Storm Australian Severe Weather Forum
Severe Weather Discussion => Tropical Cyclones, Typhoons and Hurricanes Worldwide => Topic started by: Michael Bath on 31 July 2007, 10:41:50 AM
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First TC of the 2007/2008 developed this morning per JTWC within the Australian region at 91E. The low has been in the advisories for 2 days but finally reached the threshold.
https://metocph.nmci.navy.mil/jtwc/warnings/sh0108.gif
BoM Perth put out a tropical low warming later in the day.
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Satpics don't show much yet - is it too far out! There's definite movement afoot with this one. One to watch considering they have got warnings out. Thanks, Mike for posting the thread - was not even monitoring considering the fine weather!
Here's the latest.....
At 0600UTC a tropical low was located within 20 nautical miles of
Latitude eleven decimal eight degrees South [11.8 S]
Longitude ninety one decimal seven degrees East [91.7 E]
Recent movement southeast at 8 knots.
Maximum winds 30 knots.
Central pressure 998 hPa.
AREA AFFECTED
Within 90 nautical miles of the centre extending to 200 nautical miles
in southern quadrants.
FORECAST
Sustained clockwise winds 30/40 knots in southern quadrants possibly extending
to northern quadrants should the low develop into a tropical cyclone in the next
12 to 24 hours. Rough to very rough seas and moderate swell.
At 1800 UTC 30 July: Within 60 nautical miles of 12.9 South 92.6 East
Central pressure 998 hPa.
Winds to 30 knots near centre.
At 0600 UTC 31 July: Within 100 nautical miles of 13.9 South 93.3 East
Central pressure 998 hPa.
Winds to 30 knots near centre.
Next warning issued by 1300 UTC 30 July 2007.
Mike
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Lasted less than 24 hours and just two warmings issued by JTWC. It looked better on satpics before it was classified TC strength.
Previous July TC was 20 - 27 July 1998
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Hi Michael,
Previous July TC was 20 - 27 July 1998
I almost entered a post yesterday on this basis. Well the possible implications for us. The tropical cyclone threat may have excited some but being July I took no real interest. I was going to indicate my impressions of what the positioning and timing could mean with regards to the existence of a tropical cyclone in this region. But that would have complicated the discussion. Now that the tropical cyclone threat has eased, probably more of an appropriate time.
Well the north west cloud bands and them streaming down this way - what effect could this have in terms of an impact on eastern Australia. Well 1998 saw some serious east coast lows develop with a relatievly wet August experienced. Michael do you know if other years such as 1986 or 1990 for instance may also have had tropical cyclones/tropical activity in those regions during July? Or perhaps a good Indian/Bangladesh monsoon?
Regards,
Jimmy Deguara
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Would this early TC and NWesterly inflow of moist air be as a result of a Rossby wave? I'm not that familiar with Rossby waves, but do know that it is either oceanic or atmospheric. That these waves originate from the northern hemisphere and at times a portion of this air/oceanic mass 'pulls downward' toward the equator at times?
As we have seen in the past with moist inflow streaming across central WA and NT into NSW and VIC that they have interacted with ECLs and created on large low pressure system.
Or is it just the MJO that is progressively getting closer causing all this?
Mike
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Jimmy - the earliest in those years was September. There have been a few occasions reported of weak TCs in July - at least since the satellite era. And they have all formed around 90E.
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From the BoM issued yesterday for their outlook for the northwestern area:
Computer guidance suggests a low may develop in the vicinity of 12S 115E-122E on
Tuesday or Wednesday with an increased risk of cyclone formation later Thursday
or Friday. At this stage the likelihood of a tropical cyclone developing in the
next three days is:
Wednesday: Low
Thursday: Moderate
Friday: High
MSLP maps show a progressive deepening low of 1000 to 996hpa off the coast of northwest WA by Friday.
This for Darwin by JTWC:
TROPICAL DISTURBANCE SUMMARY:
(1) AN AREA OF CONVECTION HAS PERSISTED NEAR 11.9S 129.5E,
APPROXIMATELY 65 NM NORTHWEST OF DARWIN, AUSTRALIA. ANIMATED
INFRARED SATELLITE IMAGERY INDICATES A WEAK LOW-LEVEL CIRCULATION
CENTER (LLCC) WITH POORLY ORGANIZED DEEP CONVECTION FLARING NEAR
THE CENTER. THE DARWIN RADAR CLEARLY SHOWS CONVECTION ROTATING
AROUND THIS DEFINED CIRCULATION JUST WEST OF BATHURST ISLAND. SURFACE
OBSERVATIONS NEAR THE LLCC INDICATE SLP NEAR 1005-1006 MB. THE
251058Z SSMIS AND RECENT AMSU IMAGES DEPICT CONSOLIDATING BUT WEAK
DEEP CONVECTION. UPPER-LEVEL ANALYSIS INDICATES A DEVELOPING
ANTICYCLONE OVER THE LLCC WITH FAIR OUTFLOW ALOFT ENHANCED BY
TROUGHING TO THE SOUTH. MAXIMUM SUSTAINED SURFACE WINDS ARE
ESTIMATED AT 15 TO 20 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED
TO BE NEAR 1005 MB. BASED ON THE LACK OF SIGNIFICANT CONVECTIVE
BANDING AS WELL AS THE POSITION NEAR LAND, THE POTENTIAL FOR THE
DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24
HOURS IS POOR.
