A note about storm surge

[DanKellFla]

http://news.yahoo.com/story/ap/20080911 ... _INqZxieAA

Hurricane Ike's gargantuan size — not its strength — will likely push an extra large storm surge inland in a region already prone to it, experts said Thursday.

Ike's giant girth means more water piling up on Texas and Louisiana coastal areas for a longer time, topped with bigger waves. So storm surge — the prime killer in hurricanes — will be far worse than a typical storm of Ike's strength, the National Hurricane Center said.

And because coastal waters in Texas and Louisiana are so shallow, storm surge is usually larger there than in other regions, according to storm experts. A 1900 hurricane following a similar track to Ike inundated Galveston Island, killing at least 8,000 people — America's deadliest storm.

"It's a good recipe for surge," said Benton McGee, supervisory hydrologist at the U.S. Geological Survey's storm surge center in Ruston, La. "We're already seeing water being piled up in the Gulf. On top of that you're going to have water forced into the bays along the coast."

The National Hurricane Center is forecasting a 20-foot surge — a rapid rising of water inundating
.....

[wxman57]

Reading from the U.S. Army Coastal Engineering Center's "Shore Protection Manual - Volume 1", there is a manual way to calculate storm surge on open coastlines (not suitable for bays).

Storm surge is primarily dependent on the factors below:

1. Coastal seabed bathymetry
2. Sea bottom coefficient of friction (Shoaling factor)
3. Radius of Maximum Wind (RMW)
4. Forward speed
5. Angle of approach to the coast
6. Pressure differential inside to outside the circulation

Here's an example calculation for Camille:

Pressure differential inside/outside = 3.19 inches mercury = 108mb
Forward speed = 13 kts
RMW = 14 nm

Sp = Si x Fs x Fm

Where Sp = peak surge, Si = estimated surge from RMW and pressure difference nomograph in book, Fs = coastal shoaling factor (http://myweb.cableone.net/nolasue/shoaling.gif), and Fm = correction for forward motion (angle and speed).

Si is derived from a nomograph with RMW on a diagonal axis and delta-P on the x-axis. For Camille, that gives 22 ft above MSL

Fs for Camille was 1.23

Fm, derived from the angle of approach (102deg) was derived from another nomograph as 0.97

Therefore, Sp = 22 x 1.23 x 0.97 = 26.2 ft above MSL

So, you see, Saffir-Simpson category plays no role in the calculation of storm surge. It's all about storm size, shoaling factor, angle of approach, and forward speed.

[VeniceInlet]

That's very interesting. So theoretically, each time there's a NHC report (or maybe once a day if that's too often) there could be a surge map produced for each area based on whatever are the current landfall projections. Kind of like what they do for wind field, but on a much more localized basis. And maybe start this out with the five day forecast once it gets within land-striking distance in that timeframe.

[3ABirdMan]

I'd agree, but, per this article, the surge was less - the Hurricane Research Division also ran a model yesterday and determined the surge was the height mentioned in the article:

http://www.cnn.com/2008/US/weather/09/1 ... index.html

in Katrina, it was estimated at 33 feet, if I'm not mistaken, so, more than double what was seen yesterday...

Still, as you said, the damage is severe, though very fortunately mostly in lower-populated areas, as you mentioned...

I respectfully disagree with 11' of storm surge as mentioned in the article.

While Ike was coming in, I checked the NBDC bouys (http://www.ndbc.noaa.gov/) along the coast from Galveston to Cameron Bay hourly, if not more often, watching the surge to see how bad our area would be affected. During the last hours of its' operation, the buoy at Rollover Pass (http://www.ndbc.noaa.gov/station_page.php?station=rlot2), located on the middle of the Boliver Peninsula, recorded heights of approx. 15' (near 10:30pm - 11:30 pm). The buoy failed to report for about 30 minutes, leaving a gap in its' data, but its final recorded height, which was just a blip on the screen (looked like about 10 minutes of data), was at approx. 25', recorded at about 1:00 am. From that point forward, there was no more data, as the web said the station was not reporting data.

