Tropical depression four which sits just off the South Carolina coast is expected to become the fourth named storm, as tropical storm Danny, of the 2021 Atlantic hurricane season before it makes landfall later today to the south-west of Charleston.
If tropical storm Danny is named, as meteorologists seem to be anticipating, it will be only the fourth time since satellite records began that we’ve seen four named tropical storms before the end of June.
Maximum sustained winds associated with tropical depression four are currently at 35 mph with higher gusts, NOAA says, with some strengthening expected later today as the depression moves towards the South Carolina coast and NOAA’s current forecast shows it becoming tropical storm Danny at or around landfall.
Currently, the depression is crossing the Gulf Stream, where warmer waters can help storms to intensify and gain structure, hence forecasters calling for tropical storm Danny to be named.
NOAA’s latest update on the depression warns of the potential for heavy rain across South Carolina and into Georgia, as well as into northern Alabama, while flash flooding is also possible.
Tropical storm force winds are expected for the South Carolina coast as well.
Insurance and reinsurance broker Aon’s Impact Forecasting unit shared some insight into this depression and its chances to become a tropical storm:
The inner-core cloud structure noted in high-resolution visible satellite imagery has continued to tighten up and deep convection has persisted northwest through southwest of the center. This has allowed for Dvorak intensity estimates to highlight a sustained wind estimate of 35 mph (55 kph). This intensity estimate is consistent with overnight surface wind data noted just north of the well-defined center.
The initial motion estimate remains towards the west-northwest. This is a small tropical cyclone and it is expected to maintain a west-northwestward to northwestward motion for the next couple of days, resulting in landfall along the south-central coast of South Carolina later this evening. The system is expected to dissipate within 48 hours when it traverses the southern Appalachian Mountains. The NHC track forecast lies close to the tightly packed GFS (U.S.)- and ECMWF (European)-based models due to the lack of any significant inner-core convection. This is allowing the cyclone to be steered more by the low-level flow rather than the deep-layer flow.
There is a narrow window of opportunity this afternoon for the depression to strengthen into a tropical storm before landfall occurs. Should this occur, it would become Tropical Storm Danny. During the next few hours, the small cyclone will be passing over the warmer Gulf Stream where sea surface temperatures are warm. Also, as the outer wind field begins to interact with land, low-level frictional convergence along and just offshore should help to generate deep convection just prior to landfall, helping to spin up the wind field. The NHC forecast shows the system becoming a tropical storm before landfall, and as a result a Tropical Storm Warning has been issued for a portion of the South Carolina coast.
While this could be the fourth named tropical storm of the 2021 Atlantic hurricane season, it’s unlikely to be particularly impactful for the region and certainly doesn’t pose a significant reinsurance threat at this time.