Experiencing turbulent weather while on the water can be frightening, especially if unexpected. Understanding the basics of marine meteorology can help both captain and crew to know what to expect, or more importantly, how to understand or potentially avoid the unexpected.
Wind is the key player on the scene: While it can power a sail or aid a yacht along its course, it can also reposition ocean currents, make dockside or port transiting a tricky feat, increase wave heights, or even roll a vessel. The friend/foe nature of the wind is a direct response to pressure differences in the region. Winds move from high to low values of pressure; the greater the pressure differences, the faster the wind. To visualize this process, imagine ball rolling down a hill; the steeper the slope of the hill, the faster the ball will roll.
High pressures can ultimately be thought of as the “hills,” the low pressures as the “dips,” and the wind as the “ball.” 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.
So the wind blows and the waves react as a result. While it may be easier to associate poor conditions with big weather markers, sometimes small-scale phenomena can produce localized increases such as squall lines and water spouts.
Waterspouts can be subcategorized into tornadic and non-tornadic, relative to their formation source. Fair-weather types are most frequent and are considered non-tornadic in nature, meaning they are not associated with a supercell thunderstorm. True tornadic waterspouts are less common. Typical non-tornadic waterspouts start forming on the surface of the ocean or a lake and rise up to meet the base of a parent cloud. They tend to last less than 20 minutes and produce winds less than 70 mph, which is the equivalent of an EF-0 tornado. Tornadic waterspouts 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.
Tornadic waterspouts can also be associated with squall lines, which are typically narrow but elongated bands of intense thunderstorms. The formation of a squall line in the near or offshore waters is usually ahead of 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, leaving little time for vessel preparation.
From the small scale back to the large, no weather phenomena has more power and expansive reach than a tropical cyclone. The amount of energy generated during the evaporation and condensation processes that produce the clouds and rain is almost 200 times the world’s electrical generating abilities, with roughly half that amount additionally generated via the wind. Navigating a vessel around the associated increases can be tricky and requires advanced knowledge of environmental factors to determine potential storm trajectories.
When interaction is imminent, understanding how to circumnavigate via the “Front Right Quadrant” [FRQ] becomes key. By intersecting the system with a “+” sign, the FRQ is defined as the front and right quadrant, relative to the storm’s forward motion.
This is the area of highest winds, where the storm’s winds combine with the directional wind. In other words, the side to be avoided if at all possible.
While there are many hazards at sea, advanced planning and a working knowledge of the science behind these risks can help circumvent disasters. Knowledge is power — so with that and a bit of luck, here’s hoping for fair winds and following seas.
Jordanna Sheermohamed is president and lead meteorologist of Weather Forecast Solutions, a private weather-forecasting company (www.WeatherForecastSolutions.com). Comments are welcome at firstname.lastname@example.org.