How low can a TC go?

[nig&nog]

A few of us had a quick discussion yesterday regarding how far south can a TC travel before it runs out of spin and becomes a low. We have just been watching the one over in WA and we were quite suprised that it lasted so long as a TC before it became a Low. Do any of our MET specialists have any good info that they would like to share, thanks

NIG

[morno]

Think it depends on 2 main things. The sea surface temperature and the amount of wind shear in the upper levels to break it down.

I'd say because it's now so far south, it'd be a combination of both that's breaking it down.

morno

[WannaBeBiggles]

A very simplified explantation.

Cyclones need water of about 26 degrees to form, this gives it the energy they need. If you take this away, either by dropping the temperature of the water or the cyclone hits land, it will loose this energy and start deteriorating.

Pretty sure that's how I remember it from MET anyway :)

[Cravenmorehead]

I thought once it had a central pressure less than 1000hpa it technically becomes a Tropical Cyclone. Obviously as it tracks south it loses the factors such as warm sea and the notherly winds and moisture that help it form along the monsoon trough. There is no set latitude.

[ForkTailedDrKiller]

I seem to recall that the Nth Island of NZ has been beaten up on a number of occassions by at least the remnants of cyclones that started out in the Coral Sea.

Dr :8

[MyNameIsIs]

Tropical Cyclone Information for the Australian Region (http://www.bom.gov.au/cgi-bin/silo/cyclones.cgi?region=aus&syear=1995&eyear=1995&cyclone=4&loc=0)

Check that out, a Cyclone that cuts right thru the middle of Aus back in '95.

Craven, I'm not so sure if "because its less than 1000, it's a cyclone" is quite accurate because you get plenty of low pressure systems with a central pressure lower than 1000 that do not form as a cyclone, I think they just get referred to as a tropical low. However it is probably quite correct to say that you wont have a TC with a central pressure near 1000hpa.


Sea surface temperature is one of the biggest factors to forming and sustaining a TC- as mentioned, above about 26C and you have the right stuff. Shear is also a key part.

BoM site has a lot of info about the hows and whys.


We've got some pretty warm seas this year, so far the season has been quite active- expect a few more before it ends!

Would have been interesting if Bianca crossed as an active cyclone down near Perth. She dropped a bit of water along the Pilbara.

[peuce]

I seem to remember from my Met training that there in NO Australian State that has NOT been hit by a Cyclone. But there again memory sometimes plays silly games :}

[WannaBeBiggles]

There is no set latitude

Not quite true. Cyclones can't form near the equator due to lack of Coriolis effect. No rotation = not cyclone.

[Monopole]

Play with the date on the link above, and you will see that its not really all that uncommon. 1999, saw TC Vance, cross the coast up near Onslow travel inland through the Goldfields and into the Great Australian Bight. From memory, it spent about 3 days in the bight still catagoized as a TC..

Actually, I just put in a date from 1975 till now and there are about 15 that ended south of the Bight with one, TC Harriot well into the Southern Ocean, and one TC Ned crossing the coast of Perth in 1989.

[Ex FSO GRIFFO]

TC 'Alby' in April '78 was still classed as one if I remember correctly, and it ventured well to the South of Perth, as the following link will show...

Tropical Cyclone Alby (http://www.bom.gov.au/cyclone/history/wa/alby.shtml)

The plot shows it still classed as a cyclone passing 35S - the equivalent of Albany.

We had not long moved into our new house in the Perth suburb of Thornlie, 11nm in from the coast and had a neighbour's vintage Paperbark blown over - right across our power lines, and the power was off for over three days until the authority of the time could reconnect.
Lots of mostly 'minor' damage widespread.

:ok:

[compressor stall]

Tropical Cyclone Information for the Australian Region (http://www.bom.gov.au/cgi-bin/silo/cyclones.cgi?region=shem&syear=1906&eyear=2006&loc=0)

Last 100 years of cyclones.

[Ex FSO GRIFFO]

Hey Mr 'M', not trying to pinch your post, but this link should open OK,

Severe Tropical Cyclone Vance (http://www.bom.gov.au/cyclone/history/vance.shtml)

Cheers:ok:

[eocvictim]

Last week there were 14 lows around the antarctic below 1000hp... I don't think you can call them tropical lows if they're in the polars. Interestingly there were 3 active TC's in the Aus region at the time and they were all above the lowest 3 Polar lows.

[MyNameIsIs]

Last week there were 14 lows around the antarctic below 1000hp... I don't think you can call them tropical lows if they're in the polars.

Yeah, I'd probably call them Polar Lows :ok:


If it wasn't obvious in my last post, I was referring to lows below 1000 in the regions where cyclones form, not all lows in general. . . .

[The Green Goblin]

I was waiting for the global warming factor to rear its head :ugh:

[tinpis]

Its becasuse of all the mining in the Pilbara innit Bob?

