It has been over three long, grueling days since Hurricane Florence made landfall near Wrightsville Beach, NC as a Category 1 hurricane. Though her wind intensity was not as severe as initially anticipated, the destruction she brought has been just as serious as expected.
In this edition of the Sunday Storm, let’s break down the Florence’s impacts and what to watch out for next.
As of 5pm September 16th, Florence is a Tropical Depression straddling the Savannah River just south of Anderson, SC. The storm has been barely clinging on to tropical characteristics, but torrential downpours were nonetheless widespread from Myrtle Beach northward into central Virginia and southeastern West Virginia. Crippling flooding woes will continue as the storm undergoes extra-tropical transition and embarks on a journey toward the Northeast US.
Like Sandy in 2012, Florence’s Category 1 status did not reflect the storm’s true destructive capabilities. For a “meager” Category 1 Hurricane at landfall, Florence produced an unprecedented trail of devastation and set an unfortunate number of records in the process. Florence has been blamed for a least 14 deaths as of Sunday morning, according to The New York Times. Most of these deaths are related to floodwaters engulfing homes and roadways.
Major flooding has already inundated eastern North Carolina, especially along the Cape Fear, Neuse, and Trent Rivers, which have long since overflowed their banks. Near Chinquapin, the Cape Fear River has reached a record flood stage of 24.21 feet, breaking the old record of 23.5 feet. With torrential rain spreading upstream toward the western Carolinas, the flooding will only worsen through Tuesday. Mandatory evacuations have been ordered in Fayetteville in anticipation, where the flood waters are expected to reach 62.3 ft according to the National Weather Service. In conjunction with the nearby Little River, the combined floodwaters are expected to submerge areas up to 1.5 mi from the river banks.
All this flooding has been prompted by record-shattering rainfall. An unfathomable 33.89″ of rain has fallen in Swansboro, NC as of Sunday morning. This shatters North Carolina’s rainfall record for the wettest single event in the state’s history, previously set by Hurricane Floyd’s 24.06″ deluge in 1999. In South Carolina, the state rainfall record from a tropical cyclone was also broken on Sunday with a recorded 18.13 inches of rain, beating the record from Hurricane Joaquin in 2015. Further south, Florence set a number of records in Wilmington. The city recorded its single wettest weather event ever, with 23.59″ of rain falling from Florence, breaking a record set in September 2010 of 22.54″. All of this rain has led to flooding and now the city of 120,000 people is trapped by the water with no roads passable in and out of the city. But as we warned about previously, it’s not just the coast that has been drowning in torrential rain. The observed rainfall graphic below from the Weather Prediction Center depicts just how far-reaching the flooding rains have spread through Sunday morning.
Florence also set many storm surge records. Tide levels reached 3.6 ft above the typical high tide Sunday morning, breaking the old record set only two years ago by Hurricane Matthew. Tides in Wrightsville Beach were even higher, reaching 4.11 ft above high tide, shattering a record set by Hurricane Joaquin in 2015 by more than a foot. In other words, the ocean surface sat over one foot higher than it had ever been. That is unprecedented for the area, and has brought just awful destruction to the immediate coast.
Rainfall and flooding are not the only records set by Florence. According to Dr. Philip Klotzbach of Colorado State University, Florence was a named storm for 15 days, making it only the 11th Atlantic tropical cyclone to maintain that status for at least 15 days since the beginning of the satellite era in 1966. Prior to landfall, Hurricane Florence’s central pressure of 954 mb was lower than any Atlantic hurricane of such a northern latitude since Sandy in 2012.
Flooding will continue to worsen through at least Tuesday in the Carolinas, when most rivers will crest. By then, Florence will have transitioned into an extratropical mid-latitude cyclone. The storm’s remnants will bring tropical downpours to Appalachia and the Northeast before returning to the Atlantic Ocean off the New England coast. Fortunately, a swift jet stream will ensure that flooding from Florence’s remnants won’t be nearly as severe as that in the Carolinas. But that doesn’t mean that all in the remnant storm’s path should keep their guard down.
The zombie downpours of Florence will accelerate northward Sunday night as the remnant low begins to develop a frontal structure. The low will straddle the northern Savannah River Sunday night before turning northeastward up the Appalachian mountains. The heaviest rain will be confined to the north and east of the low’s center. Moisture inflow from the Atlantic will continue such that the Wilmington area will continue to be bombarded by downpours. Elsewhere in the Carolinas, however, the rain will finally begin to depart.
