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Over the weekend, Dorian became one of the most powerful Atlantic hurricanes on record. The deadly Category 5 storm made landfall at Elbow Cay in the Bahamas with sustained wind speeds of 185 miles per hour – that’s 300 km/h!
Dorian is now tied for second place with Gilbert (1988) and Wilma (2005) both coming in with sustained winds of 185 mph. Still topping the list is Allen (1980); the historically devastating storm produced sustained winds of 190 mph.
What took Dorian to that level? It’s never just one thing.
You need moist air, warm water and converging winds.
I want to talk about the water. Hurricane strength correlates with SST. Water vapour is the fuel of hurricanes, and high sea surface temperatures or SSTs, supply the water vapour to the hurricane’s heat engine. The SST must be at least 26.5 degrees down to a depth of at least 50 metres for a hurricane to form.
For hurricane forecasting, it can also be very useful to look at SST anomalies. An SST anomaly is the difference in the current SST measurement from the long-term average temperature for the given month, in a given place. Positive-temperature anomalies indicate the water is warmer than usual and negative anomalies indicate the water is cooler than usual. Today, the average sea surface temperature just off our coastline is about 17 degrees, but it’s showing a positive temperature anomaly; the average SST is three degrees above normal.
One more very interesting fact.
Less than 300 km south of Halifax, the SST is 26 degrees.
Ongoing monitoring of sea surface temperature (SST) revealed the world’s oceans warmed 0.5 C between 1970 and 2005. Because hurricanes rely on warm water to release heat into the upper atmosphere and create spiralling winds, any additional energy can result in increased intensity.
Warming ocean temperatures matter; it’s like adding fuel to a fire and taking the world, literally, by storm.
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Cindy Day is the chief meteorologist for SaltWire Network.