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An unstable airmass brings showers & storms over northern, western & central WA. Humid & somewhat unstable onshore winds are delivering some storms to northeast QLD & showers to southeast & northeast NSW. Few gusty showers across TAS behind a cold front. Clear elsewhere.
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Today, 5:59AM UTC
Why has Hurricane Milton spawned tornadoes?
Hurricanes and tornadoes are two totally different types of weather phenomena involving swirling destructive winds – hurricanes on a macro scale, tornadoes on a micro scale – so why have the two occurred in unison as Hurricane Milton lashes Florida? The answer is that under the right conditions, hurricanes can produce exactly the type of extreme weather conditions which are conducive to tornado formation. A large tornado spawned by Hurricane #Milton was captured crossing I-95 in Fort Pierce, Florida on Wednesday. This was just one of more than 30 tornadoes to touch down in the state ahead of Milton's landfall. https://t.co/HkZB84Qqa6 pic.twitter.com/Hu4RjVRDPT — ABC7 News (@abc7newsbayarea) October 10, 2024 Hurricanes (which Australians call "cyclones" and are called "typhoons" in most of Asia) are large rotating low pressure systems formed over tropical or subtropical waters with maximum sustained wind speeds approaching or greatly exceeding 100 km/h. Hurricanes only form at sea, but as we know, their winds, rainfall, and storm surges can be devastating as they cross land. Even when a hurricane remains at sea, the storm surge from its winds can be devastating to coastal communities and can inundate low-lying land many kilometres inland. Tornadoes are violently rotating columns of air that reach the ground, usually attached to the base of a thunderstorm from which they are spawned. While often centred over a very small area no bigger than a football field, their winds can come close to 500 km/h – much more powerful than the strongest hurricane or tropical cyclone. Tornadoes, unlike hurricanes, can develop and dissipate extremely quickly. Also unlike hurricanes, they often form above land, and frequently form in temperate zones well beyond the tropics. They are particularly common in so-called “Tornado Alley” in America’s midwest. This is the Avenir neighborhood in Palm Beach Gardens, Florida. A powerful tornado passed through here earlier this evening in association with Hurricane #Milton's outer band thunderstorms. My mom lives in this neighborhood. Between forecasts tonight on @NTVNewsNL I was keeping… pic.twitter.com/FcwLUOERFb — Eddie Sheerr (@EddieSheerr) October 10, 2024 So hurricanes and tornadoes are two distinct types of dangerous weather, but as mentioned, they can also occur together, as we have seen with Hurricane Milton over the past 24 hours. How? Hurricanes contain many key ingredients for tornado formation – including plenty of heat, humidity and lightning. As hurricanes approach the coast, the friction with the land helps create the final key ingredient necessary for tornado formation: high wind shear (difference in wind speed). St Lucie County, about two hours north of Miami on Florida’s Atlantic Coast, was one of the areas devastated by tornadoes before Milton made landfall, with at least two confirmed deaths. "There were cars lifted and flipped upside down, moved hundreds of yards," County Sheriff Keith Pearson said. "I can tell you that there was nothing left to some of these places but foundations." Pearson estimated 100 residences were destroyed in the county after roughly 17 tornadoes touched down. Here in Australia, we rarely if ever hear of tornadoes being associated with tropical cyclones, although that doesn't mean it doesn't happen Weatherzone meteorologist Joel Pippard says that the isolation of much of northern Australia means that tornadoes might not be reported during tropical cyclone events. He also says that it's difficult to identify tornado damage when everything is flattened after a tropical cyclone. In heavily populated Florida, where so much footage has been taken of tornadoes in the past hours – and where in some cases the tornadoes touched down before Hurricane Milton made landfall – it has been horrifyingly clear to locals they are facing the prospect of two distinct disasters in one. Meanwhile Hurricane Milton has just been downgraded to a Category One system late on Monday afternoon (AEDT) as it tracks northeast over the city of Orlando, which is part of Florida’s third-largest urban area.
