 |
|
Non-Instrument Weather Forecasting Dennis Kawaharada (Photo below by S. Low: The appearance and movement of clouds are used to forecast weather)
Winds Basic to any observation of weather for sailing is knowing the direction and strength of the wind. Face the wind: when the pressure is even on both cheeks and ears, you are looking directly at the wind. You can tell direction also by watching in which direction the clouds are moving, the leaves of the trees are streaming, or the ripples on the ocean are running. Wind strength can be determined by feeling the wind, by watching the speed of clouds or the bend of trees and branches, and by observing the sea state (See "Wind Speed Tables" on what signs indicate what wind velocity.) But remember: the wind on land is affected by the land and may not be from the same direction or of the same strength as the wind at sea; you must be able to observe the sea or get a report from a vessel or buoy at sea to get an accurate reading of conditions at sea. Also, when you are on a moving vessel at sea, the true wind is different from the apparent wind: the apparent wind (the wind you feel) is a combination of the true wind, plus the wind your vessel is creating by moving. Knowing the direction of winds around high and low pressures systems can help a mariner understand wind patterns. The winds around high pressure systems move clockwise and outwards in the northern hemisphere and counterclockwise and outwards in the southern hemisphere.The winds around low pressure systems move counterclockwise and inwards in the northern hemisphere and clockwise and inwards in the southern hemisphere. In Hawai'i the prevailing ENE wind, called Moa'e or A'eloa, is generated by a high pressure system that is generally located to the N or NE of the islands. Hawai'i is situated toward the bottom edge of this system (called the North Pacific High), where the clockwise winds are blowing easterly. These so-called trade winds average about 14 knots, but may gust well over gale force, particularly when they are funneled through channels or mountain gaps. Wind strength is determined by (1) the strength of the high pressure; and (2) the steepness of the pressure gradient (the closer together the isobar lines are, the steeper the pressure gradient). The greater the pressure and the steeper the pressure gradient, the stronger the winds. The trade winds are the steadiest during the summer months, from May to September; during the winter months, the high pressure systems moves farther to the east, and the trade winds weaken, from October to April; however, migratory highs can bring strong and gusty easterlies during these months: "Winter months have the strongest trade wind episodes because of the passages north of the Islands by these highs but the average wind speeds do not reflect this-the average wind speed in summer is higher than that of winter in Hawaiian waters" (Haraguchi 12). When the high is centered directly over the islands, winds become light and variable. "The area under the center has light winds and low-height clouds with little precipitation outward to within about 300 miles of the center" (Haraguchi 12). Shifts in wind direction may indicate changes in weather. As low pressure systems travel from west to east, pushed along by the jet stream north of Hawai'i, or when low pressure systems form west of Hawai'i, the prevailing winds may shift southerly. Low pressure systems that remain stationary to the west of the islands bring warm, humid air from the south, and we experience a period of mugginess called Kona weather. As low pressure systems pass north of Hawai'i, cold fronts (cold air wedging under warm air) may sweep over the islands. At the leading edge of a cold front, the winds are southwesterly; rain and blustery winds often accompany these fronts. As the cold front passes, northerly winds fill in behind it, bringing dry cold air. As the cold front moves away from the islands to the east, the ENE trades may return. Ocean Surface-Swells, Seas, Currents Navigator Nainoa Thompson explains the difference between swells and seas, or locally-generated waves: "Swells are big waves generated by pressure systems far beyond the horizon, and they maintain their direction for long periods of time [and travel in the general direction of the winds generating them]. Seas are generated by local winds. Seas generally come downwind, but they may vary by as much as 30° on either side of the wind. When the wind changes, the seas become more of a mish-mash" (Kyselka 167-8). The height of swells depends on the strength