Tis the Season!
Hurricanes (How they form and the curve balls they throw)
The peak month for these self-sustaining heat engines is September closely flanked by August and October. With its name derived from ‘Hurrican’-the Carib god of evil-this cyclonic twisting Goliath requires a combination of conditions to rear its ugly head.
Sea surface temperatures must be at least 27 degrees Celsius and they tend to form five to eight degrees north and south of the equator for rotation to begin from the influence of the Coriolis force. (Remember that phenomenon that causes everything in the Northern Hemisphere to be deflected to the right but has zero effect at the equator?). As well, a warm core of air is needed. What mixes all these ingredients together is a weak weather disturbance, a tropical wave, moving westward from the area of Cape Verde, Africa. This atmospheric support acts as an impetus for thunderstorm formation grouping this newborn storm into a self-perpetual heat engine as latent (hidden) heat is released from the process of condensation, causing more vertical development.
Hurricanes are born as a tropical depression with winds less than 34 knots. The next stage, the tropical storm, sustained winds of 35 to 64 knots occurs and is when the storm is christened with an official name. Today, names alternate between the male and female gender and are predetermined for five years, after that the names are repeated. Some names are retired because of their destructive past. Andrew in 1992 was one of them. By definition, a tropical storm becomes a hurricane when winds exceed 64 knots. (A Hurricane is known as a Typhoon in the Pacific Ocean, Cyclone in the Indian Ocean and a Willy-Willy in Australia).
The most significant clouds are the cumulonimbus (thunderstorm cloud) topping at a whopping 50,000 to 60,000 feet. Reported winds can get as high as 130 to 150 knots, after that wind measuring devices (anemometers) are destroyed. Engineers estimate from structural damage that winds of 170 to 200 knots could occur. Winds drop off quickly to less than 15 knots in the ‘eye’. The diameter of the ‘eye’ is approximately 6 to 25 miles (11 to 45 kms) and in this region there is usually no precipitation and most clouds clear away. The reason for the ‘eye’ is because of subsidence. The air at the center sinks causing warming due to compression, thus a break up of clouds. Temperatures at the core tend to be five degrees warmer as a result. Just to give some indication as to the intensity of these storms, a small hurricane will drop over a period of 24 hours, 20 billion tons of water. They are equivalent in energy to 500,000 Hiroshima size atomic bombs averaging six atomic bombs per second. Typical wave heights get up to 35-40 feet (11-13 meters) although the very intense hurricanes achieve heights of 45-50 feet (15-16 meters) with unconfirmed heights of 60 to 90 feet (20-29 meters).
Typically hurricanes move westward at speeds of 8 to 16 knots and then begin to curve northward. As they track northward they will show signs of fading as colder waters prevail. As well, when they track over land, surface friction tends to take the ‘wind out of their sails.’
However, now and again Mother Nature throws a curve ball, and this is what happened in late October 1991. Hurricane Grace on October 27 moved northward and became extratropical. Extratropical means ‘beyond or outside the area of the tropics.’ Not to be confused with extra, ‘over and above what is normal.’ It was a combination of extenuating circumstances that caused a rebirth of a massive destructive monster, which the National Weather Service described as ‘the perfect storm’. From a weak low-pressure system sitting off Nova Scotia, combining with a cold intrusion of air from the continent and the moisture from Grace, this resultant storm caused millions of dollars of damage along the eastern seaboard. Also dubbed the ‘Halloween Storm,’ it sank a sword-fishing vessel; the Andrea Gail with all hands on board perishing. It became the basis for Sebastian Junger’s novel, The Perfect Storm, and now the movie. Mother Nature threw yet another curve ball because the storm found a warm water source from the Gulf Stream sending it back into Hurricane status. The Halloween storm or ‘Perfect Storm’ was then known as the ‘Unknown Hurricane.’ A decision was made not to give it a name, because the media’s attention was still focused on the enormous damage and thus it was felt it could cause major confusion. The ‘Unnamed Hurricane’ brought a bizarre ending to one of the most massive Atlantic storms on record.
This redevelopment of hurricanes also happened in October, 1954. Hurricane Hazel first struck the Carolinas as a category four. (There are five categories with ‘five’ the most intense packing winds of 135 knots or greater). She merged with a low-pressure center to become a colossal extratropical storm that devastated Toronto, causing 76 deaths.
We have come a long way in forecasting their movement and understanding the complexity of these one eye monsters, and yet only Mother Nature herself knows where the curve balls she throws will land.
Doug Morris is an Air Canada pilot and has worked at the Canadian Hurricane Center in Halifax as a meteorologist.
Tired of your job? What about working on weather reconnaissance flights that fly into the eyes of hurricanes in the name of science and research? Known as Hurricane Hunters, NOAA (National Oceanic and Atmospheric Association) flies two P-3 Orions and the American air force reserve uses C-130 Hercules all laden with meteorological instruments compiling specifics of a storm and data for research.
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Here's the TAF for CYHZ. They have the winds up to 40 knots but straight down runway (14) ....for now. Yeah baby!
BECMG 0316/0318 20012KT
FM040300 20005KT P6SM SCT120 BKN200
BECMG 0404/0406 16012KT OVC006
FM040600 16012KT P6SM OVC006
BECMG 0408/0410 14020G30KT
FM041000 14020G40KT 1SM RA BR OVC003
RMK NXT FCST BY 031800Z=