Water spouts can be scary and intimidating even to the most experienced of skippers. They are not as dangerous as their land- based counterparts; the tornado or twister, nevertheless, care should be taken when encountering one of these natural phenomena. According to the Oxford English Dictionary a water spout is a column of water formed by a whirlwind over the sea. Waterspouts can be divided into two categories: fair weather waterspouts and tornadic waterspouts.
Fair weather waterspouts are more likely to occur during late spring to early fall where the summer months offer the right atmospheric conditions of warm, moist and unstable air and a growing cloud aloft. As the name indicates, they typically occur during fair and relatively calm weather with little wind, in the mornings or late afternoons, and develop under the dark flat bottom of rising cumulus clouds. They are short lived and will form quickly, normally dissipating within 20 minutes. Fair weather waterspouts move very little if at all, they start from the surface of the water and move upwards; by the time they are visible they are near maturity.
Tornadic waterspouts are more dangerous and destructive in nature. They form over water or start life as a tornado over land and become waterspouts as they cross the coast. They form under convective storms cells when air rises and rotates around a vertical axis (mesocyclonic in action). They typically occur with afternoon or evening thunderstorms when the warm moist air provides an unstable environment. They can be accompanied by strong winds and large seas. Hail and lightening are common with these severe thunderstorms. These waterspouts develop downward and initially form as a funnel cloud or tuba at the base of the cloud when a column of swirling air starts to rotate, condensing ambient moisture into water droplets extending towards the sea. This revolving motion causes a swirling mass of spray to rise up from the sea. If it continues to develop, the funnel meets the swirling sea spray and forms the column of the spout. These waterspouts have huge potential to be dangerous.
Waterspouts are more commonplace in tropical regions but they can develop anywhere and are also common in many parts of Europe. The average wind speed in a waterspout is approximately 50mph (80kph) but can be as high as 150mph (241kph) and they can travel at speeds of anywhere from one to 80mph (128kph). Contrary to popular belief it is not sea water ‘sucked up’ that appears to make up the spout but what studies have found to be a swirling mass of condensed water vapor. The diameter of a funnel can range from a few yards to 110 yards (100m). The myth that firing canons or other projectiles into a waterspouts path will break them up has never been substantiated.
Regardless of whether the waterspout is fair weather or tornadic in origin, all sea going vessels should take caution. Never navigate through a waterspout or move closer to it for investigation. To avoid a waterspout, try traveling at right angles to its apparent direction of movement. Darks spots on the water, followed by rings or a sudden shift in wind can be warning signs of a developing waterspout. If a waterspout is in close proximity and you are unable to avoid it, take down any sail, close any hatches and if possible stay below deck. During the summer months, in light winds, look for the telltale signs in the line of flat bottom cumulus clouds or thunderstorms, or in the lines of thunderstorms that can develop any time of year. Although waterspouts are not as destructive as their land based cousins their ability to carry anything in their path makes them dangerous to vessels and small craft. Not only can waterspouts cause havoc to mariners, they can devastate coral reefs and marine organisms that are close to the waters surface.
Sources: www.noaa.gov; www.marineinsight.com; The Cloud Book – The Met Office
Rosie and her husband Sim Hoggarth, both from the UK, have cruised the Caribbean and North America for over eight years aboard Alianna their Corbin39. Visit their blog: www.yacht.alianna.co.uk