Audi Hamilton Island Race Week Weather Forecast

by Kenn Batt on 27 Aug 2009 Audi Hamilton Island Race Week Weather Forecast

Issued by Kenn Batt at 0700hr
For Thursday 27th August 2009

Nil Warnings current.

Synoptic Discussion:

No true Trade Wind flow today unfortunately. Cold fronts moving through southern latitudes have continued to prevent the formation of a firm ridge along the Qld coast. Slack pressure gradients combined with strong low level temperature inversions have worked together to keep the winds light.

A weak ridge of high pressure still lies over the race area. A slack pressure gradient persists.

Observations:

At 0600hr the surface wind at Hamilton Island was calm (temp 21C, pressure 1017hPa. At Hardy Reef (further offshore at 19.7S 149.2E) the wind was ENE at 5kn indicative of weak synoptic flow.

Forecast Winds for open water 4nm East of Surprise Rock (i.e. east of Hamilton Island) (Read Discussion below)

1000:MD120 DR(090-150) MS05 SR01-09kn chance glass-out?
1200:MD120 DR(090-150) MS07 SR03-12kn chance glass-out?
1400:MD110 DR(070-140) MS09 SR04-14kn
1600:MD100 DR(060-130) MS11 SR06-15kn could be 30deg more left?
1800:MD090 DR(050-120) MS10 SR05-14kn

Note 1: First column is mean wind direction in deg Magnetic (MD). It is the
10min average (mean) value at a height of 10m above the water leading up to the hour quoted. The second column 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.

Discussion

Some of the better computer models are hinting at some slightly better pressure today? Like the last couple of days, the wind direction is expected to crank up from the SE and then slowly trend left as the sea breeze component cuts in. Unlike the last couple of days, there is expected to be a bit more consistent pressure around?

The sea breeze potential is expected to be greatest within a 1nm or so of the mainland due to greater land/sea temperature difference.

The wind flow in the Whitsunday Passage is expected to be more variable compared to that at the more eastern forecast point above. The direction is expected to trend more right closer to the mainland coast and possibly 2-3kn stronger this afternoon due to stronger sea breeze.

Wind will be lighter and very flicky close in the lee of any landmass e.g. Whitsunday Island, etc.

Be careful today with the lightish winds coupled with a moderate flood tide.

Natural oscillations today around 25 to 35 deg!

Weather
Some early low cloud patches then dry and sunny. Take plenty of sunscreen and warm clothes in case?
Maximum land temperature at Hamilton Island: 25-26 degrees. Sea Temperature: about 23-24 degrees.

Wind Waves :
0.0 to 0.4metres, less in lee of land, more when wind wave opposes tidal current.
(Wave heights quoted are Significant wave heights).

Current : A moderate flood for much of the day. Be extremely careful in channels, etc.
Remember: Tide floods to the south and ebbs to the north in the Whitsundays.

Tide at Shute Harbour: Low of 1.02m at 1009hr and High of 2.85 at 1719hr.

Outlook

Friday and Saturday: SE-NE 5-12kn (ave)