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Freak January 2011 continues — cyclone coming our way

Posted By Joanne Nova On January 29, 2011 @ 2:21 am In Global Warming | Comments Disabled

FINAL UPDATE: The far southwest cyclone is just… drizzle. Best wishes for the Queenslanders who are dealing with the real thing right now.

UPDATE#3: Sunday morning –The Cyclone is now Category 1, and wind speeds only 100km/hr and falling, so the BOM have turned off the CYCLONE Alert, and now call it a “Low”. Their map suggests whatever’s left will have a direct hit on perth, but the infra red image suggests it’s already gone past… and will just clip the lower corner of the state.   Looks like it will just be a stormy day.

UPDATE #2: Saturday night –This glorious NASA image shows Bianca a few days ago. Right now the cyclone is losing strength over the cooler water as it heads towards the West Australian Southern coast. Windspeeds have dropped from 185km/hr to 140km/hr. But I thought the intricate detail in this photo was magnificent.

Cyclone Bianca off the North West Cape  27 – Jan – 2011
Image: NASA, Modis 1 pixel = 1 km.

With wild blizzards in the Northern Hemisphere, and mass floods across the whole Eastern seaboard of Australia, it’s good that Perth is not being entirely abandoned by freak forces of nature. We were starting to feel left out.

Cyclone Bianca tracks towards SW Western Australia. (Click on the image to go to the BOM page to watch the hourly updates of satelite images.)

Perth is 32 degrees South of the Equator. We rarely get cyclones but they do spin by every now and again (every ten or twenty years). Right now, about 1000 km NW there is “Bianca” a decent category three, on track to visit us in just over 24 hours. Cyclones being what they are, it may not perform as intended, but then, looking at the history of Perth’s Cyclones, the path is typical. It’s only expected to be a Cat 1 when it gets here: tie down your fruit trees and batten down the caravan. It’s not dire, but we will be cleaning the gutters, (and not camping). National Parks have been closed in preparation. Perhaps, south west WA might get some of that rainfall it needs.

And no, of course, I’m not seriously comparing it those floods or that blizzard.

...

Bulldust predicts:

1) Bianca will track down south and cause some serious weather impact in the populated end of the state:
http://au.news.yahoo.com/thewest/a/-/newshome/8732433/cyclone-threat-to-south-west/

2) Strong weather events (even tropical storms are not unprecendented down this far:
http://upload.wikimedia.org/wikipedia/en/6/6f/Tropical_cyclones_1945_2006_wikicolor.png

3) Someone (Lewandosky perhaps) will blog (probably at the ABC) the meme that more extreme weather events such as this one (this coming weekend) are to be expected because of global warming.

Which all sounds perfectly reasonable to me.

So to head them off at the pass here’s all the other cyclones that hit Perth that were caused by man-made carbon dioxide emissions, starting in 1843.

