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Old 03-03-2018, 16:03   #1
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How Are Gusty Conditions Forecast?

I have a basic understanding of weather and forecasts for constant wind, but what are the meteorological conditions that allow a weather forecast to predict gusty winds?

It’s pretty brilliant and mighty accurate here in Australia but I’ve never come across it in a book.

Today is a good example...
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Old 03-03-2018, 16:12   #2
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pirate Re: How Are Gusty Conditions Forecast?

Aussies play it safe..
Winds X, Sea's Y.. but expect conditions to be up to 50% worse than forecast.
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Old 03-03-2018, 16:15   #3
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Re: How Are Gusty Conditions Forecast?

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Originally Posted by boatman61 View Post
Aussies play it safe..

Winds X, Sea's Y.. but expect conditions to be up to 50% worse than forecast.


Yeah, I’ve seen and heard that, but the forecasts are very accurate. Even in the Windy app, which actually is what I’m referring to. I don’t often see BOM day gusty, but maybe a handful of times they specifically identified that with accuracy.
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Old 03-03-2018, 16:49   #4
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Re: How Are Gusty Conditions Forecast?

Like all weather forecasting ............ they gues. But they base it on science (of guessing)
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Old 03-03-2018, 17:27   #5
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Re: How Are Gusty Conditions Forecast?

Quote:
Originally Posted by theway View Post
I have a basic understanding of weather and forecasts for constant wind, but what are the meteorological conditions that allow a weather forecast to predict gusty winds?

It’s pretty brilliant and mighty accurate here in Australia but I’ve never come across it in a book.

Today is a good example...
Attachment 165402
Short answer: the use of complex mathematical models related to probability

Simple explanation for us laymen sailors:

"Gusts
Gusts are sudden, brief increases in the speed of the wind. According to U.S. weather observing practice, gusts are reported when the peak wind speed reaches at least 16 knots and the variation in wind speed between the peaks and lulls is at least 9 knots. The duration of a gust is usually less than 20 seconds.

All sailors know that it is the Gust that can do major damage and make boat control difficult, and often more dangerous than a high average wind strength. It is prudent practise to view the Gust Map, to check the maximum wind strengths you may experience. A large difference between the average wind strength, and the gusts can be very dangerous, especially if you are not prepared. So we advise that you animate your weather routing, over the Gust Maps to check for these situations."
SOURCE: https://www.predictwind.com/news/ind...evere-weather/
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Old 03-03-2018, 17:36   #6
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Re: How Are Gusty Conditions Forecast?

Around here they use precisely calibrated instruments and astute observation.
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Old 03-03-2018, 18:57   #7
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Re: How Are Gusty Conditions Forecast?

mmmm . . . guys . . . . this is standard modern Meteo . . .there are a couple standard measures of energy and turbulence (like CAPE & CIN - which you can get public grib files of if you want to look at the data directly) which translate into gust forecasts. I would look at this when we were entering an area that looked like it could be unstable to know if I should be worried about high gusts or white squalls.

It is a very important area for aviation forecasts. And they also use lidar to directly measure local conditions.
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Old 03-03-2018, 19:29   #8
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Re: How Are Gusty Conditions Forecast?

air temp consistency - largest guest i experienced when wind distinctively changing temperature in a blip. That is the time for conservative defense, especially cats.
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Old 03-03-2018, 20:19   #9
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Re: How Are Gusty Conditions Forecast?

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air temp consistency - largest guest i experienced when wind distinctively changing temperature in a blip. That is the time for conservative defense, especially cats.
You aren't getting cause and effect about face are you?

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Old 03-03-2018, 20:35   #10
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Re: How Are Gusty Conditions Forecast?

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no, that is not what i mean. Empirical evidence - if you feel these sudden changes in temp on your face, is time to go conservative. Lets call it very short term gust prediction.

I know 3 situations where in such conditions multis capsized shortly after.

Not saying that is the only situation but is definitely one to be imprinted in your subconsciousness especially if cat person.
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Old 03-03-2018, 20:58   #11
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Re: How Are Gusty Conditions Forecast?

