Matt Lanza

Debby’s flooding continues to swamp parts of the Southeast and will spread north

Headlines

  • Heavy rain from Debby will continue to impact South Carolina today and tomorrow.
  • Heavy rain expands northward after tomorrow with flash flooding likely into North Carolina and Virginia.
  • Combination of heavy rain today and Debby’s remnants may cause flash flooding in the Mid-Atlantic and New England by late week.
  • The 30% area in the Caribbean continues to look middling for awhile, and it is likely to stay somewhat suppressed to the south into next week.
Rainfall forecast for the next 5 days shows upwards of 10 to 15 inches or more of additional rain in the Carolinas, as well as a corridor of heavy rain in Pennsylvania, New Jersey, New York, and New England. (NOAA WPC)

Tropical Storm Debby’s heavy rain expands this week

Tropical Storm Debby is still a formal entity this morning, with 45 mph winds, and it is now drifting back offshore of Georgia, where it’s expected to meander through tomorrow night. It will then likely come back onshore Thursday and lift north and finally out on Friday. But before it does that, it will continue to dump copious amounts of rain on the Carolinas with an increasing signal for flooding to the north as well. Let’s walk day by day.

Radar estimated rainfall over South Carolina, showing maximum totals between Charleston and Savannah on the order of 8 to 14 inches or so. (NOAA MRMS)

Today

With Debby meandering offshore, expect heavy rain to basically continue in place. There will be rainfall rates of 2 to 4 inches an hour at times, mainly north of Hilton Head and south of Columbia. But, as 6 to 12 inches of rain has already fallen, flash flooding is underway, and it will continue.

A high risk of flash flooding (level 4/4) exists across eastern Georgia, much of southeastern South Carolina and southern North Carolina today. (NOAA WPC)

As Debby drifts a little farther offshore, the rain may become a little more scattered or intermittent, but it will continue to potentially flood areas through the day. Debby should not gain much intensity today as it meanders offshore, as it will be getting its bearings.

For a look at river forecasts in South Carolina, follow this link.

(NOAA NHC)

Wednesday

Debby will continue to meander offshore, but with generally low shear and warm water off the coast of South Carolina, it will likely begin to reorganize some. It could become a strong tropical storm again as it turns back northward toward the South Carolina coast later tomorrow.

Water temperatures off the South Carolina and Georgia coasts are running as much as 1°C above normal, favorable for Debby’s intensification. (Weather Bell)

On Wednesday, the flooding threat mostly exits Georgia and is confined to South Carolina and extreme southeastern North Carolina, including Wilmington, Myrtle Beach, and Charleston. Travel on I-95 may be a bit difficult as well through the Florence area, depending on exactly where the heaviest rainfall sets up. Another high risk is in effect in this area.

Thursday

Debby should move back inland across South Carolina on Thursday. Storm surge will again be a concern (as will high tides between now and Thursday).

Surge of 2 to 4 feet above ground level is possible along the South Carolina coast and nearby adjacent waters as Debby meanders offshore and comes back ashore Thursday. (NOAA NHC)

Surge of 2 to 4 feet will be possible along the South Carolina coast and possibly parts of Georgia and North Carolina as well with Debby moving around offshore and coming back onshore.

As Debby comes north a little more steadily Thursday, heavy rain will spread into North Carolina. While flooding risk will have mainly been confined to the extreme southeast corner of the state to this point, there will be a pretty significant expansion of heavy rain northward on Thursday that will engulf more of the state, including the Sandhills, the Raleigh-Durham area, and portions of the Piedmont in a moderate or high risk of excessive rain and flash flooding.

A high risk (level 4/4) of excessive rain and flooding will expand deep into North Carolina on Thursday, with moderate (level 3/4) risk surrounding it over a wide area even into Virginia. (NOAA WPC)

Most of the rain on Thursday will front run Debby, as the south side of its circulation will probably have lesser rain and more scattered showers. As the center gets across North Carolina late Thursday and Thursday night, we’ll see conditions slowly improve. But some serious flash flooding is a concern in both rural and urban areas of the eastern half of the state.

Friday-Saturday

Debby will continue to come northward on Friday, likely tracking across Virginia and eventually being absorbed by a trough digging into the Midwest and Great Lakes. What does this mean? Debby will become extratropical here, meaning it’ll transition from a tropical storm or depression into low pressure, a process that is meteorologically noteworthy but will have little impact on impacts seen. Heavy ran will spread across Virginia and into portions of Maryland, Pennsylvania, and New York here. These areas are expecting heavy rainfall today as well, so with soils saturated, additional rainfall from Debby will exacerbate issues.

