Key Points:
- Tropical Depression Three has formed 150 miles southeast of Charleston.
- Based on their forecast for it to strengthen into a tropical storm by early afternoon Saturday, the National Hurricane Center (NHC) has issued a Tropical Storm Watch for the South Carolina coast from Edisto Beach to Little River Inlet. The next name on our list for this year is Chantal.
- Tropical storm conditions are likely to begin along our coast around nightfall Saturday and continue through Sunday morning.
- The NHC forecast calls for it to be a tropical storm with 45 mph sustained winds (with higher gusts possible) at landfall. Their intensity errors average at 24 hours are around 12 mph, so the reasonable worst-case scenario is for it to have sustained winds of 55-60 mph by the time it makes landfall. This also implies a best-case scenario that it's only a tropical depression at landfall.
- Rainfall along the Coastal Plain, from Charleston County northeastward, is expected to be 1-3 inches from Saturday afternoon through Sunday, with locally higher amounts. Localized flash flooding can occur.
- A small storm surge of 1-2 feet will occur near and to the right of where the center makes landfall. However, low astronomical tides will result in no significant coastal flooding from the surge, except for the possibility of minor coastal flooding along the Charleston County coast.
- There will be a risk for a few isolated tornadoes Saturday night into Sunday morning to the right of where the center makes landfall.
- Conditions will improve Sunday afternoon as the storm moves away to the northeast and weakens or dissipates.
Our disturbance off the Southeast Coast has become a tropical cyclone. It's now Tropical Depression Three, centered about 150 miles southeast of Charleston.
The National Hurricane Center forecast predicts that it will strengthen into a tropical storm by Saturday afternoon. When it becomes a tropical storm, it will be named Chantal. Their forecast calls for landfall to occur at Kiawah Island at around 4:00 a.m. Sunday. However, the NHC's error cone (which refers only to the most likely area for the center to track, based on two-thirds of their forecast errors) allows for landfall to occur at any point in South Carolina. So, there is considerable wiggle room on where landfall may occur.
Also, NHC's average intensity error is about 10 knots, about 12 mph, at 24 hours out, and about 15 knots, 17 mph, at 48 hours. We're at about 30 hours before landfall as I'm writing, so let's call the margin of error 15 mph. That means the most reasonable best-case scenario is that it's a tropical depression at landfall, but the worst-case scenario is for it to be a 60 mph tropical storm.
The worst of the rain will be near and to the right of the center's path, as this will be a lopsided storm. Localized flooding can result, but widespread flooding is unlikely.
We'll see a small storm surge where the center comes ashore and to the right of that area. However, we have low astronomical tides right now (with the next full moon not until next weekend), and landfall will occur during the better part of the tide cycle, during the lower or the day's two high tides. So, we're unlikely to experience widespread problems from coastal flooding, although I can't rule out minor coastal flooding from the storm surge along the Charleston County coast.
We also have a low-end risk for isolated tornadoes (call it zero to a few may occur) Saturday night and early Sunday along our Coastal Plain to the right of the center's path. Any tornadoes that do occur would likely be brief and relatively weak (though even the weakest tornado is dangerous).
That covers it. Batten down the appropriate hatches if you live along our coast. Thankfully, this will be a relatively minor event as tropical cyclones go, and this is like a dress rehearsal. If you need advice on storm prep, visit hurricane.sc.
I leave you with the visible satellite view from this evening of our new depression.
Tropical Depression Three spins 150 miles southeast of Charleston Friday evening.
Image Source: University of Wisconsin RealEarth
Frank Strait
Severe Weather Liaison
S.C. State Climate Office