09 Oct 2024, 11:37PM UTC
Another round of storms impacting WA
Spring has been a stormy season for large areas of WA, with another few big storm days ahead in the Pilbara and Kimberley region. Merely a week ago, widespread thunderstorms lashed the interior of WA, with Weatherzone’s Total Lightning Network detecting 605,166 lightning strikes on Wednesday, October 2. Thunderstorms are again forecast over the coming days across northern Australia in response to a low pressure system and an unstable airmass and cloud band. The map below shows widespread lightning strikes already impacting northern WA and parts of the interior early Thursday morning, October 10. Image: Himawari-9 satellite image at 7:15am AWST on Thursday, October 10. Thunderstorms are set to continue over the next 48 hours over the Kimberley and Pilbara regions, particularly offshore and by the coast where a humid atmosphere is feeding the thunderstorms. These thunderstorms have the potential to grow into large thunderstorms bringing intense bursts of rain, small hail and gusty winds. The storms will be very slow moving due to weak steering flow with the potential for large totals in some areas. The cloudband during the next three days could bring widespread falls of 5 to 10mm to parts of WA, while isolated falls of 20 to 40mm could fall in thunderstorms. Image: Accumulated rainfall for the three days leading up to 8am on Saturday, October 12, according to ECMWF. Meanwhile a severe heatwave warning has been cancelled for parts of northern Australia after temperatures reached the 40s for several days. While the heatwave has passed its peak, maximum temperatures will reach the high 30s to low 40s on Thursday, before easing on Friday. Perth should also reach 30°C on Friday in response to warm northeasterly wind, before temperatures drop into the low 20s on the weekend. This heat combined with the low pressure trough and humidity is triggering these thunderstorms over the coming days. However, there is another factor behind the stormy start to spring, the unusually warm Sea Surface Temperatures (SSTs) offshore northern WA. Image: Sea Surface Temperature daily analysis for Tuesday, October 8. Source: BOM The waters offshore are around 1 to 2°C above average with some near shore waters reaching 3 to 4°C above average. The unusually warm oceans are injecting moisture laden air into WA, which is fueling the rain and storm activity that we have seen in recent weeks. This could help fuel thunderstorms in the coming months, bringing an above average risk of thunderstorms to WA. Thumbnail: @an.other.perspective/Instagram
09 Oct 2024, 5:32AM UTC
Giant hail and intense rain lash Qld, NSW
Severe thunderstorms have formed over parts of Qld and NSW this afternoon, with reports of hail around 7cm in diameter, intense rainfall and flooding and damaging winds. The combination of a surface and upper-level trough and moisture-laden easterly winds are triggering severe thunderstorms across southeastern Qld and northeastern NSW. The images below show the severe thunderstorms across the region on Wednesday afternoon. Image: Himawari-9 satellite image at 2pm AEST on Wednesday, October 9. This comes after severe thunderstorms lashed southeast Qld on Tuesday afternoon, bringing heavy rainfall to parts of Brisbane and the Sunshine Coast. On Wednesday afternoon severe thunderstorms developed across parts of NSW and Qld, with reports of giant hail and heavy rainfall: 7cm hailstones were observed north of Injune, Qld at around 1:20PM AEST. 35.6mm was recorded at Inverell in 30 minutes to 2:46pm. Intense rainfall and flooding in Southport, Qld has been reported Widespread falls of 50 to 70mm have been observed across southeast Qld and Northeast NSW in the past seven hours since 9am. Image: Rainfall observations for seven hours since 9am, Wednesday, October 9. As of 3:30pm, a severe thunderstorm warning is current for very dangerous storms which are likely to produce large, possibly giant hailstones and damaging winds across southern and central Qld. Over the border in NSW, a thunderstorm warning has been issued for heavy rainfall, large hailstones and damaging winds about the Northern Tablelands and North West Slopes. These thunderstorms have the potential to continue into Wednesday evening, before the risk eases in some areas on Thursday. While storms should clear NSW on Thursday, Qld could see severe thunderstorms develop in central and northeastern Qld on Thursday, with the potential for damaging wind gusts. Please keep an eye out for the latest warnings and forecasts as this activity unfolds.
