Dorian Rebounds to Category 3 Strength

Hurricane Dorian—once again a major hurricane as of late Wednesday night—pushed ever closer to the Southeast U.S. coast as it gradually regained strength. Hurricane Hunter data showed that Dorian’s central pressure had dropped from 964 mb at 2 pm EDT to 955 mb by 11 pm. Surface winds of around 100 knots reported by dropsonde and deduced from microwave radiometer, along with satellite-based intensity estimates, prompted the National Hurricane Center to make Dorian a Category 3 storm once again at 11 pm EDT, with top sustained winds of 115 mph.

It is difficult for any large hurricane to regain strength like this after having dropped from Cat 5 to Cat 2 strength. Certainly, Dorian is now a large hurricane, with tropical-storm-force winds extending out up to 195 miles and hurricane-force winds out to more than 55 miles. Dorian's strengthening on Wednesday afternoon and evening testifies to the hurricane's resilient structure and the favorable environment still in place for it. Dorian was traveling over the very warm waters of the Gulf Stream (sea surface temperatures of 28-29°C or 82-84°F), and the southerly winds at upper levels near Dorian—resulting in strong wind shear of around 20 knots—were working to ventilate the storm rather than tear it apart, as seen in the outstanding outflow evident on satellite. Intense thunderstorms blossomed on Wednesday afternoon and evening around Dorian's large eye (about 45 miles across).

Yet another indication of #Dorian intensifying this evening, the low-level water vapor channel is showing significant warming of the #eye & eyewall convection surrounding it is cooling. Not surprisingly ADT estimates have risen to between T5.5 to T6.0 (i.e., 105-110kt). pic.twitter.com/yrcccKPA6L

— Philippe Papin (@pppapin) September 5, 2019

Wind shear is predicted to drop to around 15 knots for a brief period on Thursday, and Dorian's over-ocean sector will still be atop warm waters. Given the inertia of its sprawling wind field, Dorian may hover near the Category 2/3 border through Thursday and perhaps even Thursday night, packing top winds in the 100- to 115-mph range. Land interaction and increasing wind shear will take their toll by Friday, and Dorian will likely exit North Carolina as a large, still-powerful Cat 1 storm before it sweeps northeast for a possible landfall Saturday in Nova Scotia.

Coastal impacts still to come

Computer guidance remains tightly clustered on a track that will bring Dorian north and northeast on Thursday, tracking near the coast from near Charleston, South Carolina, around midday Thursday to near Cape Hatteras, North Carolina, by midday Friday. One or more landfalls are possible within that swath, especially in North Carolina. The last storm to make landfall at Category 3 strength in North Carolina struck exactly 23 years ago on Thursday: Fran, on September 5, 1996.

Even without a landfall (defined as the center of the eye moving onshore), Dorian’s northern eyewall could easily push onto the coast at times, possibly bringing periods of hurricane-force sustained winds.

Figure 1. Gordon and Dina Reynolds, with their 11-year-old granddaughter, Abby, sit on cots in the hallway of the North Myrtle Beach High School, which was serving as a Red Cross evacuation shelter on Wednesday, Sept. 4, 2019 in North Myrtle Beach, S.C. Image credit: Jason Lee/The Sun News via AP.

Especially concerning is the threat of significant storm surge. Waters were lower than expected at Charleston as high tide approached late Wednesday night, but surge will also be a threat there during the early afternoon high tide on Wednesday. Storm surge will affect coastlines as far north as the Hampton Roads area in Virginia through Friday (see the NHC website for specific watches and warnings for storm surge).

Torrential rains of 6 to 12 inches, locally more than 15”, will plague areas within about 50 to 100 miles of the Carolina coast. The heaviest amounts are 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.

We'll have our next update on Dorian by midday Thursday.

#HurricaneDorian has now generated more Accumulated Cyclone Energy than 11 full Atlantic #hurricane seasons since 1950: 1962, 1972, 1977, 1982, 1983, 1986, 1987, 1991, 1993, 1994 and 2013. pic.twitter.com/gupmksyvOi

— Philip Klotzbach (@philklotzbach) September 5, 2019