Brad in Miami
Storm Tracker
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Posts: 365
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Yeah, the number of poles down is certainly interesting. I suspect it's a combination of things: the area affected was, of course, much larger than Andrew; many trees downed poles; I doubt the rating is entirely accurate as to every pole, and there certainly were gusts over 100 mph in a huge area; even if the rating were initially accurate, factors Margie suggested, as well as degredation of the poles themselves over time, could lead to a lower windspeed rating; and finally, I suspect there were areas that received gusts at, near, or slightly above 119 mph, which would be consistent with 95-100 mph sustained winds - i.e., high-end cat 1 or low-end cat 2.
And then of course, I could be wrong and there could've been sustained winds that high. Who knows.
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Margie
Senior Storm Chaser
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Loc: Twin Cities
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there could've been sustained winds that high. Who knows.
Check out the results of the Hurricanes at Landfall project (HAL). Sustained winds and even gusts are much lower than the advisories in every single hurricane they've documented. They set up the doppler right on the coast and inside the eye at landfall to get the highest winds. Remember from last year, much stronger than ...the highest wind gust they recorded with was 118mph and sustained winds were much much lower.
http://cswr.org/talk-hurricane-convention-2005-0319cpn.pdf
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Katrina's Surge: http://www.wunderground.com/hurricane/Katrinas_surge_contents.asp
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danielw
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Loc: Hattiesburg,MS (31.3N 89.3W)
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Clark and the other METS can probably elaborate on this more.
During most heavy precipitation events. There is a tendancy for the winds above the boundary layer to take on a near vertical element, due to the heavy rain. Something similar to a downburst.
During Hurricane , Mobile NWS recorded wind velocities of 127-132mph at 1359Z on Aug 29th. Just prior to 's landfall near Waveland,MS.
While the official Max Sustained Wind speed in the 1300Z Advisory was 135mph.
Yet the HRD plates indicate the Max 1 minute surface wind is at, or just under Hurricane Force of 75mph.
http://www.srh.noaa.gov/mob/0805Katrina/
http://www.srh.noaa.gov/mob/cgi-bin/imageview.php?dir=/0805Katrina&file=vel_2_mob_1359Z.GIF
http://www.nhc.noaa.gov/archive/2005/pub/al122005.public_b.026.shtml?
http://www.aoml.noaa.gov/hrd/Storm_pages/katrina2005/wind.html
ftp://ftp.aoml.noaa.gov/pub/hrd/hwind/2005/al12.2005/0829/1330/col02deg.png
I'm going to move this to the Ask/ Tell forum. As we have the possibility of Tropical Development~danielw
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Clark
Meteorologist
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The NWS profiles are always for maximum sustained winds found anywhere within the storm. Those don't necessarily occur over land; oftentimes, they do not. Furthermore, the strongest winds after landfall are generally found in downbursts as the storm starts to spin down -- as a tropical cyclone over waters that can support the storm, thereis an inherent resilency to downbursts/downdrafts; but, as it moves over land, this goes away and you see some very strong winds come to the surface. That can account for a lot of the spatial variation and localized strong winds inland found with storms.
There's not really a disconnect between any of the analyses...they are just detailing different but somewhat similar/related quantities. The HRD wind profiles go up to about 105kt -- 120mph -- over water, while Doppler velocities need to be reduced to the surface (just like recon). For 4000ft above ground level, there's going to be a reduction of 10-15% to the surface, giving you an estimate of about 115mph. Over land, you are going to see a lot of frictional and spindown processes further reducing the winds, though that 115mph-130mph gives you a fair estimate of what you might see in downbursts. The 135mph is from the over water and, with all of the new data we have that they didn't have in realtime (or just simply didn't have the time to process), we may see revisions when they do the post-season analysis for the best track data set.
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