Flood warnings, severe storms and fire | Australia weather Wed 28 Oct afternoon | Gus's Weather

Flood warnings, severe storms and fire danger in Queensland and the NT

[c00_now_radar]

GUS G'day, I'm Gus. This is the Wednesday 28 October afternoon bulletin, and it is about 4 pm in Brisbane at the time this is uploaded.

GUS We start with this hour because storms are moving quickly and you need to know what is happening now.

GUS On the model's simulated radar, the busiest cell is just north of Hervey Bay with rain at up to 41.5 millimetres an hour and gusts near 52 kilometres an hour.

GUS See the Blackwater marker, where rain is 34.3 millimetres an hour and gusts are 49 kilometres an hour.

GUS Another cell sits about 90 kilometres south of Alice Springs, with 18.9 millimetres an hour and gusts near 55 kilometres an hour.

GUS The observed Himawari satellite, not a model, sees deep storm cloud near Darwin, Katherine and Kununurra, and Darwin is the only capital with storm cloud nearby.

GUS The Bureau has severe thunderstorm warnings out for Capricornia and the Central Highlands, plus Simpson, Lasseter and Tanami, and moderate flood warnings on the Condamine and Warrego rivers as of 3:05 pm Brisbane time.

GUS If you're in a hurry, you can jump to the part you want from the chapters in the description.

[c01_verification]

GUS We look back at yesterday first, so you can judge how far to trust today's forecast.

GUS For Tuesday's overnight lows, most capitals were close.

GUS Brisbane was spot on: we said 19.3 degrees, the gauge read 19.8.

GUS Hobart was the miss: we said 2.9 degrees, the gauge read 5.8.

GUS Rain calls over the last seven days were right 37 times out of 47.

GUS That is good, but patchy storms still caught out a few inland Queensland towns.

[c02_mslp_fronts]

GUS Here is the big picture at the start of the day.

GUS Sea-level pressure tells us where the large wind systems sit.

GUS The lines are isobars, and when they sit close together the wind is stronger.

GUS A high of 1026.9 hectopascals sits over the Great Australian Bight.

GUS A low of 1006.3 hectopascals sits over western Western Australia, about 250 kilometres north of Geraldton.

GUS Another high of 1020.1 hectopascals sits east of Norfolk Island.

GUS The low and the upper trough are the two features that will steer today's storms.

[c03_upper_500]

GUS Next we look at the upper chart, around 5000 metres above the ground, because it steers the surface systems.

GUS A cold upper low sits about 200 kilometres north of Geraldton.

GUS Another upper low sits over the Tasman Sea, about 160 kilometres south of Sydney.

GUS An upper trough stretches from the Nullarbor to the Tasman Sea.

GUS The jet stream over the Southern Ocean reaches 252 kilometres an hour.

GUS That jet energy helps lift and strengthen storms to the north of it.

[c06_dewpoint]

GUS Now we check moisture, because storms need water vapour to build.

GUS Dewpoint is the temperature air has to cool to before dew forms; higher numbers mean stickier, wetter air.

GUS See the marker south-west of Rockhampton: the dewpoint is about 20 degrees Celsius.

GUS That is plenty of low-level moisture.

GUS Further north near the Gulf Country the dewpoint is about 25 degrees Celsius.

GUS With this kind of moisture, any storm that forms can drop very heavy rain.

[c07_pwat]

GUS This chart shows precipitable water, which is how much water a storm can wring out.

GUS Think of it as the depth of water you would get if you squeezed every drop of vapour out of a column of air.

GUS Near Rockhampton it is about 47 millimetres.

GUS Near Tennant Creek it is even higher at about 53 millimetres.

GUS This is a very moist airmass, so rainfall rates can be intense.

[c08_cape]

GUS Next we check storm energy.

GUS Forecasters call it CAPE, and it is the energy stored in warm, moist air.

GUS Think of it like petrol in a storm's tank.

