Audi Hamilton Island Race Week Day 7 forecast

9:36 PM Fri 26 Aug 2011 GMT

'Early morning on final day at Hamilton Island Race Week 2011' Andrea Francolini &copy

Audi Hamilton Island Race Week day seven forecast - Warnings: Nil current but any heavy shower and thunderstorm activity could produce squally and erratic winds over short time periods. Care please.

Synoptic Discussion: A high pressure area in the Tasman Sea near NZ, extends a weak ridge along the Queensland coast. A trough of low pressure over inland Qld is moving east and is expected to cross the Whitsunday area tomorrow.

Observations: At 0600hr the surface wind at Hamilton Island was 180 deg at 07kn, gusting 9kn (temp 20C, pressure 1017hPa) indicative of the synoptic wind plus some shower influence. At Hardy Reef (further offshore at 19.7S 149.2E) the wind was S at 6kn (ave). At Creal Reef (20.53S 150.38E) the wind was ENE at 14kn.

Forecast Winds for a point halfway between Henning Is and South Molle Is (Does not include effects of any precipitation)

1000:MeanDir:140d DirRange:160-110d MeanSp:10kn Gust:14kn
1300:MeanDir:110d DirRange:130-080d MeanSp:12kn Gust:16kn
1600:MeanDir:080d DirRange:110-050d MeanSp:12kn Gust:16kn

NOTE: Heavy showers and thunderstorms can produce short period squalls (up to 30kn possible) and short period wind shifts up to 90deg from the mean in showers and 180deg in thunderstorms.

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: As the inland trough moves eastward, the potential for heavy shower and thunderstorm activity will increase today. The slacker pressure gradient over the area will see the lightest synoptic wind flow of the series: Issues today are:

1. How strong the winds? I'm expecting a difficult day in this area. My thinking is a 8-12kn average speed range? Could be 2-3kn more? Any shower or thunderstorm activity close to or over the race course will however see some even more difficult conditions (gusty/squally and erratic winds) over short time periods (Eyes open)? Shower cells will move in from NE, whilst any thunderstorm cell will move from the WNW.

2. How far left any persistent wind shift? I'm thinking 050deg by mid to late afternoon? (See below under Natural Oscillations)

Audi Hamilton Island Race Week 2011 day 7. Latest surface chart (left) and forecast for 4pm today (right) -

Wind may be 2-3kn stronger at times than above in Dent & Fitzallen Passages and around headlands due to channeling/funneling/upslope acceleration (topographic forcing)?

Wind may also be channeled/funnelled and hence locally stronger between islands and out of some bays. Wind may be lighter and more variable in the lee of any land mass.

Natural oscillations: 20 to 40 deg, up to 90deg over short time periods with the passage of any heavy shower cell and up to 180deg with the passage of any thunderstorm cell.

Weather: Cloudy (lot of low cloud) with showers or drizzle, tending to rain at times. Slight chance of a thunderstorm this afternoon/evening?

Maximum land temperature at Hamilton Island: 21degrees.

Wind Waves: 0.4 to 0.8metres, less in lee of land, more in open water, in gusts/squalls and when wind wave opposes tidal current. (Wave heights quoted are Significant wave heights).

Current: A strong ebb till early afternoon, followed by a strong flood late this afternoon and evening. 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: High 2.78m at 0912hr, Low 0.26m at 1500hr, High 3.82m at 2139hr

Sea Temperature: about 22 degrees.

Audi Hamilton Island Race Week website

by Kenn Batt

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