Had I not witnessed the above, I could concede my arguement and agree with their estimates. I watched the Sabine Pass North (http://tidesonline.nos.noaa.gov/plotcom ... orth%2C+TX) and Port Arthur (http://tidesonline.nos.noaa.gov/plotcom ... orth%2C+TX) buoys rise as time went on - Sabine Pass North went to 15' for a short while (1 hour?) and began recedeing. Port Arthur rose to about 12', stayed for several hours (?3?), and then began to recede slowly. The tidal monitoring station (http://tidesandcurrents.noaa.gov/nwlon.html) on the Rainbow Bridge (http://tidesandcurrents.noaa.gov/data_m ... =View+Plot) rose to above 9.7' (it appeared the monitor maxed out) and held for much longer.

Because of all of THESE readings, I can agree with the article on 11' at Port Arthur, because I witnessed it as it happened, but I can NOT agree with the maximum storm surge as stated in the article.

[Normandy]

Ike had a much higher surge value than 11 feet. The seawall was overtopped in portions of the island, and at its lowest the seawall is 11 feet. Surge values seemed to be about 11-14 feet around Gavleston (depending on location), and Bolivar likely saw a 20+ foot surge.

[Texas Snowman]

As far as storm surge, I received this e-mail yesterday from SE Texas about a place that we stayed at last autumn at Crystal Beach (Renovare) along with a brick home/hunting lodge (that was not on the Gulf itself, was north of High Island as I recall).

Not only is the fancy bay house “Renovare” gone but so is “The Farm” south of Winnie. You remember the house with the big oak trees around it, well the oak trees survived but there is only a chimney left where the house was and the barn only has a slab to show for its existence. They estimate from the debris in the trees that the storm surge was close to 20’.

Since the hunting lodge was brick and pretty well built, I doubt that Ike's winds alone blew it down and left the barn slab clean - sounds like a big storm surge to me.

[Shoshana]

From cnn.com about the yellow house still standing in Gilchrist TX

Although the house is there, it might not continue to stand. Huge storm surges walloped the interior, making it uninhabitable and destroying many belongings.

...

Adams, a retired electrical designer, had a Galveston, Texas, engineering firm oversee a contractor as his new house was built. The columns put the house's bottom floor 14 feet above ground, or about 22 feet above sea level. Despite that, Ike's storm surge managed to get in.

I wonder if they can tell from watermarks on that house where the highest water came to?

I saw on tv that the house was supposed to survive a category 5 hurricane, and technically, it did. It's still there. But the surge was tremendous.

[Ptarmigan]

Well said Derek! I remember Hurricane Charley had Category 4 winds and produced storm surge of 4 to 6 feet and it was a small hurricane. Katrina had Category 2/3 winds and produced storm surge of 20 to 40 feet and it was a monster. Now, Ike which had Category 2 winds produced storm surge as high as 20 to 25 feet and it was huge.

[Ptarmigan]

Reading from the U.S. Army Coastal Engineering Center's "Shore Protection Manual - Volume 1", there is a manual way to calculate storm surge on open coastlines (not suitable for bays).

Storm surge is primarily dependent on the factors below:

1. Coastal seabed bathymetry
2. Sea bottom coefficient of friction (Shoaling factor)
3. Radius of Maximum Wind (RMW)
4. Forward speed
5. Angle of approach to the coast
6. Pressure differential inside to outside the circulation

Here's an example calculation for Camille:

Pressure differential inside/outside = 3.19 inches mercury = 108mb
Forward speed = 13 kts
RMW = 14 nm

Sp = Si x Fs x Fm

Where Sp = peak surge, Si = estimated surge from RMW and pressure difference nomograph in book, Fs = coastal shoaling factor (http://myweb.cableone.net/nolasue/shoaling.gif), and Fm = correction for forward motion (angle and speed).

Si is derived from a nomograph with RMW on a diagonal axis and delta-P on the x-axis. For Camille, that gives 22 ft above MSL

Fs for Camille was 1.23

Fm, derived from the angle of approach (102deg) was derived from another nomograph as 0.97

Therefore, Sp = 22 x 1.23 x 0.97 = 26.2 ft above MSL

So, you see, Saffir-Simpson category plays no role in the calculation of storm surge. It's all about storm size, shoaling factor, angle of approach, and forward speed.

Thanks for the formula WXMan57!

[mpic]

I have a question that just bumfuddles me. I am 99% sure that my property is 14' above sea level and I am 3.5 miles from Kemah. Why didn't we flood? I have it straight from some people who stayed during it.