Discoveries in Australia/Volume 2/Appendix
APPENDIX.
Winds and Weather on the Western and Northern Coasts of Australia
By Commander J. C. Wickham, R.N.
The winds on the western coast of Australia, are, for the most part, from some southern point—chiefly between S.S.W. and S.S.E.
During the summer, or from the early part of October to the beginning of April, they are almost constant from this quarter; but in the winter their regularity is broken in upon by occasional winds between north and west that at times blow with great violence, and are accompanied by heavy rain, and thick dirty weather.
Near the shore, land and seabreezes appear to be regular, the former generally dying away towards the middle of the day, after having reached as far as E. from about S.E. at sunrise; then follows a short interval of calm, after which, the seabreeze sets in, mostly at S.S.W., and draws to the eastward of south in the evening.
At times the land wind veers round the compass, and is then generally stronger than usual; blowing fresh for a short time from N.E., and bringing a parching heat from the land; upon these occasions the seabreeze comes in from a more western point, and is lighter.
At Swan River, in the months of December, January, and February, the seabreezes are very strong, for intervals of from three to five days; during which time they blow fresh throughout the night—drawing to the southward after midnight, and towards sunrise to S.S.E. and S.E., but more moderate. In the middle of the day, they back again to the southward, and soon to S.S.W., from which quarter they blow very fresh until midnight.
Intervals of such weather are from three to five days' duration, and are followed by the like number of days of moderate weather, with winds mostly off the land; sometimes strong gusts from the east, for a few hours, with oppressively hot weather.
I have noticed, that when the seabreeze sets in from a point to the westward of S.W., it does not blow so strong, and generally lulls at sunset; but if more southerly, or from S.S.W., it is a fiery breeze, and often lasts until midnight.
During the prevalence of these strong seabreezes, communication between Gage Road and the shore is very inconvenient—particularly for laden boats.
In March, the seabreezes are not nearly so strong, but are generally moderate, and not unfrequently bring in thick misty weather from southwards, with drizzling rain.
Generally speaking, when the seabreezes are the strongest, the land winds are light, and vice versa.
I cannot speak from experience of the winds or weather during the month of April, at Swan River, but have been told that the seabreezes are moderate, and the land winds of longer duration; calms are frequent—and the weather altogether seems to indicate the breaking up of the summer season; light winds are occasionally felt from the northward, with a dull, gloomy appearance between that point and S.W.
May is the month in which the winter weather fairly sets in, and it rarely happens that the middle of this month passes without the rains having commenced. This season seems to vary but little as to the time and manner of setting in—it is ushered in by blowing weather, from about N.N.E., the wind gradually veering round to the westward, as it increases in strength. The first of this weather usually lasts from a week to fourteen days; then comes an interval of fine weather, generally of a fortnight's duration, and sometimes a month; after which the rains set in more constant, and the intervals of fine weather are shorter; this weather lasts until October, and at times throughout that month.
During the intervals of fine weather the climate is delightful, and the country has a fresh and pleasing appearance; land and seabreezes are as regular as in summer, with the exception, that the latter are much more moderate.
The N.W. gales that occasionally occur during the winter months, on the southern parts of the west coast of Australia, are probably felt as far north as Shark's Bay. They blow with great violence, and are accompanied by dark, gloomy weather, and rain. It is then unsafe to be near the land—as the gale that commences at N.N.E., invariably veers to the westward, making a lee shore of the whole line of coast, and between W.N.W. and W.S.W. blows the hardest.
Fortunately these gales give ample warning; the barometer always foretells their approach, and generally begins to fall three or four days before the commencement of the gale—besides which, there are other never-failing indications of a northerly wind, such as, the change of the current, which (owing to the prevailing southerly winds) usually sets to the northward, but runs strong to the southward during northerly winds—frequently preceding them, and giving more timely notice than the barometer.
A rising of the water is likewise a certain prognostic of a northerly wind; and has been invariably noticed, at Swan River, to precede all gales from that quarter—this, of course, can only be observed while at anchor on the coast.