I'd like to see it move further north to gain some advantage of the warmer ocean temps and away from land. Viewing the 7 day animation of the MLSP BoM maps might give an indication of how the monsoon trough is moving and the tropical charts don't even have it drawn on yet. Checked out the wind profiles for new years day and there was some circulation shown on the GFS maps on WZ - but i'd like to see more stronger circulation!
Mike
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In addition to the Tropical Low mentioned above, the Coral Sea, and the southcentral Indian Ocean have potential Cyclones by the weekend as well.
Sounds like an interesting way to end the year, or start the new one.
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I have noticed that the tropical low off WA coast has now been officially recognised by the BoM. and also has been highlighted on their global severe weather (cyclone/hurricane) page.
If we do get two cyclones (one in west, one in east), expect Melbourne to be very hot and dry in the forcast.
PJ
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Just as a matter of curiosity - what is the definition on a cyclone as opposed to a low? When does it actually change status?
Is it wind speeds, or pressure? Or something else?
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Hi Richary,
In our area, it's windspeed. Once a Tropical Low has sustained 10-minute winds of 35 knots (which equates to Gusts of 90km/h), it is assigned a name and called a Tropical Cyclone. Pressure does play a part, but with this system (which is 990 as I'm typing), it's pretty intense for a Tropical Low, and would be very close to forming to a Cyclone anyway. Once they do attain Cyclone strength, they can generally intensify faster due to the rotation.
EDIT - It might actually be 10-min winds of 40 knots, and not 35; I'm not 100% sure.
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Added to that ....once the pressure falls below 1000hpa. First it's a tropical low, then a cyclone. So long as the BoM see circulation on a regular daily basis and organisation, increase of thunderstorms surrounding it then all that is taken into account when forecasting it on a three daily basis. So long as an eye develops then it shows strong, deep circulation and maturity. Best thing to do is keep an eye on the satellite animation loops and see how it all falls into place. NASA, GOES loops are the pick. you can go on the BoM site for all the information on cyclones at http://www.bom.gov.au/weather/cyclone/about/about-tropical-cyclones.shtml
BoM NT are tipping for a probably low to form by Sunday or middle next week for the Gulf of Carpentaria. Very early days and really depends on how much of the fuelling winds the cyclone on the west coast pinches from us. If both cyclones form on either side of the country the NT will get a 'break' in the monsoon as all of its energy is being directed towards other events -
From what I've seen of the models the monsoon trough is going to go deep into the NT an afar southward whilst holding onto the low just below the GOC. The trough will have to rise again back to open water for anything to spark a that low up. It's happened before a few years back when the monsoon and a low got dragged to Katherine for over a week, flooded the town, moved back up with the trough and then formed a cyclone once over water again.
Mike
Mike
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Thanks for the definitions. I knew there had to be a tipover point somewhere of when it changed from a low to a cyclone. Given the lack of activity forecast in Sydney for the next week I guess we will have to vicariously look on from a distance.
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Has anyone been tracking Cyclone Funa, as it has been a Cat4, and seems to have gone unnoticed?
Big Pete
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I see the Bureau has issued a cyclone warning for Norfolk Island.
A CYCLONE WARNING IS IN FORCE FOR NORFOLK ISLAND
TROPICAL CYCLONE FUNA [950HPA] WAS CENTRED NEAR 29.7 SOUTH 172.2 EAST
AT 200200 UTC, OR ABOUT 450KM EAST OF NORFOLK ISLAND, AND MOVING
SOUTHWEST AT ABOUT 20 KNOTS.
ON THIS TRACK THE CYCLONE SHOULD PASS ABOUT 200KM SOUTHEAST OF
NORFOLK ISLAND TONIGHT.
GALE FORCE WINDS ARE EXPECTED FOR NORFOLK ISLAND FROM THIS EVENING
THROUGH TO MONDAY MORNING ALTHOUGH THE STRONGEST STORM FORECE WINDS SHOULD REMAIN SOUTHEAST OF THE ISLAND
Bit of a messy structure on the satpics though, with not much to the north and huge mass of rain from it swirling down towards the North Island of NZ.
Looking at the NZ Met service previously it was at 930 HPA so it has weakened a lot as it has moved south.
