Sydney's overnight soaking, Top End storms | Australia weather Wed 4 Nov morning | Gus's Weather

Sydney's overnight soaking, Top End storms and extreme WA fire danger - Wed 4 Nov

[c06_radar_now]

GUS G'day, I'm Gus, and this is your morning bulletin for Wednesday the 4th of November.

GUS The big story for most of you is Sydney: a proper overnight drenching, with more possible today.

GUS It's about 5 am in Brisbane at the time this is uploaded.

GUS This is the Bureau of Meteorology's real national radar, not a model, and the newest picture is only about 7 minutes old.

GUS On it, Sydney is the one capital actually showing rain right now, with Adelaide and Canberra picking up a bit of light rain too.

GUS Perth, Melbourne, Hobart, Brisbane and Darwin are all clear on the radar this hour.

GUS Away from the cities there's heavy rain near Mackay in Queensland, over country, not towns.

[c05_obs_now]

GUS That Sydney rain isn't a guess, it's measured: Bureau of Meteorology weather stations record rain since 9 am local time, like a bucket that gets emptied every morning.

GUS Badgerys Creek in western Sydney has had 70 millimetres of rain since 9 am yesterday, Horsley Park 59 millimetres of rain, and Observatory Hill 50 millimetres of rain.

GUS Port Macquarie further up the New South Wales coast has had 47 millimetres of rain, and it's still raining lightly at the Observatory Hill gauge and at Grafton Airport right now.

GUS The ground up and down that coast was already wet from the last week of rain, so a lot of this is running straight off rather than soaking in.

GUS That's one reason some of the local creeks are rising, which we'll come back to.

GUS To be honest, the computer models only expected a few millimetres of rain through this stretch of New South Wales, so they've been caught well behind what's actually fallen.

[c07_lightning_now]

GUS Next, lightning, tracked by the Blitzortung network, a volunteer lightning detection system, over the last six hours.

GUS There's a small cluster just north-west of the Gold Coast, and another out at sea north-east of Bundaberg, both easing rather than growing.

GUS The busiest patch by far is out in remote country about 360 kilometres west of Mount Isa, with well over a thousand strikes and still active.

GUS There's also a patch at sea south-east of Coffs Harbour, and one south-west of Townsville, both fairly quiet.

GUS None of that is a warning, just where the storms are right now; for any official warning it's always bom.gov.au.

[c04_satellite]

GUS Satellite measures how cold, and therefore how high, the tops of storm clouds are, which tells us how strong a storm really is, and it can see areas the radar can't.

GUS Darwin has real storm cloud sitting nearby right now, tops down near minus 50 degrees Celsius, which is solidly into thunderstorm territory.

GUS Melbourne and Hobart both have cooler storm cloud nearby too, tied to the system we'll look at next.

GUS A handful of those satellite storms don't show up yet on the model's own simulated radar, which tells me the model is running a little behind reality this morning,

GUS so treat its storm placement with some caution today and trust the satellite and radar over it.

GUS The big picture: a wet start in the south-east, building storm energy up north, and a hot, dry pattern building in the west.

GUS Everything in this bulletin is indexed in the description, so if you're in a hurry, you can jump to the part you want from the chapters.

[c01_verification]

GUS Quickly, how did yesterday's forecast hold up, checked against the actual observed numbers.

GUS My overnight low calls were close for Perth too, missed by almost 3 degrees, it came in cooler than I said.

GUS Across the whole run my temperature forecasts were off by an average of about 1 and a half degrees, which is a bit tighter than either of the big computer models managed yesterday.

[c02_mslp_fronts]

GUS Here's the pressure map for today. Think of the lines, called isobars, as contour lines on a map, but for air pressure instead of height.

GUS A low pressure system sits over the Tasman Sea, pulling moist onshore air into the New South Wales coast, that's the engine behind this morning's soaking.

GUS An upper-level trough, a dip in the high-altitude wind pattern that helps lift air and trigger rain, stretches from central New South Wales right down through Bass Strait to south of Hobart.

GUS That same trough is why Geelong and Ballarat should pick up a decent spread of rain later today, and showers reach Hobart too.

GUS Over in the west, a low sits over the Kimberley and a high is building in over the Great Australian Bight,

GUS squeezing in hot, dry north-easterly winds ahead of it, driving the fire danger we'll get to.

GUS So, the short version: one wet system working its way down into Victoria and Tasmania, and a hot, dry pattern building over the north-west.

[c06_pwat]

GUS Before storms can form, the air needs moisture to feed them, think of it like fuel before you can even think about lighting a fire.

GUS Up near Darwin and the Gulf Country, the air holds about 45 to 50 millimetres of precipitable water,

GUS the total moisture in a column of air if you squeezed it all out as rain: a very moist, tropical airmass.

GUS Down near the Coral Sea off Hervey Bay there's less moisture to work with, around 30 millimetres, still enough for storms but not as juicy.

[c07_cape]

GUS Meteorologists measure the energy a storm can feed on, they call it CAPE. Think of it like the petrol in a storm's tank, the more there is, the taller and stronger a storm can grow.

