2014 Melbourne to Vanuatu - Weather Outlook 7 days out

Thank goodness the start is not this Sunday as the short-term outlook would make for a very unpleasant Wilson’s prom to Gabo and most likely some sheltering would be prudent.  Available outlooks at present would seem to be better with a front passing just before the start.  

Perhaps  touch and go for the front in progress or into the southerly. This far ahead is bound to be somewhat different on the day, although 7 day accuracy is quoted as being around 75%+.  This a prognosis from weatherzone (www.weatherzone.com.au) who also have a nice chart showing jetstream influence.  Next is to compare this with a picture of 10am prognosis from the BOM Access model which shows the front should be just passed and a fairly stiff southerly in place for the trip to Blairgowrie. Good news for the overnight stay!

I suspect any route prediction models will have a fairly consistent outcome as the general pattern of highs is still fairly in the 35-40⁰ latitudes with fronts in between.  ie. The westerlies are not very prominent in our area yet as spinoffs from below the highs, although this week will see some action in Bass Strait.  Now let’s look at the southern hemisphere MSLP to get an idea of the general patterns circulating which is useful to see the broad scheme although it is modified before it gets to the race area.  Also is a general jetstream chart to guess which areas COULD be influenced.  Note this Southern Hemisphere map is an analysis and not a prognosis, therefore requiring to move it ahead a bit to match the others. Significantly, all the highs are lying in much the same latitude band. During next week, we will look at how these systems have changed or progressed enabling a better idea.

The jets are displayed in a convenient way for visualisation in this aviation sigwx chart. It does not show the vertical meanders which can give entry and exit areas.  It also uses heights in flight levels.  For instance FL400 would be standardised for aircraft 40,000ft and by studying the chart one can determine the upper and lower heights of the jet.  Entry and exit points are useful in determining where low intensification or formation areas could present and as such are better represented on 200 & 500 hpa maps. (Numerical prediction products BOM). Looking back at the sigwx (significant weather) chart one can see the confluence of jets under Perth which no doubt will be responsible for the complex low situation forecast next Tuesday and on. Note also that parts of the jets are very fast-up to 200 knots. Each solid feather represents 50 kts.

We will follow all this further next week.

Robin Hewitt