What is a stingjet? Is the safest place really in the eye of the storm? And who would call a cyclone ‘Gabrielle’ anyway?
Follow the latest updates on Cyclone Gabrielle here.
What makes a cyclone a cyclone?
A cyclone is a generic term for a low pressure system with wind rotating around the centre in a cyclonic manner. “In the southern hemisphere, those winds rotate clockwise,” confirms MetService meteorologist Lewis Ferris.
What’s the difference between a hurricane and a tropical cyclone?
Nothing. “North Americans call them hurricanes. We call them tropical cyclones,” says Ferris. “There we go.”
So what’s the difference between a cyclone and a tropical cyclone?
It’s all to do with what’s fuelling it. “A tropical cyclone is what forms in the tropics, hence the name,” says Ferris. “Tropical cyclones exist over warm water. That warm water provides a lot of heat and moisture which means there’s a lot of upward movement. That convection, and thunderstorms, is what can act to lower the pressure of the tropical cyclone. So the lower the pressure, the more intense it is.” That’s why North Island residents are being told to, “Do what you can. Right now,” to prepare.
Is Gabrielle a cyclone or a tropical cyclone then?
It was tropical but it’s not anymore. “It doesn’t have that warm water at the bottom fuelling it,” says Ferris. Instead, it’s now being powered by the jet stream (winds well above the surface). Ferris says that’s happening about 10 kilometres above us. “That is what is creating, or deepening, the cyclone,” he says. Whatever you do, don’t call it an “ex” tropical cyclone, cautions Ferris. “That’s just too confusing.”
People keep using the term “stingjet”. What is that?
Stingjets are small pockets of very intense winds. “They originate above the ground but there’s the potential that they make their way down to a surface level where they can actually affect people,” says Ferris. “In low pressure systems like this we might see some localised areas get more affected by wind than other areas. That could be associated with a stingjet.” But again, be careful how you use that term. If a plastic bag is being blown around in confusing directions in your driveway, don’t call it a stingjet just yet. “It’s hard to prove that in retrospect,” says Ferris.
Is the safest place really in the eye of the storm?
Yes. But that doesn’t mean you should seek it out. “In a low pressure system, right in the centre there is not much wind and not much rain,” confirms Ferris. “It will be relatively calm near the middle.” Don’t make like Helen Hunt in Twister and go out looking for it. If you miss the middle, you’re going to get pummelled by the cyclone’s most powerful winds. “I’m not suggesting anyone gets out on their boat. There’ll be really hectic marine conditions right now,” says Ferris.
So who named this one “Gabrielle”?
That would be the Australian Bureau of Meteorology. It formed in their patch, so they get naming rights.
How does a tropical cyclone end? Does it just blow itself out?
Sort of. “It’s energy,” says Ferris. “It’s a rapidly rotating column of air. That doesn’t just happen. Something needs to be fueling that. At the moment it’s what’s happening well above the surface. That rising air as lowers the pressure at the surface where we live. It will begin to fall, then the pressure at the surface will start to rise, which means the winds will drop off.” Can you say it spins itself out? “I guess you can,” says Ferris, “but that’s not how I would describe it”.
Once Cyclone Gabrielle has passed across New Zealand, could it reinvigorate itself and swing past us again?
It could, but it’s unlikely. “Systems behave differently,” says Ferris. “This one we’re looking to see peak intensity overnight. By Tuesday, things start to ease off and then on Thursday it moves away from our shores.” Once Gabrielle leaves the conditions would need to be right for it to be reinvigorated. “In our part of the world low pressure systems tend to move eastwards so although not physically impossible that it could recurve back toward us, it would be very unusual.”
Find out how to prepare for Cyclone Gabrielle here.