON THE USE OF THE BAROMETER.
“In all parts of the world, towards the higher latitudes, the quicksilver ranges, or rises and falls, nearly three inches, namely, between about thirty inches and eight-tenths (30.8), and less than twenty-eight inches (28.0) on extraordinary occasions; but the usual range is from about 30.5 inches, to about 29 inches. Near the line, or in equatorial places, the range is but a few tenths, except in storms, when it sometimes falls to 27 inches.”
In the northern hemisphere, the effect of the veering of the wind on the barometer is according to the following law:
With east, S.E., south winds, barometer falls. With S.W. winds, barometer ceases to fall and begins to rise. With west, N.W., north winds, barometer rises. With N.E. winds, barometer ceases to rise and begins to fall.
In the southern hemisphere the law is as follows: With east, N.E. north winds, barometer falls. With N.W. winds, barometer ceases to fall and begins to rise. With west, S.W., south winds, barometer rises. With S.E. wind, barometer ceases to rise and begins to fall.
To appreciate correctly the indications of the barometer, we must have, as above stated, at the time of observation, the temperature indicated by a dry and a wet bulb
thermometer, and the thermometer attached to the barometer should be read with every reading of the latter.The wet bulb thermometer has a piece of linen tied around the bulb, wetted enough to keep it damp by a wick dipping into a cup of water. It will give a lower reading-than an ordinary thermometer, in proportion to the dryness of the air and quickness of drying. In very damp weather, with or before rain, &c., the dry and wet bulb thermometers will be nearly alike. The drier the weather, the more evaporation can take place, from the moisture surrounding the wet bulb, hence the lower the temperature shown by that bulb under such circumstances, and consequently the greater differencebetween the reading of such an instrument and that of a dry bulb thermometer. A comparison between the two affords, therefore, at all times, a means of ascertaining the relative dryness or moisture of the air. About six degrees difference between the wet and dry bulb readings is considered healthy in a temperate climate.
Pouring water over the wet bulb instead of merely moistening it imparts to the mercury the temperature of the water, which may be higher than that of the air.
If a barometer has been about its ordinary height, say near thirty inches at the sea level, and is steady or rising, while the thermometer falls and dampness becomes less, northwesterly, northerly, or northeasterly wind, or less. wind, may be expected.
On the contrary, if a fall takes place with a rising thermometer and increased dampness, wind with rain (or snow) may be expected from the southeastward, southward, or southwestward.
But a wet northeasterly wind may cause the barometer to rise, on account of the direction of the coming wind alone, thus deceiving persons who, from the rising of the barometer only, expect fine weather.
Indications of approaching changes are shown less by the height of the mercury than by its falling or rising. A rapid rise indicates unsettled weather.
A slow rise with dryness, fair weather.
A rapid and considerable fall is a sign of stormy weather and rain.
Alternate rising and sinking shows very unsettled weather.
The greatest depressions are with gales from the southeast to southwest; the greatest elevations with winds from northwest, northward, or northeast.
But the barometer may rise with a dry southerly and fall with a wet northerly wind.
Although the mercury falls lowest before high winds, it frequently sinks considerably before heavy rain. The barometer falls, but not always, on the approach of thunder
and lightning, or when the atmosphere is highly charged with electricity. Before and during the earlier or middle part of severe and settled weather, the mercury commonly stands high, and is stationary.The tides are affected by atmospheric pressure, so much that a rise of one inch in the barometer will have a corresponding fall in the tides of nine to sixteen inches, or say one foot for each inch.
“Vessels sometimes enter docks, or even harbors, where they have scarcely a foot of water more than their draught; and as docking, as well as launching large ships, requires a close calculation of height of water, the state of the barometer becomes of additional importance on such occasions.”
NOTE.-In south latitudes for north read south, and for south, north in these pages.
AND THE MEANS OF AVOIDING OR MANOEUVERING IN THEM.
Hurricanes, cyclones or typhoons are progressive, revolving gales, which may be described as great whirlwinds turning around and moving forward at the same time. Their diameter varies from 50 to 1000 miles,* within which limits currents of air move with a velocity of from 80 to 130 miles an hour around a central calm space of low atmospheric pressure; at the same time the whole storm area moves forward on a track, either straight or curved, at the rate of from 1 to 40 miles an hour. This velocity of translation, however, not only varies in different localities, but in storms passing over the same locality and even in one and the same storm during different stages of its existence.
Revolving Motion of the Storm. In each hemisphere the gyration of these storms takes place invariably in one direction, and that direction contrary to the apparent course of the sun. Hence in north latitudes the storms revolve from right to left, in south latitudes from left to right.