of the wind generating them (velocity), the distance over which the wind is blowing (fetch), and the duration of the wind (time). Given a particular wind velocity, swells grow to a maximum size as the fetch and duration increase; they may persist for several days. "A 20-knot wind might make waves of some 6 to 8 feet ('significant wave height,' meaning the average height of the highest one-third of all the waves), if the wind blows for a day or so, over a distance of about 100 miles" (Burch 36). A diminishing swell indicates the wind generating it is diminishing. The farther away the wind generating the swell, the rounder the swells will appear, and the greater the distance between the swells. A 7-8 second interval between swells indicates a well-established wind pattern far off. Shorter intervals and steeper swells indicate that the wind system is closer. Major swells in Hawaiian waters include an ENE Swell generated by the trades; a North Swell, generated by winter storms in the North Pacific; and a South Swell, generated by southern hemisphere winter storms (bringing summer surf to the northern hemisphere). While not directly related to weather, currents affect the sea state: "A strong current flowing against the wind causes an enhanced chop and steepness to the seas, whereas a current flowing with the wind diminishes the seas just as dramatically. To recognize the effect, however, requires some experience at sea, since you must be able to conclude that the seas are not consistent with the wind" (Burch 132). Grimble notes that navigators in the Gilbert Island observe the ocean surface to determine the strength of currents before departure: "Before setting sail in the fair weather season, a Gilbertese mariner will sometimes spend several days in looking at the sea. If it is streaked in places with calm patches of an oily appearance he will refuse to start until these disappear, for they speak to him of strong currents" (238). Clouds David Seidman writes, "Clouds are the harbingers of weather. Their shape, height, color, and sequence foretell coming events." "High clouds are associated with the upper atmosphere and distant weather systems up to six hours away. If they are wispy and white, the weather will be fine. Lower clouds relate to the current weather or that which is soon to come. If they are dense and dark, change is imminent, usually for the worse. Notice if clouds are lowering or lifting, and if they are gathering or dispersing. Lowering or gathering usually brings wet weather. Lifting or dispersing means the weather will improve. A cloud's color seems obvious: the darker, the more dangerous. And a sharp-edged dark cloud is the most dangerous of all. In shape, flat clouds are characteristic of stable air, while lumpy, well-rounded clouds live in unstable air" (166). Satawal navigator Mau Piailug desribes how to read an approaching squall or squall line: "If the rain cloud is black, the wind isn't strong. If the cloud is brown, the wind is probably strong. If the cloud is high, there's not much wind, but maybe a lot of rain. If it's low, probably lots of wind. [As the clouds approach, if the ocean surface beneath the clouds] is black, you know it is a real strong wind. If it's the same color as the ocean near you, then it is not a strong wind. If the water is bumpy [beneath the cloud]you know there's a strong wind" (Kyselka 145). Dark, "bumpy" water (i.e., water full of ripples and small waves, which create shadows) is a sign of a strong local gust of wind; to anticipate such gusts, an experienced sailor watches for dark patches of water moving across the ocean surface. When the sun is relatively low on the horizon (e.g. in the afternoon), the ripples caused by a local gust may reflect sunlight and the patches of wind glitter with light. The following classification of clouds and information about the significance of types of clouds are from Weather for the Mariner by William J. Kotsch. Meteorologists classify clouds by the heights at which they appear: high clouds (above 18,000 feet); middle clouds (7,000 feet to 18,000 feet); low clouds (from near ground up to 7,000 feet). Some words and roots used in naming clouds include: cumulus ("to heap up"; dense, sharply outlined clouds with high vertical development, usually rising domes or towers, with the upper part looking like a cauliflower); stratus ("spread"; cloud layers, with spread horizontally); nimbus ("rain-producing"); alto ("high"; used to refer to middle or high clouds, as opposed to low clouds); cirri, cirro, cirrus ("curl of hair," wispy high clouds).
