Hurricane Katrina's Waves Felt in California.

[Dean4Storms]

Hurricane Katrina's waves felt in California

* 11:00 24 September 2006
* From New Scientist Print Edition. Subscribe and get 4 free issues.
*

On 29 August 2005, as hurricane Katrina was rumbling towards New Orleans, a seismic hum more than 1000 times the strength of the average volcanic tremor was felt nearly 3000 kilometres away in southern California. Its source was the hurricane itself.

Hurricanes create large ocean waves, which send energy pulsing through the Earth as they pound the shoreline. To determine the power of Katrina's seismic waves, Peter Gerstoft of the University of California, San Diego, and colleagues analysed the signals recorded by a network of 150 seismic stations in southern California just before Katrina hit the Louisiana coast. They used a method known as beamforming, which preferentially picks up signals from a particular direction, to decipher the seismicity generated by Katrina (Geophysical Research Letters, vol 33, p L17805).

Seismic surface waves, which travel through the Earth's crust, were detected 30 hours before the hurricane made landfall, while body waves, which bounce down into the mantle, arrived some 18 hours later. "The body waves had travelled down to 1100 kilometres inside the Earth," Gerstoft says. This is the first time that a hurricane's seismic signal has been detected so far away.



http://www.newscientist.com/article/dn1 ... ornia.html

[JonathanBelles]

wow, what was the magnitude of those waves?

[hurricanetrack]

What about Rita? Any news from the most powerful hurricane that ever formed in the GOM? 897 mb is nothing to sneeze at. Rita also had a longer track than Katrina across the Gulf- just wondering if there is any such study on Rita.

[umguy1]

Wasn't Wilma the most powerful?

[TheShrimper]

Why was there not evidence of this happening elsewhere? I find this pretty suspect and coincedential, seeing that there are GRS all over the country, in closer proximity than CA.

[wxman57]

What about Rita? Any news from the most powerful hurricane that ever formed in the GOM? 897 mb is nothing to sneeze at. Rita also had a longer track than Katrina across the Gulf- just wondering if there is any such study on Rita.

It's not the peak wind or low pressure that produces the largest waves. Wave height is a function of wind speed, wind duration, and wind fetch - the distance across the water the wind blows. With hurricane wave generation, the two more important factors are wind fetch and duration. Winds blow around a hurricane in a circle. So a larger hurricane with lesser wind could generate larger waves than a small intense hurricane.

I said that duration was an important factor. Remember that hurricanes are moving, so the patch of water over which the wind blows (the wind fetch) is constantly changing. This leads to short duration, generally, and that reduces the size of the waves. But consider the potential for what is called "Trapped Fetch Waves". Allan W. MacAfee has done considerable research in these trapped fetch waves. I sqw his presentation in Monterey, CA last spring. Here's his paper:

http://ams.confex.com/ams/27Hurricanes/ ... 106634.htm

Basically, a wave set can be "trapped" within a hurricane if the hurricane is moving in a straight path at nearly the exact same speed as the big waves that it is generating. As waves get bigger, though, they travel faster. So for the trapped fetch waves to continue to grow, the hurricane needs to accelerate just enough to keep its strongest winds over those large waves. Hurricanes Ivan and Katrina did just that. Both had very large wind fields and both were accelerating just enough to keep those strongest winds directly over the largest (and growing) waves. Ivan had a little straighter track, so its waves were slightly larger than Katrina's.

Rita was an equally powerful hurricane, but its path was curved, so the largest waves moved away from the area of strongest winds. That's why Rita's waves were less than Ivan's or Katrina's. Wilma produced some large waves as well. Though it was large, the fetch and duration were limited by the island of Cuba and the rapid movement prior to landfall.

