Need Assisstance on Converting 1 min. to 1 hr Wind

[wxman57]

Do any of you know the conversion factor for estimating a 1 hour wind from a 1-minute sustained wind (like in a hurricane)?

I know, it's ridiculous, but I have a rig designer calling me and saying that the design thresholds are for 1 hour winds in hurricanes, not 1 minute winds. He has a 1000-year return period on specific SS categories, but he needs to convert the data to 1 hour winds.

Anyone have a clue?

[hurricanetrack]

I guess it depends on the interval of the measurement. If you have a reading every second, you could then figure out how many seconds are in an hour (3600?) and then do the division. But one would need 3600 observations in an hour just to make the equation work. That is if you were taking a reading every second like we do in HIRT.

The other method would be if the reading was taken just once per minute like a snapshot. You would then just add em up and divide by 60.

However, I think this is too easy- and you may be asking for something entirely different.

[MWatkins]

Do any of you know the conversion factor for estimating a 1 hour wind from a 1-minute sustained wind (like in a hurricane)?

I know, it's ridiculous, but I have a rig designer calling me and saying that the design thresholds are for 1 hour winds in hurricanes, not 1 minute winds. He has a 1000-year return period on specific SS categories, but he needs to convert the data to 1 hour winds.

Anyone have a clue?

I think the easy answer is 1 min average is the answer since it's expressed in terms of miles per hour. So in other words...a 60 MPH is distance (60 miles) divided by time (1 hour).

In my opinion this is where the problem gets hard. We know that winds vary over time and even 1 min averages 1 min apart could be contaminated by gusts and vary greatly from one interval to the next. There are also considerations for forward speed of the hurricane and proximity to water...so the exact measurement of maximum force exterted on an object or structure is probably a modeling issue as opposed to a strict conversion based on a one min average wind.

The measurement period of a minute is much less succeptable to these variables than the same measurement over an hour.

MW

[caneflyer]

Do any of you know the conversion factor for estimating a 1 hour wind from a 1-minute sustained wind (like in a hurricane)?

I know, it's ridiculous, but I have a rig designer calling me and saying that the design thresholds are for 1 hour winds in hurricanes, not 1 minute winds. He has a 1000-year return period on specific SS categories, but he needs to convert the data to 1 hour winds.

Anyone have a clue?

There is none.

There are conversions for estimating the MAXIMUM wind of time period x contained within a larger interval y, e.g., if you have a 10 min mean wind of 100 kt, you can estimate that the MAXIMUM 1-min wind occurring within that 10-min interval will be about 11% higher.

However, the conversions do not work in reverse. In other words, if you have a 1-min mean wind of 100 kt, you cannot conclude anything about what the mean wind might be for a longer interval.

In any event, a 1-hr mean wind for a hurricane (from a design load standpoint) doesn't make much sense, since a single location would never (well, hardly ever) experience a hurricane's strongest winds for a period as long as an hour.

[wxman57]

Yeah, I know there isn't any such conversion. Let me give you an example of what he's asking. Let's say he determines that a 100-yr storm would produce 150 mph sustained 1-min winds at 10 meters. He's trying to estimate what the max 1-hr wind might be. Of course, if the hurricane is huge like Katrina, Ivan, or Rita, then the 1-hr wind could be over 100 mph. If it's tiny like Charley, then it may be only 40-50 mph given the huge variance in wind speed over an hour.

It's probably impossible to give him a good answer, given all the variables. But I told him I'd ask around just in case somebody out there had done some research in the area of longer-term wind averages in hurricanes.

[caneflyer]

I suspect the best you can do for him would be to make up some reasonable worst case scenarios. For instance, assume a Katrina-sized eyewall moving over a point at 3-4 kt. Even so, it would be awfully difficult to come up with a good answer because there is no way of knowing the horizontal extent of that single maximum of 150 mph. Over an hour's time, it wouldn't even be located in the same storm-relative location. You might make a reasonable WAG at a worse-case scenario of perhaps 125 mph? But it would be exactly that - a WAG.