Storm surge, what is it really? News weather people may be deceiving you.

[Loudmonkey2002]

Because of TV news people making much about hurricane winds causing water to "pile up" and create the storm surge, I posted on another forum asking if coastal location was significant in the amount of flooding (ie. North of eye gets flooded, while South sees a low tide). After rethinking it, I posted the text below, but I'd like to hear from enquiring minds.

While the newscasters/weather people make much of the wind pushing the water, I'm wondering if the storm surge isn't more a result of the fairly significant low pressure under the hurricane. My initial assertion, which came from a weather report comment, would in general only apply as the hurricane passes over the coast- either direction. A hurricane at sea would just spin the sea in a circle, why would that raise the water level? It could just as easily cause it to lower. If we assume a steady unidirectional wind blows directly at an inclined shoreline the water would not rise up as a result of the air-water friction (which does cause normal waves) but may rise as a result of Bernoulli's principle. Without the low pressure, would the viscosity of the water be so great that it wouldn't spill out the sides where there were no wind? How wide would that width of wind have to be before the water could pile up faster than gravity would pull it down. In fact, if the low pressure is the culprit - which I now think it is, gravity is the cause. A storm surge is then a gigantic natural barometer.

[StingRay]

Excellent post you big weather monkey....EXCELLENT. GREAT food for thought. I'll read up some more tonight, go over your point and see what I think. I follow your line of thinking though, but you're right, it goes against what I was taught in my first met class.

[amy]

Can someone please repost the clickable link to view loop satellite shots (the moving colorful ones - I think they're water vapor) of Africa. I have found the caribbean, east & west, but no Africa. I'm still learning and would like to save the site to my toolbar and watch the blobs develop daily.

Great question about storm surge. Very interesting. I anxiously await Stingray's research and comments.

[Coriolis]

Amy - not sure which one you want but here is one:

http://oiswww.eumetsat.org/IDDS-cgi/listImages?a=0,m=8,f=1,c=5,o=1,s=0,n=6,d=1,v=400,p =0

You will need to hit the Play> to start the loop.

[StingRay]

Amy, here are all the links to the Sats:

http://www.nhc.noaa.gov/satellite.shtml

Scroll down towards the bottom to METEOSAT-7, that's Africa. All your stills and loops are there.

[jeffl]

There are 3 separate phenomena that cause storm surge: 1) wind 2) low pressure and 3) the slope of the continental shelf off the coast.

1) Wind. This is important as it has the capability to pile water against the coast when a TC is moving inland. The counterclockwise circulation will then pile water against the coast to the right of where the center makes landfall and push water offshore to the left of where the center makes landfall. This can create a large surge differences in a small area and is strongly dependant on where the center crosses the coast.
2) As you stated low pressure reduces the amount of gravity being forced on the ocean surface. The lower the pressure the higher the bulge under the center of the storm. However, this bulge is like a tidal wave, it is not very noticeable over the open ocean and you could cross over it and not know you were passing through it This leads to the next and most important point.
3) The slope of the continental shelf greatly determines how high a surge will be. As the low surge over the open ocean moves into shallow water the bulge is forced to rise vertically. This is like waves at the beach that increase in height before they break as the water becomes shallow. This can also pre-determine where a surge will be the greatest. For example, locations along the Gulf coast have very shallow coastal shelf’s and little elevation rise at the coast. This leads to high surge that can penetrate far inland. In contrast the NE US and portions of the east coast have very deep offshore waters and significant elevation rise at the coast which limits the surge and its inland penetration.

A strong category 4 making landfall on the Gulf coast would produce surge values of 15-20 feet where a similar storm striking the NE US (unlikely) would produce values around 10 feet. All of these factors work together to produce storm surge. A strong hurricane moving fast like Charley produced a moderate surge for its intensity, where as a moderate tropical storm like Frances (98) produced surge values equal to hurricane Alicia along the west end of Galveston Island and the west side of Galveston Bay. So how was Frances able to produce such a large surge??: factors 1 and 3. Frances remained nearly stationary over the NW Gulf for 48 hours. A large high to the north and the low pressure of the storm produced a strong PGF along the northern Gulf coast from the ESE. Over a span of 48-72 hours the winds increased and piled the water onto the coast creating the surge. The natural shallow coastal shelf along the TX coast only worsened the surge heights. Every TC is different and will produce a different kind and height of surge. The values listed by category from NHC are only guidance for OEM decision making and hurricane evacuation and often do not hold true for every tropical system. The angle of impact, shape of the coastline, and man-made protective structures can all affect the storm surge in addition to the atmospheric and oceanic conditions.

Hope this helps clear some of the question up. Since SE TX appears to have a strong showing on here I may post later on specific small scale surge impacts along Galveston Bay are are very interesting.

Jeff

[KyleLightning]

Regarding storm surges...especially on the Gulf Coast.

The new novel about a Category 5 Hurricane hitting the Houston-Galveston area is called SURGE. It's by author Rod Tanner. The book has a rather chilling scenario about a storm surge devastating the Gulf Coast region. Scared the heck out of me. A cautionary tale.

Anyone interested in Storm surges should check out this book.