Hurricane Dorian Pounding the Carolina Coast

Hurricane Dorian was hammering the Southeast U.S. coast on Thursday with hurricane-force wind gusts, a damaging storm surge, torrential rains and tornadoes. More than 200,000 customers were without power across the region as of 11 am EDT.

As of 11 am EDT Thursday, Dorian had weakened slightly to a Category 2 storm with peak winds of 110 mph winds. The actual winds at the surface found by the Hurricane Hunters were lower than that, and Dorian’s peak surface winds may be 100 mph or less.

The eyewall of #HurricaneDorian is just off the coast of #Charleston #SC in this "sandwich loop" from #GOESEast. Sandwich loops are a combination of visible and infrared satellite imagery. Follow the storm via our hurricane tracker: https://t.co/mmgdYBDi8D #SCwx #NCwx pic.twitter.com/pmBi4xylZM

— NOAA Satellites (@NOAASatellites) September 5, 2019

The hurricane was headed north-northeast at 8 mph, a motion that will likely bring the powerful winds of the left-side eyewall over coastal South Carolina northeast of Charleston on Thursday afternoon. These eyewall winds are likely to affect coastal North Carolina near Wilmington beginning on Thursday night, then move up the coast of North Carolina during the day Friday. The actual center of Dorian’s eye may never cross the coast, but the full fury of this formidable Category 2 hurricane will nonetheless cause a dangerous set of impacts.

Figure 1. Radar image of Dorian at 11:25 am EDT September 5, 2019.

WU commenter connerquinnking in South Carolina had this to say in the blog comments this morning:

Myrtle Beach (Surfside Beach) about 2 miles from the ocean was especially hammered with rains and storms between 1 am and about 7 am (obviously they were outer bands) but it hasn't rained a lot in the last 3 hours. It tailed off considerably. There were 3 tornado warnings ending at 4:45, 5:45 and 6:45 am. The street which is very low is filled with water and there is a creek (or drainage ditch practically in back of our property) that is almost filled. It was very very low almost down to a trickle before it hit.

Wind gusts in excess of 50 mph have been common from Dorian, according to the 11 am EDT Thursday NOAA storm summary. The highest gust thus far was 92 mph at the buoy 5 miles ESE of Fripp Island, SC. The airport at Charleston, SC reported a wind gust of 68 mph at 4:13 am EDT Thursday, and the Hilton Head, SC airport reported a gust of 67 mph at 1:35 am.

At 7:50 am EDT Thursday, winds at NOAA buoy 41004 located 47 miles southeast of Charleston, SC were sustained at 60 mph, gusting to 85 mph, with wave heights up to 25 feet. The eye crossed over the buoy, which recorded a pressure of 959 mb at 10:10 am.

Rare to see tornado probabilities in a tropical cyclone landfalll this high (15%
no significant tornado area). Already have numerous reports/videos of tornadoes this morning.

(For those who will inevitably ask: Day 3 of Ivan after landfall was Moderate Risk in the MidAtlantic.) https://t.co/2evcKHXuIh

— Patrick Marsh (@pmarshwx) September 5, 2019

Dorian spitting out tornadoes ahead of its center

Dorian spawned at least seven tornadoes early Thursday morning over coastal South Carolina and North Carolina, according to preliminary storm reports from NOAA’s Storm Prediction Center, with at least six more tornadoes since 8 am EDT. At 8:40 am  Thursday, WU commenter DJ X Factor reported: “The amount of tornados dropping around the Myrtle Beach area is insane! I have been up since 4am with non-stop Tornado Warnings hitting my phone telling me to take cover. Damage reports have been steadily coming across social media of touchdowns. We're currently under another one!”

The atmosphere just ahead of Dorian is primed for the compact, tornado-producing supercells that can develop in association with hurricanes, especially ahead and to the right of where the center is tracking. The NOAA/NWS Storm Prediction Center is calling for an enhanced risk of severe weather across coastal North Carolina, with a slight risk extending into far southeast Virginia, through Thursday night, mainly for the threat of tornadoes. Multiple mini-supercells were clearly evident on radar Thursday morning along a rainband pushing onshore.

Tornadoes associated with hurricanes are typically short-lived, but they can be intense and damaging. Overall, hurricanes represent about 3-4% of all tornadoes since 1950. In some years, such as the busy Atlantic season of 2004, hurricanes are responsible for a large chunk of all U.S. tornadoes. That year’s Hurricane Ivan produced a record 118 tornadoes, including 38 in Virginia—the most extensive tornado outbreak on record for any mid-Atlantic or Northeastern state.

A tornado in North Myrtle Beach, SC this morning was caught on video in this tweet below:

Out checking on some properties we manage and this happened. @EdPiotrowski @wpdeabc15 @WBTWNews13 @TheWeatherCH @wmbfnews pic.twitter.com/6wqtjeYiMC

— Wayne White (@NMBchiefsSports) September 5, 2019

Storm surge flooding less than feared—so far

Dorian’s large circulation and strong winds have piled up a large storm surge, but so far, the highest surge heights in Florida, Georgia, and South Carolina have occurred closer to the time of low tide than high tide, which has limited storm surge damage and coastal flooding. Dorian’s winds have also been aligned more parallel to the shore than onshore, which has helped limit storm surge heights.