GUS Out over the Arafura Sea there's about 3,000 to over 4,000 joules per kilogram of it, that is a seriously full tank for this time of year.

GUS To put a number on how that energy could organise, there's also a measure forecasters call the supercell composite,

GUS it's high across the north, meaning a storm there has a real chance of starting to rotate.

GUS The wind also changes direction and speed with height today, around 50 to 75 kilometres an hour of what's called shear through the lowest six kilometres,

GUS which is enough to help a storm build a long-lived, organised structure rather than just a quick, messy shower.

GUS But energy and shear are only two of the ingredients. The next question is whether anything actually sets the storms off.

[c08_skewt]

GUS Think of a layer of warm air sitting above the ground like a lid on a pot, it stops the warm, moist air below from bubbling up into storms until something breaks it.

GUS Over the Gulf Country that lid is weak today, about minus 100 joules per kilogram of CIN, basically a loose-fitting lid.

GUS The lid over the Arafura Sea area is even weaker, close to nothing at all, so storms there can fire up easily once the sea breeze and the daytime heat get going.

GUS With a full tank of energy and barely any lid, both areas are primed for storms to build.

[c10_sim_radar]

GUS Storms are expected to fire up inland tomorrow, Thursday, overnight in the eastern Northern Territory, in cattle station country, with the chance of large hail and damaging wind.

GUS Then Thursday evening the focus shifts to the Gulf Country near Normanton in Queensland, with the same mix of hazards possible.

GUS Out around the Gulf, the cattle stations out there will take any decent rain that lands, it's dry country.

GUS None of these are Bureau warnings yet, just the ingredients lining up: keep an eye on bom.gov.au if you're in any of those areas.

GUS Out over the Indian Ocean, well south-west of Darwin, there's a separate area the models are watching, over open water.

GUS It's just open water out there, so there's nobody in its path to worry about.

[c15_index_map]

GUS Fire danger is rated with an index forecasters call the FFDI, it folds in temperature, wind,

GUS dryness and how much fuel is available, the higher the number the more dangerous a fire would be if one started.

GUS In northern Western Australia, about 250 kilometres south-west of Broome, that index reaches a fire danger rating of 85 tomorrow, which the Bureau calls extreme.

GUS The ground there is very dry on the drought measure we use, so any fire that starts would spread fast.

GUS The Bureau of Meteorology has an Extreme Heatwave Warning out for the Kimberley and North Interior districts of Western Australia, as of 4:04 am Brisbane time.

GUS There's also a Severe Heatwave Warning for the Pilbara district, the same hot, dry airmass driving that fire danger, with daytime temperatures running well above normal and little overnight cooling.

GUS It's about 60 degree-days above normal on that measure, enough to put real strain on anyone working outdoors, from truck drivers to mine and station crews across the district.

GUS There's a separate, later Severe Heatwave Warning for the Pilbara covering the back half of the week, once this current hot spell has a brief easing before building up again inland.

GUS For all the official warnings and any fire bans, check bom.gov.au.

[c16_temp]

GUS The Bureau of Meteorology has an Extreme Heatwave Warning out for the Tiwi Islands and the Arnhem district, as of 4:04 am Brisbane time.

GUS Top temperatures up there are forecast well into the 40s for several days, with little overnight relief, which is why it's rated extreme, and it ties into the build-up pattern I'll explain in a moment.

GUS The Bureau also has a Severe Heatwave Warning out for the Daly and Carpentaria districts of the Northern Territory,

GUS as of the same time, with temperatures running about 7 degrees above normal and set to stay that way for several more days.

GUS There's also a Severe Heatwave Warning for the Peninsula, Gulf Country, Northern Goldfields and Upper Flinders districts of Queensland, part of that same spreading heat.

GUS This is the build-up, the pseudo dry season that far northern Australia gets through October and November: the winds that carried winter rain swing round and get cut off,

GUS so the heat and the humidity just keep climbing until the proper monsoon rain arrives in December.

GUS Darwin itself sits at a top of 35 degrees this afternoon, hot and sticky, with storm energy building for later.

[c18_model_compare]

GUS Comparing the American GFS, the European model and the European AI model on today's rain: for Victoria they broadly agree,

GUS all putting 5 to 7 millimetres of rain on average across the state, which matches Melbourne's forecast of around 13 millimetres of rain.

GUS For New South Wales they're all running light, a millimetre or two of rain on average.

GUS Out at the Gulf Country hotspot the models don't agree much on timing, so I'd call tomorrow evening's storms likely rather than locked in.

[c02_mslp_fronts]

GUS Since this bulletin covers tropical systems too: the European model's ensemble,

GUS that's fifty separate runs of the same model nudged slightly differently to show the range of possibilities, is watching a tropical low well out in the Pacific, east of Vanuatu.

GUS About 11 of those 50 model runs eventually grow it into something like a tropical storm, but even by day 5 the average position is still a long way east of the Coral Sea.

