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| Many people in the Southeast and Mid-Atlantic probably have not experienced a storm of the potential magnitude of Florence. |
Hurricane Florence: Watches posted as ‘extremely dangerous’ Florence churns toward Carolinas
Florence continued its path toward the East Coast overnight Monday, maintaining its monstrous Category 4 storm status. Its top winds decreased to 130 mph early Tuesday, but the storm is expected to regain strength later on Tuesday.
The National Hurricane Center is calling the storm “extremely dangerous,” and predicts its peak winds could still reach 150 mph, which is just 7 mph from Category 5. The center issued hurricane and storm surge watches for the East Coast from Edisto Beach, S.C., northward to the North Carolina-Virginia border, including the Pamlico and Albemarle sounds.
Track forecast for Hurricane Florence. Hurricane watch zone is shaded in pink. (National Hurricane Center)
Computer-model forecasts generally project the storm to make landfall between northern South Carolina and North Carolina’s Outer Banks as a Category 4 on Thursday, although shifts in the track are possible and storm impacts will expand great distances beyond where landfall occurs. More than 1.5 million people have already been ordered to evacuate coastal areas ahead of the storm.
“All interests from South Carolina into the Mid-Atlantic region should ensure they have their hurricane plan in place and follow any advice given by local officials,” the hurricane center said.
The center is warning of an “extremely dangerous” triple threat in the Carolinas and Virginia:
1) A “life-threatening storm surge” at the coast — a rise in ocean water over normally dry land.
2) “Life-threatening freshwater flooding from a prolonged and exceptionally heavy rainfall event” from the coast to interior sections.
3) “Damaging hurricane-force winds” at the coast and some distance inland.
Like Hurricane Harvey, which stalled over Texas in 2017, Florence could linger over the Southeast for several days after landfall. Forecast models suggest that at least one to two feet of rain could fall in some areas. The flooding might be similar to or worse than what the Carolinas experienced during Hurricane Matthew in 2016.
At 8 a.m. Tuesday, Florence was tracking west-northwest at 15 mph, and located about 950 miles east-southeast of Cape Fear, N.C. Its zone of hurricane-force winds doubled in size Monday as it explosively strengthened.
If Florence makes landfall as a Category 4 in North Carolina, it would be the strongest storm to come ashore that far north on record.
In coastal areas of the Southeast and Mid-Atlantic, heavy surf and elevated water levels are expected to arrive by Wednesday morning, and rainfall could begin by Thursday morning.
Tropical-storm-force winds could reach the coastline as early as Wednesday night, at which point all outdoor preparations should be completed. Extremely dangerous hurricane-force winds could batter coastal locations Thursday into Friday. Hurricane-to-tropical-storm-force winds could extend inland, depending on the storm’s track.
Models have come into agreement that a northward turn before reaching the United States is unlikely and that a building high-pressure zone north of the storm will cause it to slow or stall once it reaches the coast or shortly thereafter Where exactly the zone of heaviest rain will be is a big uncertainty. It could reasonably occur anywhere between the mountains and the coast.
If the storm stalls, some areas could see feet of rain, especially if downpours focus over the higher terrain in western North Carolina and southwestern and central Virginia.
This region will be particularly susceptible to flooding because of far-above-normal rainfall in the region since May. In addition, because the ground is likely to be saturated, trees will be vulnerable in strong winds.
Parts of the Mid-Atlantic, especially from Virginia to Pennsylvania, have received 150 to 300 percent of their normal rainfall since May.
Residents farther north in coastal and inland areas in the Delmarva Peninsula, New Jersey, Pennsylvania and New York should also monitor the storm and prepare in case the forecast shifts to the north and east.
Where the storm makes landfall has implications for where the strongest winds and biggest rise in water at the coast occurs, but strong winds and extreme rainfall could occur at great distances from the landfall location. Keeping this in mind, here is the likelihood of landfall at different locations based on our evaluation of model data:
- 70 percent in the Carolinas
- 10 percent between Virginia and New York
- 10 percent offshore
- 10 percent between northern Florida and Georgia
Even in the unlikely event that the storm center remains just offshore, it will almost certainly come close enough to bring dangerous wind and flooding to coastal areas. Inland areas may be somewhat spared in this scenario.
If a major hurricane (Category 3 or higher) does make landfall along the Southeast coast, the rarity of such an event is relevant. Since 1851, only 10 major hurricanes have done so, and the most recent was Fran in 1996, 22 years ago. Hugo in 1989 was the one before that and was a Category 4 at landfall. No hurricane has made landfall as a Category 5 in this region on record.
Many people in the Southeast and Mid-Atlantic probably have not experienced a storm of the potential magnitude of Florence.
September 10 at 4:03 PM
Washington is waterlogged, and the last thing it needs is a hurricane deluge and damaging winds. Unfortunately, this will be a possibility Friday and into the weekend. But there are scenarios in which we would avoid serious effects.
