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#246715 - 18/03/2003 11:54 Inshore Skippers Course Question
Bella Offline
Junior Member

Registered: 15/02/2003
Posts: 8
Loc: Middle Harbour, Sydney
My husband completed his inshore skippers course this last weekend, and came home with a question paper. We cannot work out the answer to one of the weather questions and we were hoping that someone could lead us in the right direction.

QUOTE
It is mid-summer in Sydney. For a couple of days a cool breeze has been blowing at a moderate 10 to 15 knots from the north east. But by early this morning, the wind is now tending more from the north to north west, and the temperature has risen markedly to over 30 degrees with clear skies.

By noon the wind has shifted quite westerly, it is very hot and dry, and the windspeed has increased to 15 to 18 knots.

By late afternoon, the humidity has increased markedly and, although there are a few puffy cumulus clouds visible distantly over the sea in the south, the skies remain mostly clear. The wind speed has increased to 18 to 20 knots.

In this scenario, has the breeze been veering or backing? What changes in wind direction speed and cloud activity are likely over the next 6 hours?
UNQUOTE

Looking forward to your suggestions

Bella

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#246716 - 18/03/2003 12:37 Re: Inshore Skippers Course Question
Craig Arthur Offline
Wind hazard researcher

Registered: 08/05/2001
Posts: 3549
Loc: 149.152009°E 35.187056°...
The wind is backing to the west (moving in an anticlockwise direction). Makes me think there is a change coming. I'd expect the wind to increase to around 25 knots from the W, then shift rapidly S within a few hours. Watching the cumulus on the southern horizon will give a good impression of how far away this wind shift is. When the wind does back around to the S, expect it to be quite gusty initially, 30 knots would not be unusual. It may stay up around 20-25 knots for several hours following the change.There may be occasions when the wind will back to the S but remain light for acouple of hours.

Expect a marked increase in the amount of low cumulus behind the wind change, and the wind shift may be heralded by a long, low roll cloud, but not always.

In short, that scenario would have me screaming 'Southerly buster!' in my head.

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#246717 - 18/03/2003 13:22 Re: Inshore Skippers Course Question
Bella Offline
Junior Member

Registered: 15/02/2003
Posts: 8
Loc: Middle Harbour, Sydney
Thanks, that was the answer I was expecting, I guess here on the coast I have never felt the breeze go round to the west before a buster comes in, and that was what threw us.

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#246718 - 18/03/2003 13:36 Re: Inshore Skippers Course Question
Craig Arthur Offline
Wind hazard researcher

Registered: 08/05/2001
Posts: 3549
Loc: 149.152009°E 35.187056°...
Quite often the early morning N/NW'ly will result in a sea breeze starting up quickly along the coast. As the day progresses, the synoptic wind will swing around to the NW/W ahead of the buster, but along the coast the sea breeze will persist. Only right near the change would the sea breeze falter. It usually takes around 20-25 knots from the W/NW to kill a well-established sea breeze on the coast.

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