Severe Tropical Cyclone Laurence

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Invest 92P has been declared Tropical Cyclone Laurence is the northern Josef Bonaparte Gulf, a couple hundred miles north of Wyndham. Deep convection is wrapping into the southern and western sides of the LLC, raising the intensity to 35kts. However, the LLC is exposed to the northeast, and this indicates moderate shear is affecting Laurence. This was not expected, and just goes to show how unpredictable shear is. Shear is likely to be a limiting factor in the development of Laurence over the next several days, though it looks like it will stay in the moderate range of 10-15kts, which shouldn't weaken Laurence. A general westwards heading is forecast by BOM, as a ridge builds to the south over mainland Australia. However, it's worth noting that data for models is sparse in this area, and therefore track forecasts are hard to pin down. At the moment, it seems Laurence will pass north of areas such as Kalumburu and Kurl Bay, but if the ridge is not as strong as analysed, then Laurence could head southwestwards towards the Australian coast.

Overall, it appears Laurence will move generally westwards over warm waters but moderate shear, which should allow some slow intensification of the system.

Satellite image below shows Laurence on the top end of Australia:

Edited December 13, 2009 by Somerset Squall

[Cookie]

Thanks for the updates mate

[Cookie]

[Somerset Squall]

Laurence looks much better organised since this morning, with deep convection exploding over the centre, and now some impressive banding wrapping into the LLC. Intensity is now 40kts. Laurence is still expected to move westwards along the northern periphery of a ridge to the south over mainland Aus, but it appears a series of troughs will eventually break down the ridge sending Laurence southwards. The timing of this turn is very uncertain. JTWC forecast Laurence to head westwards long enough to miss areas from Kalumburu to Broome an instead make landfall further down the coast at Port Hedland. BOM indicate the southward turn much sooner, with landfall near Derby, east of Broome.

JTWC:

BOM:

A large disagreement to say the least.

The timing of the turn towards the south will have a say in how strong Laurence gets. Shear is easing, and this is allowing Laurence to strengthen as evidenced by the better organisation. Obviously, the sooner Laurence turns the shorter time it will have over water. If BOM verifies- expect a peak of around 75kts. If JTWC verifies, intensity may reach 100kts (these are both estimations based on shear not increasing again and rapid intensification not occuring). Bottom line is that Laurence is going to make a land crossing somewhere (unless something drastic happens) as a fairly strong system, so Laurence needs to be closely monitored.

[Somerset Squall]

The latest forecasts show a classic example of how difficult it is to predict the path of Australian cyclones. Laurence, up until last night, had always been a poorly organised cyclone. It appears that the increase in organisation has caused the LLC to re-form to the south of the original location, much nearer the coast. BOM and JTWC still disagree, but now JTWC predicts a more easterly landfall to BOM, contrary to last night. The updated track maps above illustrate my point.

It appears that JTWC are expecting the ridge to the south to break down imminently, causing Laurence to dive into the coast around Kalumburu. BOM are analysing the LLC to be a bit further north, and expected the ridge to hold strong for the next 24hrs, with landfall occuring near Kuri Bay. When you look at the convective signature of Laurence, you can see why the LLC is difficult to pinpoint. This obviously has a large effect on just where Laurence makes landfall:

I would say both are slightly out and Laurence lies in between what the two agencies are saying! Of course, this is only my opinion. But the upshot of this is, is that eaither agency could be correct, and as always, it's a case of wait and see. What is clear however, this southward jog has done no favours for Laurence's future as it has less time over water now.

[Cookie]

Thanks for the updates, really needs to be kept an eye on this one.

