Weather Hamilton Is RW from North Sails Australia

by Kenn Batt on 27 Aug 2008 Courtesy of North Sails Australia the Weather Forecast - issued by Kenn Batt at 0630hr for Wednesday 27th August 2008 at 2008 Audi Hamilton Island Race Week.

Synoptic Discussion:

A weak ridge of high pressure currently sits over the race area. An inland trough of low pressure sits over central Qld. A cold front is currently moving through SE Oz. A new high pressure system currently over the eastern Bight will move to the south-east and reach the New Zealand area at the weekend. This high will push the cold front northwards along the NSW coast and this front will decay in the Fraser Island area during tomorrow. Ridging will then strengthen again along the entire east coast. So moderate to fresh SE winds will return to much of the Qld coast going into the latter part of the week.
[Sorry, this content could not be displayed]
Observations:
At 0600hr, the surface wind at Hamilton Island Airport was from SSE at 14kt, gusting 16kt (temp 18C pressure 1021hPa) indicative of the genera l synoptic flow, although it does suffer from the effects of topographic forcing at times. At Creal Reef, further off the coast and to SE of Hamilton Island, the wind was a SE’ly at 17kn (indicative of true surface wind). Hardy Reef not reporting.

Forecast Discussion:

Forecast confidence level: Average.

The ridge of high pressure over the area has weakened substantially during the last 24hr. As such the surface winds today will be at their lightest for the series so far. The surface wind today will be pretty much gradient-driven with a moderate sea breeze component creeping in. This should see the wind direction trending left during the afternoon. Any course today that takes yachts close to the mainland, may see them experience more of the sea breeze effect (more left in direction than forecast) than those racing further offshore.

Natural wind oscillations today around 15 to 20 deg away from effects of topography, tending 20 to 50 deg closer to the effects of any land mass.
Expect wind speed to be 3-7kn stronger in channels/passages due to localized funneling and direction flicky. ANY SHOWERS COULD SEE LOCALISED SHORT-LIVED GUSTY WINDS WITH ERATTIC WIND SHIFTS UP TO 90DEG DIFFERENT FROM NORMAL FLOW,

Forecast Winds for Hamilton Island Area in open water

1000:MD140 DR(160-120) MS13 SR08-19kn
1200:MD130 DR(150-110) MS12 SR07-18kn
1400:MD130 DR(150-110) MS12 SR07-18kn may be 10-40deg further left?
1600:MD110 DR(130-090) MS14 SR09-20kn may be 10-40deg further left?
1800:MD130 DR(150-110) MS15 SR10-21kn

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

Other Possibilities:

60% chance that wind direction reaches 10-40deg more left than forecast later this afternoon.

50% chance that wind speed will be 2-5 knots stronger than forecast above this afternoon, particularly in Dent and Whitsunday Passages.

40% chance that direction stays in 140-120deg range.

Weather

Cloudy at times with the chance of a shower or two. Take plenty of sunscreen and warm clothing.

Maximum land temperature at Hamilton Island: 21-22 degrees Sea Temp: 21 degrees

Wind Waves: 0.7 to 1.4 metre. Less near land, more when wind wave opposes tidal stream. (Wave heights quoted are Significant wave heights).

Current: Moderate ebb tide this afternoon. Care in the channels particularly.
Tide floods to the south and ebbs to the north in the Whitsundays.

Tide (Shute Harbour): High of 2.60m at 0810hr Low of 0.33m at 1357hr and High of 3.86m at 2037hr

Outlook

Thursday: Chance of early shower then fine. SE/E winds 12-18 knots,