GUS Near Rockhampton this afternoon there is about 1100 joules per kilogram.

GUS For late October that is enough to build tall thunderstorms.

GUS The Gulf Country later sees about 2280 joules per kilogram, a much fuller tank.

[c10_skewt]

GUS This is a model sounding, a core sample through the air above south-west of Rockhampton.

GUS We use it to check the lid, the cap that can stop warm air rising.

GUS Think of the cap as a lid on a pot.

GUS Here the cap is basically zero joules per kilogram, so there is no lid.

GUS The cloud base is about 1200 metres above the ground.

GUS That means once the heat of the day does its work, storms can bubble up quickly.

[c11_sim_radar]

GUS This simulated radar shows where the cap breaks and storms initiate.

GUS See the marker near Blackwater, just south-west of Rockhampton.

GUS That is where the model breaks the cap first.

GUS The second marker near Hervey Bay shows a separate coastal cell.

GUS Inland storms are stronger and better organised.

GUS Near the coast it is patchier, so some places get a storm and others miss out.

[c12_shear]

GUS Now we look at wind shear.

GUS Shear is the change in wind speed or direction with height, like a spinning top being wound up.

GUS Near Rockhampton the 0 to 6 kilometre shear is about 65 kilometres an hour.

GUS That is enough to organise storms into lines or clusters.

GUS The low-level shear is only about 9 kilometres an hour.

GUS So the chance of a strongly rotating storm near Rockhampton is low.

[c13_index_map]

GUS This index is the Supercell Composite Parameter.

GUS It combines instability and shear to flag where organised storms are possible.

GUS Near Rockhampton it is a low but real signal.

GUS Later the strongest signal is over the Nullarbor, with a value around 6.

GUS That is far from towns and cars, so the chance of damage to people and property is very low.

GUS For Rockhampton, the likely storm type is multicell clusters rather than a supercell.

[c14_index_map]

GUS This map is an index for low-level rotation in storms.

GUS Near Rockhampton it is only about 0.1.

GUS That is very low for rotating storm risk.

GUS The stronger low-level rotation signal today is not near the large cities.

GUS So for people near Rockhampton, the main concerns are heavy rain and damaging gusts, not a rotating storm.

[c15_rain_wind]

GUS Now rain and wind together, because this is a flood bulletin.

GUS Near Hervey Bay the model has 41.5 millimetres of rain an hour.

GUS Near Blackwater it has 34.3 millimetres an hour.

GUS Over the next 24 hours near Rockhampton, the models have 13 to 21 millimetres, with isolated heavier falls.

GUS Rockhampton, Emerald and Gladstone could see about 20 to 30 millimetres, but some places will miss out.

GUS The Bureau already has moderate flood warnings on the Condamine and Warrego rivers.

GUS With wet soils across south-east Queensland, run-off is fast.

[c19_model_compare]

GUS We now compare the rain forecasts from three models.

GUS The American GFS has about 20.6 millimetres near Rockhampton in the next 24 hours.

GUS The European model has 13.3 millimetres and the European AI model has 16.8 millimetres.

GUS All three models agree it is wet, so this is a confident rain call.

GUS They disagree more on placement than on amount.

GUS That is enough rain to keep rivers rising in already wet catchments.

[c18_ens_prob]

GUS Ensemble probability shows how many model runs agree on rain amounts.

GUS Near Rockhampton the chance of at least 10 millimetres of rain in the next 24 hours is about 73 per cent.

GUS The chance of at least 5 millimetres is about 94 per cent.

GUS The chance of 25 millimetres is near zero.

GUS So expect a solid soaking, not a widespread big deluge.

[c16_index_map]

GUS Now to the second active threat: fire.

GUS FFDI is the fire danger index, combining fuel dryness, wind and heat.

GUS East of Newman tomorrow afternoon the index reaches the severe range.

GUS At the worst point it touches the extreme range.