Another, and perhaps equally certain sign of approaching bad weather, during the winter season (and which is almost certain to be from the northward) is the strength of the N.E. winds—as it has been observed, that when the land winds blow strong, particularly from the N.E. and the seabreezes are light, with a falling barometer, a gale from the northward will follow. Perhaps these latter remarks, are only applicable to that distance from the shore, where a ship will be within the influence of the land and seabreezes; but as I conceive the limit of that distance to be full 30 miles off shore, a notice of such a symptom of approaching bad weather, may not be altogether useless. I am of opinion, that land winds are at times felt as far off shore as the edge of soundings, which is not less than 30 miles, and generally between that and 40.
(In lat. 30° 25' S. and 65 miles from the land, soundings were got from the Beagle, with 185 fathoms of line, upon a coral bottom. Between Swan River and Houtman's Abrolhos, soundings may be had at a greater distance from the land, than off any other part of the west coast.
The N.W. gales are of longer duration, in the lat. of Swan River, and south of that, than they are to the northward; they do not appear to be entirely confined to the winter months, as I am told that a very heavy one was experienced at Swan River, early in March, 1832, and on the 13th December, 1839, the Beagle experienced a strong breeze from the northward, while at anchor in Gage Road, in consequence of which, it was considered necessary to let go an extra anchor.
As it may be satisfactory to know more particularly the progress of these gales, and the effect they have upon the barometer and sympiesometer, I give the details of two that were experienced in H.M.S. Beagle, one at Swan River, in the beginning of June 1838, the other at Houtman's Abrolhos, in the beginning of May 1840; they may be taken as fair criterions of the strength and duration of these gales, the latter having been experienced, probably, within 5° of their northern limit, and the former near the southern extreme of the west coast.
As our barometer had been broken in March 1838, the register of a sympiesometer will be given in describing the gale of June in that year; but as this instrument had been found (by comparison with the barometer) to act exceedingly well, it will be sufficient for our purpose; the GENERAL use of a marine barometer being merely that of a weather glass, for which purpose a sympiesometer is equally good, and more sensitive.
For the gale of 1840, the register of a barometer is shown, which, although 0.2 too low, will serve to show the effect upon the mercury.
At Swan River, on the 24th of May, 1838, the wind was strong and squally from N.E. by N.; sympiesometer standing at 30.74. During the day the oil commenced to fall, and continued falling slowly until the 30th, when it was 30.16; during the greater part of this interval, the winds were light, generally from some eastern point in the morning, and going round the compass, by north and west, during the day; the nights were mostly calm, a heavy bank of clouds was collecting between N.N.E. and S.W. and the whole western horizon had a gloomy appearance. On the evening of the 30th, the water had risen considerably at the anchorage, and the stream ran to the southward; a fresh breeze also set in from N.E. and gradually veered to the northward, as it increased in strength. On the 31st it blew hard all day, between N.N.E. and N.N.W., with dark squally weather, much lightning in S.W. and heavy rain, that continued all night. On June the 1st, the gale was at its height, and at 8 a.m. (the sympiesometer having fallen to 29.93) was blowing a hard gale, with heavy squalls and rain, from N.W.; towards noon the wind veered to west, but still blew very hard; the sympiesometer now began to rise, and in the evening the wind was W.S.W. and had moderated considerably, the weather was also clearer, although heavy clouds still hung on the western horizon.
The next morning (the 2nd) the sympiesometer had risen to 30.26; but this was much too sudden a rise (0.33 in 24 hours) to allow us to suppose, that the favourable change in the weather was to be of long continuance; during the day the oil began to fall again, and the wind veered to W. and N.W. and on the 3rd blew harder than ever, with heavy rain, thunder, and lightning; and, with the exception of occasional intervals, when the wind moderated, this weather continued until the 10th. The wind during this time was variable, between N.N.W. and W.S.W., the sympiesometer between 29.81 and 30.16—falling with the N.W. winds, and rising as the wind veered to west and W.S.W.