Rainfall between today’s storms and Debby’s remnants will add up to over 6 inches in spots between Pennsylvania, New Jersey, New York, and New England. (Pivotal Weather)

Flash flooding is likely on Friday or Saturday as Debby’s exit strategy unfolds. This may include Philly, New York, and Boston.

From here, Debby’s remnants will accelerate out, likely bringing some locally heavy rain and gusty winds to portions of Quebec and Atlantic Canada. And we can finally close the book on Debby.

Rest of the tropics

We continue to watch a tropical wave with a 30 percent chance of development per the National Hurricane Center. This doesn’t look like much today, but as it comes west it may develop.

A tropical wave with minimal thunderstorm activity in the southern Caribbean has about a 30 percent chance to develop as it comes west. High pressure over Texas and the South will likely keep it tracking toward Mexico. (Weathernerds.org)

I will say that some of the more aggressive modeling with this wave has backed off considerably in the last 24 hours, and at this point there is minimal operational or ensemble model support for any development. 30 percent seems reasonable, if not a little aggressive right now. Regardless, high pressure over Texas and South will probably keep this wave fairly suppressed and tracking toward Mexico next week. We’ll continue to watch.

Behind this, there are no other areas of interest highlighted by the NHC, but the next wave emerging off Africa is showing some signs of developing in modeling. We have about a week to watch before anything happens with that one, so we won’t over-speculate. All in all, as we get into the mid-August period, things look average. That’s good. I’m sure it won’t last, but we’ll hopefully have a couple days after Debby to exhale and regain our bearings.

Debby ashore in the Big Bend, and now the potential for historic flooding begins in Georgia and South Carolina

Headlines

  • Hurricane Debby made landfall near Steinhatchee, FL as an 80 mph category 1 hurricane at 7 AM ET.
  • The storm will now meander across Florida and Georgia, with weakening winds and increasing flooding problems.
  • Historic, catastrophic flooding is likely from Debby in portions of Georgia and South Carolina with widespread heavy rain causing flooding beyond those areas as well into Florida and North Carolina.
  • The next wave behind Debby has low odds to develop but should continue to be watched as it tracks generally due west.

Debby: 75 mph or less, moving NNE 10 mph or slower

Hurricane Debby made landfall near Steinhatchee, Florida this morning as a category 1 hurricane with maximum sustained winds of 80 mph.

Hurricane Debby just after making landfall near Steinhatchee, FL this morning as a category 1 hurricane. (College of DuPage)

Debby had a pressure of 979 mb, compared to 80 mph and 979 mb with Hurricane Beryl in Texas. Two storms, identical intensities, vastly different impacts. Cedar Key saw about 6 foot surge with Debby, compared to an 8 to 9 foot surge during Idalia last summer.

Comparison of storm surge during Hurricane Debby today and Hurricane Idalia last August in Cedar Key, FL. (NOAA)

Overall, surge and wind damage will likely be less than Idalia, but still rather widespread in parts of Florida. There will continue be periodic tornado warnings in Florida and perhaps Georgia or South Carolina as Debby’s bands spread across the area. Additionally, flooding is underway in parts of Florida that have seen the heaviest rain from Debby as it moves northward.

Hurricane Debby is meandering across Florida and headed toward Georgia as it begins to unleash its flooding rains. (RadarScope)

Debby is expected to slowly track northeast and east-northeast into Georgia today, with improving conditions in parts of Central Florida but continued heavy rain and gusty winds in North Florida and Georgia, as well as South Carolina. Debby may make its way back offshore on Tuesday or Wednesday, which could allow for some re-organization to the storm. We’ve seen this a lot in the past, where people see that the storm goes offshore and fear reorganization and another big one. Usually in these cases, the system can gain a hair of strength before it comes back ashore, so we aren’t worried about Debby rejoining the ranks of hurricane or anything. Look for Debby to slide offshore, then back onshore after 24-36 hours or so, remaining a tropical storm.

Debby’s rainfall

The primary threat from Debby will remain the rain. The rainfall forecast continues to call for in excess of 20 inches on the coast of South Carolina, including Charleston, with coastal Georgia, Hilton Head, and Savannah not far off. This is in addition to rain that has already fallen.

Extreme, historic rainfall will likely produce catastrophic flooding in South Carolina, Georgia, and perhaps even portions of North Carolina with Debby. (NOAA WPC)

This will all lead to potentially historic, catastrophic flooding for portions of South Carolina, possibly Georgia, and even some bad flooding in portions of North Carolina as well. It’s tough to show river forecasts, as they only include 48 hours of rainfall forecast data, but expect major to record flooding of multiple rivers in southeast Georgia and South Carolina as we head into midweek. Anyone living in a flood zone in those areas should be prepared to take quick and immediate action. This is a fairly high confidence forecast, with fairly minimal risk that it dramatically changes unfortunately.

