U.S. vulnerability to sea level rise

By: Dr. Jeff Masters , 4:04 PM GMT on June 23, 2009

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In the last century, sea level rose 5 - 6 inches (13 - 15 cm) more than the global average of 7 inches (18 cm) along the U.S. Mid-Atlantic and Gulf Coasts, because coastal lands there are sinking. Over 50% of the U.S. coastline is vulnerable or highly vulnerable to sea level rise, according to the Coastal Vulnerability Index (CVI) developed by the United States Geological Survey (USGS). In the U.S., relative sea level rise (the combined effects of global sea level rise plus the fact the land is sinking) is highest along the Mississippi River Delta in Louisiana, where relative sea level rises of 3.2 ft (.98 meters) have been observed during the 20th century. This is one of the highest relative sea level rises in the world. According to the NOAA Tides and Currents sea level rise interactive tool, the U.S. tide gauges that have shown the highest rates of sea level rise over the past century are at Grand Island, LA (1.8 ft rise since 1947), Galveston, TX (1.1 ft since 1957), and Chesapeake Bay, VA (0.6 feet since 1975). Alaska and some areas along the Pacific Northwest coast are at low risk of sea level rise, because the relative sea level is actually falling at present. Land in these regions is rising as it recovers from removal of the weight of the great ice sheets that covered much of North America during the last Ice Age. For example, relative sea level at Kodiak Island, Alaska has fallen by 1.1 feet since 1975, despite the fact global sea level has been increasing.


Figure 1. Twentieth century annual relative sea-level rise rates in mm/year along the U.S. coast. The higher rates for Louisiana (9.85 millimeters [mm] per year, about 3.3 ft/century) and the mid-Atlantic region (1.75 to 4.42 mm per year, 0.6 - 1.4 ft/century) are due to land subsidence. Sea level is stable or dropping relative to the land in the Pacific Northwest, as indicated by the negative values, where the land is tectonically active or rebounding upward in response to the melting of ice sheets since the last Ice Age. Image credit: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region (data from Zervas, 2001).

U.S. Coastal Vulnerability
The Coastal Vulnerability Index (CVI) takes into account six factors:

1) The geology of the coast. Barrier islands, river deltas, and marshes are the most vulnerable to erosion and sea level rise, while steep, rocky cliff shores are the least. Sheltered bays like Galveston Bay and Tampa Bay are less vulnerable than the exposed coasts. (Note, however, that hurricane storm surges are typically higher in sheltered bays, at least for slow-moving storms).

2) How steep the land near the coast is. Gently sloping lands are the most vulnerable. In the Gulf Coast region, the slope variable has the highest risk ranking along the Louisiana coast, the Texas coast north of Corpus Christi, and the southwest Florida coast.

3) The local rate of sea level rise. The sea level is rising faster along the western Gulf of Mexico than the eastern Gulf. The highest rates of sea-level rise in the Gulf of Mexico (and in the United States) are in the Mississippi delta region (10 mm/yr, or 1 inch/2.5 years).

4) The amount of shoreline erosion going on. Most of the U.S. coast is moderately or severely eroding, and very few areas are gaining (Figure 2).

5) The mean tidal range. Shores that have a large difference between low and high tide are less likely to get a significant storm tide--the height above mean sea level of the sum of the storm surge plus the tide. For example, in a region like Maine, which has a 12 ft range between low and high tide, a storm having a 9 ft storm surge will have a storm tide below local high tide for a quarter of a tidal cycle. Shores with a very narrow tidal range (e.g., the 2 ft tidal range common along the Texas and Louisiana Gulf Coast) will get a storm tide of 8 - 10 feet with the 9 ft storm surge in the above example. Shorelines with a narrow tidal range always get high storm tides regardless of when the storm surge hits.

6) How high the waves at shore are. Obviously, shores that experience higher wave heights are at greater risk. In the Gulf of Mexico, wave energy is highest along sections of the Texas coast and on the southern tip of the Mississippi delta.

Figure 2. Shoreline change around the United States based on surveys over the past century. All 30 coastal states are experiencing overall erosion due to natural processes (e.g., storms, sea-level rise) and human activity. If the shoreline is uncolored, no data was available. Image credit: USGS, 1985, and taken from Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region).

The Coastal Vulnerability Index (CVI) web page gives detailed maps of each section of the U.S. coast, along with specific reasons why each portion of the coast was assigned the ranking it got. A brief summary:

The Gulf Coast
The Gulf Coast has 55% of its length in the "very high" or "high" vulnerability range. Fully 41% of the coast falls in the "very high" range, far more than the 28% in that category along the Pacific coast and 23% along the Atlantic coast. The region around New Orleans is the most vulnerable region of the entire U.S. coast. The Florida Panhandle, as well as the West Florida coast, are at low to moderate risk because the land is not sinking much, wave heights are lower, and the slope of the land is relatively steep near the coast. The Texas coast is considered to be at a high to very high risk because of the relatively high mean wave height, sinking land, and shallow coastal slope.

