About a month ago, I promised a forthcoming blog about waterspouts, which at the time were occurring with unprecedented frequency.  Shortly thereafter, the weather changed, serving up an unbroken series of days of brilliant blue skies.  With them, I thought my chance to share with you a little about this local phenomenon had been rendered untimely.

In spite of the clearing trend, we have had record-setting high temperatures, which have apparently contributed to maintaining the conditions favorable for waterspout formation.   On a recent afternoon spent in front of the inn’s computer screen, I spotted from the corner of my eye a fat column rising above the neighboring rooftops.  It extended from what had appeared to be only transient clouds down to the area a few blocks away that I knew was over water, near the Bight. It was one of the best-developed waterspouts I have ever seen, and lasted an unusually prolonged amount of time – long enough, in fact, to round up guests who happened to be in the house at the time for a bird’s eye view from the upstairs veranda.

It was all quite exciting … an impressive show, indeed, as the elongated cone formed, dissipated slightly, and reformed repeatedly, waltzing gracefully across the horizon. Then it vanished before our eyes, as if it had been only a ghostly apparition, transitioning into a cooling afternoon shower.

The Florida Keys have been called “the greatest natural vortex lab in the world”.   Waterspouts occur more frequently here than anywhere else.  It has been estimated that the waters around the Keys, especially from Marathon to Key West and westward to the Dry Tortugas, host up to 500 waterspouts a year. They are so common that most go unreported unless they cause damage.

Natural weather conditions and geography supply two basic ingredients for the formation of waterspouts.  During the summer and fall, temperatures in the mid-80s and low-90s heat the shallow water surrounding the islands to produce extreme humidity, especially in the late afternoon.  As the hot air rises, the humidity condenses into tiny water droplets that make up clouds.

The second important waterspout ingredient in the Keys seems to be the regular east or northeast “trade winds” that blow parallel to the island chain.  This causes the aforementioned clouds to bank into a line that encourages waterspouts.

You may have heard that waterspouts are tornadoes that form over water.  While they are no doubt “kissing cousins”, researchers have, in recent years, discovered some basic differences between the two.  For instance, despite being similar in intensity to tornadoes, waterspouts are generally smaller in diameter and less destructive.  Lacking high-altitude winds to draw on as do tornadoes, the fair-weather type of waterspouts so often spotted in the Florida Keys last only around 10 to 15 minutes and are not usually a threat to land. However, they can be especially dangerous to ships and planes.  In fact, it has been speculated that they may be responsible for the mysterious disappearances in the Bermuda Triangle.

While most often spotted in conjunction with skies threatening a storm, many waterspouts form during relatively fair weather. Cumulus clouds that build to around 18,000 to 20,000 feet are formed by water vapor condensing from the sea surface.  The same heat energy is responsible for the rapidly rising air currents that spawn waterspouts at the anvil, or base, of the cloud.

Waterspouts can be especially problematic to boaters because they may be relatively transparent and initially visible only by the unusual “dark spot” on the water that is a sign of a spiraling funnel of air.  Even though it is sometimes invisible in the early stages, a vortex is reaching the ocean surface from the cloud. When the wind speeds reach around 40 mph, the wind begins to kick up spray in a circular pattern — the spray vortex.

At this time, the funnel points down from the cloud toward the ring, which then develops into a pattern of light- and dark-colored bands on the water that spiral out from the dark spot.  The funnel begins to become more and more visible as the low air pressure inside it cools the air enough for water vapor to begin condensing into tiny droplets.

The mature funnel that we recognize as a waterspout is actually a swirling cloud, the dissipation of which usually occurs when rain begins falling from the parent cloud. Cool air brought down by the rain cuts off the supply of warm, humid air that is necessary to maintain the waterspout’s strength.