Queensland Flood Rivers, SEQ Storms, WA Fire | Australia weather Wed 28 Oct morning | Gus's Weather

Queensland Flood Rivers, SEQ Storms, WA Fire Risk - Wed 28 Oct

[c00_now_radar]

GUS G'day, I'm Gus, and this is your morning bulletin for Wednesday the 28th of October.

GUS It's about 6 am in Brisbane as you watch this, so here's what's happening across the country right now.

GUS On the model's simulated radar, not real radar, the biggest rain is out over the Tasman Sea, about 250 kilometres south-east of Newcastle, falling at up to 13.6 millimetres an hour with gusts to 34 kilometres an hour.

GUS There's a smaller patch inland, about 250 kilometres north of Roxby Downs in South Australia, with rain up to 2.9 millimetres an hour.

GUS On the actual satellite picture from half an hour ago, the coldest storm cloud tops are a long way offshore, over the Indian Ocean more than a thousand kilometres north-west of Broome, running as cold as minus 74 degrees.

GUS None of that is anywhere near a capital city, and no storm cloud is sitting over any capital right now.

[c00_now_radar]

GUS Before the forecast, the official warnings. The Bureau of Meteorology has a major flood warning out for the Condamine River downstream of Warwick, near Brisbane, as of 5:08 am Brisbane time.

GUS There's also a moderate flood warning for the Mary River around Gympie and Maryborough, also near Brisbane.

GUS And two severe heatwave warnings, one for the Tiwi and Arnhem districts near Darwin, and one for the Peninsula and Gulf Country in far north Queensland.

GUS For the full detail on any of those, check bom.gov.au.

GUS Today's big story is flooding on saturated Queensland rivers, with more storms possible over the outback and extreme fire danger building in the west. Everything in this bulletin is indexed in the description below, so jump straight to your city or your hazard.

[c01_verification]

GUS Quick check on yesterday's forecast before we get into today.

GUS In Brisbane we called the overnight low at 19.3 degrees; it actually got down to 19.8 degrees, spot on.

GUS Darwin was spot on too. Hobart was our miss, we said 2.9 degrees and it only fell to 5.8 degrees, so we were 2.9 degrees too cold there.

GUS Over the last week we've got 36 of 45 temperature calls within 2 degrees, and 37 of 47 rain calls right. Nationally the models caught actual rain events about 96 per cent of the time, which is why we lean on them heavily.

[c02_mslp_fronts]

GUS Here's the pattern that set up today, from overnight.

GUS High pressure systems, where air sinks and skies stay clear, sit over the Southern Ocean south of Albany at 1027 hectopascals, and over the Great Australian Bight at a similar 1027 hectopascals.

GUS A low of 1008 hectopascals sits over central Western Australia, south of Newman.

GUS Running between them is a trough, think of it as a long dent in the pressure pattern, stretching over 2500 kilometres from south-east Western Australia through South Australia to the Tasman Sea near Wollongong.

GUS That trough is the engine pulling moisture south and setting up today's storms out in the outback.

[c03_upper_500]

GUS Now let's look higher up, at the winds a few kilometres above us.

GUS There are a few cold pockets of spin up there, called cutoff lows, sitting over central Victoria, over the Indian Ocean north-west of Geraldton, and over the Bight.

GUS Higher still, about ten kilometres up, is a fast ribbon of wind called the jet stream, and today it's howling along at 240 kilometres an hour over northern South Australia.

GUS That fast air helps organise the storms forming underneath it, especially out near the Northern Territory border.

[c06_pwat]

GUS Let's zoom into south-east Queensland, near the marker just north-east of Hervey Bay.

GUS The air near the ground there is muggy, with a dew point of 22.3 degrees, that's the temperature air needs to cool to before it starts dripping like a cold drink can.

GUS Stack up all the moisture in the air above that spot and squeeze it out, you'd get 45.6 millimetres of water, meteorologists call that precipitable water, and it's a tropical-sized number.

GUS Across Queensland as a whole the ground is only moderately wet on average, but down here in the south-east it's running wet to saturated, like a sponge that's nearly full.

GUS That's exactly why new rain runs straight off into the rivers instead of soaking in, and why the Mary and Condamine are already in flood.

[c07_cape]

GUS Meteorologists measure the energy a storm can feed on, think of it like petrol in the tank, forecasters call it CAPE.

GUS Near the marker north-east of Hervey Bay there's about 1234 joules per kilogram of it, a decent tank for October.

GUS The cap, the layer of warm air aloft that normally stops storms firing like a lid on a pot, is basically non-existent here, just minus 5 joules per kilogram.

GUS With next to no lid and cloud bases only 136 metres up, storms are already able to get going this morning.

[c11_shear]

GUS How organised will these storms be? That depends on shear, how much the wind changes speed and direction as you go up.

