Tropical Storm Idalia emerged over the ocean off the coast of northeastern South Carolina early Thursday morning after hitting Florida’s Big Bend region on Wednesday morning as a high-end Category 3 hurricane with 125 mph winds. The storm’s heaviest damage was in one of the most sparsely-populated regions of the Southeast U.S., and so far, the Associated Press is reporting just one death from Idalia, from a falling tree in Georgia.
At 11 a.m. EDT Thursday, Idalia was located 85 miles southeast of Cape Lookout, North Carolina, with top sustained winds of 60 mph and a central pressure of 992 mb, moving briskly east at 20 mph. Idalia was bringing strong winds to eastern North Carolina Thursday morning. The United States Coast Guard Station Hatteras recorded sustained winds of 46 mph, gusting to 65 mph, at 9:30 a.m. EDT; Piney Island recorded sustained winds of 46 mph, gusting to 71 mph, at 8:43 a.m. EDT; and Oregon Inlet recorded sustained winds of 48 mph at 9:30 a.m.
The large wind field of Idalia was bringing storm surge flooding to portions of eastern North Carolina, and heavy rains from Idalia were affecting eastern Virginia and eastern North Carolina. The NOAA/NWS Weather Prediction Center is calling for a moderate risk of flood-producing excessive rains over North Carolina’s Outer Banks on Thursday. Moderate to borderline major flooding is predicted over the next few days in eastern South Carolina and North Carolina rivers from the six to 10 inches of rain Idalia dumped.
Storm surge flooding along the Southeast U.S. coast
Idalia’s storm surge and a full-moon “king” tide brought very high waters to the Southeast U.S. coast Wednesday night. As we discussed in a post earlier this summer, sea level rise along the U.S. Gulf Coast and Southeast U.S. coast has been approximately one centimeter per year since about 2010 — about triple the global rate. This has led to about 5.5 inches (14 cm) of sea level rise in the past 14 years alone, making it much easier to suffer coastal flooding and set top-10 water level records during storms that would not have done so during the 20th century. Some notable marks from the high-tide cycle Wednesday night:
- Charleston, South Carolina, where records extend back to 1921, recorded the fifth-highest water level on record. This was just 3.29 feet below the record set in Hurricane Hugo (1989) and caused major flooding. Considering that the city experienced major flooding last night for what was just a 2.5-foot storm surge in combination with a full-moon tide, Charleston is clearly unusually flood-prone. Without sea level rise, last night’s flood would not even have ranked in the top 15 water levels on record. We highly recommend a fantastic 2023 book on the formidable challenge sea level rise poses to Charleston, “Charleston: Race, Water, and the Coming Storm,” by Susan Crawford.
- Myrtle Beach, South Carolina, where records extend back to 1957, recorded the sixth-highest water level on record, causing moderate flooding. This was 6.87 feet below the record set during Hurricane Hugo (1989).
Forecast for Idalia
Idalia will be in the Atlantic for some days to come as it goes through a convoluted process of decay and potential restrengthening. By Thursday night, strong wind shear and dry air aloft will have shredded most or all of Idalia’s showers and thunderstorms (convection), leaving it as a post-tropical cyclone, albeit one still packing gale-force winds. The upper-level trough now hauling Idalia out to sea will eventually leave it to slow down by this weekend over the warm subtropical waters of the northwest Atlantic. If wind shear can decrease enough, Idalia might have the chance to reconstitute itself as a tropical storm, as predicted by the National Hurricane Center, which is calling for Idalia to pass near Bermuda as a weak to moderate tropical storm on Sunday night. Analyses from Florida State University agree that Idalia is likely to shift back to being a symmetric warm-core cyclone (i.e., a tropical storm) as it nears Bermuda.
