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Uesi now an Ex-tropical cyclone, but it's named for a reason - WeatherWatch

Contributor:
Fuseworks Media
Fuseworks Media

Uesi is no longer a tropical cyclone, it's now an extra-tropical cyclone as it moves over the Tasman Sea - but that doesn't mean it's weakening much.

Despite the technical change, which sees tropical air that fuelled the once tropical cyclone replaced with 'cooler' air from the New Zealand / Tasman Sea area, Uesi is named for a reason - it's still a storm of significance.

The technical change helps "unwind" the tightly packed centre of the storm, says WeatherWatch.co.nz head forecaster Philip Duncan. "The centre of the cyclone switches from a perfect circle to a more egg shaped low, while the tightly packed isobars around it spread out further". Mr Duncan says it's a bit like having a river going from a screaming Huka Falls to a larger, slower, bigger, Waikato River.

"But extra-tropical storms are well known for becoming even bigger than their tropical alter ego". In fact just the other day "Storm Ciara", an extra-tropical cyclone, helped make a British Airways 747 smash the record for quickest subsonic flight ever recorded on a trip from New York to London.

"Ex-cyclone Uesi is still a very serious storm. Air pressure maps show central air pressure in the 970hPa range today and again when it reaches the South Island on Sunday, in weather nerd talk that is a deep low that can cause flooding, slips and some wind damage". Mr Duncan says trampers, campers, those in campervans travelling the lower south western South Island all should be on high alert for the risk of road closures, flooding and slips.

But the big positive is that the storm is headed for the most remote, least populated, part of New Zealand. "Fiordland, one of the wettest places on earth, will likely take the brunt of this storm. Some people find that odd that our southern most region gets a tropical low first, but when you look at a map Fiordland and Westland are also our most western regions, so a storm dropping straight from north to south often hits Fiordland/Westland first" says Duncan.

Southland and Otago, recently in a historic summer flood, will be watching this tropical low closely as it merges with a southerly bringing in rain at the same time. "We do expect more widespread rain again in Southland and parts of Otago, but for locals using www.RuralWewather.co.nz to calculate local rainfall totals, we expect far fewer worries and issues. We also expect the waterways to better manage this system based on the high level local IBM data we use".

The remnants of Uesi may well linger from Sunday to Wednesday in the New Zealand area, then high pressure again takes control.

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