This gale, which may be said to have been of ten days' continuance, caused a very heavy sea upon the coast; the oldest residents at Swan River said they had never experienced so heavy a sea before. On the 10th the glass commenced to rise steadily, and the weather was fine, with light variable winds, until the Beagle sailed (on the 20th).
Owing to the security of Owen's anchorage, and the good quality of the bottom, the Beagle rode out this bad weather, without causing the slightest apprehension to anyone on board; but had a merchant vessel been in Gage Road, in all probability, she would have added one more to the list of wrecks, that have already done too much in prejudicing strangers against the Swan River settlement.
The gale of May, 1840, at Houtman's Abrolhos, commenced in a similar manner with that already described, but being in a lower lat., was of shorter duration, and the indications did not precede it such a length of time; still they were in every respect similar.
This gale commenced on the 2nd of May, in the evening, and lasted until the evening of the 4th. on April the 29th, the barometer stood at 30.17 (having been some days steadily high); it then commenced to fall, and on the evening of May the 2nd, was 29.86; during this interval we daily experienced strong E.N.E. and N.E. winds; they generally commenced after midnight, and lasted until noon; a bank of clouds was also collecting in the N.W. and there was occasional lightning in that quarter; the early part of May the 2nd was nearly calm, and there was a heavy bank of clouds between N. and S.W. After noon a light breeze sprang up from N.W. which gradually freshened; and during the night the barometer fell 17-hundredths.
At sunrise on May the 3rd, there was a fresh breeze from N.N.W. and the weather had a very dull and gloomy appearance, the wind increasing rapidly, and by noon it blew a heavy gale at W.N.W.; the barometer had fallen to 29.58, at which it continued until midnight, when the wind drew to the southward of west, and the mercury began to rise. The gale continued unabated, with squalls and rain, until noon of the 4th, although the barometer had been rising since the previous midnight; in the afternoon the wind moderated, and the weather became fine.
From this it would appear that the barometer gives ample warning of an approaching N.W. gale, as it had been falling nearly four days before the commencement of the bad weather, this alone ought to be sufficient to put a man upon his guard if near the shore. Between April the 29th (the first day of the fresh north-easterly winds) and May the 3rd (when the gale was at its height, and the wind began to draw to the southward of west) the mercury had fallen 6-tenths. The change of current did not precede the wind, but changed with it; when the gale was strong from N.W. and W.N.W. the current ran a knot an hour to the S.E., and when the wind changed to S.W. it ran with the same velocity to the N.E.
The west coast of New Holland is at times visited by sudden squalls, resembling hurricanes. I was told by the master of an American whaler, that in March 1839, when in company with several whalers off Sharks' Bay, he experienced some very bad weather, which came on suddenly, without having given any previous warning, but it was not of long continuance; the gusts of wind were very violent, shifting suddenly to all points of the compass. Some of the ships suffered considerable damage, in loss of topmasts, etc. others in sails, but all more or less. I think the first squall was from N.E. off the land.
The American whalers that resort to the west coast of Australia, are upon different parts of it at all seasons of the year; their range is between the parallel of 10 and 50° of south lat. In the summer they fish to the southward, and at that season visit Swan River and King George's Sound, for refreshments; but during the winter months they are rarely to the southward of Sharks' Bay; numbers are to be met off the N.W. Cape.
Between the parallels of 40 and 45° they meet much bad weather, as it is generally blowing strong with a heavy sea; but between 45 and 50° the weather is much more settled, and finer. November is said to be generally the finest of the summer months, the winds are mostly moderate, and the weather more settled than at other periods.
Two gales that were experienced by the Beagle in November 1837, between the islands of St. Paul and Amsterdam and Swan River, will serve to show the different effects upon the barometer by gales from opposite quarters, one being from N.W. and the other from S.E.