Sunday night, torrential rain will migrate away from South Carolina, across the western two-thirds of North Carolina and into eastern Tennessee, Kentucky, Virginia, West Virginia, western Maryland and the Ohio River Valley by day break Monday. The remnant low’s mid and upper level circulations will merge features to the north, carrying the low and its rainfall toward the northeast.
The heaviest rainfall Sunday night will closely follow the waning low-level jet off of the Atlantic ocean. The jet will be strongest to the northeast of the low’s center in central North Carolina and western Virginia, where moisture and warm advection parallel the low’s northward motion. Exceptionally large values of absolute vorticity still remain in the vicinity of this jet, as inertia has resisted a quick deceleration of the circulation around the low. Vorticity describes the local spinning motion of a fluid. When wind increasingly transports higher values of vorticity with height, the atmosphere is stretched, forcing air upwards. Given a jet streak of roughly 70 mph at around the typical level where moisture condenses into rain, transport of vorticity will be exceptionally robust. The atmosphere will have no problem in continuing its generation of blinding downpours in central North Carolina, western Virginia and southern West Virginia.
Topography will also play a significant role in the downpours. Easterly and southeasterly winds rush up the Blue Ridge and Alleghany mountains. It will not take much additional upward motion due to upsloping to increase the intensity of the rain bands. Since the Blue Ridge Mountains are the highest mountains in eastern North America, downpours along these eastern slopes will be especially heavy. Gravity will force the rain that falls here to rush down mountainsides and pool in valleys. Mudslides will be an inevitable result, toppling trees and bulldozing structures in their way. Debris will accumulate on roads, exasperating the emergency response.
With jet dynamics and upsloping working hand-in-hand, torrential rainfall will result in crippling floods. Cities like Fayetteville, Raleigh, and Greensboro will be the focus of the heaviest rain owing to jet dynamics through Sunday night, before moisture flow into Florence’s remnants cuts off from the Atlantic. Meanwhile, torrential rain will race down the Blue Ridge Mountains into cities like Asheville and Roanoke, where low-lying areas will quickly fill with runoff. Up to a foot of additional rain is likely in these areas through Monday morning, when widespread rain will temporarily end from south to north ahead of a cold front.
By Monday afternoon, Florence’s remnants will have become fully extra-tropical. It will have a cold center and will be powered by fronts and jet dynamics. The sun will finally tear through the clouds in the Carolinas ahead of the cold front, which will bring the last few quick rounds of rain to the Southeast. Though the sunshine will be a hopeful sign marking the beginning of the recovery process, but the flooding will continue to worsen until Tuesday as rainfall runoff upstream continues to work its way down river.
The jet stream will quickly draw the remnants up the Appalachian mountains into the Northeast Monday afternoon, when central Pennsylvania and western New York will be under the gun. The jet streak will travel northeastward through this region, thus rainfall here will be heaviest. Tuesday, a low pressure system in Québec and New Brunswick will force the undead remnants out-to-sea from the Massachusetts’ coast such that Monday night through Tuesday afternoon, eastern New York and southern New England will be the focus of the heavy rain. Downpours will be torrential in the Northeast, but they will be quick-hitting.
Less than 24 hours of rain is expected in the Northeast, so rainfall amounts will be much less here than in the south. Peak totals will generally be on the order of 3-5″ along eastern-facing slopes of Pennsylvania and New York as well as in the immediate vicinity of the warm front in New York and New England. Binghamton, Utica, Albany, and Manchester are some of the cities that could experience the heaviest of the rain. Localized totals in excess of 6″ are possible in and near these cities, but determining exactly where is difficult as it depends heavily on the position of the warm front, which currently is expected to stall near the I-90 corridor. Localized flash-flooding is possible here, but significant impacts are unlikely. Scattered rainfall totals of up to 2″ is expected almost everywhere else in the Northeast. Delaware, eastern Maryland, southern New Jersey, eastern Long Island, southern Connecticut and Rhode Island will be caught south of the warm front and east of the jet streak. Therefore, less than an inch of rain is expected here.
Overall, there are only a few grueling days of weather remaining before conditions improve enough to engage on a long period of recovery. Although most of the rain will end in the Carolinas Monday, flooding will worsen through Tuesday as rainfall from the mountains works its way downriver. Neither the mountains nor the coast will escape drowning from Florence’s undead remnants. Early this week Florence will become extra-tropical and bring rain to the Northeast US, but impacts here will be drastically more benign than the unraveling catastrophe in the Southeast. Though the impacts from Florence may finally be winding down, the recovery is yet to begin, so we will continue to provide updates at WeatherOptics. Stay dry out there.
As always, look out for our 5 Things to Watch released tomorrow morning.