2014 Melbourne to Vanuatu Weather Outlook – Wednesday 25/6 Update

Four days until the start on Sunday and the prognosis is for this vigorous westerly airstream to continue until at least early next week. The westerly pattern kicked off with a bang on Tuesday, with passage of an intense cut off Low through Bass Strait.

As shown in the satellite pic and aviation sigwx chart updated from the weekend, the Low featured an upper cold pool and a classic hook in the polar jet, enhancing the intensification and delivering severe westerly gales along the Victorian coast. Seas in Bass Strait built up quickly, with the Port of Melbourne Wave Buoy near the Heads measuring significant wave heights of 5m and maximum wave heights of 7m from the southwest by Tuesday afternoon.

For this weekend the pattern sees southwesterly cold fronts lining up along the south coast of the continent in the classic ‘shark fin march’ much vaunted by skiers, which looks set to include a cold front on Sunday and possibly also Saturday, with cold and blustery west/southwesterly winds. The passage of the Sunday cold front is shown on the prognosis map below. A well developed seaway associated with this pattern can be expected in Bass Strait, a key consideration for safe negotiation of the Rip and legs across to the Prom and Gabo.  

Of interest is how fast and in what form the High behind the westerly airstream will migrate to the east towards the Tasman. Early indications from the ACCESS, ECMWF and GFS models (ACCESS for Wednesday 2 July shown below) are that this migration will be relatively slow and centred around 35 S latitudes, and likely to maintain a favorable southerly/southwesterly flow along much of the race track until at least midweek. Further to the west and the Low shown west of WA (on the Sunday prognosis) and south of WA (in the ACCESS Wednesday model) is also a feature to watch, particularly its development and potential for intensification as it moves east. On the weekend we will look at how these systems have changed or progressed enabling a better idea.

Current-wise, CSIRO-IMOS imaging of the eastern seaboard indicate that the East Australian Current is running relatively strong for this time of year, and featuring a number of jets and eddies setting in various directions between Flinders Island and Jervis Bay. Warm water temperatures are persisting off the southern NSW coast of around 20 C.

Andrew Roberts