Audi Hamilton Island Race Week - Daily weather forecast

by Kenn Batt on 20 Aug 2013 Audi Hamilton Island Race Week - Daily weather forecast issued by Kenn Batt at 0545hr for Tuesday 20th August 2013.

A weak high [1015 hPa] over the southern Coral Sea is expected to move slowly eastwards, maintaining a weak ridge onto the north tropical coast of Queensland. A surface trough of low pressure is expected to move eastward over the Islands this morning. A cooler southerly surge is expected over the area early tomorrow morning.

Observations:
At 0530hr the surface wind at Hamilton Island was 320 deg at 15kn, gusting 19kn (temp 21C, pressure 1013hPa). At Hardy Reef (further offshore at 19.7S 149.2E) the wind was 290deg at 10kn.

Forecast Winds for Surprise Rock (to E of Hamilton Island) (Read Discussion below)

Tuesday
0800:MD210 DR(230-190) MS10 SR07-15kn could be 290-310deg at 8-14kn
1000:MD180 DR(200-160) MS12 SR08-17kn
1200:MD140 DR(160-120) MS12 SR08-17kn
1400:MD135 DR(155-115) MS11 SR07-16kn
1600:MD120 DR(140-100) MS10 SR06-15kn
1800:MD125 DR(145-105) MS09 SR05-13kn
2000:MD130 DR(150-110) MS09 SR05-13kn
2200:MD150 DR(170-130) MS09 SR05-13kn
2400:MD170 DR(190-150) MS10 SR06-14kn

Wednesday
0200:MD180 DR(200-160) MS15 SR10-20kn
0400:MD160 DR(180-140) MS22 SR18-27kn
0600:MD160 DR(180-140) MS22 SR18-27kn

Note: The wind in the Whitsunday Passage is expected to be about 2-5kn stronger than above and could be about 10-20deg more right at times.

Key: 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:
A trough of low pressure is expected to pass over the Islands at about 0800hr this morning (+/- 1.5hr). Ahead of the trough wind will be 290-310deg at 8-14kn (ave) then becoming as forecast above. There is a 65% chance that the wind speeds associated with the change are 3kn stronger than forecast, say between 0800 and 1000hr before easing back to forecast values?

A cooler southerly surge is expected to arrive between midnight and 0300hr tomorrow morning.

Wind direction and speed is expected to be more variable than forecast above over parts of the race course due to changing topographical profiles i.e. wind speed enhancement (+2 to 5kn) due to funneling out of bays, some speed enhancement and wind directional changes around headlands and in passages. Lighter and more variable winds in the lee of islands, etc

Natural wind direction oscillations: around 20 to 30 deg, more/less due to topographical influences.

Weather:
Early low cloud clearing to a mostly sunny day.
Maximum land temperature at Hamilton Island: 25 degrees.
Sea Temperature: about 21-22 degrees.

Wind Waves:
0.4 to 1.0 metres on Tuesday, rising to 1 to 2metres on Wednesday morning. Heights less in lee of land and more when wind wave opposes tidal current.
(Wave heights quoted are Significant wave heights).

Tidal Current: A strong ebb this morning and afternoon followed by slack water and then a strong flood developing this evening then becoming slack. A strong ebb developing early Wednesday, before a strong flood later.

Be extremely careful in narrow channels, etc.

Remember: In general tidal currents flood to the south and ebb to the north in the Whitsundays. There are many localized variations however so be very vigilant.

Tide at Shute Harbour: Tues: High of 3.05m at 0957hr, Low 0.08m at 1545hr and High 4.00m at 2222hr.
Wed: Low 0.30m at 0440hr and High 3.12m at 1042hr. (know your time offsets for other locations around the race courses)

Outlook:
Thursday: SE at 15 to 20 kn (ave) easing to 12 to 16kn (ave) during the afternoon.