The East Coast
The East Coast has 50% of its length in the "very high" or "high" vulnerability range. The highest vulnerability areas are typically high-energy coastlines where the regional coastal slope is low and where the major landform type is a barrier island. A significant exception to this is found in the lower Chesapeake Bay. Here, the low coastal slope, vulnerable landform type (salt marsh) and high rate of relative sea-level rise combine for a high CVI value. The coastline of northern New England, particularly Maine, shows a relatively low vulnerability to future sea-level rise. This is primarily due to the steep coastal slopes and rocky shoreline characteristic of the region, as well as the large tidal range.

The Pacific Coast
The Pacific Coast has 50% of its length in the "very high" or "high" vulnerability range. Areas of very high vulnerability include the San Francisco - Monterey Bay coast and in southern California from San Luis Obispo to San Diego, where the coast is most highly populated. The highest vulnerability areas are typically lower-lying beach areas. The low risk, least vulnerable areas generally occur at rocky headlands along cliffed coasts where the coastal slope is steep, relative sea-level is falling, tide range is large, and wave energy is lower. Examples of these areas are the northern coast of Washington, Monterey, and Cape Mendocino, California.


Figure 3. The Coast Vulnerability Index (CVI) for the U.S.

References
Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region.

National Assessment of Coastal Vulnerability to Sea-Level Rise: Preliminary Results for the U.S. Gulf of Mexico Coast (USGS, 2000).

Jeff Masters

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Quoting scottsvb:
bertha didnt form near 30W.... it was around 45W.. I could be wrong though... find a stat..Im too lazy to find it...lol!


Link
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Quoting scottsvb:



Jeff is 100% correct.... but of course you can watch it... why not? but to talk or speculate or have the "HYPE" of hoping it forms...forget about it... Cleveland will win a Championship before that happens..


Just curious Scott do you even give it a potential to develop? I have not seen any hype on here so far not even a wishcasting landfall forecast so I'm not sure why it seems to bother you so much?
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Quoting stoormfury:
QS OFF THE AFRICAN COAST


Link


Wowza...
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Quoting scottsvb:
bertha didnt form near 30W.... it was around 45W.. I could be wrong though... find a stat..Im too lazy to find it...lol!


Again lol

INITIAL 03/1500Z 13.3N 24.7W 35 KT
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Quoting scottsvb:



Jeff is 100% correct.... but of course you can watch it... why not? but to talk or speculate or have the "HYPE" of hoping it forms...forget about it... Cleveland will win a Championship before that happens..


You probably wouldve said Bertha wouldn't have formed either. But again, no one is saying this WILL form...were just watching it cause its happened before, okay?
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I'm becoming interested in the area off the nicaruga/honodurus coast near 13.5N,82.5W
Member Since: October 5, 2007 Posts: 20 Comments: 4970
bertha didnt form near 30W.... it was around 45W.. I could be wrong though... find a stat..Im too lazy to find it...lol!
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Wow, that wave that is about to come off Africa is pretty big. Will be interesting to see if it will die out or not when it hits water.
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Quoting jeffs713:

Fully agreed there. Just because it happens once does not mean that it will happen again every year. The entire atmospheric situation is different this year compared to last.

1. Shear is generally higher this year in that area.
2. This year is neutral to El Nino, last year is La Nina to neutral.
3. SSTs are somewhat cooler in that area this year, compared to last year

Also, there are several other factors to keep in mind:
1. Bertha was a freak of nature, it was well outside the "norm" for a July hurricane
2. The GFS spins up EVERYTHING with even a 0.0001% chance. IIRC, it was spinning up Cape Verde storms back in MAY.
3. It is wayyyy too early to be looking seriously at Cape Verde storms. Yes, its possible, but it is also possible for me to grow a horn out of my head and start speaking in tongues.

While I do think that it is good to watch all parts of the tropical Atlantic for storm formation, focusing on an area near the Cape Verde Islands so early in the season is pretty senseless self-pleasure at this point. Each season is different, and if people start wishcasting or hoping for a storm to form, they are just setting themselves up for disappointment.


1) Completely correct
2) Completely Correct
3) Completely correct

1) When Bertha happened, it was the second time it (We had a Cat 5 in July in 2005 that was CV wave lol and Bertha in 1996) occured so it obviously wasn't a freak of nature.
2) Well, that obviously wasn't the case last year, GFS got most of the storms days-weeks in advance and the GFS picked up on Bertha too. Drak always told us the GFS is not the Gospel last year.
3) Not after last year it isn't anymore.

