Wind speed percent offset

I see there is a wind direction offset option for Tempest, would love to see a wind speed percent offset offered as well. Since a majority of the Tempest stations are sited less than 10 meters from the ground it would be great to have a wind speed offset which would allow out Tempest station to reflect what the wind speed would possibly be at 10 meters.

Interesting idea but based on what are you going to calculate this ? There are so many factors at play, not just hight …

I personally would base my calculation on nearby weather stations that are at 10 meters and fine tune my offset until it looks good based on what I’m seeing at my location. I realize this is not a perfect solution but as a meteorologist that has been looking at weather observations my whole life I know I could get it very close. This is what I was able to do with my old weather station and it work out very well.

any trees/ houses in your area?

That is a bigger factor than height.

Any factor would have to be dependent on the wind direction since the wind reduction due to “obstacles” depends on where the wind is coming from. This may change from summer to winter if the trees lose their leaves.

I have two stations, one is very open away from anything and about 25’ off of the surrounding ground, it does not really need any wind speed offset since it reports very accurate wind speeds. My second station is in a neighborhood with tees/houses around and only about 12’ feet off of the ground, the wind speed and direction will never be perfect with this station but I can get the wind speed close to what is going on at 10 meters with a wind speed percent offset.

To be clear I would like some kind of wind speed percent offset, not just a number. I edited my original post to be more clear.

For my neighborhood station I would start with a 30% offset which would turn a 2mph wind into 2.6mph and a 20mph wind into 26mph.

FWIW, weewx can calculate based on any math you cook up, but in general it’s a bit crazy I think. You can’t possibly know what the ‘true’ speed is at any elevation, let alone presuming either high or low is accurate in order to generate some magical compensation algorithm.

The sensors read the speed ‘there’ based on where the sensor is located. Just go with what it reports.

2 Likes

Good to know weewx allows you to tweak your data, my old weather station software did as well. Not crazy at all, the wind speed most of our Tempest stations are reporting now are accurate indeed but not representative at all to unobstructed winds at 10 meters. If I’m allowed to tweak my wind speed data I can get it close (not perfect) to what it would read at 10 meters. This feature would only be used by those that want to enable it just like you can now with the wind direction offset that is offered.

very interesting point. How are you? I also have an Atmospheric Science degree. I totally get what you are saying.

i attached my link.

i have one tempest on top of a shed 15 feet above ground. Another about the 30 feet height on my roof with no obstructions.

you can see the 2 wind speeds next to each other at real time. i notice due to houses and ground frictional drag looks sometimes to be double the windspeed at 30 feet compared to 15 feet

let me know what you think. also depends on storms how well the winds mix down.

Massapequa LI ny station

if you want your station to read the same value as other stations, why have a station at all?
The idea is that you get the measurements at the position you are interested in. So you get the windspeed at 2m height (is that is were you put it). The correlation with windspeeds at 10m height in a 200 m open grass field, probably isn’t a simple multiplication with a constant.

1 Like

Love your setup. Any idea what percent stronger your winds are at 30’ feet compared to 15’?

I don’t want my second neighborhood station that is mounted at 4 meters to read the same value as other stations, I want my stations wind speeds to better reflect what is going on at 10 meters. I realize it will not be perfect but I can get it close, much better that what is reads now at 4 meters for wind speed.

then put the unit at 10meters, but even then, given your environment, you will probably find that it depends on wind direction, turbulence etc, which are factors hard to compensate for. Only in ideal circumstances will the speed at 10 m be a just constant factor higher than that at 4 meters. But if you don’t care about that, yes by all means use weewx to change the measured value to your liking.

For temperatures I prefer to keep it closer to 2 meters, as you know the higher I go the less it reflects standard observed temperatures. With Tempest there is a trade off between temperatures and wind, ideally Tempest would be a two part system with one mounted at 2 meters and the other at 10 meters.

I suggest you read the following. Even though it is using Hurricane Andrew data… the formulas are the same for lesser winds. Plus it may give you an appreciation of what is involved.

Hurricane Andrew’s Landfall in South Florida. Part I: Standardizing Measurements for Documentation of Surface Wind Fields in: Weather and Forecasting Volume 11 Issue 3 (1996) (ametsoc.org)

1 Like

Thanks, as a meteorologist I’m well aware of all of the complex variables and what is involved.

Weather & forecasting is full of inferring information, I asking for the option to do the same.

That’s fine.

If you have not read the paper yet… I suggest you do so.

Then maybe you can suggest a feature referencing the data variables that would go into it.

I skimmed through it. What I want to see is the ability for each Tempest station owner the ability to put in a percent increase multiplier for wind speed. For my neighborhood station mounted at 4 meters I would start with 30% and tweak from there. Easy option to add in settings.

I can almost guarantee the developers of Tempest would not want to touch this with a 10 foot pole.

but with a 10 m mast? :slight_smile:

2 Likes