Forward Motion of the Storm. Within the tropics these storms commence to the eastward, travel for some distance towards the westward, inclining a point or two toward the pole of that hemisphere which they are crossing, curving away from the equator. When they reach the 25th degree of latitude, they generally curve still more until they move to the northeast in the northern
* The storms in the North Atlantic are said to commence with a diameter of from 100 to 150 miles and then to increase to 600 or 1000 miles, a fair average is perhaps 500 miles. In the Arabian sea they probably do not exceed 240 miles. In the Bay of Bengal they are from 300 to 350 miles in diameter. In the South Indian Ocean, from 150 to 600 miles, and in the China Seas from 80 to 350 and possibly as high as 600 miles.
hemisphere and to the southeast in the southern hemisphere. Occasionally they cross the line of the shore and sweep over the land, as in the East Indies and China Sea; more frequently they seem to be repelled by the land.The Atlantic and Japan storms, for instance, almost always wheel round to the northward and follow the seaboard of North America or Japan.
Another remarkable feature of these storms is their increasing violence in the neighborhood of their centre, and as this is approached (unless on the direct line of its own progressive motion) the more rapid become the changes of the wind.
INDICATIONS OF CIRCULAR STORMS.
The Barometer. The barometer, as an instrument of warning, and also as an approximate measure of the distance from the centre, is of vital importance to the seaman.
First. The barometer generally indicates the approach of the storm by a restless oscillating motion of the mercury, caused by a disturbed condition of the atmosphere in the vicinity of a storm. These oscillations have been observed to vary from a just perceptible motion to 0.02 inch.
Second. The barometer often rises suddenly on the border, just in front of a storm, by reason of the air banking up there, and therefore if the general appearance of the weather indicates the approach of a storm, a rise in the barometer, instead of being a guarantee that none will come, is rather a sign that a severe storm is coming. It would probably not rise much in front of a slowly moving storm.
Third. A very rapid fall of the barometer, after fairly entering the storm disk, may be regarded as evidence of a very violent storm of small diameter, and a gradual fall would indicate the contrary.
Fourth. If a vessel is caught in a cyclone in a dangerous position near the land, the knowledge of her distance from the centre might be all-important, even if that distance could only be determined within fifty miles. To aid navigators in determining the distance of the centre probably within that amount, the following table from Piddington’s “Horn-Book” may prove of service:
Average fall of barometer per hour
Distance in miles from centre.
From 0.02 inch to 0.06
From 250 to 150
From 0.06 inch to 0.08
From 150 to 100
From 0.08 inch to 0.12
From 100 to 80
From 0.12 inch to 0.15
From 80 to 50
The fall of the barometer has been compared in a great number of cases with the above, and the result has generally proved favorable to the accuracy of the table.Other Indications. The signs of a cyclone’s approach do not differ materially from those preceding an ordinary gale. A hard steel-gray or greenish sky, a blood-red or bright yellow sunset, a heavy swell or confused. agitation of the sea not accounted for in any other way, and a threatening appearance of the weather ought to be regarded as significant signs of a more than ordinary gale, particularly if accompanied by a restless state of the barometer.
When by any such indications the navigator has reason to suspect the neighborhood of a cyclone, his first care is to devise a plan for avoiding it. If with the cyclone chart found in standard works on storms he can determine the direction of the storm’s course, he may succeed in keeping clear of it altogether. But if after failing to effect this he is still caught in the storm, he must then determine as quickly as possible:
1st. His position in the storm disk. 2d. The course of the storm.
TO FIND THE SHIP’S POSITION IN THE STORM DISK.
This is readily determined on the basis of what are known as Redfield’s “Laws of Storms.” In accordance with these, the bearing of the centre of the storm is:
In the northern hemisphere eight points to the right,
In the southern hemisphere eight points to the left of the wind point, the observer facing the wind.
A second law is that:
In the right semi-circle of the storm the wind changes with the sun, viz., N., E., S., W.
In the left semi-circle of the storm the wind changes against the sun, viz., N. W., S., E.
In the first case this N., is contrary to the rotary motion of northerly storms; in the second case it is contrary to the rotary motion of southerly storms.
But the reason for the law will be seen, if we draw a circle N., W., S., E., to represent the body of a storm, with a ship anywhere within its influence, as at A. Assuming the ship to be in north latitude, the cyclone will be revolving in the direction shown by the curved arrows, and the wind in each quarter of the storm circle will blow in the direction shown by the straight arrows; for, though it sweeps round the storm’s axis, it may, from the small segment occupied by a ship, be represented, as far as she is concerned, as a tangent to the circle.
At A. therefore, she will have the wind from the eastward, and the centre of the storm will be eight points to the right of the wind, or south of her. If it is traveling from east to west, the first shift of wind she will experience will be from the S. E.; for, while moving on its course in the direction C, C1, it will be changing the bearing of its centre from the ship, which, when at C1, will be S. W. of her, with the wind from the S.E. So that, though the storm is revolving, thus: the wind is shifting in direction thus: But if the ship, on the contrary, be in the other semi-circle, say at B, she would have the wind at west, and when the centre reached C1, at S. W.; consequently, the change being from west to S.W., would coincide with the rotary motion of the storm.
Knowing, then, how to find the bearing of the storm’s centre, and how to determine which semi-circle a ship is in, we have the elements for giving her position with reference to the storm disk.
In determining in which direction the wind is shifting, it is of the highest importance that the ship should be kept as stationary as possible.
TO DETERMINE THE COURSE OF THE STORM.
