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Old 18-12-2012, 11:33   #1
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Weather Windows

Hi All

After getting it wrong last week when the actual weather didn't equal what was forecast, I'm interested to know what all you conservative sailors look for as far as weather windows. My problem was that a forecast change came through about 12 hours earlier than predicted and I couldn't make our local (Swansea, NSW) bar before the tide turned. The weather change was funelling a 35 knots N/E wind straight into the channel, so 5 miles from Swansea, I swallowed my pride, did a u-turn and enjoyed an absolute sleigh ride back to Pittwater.

So tell me, what are you looking for in weather windows for a daysail and also for longer hops and how much do you factor in for the actual weather being different to the forecast?
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Old 18-12-2012, 11:50   #2
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Re: Weather Windows

now there is the 16 million dollar question!
generally ocean weather goes in 10 day cycles,with high and low presures passing north or south of you.
east coast weather is more un- predictable being goverend by fronts coming off the coast as they track east.
high cirrus is the best indicator ,the onset indicates a a change in 12-24 hours.
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Old 18-12-2012, 11:53   #3
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Re: Weather Windows

I mostly day sail at this point, so, the weather forcast tends to be a little more accurate. However, if the weather forcast says there is a 20 percent chance of unfavorable conditions (storms, wind on the nose, whatever), then every 5th time out I expect to get plastered. If the consequences of the unlikely are dire, I won't go out.
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Old 18-12-2012, 16:14   #4
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Re: Weather Windows

I work with wx quite some every year, mostly for other sailors and at times for non sailing adventurers (rowers, climbers, etc..).

The issue of timing you mention is very common and it tends to be more common when the weather comes onshore rather than when it comes from the shore. The explanation is that onshore wx is forecast based on models but it may be checked against local reports (with local forecasts corrected for the difference, or not, depending on your wx office of choice). Additionally, local conditions can and will influence wx fcst accuracy. Most offices DO NOT, repeat do not, allow for local conditions. Some do.

For any specific area (say the area where you reside) you may notice, over time, regularities that will help you interpret the forecast and adjust it to arrive at more accurate judgment of what the wx will do on any particular day. Needless to say, if e.g. a wx front arrival is forecast for tonight and you see all signs to the front actually approaching your location, then frcst or not, it will hit you exactly when the clouds, the wind and the glass tell you it will, not when the frcst (often X hours old by now) would tell it to be.

I think modern frcst tools are outstanding and continually improving. Some models and some services are better than others so use many sources and learn to tell which are better for any specific situation. Learn to use your tools and they will be a great support in telling you what is going on and what to expect within the next 12-24 hours.

Bueno. My two cents. Hope it helps somewhat.

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Old 18-12-2012, 18:38   #5
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Re: Weather Windows

G'Day Greg,

For passage making the selection of weather is quite dependent upon location. I don't think that there are any generic plans that apply everywhere. In general we use a combination of BOM forecasts and grib files (out a week or so) to get a general picture. But the timing of frontal passages like you experienced is both critical and difficult.

For a short trip like you were planning, have a look at the local observations on the BOM website as well as the f/c. Look for stations in the direction from which the front is coming and see just where it really is. If you do that a couple of times a few hours apart you can also get an idea of speed of advance, and then you can extrapolate arrival time at your position.

Right now we're sitting in Eden, doing the Twofold Bay shuffle awaiting the next stable high (Friday, maybe). There have been two brief N'ly flows since we arrived, but looking a bit into the future (via grib files) we saw that the oncoming front would catch us about off the end of Banks Strait... not a particularly good spot to be in near gale force W'lies, so here we sit. Nice place to be stuck, though, and Bass Strait commands my respect!

Cheers,

Jim
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Old 18-12-2012, 19:01   #6
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Re: Weather Windows

Greg, These poor forecasts must be due to the reverse gyre of the coriolis effect on your side of the equator because all our weather forecasts in the northern hemisphere are always perfect!
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Old 18-12-2012, 19:25   #7
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Re: Weather Windows

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Originally Posted by CaptForce View Post
Greg, These poor forecasts must be due to the reverse gyre of the coriolis effect on your side of the equator because all our weather forecasts in the northern hemisphere are always perfect!
Capt Force, you just don't understand -- our f/c down here are indeed perfect!

