Dorian Brushes Florida; Serious Impacts Ahead for the Carolinas

September 4, 2019, 10:33 AM EDT

Above: Strong gusts of wind push ocean waters over a walkway at the Jensen Beach Causeway Park in Jensen Beach, Fla. on Sept. 3, 2019, during Hurricane Dorian (Adam DelGiudice/AFP/Getty Images).

Hurricane Dorian steamed north-northwestward about 80 - 100 miles from the Florida coast Tuesday night into Wednesday morning. The hurricane brought sustained tropical storm-force winds and damaging storm surge flooding to several locations along the Florida coast, but Floridians can breathe a sigh of relief that they missed the full wrath of Dorian. Damage in Florida from Dorian would appear to be far lower than the multi-billion dollar price tag of Hurricane Matthew of 2016.

Dorian radar
Figure 1. Radar image of Dorian at 11:25 am EDT September 4, 2019.

As of 6:36 am EDT Wednesday, the National Weather Service in Melbourne, Florida reported numerous gusts from Dorian in excess of 39 mph (tropical storm force). The highest gust at a land-based station was 70 mph at an elevated tower at Cape Canaveral. Here are some of the tropical storm-force gusts reported so far in Dorian by ground stations with standard measuring equipment:

PORT CANAVERAL               47 MPH    0830 PM 09/03   MESOWEST             
MERRITT ISLAND               46 MPH    0215 AM 09/04   RAWS                 
COCOA BEACH CLUB             46 MPH    0825 PM 09/03   WXFLOW               
DAIRY                        46 MPH    0737 PM 09/03   WXFLOW               
PAC ACADEMY                  44 MPH    0350 AM 09/04   MESOWEST             
HOOVER MIDDLE SCHOOL         40 MPH    1130 PM 09/03   MESOWEST             
NEW SMYRNA BEACH             69 MPH    0244 AM 09/04   WXFLOW               
DAYTONA BEACH                55 MPH    0335 AM 09/04   CWOP                 
NEW SMYRNA BEACH             51 MPH    0500 AM 09/04   CWOP                 
PONCE INLET TOWN HALL        49 MPH    0300 AM 09/04   MESOWEST             
EMBRY RIDDLE AERONAUTICAL UN 42 MPH    0810 PM 09/03   MESOWEST             
HERITAGE MIDDLE SCHOOL       41 MPH    0350 AM 09/04   MESOWEST             
DAYTONA BEACH                40 MPH    0210 AM 09/04   CWOP 
 
And by marine observing sites at the coast:
 
ST. AUGUSTINE BEACH          59 MPH    0800 AM 09/04   NOAA
INDIAN RIVER DB27            61 MPH    0739 PM 09/03   WXFLOW               
BANANA RIVER - 520           60 MPH    0217 AM 09/04   WXFLOW               
ROCKY POINT                  55 MPH    0837 PM 09/03   WXFLOW               
PARRISH PARK NORTH           54 MPH    0341 AM 09/04   WXFLOW               
COCOA BEACH PIER             53 MPH    1025 PM 09/03   WXFLOW               
ROCKLEDGE                    49 MPH    0704 PM 09/03   CWOP                 
MERRITT ISLAND               48 MPH    1134 PM 09/03   CWOP                 
JENSEN BEACH                 48 MPH    0255 PM 09/03   WXFLOW               
MELBOURNE BEACH              47 MPH    0628 PM 09/03   CWOP                 
TRIDENT PIER, FL             47 MPH    0224 AM 09/04   NOS-NWLON            
MELBOURNE                    46 MPH    0701 PM 09/03   CWOP                 
VERO BEACH                   43 MPH    0327 AM 09/04   CWOP
                 

Major beach erosion occurred Tuesday at Flagler Beach, according to the National Weather Service, and at Vero Beach, according to WKMG-TV. Flooding of streets and parking lots was reported on barrier islands near Ft. Pierce at high tide just after midnight early Wednesday.

Dorian brought a storm surge of around two feet to central Florida at Port Canaveral, where minor flooding was observed. A surge of nearly three feet occurred in northern Florida near Jacksonville, but the highest surge occurred at the time of low tide and did not cause significant flooding.

Dorians rains over Florida have mostly been less than four inches, and have not caused significant damaging flooding thus far. The highest 48-hour rainfall amount reported by the NWS in Florida was 3.92" at Lake Mary.