Some Notable Cyclones Impacting Perth

Tropical Cyclone Impact Description
11 April 1843 A ‘terrific’ northwest gale lasting 4 hours struck the Perth area, then moved southwards to impact Bunbury, where the tidal surge in excess of 4 feet drove two large vessels aground.
10 March 1872 A storm described as being of ‘unprecedented severity’ occurred. The destruction of property in Perth was considerable and many trees were levelled.
27 Feb. 1893 A fierce gale blew at Geraldton and Fremantle. Several boats, including the Alastar and Flinders, broke their moorings and were damaged.
26 Feb. 1915 A storm moved southwards on the 25th from Onslow towards Perth at a speed estimated at 80 km/h. There was extensive damage to property along the track. At Midland Junction, near Perth, a child was killed and several others were injured when the Swan Mission dormitory collapsed.
9-10 March 1934 Perth recorded 77 mm and Toodyay 191 mm as flooding caused damage across Perth and the wheatbelt. The Swan river rose 5.8 m in less than eight hours at Guildford causing considerable damage to unharvested grapes.
10 Feb. 1937 Widespread property damage occurred across the southwest of the state, particularly south of Perth. Many boats were damaged at Rockingham but many more were damaged further south and the Busselton Jetty was extensively damaged. The storm surge forced people to evacuate in parts of Mandurah and Bunbury. Severe bushfires were reported from the forest areas, most notably from Denmark and Walpole. Hundreds of acres of forest, pasture and fruit trees were destroyed by the fires and stock losses were great. Widespread severe duststorms over the wheatbelt reduced visibility to just a few metres in parts.
15 March 1943 A cyclone crossed the coast near Lancelin causing extensive damage along a narrow band from Lancelin to the southeast wheatbelt. Buildings were unroofed, telegraph poles were blown down and roads were blocked by falling trees.
4 March 1956 Buildings and property were damaged in parts of the southwest including Geraldton and Perth. The Perth to Geraldton highway was blocked by numerous fallen trees.
27 March 1960 Many small boats were blown ashore and damaged as Perth recorded winds to 113 km/h. Many centres in the wheatbelt reported damage to outbuildings, wheat silos and homestead roofs.
Vida, 20 March 1975 Winds, recorded to 128 km/h at Fremantle and 109 km/h in Perth damaged many properties including St George’s Cathedral and Perry Lakes Stadium. At Rockingham a 7 m yacht sank, a 6m cabin cruiser was destroyed and many other craft were damaged.
Alby, 4 April 1978 Alby passed close to Cape Leeuwin causing a period of gale force north to northwest winds. Five lives were lost. Damage to property was widespread but was most severe in the region between Mandurah and Albany. Widespread fires and severe duststorms reduced visibility to less than 100 m over a large area
Rhonda, 21-22 Feb. 1986 The remains of cyclone Rhonda crossed the coast near Perth causing heavy rain (131 mm at Greenmount). Flooding, albeit minor was widespread across Perth. Over 100 traffic crashes were attributed to the wet conditions.
Ned, 1 April 1989. Ned crossed the coast near Rockingham. Rottnest and Fremantle reported wind gusts of more than 100 km/h between 6 and 7 am. Only minor damage was reported on land.

Source: Australian BOM –History of Cyclones in Perth

For those who are interested, that history page also has an interesting description of the changes that occur when a tropical cyclone becomes an extra-tropical system — which tends to travel faster — and paradoxically, can cause major damage through fueling bushfires. The storms become asymetrical as they traverse the surface faster.

Cyclones affecting the southwest can move at speeds greater than 70 km/h in contrast to the average 10-15 km/h speeds in the north. As they accelerate, the structure of the cyclone changes so that the regions of dense cloud and heavy rainfall are displaced towards the right quadrants of the system (when looking along the direction of the track) leaving the left quadrants largely free of significant cloud. As a result the heaviest rainfall for example, would occur when a cyclone crosses the coast near and to the north of Perth as in March 1934.

The strongest winds associated with these fast moving systems occur in the left quadrants where the clockwise rotating winds are augmented by the system’s translational speed. The cloud-free squally winds from the north or northeast are a recipe for severe dust storms and an extremely dangerous environment in which fires can engulf the countryside with frightening speed. The wildfires associated with cyclones in February 1937 and April 1978 (Alby) typify this potentially devastating weather scenario.

The change in structure described above is known as extra-tropical transition. This process is observed in other tropical cyclone basins around the world and can result in a re-intensification of the system even though it loses tropical cyclone characteristics.

UPDATE #1:

Saturday 8am: Bianca is still a category 3. Warnings are being updated 4 hourly.

At 8:00 am WST Severe Tropical Cyclone Bianca, Category 3 was estimated to be
920 kilometres west northwest of Perth and
680 kilometres west northwest of Geraldton and
moving south at 24 kilometres per hour.

Bianca is expected to weaken further during today and begin to move towards the
southwest corner of the state. As it approaches the coast it will weaken
rapidly but there is some risk that Bianca could still have an impact on the
South West on Sunday. DAMAGING WINDS with gusts to 100 kilometres per hour are
possible southwest of a line Jurien Bay to Albany.

VERY HIGH to SEVERE FIRE DANGERS are likely near the west coast on Sunday,
possibly reaching EXTREME across inland areas south of a line from Geraldton to
Leonora to Israelite Bay on Sunday.

FESA State Emergency Service (SES) advises that people should start planning
for bad weather and listen for further advice.

Details of Severe Tropical Cyclone Bianca at 8:00 am WST:
.Centre located near...... 27.5 degrees South 107.8 degrees East
.Wind gusts near centre... 185 kilometres per hour
.Severity category........ 3
.Central pressure......... 965 hectoPascals
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