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#249912 - 11/05/2004 10:00 Tasman Sea Low 11-12 May 2004
Craig Arthur Offline
Wind hazard researcher

Registered: 08/05/2001
Posts: 3549
Loc: 149.152009°E 35.187056°...
Thought this low would be worthy of it's own thread. wink

The last few hours of satellite imagery have shown two lows spinning around each other, one over NZ and the other seweeping north past the east coast of TAS towards VIC/NSW. A high pressure system is centred southwest of TAS and ridging into western VIC, resulting in a tight pressure gradient over the Tasman Sea west of around 155E. The double low system means there is a fetch of well over 1000km originating near the South Islan of NZ. Quikscat winds have been measured at over 45 knots across this region on the 20040410 22Z pass.

BoM high seas f'cast:
Code:
 TROUGH ALONG 28S164E TO LOW 1004HPA NEAR 43S164E TO SECOND LOW 1007HPA NEAR
39S152E, FORMING A DEVELOPING COMPLEX LOW SYSTEM. TROUGH NEAR STATIONARY IN
NORTH AS FIRST LOW MOVES SLOWLY SOUTH/SOUTHEAST REACHING 995HPA NEAR 38S169E BY
112300UTC AND SECOND LOW MOVES SLOWLY NORTH/NORTHEAST REACHING 999HPA NEAR
37S157E BY 112300UTC.

WITHIN 300NM OF LOW CENTRES.
CLOCKWISE WIND 20/30 KNOTS GRADING TO REACH 30/40 KNOTS IN GALE AREAS AND UP TO
45 KNOTS ACROSS SOUTHWESTERN, WESTERN, AND NORTHWESTERN SECTORS OF COMPLEX LOW
SYSTEM. ROUGH/VERY ROUGH SEAS, VERY ROUGH/HIGH IN GALE AREAS. GENERALLY MODERATE
SWELL ALTHOUGH MODERATE/HEAVY IN GALE AREAS. 
Considering the low near TAS is progged by all (BoM, TWC, NWS) models to deepen in the next 24-48 hours, it seems reasonable to expect that mean winds could exceed 50 knots in eastern Bass Strait/Tasman Sea region. With the winds acting over a substantial fetch, seas will rapidly build, up to 7/8m. Swell waves will of course take longer to build, but 5/6m and increasing in E Bass Strait and along the southern NSW coast seem reasonable. Also keep in mind that the EAC is a southerly current, so it will act to steepen both seas and swell off the coast - latest SST imagery indicates a warm tongue extending past Gaob Is which may be associated with an increased southerly current.

The low in the western Tasman is predicted to track N/NE over the next 24 hours, putting it east of Gabo Is at 20040412 00Z, with central pressure 1000 hPa. The ridge W of TAS will maintain its strength, so surface winds of 40-50 kts over water should persist. Conditions should be pretty horrid offshore for the next 48 hours.

I'd love to see the sea/swell trace from any of the oil platforms/rigs along the Gippsland coast over the next 2 days. Anyone for a jaunt down to Hobart?

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#249913 - 11/05/2004 11:28 Re: Tasman Sea Low 11-12 May 2004
Craig Arthur Offline
Wind hazard researcher

Registered: 08/05/2001
Posts: 3549
Loc: 149.152009°E 35.187056°...
Finally sourced a sea surface height image...



(Apologies for the broken necks once you look at it :p )

Indicates there should be a substantial southerly current near the NSW South coast, with a cyclonic eddy at about 154E, 38S.

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#249914 - 11/05/2004 14:27 Re: Tasman Sea Low 11-12 May 2004
Craig Arthur Offline
Wind hazard researcher

Registered: 08/05/2001
Posts: 3549
Loc: 149.152009°E 35.187056°...
Will be interested in the latest MLAPS run and the status of the wind warnings. With the recent spate of severe wind events, any Storm Warnings issued appear to be issued once MLAPS picks up winds over 50 knots. TWC-mesocast has progged +50 knots on last nights 12Z run, and, going on past events, it's been pretty accurate. If the latest MLAPS progs >= 50 knots and a Storm Warning is issued, I'll have confidence in TWC-mesocast's ability in early detection of extreme wind events - at the very least, severe wind events over western Tasman Sea and Bass Strait.

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#249915 - 11/05/2004 22:49 Re: Tasman Sea Low 11-12 May 2004
pingtang Offline
Meteorological Motor Mouth

Registered: 18/11/2001
Posts: 5525
Loc: Nowra, NSW
Tomorrow is looking big.Like I said in another forum,8-10ft looks quite possible at places fully exposed to south swell.Maybe abit more,if the winds really crank within that fetch.With a S/SW airstream,many places should turn on tomorrow.Check out the Eden Buoy.HMAX was very close to 10metres at 2100! Wave heights have also increased at Batemans Bay,but not to the extent of the Eden Buoy.Tomorrow for Sydney- 4-6ft increasing to 6-8ft later.Possible 10ft bombs at South swell magnets.Thats just my opinion anyway.

Interesting to see how this event pans out!
_________________________
RAIN YTD-
34mms

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#249916 - 12/05/2004 13:14 Re: Tasman Sea Low 11-12 May 2004
Craig Arthur Offline
Wind hazard researcher

Registered: 08/05/2001
Posts: 3549
Loc: 149.152009°E 35.187056°...
Quikscat winds appeared to peak at around 45 kts yesterday, so MLAPS was (just) on the low side and TWC-mesocast overforecast winds out there. Still seeing the impressive effects of the low system along the coast - excellent conditions at Manly this AM :p .

MHL buoy at Eden is bouncing off 4m Hsig with peaks up at 8m. Period is dropping away again, indicating that the source is getting closer. Sydney Directional shows dead south swell at around 10 sec (but that's moving up and down like a yo-yo) and Hsig around 3.5-4m.

Notably LAPS, MLAPS, GFS and TWC-mesocast all have the low off the NZ west coast retrograding back across the Tasman Sea in the next 48 hours. That means even more big swell and strong winds!

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