If you’re curious about South Carolina flooding history as it pertains to tropical systems, Melissa Griffin, an assistant state climatologist put together a pretty outstanding overview at this link.

Our thoughts are with the folks in South Carolina and beyond that will be dealing with some pretty terrible weather this week.

What comes next?

The question in the tropics is always “what’s next?” Well, we continue to watch a tropical wave moving into the Caribbean. This will carry about a 30 percent chance of development right now as it comes west.

The NHC is carrying about a 30 percent chance of development with the next system as it moves into the western Caribbean or Bay of Campeche. (NOAA NHC)

Model support for this one is not terribly strong. Odds of 30 percent seem very reasonable at this point. Yes, the GFS operational crashed a storm into Texas overnight, but it is quite the outlier right now, with little to no support from other models. One reason to expect that this system would continue to go west or west northwest is a large ridge of high pressure that’s expected to establish over Texas this week and perhaps much of next week as well. The five day average for the weekend and next week (when the GFS shows the system making it to Texas) from the European ensemble shows a rather robust pattern of high pressure.

High pressure over Texas should help steer tropical activity south of the U.S. and northern Mexico for the time being. (Tropical Tidbits)

This pattern looks similar to last summer, where Texas was essentially “shielded” from tropical activity by a persistent ridge. We do not expect that this is going to hold up beyond next week right now, but for this particular tropical wave, I would say that a track into the Bay of Campeche or southward is most likely at this time.

There is another wave behind this one that may try to develop in the open Atlantic next week. As of now, we don’t see any significant landfall threats anywhere in the tropics, but we’ll be watching.

Debby’s downpours to deluge portions of Georgia and South Carolina after making landfall in Florida as a hurricane

Headlines

  • Tropical Storm Debby is slowly intensifying off the west coast of Florida, with about 18 to 24 hours to go before making landfall in the Panhandle or Big Bend area, likely as a strengthening category 1 hurricane.
  • Debby will slam on the brakes as it comes inland leading to widespread, potentially historic flooding in coastal Georgia and South Carolina.
  • Storm surge with Debby is expected to be serious and fall just under Idalia’s levels in the Big Bend of Florida.
  • There are two additional tropical waves we are monitoring for development next week.
Debby’s forecast track over the next 5 days. (Tomer Burg)

Tropical Storm Debby: 60 mph, NNW 13 mph

Tropical Storm Debby continues to gradually organize off the west coast of Florida this morning, now a more formidable tropical storm.

Debby is slowly organizing off the west coast of Florida. The storm has about 18 to 24 hours left over water to intensify. (Tropical Tidbits)

The bad news is that Debby continues to organize, but I suppose the good news is that it does continue to have some inhibiting factors, chief among it, dry air on the west side of the storm. This will likely be a subtle player in keeping Debby from totally maxing out its intensity potential. That said, Debby is still expected to make landfall in Florida near or just west of the Big Bend as a strengthening category 1 hurricane (similar in some ways to Beryl in Texas last month). This is important for much of that area, and specifically for the Tallahassee metro area in terms of potential widespread power outages. Debby’s exact track will help determine that.

Debby’s storm surge

Starting first with surge, the expectation is that 6 to 10 feet of water could come in along the coast of the Big Bend with Debby’s current track.

Debby’s peak surge forecast on the Florida coast and beyond. Values look to be a bit under Idalia last year, but still capable of producing life-threatening conditions and significant damage. (NOAA NHC)

These values are less than were forecast during Hurricane Idalia last summer, but still extremely dangerous. Again, keep in mind that Debby is likely to be strengthening on approach whereas Idalia was weakening on approach. There may be more similarities between the two storms than expected and just because this one is “only” a category 1 storm should not factor into your preparations. Conditions will deteriorate today, so please heed the advice of local officials.

Debby’s track and wind

Debby is expected to come ashore just west of the Big Bend as a strengthening Cat 1 storm. While I noted some dry air above helping to limit Debby’s maximum potential, the biggest limiting factor for Debby may be time. Debby should come ashore in Florida late tonight or early Monday morning, so it has about 18-24 hours left to do whatever it will do.

Debby’s strongest winds will impact the coast of Florida from about Apalachicola through Cedar Key, with potential for significant wind into Tallahassee depending on the exact track. (NWS)

Squalls and bands from Debby will impact Florida’s west coast today, including Tampa with some gusty wind and heavy rain. The worst wind and rain will likely occur from Tallahassee eastward.