Jose becomes the Atlantic’s latest tropical storm
After almost two days of trying, Tropical Depression 11 managed to whip up just enough spin and convection (showers and thunderstorms) to become Tropical Storm Jose as of 5 a.m. EDT Thursday. Note that although the name is typically written as José, there are no diacritical markings on storm names for tropical cyclones as officially listed by the World Meteorological Organization.
At 11 a.m. EDT Thursday, Jose had top sustained winds of 40 mph and was located in the central subtropical Atlantic about 770 miles east of Bermuda, posing no threat to land. Wind shear is predicted to increase sharply over Jose by Thursday night, and the storm is expected to get absorbed by Hurricane Franklin on Friday.
Jose joins a frenetic 12-day burst of six named storms atop the near-record-warm waters of the tropical and subtropical Atlantic. The list includes Gert (Aug. 19), Emily (Aug. 20), Franklin (Aug. 20), Harold (Aug. 21), and Idalia (Aug. 26).
Jose is also the eleventh tropical or subtropical storm of the Atlantic season, including an unnamed, belatedly recognized tropical storm from January. On average (1991-2020), the eleventh named storm of the season develops on Oct. 2, so the Atlantic is now running well ahead of climatology.
In terms of accumulated cyclone energy, or ACE, as tracked by Colorado State University, the Atlantic season has generated 49.7 units of ACE through Aug. 31, which is well above the average to date (1991-2020) of 36.3. In fact, all four basins of the Northern Hemisphere (North Atlantic, Northeast and Northwest Pacific, and North Indian) are running well above average for seasonal ACE to date, a likely reflection of the near-record warmth across much of our planet’s ocean surface this year. The Northern Hemisphere as a whole has racked up an ACE of 387, which is more than 50% above the average to date of 257.9 and higher than the hemispheric ACE total of 385.3 achieved for the entire year of 2022. In reliable data going back to 1971, the highest Northern Hemisphere ACE for a calendar year was 880.3 in 1992.
Franklin keeps on churning
Hurricane Franklin continued at Category 2 strength as of 11 a.m. Thursday and was located about 265 miles northeast of Bermuda with top sustained winds of 100 mph. Despite strong wind shear, Franklin remained well structured, with a strong core of convection atop sea surface temperatures of 27 degrees Celsius (81°F), about one degree Celsius above average. Franklin is being hauled northeast ahead of Idalia by the same upper-level trough but it is unlikely to get left behind, gradually transforming into a powerful post-tropical cyclone by this weekend as it accelerates to the northeast.
94L near the Cabo Verde Islands expected to develop
A tropical wave designated as Invest 94L just west of the Cabo Verde Islands was given two-day and seven-day odds of development of 80% by the National Hurricane Center in their 2 p.m. EDT Tropical Weather Outlook. Light wind shear (5-10 knots), a moist midlevel atmosphere (relative humidity around 70%), and warm sea surface temperatures of 28 degrees Celsius (82°F) may allow 94L to become a short-lived tropical depression or tropical storm as soon as Friday. 94L is headed west-northwest to northwest into an area with dry air and high wind shear and is not likely to survive long enough to threaten any land areas. The next name on the Atlantic list is Katia.
Next tropical wave this weekend bears watching
A tropical wave predicted to move off the coast of Africa on Saturday has been getting model support for development next week, particularly from the European model and its ensembles. This wave is predicted to follow a more westerly track than most waves we’ve seen roll off Africa of late and bears watching.
In its 2 p.m. EDT Tropical Weather Outlook, the National Hurricane Center gave this system a near-zero chance of formation through Saturday but a 20 percent chance of development over the next seven days.
Two typhoons in the western Pacific approach landfall
Typhoon Saola, formerly a high-end category 4 storm with 155 mph winds, is weakening as it approaches Hong Kong. The Joint Typhoon Warning Center predicts that Saola will pass within 50 miles of Hong Kong on Friday, most likely as a Category 2 storm.
Typhoon Haikui is predicted to pass through Japan’s Ryukyu Islands and hit northern Taiwan this weekend, most likely as a Category 2 storm.
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