Topic: Tropical Cyclone Billy: WA 17-26 Dec 2008

[Mike]

A thread for this system while its in motion.

TROPICAL CYCLONE ADVICE NUMBER 1 
Issued by the BUREAU OF METEOROLOGY, DARWIN
at 4:00 pm CST [3:30 pm WDT] Wednesday 17 December 2008

A Cyclone WATCH has been declared for a developing tropical low for coastal and
island communities from Cockatoo Island in WA to the WA/NT Border.

At 12:30 pm CST [12:00 pm WDT] a Tropical Low was estimated to be 205 kilometres
north northeast of Kalumburu and 420 kilometres west of Darwin, moving southwest
at 13 kilometres per hour towards the Kimberley coast.

There is the possibility of a tropical cyclone developing close to the north
Kimberley coast on Friday. GALES are not expected in coastal areas within the
next 24 hours, however gales could develop later.
 
Details of Tropical Low at 12:30 pm CST [12:00 pm WDT]:
.Centre located near...... 12.5 degrees South 127.0 degrees East
.Location accuracy........ within 55 kilometres
.Recent movement.......... towards the southwest at 13 kilometres per hour
.Wind gusts near centre... 85 kilometres per hour
.Severity category........ below cyclone intensity
.Central pressure......... 1004 hectoPascals

The next advice will be issued by 11:00 pm CST Wednesday 17 December

[Mike]

This low has tracked further south/SE towards Port Keats and we're now getting some rain bands flowing through Darwin and rural areas.  A little more thunder heard than in previous days but still light but steady rainfall ATM.  Definitive circulation in the radar loop and Darwin is caught in between the bands flowing through.  Most of the heavier falls are in the Darwin-Daly area closer to the center of the low.  NO significant 'squally showers' as forecast, perhaps later on as the low moves inland.  A couple of reports of spouts seen at Bynoe Harbour which is to the west of Darwin, not surprised as that area sees many of them during the wet and with this deepening low it's bound to spin up.

http://www.bom.gov.au/products/IDR631.loop.shtml#skip

[Mike]

A few authorities have updated their comments and this is from the JTWC:  This system is a bit like TC Helen last year, a similar tack but too close to land.  For the enthusiasm factor I'd prefer it to be moving back up to the N/NE but we might see some decent rainfalls come out of it given the past 24 hours and if it decides to continue inland.  JTWC track map included.



1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN A
070 NM RADIUS OF 14.2S 128.4E WITHIN THE NEXT 12 TO 24 HOURS.
AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF NUMBERED TROPICAL CYCLONE
WARNINGS AT THIS TIME. WINDS IN THE AREA ARE ESTIMATED TO BE 25 TO
30 KNOTS. METSAT IMAGERY AT 180530Z INDICATES THAT A CIRCULATION
CENTER IS LOCATED NEAR 14.2S 128.5E. THE SYSTEM IS MOVING SOUTH-
EASTWARD AT 06 KNOTS.
2. REMARKS: THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 13.0S
127.8E, IS NOW LOCATED NEAR 14.2S 128.5E, APPROXIMATELY 175 NM SOUTH-
WEST OF DARWIN, AUSTRALIA. RECENT ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A LOW LEVEL CIRCULATION CENTER THAT IS BEGINNING TO
HAVE DEEP CONVECTIVE BANDING WRAPPING TOWARDS THE CENTER, WHICH IS
ALSO APPARENT IN ANIMATED RADAR IMAGERY.

THE SYSTEM IS IN AN REGION OF LOW VERTICAL WIND SHEAR WITH FAVORABLE UPPER LEVEL OUTFLOW
SUPPORT AND FAVORABLE SEA SURFACE TEMPERATURES. THE CURRENT LIMITING
FACTOR IS THE SYSTEMS PROXIMITY TO LAND, CURRENTLY BETWEEN 30 TO
60 NM FROM LANDFALL. AT CURRENT TRACK AND SPEED LANDFALL COULD
OCCUR WITHIN THE NEXT 10 TO 12 HOURS.

MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 27 TO 32 KNOTS. MINIMUM SEA LEVEL PRESSURE IS
ESTIMATED TO BE NEAR 1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A
SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS GOOD.

[Michael Bath]

Ity got named Billy last night in the 12z bulletin.  Track so far attached.

[Mike]

And he Billy jokes will come flying for sure eh?  It' already started up here - and yep, they're pretty boring.

[Richary]

Now made landfall.

At 9:30 am CST [9:00 am WDT] Tropical Cyclone Billy, Category 1 was estimated to
be 70 kilometres north northwest of Wyndham and 235 kilometres east of Mitchell
Plateau, moving west at 4 kilometres per hour.

GALES with gusts to 100 kilometres per hour are currently being experienced
between KALUMBURU to the NT/WA BORDER, they are expected to persist for the next
6 hours then GRADUALLY EASE.

The cyclone is expected to weaken into a tropical low later today as it
continues to move inland, but may redevelop into a tropical cyclone on Monday
if it moves off the west Kimberley coast, causing gales between KALUMBURU and
BEAGLE BAY [NOT including DERBY].

Widespread heavy rainfall is likely over the southern Darwin-Daly district, the
northern Victoria River district and northern parts of the Kimberley over the
next 2 to 3 days. Significant stream rises and local flooding are expected in
these areas today, extending westwards across the north Kimberley later today.

[Carlos E]

The system has some chance of some steady intensification (possibly rapid for a short time) once it enters the Indian Ocean.

BoM's Technical Bulletin puts Billy at around a Cat 3 in 72 hours.

REMARKS:
EX TC Billy continues to track steadily to the west over the north Kimberley.
The system has retained excellent structure over land. It is expected to remain
in a low shear environment and should redevelop quickly on Monday as it moves
offshore into an area of favourable SSTs.

[Richary]

It did intensify very quick. Crossed coast and became Cat 1 at 9am, then up to Cat 4 by 6pm. Luckily forecast to track away from the coast.

[Peter J]

I think you'll find now that Billy has reached max speeds, and is starting to slow a little -  it did reach gusts out to sea of around 250kph, but is now moderating - the sat pic has no eye within the storm, but the radar does show a "small" eye.

Big Pete