2009 Audi Hamilton Island Race Week Weather Forecast - Final Day

by Kenn Batt on 29 Aug 2009 2009 Audi Hamilton Island Race Week Weather Forecast - Final Day

Issued by Kenn Batt at 0630hr For Saturday 29th August 2009

Nil Warnings current.

Synoptic Discussion:

More of the same today - like yesterday the sea breeze component is expected to re-enforce the light E-NE synoptic flow over the Whitsundays today.

A weak ridge of high pressure still lies over the race area. A weak E-NE 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 E at 6kn indicative of weak synoptic flow.

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

0800:MD120 DR(090-140) MS04 SR00-08kn good chance glass-out?
1000:MD100 DR(080-130) MS05 SR01-09kn good chance glass-out?
1200:MD090 DR(060-120) MS08 SR04-11kn
1400:MD080 DR(050-120) MS11 SR07-14kn
1600:MD070 DR(040-110) MS12 SR07-15kn

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

The wind direction is expected to crank up from the ESE and then slowly trend left as the sea breeze component cuts in.

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 (020 to 090deg) compared to that at the more eastern forecast point above.

The wind speed is expected to be 2-3kn stronger and direction more left close to the mainland coast compared to offshore due to slightly stronger sea breeze.

Wind will be lighter and very flicky close in the lee of any landmass e.g. Whitsunday Island, etc. Some speed acceleration can be expected between islands and out of some west facing bays.

Be extra, extra, extra careful today with the light winds coupled with strong tidal flows.

Natural wind oscillations around 20 to 30 deg in unperturbed flow!

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

Current: A strong ebb this morning followed by a strong flood this afternoon. Be extremely careful in channels, etc.
Remember: Tide floods to the south and ebbs to the north in the Whitsundays.

Tide at Shute Harbour: High of 2.22m at 070hr, Low of 0.91m at 1242hr and High of 3.19m at 1930hr.