[Somerset Squall]

Laurence has strengthened over the last 12hrs, and intensity has risen to 55kts. Laurence has moved westwards along the northern periphery of a subtropical ridge to the south. The cyclone is very close to land, and land interaction will hinder any significant intensification in the near term. Additionally, the ridge to the south will break down forcing Laurence to the southwest. However, in contradiction to the previous forecast, JTWC have gone back to something resembling their intial thoughts- the ridge will hold out in the end. With the weakening of the ridge, Laurence is now forecast to move southwestwards along the coast of Aus towards Kuri Bay, cross the coast in this area, and then move back out into the Indian ocean as the ridge recovers itself in a few days time. Intensity wise, there is a little more time for intensification, before weakening occurs when Laurence crosses land. Laurence is then expected to move back over waters in excess of 32C, which could promote re-intensification at around day 4 or 5 of the forecast. Certainly going to be an interesting watch to say the least! Western Aus will be monitoring this coast hugger very closely I reckon.

[Somerset Squall]

Laurence has intensified significantly since the last advisory, and has been upgraded to a severe tropical cyclone by BOM. Intensity is now 75kts, making Laurence a cat 1 on the SS scale. The intensification is surprising, especially when you consider how close Laurence is to land. In fact, Laurence crossed Troughton Island and the winds observed there helped JTWC set the intensity at 75kts.

Once again, the track forecast has changed. This isn't really surprising. As I said before, forecasting the track of Austrailian cyclones in notoriously difficult. Both JTWC and BOM now agree on a southerly dive further inland. JTWC hasn't ruled out re-emergence into the Indian Ocean, but considers it unlikely.

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Laurence a few hours ago:

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Despite being very close to land, Laurence is bombing. 10 min sustained winds are now 90kts, which probably equates to 100kts 1 min (JTWC). Pressure is rapidly falling and is now 954mb, indicating an intense system. Laurence has wobbled westwards at times, just about keeping it offshore. It looks like Laurence is now bearing down on Kuri Bay as a cat 4 on the Australian scale, and the area is on RED alert and residents are being urged to seek shelter immediately.

So, why has Laurence strengthened so much depsite being near land? My reasoning is that the land is flat so won't disrupt the inner core much, and the eye is just about still over waters of 33C, promoting rapid intensification. Inflow is wrapping in from the warm sea which is cancelling out the effects of land interaction. With the wobbles westwards, chances are increasing once more for Laurence to survive a passage over land and emerge in the hot waters of the Indian Ocean. Laurence has to weaken at some point however, once the inflow source from the hot waters gets cut off. I think Laurence is going to wreak havoc in the Kuri Bay area and communities further down the coast need to keep a very close eye on the severe cyclone.

[Cookie]

this thing went nuts a cat 4 bearing down on Aus

Edited December 15, 2009 by cookie

[Somerset Squall]

Great image that last one Cookie, what a beast! Laurence has done remarkably well seeing as it has hugged the coast for the last 24hrs.

[Cookie]

is it a well populated area where its making landfall?

Edited December 15, 2009 by cookie

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No, quite sparsely populated which is obvsiously good, though Derby is more densely populated which is in the firing line from Laurence, though he should be a lot weaker by then.

Tiny Laurence is still intensifying. Laurence is now a cat 4 on the SS scale too with intensity now at 115kts. A very dangerous storm this one.

[Cookie]

still very dangerous like you say.

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Pressure now down to 944mb, clearly still rapidly intensifying.

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This is getting quite worrying. I would not like to be in the path of this monster. Pressure continues to fall rapidly, and is now at 933mb, a 11mb drop in two hours. Laurence is a cat 5 on the Australian scale (note that it's still a cat 4 on our scale, the SS scale), and there is still potential for further deepening. In addtion, Laurence has wobbled westwards again, meaning that the chances for Laurence to re-emerge into the Indian Ocean are rising again as the intense cyclone refuses to dive southward inland as forecast. Broome need to be watching this very closely, as do Derby and Cockatoo Island. Kuri Bay is currently getting slammed by winds and rain, though the severest winds are still out to sea as Laurence is very small and the strongest winds do not extend far from the centre. Despite this, there is the potential for some serious damage from wind from Kuri Bay down the coast westwards. Flooding is a very real risk too. Hopefully the Australians are prepared, especially as this has become an entirely different monster in the last several hours.

