Tropical storm and storm surge warnings are flying for portions of the North Carolina coast as sprawling Hurricane Erin chugs northwestward for a close pass by the Outer Banks of North Carolina, expected to occur on Thursday.
At 11 a.m. EDT Tuesday, Hurricane Erin was centered about 690 miles (1,105 km) south-southeast of Cape Hatteras, North Carolina, heading northwest at 9 mph (15 km/h), with top sustained winds of 105 mph (165 km/h). Erin’s central pressure was 961 mb. High wind shear of 20-25 knots from powerful upper-level winds out of the northwest caused considerable weakening of Erin overnight, and satellite imagery Tuesday morning showed that this shear had destroyed most of the hurricane’s heavy thunderstorms on the northwest side, partially exposing the low-level center to view.
The shear is keeping Erin from taking full advantage of the unusually warm waters beneath its path. Human-caused climate change made the sea-surface warmth at least 90 times more likely north of the Leeeward Islands, where Erin reached Category 5 strength (see embedded skeet below). Similar values extend across much of the Northwest Atlantic.
Erin’s biggest threat: storm surge, waves, and rip currents
Erin’s large size — with hurricane-force winds that extended out up to 80 miles from the center — has enabled the hurricane to create a large expanse of huge waves, which have begun to impact most of the east coast of North America, the Bahamas, Bermuda, and the northern-facing shores of the Greater Antilles and Leeward Islands. These waves will cause considerable coastal erosion and dangerous rip currents. Along the shores of portions of North Carolina, the waves will combine with a storm surge of 2-4 feet to produce damaging coastal flooding. NOAA’s National Water Prediction Service is forecasting that Erin’s storm surge will bring major flooding at five tide gauges during Thursday evening’s high tide along the northern North Carolina coast and to Chesapeake Bay in Virginia.
Although Erin’s days as a Category 5 storm are in the rear-view mirror now, the storm will continue to push huge amounts of wind and water across the Northwest Atlantic for days to come. Rip currents will remain a deadly threat along most of the U.S. East Coast for much of this week. Coastal flooding will be mostly minor yet widespread along the Eastern Seaboard.
The most serious marine impacts will be in the Outer Banks of North Carolina. Waves could reach 20 feet in the surf zone atop Erin’s storm surge, and it wouldn’t be a shock to see at least a few vulnerable coastal homes heavily damaged or destroyed. Multiple cycles of high surf will slam the Outer Banks, closing and potentially damaging roadways and causing widespread beach erosion. Extensive heavy rain is not expected, but sustained winds could exceed tropical-storm-force (39 mph), with substantially higher gusts possible.
Forecast for Erin
There is more uncertainty around Erin’s strength than its track. Since Erin is now such a large storm, it would be much more difficult for it to reintensify quickly. However, Erin is predicted to remain a Category 2 or 3 storm for several more days. The wind shear that took a toll on Erin from Monday into Tuesday is expected to relent substantially, dropping into the light to moderate range (5-10 knots) from late Tuesday through Wednesday, and Erin will remain over unusually warm waters for mid-August of 29–30 degrees Celsius (84-86 degrees Fahrenheit). By Thursday, Erin’s top winds are predicted to gradually weaken, though the circulation may grow even larger as the hurricane gains latitude, likely becoming a post-tropical cyclone by this weekend.
The broad-scale steering flow guiding Erin remains well behaved, even though Erin has consistently tracked slightly further west than expected. Erin is predicted to continue the gradual recurvature that will take it between North Carolina’s Outer Banks and Bermuda late Wednesday and Thursday, and then on an accelerating pace into the remote North Atlantic, well south of Atlantic Canada.
Two tropical waves to watch
A tropical wave in the central Atlantic was headed westward to west-northwestward at about 20 mph and will approach the vicinity of the Leeward Islands on Friday. This wave was broad and disorganized and was suffering from ingestion of dry air along its northern edge, courtesy of the Saharan Air Layer (SAL). There is limited model support for the development of this disturbance over the next five days, but more support for development to occur early next week. The model consensus is for the disturbance to pass close to or a few hundred miles northeast of the Leeward Islands on Friday and Saturday, and then turn more to the northwest and north towards Bermuda, heading toward a weakness in the steering flow left behind by Erin.
In its 8 a.m. EDT Tuesday Tropical Weather Outlook, NHC gave the disturbance two-day and seven-day odds of formation of 10% and 60%, respectively. The next name on the Atlantic list of storms is Fernand.
A tropical wave in the far eastern Atlantic, located a few hundred miles southeast of the Cabo Verde Islands, was headed west at about 15 mph. The system, designated 99L by the National Hurricane Center, has modestly favorable conditions for development, with sea surface temperatures near 28 degrees Celsius (82°F), moderate wind shear of 10-20 knots, and a moderately moist atmosphere with a mid-level relative humidity of about 60%.
Satellite images on Tuesday afternoon showed 99L had a decent-sized area of heavy thunderstorms featuring plenty of spin at mid-levels of the atmosphere, but no signs of a surface circulation. A large area of dry air to the north, associated with the Saharan Air Layer, was impeding development and will likely continue to do so during the week. There is limited model support for the development of this disturbance over the next five days. In its 8 a.m. EDT Tuesday Tropical Weather Outlook, NHC gave 99L two-day and seven-day odds of formation of 30%.
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