As feared back on Friday, we have a new named Atlantic storm that threatens South Carolina later this week. Allow me to introduce you to Subtropical Storm Nicole.
A loop of visible satellite imagery of the southwestern Atlantic Ocean,centered on Subtropical Storm Nicole.Source: University of Wisconsin RealEarth
Some of you may be wondering what is a subtropical storm. In simple terms, it is a hybrid storm that has characteristics of both a tropical storm and an extratropical storm. An extratropical storm is an ordinary low-pressure area that we see typically move from west to east across North America with attached warm and cold fronts. Nicole formed out of a strong tropical wave joining forces with an upper-level low that was spinning east of The Bahamas.
The National Hurricane Center (NHC) forecast indicates a wandering track in the general direction of Florida, then a northward turn toward us.
The NHC forecast track for Nicole, uncertainty cone,and current watches and warnings as of 11 a.m. Monday.
Remember that the track forecast indicates where NHC predicts where storm’s center will go and that the uncertainty cone refers to the range of possible center tracks, and not where actual impacts will occur. Significant effects from Nicole will occur outside of the cone. A full description of the cone is on NHC’s website.
The forecast track will take Nicole over water that is still around 82°F.
The 11 a.m. Monday NHC forecast track superimposed overa plot of sea surface temperatures.Source: NOAA PhOD Observations Viewer.
The forecast calls for Nicole to become a tropical storm by tomorrow evening, then a Category 1 hurricane by Wednesday morning. Interaction with land as it passes over Florida and perhaps Georgia will weaken Nicole as it turns northward, but it is still forecast to be a tropical storm with 50 mph winds when it passes over or near South Carolina on Friday night and early Saturday.
The current forecast track keeps the impacts from the storm mainly over the Coastal Plain, with limited rain and wind risks into the Midlands and Central Savannah River Area. Unless Nicole goes farther west than currently forecast, the parched Upstate will welcome the inch or so of rainfall Nicole will bring.
However, significant impacts will be felt in South Carolina well ahead of Nicole’s passage. Like we saw with Hurricane Ian, a strong high pressure area will be moving into the northeastern part of the country as Nicole approaches Florida. The resulting steep pressure gradient (the change in pressure over a distance) between these two weather features will cause gusty winds as air flows rapidly from high pressure toward low pressure.
These gusty winds will be out of the northeast on Wednesday, then becoming more easterly on Thursday, pushing water ashore along our coastal areas. If this wasn’t enough of a problem, we also have a full moon tomorrow (I incorrectly said a new moon in Friday’s alert … sorry for having my head in the clouds), and high astronomical tides from that will last all week. The onshore flow and high astronomical tides will cause another round of tidal flooding. This becomes a problem with tomorrow’s high tides and flooding will occur with each high tide the rest of this week. There is potential for major coastal flooding on Thursday morning along the Lowcountry coast.
Forecast tide levels from the National Weather Service in Charleston this week.Major tidal flooding is in the forecast for Thursday.
Coastal flooding will also be a concern along the Grand Strand, but the Lowcountry coast tends to be more vulnerable. Another round of coastal flooding appears likely Friday and Friday night as Nicole passes along our coastline and generates a storm surge. If this happens at high tide, major flooding will occur again.
With the current forecast track, the heaviest rain will occur over our Coastal Plain. The storm should be moving fast enough to prevent extreme rainfall totals, but there is potential for 3-6 inches in the Lowcountry and Pee Dee regions. That’s still a lot, so there will be a flash flooding risk. Of course, heavy rainfall at high tide will exacerbate coastal flooding, especially if there’s a storm surge ongoing. However, aside from the soaking that we saw from Ian, it’s been dry across the state for months, and river flooding will not be a big concern.
If Nicole passes along our coast as forecast, the risk for isolated tornadoes will remain confined to our coastal areas. Should Nicole track farther west while passing through South Carolina, the tornado risk will be higher and affect more of the state. A track more to the east will mean little or no tornado risk in the state but might result in more wind and surge along our coast.
It’s still early in the game with Nicole and some adjustments to the forecast are likely to happen. Still, it’s time to batten those hatches again if you live along our coast. Visit hurricane.sc for storm preparation tips. Meetings may keep me from issuing an alert tomorrow, but you can expect regular updates on Nicole Wednesday until the storm passes.