Here's another link to trapped fetch or "dynamic fetch" waves. Has a good animation:

http://meted.ucar.edu/marine/mod2_wlc_gen/print.htm#36

Here's a link just to the dynamic fetch animation:

http://meted.ucar.edu/marine/mod2_wlc_g ... _fetch.htm

[hurricanetrack]

Also, I did not see any large waves crashing on the beaches along Mississippi. The waves were MUCH larger along the Outer Banks during Isabel. None of the footage I have seen from the beaches of Mississppi show large waves. There were waves, but not large ones- not like on the Atlantic or farther east like say, Gulf Shores or Pensacola. I saw huge waves coming in during Ivan and Dennis. Not during Katrina- more like rolling swells on top of 25+ feet of water rise. Not sure if these waves were making all this seismic racket out in the open Gulf or near shore. They mention Louisiana, but I would think the waves were not much higher there- a more shallow bathymetry should yield higher water rise but lower waves, right?

[TheShrimper]

Again I ask, why were there not readings of the like in the southern Appalachians? I am not a geologist or have any credentials regarding siesmic activity, but i would like an explanation please as to why evidence of the above mentioned was not shared elsewhere on the continent, TheShrimper

[JonathanBelles]

Again I ask, why were there not readings of the like in the southern Appalachians? I am not a geologist or have any credentials regarding siesmic activity, but i would like an explanation please as to why evidence of the above mentioned was not shared elsewhere on the continent, TheShrimper

probabaly because of the faults in California, but that leaves this question until answered: why was the mississippi area unaffected? (the new madrid fault)

[wxmann_91]

a more shallow bathymetry should yield higher water rise but lower waves, right?

Yeah. Derek touched on that quite vigorously during the off-season.

Interesting article - thanks for sharing. Although, I certainly did not feel anything here.

[JonathanBelles]

whats "bathymetry?"

[hurricanetrack]

The shape and what not of the underwater topography.

[JonathanBelles]

thanks hurricanetrack

[brunota2003]

I would think that in California no one would feel it as the "quakes" would not be strong enough to be felt by anyone...however the seismographs (sp) can pick up even the slightest movement...as for the fault off Mississippi...you mentioned it was new...how new? plus the fact that as Katrina passed by, chances are any machines right on the coast were most likely totally destoryed, if there are even any in that area...

[wxman57]

Also, I did not see any large waves crashing on the beaches along Mississippi. The waves were MUCH larger along the Outer Banks during Isabel. None of the footage I have seen from the beaches of Mississppi show large waves. There were waves, but not large ones- not like on the Atlantic or farther east like say, Gulf Shores or Pensacola. I saw huge waves coming in during Ivan and Dennis. Not during Katrina- more like rolling swells on top of 25+ feet of water rise. Not sure if these waves were making all this seismic racket out in the open Gulf or near shore. They mention Louisiana, but I would think the waves were not much higher there- a more shallow bathymetry should yield higher water rise but lower waves, right?

Mississippi's coast is protected from large waves by the barrier islands a few miles offshore. Also, the slope of the sea bed along the MS coast is very gradual. Waves break at water depths 2/3 their height, so a 60 ft wave would be a breaker in 40 ft of water. That's quite a long ways offshore along the MS coast. For the most part, water depths a mile or so off the MS coast are under 20 feet, so even if the barrier islands weren't there, the maximum wave height in 20 feet of water (well offshore) would have been about 12-14 ft. You're not going to see the large waves along most of the Gulf coast for this reason.

As one moves eastward along the eastern AL coast and western FL panhandle, the bathymetry changes quite dramatically. Deep water lies a short distance off the coast of Pensacola, allowing larger waves to reach the beach.

The east U.S. Coast is completely different. Water depths increase rapidly just a short distance offshore, allowing the big waves to reach the coast.

[TheShrimper]

They are everywhere for Christ sakes, everywhere. Do you know what to look for? I will tell you what, if Katrinas waves registered siesmic activity in Ca., then how do you explain my eating of ham and beans on a weekly basis, not causing the siesmographs to go off the wall anywhere across the USA??????????

[Aslkahuna]

Detection of seismic waves from hurricanes is not new having been done with the 1938 Long Island Express. I suspect that in this case, they were looking for them and were employing a special technique to ID them


Steve

[Ptarmigan]

Interesting. I know the 1938 hurricane, it was detected through seismic instruments.