Beyond the Big Bend, Debby’s forecast track becomes extremely uncertain. In general, we expect Debby to slam on the brakes and drift northeast, then east-northeast, then, well your guess is as good as ours right now. There are questions as to whether Debby emerges off the East Coast, meanders around so erratically that it ends up back in the Gulf, or perhaps it even just drifts north into eventual oblivion. This leads us to our next issue.

Debby’s potentially historic flooding

Debby is a hurricane first and foremost, and we’re obviously concerned for Florida. That said, the most obvious threat from Debby continues to be flooding rainfall.

As much as 20 to 30 inches of rain is expected from Debby on the coast of South Carolina and Georgia through the upcoming week, likely leading to widespread, potentially catastrophic flooding. (NOAA WPC)

We are now entering some historic territory with Debby’s rainfall forecast. 20 to 30 inches of rain is now expected between Savannah and Charleston, SC, including Hilton Head. This will cause widespread, possibly catastrophic flash flooding, urban flooding, and river flooding in coastal Georgia and South Carolina. The worst will likely be south and east of I-95, but significant flooding concerns will also exist back toward Columbia, SC, Augusta, GA, possibly up toward Myrtle Beach and into southeastern North Carolina as well.

The standing record for rainfall from a tropical system in South Carolina is 23.63″ from Florence in 2018. Joaquin in 2015 aided in over 26″ as well, so we are currently forecasting that rain totals may approach these record levels. For Georgia, the standing record is almost 28″ during 1994’s Tropical Storm Alberto. Whether it’s a record or not, there are unique aspects to this event, including the potential for coastal flooding to exacerbate flooding conditions in places like Savannah, Charleston, Hilton Head, and Myrtle Beach.

I cannot emphasize enough how serious of a flooding threat this is for southeast Georgia and coastal and Lowcountry portions of South Carolina. Please ensure folks in these areas are prepared for this potential.

As always, isolated tornadoes are a possibility as Debby comes ashore.

So, in summary:

  • Debby is a historic, potentially catastrophic flooding threat for coastal Georgia and South Carolina.
  • Debby will make landfall as a hurricane late tonight or Monday morning near or just west of Florida’s Big Bend.
  • Debby will meander for several days, with uncertainty higher than usual on where exactly it ends up.
  • Debby will cause damaging storm surge in the Big Bend of Florida, just under Idalia’s levels from last year.

Elsewhere in the tropics

A quick note on the rest of the tropics this morning. We currently have two tropical waves worth watching. One is entering the Caribbean today, while the other sits just off Africa.

We are monitoring two additional tropical waves in the Atlantic that may try to develop over the next week or so. Little clarity exists on exactly how that may unfold, however. (College of DuPage)

The National Hurricane Center has 20 percent odds for the Caribbean wave to develop as it meanders west. Some modeling does try to allow it to gain some latitude eventually, so I would say we should keep an eye on this one. Same with the one behind it that will be moving into an Atlantic that should be modestly more hospitable for tropical development. We’ll continue to watch. For now, no specific area should be worrying, but it’s now time to check in on the tropics every day or two from now through September or October.

Tropical Storm Debby forms, poised to track into Florida and then unleash copious amounts of rain on Georgia & South Carolina

Headlines

  • Tropical Depression 4 is now Tropical Storm Debby.
  • Debby is expected to track toward the Panhandle or Big Bend of Florida as a strong tropical storm or intensifying Category 1 hurricane Monday.
  • Copious amounts of rain will follow Debby into Georgia and South Carolina where significant flooding may unfold.
  • Debby’s exact track beyond Monday or Tuesday is highly uncertain.
  • There is another wave beyond Debby worth monitoring next week.
Debby’s latest forecast at 5 PM ET shows a broad northward move, followed by a shift to the east and a sharp slowdown in forward speed. (NOAA NHC)

Tropical Storm Debby: 40 mph, NW 15 mph

Well, here we go again on the west coast of Florida, with another system that will generate some headaches in terms of track. This afternoon, newly minted Tropical Storm Debby looks reasonable. The center shows up nicely on visible satellite, and there is plentiful thunderstorm activity surrounding all sides of the system. As this lifts northward into the Gulf and gets out of the way of Cuba, I suspect we’ll begin to see some consolidation and steady intensification of this one.

