Storm surge
A storm surge is an abnormal rise of water generated by a storm, which exceeds the predicted tide levels.[1] A storm surge is produced by water being pushed toward the shore by the force of the winds moving around the storm.[1] This rise in water level can cause extreme flooding in coastal areas mainly when the storm surge overlaps with normal high tides, which can result in storm tides reaching up to 6 meters or more in some cases.[1] In situations where the water rises 6 m it doesn’t mean there is one 6 m wave that quickly goes away; it means that the water level rises to such an extent, it can go quite far inland if the ground is flat.[2] A storm surge is the change in the water level that is due to the presence of the storm. So since it is the difference between water levels, it does not have a reference level.[3] During Hurricane Ike, the storm surge moved inland 45 km in some locations in southeastern Texas and southwestern Louisiana.[3]
Strong winds are responsible for most of a hurricane’s storm surge, although extremely low air pressure in the eye of the storm also plays a small role. The low pressure in the eye allows the surrounding atmosphere to compress the ocean surface into a small bulge.[4] The wind circulation around the eye of a hurricane blows on the ocean surface and produces a vertical circulation in the ocean.[3] In deep water, there is nothing to disturb this circulation and there is very little indication of storm surge. However once the hurricane reaches shallower waters near the coast, the vertical circulation in the ocean becomes unsettled by the ocean bottom. The water can no longer go down, so it has nowhere else to go but up and inland.[3]
Surge Vulnerability
- From 1990-2008, there was a 32% population density increase in the Gulf coastal countries, 17% in Atlantic coastal countries, and 16% in Hawaii.[1]
- Coastlines on the Atlantic and Gulf lie less than 3.0m above mean sea level.[1]
- 72% of ports and 27% of major roads within the Gulf Coast region are at or below 1.2m elevation.[1]
North Atlantic sea surface temperatures are increasing, which is partially due to global warming.[1] Hurricanes are subject to various climate change related influences. Warmer sea surface temperatures will probably intensify tropical storms wind speeds, potentially delivering more damage if they make landfall. Thus, storm surges will become a larger threat as the severity of climate change increase.[1]
Storm Surge Factors
Central Pressure
- A higher surge is produced by low pressure. However, central pressure is a minimal contributor compared to the other factors listed below.
Storm Intensity
- A higher surge is produced by stronger winds.
Storm Forward Speed
- In closed bodies of water such as a bay, higher surges are produced with a slower storm. In contrast, open bodies of water such as a coast, produce higher surges with faster storms.
Width and Slope of the Ocean Bottom
- Higher storm surge occurs with wide, gradual sloping continental shelves are associated with higher storm surges, narrow, steeply sloping shelves are associated with lower storm surges.
Size
- A larger storm will produce higher surge. This is because winds in a larger storm push larger areas of the ocean and stronger winds in a big storm typically affect an area longer than a smaller storm does.
Angle of Approach to Coast
- A storm that moves towards the shore perpendicular to the coast is more likely to produce a higher storm surge than a storm that moves parallel towards the coast.
Examples of storm surges occurring include:
- * Hurricane Irene, category 1, produced a 3 m storm surge[3]
- * Hurricane Ike, category 2, produced a 6 m storm surge[3]
- * Hurricane Katrina, category 3, produced a 8 m storm surge[3]
- * Hurricane Charley, category 4, produced a 2 m storm surge[3]
Below is a video from [NOAA.gov][7] explaining storm surge. The most important point is, if officials say evacuate, then go:
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 "Storm Surge Overview", Nhc.noaa.gov, 2016. [Online]. Available: http://www.nhc.noaa.gov/surge/. [Accessed: 05- Jun- 2016].
- ↑ ”Storm Surge", Scijinks.jpl.nasa.gov, 2016. [Online]. Available: http://scijinks.jpl.nasa.gov/storm-surge/. [Accessed: 02- Jun- 2016].
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 ”Introduction to Storm Surge", NOAA, 2016. [Online]. Available: http://www.nws.noaa.gov/om/hurricane/resources/surge_intro.pdf. [Accessed: 03- Jun- 2016].
- ↑ ”Introduction to Storm Surge", NOAA, 2016. [Online]. Available: http://www.nws.noaa.gov/om/hurricane/resources/surge_intro.pdf. [Accessed: 03- Jun- 2016].
- ↑ P. Ronan, Gringer. (2013, Feb. 19). ‘’Storm Surge’’ [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/thumb/3/32/Surge-en.svg/800px-Surge-en.svg.png
- ↑ wikicommons. (July 22, 2016). ‘’Storm Surge’’ [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/6/6b/Storm_surge_graphic.gif
- ↑ The group is: NOAA/NWS National Hurricane Center in Florida, their youtube channel is here: https://www.youtube.com/user/nwsnhc accessed August 1st, 2016.
