Sea Science: by Jordanna Sheermohamed
Before the invention and integration of high-tech weather instruments such as satellites, radar, and computer models, individuals often used environmental observations to determine impending weather. At a recent lunch with retired Captain Terry Pope, the topic of historical seafaring methods of weather prediction came up. For example, captains sometimes kept an elderly sailor on board whose rheumatic pains could warn of incoming low pressure or rain.
Many weather proverbs were born of natural observations, with sailors and farmers adding credibility to their catchiness. It turns out that examining these sayings through a scientific lens actually proves that one really can trust the great salty grandfathers of the high seas.
One of the most well-known of these sayings is “Red sky at night, sailor’s delight; red sky at morning, sailors take warning.” In order to make sense of this proverb, there are a couple of scientific points to understand: the vertical direction of air during high/low pressures, the general movement of weather patterns from west to east, and how the human eye perceives the specific colors of visible light.
Of all the colors of the visible light spectrum, red has the longest wavelength and violet has the shortest. Therefore, when traveling long distances or through a region of atmospheric contaminants, such as dust or pollution, the shorter wavelength colors are scattered while the longer wavelength colors make it through. This is often why we see red and orange at sunset, when the sun is lowest on the horizon and the light has to travel the farthest. This also explains why the sun appears white during noontime hours; the sun’s position directly overhead means the light has the shortest distance to travel, with all colors effectively making the journey to the human eye. Another way to understand this concept is by observing something in the dark. The object doesn’t change color, but the human eye is unable to perceive it because of the absence of light, so it appears black.
With the sun setting to the west, red color indicates sinking/drier air associated with an incoming high pressure, which prohibits the rising air and upward cloud development that lead to thunderstorms. Conversely, a red sunrise to the east indicates the high pressure is to the east of an observer’s position, meaning a relatively low pressure is located to the west. The rising air associated with a low pressure instigates clouds that, with enough vertical ascent, lead to the potential for stormy weather.
Another useful proverb, “Mackerel skies and mares’ tails make tall ships carry low sails,” scientifically makes the grade as well.
The names of clouds are often a Latin derivation that describe the clouds’ pattern, the type of particles they contain or their height in the atmosphere. Clouds are a useful way for an observer to determine the state of the atmosphere at a given time. In Latin, cirrus means “curl” and cumulus means “mass or pile.” So when cirrocumulus clouds are observed in tandem with cirrus clouds, it generally indicates convection occurring at high altitudes, and usually precedes rain within a day. Cirrocumulus clouds also appear quite similar to the scales of a mackerel fish, and cirrus clouds are much like the strands of a mare’s tail, so this saying delivers a general warning to lower the sails, as the higher winds associated with thunderstorms are impending.
“A wind from the south, has rain in its mouth” is a third axiom that jibes with sound science. Winds will always move from high to low pressure, so a breeze from the south will indicate a high pressure is situated to the south or southeast of a location, blowing towards a lower pressure located somewhere to the north or northwest.
Since low pressure induces rising air, cloud formation becomes possible. With enough moisture and rising air, storm development occurs, increasing the possibility of precipitation. Another useful fact to consider is that the faster clouds move, the more imminent the arrival of a frontal boundary associated with an advancing low pressure.
Accurate and long-range weather forecasts depend on technology. Without its aid, the time frame for a credible forecast drastically drops from five days to about 24-48 hours. Even so, it’s good to know that if modern weather forecasting tools are unavailable or not working for some reason, a pretty credible weather forecast can still be produced by simply turning to the sky.
Captains who would like to see a particular ocean/weather topic addressed in a future column are welcome to send a request to jordanna@WeatherForecastSolutions.com.
Jordanna Sheermohamed is president and lead meteorologist of Weather Forecast Solutions, a private weather-forecasting company ( www.WeatherForecastSolutions.com). Comments are welcome below.