Flooding rain and winds strong enough to bring down trees are the biggest concerns. But other storm hazards could affect the region, as well.
Depending on the track of Category 4 Hurricane Florence, a storm surge could come up the tidal Potomac and Chesapeake like a bulldozer, pushing water multiple feet above normally dry land along their shores.
[‘Extremely dangerous’ Hurricane Florence may approach Category 5, as it churns toward the Carolinas]
In addition, quick-hitting tornadoes could form in some of the storm bands that pass through the region.
"The potential for a disaster is high,” said Jim Lee, meteorologist in charge at the National Weather Service serving the Washington area. But he stressed uncertainties in the specific outcomes, noting that storm effects are still several days away. “Time will tell as the week unfolds."
Seven-day rainfall forecast from the National Weather Service. It predicts 3 to 5 inches of rainfall in the general area over the next seven days but much larger amounts to the southwest, where confidence is higher that excessive amounts of heavy rain will occur. (Capital Weather Gang)
We are very vulnerable
Our soils are saturated and our rivers, creeks and streams are full, if not already overflowing. If we receive several inches of rain or more, flooding will be inevitable, and it could become severe in a worst-case scenario.
"Certainly we're primed," Lee said of any flooding. “Even if we're on the northern fringe [of the storm], we're going to have flooding issues. We're sitting on a powder keg."
As of late August, Washington had already received a year's worth of rain, about 40 inches. Since then, we've picked up another half a foot. The 45.86 inches of rain so far this calendar year ranks it as the fourth-wettest in records that date to 1872.
Because our soils have been essentially transformed into mush, trees are no longer well rooted to the ground. Strong winds, possibly up to tropical-storm force, could bring them down in great numbers.
Lee said his office received eight reports of downed trees over the weekend from gusts of 30 to 35 mph. He expects tree damage would increase markedly if winds reach 40 mph or higher.
Storm scenarios
Scenario 1: Florence tracks into southwest and west-central Virginia. (40 percent chance)
In this scenario, the storm would make landfall between northern South Carolina and the North Carolina Outer Banks and move northwest through central North Carolina into southwest or south-central Virginia, where it would slow or stall.
In the Washington region, there would be a sharp gradient between more-moderate rains to our north and northwest and extremely heavy rainfall to our southwest and south that could continue for days — even into early next week.
Serious, possibly disastrous flooding would occur in central Virginia and could spill into the central and northern Shenandoah Valley and north-central Virginia piedmont.
The immediate Washington region would receive several inches of rain, certainly enough to cause flooding but perhaps short of widespread, severe flooding.
Wind gusts would probably reach tropical-storm force, causing downed trees and scattered power outages.
As the storm moved north, southerly winds would push enough water up the Chesapeake Bay and Potomac River to cause minor tidal flooding.
The European weather model supports this scenario.
Scenario 2: Florence slowly tracks northward just west of Interstate 95 (25 percent chance)
In this scenario, the storm would make landfall between northern South Carolina and the North Carolina Outer Banks, and progress north through eastern North Carolina and east-central Virginia along the Interstate 95 corridor. It would eventually pass through Northern Virginia west of I-95.
This is a worst-case scenario for the region. It would push a large storm surge up the Potomac and Chesapeake Bay, causing severe coastal flooding, perhaps not unlike Hurricane Isabel in 2003 or the 1933 Chesapeake Potomac hurricane.
Depending on how fast the storm was moving and whether it slowed or stalled along its track, significant-to-severe flooding from heavy rainfall would affect the region.
Sustained winds would probably reach tropical-storm force, with gusts over 60 mph causing widespread downed trees and power outages.
The UKMet model, run by Britain's Met Office, forecasts a scenario similar to this.
Scenario 3: Florence tracks well to our south, remaining in North Carolina (20 percent chance)
In this scenario, the Washington region generally dodges the bullet as the heaviest rain and strong winds remain well south of the region. Some rain and gusty winds could still skirt the area, especially on the south side, and cause pockets of flooding and a few downed trees, similar to the rain and wind this past weekend.
The American (GFS) model keeps Florence's storm center near the Outer Banks of North Carolina and never brings it far enough north or west to bring significant wind and rain to the Washington area.
The American model (both the new and old) favors this kind of scenario.
Scenario 4: Other (15 percent)
As or just after Florence makes landfall, steering currents will become weak, which turns its future motion into a bit of a wild card. While we have outlined above what we think are the most likely scenarios, there's still the possibility it just meanders near the coastline or edges north or south of current expectations.
We're still four to five days, at least, from any direct effects from this storm, and we will try to reduce the number of scenarios and provide more specifics about what to expect as time wears on.
Preparation
While there is a great deal of uncertainty with respect to the specific effects from the storm in our region, now is certainly the time to begin thinking about preparation for this storm. Prepare for flooding by decluttering drains and gutters. If you have a basement that floods, think about moving any valuables to higher ground.
Do you have trees that could fall on your house during a windstorm? Trim them now.
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