Coastal Trough Threat: Watching Bertha's Remnants

The remnant mid-level circulation of former Tropical Storm Bertha is currently spinning off the Southeast US coast, and both the GFS and ECMWF operational runs bring it inland late Thursday into Friday. This isn't the tropical Bertha of the National Hurricane Center's advisories anymore — it's a warm-core mid-level low that's decoupled from the surface, but it's still packing enough vorticity to focus deep convection along the coast.

What the Models See

The 12Z GFS spins the remnant low up to about 40 kt at 700 mb by 00Z Friday, tracking it over Statesboro toward Athens by Saturday morning. The ECMWF is a touch slower and further south. Both agree on a plume of 60-70 kt of 500-1000 mb bulk shear rotating around the low's northeast quadrant — that's the setup for tropical-adjacent supercells if instability shows up.

Severe Weather Risks

The SPC has hoisted a marginal (Day 4) severe risk for the Georgia coast Friday afternoon. The primary threats are:

- Tornadoes (spin-up variety, common in tropical remnants) - Damaging wind gusts from bowing line segments - Isolated large hail in any pulse cell with 2000+ J/kg CAPE

Coastal Georgia's flat terrain and abundant moisture make it particularly susceptible to weak, fast-moving tornadoes when tropical remnants pass through.

Bottom Line

Savannah, Brunswick, and the Golden Isles need to be paying attention Thursday night into Friday. Have your NOAA weather radio ready and know the route to your safe room. Metro Atlanta stays on the drier side of the circulation and should escape with just breezy conditions.

We'll continue to update as new HRRR runs come in.

— Trey