Tropical Storm Debby late on Saturday afternoon shows lots of thunderstorm activity and a pretty well defined circulation. (Tropical Tidbits)

The current intensity has it sitting around 40 mph maximum sustained winds, hence the upgrade to a tropical storm. Debby is large in size, (not quite a “Little Debby”) which means it may take a little effort to strengthen. Debby should become a formidable tropical storm, if not a category 1 hurricane before coming ashore. Hurricane warnings are now posted from the Suwannee River to the Ochlockonee River on the Florida Gulf Coast. Tropical Storm Warnings are posted for the west coast of Florida into the Keys. Storm Surge Warnings are in effect between Aripeka north to Indian Pass.

Debby’s track

Debby will be steered north and northeast in between two ridges and in the direction of a trough over the East Coast. Arguably, the track forecast for Debby has the least uncertainty over the next 48 hours or so, and most modeling is in good agreement on that.

European ensemble members show strong agreement on Debby’s general track north and northeast-ward over the next 48+ hours, coming ashore in the Big Bend or Panhandle of Florida. (Weathernerds.org)

After Debby comes ashore somewhere in the Big Bend or Panhandle, that’s when forecast confidence begins to nosedive a bit. A generally slow east or northeast drift to Debby’s motion should set in. But exactly whether or not that gets Debby back offshore and with an ability to try and restrengthen off the Georgia or South Carolina coasts remains to be seen. Expect a very erratic motion to Debby after Monday.

Debby’s intensity

As noted above, there is some chance that Debby can become a hurricane before it comes ashore in the Big Bend or Panhandle Monday morning or so. The obvious comparison for this storm will be Idalia from last year. Idalia made landfall as a weakening category 3 hurricane with 125 mph maximum sustained winds. Debby is likely to make landfall not far from where Idalia did but as a strengthening tropical storm or category 1 hurricane. Much like we witnessed in Houston and coastal Texas last month with Beryl, there are elements about strengthening category 1 storms that are often underplayed ahead of time. Folks in the Panhandle and Big Bend should be taking Debby seriously and listen to local officials in terms of evacuation orders or preparedness recommendations.

After landfall, Debby will lose some of its intensity, though some locally strong winds are possible across south Georgia or North Florida as it turns east. Again, the big wild card right now is what Debby does when it approaches the Georgia coast and makes an effort to get offshore.

Debby’s rainfall

While folks on the Florida coast need to be preparing for a strengthening category 1 hurricane, people across North Florida, Georgia, and the Carolinas need to be preparing for a potentially major rain and flooding event.

Debby is likely to bring copious amounts of rain, flooding, and flood damage to Georgia and South Carolina heading into next week. (NOAA WPC)

The very latest rainfall forecasts is suggesting anywhere up to 12 to 20 inches of total rain from Debby on the coast of Georgia and South Carolina, including Savannah, Hilton Head, and Charleston. This has the potential to also produce a wide swath of 8 to 12 inch rains in the Lowcountry of South Carolina and much of southeast Georgia (as well as parts of North Florida) also. Combine this with rough seas and high tides, and we could be looking at an especially dangerous, damaging flooding scenario in coastal spots and a significant, locally damaging flooding event away from the coast. Heavy rain will extend up to North Carolina at times as well, but we are really concerned with South Carolina and Georgia first in this scenario. Slow moving tropical systems loaded with abnormally high amounts of atmospheric moisture are never a good combination. Please take this threat extremely seriously in those areas.

How long the rain lasts and how far north it gets remain questions to monitor over the next few days.

So, in summary:

  • A strong tropical storm or intensifying category 1 hurricane is likely to turn into the Big Bend or eastern Panhandle of Florida by Monday.
  • Debby will slow down as it tracks across Georgia and North Florida, delivering copious amounts of rain to Georgia and South Carolina.
  • A major flooding threat exists, particularly along the coast, including Savannah, Hilton Head, and Charleston.
  • Debby’s future remains a bit uncertain beyond that, and folks in North Carolina should continue to monitor the system’s progress in the days ahead as well.

Some quick miscellany

First, we have people wondering why we are on Debby and not Chris. Well, if you blinked, you missed Tropical Storm Chris. It formed for about 8 hours before coming ashore in Mexico in early July. This occurred while Beryl was hammering the Caribbean, so it obviously got lost in the shuffle.

Second, we are monitoring another tropical wave behind Debby. This system has shown up on various deterministic/operational model guidance at times as a formidable Gulf storm. Remember, we try not to use deterministic guidance 10 days or so out, as it is prone to wild and extreme variability run to run. Looking at ensemble guidance is more useful, and in this case, we have decent European ensemble agreement on something in the western Caribbean or near Cuba again in about 6 days.

Behind Debby, another tropical wave is beginning to generate buzz, but it’s too soon to say much of anything coherent about this one’s future. (Weathernerds.org)

For now, we’ll wait for Debby to get out of the way and then focus on that as well.