On November the 1st, the barometer stood at 29.90, having been gradually rising for some days previous to that, and the wind had been fresh between north and west. After 8 p.m. on the 1st, the mercury began to fall, and on the 2nd, the wind was strong from N.N.W.-barometer falling all day. During the night it blew a heavy gale, and the barometer fell to 29.34. On the morning of the 3rd the wind veered to the westward, and the mercury began to rise, the weather also became more moderate, and gradually fine.
On the 8th of the same month, the barometer was 30.05 at 8 p.m. with fine weather, wind S.E. by E., it then commenced to fall, and at 8 p.m. on the 9th was 29.80, and blowing a heavy gale at S.E., which continued all night, and until 8 p.m. on the 10th, at which time it became more moderate, and the barometer began to rise.
What a different effect these gales had on the barometer; that from the N.W. causing the mercury to fall nearly 6-tenths, whereas, the last, from S.E. only lowered it 2-tenths, and 5-hundredths; they were of equal strength and duration, and both accompanied by heavy rain.
The great extent of the N.W. coast of Australia, lying as it does between the parallels of 12 and 22° of south lat., no doubt subjects it to a variety of winds and weather, that is not experienced on the north coast; although, on that part of it north of the parallel of 15°, there is probably much similarity.
As I cannot speak with certainty of the winds and weather that prevail on this extent of coast, at all seasons of the year, the following remarks will be confined to such portions of it as were visited by the Beagle, and will apply only to the particular seasons in which she was employed there.
To the eastward of the meridian of 123° east long., and at a short distance from the land, the east and west monsoons will be found regular; but the easterly monsoon is very light to the southward of 13° lat.
Between Clarence Straits and Cambridge Gulf, and during the months of September, October, November, and December, the wind during the day is a seabreeze between N.W. and W. In September, and until the middle of October, we found the wind as follows: About sunrise, a light breeze sprang up from S.E. or E. which gradually drew to the northward towards the middle of the day, in the afternoon, a seabreeze from N.W. or west, becoming light towards sunset, but freshening again soon after that, and blowing a moderate and pleasant breeze between N.W. and S.W. all night.
During the latter part of the period (November and December) the winds were more constantly from the W. or W.N.W., blowing from that quarter throughout the twenty-four hours, but much more moderate at night than during the day; at full and change of the moon, the breezes were much stronger than at other times, and upon one or two occasions, at the time of the moon's quartering, there was a light breeze from S.E. in the morning.
During the month of November, the ship was at anchor, twelve miles within the entrance to Victoria River, and sixty-five from Point Pearce, on the sea coast. For the first three weeks of this time, the seabreeze was regular from N.W. or W.N.W., generally setting in about noon, and lasting the greater part of the night; in the mornings, and until noon, it was mostly calm, or very light winds from the northward. In the last week of this month the weather was very unsettled and squally, with much thunder and lightning, and rain, the wind mostly between S.E. and N.E.; after which, the westerly breezes set in again, and continued until we left the coast in the middle of December.
During the whole of this period the westerly winds did not appear to come from any distance, but to be merely local seabreezes, as they did not cause any sea upon the coast, nor did they reach far in shore; as we frequently observed smoke at no great distance from the coast, rising perpendicularly, or influenced by a light south-easterly wind, and this at times when the seabreeze was strong. From this it would appear, that the westerly monsoon had not reached so far to the southward, nor did we find, after sailing from Point Pearce, that the winds were at all steady from the westward, until we had reached to the northward of Cape Londonderry, which is in lat. 13° 45' S. To the northward of this, the winds were from the westward, accompanied by fine weather during the day to the southward of that point—sometimes as far as S.W.-and at night inclining to the northward of west, but generally speaking, we found the wind to the southward of west, and the current running from half a mile to a mile an hour to the N. or N.N.E.
