Demonstrating why a hurricane’s forward speed matters
The rapid forward speed of Hurricane Elsa the past several days has been a noticeable statistic anyone following the storm’s movement has surely noticed. In the last two days, Elsa’s been racing across the ocean anywhere from 25 to 30 mph.
When we talk about forward speed, we’re looking at how fast the entire storm system is moving across the map. We’re not talking about the winds around the storm, as they’re much faster (gusting up to 86 mph in Barbados on Friday morning for example).
So when looking at just the forward speed, if Elsa had a speedometer like your car does, it’d be telling us the storm is moving west-northwestward as fast as 30 mph the past two days. For a tropical system, that’s the equivalent of driving above the speed limit on I-75.
Typically, an average forward speed for a system in the tropical Atlantic is between 10 and 15 mph.
So the forward speed of 25 to 30 mph like Elsa has been doing makes it an exceptionally fast-mover.
This fast forward motion influenced the impacts Elsa brought to places like Barbados today which experienced hurricane weather conditions this morning, but only for a relatively short period of time because of how fast Elsa was speeding across the ocean.
The relationship between impacts and forward speed is fairly straightforward. In most situations, fast-moving storms (like Elsa) drop less rainfall and produce less storm surge than slow-moving storms. The reason why?
Fast-moving storms are physically over a location for a shorter period of time than slow-moving storms, so they have less time to drop rain over any one particular location.
Like the connection with rainfall, slow-moving storms have more time to collect and push water around to generate deeper and more impactful storm surge amounts.
So though it’s never good to be hit by a tropical storm or hurricane, if you have to be, you’re better off if it’s a fast-moving storm instead of being slow-moving or stationary.
To visualize how rain amounts can vary between fast-moving and slow-moving storms, picture a watering can like you’d use to water a garden.
If you were to move a watering can over an area quickly you’ll drop water from it, but not as much would fall when you compare what would happen when you slowly move a watering can over an area.
This works just like a storm does when producing rain: the faster they move, the less water falls and the slower they move, the more water falls.
A good example when discussing forward speed would be looking at a few storms in history.
Hurricanes Dorian, Harvey, and Florence for instance were all very slow-moving storms.
At one point or another in their lifespans, they were in some cases completely stationary.
This is why Harvey and Florence were able to produce such dramatic rain totals in Texas and North Carolina.
It’s also why Dorian was able to produce so much storm surge on the Bahamas.
None of these storms were in a hurry so they had abundant time to drop heavy rain for long stretches of time and in Dorian’s case push extreme amounts of water on land in the form of storm surge (topping 15 feet in some areas).
It’s important here to say though fast-moving storms might end up producing less storm surge and drop less rain compared to slower-moving storms, fast-moving storms still cause extreme wind damage.
On Friday Elsa caused a lot of wind damage to homes in Barbados where measured wind gusts shot up to 86 mph even though it wasn’t over the island for very long.
Hurricane Charley that hit Charlotte County in 2004 was also a very rapid-moving storm with a fast forward-motion but produced catastrophic damage in the county with Category 4 force winds.
The NBC2 team of meteorologists will continue monitoring Hurricane Elsa and all the twists and turns it takes this weekend. Read up on the latest with the storm here.
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