Technically, Dorian was done as a hurricane when it landed on P.E.I., but as a post-tropical storm it was still more damaging than 2003’s Hurricane Juan.
“Under the right conditions, post-tropical storms can produce hurricane-strength winds,” said CBC meteorologist Jay Scotland.
“Dorian serves as a good example that the difference between a hurricane and a post-tropical storm is more about the storm’s structure and not its intensity.”
Hurricanes are defined partly by wind speeds, but mainly by their structure. They pull energy from warm ocean water, and from space, a distinctive saw-blade shape can be seen. They lose that structure when they become post-tropical storms, and become fuelled more by temperature and pressure difference as warm and cold air masses come together, much like a nor’easter.
But in Dorian’s case, while the structure was gone, the storm picked up energy from another system moving in from the west. Winds grew to hurricane strength, and the storm was spread out over a larger area than Hurricane Juan.
“The result was much higher rainfall and more widespread destructive winds across the Island with Dorian compared to Juan,” said Scotland.
Hurricane Juan was mainly an issue in Queens County, and Charlottetown was particularly hard-hit. The maximum wind gust in the capital was 139 km/h.
But none of the other main stations on the Island saw wind gusts over 100 km/h. By comparison, almost all areas of the Island saw triple-digit winds, and there was much more rain with Dorian.
The difference in the two storms was particularly evident in Summerside. Juan brought a peak gust of just 83 km/h and 22.1 millimetres of rain, while Dorian dumped about 90 millimetres of rain and produced a peak gust of 115 km/h.
Lessons from Hurricane Juan
Another key difference between Juan and Dorian is changes in technology and in practices at Environment Canada in the intervening 16 years.
Last Friday evening, most Islanders knew there was a hurricane warning for Nova Scotia and a tropical storm warning for Prince Edward Island. That was not the case the night before Hurricane Juan struck, because there was no such thing in Canada.
That changed as a direct result of Juan, said Bob Robichaud, a meteorologist at the Canadian Hurricane Centre.
“We didn’t have the capability to issue, for instance, a tropical storm or hurricane watch or warning,” said Robichaud.
“That’s one of the things that we had learned from Juan, was people said, ‘Yeah, you told us there was going to be a storm you just really didn’t emphasize it enough.’ So we didn’t have that capability to do that because we never figured that we would need to.”
In 2003, people went to bed on Sept. 28 with a wind warning in effect, something that is not uncommon at the end of September and into October on P.E.I.
Robichaud said those warnings would have mentioned wind speeds of up to 120 km/h, but that information was coming at people differently in 2003. They might have fired up the desktop and loaded a web page to see the full warning, but it is more likely they heard it on the radio. Maybe they didn’t pay attention to the whole warning, or maybe the broadcaster didn’t read the whole thing at the time the person happened to be listening.
“Now we have an app where that gets highlighted. As soon as you get on there it gets highlighted,” said Robichaud.
So if you missed the details on the radio, you can get them on your phone.
Another change, that was in the process of being implemented in 2003, is Environment Canada now has meteorologists that work directly with Emergency Measures Organizations in the provinces to help prepare for storms.
Forecasting, said Robichaud, has also improved.
“If we look at some of the track errors, say at 24 hours out, the average track error back in 2003 was 133 kilometres,” he said.
“The track errors for a 24-hour position now are 76 kilometres. So that cone [of uncertainty] is about 30 per cent smaller than it was back in 2003, meaning that we’re much better at predicting the track of these storms.”
With meteorologists working directly with EMO, better forecasting, and improved methods for getting the message out, it is much easier now to make sure everybody is ready when a hurricane comes.