(Drawing from William Crawford's Mariner's Weather. New York: Norton, 1992.) High Clouds Cirrus: "detached wisps of hair-like (fibrous) clouds, formed of delicate filament patches, or narrow bands"; "Cirrus clouds that are scattered and are not increasing have little weather meaning except to signify that any bad weather is at a great distance. Cirrus clouds in thick patches mean that showery weather is close by. These clouds are associated with, and formed from the tops of thunderstorms. Cirrus clouds shaped like hooks or commas indicate that a warm weather front is approaching, and that continuous-type rain will follow-especially if the cirrus is followed by cirrostratus." Cirrostratus: "transparent, whitish clouds that look like fine veils or torn, wind-blown patches of gauze"; "when in a continuous sheet and increasing, [cirrostratus] signify the approach of a warm weather front with attendant rain and stormy conditions. If these clouds are not increasing and are not continuous, this means that the storm is passing to the south of you and no bad weather will occur at your location." Cirrocumulus: "thin, white, grainy, and ripped patches, sheets, or layers showing very slight vertical development in the form of turrets and shallow towers. When these clouds are arranged uniformly in ripples, they form what seafaring men call a mackerel sky"; "quite rare and of mixed significance. In some areas, these clouds foretell good weather; in others, bad weather." Middle Clouds Altostratus: "grayish layers of clouds usually uniform in appearance and cover part, or all, of the sky"; among the most reliable weather indicators of all the clouds. They are indicative of warm air flowing up over colder air and impending rain or snow of the continuous type, especially if the cloud layer progresses and thickens. These clouds are a good indication of a new storm development at sea with poor visibility, large waves, and heavy swell." Altocumulus: "extensive 'cloudlets' arranged in a regular pattern"; "significant primarily when they are followed by thicker high clouds or cumuliform low clouds. When they are in parallel bands, these clouds are in advance of a warm front with its associated steady rain or snow. When altocumulus clouds occur in the form of turrets rising from a common flat base, they are usually the forerunner of heavy showers or thunderstorms." Low Clouds Nimbostratus: These rain clouds are "low, amorphous, dark and usually quite uniform"; they are of "little help as a forecasting tool, since the bad weather is already at hand when these dark clouds with their associated heavy rain are overhead. But if they are at some distance from you, and you have a report that they are coming your way, you know bad weather, high winds, and hazardous sea conditions (for small boats) will persist for many hours." Stratus: "low, gray cloud layers with rather uniform bases and tops . Only a fine drizzle falls from true stratus clouds because there is little or no vertical motion in them"; "Stratus clouds do not signify much danger. If the wind speed should decrease markedly when stratus clouds are present in a large quantity, the base of the cloud could lower to the earth's [or ocean's] surface, resulting in a thick fog." Stratocumulus: "gray or whitish irregular layers of clouds with dark patches formed like rolls. These clouds look like altocumulus clouds, but they are at a much lower level. These clouds do not, as a rule, produce anything but light rain or snow"; stratocumulus clouds "form from degenerating cumulus clouds," and "are usually followed by clearing at night and fair weather . Visibility, however, can be seriously reduced in stratocumulus drizzle or snow." Cumulus: "puffy, cauliflower-like clouds whose shapes constantly change brilliant white in the sunlight, often extending from a relatively dark and horizontal base"; "when detached and with little vertical development [the] weather is fine, and nothing hazardous is in the offing. However, when cumulus clouds swell to considerable vertical extent, heavy showers are likely, associated with gusty surface winds in the vicinity of the showers. Since these clouds normally cover about 25 percent of the sky, they can often be circumnavigated." Cumulonimbus: "heavy dense clouds of considerable vertical extent (often to 45,000 feet and higher) in the form of a mountain or huge tower. These clouds are the familiar thunderheads. The upper part of these clouds is usually smooth, sometimes fibrous, with the top flattened to an anvil shape or a vast cirrus plume"; "very gusty surface winds in the vicinity of the thunderstorm, heavy rain, lightning, frequently hail, and in general, a bad time can be expected in the immediate vicinity of these clouds. a tornado or waterspout could possibly develop." Readings the Clouds and Sea State: During Hokule'a's voyage from Tahiti to Hawai'i in February, 2000, documentor Sam Low photographed clouds and sea state and