2007 Audi Hamilton Island series Weather Wednesday

by Kenn Batt on 22 Aug 2007 Weather Forecast issued by Kenn Batt at 0600hr, for Wednesday 22nd August 2007 courtesy of North Sails.

2007 Audi Hamilton Island Race Week Weather Wednesday

Yesterday:

Over the last two days the low to the south has had a big impact on the race area. On Monday the low formed and moved onto the coast near Brisbane ( I was expecting the low to stay off the coast and hence freshen the winds during the day). This effectively shut out the ridge and thus the winds abated over the day. Yesterday the low moved off the coast and toward the north. This essentially opened up the gradient over the Whitsundays. This saw the wind slowly abate from a fresh S’ly in the morning to a light E’ly by late afternoon.

Synoptic Discussion:

Analysis Prognosis for 2200hr Wed

At the surface level a low pressure system is off the SE Qld coast. A trough of low pressure extends north from the low. This system is expected to move to the N during the day and deepen under the influence of an upper trough. The prognostic chart above for 2200hr this evening hasn’t captured the situation too well. Most models are wanting to keep the strongest winds and precipitation to the south of St Lawrence today.

All this leads to a tricky situation over you.

Observations:

At 0600hr, the weather radar was showing clear conditions over the Islands. Surface wind at Hamilton Island was from 270 degT at 03kn gusting 04kn (land breeze component), temp 17deg and pressure was 1013.5hPa. At Hardy Reef the wind was 174deg averaging 06kn

Forecast Discussion:

Today should be a difficult one weather wise. I’m not overly confident of the situation. Based on model output and rubbing of the gut, I expect the wind to come away from the south and tend left during the morning. How far left is the fifty million dollar question? How strong is also a difficult one? You’ll have to have your wits about you today?


Forecast confidence level: Below Average.
Natural oscillations today around 10 to 30 deg away from effects of topography, tending 20 to 50 deg closer to the effects of any land mass.

Weather

Fine though partly cloudy at times.
Maximum land temperature at Hamilton Island: 20-21 degrees Sea Temp: about 21 degrees.

Wind Waves: 0.5 to 1.2 metre. Less in lee of land. More when wind opposes tidal current. (Wave heights quoted are Significant wave heights).
Current: Tidal stream floods to the south and ebbs to the north in the Whitsundays.
The flood should be a good one this afternoon?
Tide (Shute Harbour): High 0608 1.96m Low 1154hr 1.07m High 1905hr 2.89m
Remember the tidal offsets for the various locations around the area.

Forecast Winds for offshore Hamilton Island

0900: 200deg (220-180) 08kn (05-11)
1100: 160deg (180-140) 10kn (07-13)
1300: 150deg (170-130) 12kn (09-16)
1500: 140deg (160-120) 13kn (10-17)
1700: 130deg (150-110) 14kn (11-18)
1st group=mean dir T 2nd =dir range T 3rd =mean speed 4th=speed range

Channelling and funnelling out of bays and around headlands and between islands could produce 2-5kn stronger winds than forecast above.

Hedge:

1. Wind speed may be a little lighter than above at times today?
2. 30% chance that direction could bang right 170 to 210deg and freshen this afternoon to 15 to 18kn?
3. 50% chance that direction may get 10-20deg more left this afternoon?


Outlook

Thursday: Partly cloudy but mostly fine. SE winds 15 to 25 knots.