The currents between New Holland and Timor, are said to run to the westward, during the easterly monsoon—and in the opposite direction with the westerly; but they seem to be influenced by every trifling change of wind—as on the 20th, 21st, 22nd, and 23rd of December (when the westerly monsoon might be supposed at its height) we experienced light, variable winds, between S.E. and E.N.E.-during which period the current ran to the westward—at times, a knot an hour. We were then between the parallels of 11½ and 13°, south of which we experienced winds between S.S.W. and W. until we were to the southward of the N.W. Cape, when they became more southerly, and at times S.S.E. (in January). Throughout all this period, the weather was fine, and different from what was expected during the westerly monsoon.
All that part of the N.W. coast of New Holland, between the N.W. Cape, and Cape Londonderry, appears to be very much subjected to light winds, particularly during the easterly monsoon, the strength of which is not felt to the southward of 13 or 14° of south lat. During the westerly monsoon, strong winds and gales from the N.W. at times blow upon the coast, but they do not appear to be frequent. The strongest winds at this season, are the heavy squalls between E.S.E. and N.E. (and which may with propriety be termed hurricane squalls); fortunately they are not of long duration, rarely lasting over two hours. They give ample warning of their approach, by the gathering of a heavy bank of clouds between N.E. and S.E., and much lightning in that quarter. Appearances such as these frequently precede the squall some days, but coming gradually nearer (to the westward). The barometer shows no indication of approaching bad weather, being only acted upon by the immediate change; these squalls mostly occur in the night, or between sunset and sunrise.
During the latter part of the westerly monsoon, on that part of the coast between Cape Villaret and Point Swan, we found the weather remarkably fine, with the exception of an occasional short, but severe squall, from the eastward. During the day there was generally a moderate seabreeze between N.W. and S.W. commencing in the forenoon, and lasting sometimes nearly until midnight—on which occasions it blew strongest during the night); during the other part of the twenty-four hours the wind was light from the eastward or calm. Captain King experienced similar weather in August.
It was not until we had reached Point Swan, in lat. 16° 20' S. that we experienced any of the bad weather that is usually met with, at this season of the year, a few° to the northward; it commenced in the last week of January, and continued until the middle of February, during which period, there were some strong gales from the westward, between N.W. and S.W. accompanied by heavy rain, thunder and lightning; but although there was a good deal of dirty weather, it was by no means constant, as there were occasional intervals of fine weather, with moderate westerly winds. This was the only bad weather on this part of the coast, during the season, that could be said to be caused by the westerly monsoon, if we except the E.S.E. squalls, that do not occur in the easterly monsoon.
While this weather lasted, the easterly squalls were quite suspended, and the heavy bank of clouds that had generally been noticed in the S.E. had dispersed for the time; but after the strong westerly winds had ceased, the weather was generally fine, and the wind mostly from some western point; there were occasional showers, and the clouds in the eastern horizon resumed their threatening appearance, bringing some hard squalls, and rain from that quarter. In the middle of March (being the time when equinoctial gales are looked for in most parts of the world) there were two or three days of squally, unsettled weather, with rain, that seemed to terminate the season of the westerly monsoon. After the 1st of April, the weather was invariably fine, and the easterly squalls had ceased to trouble us; land and seabreezes became regular, and the easterly monsoon had no doubt set in to the northward; the strongest breezes now were from S.E. but, generally speaking, the winds were very light near the land.
It does not appear that the westerly monsoon blows with any degree of regularity, to the southward of the 13th degree of south lat.; although for some° south of that, the weather is influenced by it, and winds between W.N.W. and S.W. will be experienced, and from the appearances on many parts of the coast, there are no doubt strong gales at times from the westward, that send in a very heavy sea. During the easterly monsoon, the weather is fine on the N.W. coast, particularly in the months of May, June, July, and August; this is undoubtedly the best time for visiting it; land and seabreezes are regular, and the temperature is very agreeable.
The average range of the thermometer on that part of the coast, between the N.W. Cape, and the meridian of 120° east long., during the above-mentioned period, was between 75° in the middle of the day, and 60° at night, on board the ship, and the general course of the wind as follows, viz.
