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Old 12-28-2018, 11:22 AM   #1
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Hurricane surge considerations along the coast

The recent thread on where would you base your boat had a few veiled references to storm surge, so I thought it might be interesting to explore that issue more fully.

I do have some experience with storm surge having experienced surge of about 9' during hurricane Irene in Oriental, NC and noted the same from Florence. Also the effects of surge on Mexico Beach, Fl from hurricane Michael are well known.

Hurricane surge is wind driven tide rising due to strong or prolonged winds. In the case of Mexico Beach the winds weren't particularly prolonged but were very strong, maybe 150 mph. That pushed the water up to 10+'.

Irene's effect on NC was due to prolonged winds not so much wind strength which was Cat 1 or 2. The storm's track and slow passage through the Neuse River and Pamlico Sound let the wind build up its surge. If it had not partially stalled or had come on a different track, I suspect the surge would have been much less. I recall strong NE winds for about 24 hours before passage and the water was 6' high at least 8 hours before passage. Once the eye passed the tide quickly reversed and the tidal creek I was living on became a rushing river flowing out to the Neuse.

Florence's effect was due to stronger winds and a track that let the surge build up quickly.

So look at hurricane tracks along the coast and combine that with your own geography to see what might happen.

We currently live 6 mo out of the year in Punta Gorda, Fl. At one point the surge in PG was forecast to be 10+' from Irma. But Irma shifted its track and passed well to the east, resulting in NE wind down Charlotte Harbor pushing the water out, not producing surge. My neighbors tell me the canal in back of our condo was down to the mud before passage then quickly went up above normal afterwards. If Irma had tracked maybe 30 miles to the west, the wind would have been out of the SW which would have pushed water up into Charlotte Harbor and probably would have hit 10' or better. Most homes in PG are at 8-9' floor elevation so thousands would have had water damage.

What is the take away? Well if you are in a hurricane prone area and you live right on the coast, then 10+' of surge is possible. If you live inland from the coast on a long bay like Charlotte Harbor or Pamlico Sound, even though you won't be hit by ocean wind driven surge like Mexico Beach but it could be just as bad in the bay depending on its track.

The effects of global warming are another consideration. These include more severe storms and sea level rise over time.

For my money if I were in one of these areas (as I now am) I would want my house to be built up to at least a 12' floor elevation or live on the second floor or higher of a sturdily built condo.

David
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Old 12-28-2018, 11:38 AM   #2
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Quote:
Originally Posted by djmarchand View Post
The recent thread on where would you base your boat had a few veiled references to storm surge, so I thought it might be interesting to explore that issue more fully.

I do have some experience with storm surge having experienced surge of about 9' during hurricane Irene in Oriental, NC and noted the same from Florence. Also the effects of surge on Mexico Beach, Fl from hurricane Michael are well known.

Hurricane surge is wind driven tide rising due to strong or prolonged winds. In the case of Mexico Beach the winds weren't particularly prolonged but were very strong, maybe 150 mph. That pushed the water up to 10+'.

Irene's effect on NC was due to prolonged winds not so much wind strength which was Cat 1 or 2. The storm's track and slow passage through the Neuse River and Pamlico Sound let the wind build up its surge. If it had not partially stalled or had come on a different track, I suspect the surge would have been much less. I recall strong NE winds for about 24 hours before passage and the water was 6' high at least 8 hours before passage. Once the eye passed the tide quickly reversed and the tidal creek I was living on became a rushing river flowing out to the Neuse.

Florence's effect was due to stronger winds and a track that let the surge build up quickly.

So look at hurricane tracks along the coast and combine that with your own geography to see what might happen.

We currently live 6 mo out of the year in Punta Gorda, Fl. At one point the surge in PG was forecast to be 10+' from Irma. But Irma shifted its track and passed well to the east, resulting in NE wind down Charlotte Harbor pushing the water out, not producing surge. My neighbors tell me the canal in back of our condo was down to the mud before passage then quickly went up above normal afterwards. If Irma had tracked maybe 30 miles to the west, the wind would have been out of the SW which would have pushed water up into Charlotte Harbor and probably would have hit 10' or better. Most homes in PG are at 8-9' floor elevation so thousands would have had water damage.

What is the take away? Well if you are in a hurricane prone area and you live right on the coast, then 10+' of surge is possible. If you live inland from the coast on a long bay like Charlotte Harbor or Pamlico Sound, even though you won't be hit by ocean wind driven surge like Mexico Beach but it could be just as bad in the bay depending on its track.

The effects of global warming are another consideration. These include more severe storms and sea level rise over time.

For my money if I were in one of these areas (as I now am) I would want my house to be built up to at least a 12' floor elevation or live on the second floor or higher of a sturdily built condo.

David

"What is the take away? Well if you are in a hurricane prone area and you live right on the coast, then 10+' of surge is possible."

What is the takeaway for us?....
- check the hurricane frequency map by strength posted
- check the SLOSH map for your exact potential location and strength
- check the red tide map for your location and intended usage areas.

With those tools in your possession make the decision that fits your goals.
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Old 12-28-2018, 12:16 PM   #3
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My family and I have been in many hurricanes over the last 25yrs. Me in coastal Carolina, folks in Cudjoe Key Fla. I own a micro marina near Wrightsville Beach, and was living in Isle of Palms SC when Hugo hit. Lost most everything in that one. My folks have been hit three or four times, about the same for me. Lost count, really.

So I have some experience with storms.

Surge is very dynamic. You have to look at storm direction and speed, and wind direction and speed. Surge is a combination of low barometric pressure, and inward flowing wind. Carolina has many miles of 50' depth and the storm will suck up a ball of water. Has little opportunity to flow outward like it would if the water was deeper. Acts more like 1/4" of water on a really big sheet of glass. The wind has its way with it.

Flo last fall nearly stalled. We had winds directly from offshore. Not a strong storm, but persistent. I am in a protected creek right off the ICW. Water came up about 7' over normal high tide. A mile away is Pages creek that probably runs 3-4nm inland from the ICW. Due to the fetch and that the creek was nearly aligned with wind direction, the head of the creek got much more surge than I did. Same sort of thing happens in the NC Sounds well to the north. Wind driven surge in relatively shallow water.

Hugo was a different one. The storm was moving very fast, like 30kts, and the ball of water under it had enough momentum to literally go over obstacles (islands). Got like 15' of surge on low parts of the islands, but if island was high (like 15' above msl), those still got 5' plus of water. Just went right over it.

Fran came within 10" of coming in my house, 12' above msl. The house was a POS and ended up doing a "remodel by Caterpillar". New house is 16.5'. Could still get damage from a Hugo type storm, but I do sleep a little better.
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Old 12-28-2018, 01:01 PM   #4
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Generalizations such as 10' of surge is possible and other generalizations are dangerous. Look at the SLOSH maps, but also look at the Flood zones and maps and look at history. Where we are, 10' of surge would be several feet over any previous record, over the SLOSH map and greater than the official flood zone which is a maximum 100 year flood of 6'.

Now, there is one other factor and that is the changes as the seas have risen and temperatures raised which also fuels stronger storms. That could make all data we have obsolete.
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Old 12-28-2018, 01:26 PM   #5
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A floating dock vs a fixed dock is a consideration. With adequate pile height, a floating dock is king. Irma last year proved that in JAX. Boats that were in nearby marinas with fixed docks and floating docks with shorter piles were damaged. OTL Marina has extra high piles and the only damage was to a couple of ramps. As the water rose the ramps went pretty much vertical but the docks/boats floated fine. People who stayed on their boats were confined to docks till the water receded but they weren’t complaining.

The blue tape was the high dock height.
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