9:11 PM Tue 18 Aug 2009 GMT
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'Day 5 4am'
Bureau of Meteorology
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A Strong Wind Warning is current.
Synoptic Discussion
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Still under the spell of the Trades.
A firm ridge of high pressure currently resides over the race area. It's expected to weaken from tomorrow as the high centre further to the south moves slowly eastward.
Observations
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At 0600hr surface winds over the Airlie Beach area were out of the SSW averaging around 5-10kn (land breeze plus synoptic wind) and the temperature was around 12 deg. At Hamilton Island the wind was SE'ly at 22kn gusting 27n, (temp 21C, pressure 1022hPa) indicative of the synoptic flow plus some topographic forcing.
Forecast Winds for Middle of Pioneer Bay
(Read Discussion below)
1000:MD130 DR(120-160) MS17 SR14-27kn may be 140-150deg in close?
1200:MD120 DR(110-150) MS18 SR14-28kn
1400:MD110 DR(100-140) MS18 SR14-29kn
1600:MD110 DR(100-140) MS16 SR13-26kn
1800:MD120 DR(110-140) MS15 SR12-23kn
Note : 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.
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Day 5 10pm prognosis - Bureau of Meteorology
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Discussion
The BIG questions today are:
1. When will the speed start easing? From around mid-afternoon. So good pressure for all your racing.
2. How far left will the wind direction go? Around 100deg by mid to late afternoon. Closer inshore in Pioneer Bay, the direction has a better chance of achieving this.
Remember: Wind will be lighter close in the lee of any landmass and stronger between islands (in channels due to acceleration) and around some headlands, in the form of "bullets" (you know the culprits!).
Wind direction is expected to be 10-30 degrees more left and 3-5kn stronger than forecast above in the Passage and Channel at times.
Natural oscillations today around 15 to 20 degrees away from effects of topography, tending around 30 to 50 deg closer to the effects of any land mass.
Note: Any shower activity can radically alter the wind field over short time intervals. Winds can be very gust and erratic.
Weather
Cloudy at times with the chance of a shower or two, chiefly this morning. Take plenty of sunscreen and very warm, waterproof clothes today.
Maximum land temperature at Airlie Beach: 24 degrees. Sea Temperature: about 22 degrees. Much cooler on the water though!
Wind Waves:
0.8 to 1.8metres, 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 very strong flood late this afternoon. Be very careful particularly in the Passage, Channel, etc.
Remember: Tide floods to the south and ebbs to the north in the Whitsundays.
Tide at Shute Harbour: High of 2.88 at 0943hr , Low of 0.03m at 1530hr and High of 4.12 at 2210hr.
Outlook
Thursday: Possible morning shower or two with SSW at 8-12kn turning SE at 10-15kn during the morning and tending more E during the afternoon.
by Kenn Batt
Click on thumbnails to enlarge and find more photos:
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