recorded navigator Nainoa Thompson's readings of them: (1) February 11; (2) February 14; (3) February 15; (4) February 20 Color in the Atmophere Red skies at sunrise or sunset indicate humidity in the air. As raindrops form, the water particles scatter the short-wavelength blue light so that only the long-wavelength red light reaches the observer (Freier 32, 96-96). The observer needs to know which way the weather is coming from, though, east or west, to read this sign. If the eastern sky is red at dawn, and the weather is coming from the east (i.e., on the trade winds), then the red sky could indicate rain or stormy weather is approaching; if the weather is moving from west to east, then red skies at dawn indicate that the bad weather has past. Light Around Celestial Bodies "A halo around the moon is another sign of rain. The halo is caused by the moon shining through ice crystals of moisture-laden clouds. If the halo is a tight fit, rain is still far off. If the halo forms a large ring, rain is near. If the clouds close in and the moon loses its outline, rain can be expected in about ten hours. The same is true with the sun" (Seidman 167). Navigators in the Gilbert Islands count stars in the halo around the moon: "if [the moon] had a halo in which more than ten stars could be counted, there would perhaps be rain, but not a great downpour; if fewer than ten stars were visible there would be much rain and probably wind. "If, again, the moon had a double halo, the inner one reddish brown in colour, it promised a torrent on the wings of a gale" (Grimble 237-8). The appearance of stars is also a clue to weather-twinkling indicates that the atmosphere is unstable and turbulent, a sign of stormy weather. (Freier 54-55) When the dark side of the moon can be seen, the air is usually clear and stable in the direction of the moon, hence a sign of good weather if the weather is coming from that direction (Freier 55). Smells Rising humidity and increasing moisture in the air (accompanying dropping air pressure) enhances smells. Particles of odor become "hydrated"(wet) and cling more easily to the olfactory membranes in the nose. Thus stronger smells may be a sign of rain or stormy weather approaching (Freier 29). Animals Behavior Hawaiian proverbs suggests that observations of the flights of seabirds were used to predict weather; generally birds and other animals hunt for food in good weather and seek shelter from stormy weather: Lele ka 'iwa, malie kai ko'o: "When the 'iwa [frigate bird] flies [out to sea], the rough sea will be calm." (Pukui 'Olelo No'eau, No. 1979) 'Olelo ke kupa o ka 'aina ua malie; ua au koa'e: "The natives of the land declare that the weather is calm when the tropic bird travels afar." (Pukui 'Olelo No'eau, No. 2498) Ua ho'i ka noio 'au kai i uka, ke 'ino nei ka moana: "When the noio bird returns from sea to land, the sea will be stormy." (Pukui 'Olelo No'eau, No. 2787) A western proverb suggests, "Porpoises in a harbor, expect a storm." Freier explains "These animals need to come to the surface to breathe. Apparently this is more difficult in rough water" (122). Emma Kauhi remembers that when she was growing up in Kapa'ahu, Puna, on the Big Island, she was told, "Ina 'au ka nai'a ma Hilo, 'a, e malie ana ke kai. Ke 'au ka nai'a ma Ka'u, 'a, e 'ino'ino ana ka moana: "If dolphins swim toward Hilo, the sea will be calm; if the dolphins swim toward Ka'u, the ocean will be rough" (61). The proverb suggests a sheltered sea toward Ka'u. Navigators in the Gilbert Islands also use observations of animals to predict weather: "When a voyage had to be made during the bad season, the navigator knew several weather signs to help him choose his day. He would watch the small red ants which infest most houses: if they were returning in numbers to their nests, laden with food, and were blocking up their doors with particles of sand, foul weather was impending; but if they swarmed out, leaving their doors wide open, it promised good weather. "The spider was another prophet: when the weather was set fair he would stay in the middle of his web; but if wind and rain threatened, he would retire to something more solid." "But the most reliable barometer in the opinion of the Gilbertese navigator was (and still is) the shellfish nimatanin (Nerita plicata). This is found in the shallows on the reef by the ocean beaches of the islands. When fair weather promises, it remains on the surface of the rock, and if it is found thus in any great numbers there is every hope of a long fine spell; but if the creature remains in the crevices of the reef, it is an infallible sign of heavy weather, and the deeper it hides itself the worse will be conditions for sailing" (237-8). Hawaiian Traditions of Weather Prediction Paka'a, who served as ho'okele-wa'a, or navigator, for Keawenui-a-'umi, a ruling ali'i of the Big Island during the 16th century, was famous for his ability to read the signs of the sky to predict weather