classifying windspeed

[docjoe]

All the talk about the poof thread(which I thought was an excellent point mac) got me thinking. When an advisory gives the details on a storm it may say, for example, maximum sustained winds of 135 MPH. Most likely these winds are confined to a small area of the NE eyewall. Since we know that the winds dont maintain a constant speed around the eyewall this is not indicative of the entire eyewall. Different areas will have markedly different winds depending on their relation to the eyewall. Would it make sense to somehow give some type of average windspeed to be expected by most people at landfall while not diminishing the fact that you have 135 MPH winds in the storm. For example maybe the NE quad has 135 winds, the SE quad has 125 , the NW quad has 110 and the SW has 100. One could then say that while the highest winds are 135 the average windspeed in the eyewall is 115-120. I would appreciate some honest input on this. thanks!!!

docjoe

[Aslkahuna]

Well, if it were possible then yes it would be a good idea but you have to tailor that to each individual storm. For example, Emily is a western moving hurricane so the strongest winds are likely to be found in the NW quad though the return wind on the backside may not be much less. Then there are storms like Celia (which followed a track similar to Emily with a RIC just before landfall which was further to the north) where the winds were strongest in the southern quadrants.

Steve

[docjoe]

i understand that each given storm has its unique characteristics. I just wonder if it would give more people a grasp of an impending storm to be able to say that average winds in the vicinity of landfall to be say 115 MPH with quadrant x having the highest winds at 130. I dont mean this to suggest an exact forecast. I do know that there are still people around here that think they weathered a cat 3 with ivan when in reality our area did not have measured sustained cat 3 winds. This has led to some complacency. If they had a better understanding that the damage in our area was from sub cat 3 winds it might get some peoples attention better...(can you tell grammar is not my forte!)

docjoe

[EDR1222]

I think if they find for instance category 3 winds in a storm, the NHC has to forecast based on a category 3 hurricane even though as you say, if it were say 115 mph, only a very small area may experience category 3 conditions. The other thing the NHC does I believe is they tell officials in a given area where there might be a warning to prepare for one category higher than forecast.

Please someone correct me if I am wrong, but I remember hearing this I believe during an interview on talkin tropics.

[jasons2k]

This is an interesting point and something to this effect was brought up in the Dennis threads.

I think there was some controversy b/c JB mentioned this in his column one day. He basically put forth the argument that measuring wind via recon is one of the most ineffective ways to measure a storm's intensity. For one, you are only sampling a very small surface % of the storm. Second, surface winds are estimated off of flight level winds. Shear becomes a factor as well. In summary, he said pressure, and especially pressure trend, would be a better "true" indicator of storm intensity.

[Aslkahuna]

Problem with that argument is that pressure isn't always that good of an indicator of winds either. The threshold pressure for a Cat 5 storm is 920 mb, but you can have a Cat 5 at a higher pressure if the strom is small in size or if the ambient pressures surrounding the storm are higher than average. Andrew never got below 922mb yet it was assuredly a Cat 5 based upon reanalysis. Take WPAC, because the ambient pressures are usually lower than the ATL, it takes a lower pressure to come up with a given windspeed-usually. During the passage of STY Paka over Guam, they were clearly dealing with a Supertyphoon yet there is no way the pressures could have been down around the 910mb threshold for 130kt in WPAC based upon the synoptic observations as the storm passed over the northern end of the island. The people at JTWC surmised that since the storm occurred in December that the ambient pressures were higher than normal and that the ATL wind/pressure relationship might be more valid for late season storms in WPAC Thus Paka was a 930 mb 130kt storm rather than the 910mb the pressure relationship called for. So until we can find a way of measuring winds in situ throughout the eyewall it's best to go with recon because that's the best we have. JB needs to read up more on Tropical Cyclones and expand his knowledge base about them by studying the literature on storms in other regions as well.

Steve

[Hurricaneman]

True

[docjoe]

just for the record this post had nothing to do with JB. I do not listen to his forecasts. nothing personal i just dont.

docjoe

[wxman57]

You make a good point, the NHC reports the MAXIMUM wind that you COULD see at landfall. In most cases, observed winds are a good bit lower than those maximum winds, which typically exist only over the more frictionless ocean. We actually account for this asymmetry in our forecasts, identifying the max wind and radius to max wind in each quadrant, then qualifying it with a lower and upper range of predicted wind speeds for any specific location.

You can go to the Hurricane Research Division web site and view almost real-time wind contours around hurricanes that they're flying into:

http://www.aoml.noaa.gov/hrd/Storm_page ... /wind.html

Check out Emily. Not a very symmetrical storm, even though it looked symmetrical on satellite imagery.

[Astro_man92]

http://www.srh.noaa.gov/srh/jetstream/tropics/tc.htm

her is a wind speed table (table is at the bottom of the page_

[Derek Ortt]

I hope that after Dennis that people in the Santa Rosa area now know what real cat 3 winds are as they experienced them in Dennis

[docjoe]

First of all Derek thanks for your hard work here.!!! Speaking from my personal experience at my house there is no doubt I had noticeably stronger sustained winds from Dennis. The big difference was that Ivan, with slower sustained winds in my neighborhood (about 10 miles inland), lasted for hour after hour after seemingly endless hour while Dennis came and went in about 90 minutes. Dennis also is requiring me to get a new roof whereas Ivan didn't. Most of us here in Santa Rosa have a healthly new respect for hurricanes. Getting back to my original post about average windspeeds it is interesting to note that after the eye passed we experienced no more heavy weather. It was all preceeding the eye and in the northern half of the eye itself.

docjoe
p.s.--i had about 30 minutes of great video(limbs and debris flying, trees falling over, etc but my dumb@#$ recorded over it