Debby strengthening as it bears down on Florida, bringing serious surge and winds, with significant flooding into next week

Headlines

  • Tropical Storm Debby is intensifying, and will soon reach hurricane strength
  • A landfall will occur on Monday, in the coastal bend area of Florida, with a strong surge only slightly less than that of Hurricane Idalia
  • Significant rains and winds will spread over much of the northern half of Florida on Monday
  • From Tuesday onward the focus turns to the Atlantic coastal regions, from Jacksonville north through South Carolina, with the threat of very heavy rainfall

Debby status at 8 pm ET Sunday

As of this evening, Tropical Storm Debby is nearing hurricane strength with 70-mph sustained winds. It likely will reach hurricane strength tonight, and then continue to intensify before making a landfall somewhere in the parklands along the coastal bend of Florida on Monday. A hurricane warning is now in effect for the Florida coast from the Suwannee River to Indian Pass.

After Monday night, the track of Debby becomes highly uncertain. (National Hurricane Center)

Immediate threats to Florida

Debby has lashed the west coast of Florida for much of the weekend, bringing heavy rains, tropical storm-force winds, and bands of rainfall to the Sunshine State. The storm has more or less been moving north for much of Sunday, and that will not change a whole lot overnight before the storm makes a slight northeastern turn towards the coastal bend of Florida on Monday. The storm will bring three major hurricane threats to the Florida coast tonight and on Monday.

Storm surge

As Debby has strengthened and grown larger today, it is likely to produce a more potent storm surge. Nearby residents will well remember the surge of Hurricane Idalia, a more powerful hurricane that made landfall a little more than 11 months ago in a similar location. Although Debby’s storm surge will not be as potent as that of Idalia, it will nonetheless be significant. Forecasters from the National Hurricane Center now anticipate a surge as great as 6 to 10 feet from the Suwannee River northward to the Ochlockonee River at high tide.

Peak storm surge forecast. (National Hurricane Center)

Winds

Hurricane force winds could arrive at these coastal areas of Florida as early as Monday morning, with tropical-storm force winds likely for much of the northern half of Florida, and into southern Georgia. The area of hurricane-force winds (shown in the map below) will be smaller. Such winds can knock down power poles and do considerable tree damage. The landfall of Debby is also likely to spawn several tornadoes across the northern half of Florida.

Map showing areas most likely to be impacted by hurricane-force winds. (National Hurricane Center)

Inland rainfall

The third major threat from this storm will be heavy rainfall, which leads to flooding away from the coast. As much as 8 to 16 inches of rainfall will be possible along and north of a line from Tampa Bay to Orlando, with the heaviest showers likely along and to the immediate right of Debby’s track. Where training bands set up, there will be considerable street flooding and the potential for flooding of homes and businesses. This will compound the effects of damaging winds.

Longer-term impacts

By late Monday or Tuesday the center of Debby should be crossing through Southern Georgia, and then emerge into the Atlantic Ocean somewhere between Jacksonville, Florida, and Hilton Head Island, South Carolina. And then, it’s going to sit and spin awhile. Our latest modeling (18Z) is not helping much, but there’s a general trend toward Debby being forced back toward the Atlantic coast of Georgia by Wednesday or Thursday in response to a high pressure system building over the central Atlantic Ocean.

Extreme rainfall accumulations are likely this week from Tropical Storm Debby. (Weather Bell)

All of this is likely to bring some pretty serious winds and surge to coastal areas from northern Florida to Georgia and through at least South Carolina. We can be highly confident in a significant rain event for these areas, but winds and seas will depend on the ultimate track of Debby. The bottom line is that these areas should be prepared for impactful weather from Tuesday through Thursday. Hopefully, in the next day or so, we can better define the timing and the extent of these threats.

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.

A tropical storm, or possibly a hurricane, is likely to reach Florida late late Sunday or early Monday

Headlines

  • Tropical Depression Four is crossing Cuba and will enter the Gulf of Mexico later today
  • This storm will menace the west coast of Florida with winds and surge this weekend, with heavy rainfall also likely
  • The system may reach tropical storm status, or possibly even become a hurricane before landfall along Florida’s coastal bend
  • Downstream there is a significant threat of flooding in Georgia and the Carolinas

Tropical Depression status

The tropical disturbance we’ve been tracking for much of this week has become Tropical Depression Four, with sustained winds of 30 mph. The center of the storm is in the vicinity of western Cuba as of Saturday morning, and moving to the west-northwest. As it moves into the southeastern Gulf of Mexico later today the depression should find favorable conditions for some strengthening, and forecasters believe it will become a strong tropical storm or possibly a hurricane before landfall somewhere along the coastal Bend of Florida on Sunday night or Monday.

Official track from the National Hurricane Center at 8 am ET on Saturday.

This will basically be a tale of two storms. There is the first part, the storm’s path across the Gulf of Mexico and impacts on Florida. Then, it now appears more likely than not the storm will cross the Florida peninsula and move into the Atlantic Ocean off the coast of Georgia and the Carolinas. There, the storm’s track is far less uncertain. So this post will discuss the first half impacts to Florida, and the second-half impacts to the southeastern United States.

Confidence in the track prior to landfall in Florida is high. There is considerable uncertainty thereafter. (Weather Bell)

Florida impacts

Tropical Storm Warnings are in effect for most of the western coast of Florida, with Hurricane Watch in effect for the coastal bend portion of the state. Because the models are increasingly confident in a track between now and a landfall in about 48 hours, or less, the larger question is how strong the storm will get. The majority of model guidance this morning still indicates the storm will remain at tropical storm strength prior to landfall. However, the eastern Gulf of Mexico is rather warm, and could support further strengthening. The bottom line is that some areas of Florida north of Tampa Bay and to the east of Indian Pass, may see hurricane-force wind gusts. Surge impacts look fairly modest, 3 to 5 feet in areas near and to the right of the storm’s landfall.

Where tropical-storm force winds are most likely from this system. (National Hurricane Center)

Probably the largest impact to Florida will be rainfall totals, as the entire west coast of the state, from Key West north to Tallahassee, could see between 4 to 10 inches of rainfall over the next two days as the storm’s center moves north in the Gulf of Mexico, remaining just offshore the state. This puts Florida to the right of the center, where heavy rains are most likely.

NOAA rain accumulation forecast for now through Monday. (Weather Bell)

For much of Florida, as the storm moves away by Monday afternoon or evening, these impacts will lessen. The bottom line is that state residents need to be vigilant for heavy rainfall beginning as soon as this morning.

Southeastern US impacts

The storm should cross over northern Florida and perhaps southern Georgia on Monday before reemerging into the Atlantic Ocean late on Monday night or some time on Tuesday. At this point our uncertainty ratchets up. This is because, increasingly, it looks like the storm may stall offshore, near the Georgia or South Carolina coast. If it does, it could re-strengthen some, battering the coast with winds and waves. Given the model uncertainty, I don’t feel confident in making a forecast for wind strength yet, but the southeastern United States, including Georgia and the Carolinas, should be prepared for impacts from this storm from Monday night through at least Wednesday. Again, the timing and intensity of the storm will depend on the extent to which its center moves offshore, and how long it lingers in the absence of steering currents.

The potential for flooding is high in the Southeast next week. (Weather Bell)

The other significant impact of a stalling storm, of course, would be the potential for heavy rainfall over a longer period of time. Forecast models are indicating some pretty high rainfall totals for coastal areas of Georgia and South Carolina, especially. There is the threat that these areas may see 10 inches or more, with significant flooding possible should the storm linger offshore, or just inland for a couple of days.

We will have an additional post on this tropical cyclone later today.