Hurricane Arthur

[1900hurricane]

Radar velocities have the southern/backside eyewall looking angry.

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[Dunkman]

85mph wind gust at Fort Macon on the back side.

[wxmeddler]

WeatherFlow Stations. For those who don't know they are a company with a pretty dang good mesonet serving marine interests.
http://www.windalert.com/map#35.24,-75.796,10,1

[RU848789]

Generally speaking, you can use a logarithmic equation to determine wind speed between 0-10m. Vertical wind shear at that height varies drastically depending on land cover at that height.

A forest will have a shear coefficient (alpha) of 0.6

Farmland will have a shear coefficient of (alpha) of 0.3

Water has an alpha of 0.15.

The equation to determine wind speed from one height to another is

XmWS=10mWS* (x/10)^alpha

X is the height you want to determine.

Thanks!  I also found a very nice description of this on wikipedia. For Arthur, so far, we've seen the 100 mph max sustained wind for the storm and a max sustained wind on land (also at 10 m, I assume) of 77 mph, which is 23% less.  Historically, in hurricanes, is there some sort of average difference in max sustained wind measured on land, presumably at the coast vs. what is reported for the storm, itself, i.e., over water? 

  

http://en.wikipedia.org/wiki/Wind_gradient

[gulfcane]

EDIT: several of those SFMR were flagged...although 89kts was not flagged in the NE quad. 

[wxmeddler]

The weatherflow station just off the coast of Okracoke is 60G78 mph as of 12:20a.

[jm1220]

Thanks! I also found a very nice description of this on wikipedia. For Arthur, so far, we've seen the 100 mph max sustained wind for the storm and a max sustained wind on land (also at 10 m, I assume) of 77 mph, which is 23% less. Historically, in hurricanes, is there some sort of average difference in max sustained wind measured on land, presumably at the coast vs. what is reported for the storm, itself, i.e., over water?

http://en.wikipedia.org/wiki/Wind_gradient

I would imagine it's hard to say since sometimes reporting stations are far away from landfall locations. Also hurricanes seem to have different characteristics in terms of mixing winds down. Having been through Irene and Sandy there were many differences. From what I saw Irene had more of a uniform wind and Sandy was much more gusty, lots of lulls and huge gusts.

[friedmators]

I would imagine it's hard to say since sometimes reporting stations are far away from landfall locations. Also hurricanes seem to have different characteristics in terms of mixing winds down. Having been through Irene and Sandy there were many differences. From what I saw Irene had more of a uniform wind and Sandy was much more gusty, lots of lulls and huge gusts.

i concur about sandy here in Edison.  Relatively calm to 60-80 mph and back down repeatedly.

[NorthNJwx]

Thanks!  I also found a very nice description of this on wikipedia. For Arthur, so far, we've seen the 100 mph max sustained wind for the storm and a max sustained wind on land (also at 10 m, I assume) of 77 mph, which is 23% less.  Historically, in hurricanes, is there some sort of average difference in max sustained wind measured on land, presumably at the coast vs. what is reported for the storm, itself, i.e., over water? 

  

http://en.wikipedia.org/wiki/Wind_gradient

 

It's important to note that 77 mph was the peak 10-minute average wind speed (indeed at the 10m height - 9.8m to be exact, according to the NDBC), and that the NHC uses the peak 1-minute average wind speed, such that the 100 mph figure is a 1-min average. Also, 77 mph was the peak 10-minute average from obs sampled and archived at 10-minute intervals - so it's possible that a somewhat stronger 10-minute average occurred in between observations. But more important is the difference between peak 10-min winds and peak 1-minute winds; since the 1-min average varies much more than the 10-min average, the peak 1-min value is always higher. Exactly how much higher a peak 1-min speed is than a peak 10-min speed can be estimated via a conversion factor (unfortunately, I don't know what the factor is off the top of my head, but there are studies on the topic). 

