Bertha (2020)

Bertha formed very quickly just off the coast of the southeastern United States. A weak low moved northeastward from central and northeastern Florida and developed a well-defined center and enough organized thunderstorms to be designated a tropical cyclone at 0600 UTC 27 May 2020, about 30 nautical miles east-southeast of Charleston, South Carolina. It strengthened slightly to a peak around midday on 27 May, made landfall the same day, weakened rapidly inland to a depression by 1800 UTC, became extratropical over western Virginia by 0600 UTC 28 May, and dissipated over the Ohio Valley about 12 hours later.

The storm made a single U.S. landfall near the Isle of Palms, South Carolina, at about 1330 UTC on 27 May 2020 while producing tropical-storm-force winds. A tropical storm warning was issued for the South Carolina coast from Edisto Beach to the South Santee River; the warning was short-fused because Bertha’s formation and strengthening occurred quickly near the coast.

Bertha’s maximum sustained winds were 45 kt (about 52 mph), with the highest observed sustained wind 43 kt (about 49 mph) and a gust to 51 kt at NOAA buoy 41004. The minimum central pressure at peak was 1005 mb. These values correspond to a moderate tropical storm, below hurricane strength.

Storm surge and rainfall impacts were generally minor along the coast. Measured storm surge/inundation values reached about 1.3 ft above Mean Higher High Water at several locations: Wrightsville Beach, North Carolina (1.32 ft), Fort Pulaski, Georgia (1.31 ft), and Charleston, South Carolina (1.28 ft). Rainfall totals from Bertha itself were mostly 2–4 inches across eastern South Carolina with isolated 5-inch amounts; precursory disturbances produced much heavier rain in southeastern Florida, with totals up to about 15 inches at some locations. Specific South Carolina rain reports include 4.66 inches at Wadmalaw Island and around 3–4 inches at Mount Pleasant, Kiawah Island, and Charleston.

There were no reported deaths directly or indirectly associated with Bertha. Damage was mostly minor: some flooded streets and temporary closures in downtown Charleston, isolated tree damage near the landfall area, and more notable flood damage in parts of southeastern Florida tied to the precursor disturbance rather than the storm’s tropical phase.

Noteworthy aspects include the short fuse for genesis and warnings: Bertha’s development so near the coast made its formation difficult to anticipate and left little lead time for warnings. Because the cyclone was short-lived, only one verifying 12-hour forecast was available; that forecast had a 12-hour track error of 24.5 nautical miles and zero intensity error, comparable to recent 12-hour averages.