Sea Science: Weather Lore Jibes With Modern Science

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.

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The warm colors of sunset are a resultant of the longer wavelengths associated with reds, oranges, and yellows.

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.

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Cirrocumulus clouds are often referred to “mackerel sky” for their resemblance to the fish’s scales.

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.

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Winds will move from high to low pressure.

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.

This article was published in our monthly column within The Triton newspaper (Nautical News for Captain and Crews), and can additionally be found here.

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Severe Weather on the High Seas

Nothing makes a body feel as protected from the elements as a solid set of four walls and an up-to-code reinforced roof, but these protective features may not be present when active weather strikes.  Many seafarers find themselves subjected to harsh elements, putting them at the mercy of the skies above and the waves alongside their trusted vessels.

When it comes to the ocean, nothing “stirs the pot” like the wind; and the winds are a response to pressure differences.  More specifically, winds move from high to low values of pressure, and the greater the differences between the pressure fields, the faster the wind moves.  A good way to visualize this process is to imagine a ball rolling down a hill: the steeper the slope of the hill, the faster the ball will roll. Oh gravity, thou are a heartless force.

Ball Trajectory
The steeper slope will yield a faster speed as a result of gravity.

High pressures can ultimately be thought of as “hills”, the low pressures as the “dips”, and the ball is the “wind”.  So when analyzing atmospheric pressure patterns, much like a contour elevation map would indicate the steepness or grade to a hiker, tightly spaced pressure contours indicate a steep pressure change pattern, hence higher winds.

3D render of Pressure
Winds will flow from high to low pressures, and the steeper the slope, the faster the winds.
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Tightened pressure contours between a high and low pressure indicates a steep slope, which yields faster moving winds.

So the wind blows and the waves react as a result. Now depending on the size and location of the pressure patterns, winds and therefore waves of various sizes can be produced and travel away from their origin location.  Wind waves are a result of local winds blowing across the surface of the water that eventually break or reach a shoreline.

Waves

If no deterrent is present, these waves have the ability to propagate over hundreds of miles as a result of their momentum.  This is known as groundswell

Waves can often aid a vessel along its course, acting like a turbocharged engine to work in tandem with the boats own gas/diesel power.  However there are the other instances in which the waves become the foe.  Increased wave heights, including the elusive rogue waves can roll and/or even break a vessel, overpower engines or snap rudders, leaving a craft at the mercy of the winds.

While most know the tale of the RMS Titanic, other maritime disasters have encountered similar fates as a potential result of winds and their respective waves. A 656 ft German merchant ship, the MS München, departed Bremerhaven, Germany on December 7th, 1978 on a transatlantic voyage towards Savannah, GA.  In the early morning hours of December 12, the MS München sent out an S.O.S. signal, with its last reported position.  All search efforts were officially called off on December 22, with emergency buoys, life rafts, life vests and belts, and lifeboats retrieved from search operations and random encounters. The MS München was never located, but via investigations done on the salvaged lifeboats, it has been theorized that via severe weather, she likely succumbed to a series of large waves which both broke over the bow and eventually flooded the vessel, causing it to sink.

While it may be easier to associate poor conditions with big patterns, sometimes small scale phenomena can produced localized increases not seen in the big picture.  Two examples of this would be squall lines and water spouts.

Waterspouts can be sub-categorized into tornadic and non-tornadic, as a result of their formation source. The fair-weather types are most frequent, and are considered non-tornadic in nature, meaning they aren’t associated with a supercell thunderstorm as are the rarer tornadic waterspouts. Typical non-tornadic waterspouts start forming on ocean/lake surface and rise up to meet the base of a parent cloud.  They tend to last less than 20 minutes and produce winds less than 70mph, which would classify it as the equivalent of an EF-0 tornado.  Tornadic water spouts are a result of a rotating cloud which produces a tornado that then descends and connects to the surface of a body of water.  While limited in space and time, either type of waterspouts can locally whip up winds and waters, and boaters are advised to stay clear.

