9:40 PM Sat 20 Aug 2011 GMT
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'Forecast chart for 4pm today - Audi Hamilton Island Race Week 2011 day 2'
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Audi Hamilton Island Race Week day two daily weather forecast - Warnings: Nil Warnings current for area today at time of forecast issue. However a Strong Wind Warning has been issued for Monday.
Synoptic Discussion: A large slow moving high pressure system with a central pressure of 1037 hPa situated east of Tasmania, is moving eastward into the southern Tasman Sea and is expected to strengthen further during the next couple of days. A low pressure system [1016 hPa central pressure] situated off the northern NSW coast is expected to move northwards and weaken today.
Observations: At 0600hr the surface wind at Hamilton Island was 150 deg at 14kn, gusting 17kn (temp 18C, pressure 1020hPa) indicative of the synoptic wind. At Hardy Reef (further offshore at 19.7S 149.2E) the wind was unavailable. At Creal Reef (20.53S 150.38E) the wind was SSE at 19kn.
Forecast Winds for Surprise Rock (Read Discussion below)
1000:MeanDir:150d DirRange:170-130d MeanSp:16kn Gust:19kn
1300:MeanDir:140d DirRange:160-120d MeanSp:15kn Gust:20kn
1600:MeanDir:130d DirRange:150-110d MeanSp:18kn Gust:22kn
1900:MeanDir:130d DirRange:150-110d MeanSp:20kn Gust:25kn
Key: MeanDir: Mean wind direction Degrees True, DirRange: Wind direction range Deg T , MeanSp: mean wind speed in Knots, Gust: Maximum wind speed possible in the 10secs leading up to the hour in Knots.
Discussion: Good model agreement today. Similar to yesterday, the trend is expected to be a SE'ly tending left during the afternoon.
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Latest surface chart - Audi Hamilton Island Race Week 2011 day 2 -
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The two big question marks today however are:
1. How far left the wind direction? I'm thinking 110deg max left.
2. When will the surface winds strengthen in response to the low weakening and a SE surge push into the area (as the high pressure ridge dominates)? I'm expecting the wind to slowly strengthen after 1600hr, with the strongest surge occurring overnight.
Wind may be a little stronger at times than above in Dent/Fitzallen/Whitsunday Passages due to funnelling?
Wind may also be channeled/funnelled and hence stronger between islands and out of some bays. Wind may be lighter and more variable in the lee of any land mass.
Natural oscillations: around 15 to 20 deg away from the effects of the land.
Weather: Dry and mostly sunny. Maximum land temperature at Hamilton Island: 23 degrees.
Wind Waves: 0.5 to 1.7metres, less in lee of land, more in open water and when wind wave opposes tidal current. (Wave heights quoted are Significant wave heights).
Current: A good flood for racing today. Be extremely careful in channels, etc.
Remember: Tide floods to the south and ebbs to the north in the Whitsundays but there can be huge localized variations.
Tide at Shute Harbour: Low 1.21m at 0933hr, High 2.50m at 1639hr
Sea Temperature: about 22 degrees.
Outlook
Monday: Showers. Slight chance of a thunderstorm. SE winds at 20-25kn (ave), stronger further offshore.
Audi Hamilton Island Race Week
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by Kenn Batt
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Double Is Pt, QLD
