Dorian

I had little idea when I wrote in my last post about hurricanes that my decision-making would be tested so soon. And yet here we are, as always, closely following every bit of news we can get on Hurricane Dorian. The National Hurricane Center advisories come out every six hours, at 5 and 11 AM and PM, EDT. This particular hurricane has been a surprise that no one was concerned about five days ago, and it has been very difficult for forecasters to narrow down its future path. The 11 PM advisory has just been released, and here is where we are according to the NHC:

At 1100 PM AST (0300 UTC), the center of Hurricane Dorian was
located near latitude 23.3 North, longitude 68.4 West. Dorian is
moving toward the northwest near 12 mph (19 km/h), and this general motion is expected to continue through Friday.  A west-northwestward to westward motion is forecast to begin by Friday night and continue into the weekend.  On this track, Dorian should move over the Atlantic well east of the southeastern and central Bahamas tonight and on Friday, approach the northwestern Bahamas Saturday, and move near or over portions of the northwest Bahamas on Sunday.

Maximum sustained winds have increased to near 105 mph (165 km/h) with higher gusts.  Dorian is expected to become a major hurricane
on Friday and remain an extremely dangerous hurricane through the weekend.

Hurricane-force winds extend outward up to 25 miles (35 km) from the center, and tropical-storm-force winds extend outward up to 105
miles (165 km).

The latest minimum central pressure estimated from Hurricane Hunter data is 977 mb (28.85 inches).

What is making this hurricane so difficult to forecast is that its course will be affected by its speed. The storm is expected to turn westerly because of a high pressure ridge north of it that will keep it from going north. However, the ridge is expected to fall apart and stop influencing the storm by Tuesday, allowing it to turn north. If the storm moves quickly, it would likely cross south Florida into the Gulf of Mexico before turning north. However, if the storm moves more slowly, the high ridge could dissipate, allowing it to turn north while over land in Florida or even before reaching the coast of Florida. 

All of this makes planning extremely difficult, and people along the coast all the way from Louisiana to North Carolina could be in the line of fire. The NHC does, however, need to draw a cone. The latest one shows that The Ford Plantation is in an area with less than a 20% chance of having tropical storm force winds.

The more detailed cone showing estimated times has tropical storm force winds reaching our area, if at all, some time around 8 PM Monday. This time has changed from the 11 AM forecast, which had us at an 8 AM arrival time Monday:

As you can see, while we are not on the forecast track, we are just barely outside the cone. Statistics show that in 2/3 of cases, hurricanes make landfall somewhere within the cone. So we are not at all out of the woods yet. However, it's even possible for the storm to really slow down over the weekend and then make a sharp turn north, missing land altogether. Let's hope that's the case. This will come ashore as a Category 3 or 4 hurricane, that can be totally devastating.

A final note on surge. We learned here painfully two years ago that even a tropical storm that travelled up near us from the Gulf coast can cause serious tidal surge when strong offshore winds coincide with high tides. Here, the river rose over its banks, flooding parts of our Club property. Unfortunately, with no surge at all, we are having very high tides right now on the Ogeechee River. Our normal tidal range is from a low of around sea level (0) to a high of six to seven feet. Based on Ft. Mcallister tides that occur about two hours before ours, the Monday tides here are:

1:28 AM High 8.6'

8:23 AM Low -0.8'

2:03 PM High 8.2'

8:52 PM Low -0.5'

So we enter Labor Day weekend on edge. Here's hoping this storm takes a more favorable turn, and that our winds and tides don't conspire against us as they did in 2017.

Sea Level

A few weeks ago, I went to check on my boat at the Hinckley Marine boatyard in Thunderbolt, just east of Savannah. When I arrived, the entry road to the yard was under water. All of the employee cars were parked along the road a few hundred yards from the entrance, and one employee was directing traffic. He told me the tide had gone down already and that I could probably get through and find a dry parking spot, but getting to the dock and my boat might be a challenge. He also recommended a quick car wash that afternoon to get the salt off.

I tentatively made my way in and found all of the employees wearing tall rubber boots and sloshing around the soaked boatyard. I did manage to park in a dry spot and made my way along a narrow wall to get to the docks. While we all know that sea levels are rising, the experience led me to some reading on the subject. This is not a discussion of the causes of climate change, nor is it political. I simply wanted to find out what is happening right here where I live.

There are tremendous tides in our area, and on the day of this experience, they were much higher than average. In Thunderbolt, the high tide that day, February 20, was 9.8 feet while the low tide was -2.1 feet, a big day to be sure. But the measurement of tides is in relation to mean sea level, a number that is constantly rising. The tide gauge at Fort Pulaski is the only official measurement in the state. It was commissioned in 1935 and, since that time, the sea level has risen more than nine inches, a rate of more than a foot every hundred years. And the rate of rise is increasing. The low projections show a sea level rise of two feet by the end of this century while the most extreme show a rise of more than 10 feet in the same period. Almost all of the increase is attributable to the water rising rather than land sinking.

Someone asked me recently why the sea level would rise when glaciers melt that are already in the sea. It doesn't. Sea level rise is caused by runoff from the melting of glaciers that are on land, and by the expansion of sea water as its temperature increases. There are conflicting estimates of how much is caused by each of these factors, but there seems to be a developing consensus that thermal expansion of sea water will play the larger role long term.

Around here, there are signs everywhere of the issues that sea level increase is already causing. More and more frequently, U.S. Highway 80 to Tybee Island has to be closed as it is under water. Low areas along the Thunderbolt area are also routinely disrupted. A portion of President Street in Savannah is being elevated five to eight feet to prevent flooding.

Projecting the exact time that any area of the country succumbs to what is called "chronic inundation" is extremely difficult, as it involves estimating how trends change in the future. But we do know now that Savannah, along with Miami and New Orleans are high on the list of cities that will be affected the most quickly. For a more detailed study by the Union of Concerned Scientists pointing this out, see "When Rising Seas Hit Home". An interesting exercise is an interactive map published online by NOAA where you can zoom into an area of interest and slide the sea level up as much as 10 feet above its current level. For our area of the world, it looks pretty scary even to see the effect of a one or two foot rise.

Work has progressed slowly on the few projects for the boat. I hope to have it out of the boatyard this week or next.