If in the right semi-circle, where the wind changes to the right, N., E., S., W., heave to on thestarboard tack.
If in the left semi-circle, where the wind changes to the left, N., W., S., K, heave to on the porttack.
This places the ship in a safe position north or south of the equator, until the course of the storm is determined.
Two bearings of the centre, with an interval of from two to three hours between, will in general be sufficient to determine the course of the storm, provided an accurate account is kept of the ship’s way, but if the storm is moving slowly, a longer interval will be necessary. There are but two points in the storm disk of a cyclone where a vessel hove to will not experience a change of wind-one is in front of the centre on the line of its axis, and the other in rear of the centre on the same line. For these two cases the barometer must be the guide; in front of the centre it falls, and in rear of the centre it rises.
There are also five points in the storm disk of a cyclone, where a vessel may run along with the storm, parallel to its course and at equal speed without having any change of wind, and with a steady barometer.Northern Hemisphere:
1st. In front of the centre on a line with its axis: Wind on starboard beam.
2d. Anywhere in the right forward quadrant: Wind on starboard side abaft the beam.
3d. Abreast and to the right of the centre: Wind aft.
4th. Anywhere in the right rear quadrant. Wind on port side abaft the beam.
5th. In rear of the centre in a line with its axis: Wind on port beam.
1st. In front of the centre in a line with its axis: Wind on port beam.
2d. Anywhere in the left forward quadrant: Wind on port side abaft the beam.
3d. Abreast and to the left of centre: Wind aft.
4th. Anywhere in the left rear quadrant. Wind on starboard side abaft the beam.
5th. In rear of centre in a line with its axis: Wind on starboard beam.
The above manoeuvres are possible if sail can be carried, but only the last three in each hemisphere are advisable, viz., the position abreast of the centre, in the rear quadrant, or in rear of the centre. Running along with the storm in front of the centre, or in the forward quadrant, should never be resorted to; an accident temporarily disabling the vessel would at once place her in great danger of being overtaken by the centre.
TO RUN OUT OF THE STORM.
Northern Hemisphere. (See Storm Card, Plate 117):
Right Semi-circle. Haul by the wind on starboard tack, and carry sail as long as possible; if obliged to heave to, do so on starboard tack.
Left Semi-circle. Bring the wind on starboard quarter. Note the direction of the ship’s head, and steer that course. If obliged to heave to, do so on port tack.
On the storm track, in front of centre: Square away and run before it. Note the course and keep it, and trim the yards when the wind draws on the starboard quarter. If, however, obliged to heave to, do so on port tack.
On the storm-track, in rear of centre: Run out with wind on starboard quarter, or heave to on starboard tack.
Southern Hemisphere. (See Storm Card, Plate 118.)Right semi-circle: Bring wind on port quarter. Note the course and keep it. If obliged to heave to, do so on starboard tack.
Left semi-circle: Haul by the wind on port tack. Carry sail as long as possible, and if obliged to heave to, do so on port tack.
On the storm-track, in front of centre: Run before it. Note the course and keep it, and trim the yards as the wind gradually hauls on the port quarter. If obliged to heave to, do so on starboardtack.
On the storm-track, in rear of centre: Run out with the wind on port quarter, or heave to on porttack.
A rise of the barometer, improvement of the weather, and a gradual abatement of the force of the wind, will result from the above manoeuvres; and the ship should in each case be kept on her course until, by these signs, it is made evident that she is out of danger.
All the above manoeuvres depend of course on sea-room, and the ability to carry sail. If sail cannot be carried, or land interferes, the ship must be hove to on the starboard tack in the Right semi-circle, and on the port tack in Left semi-circle, and never otherwise. The old popular idea of heaving to on the starboard tack in the northern hemisphere, and on the port tack in the southern hemisphere, under all circumstances, is dangerous practice, and may lead to serious consequences.
The results of the manoeuvres herein recommended should, as before stated, be a rising barometer and improvement in the weather. If, however, the barometer continues to fall, or remains stationary, and the weather becomes either worse or remains the same, it is evidence that the indraft is very great, and in either case the ship should be hauled up as near the wind as possible under the circumstances of wind and sea, and so kept until a decided rise of the mercury and improvement in the weather take place.
Thus the barometer is always a measure of safety, even when the rules laid down for avoiding the centre fail to carry a vessel out of the dangerous part of the storm.
In a very extreme case of indraft, where it is found impracticable to distance the centre by sailing, the vessel should be prepared for a heavy blow, and hove to on the proper tack, until either the centre has passed or an opportunity occurs (by a change in the wind) for avoiding it.
It sometimes occurs, although the cases are very rare, that a cyclone takes a sudden turn, and recurves on its track so much as to render a vessel liable to run into it a second time.
Storm Seasons. The period of the year during which cyclones are most frequent may, in a general way,
be considered. In north latitude, from June to November; August and September being the worst months. In south latitude, from September to May; February and March being the worst months. In other words, the cyclone season appears to correspond to the time when the sun is nearing the equator, on the return from the highest declination in either hemisphere.