Gale days settings ?

[1080]

Hi Steve & everyone
Steve, First off....thanks for Cumulus
I have just purchased a WH1091 & we have some windy days here in....Victoria Australia.
I have had 2 Gust readings of 85.7 kph on different days....may be the little spinner won't go any faster

What speed wind or whatever = a gale day
Thnx Phil

[steve]

They're supposed to be able to go up to 160 km/h. I haven't had my Fine Offset station long enough for it to get a good bashing, but it should get some testing in the winter as we can typically expect gusts around 140-145 km/h at least once during a winter. It may be just coincidence that you had the same peak gust twice - I suspect that there is a limited set of values that these stations will give.

Cumulus uses the definition of a gale as used by the UK Met Office and the US NWS (and also, I suspect, by the Australian BOM); that is, sustained wind speeds of 39 mph (62 km/h, 34 kts) or more, equivalent to Beaufort F8 or above.

[Super-T]

My WH-1081 has shown a high wind gust of only 66.2 KPH in Auckland but I suspect that it has been higher than that.

[1080]

That was the actual reading 85.7k at about 2m above ground, dont know what the difference would of been up at 10m.
This is very windy for here.......normally strong gusts for here are about 30 to50k.

I think there is some way of caculation it..... but my ability to work out
v+h/???* or what ever......is very limited

Does anyone know if there is a caculator for this......anywhere.

Phil

[beteljuice]

Obtained from elsewhere:

For wind speed measured at a height between: Multiply by:
0 and 2.0 m 1.5
2 and 2.9 m 1.48
3 and 3.9 m 1.35
4 and 4.9 m 1.25
5 and 6.9 m 1.15
7 and 8.9 m 1.07
9 and 11.9 m no correction

This is a rough approximation, and takes no account of the height / distance of local terrain / obstacles !

[1080]

Thnx.....betlejuice that makes 85.7 = 128.55k's

Steve....Now I have visited Sanday....I can see why u get the very high winds. Sanday looks a very beautiful part of the world

Steve.....I travelled there last night by g00gle air....

140-145k gusts and most farm houses around here would be without there Roofs.

[steve]

I can see why u get the very high winds.

Yes, we're a bit... exposed.

Sanday looks a very beautiful part of the world

It is. Not everyone's cup of tea, I suppose, and we do occasionally miss the forests and mountains of mainland Scotland where we used to live, but the wonderful coastline makes up for that.

140-145k gusts and most farm houses around here would be without there Roofs.

Most of the houses here have been around a long time and were built to withstand the weather. There's very little damage anywhere after a storm.

[skyewright]

I can see why u get the very high winds.

Most of the houses here have been around a long time and were built to withstand the weather. There's very little damage anywhere after a storm.

I can attest to the sense behind the Scottish building regulations that require 'sarking' (a layer of boards that go between the roof timbers and the felt & tiles/slates).

In the January 2005 storm we lost some ridge tiles and a few others. Thanks to the sarking that was the limit of the damage and we just needed to spread polythene in the loft to catch the water till a proper repair was done. Without the sarking the wind would have got straight into the roof space and would very likely have taken the whole lot off.

[alexferg]

Hi everyone
Have been doing some testing in some good Gale winds in the last couple of days. I have 4 stations set up-1x1081 & 3x XC0348 (think these are 1083?) and are having a common problem with high end wind & gust readings! One station has a max read of 127Km & Cumulus gave max of 91.8Km. I think this was a true reading until next gust of 127Km. This problem is the same with my other stations.
Observations of the station read outs showed any readings over 100Km, & Cumulus temporily froze until the readings came down under 100Km it then resumed reading as normal.
Also looking at data the max gust was 91.8Km & high wind 88Km! TOO close I would have thought, when very gusty & not constant.
I dont think this freezing up starts at 100Km but somewhere just under that. Had originaly thought this may have been a 3 digit or decimal point issue transferring to cumulus, as there is no fraction of Km on station over 99.9Km, just 100Km 101Km & so on.
Just wondering if some one else in a windy area could check the max gust reading on their station and see if it is over 100Km & Cumulus read is under.
Any thoughts or advice on this problem would be appreciated.

Many thanks
Alex

[steve]

I apply a cut-off to catch 'silly' readings, but that is set at 60 m/s, which is over 200 kph.

91.8 kph is 25.5 m/s, which is significant. The station supplies wind speed (but apparently not the gust speed) as a single byte in tenths of a m/s. No-one seems to know what happens when the speed gets over that. I haven't had my Fine Offset long enough to find out for myself.

From what you say, perhaps the speed as well as the gust is a single byte, and there is an overflow bit somewhere. The (reverse-engineered) documentation I have says that it uses two bytes.

Could you repeat the exercise, please, and turn on the debug log? Cumulus will then log all the data it reads, and will also log a message if it detects a 'silly' value.

[steve]

Actually, as my Fine Offset station is primarily for testing purposes, I suppose I could try to simulate a high wind speed and see what the data looks like myself.

[steve]

In the interests of science, I got out my compressor and a ladder...

Several hurricanes later, I've found the error in the (unofficial) memory map I'm working from. It says that the wind speed is one byte and the gust is two bytes. It's actually 1.5 bytes each. What was thought to be the top byte of the gust actually holds the top byte of both speed and gust. I'll upload a new version of Cumulus with the fix shortly.

[jim-easterbrook]

Several hurricanes later, I've found the error in the (unofficial) memory map I'm working from. It says that the wind speed is one byte and the gust is two bytes. It's actually 1.5 bytes each. What was thought to be the top byte of the gust actually holds the top byte of both speed and gust.

Bizarre! Any chance of some more detail about this discovery?

[steve]

Hi, Jim. You may recall we had a brief discussion in Pendec's forum, where I asked what happened when the wind speed went above 25.5 m/s, since the memory map said it was held as tenths of a m/s in single byte? The memory map says that byte 9 (numbering from zero) of the current location is the wind speed, and bytes 10 and 11 are the wind gust. What I have found is that byte 11 is actually shared by the speed and the gust; the top nibble is the most significant part of the gust, and the bottom nibble the most significant part of the speed.

[alexferg]

Hi Steve
Thanks for the outstanding dedication with the testing!! Will turn debug on next data download. One station is in a really good position for wind & had over 1000Km of wind run for the day. Also logged 4 gale days out of 4 days it had been running. Just a typical spring breeze for North Canterbury NZ!
Looking foward to the fix for this problem.
Am happy to do any further testing if required.
Thanks again
Alex