Weather in Business
28 Aug 2024, 3:51AM UTC
Gales and crosswinds cause disruptions at Sydney Airport
Gale force west to northwesterly winds are creating havoc at Sydney airport on Wednesday afternoon, with all six landing and takeoff options impacted by very strong cross winds. Sydney airport saw gale force west to northwesterly mean wind speeds of 65km/h at 12:30pm, while the site has been gusting up to 82km/h. These winds are too strong for all three runways (six landing and takeoff options) to be used safely, airport traffic typically peaks during light winds. The image below shows that two of Sydney Airport’s parallel runways are orientated from north to south, and one single runway runs from west to east. Image: Sydney Airport runway orientation showing two parallel runways running north/south and one west/east, Source: Sydney Airport The west-east runway is the longest and can accept the largest aircraft, the A380. The gale force west to northwesterly winds on Wednesday are causing around 25 knots of crosswind on each of the six runway options. Image: Weatherzone’s cross wind calculator in our Aviation Dashboard showing cross wind or X wind of 24 to 25 knots. The term ‘crosswinds’ refers to winds that blow perpendicular to the runway, which can generate a significant lateral force on the aircraft, making it difficult for pilots to maintain a stable trajectory. The strong crosswinds can cause the plane to drift off course, posing a serious risk to both the aircraft and its passengers. Sydney Airport typically changes runways when there’s sustained crosswind gusts above 20 knots (37km/h). However, on Wednesday crosswinds are affecting all runways, meaning that aircraft are often opting to use the two north-south runways to increase traffic. This has meant that some flights have tried twice to land in these difficult conditions. It is very rare for crosswinds to impact all runways and therefore this event is causing significant disruptions at the airport on Wednesday. This event is not isolated to the Sydney area, numerous severe weather warnings for gales and damaging and/or destructive winds are in place across four states and the ACT, as a strong cold front lashes Tasmania and southeastern parts of the continent. So when will these winds die down? Conditions will ease somewhat by Wednesday evening, but not before the Sydney airport peak hour between 5 and 7pm. Winds will intensify again on Friday and into the weekend as further fronts whip through southern parts of the country.
23 Aug 2024, 5:01AM UTC
A great week for Tassie Hydro
Hundreds of millimetres of rainfall are forecast for western Tasmania in the next week, which will help replenish hydroelectric lakes in the region after some of the lowest rainfall on record. Hydropower is Tasmania’s main source of electricity, with frequent rain filling Tassie Hydro’s 54 major dams and feeding into 30 hydropower stations. In fact, during winter, the state usually exports electricity to Victoria, via the underwater Basslink. In summer, when it is usually drier, the state relies on the National Electricity Market (NEM) for a top up of power. Image: Hydroelectricity dam at Strathgordon in Tasmania According to Hydro Tasmania, they produce around 9000 gigawatts of clean renewable electricity from hydropower, enough to power 900,000 homes or businesses. The map below shows the catchments and power stations scattered across Tasmania; the largest lakes used for hydro are the Great Lake and Gordon-Pedder. The rain that falls in these catchments or dams is collected and used to generate electricity. Image: Hydro catchment areas. Source: Hydro Tasmania Usually, the west coast of Tasmania is the wettest due to prevailing westerly winds from cold fronts passing over the state, which tend to be blocked by vast mountains through central areas. During the past three months, unfortunately, this has not been the case for the west coast. Overall, the area has seen below average rain, reaching record lows in the far northwest, while the east coast saw average to above average rain. Image: Tasmania rain deciles between May 1 and July 31, 2024. Source: Bureau of Meteorology During July 2024, rain in western and central Tasmania was in the lowest 10% of Julys since 1900. The below average rain has affected water storage across western Tasmania, with some areas seeing record low or very much below average streamflow. The Great Lake was only 25.1% full by the end of July, which is a 10.4% decrease from the same time last year. Image: Streamflow decile categories for July 2024. Source: BOM The good news is that rain is on its way, with a complex low pressure system set to direct several cold fronts across the state in the coming week. Western Tasmania is forecast to see around 100 to 200mm of rain in the next 7 days, which could help fill up the western lakes, including the Gordon-Pedder. Eastern Tasmania, however, will see slightly less rain, with widespread falls of 30 to 50mm and isolated falls of 60 to 80mm. Image: Accumulated rain forecast for the next 7 days leading up to 10pm AEST on Thursday, August 29. Some of these totals will fall as snow as a cold airmass moves over the state from mid to late next week. Looking ahead, the rain should continue next Friday, August 30, and into the weekend as the low continues to linger over the region.