GUS Very few people live out there; the risk is to highways, stations and unsealed tracks.

GUS Any fire in that country can move fast.

[c21_town_table]

GUS Here are the eastern capitals first.

GUS Brisbane high near 28 degrees today; tomorrow low 15 degrees, high 27 degrees, and about 2 millimetres of rain.

GUS Sydney high near 24 degrees today; tomorrow low 13 degrees, high 22 degrees, no rain.

GUS Melbourne high near 18 degrees today; tomorrow low 11 degrees, high 19 degrees, about 0.6 millimetres of rain.

GUS Hobart high near 16 degrees today; tomorrow low 10 degrees, high 17 degrees, about 0.2 millimetres of rain.

GUS Canberra high near 17 degrees today; tomorrow low 3 degrees, high 24 degrees, no rain, so keep the doona ready.

[c21_town_table]

GUS Now the southern and western capitals.

GUS Adelaide high near 17 degrees today; tomorrow low 11 degrees, high 21 degrees, no rain.

GUS Perth high near 26 degrees today; tomorrow low 15 degrees, high 24 degrees, no rain, good barbecue weather.

GUS Darwin high near 34 degrees today; tomorrow low 26 degrees, high 33 degrees, about 5 millimetres of rain.

GUS Darwin is in the build-up: hot, humid and stormy, with the reliable monsoon still a month away.

GUS That is why the washing never really dries up there in October.

[c21_town_table]

GUS Looking at the European model's nine-day rain signal, south-east Queensland stays mostly dry until next Wednesday.

GUS Next Wednesday Brisbane could get about 14.2 millimetres of rain, the wettest town in the region.

GUS Central Queensland has a heavy signal on Friday and Saturday; Charleville near 23.3 millimetres, Emerald near 21.8 millimetres.

GUS North Queensland has Mackay near 23.4 millimetres tomorrow and 23.8 millimetres on Saturday.

GUS Victoria and Tasmania turn wet later, with Melbourne near 21.9 millimetres next Wednesday.

GUS Perth gets showers on Saturday with about 5.8 millimetres, and mostly small amounts after that.

GUS This is a rain signal only, with no thunder or hail information.

[c21_town_table]

GUS We also look at the ingredients for storms, not the storms themselves.

GUS CAPE is stored storm energy in warm, moist air, like a spring being wound up.

GUS South-east Queensland on Sunday shows about 1438 joules per kilogram, enough fuel, but that alone is not a storm.

GUS Victoria and Tasmania on Saturday show falling pressure and both models wet, so a trough or low is arriving.

GUS For days 5 to 7 confidence is low, because tiny model errors double every day or two.

GUS Next Wednesday south-east Queensland shows unstable air, but the models disagree on rain.

GUS So the ingredients are there and worth watching, but don't lock it in yet.

[c90_events]

GUS The major events this week look mostly kind, but a few have a little rain.

GUS Sculpture by the Sea at Bondi runs until Monday; top near 21 degrees with wind gusts near 49 kilometres an hour.

GUS Victoria Derby Day at Flemington on Saturday has a top near 21 degrees and about 4 millimetres of rain, so take a brolly.

GUS Melbourne Cup on Tuesday has a top near 24 degrees and about 3 millimetres of rain.

GUS The Rugby League World Cup on the Gold Coast on Saturday is dry with a top near 23 degrees.

GUS If there is lightning at any open venue, play stops and you should head for shelter.

[c21_town_table]

GUS Overall confidence today is the middle band.

GUS The wet signal near Rockhampton is the strongest part of the forecast.

GUS The main uncertainty is exactly where the heaviest cells sit.

GUS A small shift of the low would move both the fire danger and the storm line.

GUS For all the official warnings, check bom.gov.au.

GUS The next bulletin is tomorrow morning.

GUS Subscribe so you do not miss it. If you've got a weather question, put it in the comments and I'll get to as many as I can during the day.

GUS Gus's Weather is a PandaVision production.