Latest track from BOM (Note the westwards turn at the end of the forecast period, will Laurence make it back over water?):

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Laurence made landfall just east of Cockatoo Island, and is moving south-southwestwards towards Derby. The structure of Laurence has weakened as it heads inland, and intensity has been reduced to 90kts. Ridging will eventually build to the south which will force Laurence westwards, but it is touch and go whether the cyclone makes it back out into the Indian Ocean. Certainly, it would be a remnant low at this point as Laurence will spend 3 days overland. If the circulation remains intact, it could be quite slow to re-organise despite the very warm waters north of Port Hedland.

[Cookie]

it stalled for around 6 hrs earlier.

All this taken from late last night

TROPICAL CYCLONE ADVICE NUMBER 40

Issued at 12:00 pm WST on Wednesday, 16 December 2009

BY THE BUREAU OF METEOROLOGY

TROPICAL CYCLONE WARNING CENTRE PERTH

A Cyclone WARNING is current for coastal areas from Kuri Bay to Beagle Bay and

adjacent inland parts.

A Cyclone WATCH has been declared for Beagle Bay to Bidyadanga and extending

inland towards Fitzroy Crossing.

At 11:00 am WST Severe Tropical Cyclone Laurence, Category 5 was estimated to be

55 kilometres southwest of Kuri Bay and

170 kilometres north northeast of Derby and

moving south southwest at 11 kilometres per hour.

Severe Tropical Cyclone Laurence is a small but very intense tropical cyclone

having VERY DESTRUCTIVE WINDS with gusts to 285 kilometres per hour close to the

cyclone centre. VERY DESTRUCTIVE wind gusts are possible on the coast south of

Kuri Bay during this afternoon and evening.

GALES with gusts to 100 kilometres per hour may extend further southwest along

the coast, reaching Cockatoo and Koolan Islands during this afternoon and

evening. Should the centre pass close by VERY DESTRUCTIVE winds are possible

during the afternoon and evening. GALES, and possibly DESTRUCTIVE winds may

extend to Derby and Beagle Bay early Thursday morning.

HEAVY RAIN is expected to continue over the north and west Kimberley. Daily

rainfall totals in excess of 100mm are possible near the coast with totals

decreasing further inland.

FESA-State Emergency Service advises of the following community alerts:

RED ALERT: People in or near the communities of Koolan Island and Cockatoo

Island need to go to shelter immediately.

YELLOW ALERT: People in or near the communities of Cape Leveque, One Arm Point,

Djarindjin, Lombadina and Derby should be taking action.

ALL CLEAR WITH CAUTION: People in or near Mitchell Plateau and Kuri Bay wind and

storm surge dangers have passed but you need to take care to avoid the dangers

caused by damage.

Details of Severe Tropical Cyclone Laurence at 11:00 am WST:

.Centre located near...... 15.9 degrees South 124.2 degrees East

.Location accuracy........ within 35 kilometres

.Recent movement.......... towards the south southwest at 11 kilometres per hour

.Wind gusts near centre... 285 kilometres per hour

.Severity category........ 5

.Central pressure......... 934 hectoPascals

The next advice will be issued by 3:00 pm WST Wednesday 16 December.Cyclone

advices and State Emergency Service Community Alerts are available by

dialling 1300 659 210

A map showing the track of the cyclone is available at:

http://www.bom.gov.au/weather/cyclone

[Somerset Squall]

Laurence, a small system, is now entirely over land. As a result, rapid weakening has occured, and intensity is just 65kts. Laurence is forecast to remain over land for the next 48hrs, and based on recent trends, the system is likely to degenerate into a low within the next 24hrs. Laurence is moving southwards but is forecast to turn to the west in the low level easterly flow as a shallow system. This does bring Laurence back over water after 48hrs, where re-development is possible, if the low survives this long. BOM are keen on some rapid re-development once the remains pop back out over water, but surprisingly, JTWC have terminated advisories and don't expect Laurence to remain intact until it moves over water- which is a backtrack on what they were previously saying. It's hard to say what will happen, but past systems like Billy last year did very well despite traversing land for periods of days- primarily as the land is flat. We shall see.

