1-minute vs 10-minute

[senorpepr]

Just another reminder during this "break" in cyclone activity around the world.

The DOD classification for TCs is based on the one-minute average mean wind speed. Most other forecast agencies around the world use a ten-minute average mean. This difference in intensity results in confusion between intensity forecasts among the warning agencies. Table A-1 shows a comparison of the one-minute and ten-minute mean winds for a given sea level pressure. The following are the five intensity classes used by DOD.

As for the "super hurricane" question...

(5). Super-Typhoon or Super-Hurricane.
A TC with maximum sustained 1-minute mean surface wind speeds of 130 kt or greater. West of 180 degrees longitude they are called super-typhoons and east of 180 degrees longitude they are called super-hurricanes.

However... it should be noted...

The DOC/NOAA/NHC uses the same intensity classification as DOD does except that there is no super-hurricane class.

[Thunder44]

Why doesn't our government office use the "Super Hurricane" classfication? Perhaps they don't want to appear to over dramatic, by sensetionalizing a major hurricane. The media here in the states would probably hype it up to be some kind of superstorm like in "The Day After Tomorrow"

[vbhoutex]

Mike, I understand that JTWC uses 10 min. instead of 1 min. averages. What I don't understand is why that would equate to a higher wind speed as shown in the chart. I figure wind speed is wind speed. And if I had 10 mins. at 150 mph vs 1 min. at 150 mph I would think the only difference would be that the one with 10 min at 150 mph would cause much more damage due to duration of the wind speed. So tell me what I am missing here(ie not understanding).

[Air Force Met]

vbhoutex - The reason for the difference is you are talking max wind..not highest wind. When we take weather observations...we look at wind over the last minute. You are basically taking a reading every second and then adding up all the data and dividing by 60. So...when we say one minute average we are looking for that one little area in the storm...maybe a few square miles...where the maximum 1 minute average is occuring.

However, if you take a 10 minute average of the wind you will now be taking 600 observations and dividing by 600. Max winds in a storm only blow for a very short time at the maximum intensity...most of the time (and everywhere else...other than where the max wind is) it is below the stated max wind. So...when that one little area of max winds moves away from you...you now have areas of lesser winds that get thrown into your average...so now your 10 minute average wind speed is less than that wind speed average you had 7 minutes ago.

Clear as mud?

[vbhoutex]

VERY CLEAR!! And somewhat obvious after reading your explanantion. The part I didn't realize was that the data is collected on a second to second basis.

[Air Force Met]

Yep. In the old days we had a wind machine that traced a line on a rolling sheet of paper so you looked at the graph paper with all the lines on it and tried to find the "average" over one minute...which basically turned into an exercise of finding the max and min and then averaging them together. Now-a-days it is stored in a computer and the computer averages it out for you.

An example of the first can be found at:
http://www.srh.noaa.gov/crp/stories/hur ... _wind.html

[Aslkahuna]

A couple of points; JTWC uses 1 minute averages not 10 minute which is why they have higher windspeeds than Tokyo and other National Agencies in WPAC. Secondly note that 55kt 10 minute equates to 63kt which is just below the minimal for a typhoon and is just slightly below 100 km/hr for 10 minute which is the threshold used by Tokyo for a typhoon. Finally, the sampling interval on a digital readout has to be set to one second, otherwise you will miss the high intensity short duration gusts. On most commercially available digitial readouts that amateurs use (like Davis) the sampling interval is around 3 seconds so peak gusts read from such instruments will be a little low usually.

Steve

[Derek Ortt]

I have also noticed that JMA's advisories have different pressures than do JTWC. Systems that JTWC is carrying as a 900mb typhoon have been carried as 930mb typhoons by JMA. I have noticed that this causes descrepencies greater than those included in the chart between the two advisories

[The Dark Knight]

Interesting.......