Tropical Storm Ophelia to rake the U.S. East Coast this weekend » Yale Climate Connections – GWC Mag

The storm surge threat: Moderate to major coastal flooding possible in southeast Virginia and the Delmarva

Ophelia is on track to bring a smorgasbord of impacts to a heavily populated area on a busy September weekend.

The track of the intensifying low will favor strong east to northeast winds pushing water into shores, bays, and inlets from the Outer Banks to the Delmarva. Waves of 10-15 feet will be riding into the coast atop the storm surge. A storm surge warning was in effect from Beaufort Inlet, North Carolina, to Chincoteague, Virginia, including parts of the Chesapeake Bay and Pamlico and Albemarle Sounds as well as the Neuse and Pamlico Rivers. How high the water rises will depend on the amount of storm-produced surge as well as the timing of the arrival of peak surge. Peak astronomical tides will be boosted slightly by the fall equinox, which arrives early Saturday morning, September 23.

The highest surge, perhaps reaching inundation levels of three to five feet, was predicted for the Pamlico, Pungo, Neuse, and Bay Rivers. Potential inundations of two to four feet are possible northward across the Outer Banks and Lower Chesapeake Bay, as well as the Lower Potomac extending close to the Washington, D.C., area. Inundations of one to three feet are possible for the Upper Chesapeake and Delaware Bays and the southern coast of New Jersey coast.

Below is a sampling of crests predicted on outlets near the coast for Saturday afternoon and evening; how those predicted crests would rank among the long-term National Weather Service gauge records at each site, where available; and expected flood impacts at or near the predicted values. The Hampton Roads area of southeast Virginia, including Norfolk, appears to be at the highest risk of major flooding among urban areas near the coast.

• Delaware Bay at Lewes, Delaware: Eight feet (eigth-highest in the long-term record). At eight feet, “flooding starts to become severe enough to begin causing structural damage along with widespread flooding of roadways in the coastal communities of Sussex County. Vulnerable homes and businesses may be severely damaged or destroyed as water levels rise further above this threshold.”
• Atlantic coast near Ocean City Inlet, Maryland: 4.9 feet. At five feet, “Widespread flooding of vulnerable areas will result in an elevated threat of property damage to homes and businesses near the waterfront and shoreline.”
• James River at Sewells Point, Virginia (Norfolk): 6.4 feet (13th-highest in the long-term record). At 6.5 feet, “Severe flooding will cause extensive inundation of numerous roads and buildings … Some areas will need to be evacuated.”

Winds, rains, and possible tornadoes

The strongest winds can be expected east of Ophelia’s center from Friday night into Saturday morning across eastern North Carolina. Sustained winds could reach 40 to 60 mph, especially across the Pamlico Sound and Outer Banks, more than enough to damage trees and power lines.

Heavy rains will intensify over eastern North Carolina and work their way up the East Coast from Friday afternoon into Saturday with the approach of Ophelia, posing the threat of localized flash flooding. The heaviest totals, perhaps six to 10 inches, can be expected near and just north of the storm’s center as it pushes onshore. Totals of four to six inches may be quite common from eastern North Carolina into southeast Virginia and much of the Delmarva, and a solid two- to four-inch drenching can be expected over most areas east of the Appalachians from Virginia, Maryland, and the Delmarva into Pennsylvania and New Jersey, as well as New York and southern New England.

Tornadoes will be possible ahead of Ophelia, especially late Friday into early Saturday across southeast Virginia and northeast North Carolina. Moist onshore flow will be increasing, enhancing both instability and the vertical wind shear that supports rotating thunderstorms. The NOAA/NWS Storm Prediction Center placed this area under a slight risk (level 2 of 5) for severe weather through early Saturday.

The Atlantic’s next disturbance may become a tropical depression or tropical storm over the weekend

A large but still-disorganized system west of the Cabo Verde Islands is on track to become the Atlantic’s next named storm, perhaps just after the system near the U.S. East Coast. Designated as Invest 90L, the disturbance showed increasing spin on Friday, and a large area of showers and thunderstorms was gradually organizing. In its Tropical Weather Outlook issued at 8 a.m. EDT Friday, the National Hurricane Center gave 90L a 70% chance of development over the next two days, with a 90% chance over the next week. With a moist atmosphere and very warm sea surface temperatures ahead of its path (around 29°C or 84°F), 90L may be able to fend off moderate to strong wind shear of 10-20 knots and gradually intensify over the next several days. The next name on the Atlantic list after Ophelia is Philippe.

Through this weekend, 90L is expected to continue moving west-northwest across the central tropical Atlantic. Beyond that point, it appears increasingly likely that 90L will angle northwestward next week, staying clear of the Lesser Antilles much as Lee and Nigel did. It is too soon to entirely rule out the idea of 90L entering the Caribbean, as any approach to the islands would still be five to seven days from now. However, nearly all of the ensemble members of the Thursday-night runs of the European and GFS model angle 90L away from the islands and into the open Atlantic.

Nigel is no more

Former Category 2 Hurricane Nigel was declared a post-tropical cyclone at 5 a.m. EDT Friday almost exactly a week after it emerged as a tropical depression in the central tropical Atlantic. Nigel was spinning more than 600 miles north-northwest of the Azores, and it is expected to merge with a mid-latitude storm this weekend. The National Hurricane Center typically maintains advisories on a post-tropical cyclone as long as warnings are still in effect, but Nigel’s entire life has played out without incident in the remote North Atlantic east of the Caribbean and Bermuda, so the early-Friday advisory was the final one for Nigel.