Severe Tropical Cyclone Billy

[Somerset Squall]

Tropical Cyclone Billy (05S) has formed just north of the Northern Territory/Western Australia border, around 150 miles southwest of Darwin. The environment is excellent for strengthening, with very hot waters, low shear and excellent dual outflow. However, Billy only has around 24 hours to strengthen as it is drifting southwards towards land. Current intensity is around 30kts but Billy is expected to peak at around 45kts as it rapidly consolidates over the next few hours. Rapid weakening will then occur over the dry, dusty terrain of mainland Australia. Billy is likely to bring some very heavy rains to the border region, which will be very welcome but at the same time, could cause flooding.

[Somerset Squall]

Billy really isn't moving anywhere fast, it's currently sat in the Josef Bonaparte gulf and is still roughly the same distance from the coastline as it was this afternoon (around 50 miles). Billy hasn't moved southwards and if anything he has inched slightly westward. Billy is forecast to move generally westwards and make landfall north of Wyndham, then rapidly weaken due to land interaction. The less Billy moves south, the less land he will have to deal with on the predicted west track, and therefore increases the chances for him to emerge into the Indian Ocean intact.

Billy has also strengthened to 40kts this afternoon. Deep convection persists over the centre and good banding features are already bringing heavy showers and thunderstorms to the coastlines of the JB Gulf. Further strengthening is possible if Billy doesn't make a short hop to land.

Edited December 18, 2008 by Somerset Squall

[Cookie]

thanks for the updates mate

Tropical Depression BILLY is forecast to strike land to the following likelihood(s) at the given lead time(s):

Yellow Alert Country(s) or Province(s)

Australia

probability for TS is 55% within 12 hours

Green Alert City(s) and Town(s)

Wyndham (15.2 S, 128.2 E)

probability for TS is 50% within 12 hours

Kununurra (15.8 S, 128.9 E)

probability for TS is 35% within 12 hours

Note that

Yellow Alert (Elevated) is CAT 1 or above to between 10% and 30% probability, or TS to above 50% probability.

Green Alert (Low) is TS to between 31% and 50% probability.

CAT 1 means Tropical Cyclone strength winds of at least 74 mph, 119 km/h or 64 knots 1-min sustained.

TS means Tropical Storm strength winds of at least 39 mph, 63 km/h or 34 knots 1-min sustained.

[Cookie]

new update

Tropical Storm BILLY is forecast to strike land to the following likelihood(s) at the given lead time(s):

Yellow Alert Country(s) or Province(s)

Australia

probability for CAT 1 or above is 10% within 12 hours

probability for TS is 85% currently

Yellow Alert City(s) and Town(s)

Wyndham (15.2 S, 128.2 E)

probability for CAT 1 or above is 10% within 12 hours

probability for TS is 70% currently

Kununurra (15.8 S, 128.9 E)

probability for TS is 60% within 12 hours

Port Keats (14.2 S, 129.6 E)

probability for TS is 55% currently

Note that

Yellow Alert (Elevated) is CAT 1 or above to between 10% and 30% probability, or TS to above 50% probability.

CAT 1 means Tropical Cyclone strength winds of at least 74 mph, 119 km/h or 64 knots 1-min sustained.

TS means Tropical Storm strength winds of at least 39 mph, 63 km/h or 34 knots 1-min sustained.

[Somerset Squall]

Thanks for the landfall updates Cookie.

Billy's intensity has increased to 45kts. There is still some good banding and good central convection but land interaction is hindering significant spin-up of the storm. Heavy rainfall is already being felt and Billy is finally nearing landfall as it inches westwards at 2kts. The Wyndham area will receive the worst conditions and then Billy will weaken as it moves inland.

[Somerset Squall]

Billy has weakened to 35kts due to land interaction. Convection has decreased due to dry air zapping the moisture out of Billy but the system maintains a well defined LLC. Because of this, both BOM and JTWC forecast the LLC to survive the track over land and to re-develop once in reaches water again. Shear will remain low and outflow good which should help the LLC remain intact and in a good state for some re-intensification once it hits water.

[Somerset Squall]

Billy has lost practically all of his convection and all that remains is an exposed, yet well defined LLC. Intensity has been reduced to 20kts. The forecast remains however for the circulation to remain intact for the next 48hrs until it hits water again and redevelops. BOM are very keen on some significant strengthening once Billy reaches water again but the JTWC are more cautious. As there is very little convection and surface winds of only 20kts, I am against any immediate rapid strengthening if the circulation does indeed survive the long track over land. I think recovery will be fairly slow as there won't be much left of Billy by the time it does reach the coast IMO.