[eocvictim]

Yes, Yes. There's flooding rain in summer over the better part of the country, its cold, its hot, there have been 10 TC so far this wet season and extensive frontal activity down south, end times approach, everyone into the doomsday bunker.

[Kanga767]

Cyclones can't form near the equator due to lack of Coriolis effect.

Although quite rare, it can happen, as in Tropical storm Vamei in 2001 near Singapore and Typhoon Sarah in 1956. However, it would appear that rotation does not come from the Coriolis effect, so you are half correct, but rather just the right combinations of weather conditions in the 800 to 500 hPa layers and the terrain.


K

[Mr. Hat]

I thought you were talking about Terms and Conditions and was going to direct you to the Tiger/Jetstar/VAustralia/Centrelink websites

[maverick22]

There you go, straight from the BoM website:

A tropical cyclone is defined as a non-frontal low pressure system of synoptic scale developing over warm waters having organised convection and a maximum mean wind speed of 34 knots or greater extending more than half-way around near the centre and persisting for at least six hours.

[peuce]

My memory's coming back a bit now ....

Looking through the historical Cyclone tracks ( I know, I should get out more often) it appears that Victoria and Tassie have missed out ... :{

However, I do remember the fact that a cyclone has crossed the coast of Australia ... in every month of the year.:cool:

No, not this year ... but historically ! :E

[Capn Bloggs]

However low TCs can go, Bianca carked it big time at a great rate of knots. It's disappeared!

[tinpis]

Tin found one once back around '81-2. Dunno if the BOM had lost it or they didnt bother about 'em much around the Kimberly coast at that time
This one was down near Bigge Island. Weird sensation, over water laying off big mobs of drift but smooth. I told me mates in the Kunnerwuckers FSU it was there. Never got a medal or nothin' tho.

[sisemen]

While everyone was gazing intently at Bianca out to sea in the opposite direction a good old fashioned storm developed inland on Saturday and destroyed the Avon Valley.

Lots and lots of damage close by me.

[morno]

Nice animated satellite pic here of Yasi.

MTSAT Infrared Colorized Image Loop - Satellite Services Division - Office of Satellite Data Processing and Distribution (http://www.goes.noaa.gov/sohemi/sohemiloops/shirgmscol.html)

Word going around is this could be the worst cyclone to hit Australia since Cyclone Tracy.

morno

[Jabawocky]

morno......Great News.......and guess where I am going on Thursday :rolleyes:

You might be going on holidays again too! :)

[morno]

Ummmm, Rocky?

Pleeeeeease no more holidays, :(.

[Capn Bloggs]

Yikes! :eek: I'm happy with Bianca, thanks all the same.

[ForkTailedDrKiller]

Yasi = female = BAD news!

In other parts of the world people get the hell out of Dodge when something like that is headed their way. In Nth Qld we go, "Come on - I dare ya"!

So I am off fishing tomorrow. Opening of the Barra season and the falling air pressure usually gets them on the chew.

Dr :8

[Ex FSO GRIFFO]

How're ya goin' to get back agin, Doc..??

:eek::eek::ok::ok:

[Jabawocky]

So I am off fishing tomorrow. Opening of the Barra season and the falling air pressure usually gets them on the chew.


Thats coz the FTDK is engineless and the fill-in Piper Tailed Bannana Boat is down at YRED so not much flying for Forkie:{. you could slum it in a C210 ya know.;)

Now you better post pics live from the Barra Boat then tomorrow, or we will be disappointed

[FOCX]

Your question about how far south a TC can/has traveled needs to address what is a TC. In Oz a cat 1 TC has w/spds of 63-88kph, cat 2 TC 89-117. In the NH a storm of our cat 2 TC would only be rated as a TS.

[MetGirl]

As mentioned in some of the previous posts, central pressure is not the key factor. For example, recent TC Vania was a low for a long time with the pressure down to 988hPa before it was named.
The WMO definition of a TC is "a non-frontal low pressure system of synoptic scale developing over warm waters and having a definite organized wind circulation with a maximum 10-minute average wind speed of 34kt or greater near the centre".
Sea surface temp >26.5degC is the generally accepted criteria for "warm waters" and it is also true that they usually need to be further than 5deg from the equator.
Different parts of the world do have different ways of naming and categorizing TCs.
What becomes interesting is when they move out of the tropics and head towards NZ (or parts of Australia further south). A TC has a structure quite different from a mid-latitude (or polar) system, with a deep warm core. Once they move south, as well as moving over cooler seas (or land), the jetstream usually becomes influential in shearing the TC and weakening it. Sometimes, the remains of a TC can become re-invigorated by the jet. But the structure will be quite different from the structure of a TC. Interestingly, TC Wilma kept its TC structure much further south than what we would usually see. I guess the thing to keep in mind is that they may be re-classified (ie lose their name) but can still be a major weather system.
Phew, that got a bit long