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Around here they use precisely calibrated instruments and astute observation.


I’ll have to get one of those for my boat...
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Old 03-03-2018, 21:02   #12
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Re: How Are Gusty Conditions Forecast?

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air temp consistency - largest guest i experienced when wind distinctively changing temperature in a blip. That is the time for conservative defense, especially cats.


I thought cats had more cabin room to accommodate larger “guests”...
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Old 03-03-2018, 21:11   #13
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Re: How Are Gusty Conditions Forecast?

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mmmm . . . guys . . . . this is standard modern Meteo . . .there are a couple standard measures of energy and turbulence (like CAPE & CIN - which you can get public grib files of if you want to look at the data directly) which translate into gust forecasts. I would look at this when we were entering an area that looked like it could be unstable to know if I should be worried about high gusts or white squalls.

It is a very important area for aviation forecasts. And they also use lidar to directly measure local conditions.


Ahhh, I’ll dive into this a bit more... I’ve definitely heard of CAPE/Convection being associated with thunderstorms (rain), but not gusty conditions.

Here’s the CAPE for the Sydney area and it shows nothing, but definitely gusty here 17-35kts. Coffs Harbour however shows red (2322j/kg), but wind shows 5-10kts.

Maybe I’m reading it wrong

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Old 03-03-2018, 22:55   #14
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Re: How Are Gusty Conditions Forecast?

My rather primitive gustometer.....

I have learnt over time that the wind under that heavy cloud marked by line '1' will be a steady honest wind.... strong maybe but honest.

What looks like fair weather cumulus around the '2' is nothing of the sort... that's where the gusty squally nasty stuff lives.

How that relates to Australia , 2nd pic was 10 minutes ago, I don't know.... but think it is the same.
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Old 04-03-2018, 01:14   #15
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Re: How Are Gusty Conditions Forecast?

Like all aspects of the weather, there are so many variables that nailing down any particular item, or group of items as to causes of gustiness is near impossible.

I'm guessing that, over open water, a lot of it has to do primarily with the source of the wind, in combination with localized environmental conditions, such as water temperature, time of year, time of day, cloud cover, etc.

For instance, while the wind is always to some extent gusty, around here (30N) when the wind is from the south, i.e. a warm wind, the gusts seem to be shorter, with a larger range in velocity, whilst a wind from the north, i.e. a cold wind, seems to have longer gusts that have a comparatively smaller range in velocity. I assume the situation is reversed in the Southern Hemisphere.

Speculating even further, while the primary 'cause' of the wind is pressure differences, there other contributing factors. Running with the warm/cold scenario above, with the warm wind in the south, the air is lighter, tending to rise as the sun warms it, there are generally scattered clouds causing uneven heating, which results in different areas rising at different rates, with the air replacing it doing so at different rates (velocities).

Contrast this with a north, cool, dense wind. Typically areas of high pressure are much larger than lows. The coolness and large volume tend to add stability to the air mass; the generally clear weather cuts down on the uneven heating induced by variable cloudiness. This stability seems to (usually) moderate the intensity of the change over the 'base' wind, and generally lengthen the duration, at least in my experience in my part of the world.

Proximity to land also has huge effects on gustiness, the differential heating of land and water and the relative smoothness of water as compared to land are probably primary drivers. We used to sail on the south shore of Lake Pontchartrain, in what were the gustiest conditions I've ever seen, before or since. It only happens in the spring, and has never been adequately explained to me, but while the lake water is still cool, apparently the heating of the land generates enough of a thermal for the (highly variable) wind to stay at the surface for 2-3 miles into the lake. I'm talking about near 0 to 30-35 knots, for gusts lasting for 15 seconds if you're unlucky, to a minute or a minute and a half if you were lucky (we were on windsurfers). After that, 2 or 3 miles into the lake, the wind would die off to a more steady but less than shortboardable 10 knots or so, and if you got out that far, you had to swim back, get rescued, or drift 24 miles across the lake (the wind was from the south, directly offshore).

Obviously these are my subjective opinions. I hope someone with some hard scientific information will chime in to shed some 'official' light on the subject...
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