 

That said, Cape Lookout probably didn't get into the max winds. I think the idea thrown around by others here about Hatteras Island getting closer to the max winds later is correct - it should get more squarely into the eastern eyewall. But I'm not sure if any of the stations on Hatteras are as well-exposed as the Cape Lookout station, which seems to be in a perfect spot. That 77 G 101 is a beautiful ob. 

[Absolute Humidity]

Love the well defined spiral bands on this thing

[SluggerWx]

Awesome presentation with the BR color table I'm using on MRLevel3...

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[OSUmetstud]

Backside is decently intense, 60 kt 10-minute mean at Cape Lookout out of the west.  

[1900hurricane]

Alex Lamers seems to think that the 77 mph wind was a 2 minute sustained reading.

https://twitter.com/alexjlamers/status/484906343674167296

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[OSUmetstud]

Alex Lamers seems to think that the 77 mph wind was a 2 minute sustained reading.

https://twitter.com/alexjlamers/status/484906343674167296

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Thanks for the clarification.  

[NorthNJwx]

Alex Lamers seems to think that the 77 mph wind was a 2 minute sustained reading.

https://twitter.com/alexjlamers/status/484906343674167296

Sent from my iPhone

 

It's a bit confusing with the NDBC stations, but I think the current wind speed reported at the hourly obs is a 2-min speed and the continuous winds data (from which the 77 mph ob was pulled) is a 10-min speed.

 

Here's the continuous winds data showing the 77 mph ob (in m/s): http://www.ndbc.noaa.gov/data/5day2/CLKN7_5day.cwind

Here's the description of continuous winds data: http://www.ndbc.noaa.gov/measdes.shtml#cwind

 

So I'm pretty sure the 77 was a 10-min average. 

[OSUmetstud]

Also,

 

WSPD Wind speed (m/s) averaged over an eight-minute period for buoys and a two-minute period for land stations. Reported Hourly. See Wind Averaging Methods.

[1900hurricane]

2 minute or 10 minute, either way is still pretty impressive.

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[NorthNJwx]

 

Also,

 

WSPD Wind speed (m/s) averaged over an eight-minute period for buoys and a two-minute period for land stations. Reported Hourly. See Wind Averaging Methods.

 

 

Yeah, I think this reflects the difference between the hourly obs and the continuous winds data. The NDBC stations with continuous winds data use two different averaging periods for two different sets of data. 

 

 

2 minute or 10 minute, either way is still pretty impressive.

Sent from my iPhone

 

 

Oh, of course. 10-min is even more impressive; and it seems that two consecutive 10-min obs were at 77 mph. 

[Jayhawkers]

Hatteras appears to be directly in the path of the eastern eye wall... Guess we'll see what the real strongest gusts/sustained winds are at the surface within an hour or less.

[Normandy]

There is actually a pretty decent chance the eastern eyewall misses Hatteras to the west, but itll be a close call

[wxmeddler]

Sailflow station on the sound side of Okracoke as of 12:55am reporting sustained at 72 gusting to 98 mph.

[BuffaloWeather]

Hatteras is about to get hit pretty hard.

[SharonA]

Marshall Shepard just posted this paper on Birds and Hurricane eye's. Not the first time it's happened.

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1407&context=geosciencefacpub

(Interesting - thanks for posting that!)

 

And a snippet from pg 7 of that paper:

"Hurricane Irene (2011) was the first well-structured

tropical cyclone to make landfall within the domain of

an operational polarimetric WSR-88D weather radar."

[tmagan]

Hatteras is about to get hit pretty hard.

This is pretty close to a worse case track considering the strength of the storm.

[SN_Lover]

eye looks like its becoming more organized again...

[bdgwx]

The outer banks have be getting mauled right now. The KMHX beam radials are starting to align more with the right half. I'm seeing a lot of 95+ kts bins at < 3000 ft in that SE quadrant area.

 

[WE GOT HIM]

Looks like some intensification is going on and the eye is tightening up again. Also looks like it is wobbling north.

[Superstorm93]

[Cheeznado]

Pressure at the Ocracoke weatherflow station was 975 with strong wind- so it seems to be deepening

[WE GOT HIM]

Water is nice and warm in the sound