It is the wx that is defective...

Cheers,

Jim
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Old 18-12-2012, 19:39   #8
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Re: Weather Windows

Good question and some very experienced answers.
Weather forecasting is the ‘science of variables’ and as such, constantly being updated.
So that means that you must be your own weather forecaster for your location and intent, in order to decide on a prudent weather window.

As Jim indicated, he took the worst possible scenario of a planned passage and where he might end up (Banks Strait) and opted to delay.

This takes experience in knowing your own conservative performance and applying a ‘seaway’ percentage to your normal speed made good.

For me, on a pleasure craft, a good weather window for ETA on a difficult entry as you described would have been at least 24 hours. Otherwise, I would delay or plan alternate landfalls as you did.

On long ocean passages I never try to beat the weather, but when forecast and sense it is coming, I am already diverting course so as minimize its effects on boat and crew.

At sea, that is your window to prep, rest, pre-cook and accept that things will get rough….
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Old 18-12-2012, 21:53   #9
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Re: Weather Windows

Coastal weather forecasts are the most variable. Offshore and onshore breezes, couple with other local weather conditions are hard to "predict". In many cases local knowledge is helpful. For example the winds in Johnstone Strait generally.pick up as the day goes on, so I like to get out early and monitor what is happening at Fanny Island, a weather station at the point where I enter the Strait. I also know that on the West Coast of Vancouver Island I can avoid strong winds near the Brooks Peninsula by getting further offshore; I use an offshore weather buoy to verify that.

Ocean forecasts on passages involve trying to "predict" the optimum wind.
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Old 19-12-2012, 15:08   #10
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Re: Weather Windows

Thanks for the answers, I've found them most helpful although no one has mentioned minimum & maximum windspeed or wave characteristics that they try to plan for the duration of a trip. Any comments on this?
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Old 19-12-2012, 16:02   #11
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Re: Weather Windows

Greg
We are all learning as we go always. Nobody has the answer to this question cause everybody and every boat is different. Some will go out in 40 or even 50 knots and love it.
They have the confidence from experience. Others will sit at home and not want to get too sun burned.
Going out as many times as you can and enjoying it is the key. Sharing with others like minded learning always.
Prudent management keeping a watch on the weather at all times, with all the tools you can afford and operate well. Your judgement will serve you well.
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Old 19-12-2012, 16:18   #12
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Re: Weather Windows

Hey Greg,
That boat of yours could handle almost anything.
We like to downwind sail and usually apply the 3meter 30kt rule as the norm.
Derek
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Old 19-12-2012, 16:28   #13
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Re: Weather Windows

Quote:
Originally Posted by Sabbatical II View Post
Thanks for the answers, I've found them most helpful although no one has mentioned minimum & maximum windspeed or wave characteristics that they try to plan for the duration of a trip. Any comments on this?


Depends on the boat's direction respect to the wind/sea state. Where are your general plans? Up from Cabo I look for 2-3 day windows of not more than 20+ kts. Sometimes can't be avoided so you bite the bullet for as little exposure as possible.
Also depends on the boat and her crew's ability. Generally forecasted wind speeds near Capes is under forcasted by 5 to 10 kts. Off the wind passages can handle much more wind and sea state. Generally, small craft warnings keep me in. Since I am mainly delivering boats, don't want to stress the boat or crew. Making 3-4 kts sog on a 40+ ft boat up from Cabo makes perfect sense to wait for better weather.
Also, if it's a couple day passage of 1-3 days, you may be wiling to take a bit more pain...lots of variables. Trust your gut and your experience level. Never hurts to pack it in and wait for better weather. Prudent thinking is a very good thing! Trust me!
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Old 19-12-2012, 16:34   #14
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Re: Weather Windows

Hey whats the 3 metre 30 knot rule
May i ask?
Ross
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Old 19-12-2012, 16:59   #15
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Re: Weather Windows

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Originally Posted by rossad View Post
Hey whats the 3 metre 30 knot rule
May i ask?
Ross
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