Florida rain
Figure 2. Estimated precipitation from the Melbourne, Florida radar from Dorian as of 9:54 am EDT September 4, 2019. Rainfall amounts of 2 – 4” were common in central and northern Florida.

Storm surge threat will progress along the Southeast coast today into Friday

Now that Dorian is starting to accelerate northward, the storm surge threat to the vulnerable Southeast U.S. coast will increase. Dorian’s enlarged circulation is pushing vast amounts of water, so the surge will be larger than one might assume from Dorian’s decrease from Category 5 to Category 2 strength. Hurricanes such as Ike (2008) and Sandy (2012) produced massively destructive surge long after their peak winds decreased and their circulations expanded.

Fortunately, Dorian will be moving mainly parallel to the Southeast coast; all else being equal, that produces less surge than a hurricane striking the coast at a right angle, such as Ike and Sandy. Even so, as we saw with Matthew in 2016, a large, coast-hugging Southeast U.S. hurricane can produce a major, destructive storm surge.

Savannah and Charleston can both expect top-three all-time highest crests on Wednesday night, based on forecasts at river outlets:

Fort Pulaski, Georgia (Savannah)
Record crest:  12.56’ over mean high high water (Matthew, Oct. 8, 2016)
Second place:  12.24’ (Irma, Sept. 11, 2017)
Forecast peak for Dorian:  11.4’ late Wednesday night (third highest on record)

Charleston Harbor, South Carolina
Record crest:  12.52’ (Hugo, Sept. 22, 1989)
Second place:  10.23’ (Oct. 8, 1940)
Forecast peak for Dorian:  10.3’ late Wednesday night (second highest on record)

Note that for Charleston, the fact that the water level from Dorian is expected to be about two feet less than Hugo does not apply to the region where Hurricane Hugo's surge reached its maximum—the region north of Charleston near McClellanville, where Hugo's storm surge of close to 20 feet will come nowhere near to being matched.

Significant surge from Dorian may extend up the coast all the way to the Hampton Roads area of southeast Virginia. After Dorian passes, unusually low tides could occur in many areas for a cycle or two.

Inland flooding a threat as Dorian advances

Torrential rains are expected along and near Dorian’s path as it moves up the Southeast coast. The NOAA/NWS Weather Prediction Center has placed most of coastal South Carolina and southernmost North Carolina under a high risk for excessive rains leading to flash flooding from Thursday into early Friday morning.

The very heaviest rains may not extend quite as far inland from Dorian as with some other recent hurricanes that hammered the Carolinas with catastrophic inland flooding, such as Matthew (2016) and Florence (2018). Dorian is not being steered by a strong upper trough, and the hurricane will not be crossing a strong preexisting frontal zone, two factors that can enhance rainfall. Extensive dry air may also limit inland rainfall. Still, inland flooding along and near the coastal zone will remain a serious threat, and it could exacerbate any storm surge flooding in estuaries and coastal rivers. We can expect widespread 6 - 10” rains within about 100 miles of the coast, with localized totals of 10-15” or more.

For those interested in monitoring Dorian’s rainfall and river flooding in detail, the U.S. Geological Survey has created a Dorian-focused tool that provides a real-time look at how various stream levels compare to various percentiles, ranging from normal to all-time daily highs and lows. 

3-day Dorian rainfall starting 12Z 9/4/19
Figure 3. Predicted 3-day rainfall in association with Dorian from Wednesday morning, September 4, 2019, to Saturday morning, September 7, by which time the storm will have moved well away from the Southeast. Image credit: NOAA/NWS/WPC via NHC.

Tornadoes could develop in coastal Carolinas as Dorian approaches

The atmosphere just ahead of Dorian will be primed for the compact, tornado-producing supercells that can develop in association with hurricanes. As surface winds rotating around a hurricane in advance of the storm are slowed and turned leftward by friction, the vertical structure of the atmosphere will gradually favor the type of wind shear that supports rotating thunderstorms. Thermodynamics will also favor supercells with Dorian, as very warm, humid air atop the Gulf Stream flows beneath somewhat drier air aloft, leading to enhanced instability.

The NOAA/NWS Storm Prediction Center is calling for a slight risk of severe weather across coastal South Carolina, mainly for Wednesday night, and for the North Carolina coast for Thursday and Thursday night. Tornado frequency with hurricanes is heavily concentrated in the right-hand forward quadrant, so given Dorian’s track near shore, tornadoes would be most likely close to the coast.

Tornadoes associated with hurricanes are typically short-lived, but they can be intense and damaging. A single rainband can spawn several small, tornado-producing storms. Overall, hurricanes represent about 3-4% of all tornadoes since 1950, but 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.