[Cookie]

may just make the other side and back into the ocean

[Somerset Squall]

may just make the other side and back into the ocean

Indeed, a very interesting possibility, that is looking very real right now. Intensity has crept back up to 25kts as TD Billy is pulling moisture in from the ocean and fuelling some renewed convection over the still well defined centre. Billy is nearing the coast and is expected to emerge over water later today. Both BOM and the JTWC are forecasting some rapid development as he does so, and I have to say that Billy is looking in far better shape than I expected him to be after so much land interaction, so this potential is very real and it may not take Billy long to re-intensify at all. Environmental conditions are set to be excellent once Billy makes it over water, waters are in the region of 32C, shear is expected to be low and Billy will be sat under an anticyclone which will provide a great exhaust mechanism for the storm. Therefore, JTWC forecast Billy to gain cat 1 status on the SS scale in a few days time and BOM forecast a similar intensity at this time frame of 75kts (cat 2 on the Australian scale). Billy has the potential to become a dangerous threat to NW Australia over the xmas week as the potential for some rapid strengthening exists along with the fact of Billy remaining fairly near to the coast providing strong winds and rain. It is uncertain where a final landfall location may be, if indeed there is one as it is entirely possible Billy may continue to drift westwards out into the open Indian Ocean. Billy needs to be closely watched as does any storm which could become powerful near land.

Edited December 21, 2008 by Somerset Squall

[Cookie]

thanks for a great update mate, looks very interesting indeed

new update

Tropical Depression BILLY is forecast to strike land to the following likelihood(s) at the given lead time(s):

Yellow Alert Country(s) or Province(s)

Australia

probability for TS is 55% in about 24 hours

Yellow Alert City(s) and Town(s)

Kuri Bay (15.6 S, 124.5 E)

probability for TS is 55% in about 24 hours

Green Alert City(s) and Town(s)

Lombadina (16.5 S, 122.9 E)

probability for TS is 45% in about 36 hours

Derby (17.3 S, 123.7 E)

probability for TS is 35% in about 36 hours

Note that

Yellow Alert (Elevated) is CAT 1 or above to between 10% and 30% probability, or TS to above 50% probability.

Green Alert (Low) is TS to between 31% and 50% probability.

CAT 1 means Tropical Cyclone strength winds of at least 74 mph, 119 km/h or 64 knots 1-min sustained.

TS means Tropical Storm strength winds of at least 39 mph, 63 km/h or 34 knots 1-min sustained.

[Somerset Squall]

Billy's centre is right on the coast and convection is already exploding in the western quadrant (over the ocean). Intensity has increased to 30kts and intensification is now beginning. The fact that Billy isn't even over water yet bodes well for some more rapid intensification once he is. The only limiting factor for fast intensification is if Billy dips too far south and continues to interact with land. Excellent outflow, hot sea temps (32C) and non-existant shear should allow Billy to rapidly intensify as I said above, and the BOM are particularly agressive with the intensity forecast forecasting Billy to be at 80kts in a few days time. Billy has oppurtunity to become much stronger than this if he makes good use of the conditions.

Image of Australia with Billy at around 15S, 125E.

[Cookie]

its going to be an interesting watch to see what happens with this system

[Somerset Squall]

Billy has re-strengthened to a 40kt tropical storm. However, he has also dipped southwestwards and is consequently dragging along the coast near Derby and Broome. This will limit intensity gains for the next 12-24 hrs. After which, a bend to the west as the subtropical steering ridge re-orientates itself to the south of the storm will ensure land interaction will be minimised and proper intensification can begin. Just how strong Billy will get is open to question, conditions are certainly favourable for the next few days but if Billy travels too far west it may reach cooler waters and a less conducive upper level enviroment (eg. higher shear).

Thanks for the image Cookie, certainly shows the convection exploding as Billy hit water again!