GUS Through the lowest six kilometres here it's about 66 kilometres an hour, modest for this part of the world.

GUS That's not enough to build well organised rotating storms, so expect clusters of multicell storms rather than anything more structured.

GUS The risk with these is less about any single violent storm and more about dumping heavy rain on ground that's already full.

[c12_index_map]

GUS Let's jump out to the southern Northern Territory, about 250 kilometres south-west of Alice Springs.

GUS Forecasters combine energy, spin and shear into one number called the Supercell Composite. Here it's a supercell value of about 5, which is high.

GUS There's also a hail index pointing to a moderate to high chance of large hail if a storm holds together, maybe big enough to dent a car.

GUS This is guidance about the environment, not a guaranteed hail forecast, so treat it as a heads up rather than a certainty.

GUS Across the country there are also patches meeting the bar for storms that can start to spin near the ground, about 88 of them on the model, mostly out here, not near the coast.

[c13_index_map]

GUS Despite that high supercell number, a second index that looks specifically at spin near the ground is basically nothing here.

GUS Picture a spinning top, the air just above the ground isn't turning much, so even a strong storm up top is unlikely to develop that low-level spin.

GUS There's also enough energy here, and over the Great Victoria Desert hotspot further south, to drive sharp downward bursts of wind, so damaging gusts are the main worry, not rotation near the ground.

[c15_index_map]

GUS Let's look ahead to Thursday afternoon over the Nullarbor in Western Australia, near Eucla.

GUS Forecasters rate fire danger with an index called FFDI. By Thursday afternoon it reaches about 62, which is severe.

GUS Part of that comes from a drought factor of 9.2, how dried-out the fuel is, and that's measured from the actual rainfall records there, not assumed.

GUS A patch further south-west hits an even higher 77, extreme, and a wind change is due through there too, swinging direction by almost 100 degrees and dropping the temperature a few degrees.

GUS If a fire starts out there on Thursday, that wind change could turn a flank into a new front very quickly.

[c18_model_compare]

GUS Let's see whether the models agree on how much rain falls near Hervey Bay by tonight.

GUS The American GFS has 18.6 millimetres, the European model 14.8 millimetres, and the European AI model 21.5 millimetres, all in the same ballpark.

GUS That's good agreement, with most of the ensemble landing close together.

GUS Zoom out to the whole of Queensland and the average drops to 3 to 5 millimetres state-wide, but some spots still reach past 50 millimetres, so this rain is patchy, not blanket.

GUS Patchy or not, it's falling on catchments that are already running high.

[c17_ens_prob]

GUS Here's the chance of further heavy rain near Hervey Bay between this evening and Thursday morning.

GUS The ensemble gives about a 76 per cent chance of at least 10 millimetres, and roughly a one in five chance of 25 millimetres or more.

GUS On ground that's already wet to saturated, even that lower-end rain adds up quickly in the rivers.

GUS Keep an eye on the Mary and Condamine catchments through Thursday.

[c20_town_table]

GUS Quick lap of the capitals for today.

GUS Brisbane, hot and sticky, 28.8 degrees with showers likely, about 9.2 millimetres. Sydney milder at 24.6 degrees with a little rain.

GUS Melbourne 17 degrees, Canberra 19.3 degrees, Hobart 16 degrees, Adelaide 18.6 degrees, all mostly dry.

GUS Perth 25.9 degrees and breezy. Darwin swelters at 33.4 degrees under that heatwave warning we mentioned earlier.

[c90_events]

GUS A look ahead to some of the big outdoor events this week.

GUS Victoria Derby Day at Flemington on Saturday is forecast about 19 degrees with 16 millimetres of rain, bring a coat and expect the track to soften up.

GUS Seasons Halloween in Perth's Wellington Square, also Saturday, has about 5 millimetres forecast, nothing major but pack a light jacket.

GUS Sculpture by the Sea opens today in Sydney and runs over a week, with only about 1 millimetre forecast across that run, kind weather for the hundreds of thousands expected to walk it.

GUS Most other events this week, including the Rugby League World Cup matches, look to have low weather impact.

[c19_plume]

GUS So how confident am I in all this? I'd call it a high confidence day for us.

GUS We're very sure about the quiet patch over the Great Victoria Desert and a couple of the drier hotspots, better than 90 per cent agreement on timing there.

GUS The least certain spot is the southern Northern Territory, where the American, European and European AI models still differ by more than 10 millimetres on rainfall two days out.

GUS If that spread closes up, I'll have a tighter number for you this afternoon.

[c20_town_table]

GUS That's the morning bulletin. For the official warnings on flooding or heatwaves, always check bom.gov.au.

GUS I'm back this afternoon with the next bulletin.

GUS If you've got a weather question, pop it in the comments and I'll get to as many as I can during the day.

GUS Subscribe if this helped, it helps the channel, and I'll see you next time.

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