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Also to note that according to BoM's high seas forecasts. Funa has now become Subtropical (extra-tropical), and will become an intense low over the next 24-48hrs as it tracks southwards towards NZ
Big Pete
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Hadn't come across this site before but it shows the tracks quite well. And intensity levels.
http://tsr.mssl.ucl.ac.uk/tracker/dynamic/200812P.html
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Mike, amd Richary,
Seeing you both live in the NT, have either of you ever seen tornadoes develop within TC's?
Big Pete
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Hi Pete.
We've had the occasional one. Last year of note with Pre-TC George that was deepending over darwin on its way to WA. It produced a supercell which spawned an EF2 perhaps EF3 tornado in Kakadu National Park - I've posted a thread about that in the forum. Caused some damage to outback home and car trailer, with several trees down. There was a damage path also.
They do occur with depressions and cyclones, in fact most hurricanes per se can develop tornadoes once they reach landfall due to rain bands with large cells embedded and strong shear associated with them.
There's some dispute at the moment whether the NT holds some kind of tornado frequency in this country - and yes I'm fully aware of what that state is people and it aint here!!! We don't have the conditions to support supercellular activity unless provided for by tropical cyclones or depressions. There's not enough helicity/shear/vorticity during even severe TS's. We get a few water spouts from strong updraughts in some storms, mostly unseen.
The argument raging here between some folk is that because they may be unseen or unreported due to our expanse of uninhabited land that there may be more than what's actually known and that dry line supercellular storms actually do exist here due to the separation of a desert and the tropics - a dry line.
For me I stand by the simple fact that we don't get 'dry line' storms - in the actual sense of the meaning. Anyone can get storms 'on a dry line' but not the type that most seasoned/experienced chasers have seen and usually they're supercells. I've looked up every available online info article on tropical storms and yes, they can form on dry lines, BUT they are not 'dry line' storms in essence of being supercellular.
I quoted an article to some folk by Tim Marshall, a well-known and respected chaser/meteorologist with the SPC and NSL on such matters - even that did not change the minds of a few - goodness sake, they did not even believe him!
...another thread perhaps on this topic - in fact I'll start one. I'd like a few answers and there's plenty of resource bodies on this forum to give it.
But, yes. We get the odd one with monsoonal lows only if the right conditions prevail.
Mike
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Mike, amd Richary,
Seeing you both live in the NT, have either of you ever seen tornadoes develop within TC's?
Big Pete
Sorry, not me. I'm in Sydney. Have only been to Darwin once for a holiday and it wasn't storm season. Though after spending 5 years in Adelaide where there was only one decent light show I can remember, I sometimes wished I did live in Darwin!
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Yeah only for six months though Richary, the rest is, mmm, well - boring weather wise if you're a storm chaser/observer!
Mike
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Hi all,
Just thought i'd inform all of the impending TC forming off the WA coast at the moment - possible TC should form in the next 24 hrs according to BoM. Also, a low in FNQld may also become a cyclone if it decides to head to the Coral Sea.
Worth keeping an eye on both storms.
Big Pete
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I've been away from my computer over the weekend, and I almost missed a nice looking TC that is churning on the NW WA coast - TC Ophelia. Its a Cat 2 storm - much smaller than TC Nicholas, and has the potential to go deeper. Worth keeping an eye on for those who are not too far away.
Big Pete
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Welcome on board to the newest TC off Aus shores.
Cyclone Pancho (nice name), was born this afternoon (Melbourne time) - tracking south east from quite a fair way off the NW WA coast - it is currently Cat1, but expected to be Cat 2 by tonight - if it follows the forecasted path of BoM, then it is possible for the west coast of WA to be impacted at some stage in 3 days time.
Worth keeping an eye on.
Big Pete
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Seems like TC Pancho is picking up speed. May become a Cat 3 storm in the next 6-12hrs. It also has quite a violent turning near its eye, and is spraying a lot of moisture clouds back into the mainland Aussie trough - that's spread between NW WA, inland NT, SE Qld and N NSW.
Big Pete
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Looks like another cyclone is due for WA's area. Another Tropical Low (which started very close to the equator) has moved into the region.
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It would be a late season, if not beyond the normal season, for one to be forming there right now, but like Mike, I also will be scrutinising it. There also is a tropical low affecting the Fijian region too. Seems to be holding its own at the moment amongst a broad trough/front. Still not growing too much yet, but will be worth looking at.
Big Pete
(BTW - nothing happening in Melb lately, just cold foggy starts and warm clear days - no rainfall - just 6mm for April so far)
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I see that Christmas Island is under a watch.
Details of Tropical Low at 8:00 am WST:
.Centre located near...... 9.4 degrees South 99.4 degrees East
.Location accuracy........ within 75 kilometres
.Recent movement.......... towards the east southeast at 14 kilometres per hour
.Wind gusts near centre... 85 kilometres per hour
.Severity category........ below cyclone intensity
.Central pressure......... 998 hectoPascals
Must be some instability in that region one thinks! Still early days, but perhaps the west coast might see some rain out of this if nothing else - stranger things have happened, remember TC Monica!