[Cookie]

looks like it could make cat 1, according to you're image above!

new uodate

Tropical Storm BILLY is forecast to strike land to the following likelihood(s) at the given lead time(s):

Yellow Alert Country(s) or Province(s)

Australia

probability for TS is 80% currently

Yellow Alert City(s) and Town(s)

Lombadina (16.5 S, 122.9 E)

probability for TS is 80% currently

Derby (17.3 S, 123.7 E)

probability for TS is 70% within 12 hours

Broome (18.0 S, 122.2 E)

probability for TS is 60% in about 24 hours

Green Alert City(s) and Town(s)

Lagrange (18.7 S, 121.8 E)

probability for TS is 45% in about 24 hours

Anna Plains (19.3 S, 121.6 E)

probability for TS is 35% in about 36 hours

Note that

Yellow Alert (Elevated) is CAT 1 or above to between 10% and 30% probability, or TS to above 50% probability.

Green Alert (Low) is TS to between 31% and 50% probability.

CAT 1 means Tropical Cyclone strength winds of at least 74 mph, 119 km/h or 64 knots 1-min sustained.

TS means Tropical Storm strength winds of at least 39 mph, 63 km/h or 34 knots 1-min sustained.

[Somerset Squall]

looks like it could make cat 1, according to you're image above!

Certainly more than possible Cookie, however, Billy needs to get away from land first. Seems to love hugging land this one! Your landfall update clearly shows that Billy is still a threat to land, more from rain than wind. Low level flooding is possible but for many areas the rain will actually be welcome as it has been very dry across the NW of Australia (this is not uncommon).

[Cookie]

is it me or is their a smaller system near AUS as well as billy?

[Somerset Squall]

is it me or is their a smaller system near AUS as well as billy?

Indeed there is, a tropical low (invest 98P) in the Gulf Of Carpentaria (east of Billy) that is moving southwestwards slowly inland. Therefore, development isn't expected but it certainly looked impressive for a while and could easily have become a tropical storm if it had longer over water. It has a small shot at development if it veers west and manages to get over to the Josef Bonaparte Gulf (where Billy developed) but it's a VERY long shot. Well spotted though.

[Cookie]

cool busy busy at the moment, which I like hate it when their ain't anything going on.

[Somerset Squall]

Me too!

Things are now getting very interesting with Billy. Intensity was increased to 50kts this morning but Billy has now began to move westwards so land interaction is decreasing, and in the last few satellite images, you can clearly see Billy has developed an eye. I expect some fairly rapid intensification in the next 24 hours or so. Billy is a small system so can rapidly strengthen in favourable environmental conditions, but can also just as rapidly weaken if the environment deteriorates. I would expect weakening beyond 48hrs as waters will gradually cool on the westwards track and shear may increase. But for now, shear is low, waters are hot and outflow is good, and the appearance of an eye suggests Billy is going up.

[Somerset Squall]

Billy continues to rapidly intensify. Intensity has leapt up to 75kts, and further strengthening is forecast, with the JTWC estimating a peak of 90kts before the environment becomes less favourable. Billy does have the chance to get even stronger than that if the present trend continues!

[Somerset Squall]

Billy continues to push westwards in an environment of low shear, high ocean heat content and good outflow enhanced by an anticyclone parked over the storm. Intensity is now at 80kts, and Billy maintains an eye which is slowly become better defined. I think Billy could well peak at 100kts, maybe even a little higher- the storm is small so can respond fast to the good conditions. He certainly looks very impressive at the moment.

[Supercell Hunters]

http://www.weatherzone.com.au/models/index...68&focus=mh

Another 1 on other side?

[Somerset Squall]

http://www.weatherzone.com.au/models/index...68&focus=mh

Another 1 on other side?

Quite possibly, there is an invest (90P) out in the South Pacific right now which is currently looking disorganised but models are hinting at development as you've shown. That chart also shows Billy continuing westwards out into the Indian Ocean, making further impact for NW Aus itself increasingly unlikely.

Image of 90P currently (it still has a long way to go):

Edited December 24, 2008 by Somerset Squall

[Somerset Squall]

Billy has quite literally bombed in intensity today, and he is now a 105kt, cat 3 (SS scale) severe tropical cyclone. This is roughly a 40kt intensity gain in 12 hours!! There is a strong convectional band flanking the southwest quadrant of the cyclone, which is bring heavy rains to Port Hedland and other neighbouring coastal communties. Billy has a small, tight core with a well defined, if slightly cloud obscured eye. Don't be surprised to see further intensification today with perhaps Billy attaining cat 4 status, I think there is a fair chance. Beyond 24hrs, Billy will begin to weaken as shear increases and waters cool on the west-northwest track into the open waters of the South Indian Ocean.

Edited December 24, 2008 by Somerset Squall

[Cookie]

wow billy has gone nuts since I was last on!