and winds. In a 19th century account of his life, Samuel Kamakau describes Paka'a's ability to read weather signs: "Paka'a was trained to read signs (kilokilo) and knew how to manage a canoe in the ocean, out of sight of land. He knew how to tell when the sea would be calm, when there would be a tempest in the ocean, and when there would be great billows. He observed the stars, the rainbow colors at the edges of the stars, the way they twinkled, their red glowing, the dimming of the stars in a storm, the reddish rim on the clouds, the way in which they move, the lowering of the sky, the heavy cloudiness, the gales, the blowing of the ho'olua wind, the a'e wind from below, the whirlwind, and the towering billows of the sea" (Ruling Chiefs of Hawai'i 36). Another account of Paka'a depicts him as not only able to predict weather, but to control winds with a gourd containing all the winds of Hawai'i, which Paka'a called forth by name. (For chants containing the dozens of wind names of each island, see Moses K. Nakuina's Moolelo o Paka'a a me Ku-a-paka'a, or the English translation of Nakuina's work, The Wind Gourd of La'amaomao by Esther T. Mookini and Sarah Nakoa; or a shorter version of the Paka'a legend accompanied by an English translation, in the Fornander collection, Vol. 4, 72-135). In Nakuina's story, Paka'a is given the wind gourd by his mother, who received it from her grandmother La'amaomao, the Hawaiian wind goddess. (In other Hawaiian traditions, La'amaomao is said to be a god rather than a goddess; he came to Hawai'i with the voyaging chief Mo'ikeha, and settled at Hale-o-Lono, Moloka'i). The notion of a wind gourd is traditionally Polynesian: "In Mangaia of the Cook [Islands], the high priest possessed a magic calabash, a miniature universe, which had holes bored in a circle at equal distances around its middle, representing the openings on the horizon through which the thirty-two winds of the compass were supposed to blow. When a voyage was contemplated to a distant island the priest was induced to stop up all the holes in the calabash except the one at the particular point of the compass from which the prospective travelers desired the wind to blow for the speedy consummation of the voyage" (Makemson 147). Lewis quotes Gill about the importance of knowledge of the winds: "'In olden times, great stress was laid on this knowledge for the purpose of fishing, and especially for their long sea voyages from group to group. At the edge of the horizon are a series of holes through which Raka, the god of winds, and his children, love to blow'" (75). David Malo, in Hawaiian Antiquities (12-13), gives the following classification of Hawaiian cloud names and their signficance: "The clouds, objects of importance in the sky, were named for their colors. A black cloud was termed 'ele'ele; if blue-black, it was called uliuli; if glossy black hiwahiwa or polo-hiwa. Another name for such a cloud was panopano [Pukui-Elbert: "thick clouds"; PE also lists ao lalahiwa, "dark clouds," and ao kokoli'i, "thick, black clouds; Andrews gives ao pouli, "dark clouds"] "A white cloud was called ke'oke'o, or kea. [Another name for a white cloud was ao 'opiopio.] If a cloud had a greenish tinge, it was termed maomao; if a yellowish tinge, lena. A red cloud was termed ao 'ula or kiawe 'ula [PE: "faint streaks of red in a cloud"] or 'onohi-'ula, red eye-ball [PE: ao 'onohi-"cloud with rainbow colors," and -'onohi 'ula-"clouds with red hues of a rainbow."] "If a cloud hung low in the sky, it was termed ho'o-lewa-lewa ["suspended"], or the term ho'o-pehupehu, "swollen," was applied to it. [PE: ao ho'opehupehu-billowy, swollen clouds; cumulus clouds]. A sheltering cloud was called ho'o-malumalu; ["darkened," "shady"]; a thick black cloud was called ho'o-kokoli'i; a threatening cloud was called ho'o-weli-weli. "Clouds were also named according to their character. If a cloud was narrow and long, hanging low in the horizon, it was termed 'opua, a bunch or cluster. There were many kinds of 'opua, each being named according to its appearance. If the leaves [lau] of the 'opua are slanting downward [hina], it might indicate wind or storm, but if the leaves [lau] were upright [kupono], calm weather. If the cloud was yellowish and hung low in the horizon it was called newe-newe, "plump," [PE: "full, billowy"] and was a sign of very calm weather. [PE: 'opua or kaupua: "cumulus clouds; puffy clouds as banked up near the horizon"]." [In Kona, on the west side of Hawai'i Island, the appearance of 'opua over the ocean to the west was a promise of rain: Mama Kona i ka wai kau mai i ka maka o ka 'opua: "Kona is relieved, knowing that there will be no drought, when the clouds promise rain." (Pukui 'Olelo, No. 2134). [Two other proverbs link 'opua to rain: Aia ka wai i ka maka o ka 'opua: "Water is in the face of the 'opua" (Pukui 'Olelo, No. 55); Ola i ka wai a ka 'opua: "There is life in the water from the 'opua" (Pukui 