[Ptarmigan]

What about Rita? Any news from the most powerful hurricane that ever formed in the GOM? 897 mb is nothing to sneeze at. Rita also had a longer track than Katrina across the Gulf- just wondering if there is any such study on Rita.

It's not the peak wind or low pressure that produces the largest waves. Wave height is a function of wind speed, wind duration, and wind fetch - the distance across the water the wind blows. With hurricane wave generation, the two more important factors are wind fetch and duration. Winds blow around a hurricane in a circle. So a larger hurricane with lesser wind could generate larger waves than a small intense hurricane.

I said that duration was an important factor. Remember that hurricanes are moving, so the patch of water over which the wind blows (the wind fetch) is constantly changing. This leads to short duration, generally, and that reduces the size of the waves. But consider the potential for what is called "Trapped Fetch Waves". Allan W. MacAfee has done considerable research in these trapped fetch waves. I sqw his presentation in Monterey, CA last spring. Here's his paper:

http://ams.confex.com/ams/27Hurricanes/ ... 106634.htm

Basically, a wave set can be "trapped" within a hurricane if the hurricane is moving in a straight path at nearly the exact same speed as the big waves that it is generating. As waves get bigger, though, they travel faster. So for the trapped fetch waves to continue to grow, the hurricane needs to accelerate just enough to keep its strongest winds over those large waves. Hurricanes Ivan and Katrina did just that. Both had very large wind fields and both were accelerating just enough to keep those strongest winds directly over the largest (and growing) waves. Ivan had a little straighter track, so its waves were slightly larger than Katrina's.

Rita was an equally powerful hurricane, but its path was curved, so the largest waves moved away from the area of strongest winds. That's why Rita's waves were less than Ivan's or Katrina's. Wilma produced some large waves as well. Though it was large, the fetch and duration were limited by the island of Cuba and the rapid movement prior to landfall.

Here's another link to trapped fetch or "dynamic fetch" waves. Has a good animation:

http://meted.ucar.edu/marine/mod2_wlc_gen/print.htm#36

Here's a link just to the dynamic fetch animation:

http://meted.ucar.edu/marine/mod2_wlc_g ... _fetch.htm

I wonder what was the highest waves in Wilma? I know Ivan had 131 feet high waves! Katrina had 65 foot waves. Rita had 60 foot waves. I remember reading that a 78 mph hurricane/typhoon producing 130 foot waves in the Pacific Ocean. I know the Perfect Storm of 1991 produced 100 foot waves, even though sustained winds were 75 to 80 mph. The Perfect Storm sat in the Atlantic and was a large storm. I believe a crude way to measure wave height is sustained winds divide by 2. I don't want to even know how Supertyphoon Tip wave heights were or even a monster hypercane.

[wxman57]

I wonder what was the highest waves in Wilma? I know Ivan had 131 feet high waves! Katrina had 65 foot waves. Rita had 60 foot waves. I remember reading that a 78 mph hurricane/typhoon producing 130 foot waves in the Pacific Ocean. I know the Perfect Storm of 1991 produced 100 foot waves, even though sustained winds were 75 to 80 mph. The Perfect Storm sat in the Atlantic and was a large storm. I believe a crude way to measure wave height is sustained winds divide by 2. I don't want to even know how Supertyphoon Tip wave heights were or even a monster hypercane.

I have the wave data for Ivan, Katrina, Rita, and Wilma on my work PC. When you're talking about waves, we mostly refer to the "significant wave", which is the highest 1/3 of all waves. For Ivan, the significant wave height maxed out at 52-53 feet. We also estimate the "occasional" wave, which is about 1.5 times the significant wave (75-80 ft for Ivan). And there are the absolute peak waves. For Ivan, that peak was in the 90-100 ft range. I know of no measurements of waves larger than that from ivan. The only sensors capable of measuring Ivan's large waves were pressure sensors on the sea bed, as buoy 42040 broke free just before Ivan's waves reached their peak.

I think that Wilma's trapped fetch waves were in the 12-15 meter range (40-50 ft). I can check on that tomorrow.