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takyon: Florence is currently expected to make landfall in North Carolina during the early morning or afternoon on Friday. There have been mandatory evacuation orders, but they may be widely ignored.

martyb writes:

A category 2 (formerly category 4) hurricane named "Florence" is heading for the eastern coast of the US. This being around the midpoint of the hurricane season, that's not unusual. This hurricane is, however, expected to make landfall much further north than is usual: near the border between the states of North Carolina and South Carolina. As you may recall, Hurricane Harvey devastated Houston, Texas last year with many areas receiving over 40 inches of rain (peak total was 60 inches) over a four-day period. Florence is similar in that there is a high pressure ridge just north of the point of landfall. It is anticipated that this will keep Florence part way over the ocean (picking up additional moisture) and part way over land (dumping copious amounts of rain).

Hurricanes cause damage in three ways: wind damage, storm surge, and rain (flooding).

Let's start with the wind. Recent readings (according to Wikipedia): sustained winds 110 knots (120 mph; 205 km/h) (1-min mean) gusting to 140 knots (150 mph; 250 km/h). (Aerodynamic drag is proportional to the square of the wind velocity. Stick your arm straight out the window of a vehicle travelling at 60 mph. Now take that force and double it. And then double it again. Now imagine that force being applied against something the size of a building. Widespread structural damage is likely.

Next, there's the Storm Surge which "is produced by water being pushed toward the shore by the force of the winds moving cyclonically around the storm." This would be above and beyond the normal tides for the area. For this storm, Scientists say Hurricane Florence could produce historic storm surge of up to 20 feet (~12 meters). To provide some perspective, tides around Myrtle Beach (near the northern-most part of South Carolina) usually has tides of up to 2.5 feet (0.75 meters). In short, flooding at the coast will be of historic proportions.

And then on to the rain. Expected rainfall totals over a period of four days generally range up to 20 inches — with 30 inches being possible in isolated locations. The general area has already had steady rains over recent weeks saturating the soil. Most of the rainfall will, therefore, not be absorbed by the soil but will instead just run downstream. In the mountains and hills away from the coast are a great many valleys which will further funnel the water and produce major flooding. It gets worse. Tree roots in waterlogged soil will likely give way under the onslaught of the rain and wind; many of which will fall on power lines. Power outages of several days or even over a week can be expected. Temperatures in the area vary around 70-90°F (21-32°C) so expect much food spoilage when refrigerators stop running.

Further complicating things, Hurricane Florence's risks include toxic sludge and lagoons of pig manure. In 2014, about 39,000 tons of coal ash spilled in from a pond near Eden, North Carolina. As of August 2017, Duke Energy had 31 coal ash basins in North Carolina which contained about 111 million tons of coal ash, a byproduct of burning coal to generate electricity. It contains metals including arsenic, chromium, and mercury. The extreme rainfall could cause some ash ponds to overflow and send their toxic waste downstream.

North Carolina is a top producer of turkey, chicken, and hogs. More than 10 billion pounds of wet animal waste is produced annually in the state and is held in lagoons because it's generally considered a safe way to store the manure before it's used to aid crops. Though most lagoons will likely survive the storm intact, there will certainly be some which overflow sending their "aromatic essence" downstream.

Links:

National Hurricane Center
NYT: Hurricane Florence's Path: Category 2 Storm Closes In on Carolina Coast
Ars Technica 2018-09-13: Florence is now “only” a Category 2 hurricane. That won’t matter much
Ars Technica 2018-09-12: The Hurricane Florence forecast has gone from bad to worse
Ars Technica 2018-09-10: Hurricane Florence represents a grave threat to the East Coast
CBS News: Hurricane Florence closes in on Carolinas, Virginia – live updates
Washington Post Hurricane Florence charges toward Carolinas with ‘potential for unbelievable damage’
Wikipedia entry on Hurricane Florence
GOES-East Satellite Loop
Earth.nullschool.net: earth :: a global map of wind, weather, and ocean conditions

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