You got to remember, we've just endured 2 wierdo seasons plus 2005 2 years before 2007.
Member Since: July 8, 2005 Posts: 259 Comments: 24032
Why are some bloggers so concerned what areas other bloggers watch? I find the insight on this blog of great value let em blog!
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Quoting hurricane2009:


Not one person here has wishcasted anything about this tropical wave. Just because we talk about it doesnt mean we are freaking out about it

I guess to make others happy we should just not say a word about anything east of 60W until later July.



Jeff is 100% correct.... but of course you can watch it... why not? but to talk or speculate or have the "HYPE" of hoping it forms...forget about it... Cleveland will win a Championship before that happens..
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Quoting extreme236:


Yeah, I just couldn't remember the exact coordinates

INITIAL 03/0900Z 12.6N 22.7W

And if it happens once, who could say it couldn't happen again? Just simply because its happened before makes me more inclined to watch it, because now I know it can happen.


And the fact it just happened last year.
Member Since: July 8, 2005 Posts: 259 Comments: 24032
QS OFF THE AFRICAN COAST


Link
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Quoting hurricane2009:


Actually it became a tropical depression at 22.7W


Yeah, I just couldn't remember the exact coordinates

INITIAL 03/0900Z 12.6N 22.7W

And if it happens once, who could say it couldn't happen again? Just simply because its happened before makes me more inclined to watch it, because now I know it can happen.
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Quoting extreme236:


Hurricane Bertha...all I have to say


Both Bertha's actually. We're not being silly, the almost exact same scenerio is setting up. GFS forecasting weeks in advance a system off CV forming in July, everyone think's were crazy to watch it, then wallabam, Category 3/4 in Early July.
Member Since: July 8, 2005 Posts: 259 Comments: 24032
1259. lavinia
Quoting KEEPEROFTHEGATE:
according to latest info looks like by 1 pm is when storms should ramp up and break out by 7 pm they should be out over the lake with maybe a few smaller cells following behind i figure the strongest will be between 2 pm and 5 then they should start movin se with the front


Thank you for the info.
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Quoting scottsvb:
Bertha was that 1 time.. :)

Fully agreed there. Just because it happens once does not mean that it will happen again every year. The entire atmospheric situation is different this year compared to last.

1. Shear is generally higher this year in that area.
2. This year is neutral to El Nino, last year is La Nina to neutral.
3. SSTs are somewhat cooler in that area this year, compared to last year

Also, there are several other factors to keep in mind:
1. Bertha was a freak of nature, it was well outside the "norm" for a July hurricane
2. The GFS spins up EVERYTHING with even a 0.0001% chance. IIRC, it was spinning up Cape Verde storms back in MAY.
3. It is wayyyy too early to be looking seriously at Cape Verde storms. Yes, its possible, but it is also possible for me to grow a horn out of my head and start speaking in tongues.

While I do think that it is good to watch all parts of the tropical Atlantic for storm formation, focusing on an area near the Cape Verde Islands so early in the season is pretty senseless self-pleasure at this point. Each season is different, and if people start wishcasting or hoping for a storm to form, they are just setting themselves up for disappointment.
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Quoting scottsvb:
Bertha was that 1 time.. :)


Bertha actually formed near 30W though lol
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I saw that but no, I'm looking at west of Tampa
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1255. beell
A big difference in the July waves of last year-including Bertha's wave. They all left the African coast at a fairly high latitude. At or above 15N. I thought this was unusual although other opinions may be just as valid. A different set-up over the ATL last year.
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RitaEvac, you talking about the cluster of storms N of Key West? Looks like rotation from the Key West radar.
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1253. KEEPEROFTHEGATE (Mod)
Quoting lavinia:
KOG...my hubby has to fly out of Hamilton this evening. Do you know how long this storm is going to hang around today? Not that I wouldn't mind a break in this heat!
according to latest info looks like by 1 pm is when storms should ramp up and break out by 7 pm they should be out over the lake with maybe a few smaller cells following behind i figure the strongest will be between 2 pm and 5 then they should start movin se with the front
Member Since: July 15, 2006 Posts: 171 Comments: 53841
Hurricane Dennis began as a tropical depression on July 4th, 2005 in the eastern Caribbean.

July 4th is now just 10 days away...

Anything and everything is possible cause it's hurricane season.
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1251. K8eCane
Quoting KEEPEROFTHEGATE:
morning 09 and i watch what ever i like for as long as i like

i always follow this rule

what they say it will be and what it will be are two different things


Precisely: thats why i'm watching a little area off NC/SC coast
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The July tack guidance east of 60 is mostly for July 15-July 31st ...later in July you get...the further east you look.
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1249. Ossqss
This is why the comment was made on the A wave.