At Charleston, SC, the storm surge during this morning’s 1 am EDT high tide cycle was high enough to cause only moderate flooding and did not fall in the top-ten highest water levels on record. The peak storm surge of approximately 3.5’ came at the time of low tide, later in the morning. A surge of this level would have caused a top-five water level on record and major flooding had it hit at high tide. Charleston still has one more high tide cycle of concern, due to come early Thursday afternoon; the storm surge riding on top of the high tide is predicted to cause only minor coastal flooding then, though (Figure 2).

Figure 2. Predicted water levels in Charleston, SC. Moderate coastal flooding occurred during the 1 am Thursday high tide, due to Dorian’s storm surge. The surge is predicted to cause flooding just above the “Major” level during this afternoon’s high tide cycle. Image credit: NOAA.

A storm surge of about 4.0’ hit Fort Pulaski, Georgia near the time of low tide on Wednesday, and water levels there stayed just below the moderate flooding threshold. Had Dorian’s peak storm surge coincided with high tide, it would have been the third highest water level on record, about a foot lower than the record set during Hurricane Matthew of 2016.

The highest water levels at Fernandina Beach, FL, near the Georgia border were 2.54’ above the high tide mark (called Mean Higher High Water, MHHW), ranking as the eighth highest on record (their record highest: 6.91’ in the October 1898 hurricane; second place was 4.13’ in Hurricane Matthew of 2016).

Dorian’s storm surge is expected to cause minor to major flooding along much of the South Carolina coast during the high tide cycles Thursday afternoon, and along much of the North Carolina coast during the Friday high tide cycles. In their 11 am EDT Thursday Dorian advisory, NHC called for coastal storm surge flooding of up to 5 – 7 feet above the high tide mark from Myrtle Beach, SC to Duck, NC. Flooding at Myrtle Beach is expected to reach the "major" level.

Figure 3. Estimated precipitation from Dorian over South Carolina as of 10:49 am EDT September 5, 2019. Rainfall in excess of 8” (dark red colors) with a few areas of 10” (pink colors) were indicated.

Heavy rain threat

The heaviest rain amounts from Dorian thus far according to the 11 am EDT Thursday NOAA storm summary has been 7.52” at Socastee, SC. Charleston, SC, recorded 6.05”. Torrential rains of 6 to 12 inches, locally more than 15”, will plague areas within about 50 to 100 miles of the Carolina coast during the coming day, with the heaviest amounts likely to fall in coastal South Carolina, where Dorian will be moving more slowly. These rains could not only cause localized flash flooding but may also exacerbate coastal flooding during times of surge. The heavy rains are predicted to drain into the Cape Fear River in Wilmington, NC, causing a crest above major flood stage on Sunday, reaching the fifth highest water levels on record.

The next potential threat: a tropical wave off the coast of Africa

The next system that has the potential to be a threat is a tropical wave that emerged from the coast of Africa Wednesday morning. Satellite images on Thursday afternoon showed that this system, which had not yet been given an “Invest” designation by NHC, was not very impressive, with only a limited amount of heavy thunderstorm activity and spin. However, the atmosphere in front of it has favorable conditions for development, with low to moderate wind shear, plus a good deal of mid-level moisture, as seen on the latest Saharan Air Layer Analysis. This moisture is partially due to the passage of Dorian across the tropics in late August.

Recent runs of our three top models for predicting tropical cyclone genesis—the GFS, European and UKMET—have all shown support for development, with several runs depicting the wave developing into a long-track Cape Verdes-type hurricane. The wave is predicted to take a west to west-northwest track over the coming week, and it has the potential to be a long-range threat to the Lesser Antilles Islands as early as September 12. However, recurvature into the open central Atlantic is also a good possibility, and there’s lots of time to watch this one before we need be concerned. In their 2 pm EDT Thursday Tropical Weather Outlook, NHC gave this system 2-day and 5-day odds of development of 20% and 60%, respectively. The next name on the Atlantic list of storms is Humberto.

The other tropical systems and threat areas out there—Tropical Storm Gabrielle, Invest 92L, and a new disturbance a few hundred miles northeast of the Leeward Islands—are all no threat to land, and not worthy of further discussion currently.

Cockpit video from inside the eye of Hurricane #Dorian from today's flight off the coast of South Carolina. Continue to monitor https://t.co/3phpgKMZaS for the latest updates and advisories. #FlyNOAA

Credit: Lt. Kevin Doremus, NOAA pic.twitter.com/iqpXyHUX8y

— NOAA Aircraft Operations Center (@NOAA_HurrHunter) September 5, 2019

Bob Henson co-wrote this post.