TLDR: Landfall expected mid-day Monday south of Tallahassee as a Cat 1. Expect usual stuff there – minor damage, trees down, power outages, some coastal flooding. Perhaps a bigger threat is on the Georgia/South Carolina coast as the decaying storm will likely stall, winds will be gusty and this will drop a lot of rain starting Monday morning and persisting until Friday morning. As a reminder the best official source of information are NHC’s Key Messages regarding Tropical Storm Debby (en Español: Mensajes Claves). Here’s the details, and a closer look at what to expect in GA/SC.
Tropical Storm Debby continues to gain organization and intensity this morning, and expected to make landfall on the Big Bend coast of Florida south of Tallahassee mid-day on Monday as a Category One hurricane. Here’s what it looks like at 5:50am on Infrared (the sun isn’t up yet over the storm):
IR images show cloud top temperatures. Colder clouds indicate stronger convection, which means a better organized and intense storm. Debby is now a 50mph storm, and given the hot fetid waters of the Gulf right now, combined with favorable upper level winds, it should develop into a hurricane over the next day before landfall.
Here is another IR view with the watches and warnings as of 5am. Notice they are now being posted for the Georgia coast, in this case the Brunswick area. Expect that to creep northward to include the entire GA coastline and eventually most of the South Carolina coast as well … (Update: at 8am, tropical storm watch extended to north of Charleston)
About half of the storm is within range of coastal radars, here is the MRMS composite showing Debby as well as showers associated with the trough to the north that will guide it across Georgia. That system brought a brief thunderstorm to the Savannah area early this morning and is now offshore …
The forecast hasn’t changed too much over the last 24 hours, other than the intensity being bumped up a little from maximal tropical storm to a low/middle Category One at landfall. Here is the “plain language” impact estimate map based on the 5am official forecast. Notice also NHC backed off a lot on the storm wind extent, reflective of a more organized storm:
For Florida, this should be a typical Category One hurricane event. That means some scattered damage, trees down, power outages, and right on the coast where a meter or so (3ft-5ft) of storm surge will cause some flooding and wave damage. Hazardous, but with some common sense not too dangerous, and following the advice of your local emergency managers should help keep you out of trouble. As the storm moves north today, the coast from Tampa north to the landfall area will be side-swiped by rain bands from the storm, and may see some coastal flooding from onshore winds and waves.
The track models are, in one sense pretty consistent, but as will be discussed below there are some nuances and details that can make a big difference in the outcome, especially for the Savannah area. Here’s the track models as of 5:30am …
Notice they get wonky over south Georgia (OK, that joke writes itself 😛 ). Some dedicated models like the new HFS models have the storm meander and die inland. The GFS and ECM model go offshore then return and whack Charleston. A few models have the storm encounter Valdosta and flee in terror to the west (and who wouldn’t).
But the most likely case is shown by the official track and global models: the storm will reach the coast near or over the Savannah area and stall for 48 to 72 hours. It won’t be very strong by then – most likely a minimal tropical storm. The problem isn’t going to be wind (although some thunderstorm wind gusts might knock down limbs, and the odd weak tornado or two can’t be ruled out). The problem is going to be rain. Here we face three broad scenarios:
Scenario A: This is the NHC scenario. The storm hugs the coast close enough to stay organized enough to pump an epic amount of rain into Savannah and the SC Lowcountry. What is epic? This is the current estimate from NOAA:
Yep, that’s 20 inches of rain over the area between Fort Stewart and just south of Charleston (Kiawah Island area). Using the NHC track, our in-house RCLIPER rainfall climatology model is indicating 15.7″, and the other models are in that ball park as well.
Scenario B: The storm moves a bit farther offshore and remains organized. That might keep the core of the storm far enough out to put the Georgia coast in a drier zone. Bad for South Carolina, because unless the storm ejected north offshore, Charleston would likely see a stronger tropical storm, and SC would bear the brunt of the rain. This is possible, both GFS and ECM have shown this at times.
Scenario C: The storm stays far enough inland so that it decays and loses organization. That could easily drop the rain totals by half.
If I had to lay odds, I’d say “A” is at 70%, “B” at maybe 5%, and “C” at 25%. It will be late tomorrow before we know which way things are going.
But don’t count on “B” or “C” – expect lots of local flooding. All of the spots that flooded during the heavy rain episodes last month will probably see at least that bad and likely a bit worse over the next four days. Travel around the area will be really hazardous, so just stay home if you can, especially as we get in to Tuesday and Wednesday if the forecast verifies.
As for the coast, it all depends on the onshore winds, and that depends a lot on how much and how quickly the storm decays. It looks like the greatest potential for shallow coastal flooding will be during the high tide cycles on Wednesday. Continuing to watch that.
People have asked about timing, for the Brunswick area,
For Savannah, conditions will deteriorate over night and by Monday morning we will be having 20mph winds gusting to 30 or so, with thunderstorms and rain. Winds will probably peak around 9pm Tuesday night (25 or 30 gusting 35 to 40 for a couple hours), then back to the 20mph range probably through the end of the day Friday, all with thunderstorms and rain.
So to sum up for the GA/SC area, still looking at heavy rain and flooding as the biggest risk. Wind isn’t likely to be a huge problem, but the water logged trees are likely to shed limbs or worse and cause power outages and damage (looking at you, sweet gums!). Some weak tornadoes possible, stay alert for warnings. The usual spots will almost certainly go under, locals know the vulnerable spots so if you are new to the area ask around. DO NOT TRY TO DRIVE THROUGH WATER UNLESS YOU ARE ABSOLUTELY SURE YOU KNOW HOW DEEP IT IS! And even then think twice. we’ve all seen the pics of dead cars littering the sidewalks after these storms …
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Thank you for this! Would you expect a lot of power outages in the Savannah area?
It’s Georgia Power, so if somebody sneezes, there will be outages. That said, they have been aggressively doing tree trimming lately so hopefully that will cut down on the outages but hard to see how scattered outages can be avoided.
Hell, we randomly lose power on sunny windless days on a regular basis. Our neighborhood was without power for 2 weeks after Matthew. I’m expecting a similar experience this go ’round.
Thank you!