North Sails Weather - Day 5 Audi Hamilton Is RW

'Day 5 racing - Audi Hamilton Island Race Week 2008' Bureau of Meteorology

Weather Forecast issued by Kenn Batt at 0630hr for Thursday 28th August 2008, Day 5 racing at 2008 Audi Hamilton Island Race Week. This forecast is courtesy of North Sails Australia.

Yesterday:

Oh what a weird place, weather wise that is, the Islands can be at times? The wind direction cranked left to around 110deg at around start of racing yesterday before trending right to around 160deg and then left to 130deg by mid afternoon. The speeds were pretty much as forecast i.e. 11-14kn average. In all a lightish day relative to what you had already experienced so far in this excellent race series.

Synoptic Discussion:

A weak ridge of high pressure currently sits over the race area. An inland trough sits over central Qld and extends to a weak low and trough situated near Brisbane. This front will decay in the Fraser Island area later today.
A new ridge of high pressure extending from a high pressure system currently centred to the south of Adelaide, will strengthen again along the entire east coast. So the good old SE'ly trade winds will return to much of the Qld coast going into the latter part of the week.

Day 5 racing - Audi Hamilton Island Race Week 2008 - Bureau of Meteorology

Observations:

At 0600hr, the surface wind at Hamilton Island Airport was from SSE (150degT) at 15kt, gusting 18kt (temp 18C pressure 1020hPa) indicative of the genera l synoptic flow, although it does suffer from the effects of topographic forcing at times. At Creal Reef, further off the coast and to SE of Hamilton Island, the wind was a E'ly at 19kn (indicative of true surface wind). Hardy Reef (offshore to NE) was reporting a wind from 131deg at 16-17kn.

Forecast Discussion:

Forecast confidence level: Above average.
A ridge of high pressure over the area has weakened further during the last 24hr. As such the surface winds for racing today will be pretty much like yesterday. There is however a better chance than yesterday of a moderate sea breeze component creeping in. This should see the wind direction trending left during the afternoon. The wind is expected to freshen tonight out of the SE as a new ridge slowly tightens along the coast.

Natural wind oscillations today around 15 to 25 deg away from effects of topography, tending 25 to 60 deg closer to the effects of any land mass.

Expect wind speed to be 3-7kn stronger in channels/passages due to localized funneling and direction quite flicky.

Forecast Winds for Hamilton Island Area in open water

1000:MD140 DR(160-120) MS14 SR08-20kn could be 110-120deg?
1200:MD130 DR(150-110) MS14 SR08-20kn
1400:MD120 DR(140-100) MS15 SR10-22kn
1600:MD110 DR(130-090) MS15 SR11-22kn may be 10-20deg further left?
1800:MD120 DR(140-100) MS16 SR12-24kn

Key:First column is mean wind direction in deg Mag (MD). It is the 10min average (mean) value at a height of 10m above the water leading up to the hour quoted. The second cloumn is the directional range (DR) of the wind direction in deg Mag. This takes into account the natural oscillation of the wind and is a function of the atmospheric stability, etc. The third column is the mean speed (MS) in knots (kn) and is the average 10min value leading up to the hour quoted at a height of 10m above the water. The last column is the wind speed range (SR) in knots and is the lowest wind speed to highest wind speed in the 10min leading up to forecast hour.

Other Possibilities:

50% chance that wind speed will be 2-5 knots stronger than forecast above later this afternoon, particularly in Dent, Fitzallan and Solway Passages.
40% chance that direction stays in 150-130deg range.

Weather

Dry (apart from the odd beverage at Whitehaven?) and mostly sunny. Take plenty of sunscreen and warm clothing (for after the swimming of course).
Maximum land temperature at Hamilton Island/Whitehaven: 21-22 degrees
Sea Temperature: 19-20 degrees

Wind Waves: 0.5 to 1.4 metre. Less near land, more when wind wave opposes tidal stream. (Wave heights quoted are Significant wave heights).

Current: Good ebb tide this afternoon and flood this evening. Care in the channels particularly.

Tide floods to the south and ebbs to the north in the Whitsundays.

Tide (Shute Harbour): High of 2.75m at 0858hr Low of 0.22m at 1525hr and High of 3.95m at 2120hr

Outlook

Friday: Chance of showers. SE/E winds 14-18 knots (ave)
Saturday: Chance of showers. SE/E winds 18-22 knots (ave)

by Kenn Batt

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