About sunrise, or sometimes a little before that, a breeze springs up between S. and S.S.E. and draws to the eastward as the sun rises, rapidly increasing in strength, and between 8 and 11 a.m. often blows a fiery breeze; towards noon it moderates, and rarely lasts until 2 p.m., after which there is a light breeze from N.E. which at times reaches to north; the nights are mostly calm, or a light breeze from the south-westward; at the full and change of the moon, we found the south-easterly winds stronger than at other times; dews at times very copious.
All this part of the coast is subject to the effects of mirage, by which its outline is at times very much distorted, but generally speaking it ceases with the strength of the breeze, and as the sun attains a little altitude. When the effects of mirage was observed in the morning, I noticed that the winds were much lighter throughout the day, than usual.
During this part of the year, the atmosphere is clear, with a cloudless sky, and the coast is exempted from the violent E.S.E. squalls, that are of frequent occurrence, while the sun is in the southern hemisphere, and the land consequently very much heated.
Towards the latter end of August, and in September, the winds are not quite so regular, and there are occasional intervals of two or three days of westerly winds.
That part of the N.W. coast between the N.W. Cape, and the 116th degree of east longitude, seems to be subject to westerly winds at all times of the year. The prevailing southerly winds that blow along the west coast, appear to draw round the Cape, and follow the direction of the land. Between April and October (when the easterly monsoon is blowing to the northward) they are generally to the southward of west, or between that point and S.W., but during the westerly monsoon between W. and N.W.
Upon getting to the westward of the N.W. Cape, the wind becomes more southerly, and draws to the eastward of south as the distance from the land increases, and will be found varying between S.S.E. and E.S.E., generally speaking as far south as the parallel of 30° of south lat., after which it is mostly to the westward of south, so that ships making a passage to the southward, along the west coast of New Holland, will rarely be able to make any easting, before reaching that lat., particularly during the summer months. In the winter a ship may occasionally make a quick passage to the southward, if happening to be upon the coast during a northerly gale; and as all these gales are preceded by N.E. winds, a sufficient offing may be gained to enable her to run on, when the wind gets to the southward of west.
That part of the coast of New Holland from Cape York to Cape Van Diemen, and extending as far south as the parallel of 12° south lat., may be said to be within the limit of the east and west monsoons, as at a short distance from the coast, these periodical winds will be found to blow with great regularity.
Near the land, the easterly monsoon sets in between the 1st and middle of April, and the westerly monsoon in October, and sometimes not until November. At a distance from the land they are probably more regular, as the changes of the monsoons are said to take place about the first week in April and October.
In the month of July, we found the winds between Booby Island and Port Essington, fresh from the eastward, veering at times to E.S.E. and occasionally to S.E. but rarely to the northward of east. Close to the land these winds are not so constant, but take more the character of land and seabreezes, and the nights are mostly calm; this we found to be the case during part of the months of July and August, while at anchor in Port Essington. The general course of the winds during that period was as follows. A little before sunrise, a breeze sprang up from S. or S.S.E. which gradually became more easterly as the sun approached the meridian; sometimes in the middle of the day, it was light from the eastward, or calm, and at other times veered gradually to N.E., from which quarter there came a fresh seabreeze every afternoon; this breeze lasted until sunset, and at times later, but the nights were always calm.
We experienced similar winds between Melville Island and Port Essington, but being a short distance from the land, the nights were not calm, although the winds were very light.
During the easterly monsoon, it is difficult to get to the eastward, as at a few miles from the land the current is always running to the westward, and runs strong past the projecting points; but by contriving to be near the land at daylight, at which time the wind is always more southerly, something may be gained.
At Port Essington, the rainy season can scarcely be said to set in before the middle of November; there is then, squally, dirty weather, with rain from the westward and N.W., and at this season, there are at times heavy squalls from S.E. accompanied by rain, thunder, and lightning.
In 1838, the westerly monsoon set in at Port Essington, in the first week in November; there had been no rain before that.