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1248. KEEPEROFTHEGATE (Mod)
morning 09 and i watch what ever i like for as long as i like

i always follow this rule

what they say it will be and what it will be are two different things
Member Since: July 15, 2006 Posts: 171 Comments: 53841
Quoting CycloneOz:


No...it's probably just me 1st thing in the morning...


I hope so, unless it is a very weak TS that just dumps about 6-10 inches of rain spread out over a few days.
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Bertha was that 1 time.. :)
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1245. lavinia
KOG...my hubby has to fly out of Hamilton this evening. Do you know how long this storm is going to hang around today? Not that I wouldn't mind a break in this heat!
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Cut off Low in Gulf beginning
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Quoting scottsvb:
All you guys are acting silly for talking about a tropical wave off Africa... does everyone know how many come off Africa each year? Ok so the GFS shows a weak low.. but this will fall apart once it gets to 30-35W... this happens every year @ this time of year. 1 time every decade something will form near 45-50W near 10dg..but usually they wait till it gets near 55-60W or until it gets into the western carribean.

Anyways you have to wait a few more weeks. Right now...some waves that are going to start to come off the coast will look nice with a low-midlevel circulation... but will die out!..and unless 3 models support development with the GFS..aka ECMWF-Ukmet... I would give it under a 10% chance of developing east of 50W.

Pay more attention to home grown stuff this time of year for the next 2 weeks @ least.


Hurricane Bertha...all I have to say
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1241. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 171 Comments: 53841
Quoting PensacolaDoug:
Wishful thinking there Brian?


I'd love to see the gulf coast of Texas get soaked! :)
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1239. Ossqss
Pulled down for the linked site is way too slow to support the image refresh :(
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All you guys are acting silly for talking about a tropical wave off Africa... does everyone know how many come off Africa each year? Ok so the GFS shows a weak low.. but this will fall apart once it gets to 30-35W... this happens every year @ this time of year. 1 time every decade something will form near 45-50W near 10dg..but usually they wait till it gets near 55-60W or until it gets into the western carribean.

Anyways you have to wait a few more weeks. Right now...some waves that are going to start to come off the coast will look nice with a low-midlevel circulation... but will die out!..and unless 3 models support development with the GFS..aka ECMWF-Ukmet... I would give it under a 10% chance of developing east of 50W.

Pay more attention to home grown stuff this time of year for the next 2 weeks @ least.
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Quoting leftovers:
tw coming off of africa? if it were august. didnt i write that last yr and had to have bird for dinner.


Yup lol
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1236. KEEPEROFTHEGATE (Mod)
Hot and humid conditions will linger across southwestern Ontario for
one more day. The mercury will climb into the 31 to 34 degree range
by early afternoon, pushing humidex values to near or just over the
40 threshold.
Discussion of thunderstorm potential.

Today into this evening..There is a risk of severe thunderstorms
today in southern Ontario along and ahead of a slow-moving cold
front. Ample heat and humidity will almost ensure a few severe
thunderstorms will develop by early afternoon with damaging wind
gusts to 100 km/h, very large hail in excess of 3 centimetres,
torrential downpours giving over 50 mm of rain within an hour, and
frequent intense lightning. They may be particularly severe in areas
in and around the Golden Horseshoe. Isolated non-severe
Thunderstorms are expected in the northwest this morning spreading
into the northeast by this afternoon.

Member Since: July 15, 2006 Posts: 171 Comments: 53841
Ok, I am looking at the Blob coming off of Africa... the shear around it is minimal, but all of the shear in front of it is 30-60 knots, with the shear tendency increasing in most cases. What am I missing.. should it not get ripped apart pretty good in the next few days?
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1233. KEEPEROFTHEGATE (Mod)
we got a good chance of severe weather later this afternoon with day time heat humity combine with a weak slow moving cool front and a dev lake breeze it may get quite nasty a little later today
Member Since: July 15, 2006 Posts: 171 Comments: 53841
Wishful thinking there Brian?
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the forecast track of this tropical wave, were it to evolve would put it at 14-15 deg lat before entering the caribbean. if it were to hold together ,it could be a force to be reckoned with, sst's are high from 50 deg west all the way to the GOMEX
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1230. KEEPEROFTHEGATE (Mod)


humidex 98f
Member Since: July 15, 2006 Posts: 171 Comments: 53841
Quoting KEEPEROFTHEGATE:
ya orca its hot hazy humid and the new word stinky


Nothing like 100 degree weather and a garbage strike.. I hope it doesn't last more then a month or two :)
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1228. KEEPEROFTHEGATE (Mod)
ya orca its hot hazy humid and the new word stinky
Member Since: July 15, 2006 Posts: 171 Comments: 53841
1227. KEEPEROFTHEGATE (Mod)
just after 9 am its 81.1f with a heat index of 97 going to a high of 86 with heat indexs at or above 100
Member Since: July 15, 2006 Posts: 171 Comments: 53841

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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