How do hurricanes form? A lesson from the science behind the storm

What are hurricanes?

Hurricanes are part of a family of storms known as tropical cyclones — storms which rotate quickly around a low-pressure centre and create heavy rain and powerful winds. If one of those storms strikes a sustained top end speed of 119 kilometres an hour and looks in the Atlantic or eastern North Pacific, it qualifies as a hurricane. (Much like storms in the western North Pacific are known as typhoons.) The Saffir-Simpson storm wind scale extends from there, through to Category 5, which has no ceiling and signifies storms with wind speeds greater than 252 km/h. Anything from Category 3 and up is a “major” hurricane.

How do hurricanes form?

Hurricanes begin as atmospheric disturbances across the tropical waters due west of Africa near the Cape Verde islands. Typically, when sea-surface temperatures are over 26.5 C, water vapour in the sea condenses and releases heat, which increases and creates an inward motion of air. The air starts to spiral toward the middle of the disturbance, which graduates to a tropical depression and then a tropical storm. So long as winds in the upper air do not create a shear force to interrupt the system, it may increase in breadth and height until it reaches hurricane status, gaining strength as it moves westward toward the Caribbean and picking up energy from the warm Atlantic waters.

How can they cause harm?

Hurricanes can lead to damage in one of three chief ways: rain, wind and storm surge. Since they produce eye-popping wind-speed amounts, and are most often measured that way, whipping winds are possibly the most common risk associated with hurricanes. However, Hurricane Harvey, which devastated Houston and environs in late August, really did its damage by hovering over town and unloading trillions of gallons of rain onto it. In 2012, Hurricane Sandy had shrunk into a post-tropical cyclone by the time it hit New York State and New Jersey. Storm surge did a lot of the damage in these countries, reaching almost eight feet on the Jersey Shore. The phenomenon, which Princeton University climate scientist Gabriel Vecchi likened to a “wall of water” from the sea, is generated by a variety of factors, including the strength of winds pushing water toward the shore. In Irma’s case, of the three kinds of hurricane damage, “it’s probably not clear that one will be worst, just because they’re going to be very bad,” said Bob Robichaud, a meteorologist at the Canadian Hurricane Centre in Dartmouth.

How are their paths prediction — and how correctly?

The paths of hurricanes are easier to forecast than their intensity, which will be inconsistent and variable, said Tom Knutson, a research meteorologist with the U.S. National Oceanic and Atmospheric Administration. Better data feeding into the mathematical models used to monitor storms have helped. So has enhanced jet technologies, allowing planes to scale and circumnavigate hurricanes, Mr. Robichaud said. Each year, hurricane tracking improves just a little bit. Nonetheless, it remains uneven: 24 hours the models may only show to inside a 100-km range at which the middle of the storm will be. And the effectiveness of monitoring depends on whose versions are used: In 2012, the European Centre for Medium-Range Weather Forecasts in Reading, England, predicted Sandy would turn to New Jersey, while the U.S. National Weather Service didn’t.

What danger does Canada face from hurricanes?

Once Irma strikes the Florida peninsula, it’s now projected to go northward along a line that roughly parallels U.S. Interstate 75 through Georgia and Kentucky. Cut away from warm water, it will quickly weaken. By next week, it might turn into a mid-latitude storm that brings rain to Ontario and Quebec. Of greater concern to Canada are hurricanes which directly strike the Atlantic states while coming in off the sea full force, such as Hurricane Igor, which hammered Newfoundland in 2010. A similar risk is posed by hurricanes that hit the U.S. mid-Atlantic area and cross the comparatively short distance over Pennsylvania to reach Southern Ontario. This is what happened in 1954 when Hurricane Hazel famously devastated Toronto, asserting 81 lives, most due to flooding.

Is climate change making hurricanes more powerful or more frequent?

This is a tricky question, because contemporary hurricane science dates back only a few decades, to the advent of meteorological satellites. A warming climate surely will bring climbing sea-surface temperatures, which might extend hurricane seasons on a more regular basis. There’s also some evidence that a warming climate will gradually create the most intense hurricanes more so, even though it isn’t clear yet if this change can be observed. Nowadays, global climate models, which are utilised to examine how the atmosphere behaves over hundreds of kilometres, are normally unable to say much that’s definitive about hurricanes. “As we move to higher resolution in the future, we will be able to better reflect hurricanes in our models,” state Nathan Gillett, manager of the Canadian Centre for Climate Modelling and Analysis in Victoria. What is somewhat more certain is that climate change will mean increased rainfall from hurricanes and more critical storm surges along coastlines because of sea-level rise.

Courtesy: The Globe And Mail

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