by Kenn Batt
Warnings: Nil Warnings current at time of issue.
Synoptic Discussion: A high pressure system in the Great Australian Bight will move eastwards over New South Wales today, extending a ridge of high pressure over Queensland. An upper level trough will move east over the interior of Queensland today.
Observations: At 0630hr the surface wind at Hamilton Island was 140 deg at 11kn, gusting 13kn (temp 18C, pressure 1019hPa). At Hardy Reef (further offshore at 19.7S 149.2E) the wind was 140deg at 11kn.
Forecast Winds for Surprise Rock (Read Discussion below)
0800:Mean dir 140d Dir range 160-120d MeanSp: 13kn Gust:17kn
1100:Mean dir 140d Dir range 160-120d MeanSp: 15kn Gust:20kn
1400:Mean dir 130d Dir range 150-110d MeanSp: 20kn Gust:27kn
1700:Mean dir 130d Dir range 150-110d MeanSp: 20kn Gust:26kn
Key: MeanDir: Mean wind direction Degrees True, DirRange: Wind direction range Deg T , MeanSp: mean wind speed in Knots, Gust: Maximum wind speed possible in the 10secs leading up to the hour in Knots.
Discussion: Pretty good model agreement for today with a S’ly surge pushing into the area this morning from about midday. The resulting winds, in the 15-20kn average speed range, are expected to hang in for your racing period today.
The cloud cover (middle level) is expected to increase this morning with some light rain developing this afternoon. If thick enough, it may dampen the wind speed field by 5kn or so. The S’ly surge may bring some low level cumulus cloud this afternoon and as such some shower activity is possible. The middle-level cloud (and light rain) is expected to move in from the NW, whilst any low level cloud (showers) will move in from roughly the SE.
Other Possibilities: 45% chance that wind speed doesn’t build to the forecast strengths above, due to middle level cloud and or surge not as strong as forecast?
30% chance that wind speeds are 2-3kn stronger than forecast this afternoon (neglecting localized topographic forcing of the wind speed field)
Note: Wind may be channelled and hence a little stronger at times between islands and out of some bays. Winds may be lighter and more flicky in the lee of Islands and land masses generally?
Natural wind oscillations: about 20deg and up to 60deg in the lee of land masses.
Note: that winds can be gusty and erratic over short time periods with any shower cloud that is close to you.
Weather: Possible early mist patches. Becoming cloudy during the day with some light rain developing this afternoon. Chance of a few showers later this afternoon.
Maximum land temperature at Hamilton Island: 21 degrees.
Wind Waves: 0.8 to 2.0metres, less in lee of land, more when wind wave opposes tidal current.
(Wave heights quoted are Significant wave heights).
Current: A weakening flood this morning then slack followed by a strong ebb this afternoon. Be extremely careful in channels, etc.
Remember: Tide floods to the south and ebbs to the north in the Whitsundays (there are many localized variations so be alert).
Tide at Shute Harbour: Low of 0.55m at 0533hr, High of 2.90m at 1139hr and Low of 0.51m at 1725hr
Sea Temperature: about 19 degrees.
Outlook: Monday 20th: Cloudy with some early light rain clearing to a fine day. Max temp 21deg. SE-E winds at 12-20kn (ave)