'Olelo, No. 2483).] "If the sky at the west horizon was blue-black, uli-uli, at sunset, it was said to be pa-uli ["gloomy"] and was regarded as prognosticating a high surf, kai-ko'o. If there was an opening in the cloud, like the jaw of the au (swordfish), it was called 'ena and was considered a sign of rain. "When the clouds at the eastern heavens were red in patches before sunrise, it was called kahea ("a call, alarm") and was a sign of rain. [PE gives this cloud name as kaha'ea-"cumulus clouds, often colored and thought to be a sign of rain."] If the cloud lay smooth over the mountains in the morning, it was termed papala [PE-"haze, fog"] and foretokened rain. It was also a sign of rain when the mountains were shut in with blue-black clouds, and this appearance was termed palamoa [PE: palamoa: "thick, dense, as clouds"]. There were many other signs that betokened rain. "If the sky was entirely overcast, with almost no wind, it was said to be po'i-pu (shut up), or ho'o-ha-ha [PE: "overcast, calm"], or ho'o-lu-luhi [PE: "overcast, threatening"]; and if the wind started up, the expression ho'o-ka-ka'a, "a rolling together," was used. If the sky was shut in with thick, heavy clouds, it was termed hakuma; and if the clouds that covered the sky were exceedingly black, it was thought that Kulani-ha-ko'i [a lake in the sky] was in them, the place whence came thunder, lightning, wind, rain, violent storms. "When it rained, if it was with wind, thunder, lightning and perhaps a rainbow, the rain storm would probably be a prolonged storm. When the western heavens are red at sunset, the appearance is termed aka-'ula (red shadow or glow) and it was looked upon as a sign that the rain will clear up." The Pukui-Elbert dictionary contains the following additional cloud names (compiled by Nalani Minton):
A proverb notes the weather significance of the ao pua'a: Kaka'i ka puapua'a i ka malie, he 'ino: "When the piglets follow one after another in the calm, bad weather is coming" (When the clouds called ao puapua'a or pua'a "pig" clouds, follow one after the other on the mountaintops in calm weather, bad weather is to be expected.) (Pukui 'Olelo, No. 1416). (The ao pua'a are apparently altocumulus clouds. See a decsription of this cloud and its weather significance under "Clouds"). Some Comments by European Explorers Concerning Polynesian Traditions of Weather Prediction Andia y Varela made the following observation of Tahitian weather predicting skills: "What took me most in two [Tahitians] whom I carried from [Tahiti] to [Ra'iatea, 160 miles away] was that every evening or night, they told me, or prognosticated, the weather we should experience on the following day, as to wind, calms, rainfall, sunshine, sea, and other points, about which they never turned out to be wrong: a foreknowledge worthy to be envied, for, in spite of all that our navigators and cosmographers have observed and written about the subject, they have not mastered this accomplishment (Corney 286-287). Oliver notes: "For sailors and fishermen, livelihood and even survival sometimes depended upon ability to predict the weather, a skill which, some observers such as Banks claimed, the Maohis had in considerable measure: 'The people excell much in predicting the weather, a circumstance of great use to them in their short voyages from Island to Island. They have many various ways of doing this but one only that I know of which I never heard of being practised by Europeans, that is foretelling the quarter of the heavens from whence the wind shall blow by observing the Milky Way, which is generally bent in an arch either one way or the other: this arch they conceive as already acted upon by the wind, which is the cause of its curving, and say that if the same curve continues a whole night the wind predicted by it seldom fails to come some time in the next day; and in this as well as their other predictions we found them indeed not infallible but far more clever than Europeans.' "Banks' high opinion of Maohi weather prediction was not, however, shared by Cook, who, after describing the more common local changes in wind direction and velocity, wrote,'The natives seem not to have a very accurate knowledge of these changes'." Bibliography-Winds and Weather Prediction |
Before the invention of modern weather instruments, seafarers relied on observations of nature to predict weather; today, while weather station and buoy reports, National Weather Service forecasts, and satellite photos are excellent sources of weather information, a mariner should also understand seasonal weather patterns and be able to read signs in the environment both before and during a trip: the wind, sea state, clouds, appearance of celestial bodies, smells, and animal behavior contain clues to current and approaching weather. The art of non-instrument weather forecasting can be used to confirm weather reports or to predict weather when instruments and reports are not available.