Dorian flooding
Figure 4. Satellite-observed flooding on Great Abaco Island in The Bahamas on September 2, 2019, after Hurricane Dorian. Storm chasers Josh Morgerman and Jim Edds rode out the storm in March Harbor. Image credit: NASA.

Two well-known storm chasers survive Dorian’s assault on Abaco Island

Two veteran storm chasers—Josh Morgerman of iCyclone.com and Jim Edds (@ExtremeStorms)—holed up in Marsh Harbor on Great Abaco Island and experienced the eyewall winds and calm eye of Hurricane Dorian. Since Dorian made landfall there as the third strongest landfalling tropical cyclone in world history—with sustained winds of 185 mph gusting to 220 mph—these storm chasers had the opportunity to take videos of the strongest hurricane winds ever caught on camera. The only stronger tropical cyclones at landfall in world history were Super Typhoon Haiyan (Philippines, 2013) and Super Typhoon Meranti (Philippines, 2016), which both had 190 mph winds at landfall. Morgerman did intercept Super Typhoon Haiyan, but not at its initial landfall point when it was at peak intensity.

After not being heard from for over two days after the storm hit, Morgerman finally reported in yesterday that he was safe. A tweet from this morning announced that he had measured a pressure of 913 mb in the eye:

I received two satellite phone email messages yesterday from Jim Edds. He took a portable barometer and relayed an eye pressure that agreed with the 911 mb pressure that NHC estimated for Dorian at its initial landfall. Jim’s message:

Jeff, Jim Edds here in Hope Town, Bahamas, east of Marsh Harbor. Recorded 911.2mb, blue sky eye w/ intermittent thin low cirrus.180-degree wind shift after eye passage. No home is livable. I am next to Lighthouse @ place called Hope Town Inn & Marina.

94L
Figure 5. The newest tropical wave to emerge from the coast of Africa, as seen on Wednesday morning, September 4, 2019, by NASA's Terra satellite. Image credit: NASA.

The next potential serious threat: a tropical wave emerging from the coast of Africa

The next system that has the potential to be long-track Cape Verdes-type hurricane is a tropical wave that emerged from the coast of Africa Wednesday morning. Satellite images on Wednesday morning 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 at least limited support for development, with the GFS model showing gung-ho support for development of the wave into a hurricane in several runs (though not the latest 6Z and 12Z Wednesday runs). 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, North America and/or Bermuda. There’s lots of time to watch this one before we need be concerned, though. In their 8 am EDT Tropical Weather Outlook, NHC gave this system 2-day and 5-day odds of development of 0% and 60%, respectively.

Fernand, Gabrielle, and 92L

Tropical Storm Fernand formed on Tuesday afternoon in the far western Gulf of Mexico, about 185 miles east-northeast of Tampico Mexico, and made landfall Wednesday morning on Mexico’s northeast Gulf Coast. Very heavy rains—6 to 12 inches, with isolated 18” amounts—could produce dangerous mudslides and flash floods from the coast into the higher terrain of the Sierra Madre Oriental. Radar estimates from the NOAA Doppler weather radar in Brownsville, Texas (KBRO), indicate that 9 to 12 inches of rainfall may have already occurred across portions of these areas. South Texas and the Lower Texas Coast are expected to receive 2 to 4 inches of rain from Fernand, with a chance of a few tornadoes.

Tropical Storm Gabrielle formed off the coast of Africa on Tuesday night, and is headed to the northwest into the open central Atlantic. The good news is that Gabrielle is expected to be a fish storm, with no impact on any land areas. At 11 am EDT Wednesday, Gabrielle had winds of 50 mph, and was expected to gradually intensify to 65 mph winds in five days.

Another disturbance (Invest 92L) was just east of Bermuda, heading northeastward. Sea surface temperatures ahead of this system are unusually warm (28-29°C or 82-84°F, about 1-2°C above average), but satellite images show that high wind shear is keeping 92L’s heavy thunderstorm activity far away from the well-defined surface circulation. 92L is not a threat to any land areas. In their 8 am EDT Tropical Weather Outlook, NHC gave 92L 2-day and 5-day odds of development of 50%.

Bob Henson co-wrote this post.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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Dr. Jeff Masters

Dr. Jeff Masters co-founded Weather Underground in 1995, and flew with the NOAA Hurricane Hunters from 1986-1990.

jeff.masters@weather.com

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