Audi Hamilton Island Race Week day 5 weather

by Kenn Batt on 23 Aug 2012 Latest weather from Kenn Batt:

Audi Hamilton Island Race Week day 5 - Warnings: Nil Warnings current at time of issue.


A high pressure system currently centred in the Tasman Sea will maintain a ridge of high pressure over Queensland.

Observations: At 0630hr the surface wind at Hamilton Island was 180 deg at 09kn, gusting 11kn (temp 20C, pressure 1019hPa). At Hardy Reef (further offshore at 19.7S 149.2E) the wind was 140deg at 8kn.

Forecast Winds for Surprise Rock (Read Discussion below)

1000:MD140 DR(160-120) MS08 SR05-12kn
1300:MD120 DR(140-100) MS08 SR04-12kn
1600:MD100 DR(120-070) MS08 SR04-13kn

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:

Forecast Confidence: Below Average

It’s going to be a very trying day!!!

The three biggest questions today will be 1. Will there be enough wind to race? 2. If enough wind, will the direction trend east during your race period? And 3. If so when will this occur?

Yesterday at the Airport weather station, the wind direction hung in from 130deg at 9-10kn before quickly going to 100deg at 7kn from about 1630hr. The ACCESS model (above) is essentially telling us that a SE trending E is the go, but doesn’t tell us exactly when. The CMC and the GFS essentially hold 130-120deg with a slight hint to about 100-110deg mid-afternoon, before flicking right.

The wind on the mainland coast should be 120-070deg at 5-10kn (ave) today.

Low cloud cover over the islands this morning will delay any left trend?

Localised wind direction and speed variations to those forecast above can be expected within the general Whitsunday area.

Other Possibilities:

65% chance that the wind direction trends left earlier than forecast above (from 1300hr)?

55% chance that wind speeds could be about 2kn stronger this afternoon from about 1300hr?

50% chance that not enough wind to race??

30% chance that there is a period of light and variable winds later this morning or early afternoon before a 5-10kn (ave) E-NE sea breeze develops?

Other: Wind may be channelled and hence a little stronger at times between islands (e.g. Fitzalan and Dent Passages) and out of some bays. Winds may be lighter and more flicky in the lee of Islands and land masses generally?

Natural oscillations: around 15-30deg and up to 60deg in the lee of land masses.

Weather: Cloudy or overcast this morning with some morning drizzle patches. Becoming less cloudy during the late morning with the chance of an afternoon shower.

Maximum land temperature at Hamilton Island: about 22 degrees.

Wind Waves: 0.3 to 0.8metres. Less in lee of land, more when wind wave opposes tidal current. (Wave heights quoted are Significant wave heights).

Tide at Shute Harbour: Low of 0.71m at 0824hr, High of 2.91m at 1509hr and Low of 1.20m at 2128hr

Some tidal offsets to apply to Shute harbour: Dent Is +5min, Haselwood Is +7min, Blacksmith Is +16min

Current:A moderate to strong flood this morning and early afternoon then slack followed by a moderate ebb this evening. 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).

Sea Temperature: about 20 degrees.

Outlook

Friday 24th: Partly cloudy with the chance of an afternoon shower.
Max temp 23deg.
Wind: SE-NE 5-12kn (ave)