Weather Day 2 Hamilton Is - courtesy North Sails

by Kenn Batt on 24 Aug 2008 Weather Forecast Issued by Kenn Batt at 0630hr For Sunday 24th August 2008 - 2008 Audi Hamilton Island Race Week. Forecast courtesy of North Sails Australia.

Yesterday: The wind behaved pretty much as expected with max right 155degM and max left 120degM. The speed commenced in the 20-24kn (ave) range and eased during the afternoon to be 14-17kn (ave) by early to mid-afternoon.

Synoptic Discussion:

The high over South Australia will continue to move eastwards and decay over the Tasman Sea about mid week as a new high moves into the Bight. As the high moves eastwards the onshore flow will become more moist and isolated
showers will develop over the Whitsunday islands from tomorrow and persist till mid week.

A series of upper troughs will move across southern Queensland during next week.

The first trough will bring some middle level cloud on Monday but no rain is expected from this cloud.

The second trough will begin to intensify over South Australia on Tuesday with
some isolated showers and possible thunderstorms developing over Whitsundays on Wednesday. This upper trough will be accompanied by a surface cold front.
[Sorry, this content could not be displayed]
Observations:

At 0600hr, the surface wind at Hamilton Island Airport was from SE at 22kt, gusting 26kt (temp 17C pressure 1021hPa) indicative of the general synoptic flow, although it does suffer from the effects of topographic forcing. At Hardy Reef, further off the coast, the wind was a SE’ly at 20kn (indicative of true surface wind)

Forecast Discussion:

Forecast confidence level: Medium

The ridge of high pressure over the area seems to have reached its maximum intensity. As such a slow easing trend in the winds can be expected over the next day or so. The wind today is expected to be pretty much gradient-driven and you can expect fresh and gusty SE’ly over the area. The sea breeze component will have the effect 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 5-8kn less than further offshore to boot!

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 due to localized funneling and direction flicky. There is a chance that the wind speed may decrease by 3-5kn later this afternoon and direction reach 10-20deg more left than forecast?

Forecast Winds for Hamilton Island Area in open water

0800:MD150 DR(170-130) MS21 SR17-29kn
1000:MD130 DR(150-110) MS19 SR16-28kn
1200:MD130 DR(150-110) MS18 SR15-26kn
1400:MD120 DR(140-100) MS17 SR13-24kn
1600:MD120 DR(140-100) MS16 SR12-22kn
1800:MD110 DR(130-090) MS15 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

Dry with some high cloud around. 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: Another strong flood tide for much of the day. Care in the channels particularly.

Tide floods to the south and ebbs to the north in the Whitsundays.
Tide (Shute Harbour): Low of 0.83m at 1025hr and High of 3.07m at 1731hr

Outlook
Monday: Chance of shower. SE winds 15-22 knots.
Tuesday: Chance of shower. SE winds 12-18 knots