Weather Day 3 Hamilton Isl. courtesy North Sails

'Hamilton Island latest surface weather map Day 3' Bureau of Meteorology

Weather Forecast - for Monday 25th August 2008 Hamilton Island Race Week
supplied courtesy of North Sails

Yesterday:
The wind behaved pretty much as expected with max right 160degM and max left 130degM. The speed commenced in the 20-22kn (ave) range and eased during the afternoon to be 15-18kn (ave) by early to mid-afternoon.

Synoptic Discussion:
The high pressure system currently over SE Oz will continue to move eastwards and decay over the Tasman Sea about mid week. A firm ridge persists over the race area with the strongest winds to the north of Bowen. As the high moves eastwards the onshore flow will become more moist and isolated showers will develop over the Whitsunday from today and persist till mid week.

Observations:
At 0600hr, the surface wind at Hamilton Island Airport was from SE at 17kt, gusting 19kt (temp 18C pressure 1021hPa) indicative of the general synoptic flow, although it does suffer from the effects of topographic forcing at times. At Hardy Reef, further off the coast, the wind was a SE'ly at 20-21kn (indicative of true surface wind)

Forecast Discussion:
Forecast confidence level: Above average.

The ridge of high pressure over the area has reached its maximum intensity. As such a slow easing trend in the winds can be expected over the next couple of days. The wind today is again expected to be pretty much gradient-driven and you can expect moderate to fresh and gusty SE'ly over the area generally. The sea breeze component will have a better chance today of pulling the direction left during the afternoon. Any course today that takes yachts close to the mainland, may see them experience more of the sea breeze effect (more left in direction than forecast) than those racing further offshore. The wind speed could be about 3-5kn less than further offshore.

Natural wind oscillations today around 15 to 20 deg away from effects of topography, tending 20 to 50 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 flicky.

Forecast Winds for Hamilton Island Area in open water

0800:MD150 DR(170-130) MS18 SR14-24kn
1000:MD130 DR(150-110) MS17 SR13-25kn
1200:MD130 DR(150-110) MS17 SR13-26kn
1400:MD130 DR(150-110) MS16 SR12-24kn
1600:MD120 DR(140-100) MS16 SR12-24kn
1800:MD120 DR(140-100) MS15 SR10-21kn
2000:MD120 DR(140-100) MS15 SR10-21kn
2200:MD120 DR(140-100) MS14 SR10-21kn
2400:MD130 DR(150-110) MS14 SR10-21kn

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 3-5 knots less than forecast above this afternoon.

30% chance that wind direction reaches 10-20deg more left than forecast later this afternoon.

Weather

Cloudy at times with the chance of a shower or two this afternoon/evening. Take plenty of sunscreen and warm clothing.

Maximum land temperature at Hamilton Island: 21 degrees Sea Temp: 21 degrees

Wind Waves: 1.0 to 2.0 metre. Less near land, more when wind wave opposes tidal stream.

(Wave heights quoted are Significant wave heights).

Current: Strong flood and ebbs tide for today (and tomorrow). Care in the channels particularly.

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

Tide (Shute Harbour): Low of 0.70m at 1149hr and High of 3.38m at 1847hr

Low of 0.83m at 0132hr (Tues) and High of 2.41 at 0711hr (Tues)

Outlook

Wednesday: Chance of early shower. SE/E winds 10-14 knots

by Kenn Batt

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