GUS There is nothing for Australia to act on from this one yet, it's simply one to keep half an eye on over coming days.

[c92_river_gauges]

GUS The Bureau of Meteorology has a Moderate Flood Warning out for the Balonne River from Surat down to Warkon and further downstream,

GUS with the river at Warkon sitting at 6.5 metres on its gauge and rising, as of 4:04 am Brisbane time.

GUS There's also a Moderate Flood Warning for the Bulloo River downstream of Quilpie and the Bulloo River at Thargomindah,

GUS out in the state's south-west, both expected to stay in flood for some days yet as the slow rise moves through.

GUS The Barcoo River at Blackall is steady at 5.4 metres.

GUS Ropes Creek in western Sydney is rising fast, up over a metre at Debrincat Avenue since the last bulletin.

GUS Elsewhere it's quiet: the Southern River near Perth is steady and unremarkable.

GUS A gauge height is just the level of water against the pole, not a flood category, so for any actual flood warning always check bom.gov.au.

[c90_events]

GUS A quick look at the week's big outdoor events.

GUS The Rugby League World Cup semi-final in Newcastle on Saturday evening has a moderate weather watch, around 11 millimetres of rain forecast, so pack a poncho if you're going.

GUS The Everest Carnival Ladies Day at Rosehill on Saturday has a light rain and wind watch, nothing to cancel plans over.

GUS Supercars at Sandown over the weekend looks mostly fine, just a few millimetres of rain possible.

GUS Everything else on the events board, including both Foo Fighters shows and the Flemington racing days, looks weather-kind right now.

[c20_town_table]

GUS Now the lap of the capitals, today's daytime high, and tomorrow's overnight low and high, plus the rain.

GUS Brisbane: a top of 32 degrees today with 9 millimetres of rain, tomorrow 34 and no rain.

GUS Sydney: a top of 24 degrees today with 9 millimetres more rain, tomorrow 18 and 21 with 2 millimetres of rain.

GUS Melbourne: a top of 22 degrees today with barely a sprinkle, but tomorrow a low of 8 degrees and a high of 17 degrees with a solid 13 millimetres of rain as that trough arrives.

GUS If you're at the footy tonight, pack the poncho, typical Melbourne.

GUS Canberra: a top of 24 degrees today with 13 millimetres of rain, tomorrow a low of 7 degrees, a high of 21 degrees and a bit more showers about.

GUS Hobart: a top of 20 today, a low of 11 and a high of 18 tomorrow, with 7 millimetres of rain.

GUS Adelaide: a top of 18 degrees, dry both today and tomorrow, with a low of 11 degrees and a high of 18 degrees tomorrow. Good drying weather in Adelaide, so the washing's laughing.

GUS Perth: a top of 25 degrees and bone dry again tomorrow too, a low of 13 degrees and a high of 25 degrees.

GUS Perth's doing its usual thing, sunshine, and a bit of smugness while the east coast gets soaked.

GUS Darwin: a top of 35 degrees today with 5 millimetres of rain, tomorrow a low of 28 and a high of 35, stinking hot and sticky either way.

GUS Why did Darwin's thermometer need a holiday? It couldn't handle the pressure of staying in the mid thirties every single day. I'll see myself out.

[c20_town_table]

GUS Looking further out, this next bit comes from a European model's nine-day rain forecast,

GUS which only tells us how wet it might get, not whether there'll be thunder or hail, so I'll say wet, never storms, for these days.

GUS Days 2 and 3 are fairly reliable, days 4 and 5 are a guide,

GUS and days 6 to 8 are only a loose signal that can flip completely by the next run, small errors in a forecast double roughly every day or two.

GUS South-east Queensland stays mostly dry this weekend, with about 16 millimetres of rain for Brisbane by next Thursday.

GUS Tasmania gets more rain Friday and heavier again midweek, with 16 millimetres near Hobart.

GUS Northern New South Wales has a genuinely heavy signal for Saturday, up to 28 millimetres of rain around Newcastle and Port Macquarie, which lines up with that Rugby League semi-final we mentioned.

GUS South-east Queensland has over 1,700 joules per kilogram of stored storm energy for Saturday, but nothing to set it off yet, so it could fizzle.

GUS The Top End has even more, well over 2,900 joules per kilogram, also without a clear trigger, so don't lock it in.

GUS For the weekend verdict: south-east Queensland Saturday is a watch, not a lock, the NSW coast has a real wet signal, and Canberra and the south look fairly quiet on the storm front, just showery.

[c06_radar_now]

GUS My overall confidence in today's call is high, mostly because the rain pattern and the main low pressure systems are tracking very similarly across the different models.

GUS What would change my mind is if that Top End storm energy finds a trigger it currently doesn't have, so I'll be watching that closely through the day.

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

GUS I'll be back again this afternoon with the next bulletin.

GUS If you've got a weather question, or you want to tell me what the sky's doing where you are,

GUS put it in the comments and I'll get to as many as I can during the day.

GUS Stay curious, and keep a brolly handy.

GUS Gus's Weather is a PandaVision production.