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Waterspouts in St. Thomas, US Virgin Islands | Photo by Erickson
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Waterspouts on the Mediterranean | Photo by Mehmet Gökyigit
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Waterspouts off the coast of Turkey | Photo by Tufancetiner

Tornadic waterspouts can also be associated with squall lines, which is a typically narrow but elongated band of intense thunderstorms.  The formation of a squall line in the near or offshore waters is usually ahead with an oncoming cold front associated with a low pressure.  While generally measuring about 10-20 miles wide, squall lines can stretch for hundreds of miles, and are capable of producing, tornadoes/waterspouts, damaging winds, and frequent lightning.  An incoming frontal boundary from the West or Northwest will alter winds in a location as follows:  Initial winds will be from the east/southeast to south, as the winds begin blowing from the local higher pressure towards the incoming lower pressure.  As the frontal boundary nears, winds will become south/southwest, finally becoming west/northwest as it departs. When a squall line approaches ahead of the frontal boundary, wind shifts can be sudden and fierce which leaves little time for vessel preparation.

From the small scale back to the large, no other weather phenomena has the power and expansive reach than that of a tropical cyclone.  The amount of energy generated during the evaporation and condensation processes that produce the clouds/rain is almost 200 times the world’s electrical generating abilities, while the amount generated via the wind is roughly half of the world’s electrical generating abilities.  The movement across the ocean basins can generate long range swells that can be felt several hundred miles away.  Navigating a vessel around the associated increases can be tricky and requires advanced knowledge of environmental factors to determine potential storm trajectories.

Tropical_Vis and RH
Visible satellite, mid-level relative humidity, and steering flow of 2016’s Hurricane Matthew.  This image was produced while Matthew was a category 3 system; less than 8 hrs later, Matthew would briefly strengthen into a category 5 system.  This system made 4 separate landfalls:  Haiti [cat 4], Cuba [cat 4], The Bahamas [cat 3 & 4], and South Carolina [cat 1]

When interaction with a system is imminent, understanding how to circumnavigating via the “Front Right Quadrant” [FRQ] becomes key.  If one was to intersect the system with a “+” sign, the FRQ is defined as the front and right side of the system, relative to the storms forward motion. This is where the storm’s winds work in tandem with the directional wind to produce the highest winds of the cyclone.  In other words, the side to be avoided if at all possible.

FRQ
The front right quadrant, relative to the direction of motion, indicates where the strongest winds of a tropical cyclone are located.  This is where the systems’ winds work in tandem with the motion.

While there are many hazards out to sea, advanced planning and a working knowledge of the science behind these risks can help minimize disasters out to sea.  Knowledge is power and coupled with a bit of luck, here’s hoping for fair winds and following seas.

Boating Conditions Along Gulf of Mexico and Atlantic

For all the #boaters in the [aquatic] house, increased conditions in vicinity of [20-25 kts] winds and [4-6 ft] seas behind the frontal boundary [white line] in the NW Gulf of Mexico.

SWH Analysis

These increases will continue to propagate eastward through the Gulf through early Tuesday, arriving along the East Gulf waters by Monday afternoon. Strong northerly winds will continue to build in behind the boundary, likely remaining in and around [10-15 kts] through early Monday morning.

Elsewhere, southerly flow along the U.S. East coast will continue to increase through midweek, with sea heights additionally increasing beyond [6 ft] as the weak low off the East Coast of #Florida lifts northwards and towards the #MidAtlantic.

NOTE: Img indicates significant wave heights in ft and winds in kts.

Dangerous Sea State Along ATL Coast

Currently, widespread sea state increases along the U.S. Atlantic Coast, with the highest conditions in vicinity of [10-15 ft].  Offshore conditions even higher, ranging within [15-30 ft].  Conditions to begin reducing from south to north, beginning Wed PM/Thu AM along the SE, Thu PM/early Fri AM along the Mid-Atlantic, and Fri AM/PM in the Northeast.#BoatersBeware

SWHani