Weather by Malcolm RileySydney to Hobart Weather

The Sydney to Hobart yacht race is followed in varying degrees by many Australians and interested yachties around the globe. Add to this race the Melbourne to Hobart (east and west coast), Melbourne to Devonport and Launceston to Hobart; it is a busy racing schedule packed into a few days for southeastern Australia.
The weather is an all encompassing factor that will affect every boat, every minute and eventually every result.
The days of the crusty skipper looking at the sky, sucking on their pipe and making a weather related decision have been superseded by an array of technology to assist the mariner. [In the same vein, while many get Afloat as a printed copy you may wish to also read this article online at the Afloat website www.afloat.com.au as you can just click on links and then bookmark them.]
This article is a bit of a ‘time line’ of what a potential competitor or armchair enthusiast interested in a race may be looking at.
Many competitors will be keeping an eye on the weather along their intended route for a few months out trying to get a ‘feel’ for what’s going on this year.
There is an analysis chart archive that goes back at least ten years in six hourly time steps at www.bom.gov.au/australia/charts/archive/index.shtml
This archive can be looped or looked at individually.
You would also want to see what the currents are up to, especially those that are affected by the East Australian Current. The CSIRO have a site that shows daily ocean currents. These currents are derived from various buoys and satellite data at www.marine.csiro.au/remotesensing/oceancurrents/SE/latest.html
You now may have built up a picture of what the atmosphere and the oceans have been up to for the last month or so.
It is now the 20/21 December and the first indications of the weather conditions for the early part of the race will be on websites.
For broad scale weather patterns www.bom.gov.au/australia/charts/viewer/index.shtml will give the forecast location of weather systems and coarse scale wind speeds and directions.
For broad scale wind waves and swell information go to www.bom.gov.au/australia/charts/viewer/index.shtml?domain=combinedW&type=sigWaveHgt there are dropdown menus to select various wave data.
By choosing different ‘Domains’ from the dropdown menus you can get more detailed wind information but these do not extend as far into the future as the coarse data.
For forecast ocean currents visit the ‘Bluelink’ site. Blue link is a joint project between the Royal Australian Navy, CSIRO and the Bureau of Meteorology.
Go to www.bom.gov.au/oceanography/forecasts/index.shtml select your area of interest from the map and then select ‘Sea Levels and Currents’. If you play the loop you will see the forecast of the ocean current extending up to seven days.
The company Tidetech www.tidetech.org/ has a fee‑for‑service site that provides ocean current data and tide flow data for Sydney Harbour environs, Bass Strait and the Derwent. The Launceston to Hobart race goes through Banks Strait and tide flow can exceed five knots and create ‘unusual’ wave action.
Remember that all these forecasts can change so you should be monitoring the various forecasts each day prior to the race.
On the evening of the 23rd the Bureau of Meteorology will issue the first written forecast for race day. There is a wealth of information available including more detailed forecast wind maps at this site www.bom.gov.au/marine/index.shtml
On the morning of the race you can review all the forecast weather and current data and refine ‘your’ weather strategy for the race.
For the all important Sydney to Hobart start go to www.bom.gov.au/nsw/forecasts/localwaters.shtml
This site gives a more detailed look at the waters adjacent to Sydney Harbour.
Once the race is underway you now have all the sites where you can pick forecast wind changes and areas where the currents may give advantage.
Current ChartWeather forecasts are not ‘set in stone’ and do change. You will need to monitor the weather forecasts for your entire route not just the next day. The RYCT usually provides a radio relay ship that broadcasts the forecasts along the Sydney to Hobart track although many yachts will have the internet and get the lot. Coast radio stations will broadcast forecasts and warning – check local skeds.
Remember the Bureau of Meteorology issue warnings up to 24 hours in advance of adverse conditions although usually these conditions are on the forecast three or four days out. An example of a warning is given below (note the date and time of issue):
Wind ChartBUREAU OF METEOROLOGY VICTORIAN REGIONAL OFFICE
Storm Warning for Victorian coastal waters east of Wilsons Promontory.
Issued at 1358 on Saturday the 26th of December 1998.
West/southwesterly wind change of 20/30 knots extending from the west this afternoon then increasing to 35/45 knots tomorrow morning and 45/55knots late Sunday afternoon.
Seas rising to 2 to 3 metres this afternoon, 3 to 4 metres tomorrow morning and 4 to 6 metres late Sunday afternoon.
I’m a regular reader of Afloat and I read your article Microburst or Squall. It was then I recalled the photos that I took on my way to Platypus, Bay North Frazer Is a couple of months ago and at the time mystified how they were formed.
Your article described the ‘down draft’ formed by a microburst, in my photo there was no sign of a storm. My question is … what would you call the cloud formation and how was it formed?
Peter Leslie (by email).

aeroplane contrail of a heartThey are commonly known as hole punch clouds or fall streak clouds.
The layer of cloud (altocumulus) would have been supercooled; made of liquid particles that are well below freezing.
Often an aeroplane passes overhead and forms a contrail (cloud made of ice crystals) these ice crystals fall into the supercooled cloud layer. This causes the liquid cloud to freeze and then in turn these ice crystals fall from the cloud layer.
aeroplane contrail of a crossWhy they usually form circles and not lines is not clear. In the cross image above it would have probably have been caused by two jets flying on perpendicular courses both leaving contrails.
You can watch a video explaining supercooled water (basically the freezing point of pure water is not necessarily 0° degrees but the melting point is) at www.youtube.com/watch?v=fSPzMva9_CE
Mal Riley.