Posted by: Rob Viens | March 20, 2012

Waterspout to Starboard!

March 20th – Excitement on board the Beagle today as a waterspout formed near the ship:

“In the forenoon a water-spout took place at a few miles distance & was to me a very interesting phenomenon. — From a stratus or black bank of clouds, a small dark cylinder (shaped like a cows tail) depended & joined it self to a funnel shaped mass which rested on the sea.” (Mar 20)

Waterspouts over Lake Huron (from NOAA):

Waterspout over Lake Huron

This was not the “itsy bitsy spider” variety of water spout, instead this was an intense vortex of air, generated and “fueled” by air temperature differences. Waterspouts come in two varieties – (1) tornadic and (2) non-tornadic (or fair-weather) waterspouts.  Not surprisingly, the first variety is basically a tornado over the water (and like a tornado over land, it is almost always associated with a severe thunderstorm).  The second variety – almost certainly the type Darwin saw on March 20 – can form during “fair-weather” conditions and are not nearly as ominous as a true tornados.  These waterspouts are typically short-lived (up to 20 minutes), have relatively slower wind speeds (say 30 m/s), and more very slowly over the water.

Tornados (and tornadic waterspouts) form from the intense wind shear that can develop at the “front” between high and low pressure air masses. Thunderstorms and associated tornados form at cold fronts – where cold (high pressure) air moves in to replace warm (low pressure) air. At these fronts warmer air is forced up over the cold air generating rain and high winds.

Fair-weather waterspouts form along the base of dark, flat-bottomed cumulus clouds. The funnel starts to develop on the water surface (kicking up a lot of spray) and grows upward.  The bulk of what you see (beside the spray near the base) is not water being sucked upward, but water vapor condensing in the funnel as the moist air rises. The Weather Doctor has a nice description of waterspouts, with more detail if you are interested in reading more.

Here is some newsfootage of a waterspout in Australia (though the banter is universal “newscaster-speak”):

It must have been thrilling to see a waterspout from the ship (and a little scary, too).  Though they are not as devastating as a tornado, they can be potentially dangerous to ships and have been know to cause damage. Luckily, this one only lasted a short time and did not threaten the ship – otherwise they’d have had to bring out the “big guns” – literally:

“It lasted some moments & then the whole appearance vanished into an exceedingly heavy rain storm. — When they approach near to a vessel, it is usual to fire a big gun in order to break them.” (Mar 20)

On no account does NOAA recommend boaters “get closer to investigate” waterspouts. However, modern boater warnings do not suggest firing a cannonball into the spout to break it up.  I don’t want to belittle the experience of 19th-century sailors but I just can’t see how a cannonball would physically effect a waterspout. I suspect that since they had a short life, odds were good that whether you fired a cannonball or not, they would dissipate. If anyone knows otherwise – please feel free to share. (RJV)

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Responses

  1. Don’t know much about waterspouts, but I have experienced tornadoes up close and personal. Growing up in Michigan, the family would head for the basement about a half-dozen times a year and getting sent home from elementary school because of a tornado warning was quite common and almost always an adventure. People got savvy about watching the weather , especially the ominous stillness in the air right before the arrival of the tornado. On a family camping trip to Minnesota a twister came racing through the campground in the middle of the night, uprooting trees just inches from our tent and unleashing a violent thunderstorm that was breathtaking. Despite often genuine fear, I also enjoyed the excitement surrounding tornadoes and it’s probably why I still enjoy the corny movie Twister…

  2. […] a waterspout back in March, but there is no indication that they fired them at that time (see Waterspout to Starboard!).  However, the cannons would soon be prepped for action when the Beagle had a need to show force […]


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