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Laurence seems to be inching westwards now, and is holding up pretty well at the moment with some deep convection over the well defined LLC. Intensity has fallen to 55kts. I think there is a good chance of Laurence recovering when it moves back out into the Indian Ocean

[Cookie]

thanks for the updates, a very interesting track.

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Indeed Cookie!

Laurence has re-developed into a tropical cyclone, with winds increasing to 35kts. Over the last 6hrs, banding has increased and central convection has re-developed over the LLC. Laurence is still over land, so this bodes well for significant intensification tomorrow when he moves back over hot water. Ridging to the south has forced the practically stationary remnant low towards the coast and moist inflow from the Indian Ocean has allowed the system to intensify despite being over land. The ridging will break down in around 72hrs, which will allow Laurence to turn southwards again. Another landfall near Port Hedland seems likely, though this may change (much depends on the ridge). Intensity is difficult to predict; shear is low and waters are above 30C, and the fact that Laurence has become so strong in his first life despite hugging the coast suggests that Laurence could become just as powerful again. The conditions, along with the well defined LLC (which is impressive as Laurence has been over land for the last 48hrs) makes Laurence a rapid intensification candidate.

[Cookie]

TROPICAL CYCLONE ADVICE NUMBER 62

Issued at 5:50 am WST on Saturday, 19 December 2009

BY THE BUREAU OF METEOROLOGY

TROPICAL CYCLONE WARNING CENTRE PERTH

A Cyclone WARNING continues for coastal areas from Cape Leveque to Bidyadanga.

A Cyclone WATCH continues for coastal areas from Bidyadanga to Pardoo.

At 5:00 am WST Ex-Tropical Cyclone Laurence was estimated to be

145 kilometres north northeast of Broome and moving

west northwest at 12 kilometres per hour.

Ex-Tropical Cyclone Laurence has moved over the Dampier Peninsula and crossed

the west Kimberley coast.

The low is expected to reintensify into a tropical cyclone in the next three to

six hours. GALES could develop along the west Kimberley coast between Cape

Leveque and Bidyadanga, including Broome during the morning. As the system moves

south westwards GALES could extend further down the coast to Pardoo late on

Sunday.

Heavy rainfall is expected to continue in the west Kimberley with 24 hour falls

in excess of 200mm possible. Curtin has reported 142mm since 9am Friday.

FESA-State Emergency Service advises as a precautionary measure the following

community alerts:

BLUE ALERT: People in the communities from Cape Leveque to Beagle Bay, including

One Arm Point, Djarindjin and Lombadina need to prepare for cyclonic weather and

organise an emergency kit including first aid kit, torch, portable radio, spare

batteries, food and water.

Communities in the remainder of the western Kimberley and northern Pilbara

should listen for the next advice.

Details of Ex-Tropical Cyclone Laurence at 5:00 am WST:

.Centre located near...... 16.7 degrees South 122.5 degrees East

.Location accuracy........ within 35 kilometres

.Recent movement.......... towards the west northwest at 12 kilometres per hour

.Wind gusts near centre... 85 kilometres per hour

.Severity category........ below cyclone intensity

.Central pressure......... 996 hectoPascals

The next advice will be issued by 9:00 am WST Saturday 19 December.Cyclone

advices and State Emergency Service Community Alerts are available by

dialling 1300 659 210

A map showing the track of the cyclone is available at:

http://www.bom.gov.au/weather/cyclone

[Somerset Squall]

BOM are forecasting a 100kt peak, wheras JTWC only 65kts. Based on the latest satellite image of Laurence I think I know who will be nearer the mark:

Eye feature already developing nicely and Laurence has only just emerged over water. Intensity is 45kts currently, though expect this to rise significantly during this afternoon.

Track forecasts still keen on the southward turn towards the Pilbara coast, but timings are still open to question. Latest thoughts have Laurence hitting well to the east of Port Hedland in the reletively unpopulated 80 Mile Beach. We shal see. Hopefully, this track forecast eventuates as Laurence is set to become a monster yet again.