Your Reading List

Trying to understand Hurricane Dorian’s power

Dorian did not move like the typical hurricane

A man walks through the rubble in the aftermath of Hurricane Dorian on the Great Abaco island town of Marsh Harbour, Bahamas on Sept. 2.

As we head into fall, we move into that tough time of the year. You hope for perfect weather conditions, but with the dry year some regions have had, what’s perfect for some will be terrible for others. Recent rainfall is welcome in most pasture and haying areas, but for those wanting to get their crops off, the rain is causing nothing but problems. One of the bigger issues with fall rainfall is that with falling temperatures, decreasing daylight, and plant growth slowing to stopping, it takes an increasingly longer and longer time for the soil to dry out. With the chance of more significant rains over the next week or so, I will wait another issue or two before taking a deeper look at soil moisture levels across our region.

So, what weather topic do we delve into for this issue? Everyone must be pretty darned busy as I haven’t received any weather-related email questions for quite awhile now. It’s too early to talk about snow. That’s right, I said it: snow. We know it’s coming. We know winter will be here quicker than we would like, but I just can’t get myself to talk about snow yet. I am still waiting for a couple more long-range winter forecasts to come out, so the winter long-range article has to wait a little while longer as well.

On that note, I can’t help to point out that it seems like the geese have begun to migrate a little earlier than usual this year. I noticed several — well, more than several — flocks of geese heading south as early as the last weekend of August. Weather folklore tells us that early geese migration means an early, long, and hard winter ahead. If you know me, I’m not a huge believer in all the different weather folklore, but some of it does seem to have some truth. That said, I think we’ve all seen geese show up way too early in the spring, so if they can screw that up, I guess they can get the fall wrong too.

Record-long impact

Stepping back to look at the big weather picture, I think the biggest weather story so far this September has to be Hurricane Dorian. Now, I have never experienced a hurricane, but I have read a lot of different personal historical accounts of these events, and being a weather nerd I have spent a lot of time learning about them. I’m guessing most people who have grown up and lived on the Prairies have never experienced a hurricane, and after discussing this with several people I know, I believe most people really don’t understand just how bad a hurricane can be — even a weak hurricane.

To understand what a hurricane would be like, imagine the worst thunderstorm you have ever experienced. For most of us, that would probably be heavy rain, maybe even blinding rain, with winds gusting to just over 100 km/h, along with intense lightning and the threat of tornadoes. If we look at Hurricane Dorian as it hit the Bahamas as a high-end Category 5 hurricane, it had the same heavy rains and intense lightning — but you would need to triple the windspeed. That’s right, triple the windspeed! At its peak, Dorian’s winds were pushing 300 km/h. You might think you could imagine what that would be like, but you would probably be wrong.

When we are dealing with Prairie thunderstorms, the worst part of the storm usually lasts for 15 to 30 minutes. Sometimes, if the storm is really bad and slow moving, or we get training storms, we may see on-and-off severe conditions for an hour or two, but that is pretty rare. In a hurricane, under average conditions, these severe conditions will last from three to six hours. The trouble with Dorian was that it didn’t move like an average hurricane.

As Dorian moved toward the Bahamas the upper-level steering currents collapsed, which caused the hurricane to stall out right over the northern Bahamas. Hurricanes need a warm ocean to stay strong, and usually when they encounter land they start to weaken. The islands that make up the northern Bahamas were not big or mountainous enough to impact the hurricane, so it was able to maintain its strength. Now, imagine sitting on an island with heavy rain, intense lightning and winds gusting to nearly 300 km/h for hour after hour after hour. In fact, Dorian’s impact on the Bahamas broke the world record for the longest impact of a Category 5 hurricane on Earth. Grand Bahama Island experienced high-end Category 5 wind speeds for nearly 14 straight hours and experienced an astonishing 36 hours of hurricane wind speeds in excess of 180 km/h.

Again, imagine that worst thunderstorm, when you were sure your house might be blown apart as a few wind gusts hit maybe 120 km/h; now, make it much worse and have it last for over a day.

It doesn’t end there. While the wind and rainfall are bad enough, there is an even more devastating part of a hurricane: the storm surge. That’s a rise in ocean levels caused by the low atmospheric pressure above the storm, along with the winds and waves pushing and piling up the ocean water as it hits land. So, not only are the winds tearing everything apart from above, but now water, at levels as deep as two to six metres, is flowing through your property.

As I write this, the first images of the destruction Dorian has caused to the Bahamas are just coming in. The death toll is currently reported at 22, with estimates that it will dramatically rise as rescue workers start to arrive and begin working their way through the destruction. My thoughts and prayers go out to all involved.

About the author

Co-operator contributor

Daniel Bezte

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.



Stories from our other publications