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A front is bringing gusty winds, a cool change & patchy rain to northern SA & NSW & brisk winds & showers to VIC, TAS & southern SA. Moist, showery winds are affecting the tropical QLD coast. A high is clearing skies in WA & is keeping much of the remainder of the country dry.
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Today, 5:25AM UTC
Very warm September morning for parts of NSW
A trough and cold front dragged warm air across NSW and Vic on Friday causing daytime maximum temperatures to soar more than 10 degrees above the mean for some areas. Image: Difference from average of maximum temperatures for 6th September. Source: BOM The trough moved across Vic and southern NSW overnight, bringing rain and a few rumbles of thunder and flashes of lightning. The warm air to the northeast of the trough helped overnight temperatures stay elevated for parts of NSW. Image: Himawari-9 infrared satellite imagery, BOM radar, Weatherzone lightning, and observed temperatures at midnight 7th September. It was particularly warm compared to average between the Shoalhaven and the Hunter. It was the warmest September morning in: At least 25 years at Albion Park (18°C) 21 years at Cessnock Airport (18.9°C) 7 years at Newcastle (19.6°C recorded at Nobbys signal station) 4 years at Sydney Harbour (19.5°C) 4 years at Bankstown (15.4°C) Although these places experienced a warm night, and even though today is still a warm day by September standards, a cool change moving up the NSW coast is preventing some places from seeing the highs of yesterday. For example, Sydney reached 29.7°C yesterday (nearly 10 degrees above average) but as of about 3pm today has only reached 25.5°C (still 5 degrees above average). The warm air from northwest and central Australia that has been dragged to the southeast by fronts and troughs should linger through the next week or so but there are signs of a cool down around the middle of this month as cold air may be drawn up from the Southern Ocean. Image: European model forecast (ECMWF) of 2-metre temperature difference from average for 10am Monday 16th. Further ahead, with La Nina like conditions currently developing, and increasing the chances of wetter conditions in the east and north of the country later in spring and summer, daytime highs in NSW may be moderated by cloud and rain but overnight lows will be warmer. This can be seen in the latest forecast from the European Seasonal model released overnight. Image: European forecast for monthly maximum temperature anomaly for November. Image: European forecast for monthly minimum temperature anomaly for November.
06 Sep 2024, 8:33PM UTC
The long road to the World Surf League finals
The world surfing tour final is underway in California, with three Australians in the draw for the world championship, but not just these surfers have made the long travel to the northern hemisphere. Trestles, in southern California, is the home of the World Surf League finals. This is the showdown that concludes the world tour championships, with the best five surfers in the rankings battling it out to crown the world champion for that year. The three Australians that went into this finals showdown are Jack Robinson, Ethan Ewing and Molly Picklum, sitting in either fourth or third place. Sadly, our Aussies were later eliminated. During the northern hemisphere summer, Californian surfers often find themselves relying on storms from Australian and New Zealand latitudes, more than 8,000 or 9,000 kilometres away, to bring them surf. Powerful storms that move across the roaring forties, brushing past Australian and New Zealand, generate very large seas. These waves propagate away from the storm area, migrating northwards as swell. As the swell travels the length of the globe, the size decreases, but the period increases, maintaining roughly the same amount of overall energy. The long period swells that California (and much of North and Central America) receive often travel more than 10 days after being generated before breaking on the distant shores. Figure 1: ASCAT satellite data showing a Southern Ocean storm blowing gales directed towards the northern hemisphere in late August. (NOAA) The figure above shows ASCAT wind data, which is collected by a satellite measuring the “roughness” of the ocean as the wind blows over it. The figure shows a vigorous Southern Ocean storm blowing gales well to the east of New Zealand, over a week and a half ago, on August 28th. This satellite data is also just a momentary image of the storm, but satellite imagery looped of the day shows the storm tracking northwards, a positive sign for a more powerful swell. Wave heights generated by the storm of around 8 metres will have decayed on the long journey north, arriving in Southern California from the south-southwest around the 1 metre mark, with the period having grown to about 15-17 seconds. Taking about 10 days to reach Trestles, this conveniently had the swell filling in yesterday, the day before the first day of the competition window, which runs between September 6th and 14th. Figure 2: Swell window and optimal winds for Trestles surf spot in Southern California. (Google Maps). Conditions have been favourable this morning as Southern California swelters through a string of hot summer days, with light winds and clean head high waves rolling through. As of writing this, both surfers starting in the number 5 seed—Tatiana Weston-Webb on the women’s side and Italo Ferreira on the men’s—have made an impressive run of wins, reaching match 3 and defeating all the Australians in the draw. Tatiana succumbed in her match 3 to defending world champion Carolina Marks, setting up an all-American title match on the women’s side. Italo defeated the Californian Griffin Colapinto, sending him into the title match from the lowest finals day starting seed. A weak seabreeze has been strengthening over the coast but the surface conditions remain mostly smooth into the title matches.
06 Sep 2024, 1:59AM UTC
Why Melbourne hit 21°C at 3am last night
Melbourne saw an unusual spike in temperature last night when the mercury jumped to 21°C at 3am, making the middle of the night feel warmer than an average spring day. Thursday night started off warm for this time of year as light northerly winds had the temperature sitting on 16°C at 10pm. The mercury then cooled to 14°C by midnight, which is about 6°C above the average minimum temperature at this time of year. A surge of northerly winds then brought much warmer air into the city from central Victoria. By 3am Melbourne’s temperature had shot up to 21°C, a jump of more than 6°C in under three hours. Image: Northerly winds over central Vic at 4am AEST on Friday, carrying warm inland air towards Melbourne. It’s rare to see overnight temperatures exceeding 20°C in Melbourne at this time of year: The city’s average minimum temperature in September is 8°C It’s average daytime maximum temperature in September is 17°C The warmest September night on record for Melbourne had a minimum temperature of 20.5°C Image: Temperature observations in Melbourne during Thursday night and Friday morning, showing abrupt warming between midnight and 3am. Melbourne has remained warm throughout Friday morning, although cooler southwesterly winds and showers will drop the temperature in the afternoon following the passage of a cold front. Damaging winds are also likely to affect parts of eastern Vic on Friday ahead of this cold front, so be sure to check the latest severe weather warnings throughout the afternoon.
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.