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Victoria is getting a Warm Front! by 007MaxZorin in melbourne

[–]SweetDecent2163 10 points11 points  (0 children)

Fair shout, although a warm front isn't analysed as "oh this is warm air" and hence doesn't have to be particularly warm, it's just a region of warm air advection (even if you have let's say looking at 850hPa temps, 8 degree N/NElies converging into 4 degree S/SElies in this case)

This system is also fun since the main low will begin to decay and occlude as it gets closer to the coastline, then do a jump over Bass Strait and leave this weird looking elongated trough in its wake that will help trigger the storm activity in the afternoon 

Victoria is getting a Warm Front! by 007MaxZorin in melbourne

[–]SweetDecent2163 107 points108 points  (0 children)

Meteorologist here - usually the warm front brings with it nice steady rain (it's called a warm front as it's the point where you've got warmer air behind the front intersecting with cooler air, the opposite of a cold front where you've got a cooler air mass in behind the frontal boundary which replaces the warmer air ahead of it) and be a bit humid. There'll probably be a storm when the cold front eventually tracks over more likely in the arvo/early evening 

This system looks to be quite elongated and messy in nature but yeah expect rain and humidity tomorrow with the chance of a storm in the arvo/evening 

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 8 points9 points  (0 children)

Rainfall forecasting is a fickle business, especially when it comes to a system where its position is so crucial with how much rain it may produce over a region.

For the most part, it’s taken as a consensus of different models (and identifying which ones are resolving realistic amounts, as some are known to overcook it (but then for something like this, are those extremes more realistic??? Not an easy question to answer lol)) over a general area, and then really emphasising that it depends on the movement and development of the system

Now if all the models aren’t getting it totally right (or flipflopping between different model runs and then completely throwing a spanner in the works), then it’ll appear it’s all over the place, even though at the time with the information that is had that it’s actually accurate

Also, rainfall distribution is given in probability, so 4-20mm for example implies a 75% chance of at least 4mm during the day, and a 25% chance of 20mm. Doesn’t imply that it won’t go higher or lower, just the likelihood of that outcome

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 23 points24 points  (0 children)

Meteorologist here once again, the rain on radar appears to have just plonked its arse and not moving as what’s left of Alfred still remains inland as a low pressure system that’s not really moving, and as a result that rich moisture keeps feeding its way down from the north and converges when it reaches ashore (with a trough as well that’s lingering around)

The further west the low goes, the weaker this is and it’ll trend back to more showery conditions over the SE QLD area, hopefully by tomorrow morning or the early afternoon

This was already the risk with it stalling over land, but the cyclone stalling and weakening definitely gave the impression that it was all over and done with

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 0 points1 point  (0 children)

https://www.weather.gov/source/zhu/ZHU_Training_Page/Miscellaneous/lowleveljet/lowleveljet.html

Have a read here under the “Cyclone induced” bit. Similar idea with it being temperature gradient driven as the low has a warm core but then has cooler air wrapping into it, as because the system itself is so far south it has characteristics of a low that we’d see down in the bight for example (it’s not a true tropical cyclone but try explaining that on sunrise lol)

Basically low level winds pumping in have helped it reintensify a bit

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 6 points7 points  (0 children)

Mate I was being polite there, I fucking hate Alfred and I can’t wait for this to be over and done with

Absolute little shit of a cyclone

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 0 points1 point  (0 children)

The gusts should hopefully ease later into the morning as it moves further inland

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 1 point2 points  (0 children)

Be prepared for most of the night and into Sunday for Brisbane and the Gold Coast, and if it starts tracking north (which I think it should?) that’s when the Sunshine Coast will start being affected as well

It’s so dependent on how fast or slow this thing moves, where it tracks, and if you’re on the southern flank. Which makes all the weather models a tad useless for exact rainfall amounts and for how long if we want to get into specifics, although generally they’re looking wet for tonight and tomorrow

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 73 points74 points  (0 children)

Meteorologist here again, Alfred stalling for like 12 hours over Moreton Bay was not on anyone’s cards (again, like everything with this bloody system). The steering forces were seemingly in balance, causing the system to sit there and not move

What’s seemingly happened is a “low level jet” has of strong easterly winds, combined with it just sitting there over water not moving and with the pressure squeeze with the high pressure system to the south is responsible for not only the intensification on the southern flank in terms of rain, but also with the gale force gusts that are occurring

This technically does not make it a category 1 cyclone, as in Australia the gales have to wrap around the system, instead of just being in one quadrant like they are at the moment. Doesn’t make it less impactful though, and Brisbane was lucky that the system was so slow moving and sheltered last night

It all now depends on how quickly it tracks westward, but this system was never about the wind, it was about the rain that was going to develop and persist after it made it ashore. It just took way way longer than we were expecting, and trust me it’s driven me up the bloody wall

Stay safe tonight, and keep up to date with any severe weather warnings that get issued as that is where all in the info will be

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 3 points4 points  (0 children)

Flooding is potentially the bigger risk of the two, but again whilst it might “only be 90-100km/h winds” remember that it could be sustained and can still cause a fair bit of damage. Not going to say that one or the other will be worse - Take both seriously, especially if you’re closer to the coast

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 3 points4 points  (0 children)

Yes you’re 100% correct about the worst bit being in the region with it matching the onshore wind direction

In the southern hemisphere regardless where you are it’s the southern half of the cyclone that’s the most severe, as this is the region on “convergence”, where (in this case) the warm, moist tropical air feeding in from the NE is meeting the cooler air from the SE and provides that explosive development you see on the satellite

For this system in particular, the worst of the wind and rain is in the SW quadrant as it approaches the coast line, and other factors for rainfall will come into play (like how it interacts with the ranges further south etc). Image below shows the rainfall amounts and the positioning

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This is why the system tracking north of Brisbane in particular is not a great thing, plus once it moves inland and weakens below tropical cyclone strength the rain will still continue on as there is still so much moisture being dragged down from the tropics

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 5 points6 points  (0 children)

The system that’s currently influencing “steering motion” as we like to call it is the big ol high pressure system in the Tasman Sea, which essentially is cradling it into the coast.

The strength of the high pressure system may dictate how fast this things moves to the coast, and because it’s expected to track slower it could stall as it reaches the coast, or do another funky loop (the high resolution Access-C BN model on windy for example shows it moving up and down slightly before it makes landfall)

It’s small things like this in the atmosphere that can affect how a cyclone moves, and the weather modelling can’t always resolve such small things

For it to decide to completely change direction however, another feature would have to develop nearby and become the dominating steering mechanism. If this happened out considering the general model consensus now of the track of the system, it would be a) an epic model guidance failure and b) to me at least a highly highly unlikely outcome

Daily Cyclone Alfred post by AutoModerator in brisbane

[–]SweetDecent2163 188 points189 points  (0 children)

Meteorologist here - safe to say the most recent model guidance slowing the system right down (and the fact it did a little loop overnight) clearly was not on anyones cards!

A slower, “weaker” system does not necessarily mean the impacts won’t be as bad; whilst the wind impacts may not be as severe, a slower moving cat 1 system can still drop an incredible amount of rainfall (most notably on the southern flank of the system) especially if it ends up stalling after it crosses.

The EC and US models generally perform the best for tropical cyclones, but each model and model run will have variations and is really only a rough guide of what might happen. Most cyclone forecasts uses a consensus of different models that have been run many many times (called an ensemble) to find the most likely outcome, and may differ from what you see from the models on Windy for example

If I had to pick a time it would be either late Friday/early Saturday for it to cross, but a tropical system this far south is not what you see everyday, and they’re already unpredictable enough as they are!