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.

Forecast for tropical disturbance becomes clearer: A threat to Florida, and then the US East Coast

Headlines

  • Invest 97L has reached Cuba, and will near the Florida Keys by Saturday
  • Our confidence in its track is increasing, raising the risks to Florida, and lowering them for the northern Gulf of Mexico coast
  • All tropical threats are in play, but we’re most concerned about heavy rainfall at this time
  • Risks are also rising for the southeastern United States, particularly coastal regions of Georgia and the Carolinas

Status of Invest 97L

The tropical wave we’ve been tracking continues to get better organized, and it now has the designation Invest 97L. The approximate center of the system is now near or over the eastern end of Cuba, and it should move along the island today bringing showers and thunderstorms to Cuba and other Caribbean islands. Interaction with land may limit any attempts to organize today, but by Saturday it should emerge near the Florida Keys and move into the southeastern Gulf of Mexico. At this point the National Hurricane Center gives the system a 90 percent chance of eventually becoming a tropical depression or storm. In this case it would be named Debby.

Tropical outlook from the National Hurricane Center as of Friday morning.

Forecast clarifies some

If you read our update on Thursday, you’ll recall we were in “watch-and-see” mode with this tropical system. Well, we’ve watched. And now, we’ve seen. All of our major model guidance now predicts that 97L will move into the southeastern Gulf of Mexico, and likely remain near—perhaps just offshore—the coast of Florida on Saturday and Sunday. During this time it could well strengthen into Tropical Storm Debby, but this is not sure thing as I don’t know how disorganized 97L will be when it moves off of Cuba.

At some point this weekend, perhaps on Sunday, or Sunday night, 97L is likely to turn toward the northwest. This could bring the system into Florida anywhere from south of Tampa Bay to the coastal bend of Florida. A stronger storm would likely turn more quickly. In any case, residents of the Florida Keys and the West Coast of Florida should be preparing for tropical weather as early as Saturday.

There are questions about where the tropical system will move inland into Florida, and how long it may spend over the Atlantic Ocean. (NCAR)

After 97L crosses the Florida peninsula it may reemerge into the Atlantic Ocean somewhere near Jacksonville, Florida. At that point its center should remain just inland, or perhaps move offshore before moving into South Carolina or North Carolina as a stronger storm. East Coast regions from Jacksonville north to coastal Carolina and possibly even Virginia should be prepared for tropical impacts from Monday through Wednesday of next week.

We mentioned that residents of the northern Gulf of Mexico coast should remain vigilant in yesterday’s post, but at this point all of our guidance suggests the storm’s impacts will occur from the Florida Panhandle and to the east.

97L impacts

So far we’ve mentioned that coastal residents in Florida and up the East Coast should prepare for tropical weather, because all of the impacts associated with a tropical system are in place: strong winds, storm surge, and inland rainfall. The extent of these impacts will depend on how much 97L strengthens before moving into the west coast of Florida, and then whether it has time to restrengthen over the Atlantic Ocean if it spends time offshore of Georgia and the Carolinas. That is impossible to forecast at this time, and probably won’t be until 97L develops a better defined center of circulation.

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

The one bit of good news is that it now appears that this tropical system will probably miss an area of low steering currents over the northern Gulf of Mexico. This means that its track should be more conventional, first turning north, and then to the northeast as it moves poleward. This should help to limit rainfall totals, but some of our models are still showing very high amounts in coastal areas of Western Florida and coastal Carolina. Again, these totals will depend on the location and forward speed of the storm this weekend and during the first half of next week. Regardless, flooding is a concern.

Elsewhere in the tropics

Beyond 97L, as we get deeper into August, there is likely to be some activity over the next week or 10 days. At this point the area of greatest interest may be the southern Caribbean Sea, where something may spin out of the gyre in that region next week. We shall watch and see what happens.

With weak steering currents downstream, we are in watch-and-see mode with a tropical wave near Puerto Rico

Headlines

  • A tropical wave is moving near Hispaniola, and likely to cross Cuba over the next couple of days
  • We have a lot more questions than answers about the strength and intensity of the tropical system after this
  • However, it poses a distinct threat to Florida and the northern Gulf of Mexico coast
  • Rainfall is a particular concern due to a lack of steering currents next week

Tropical wave getting better organized

The tropical wave we’ve been discussing for much of this week has a better satellite appearance today as it is bringing a large area of showers and thunderstorms to the Caribbean. As of Thursday morning, the center of this activity appears to be situated near Hispaniola, and the system should continue to move steadily to the west-northwest.

Our forecast models have really struggled to get a handle on the evolution and track of this tropical system over the last couple of days, and there has been a decided westward shift in the guidance. Whereas it once appeared that the tropical system—which if it were to develop would be named Debby—would travel to the east of Florida, it now appears as though it will remain south of Florida and move into the eastern Gulf of Mexico.

Tropical outlook as of Thursday morning. (National Hurricane Center)

One reason for this is that it no longer appears as though the tropical wave will become Debby any time soon. A more rapidly strengthening system favored a poleward turn more quickly into the Atlantic. However, most of the model guidance now keeps the system below tropical depression strength for the next several days as it moves over Cuba and into the southeastern Gulf of Mexico this weekend.

What happens in the Gulf of Mexico?

If only what happened in the Gulf stayed in the Gulf. As the outlook from the National Hurricane Center outlook above makes clear, there is broad uncertainty about what happens to the system as it moves off of Cuba. It could conceivably move into Florida, or over any part of the eastern Gulf of Mexico. As of this morning most of the guidance favors a blob moving into the Eastern Gulf.

If the storm remains offshore, it would find more favorable conditions for development this weekend, or early next week. So it’s possible, and perhaps even likely, that we’ll see a tropical storm off the west coast of Florida in three to five days time. At a minimum, this will be a rainmaker. And depending on how strong it gets, there could be wind and storm surge threats as well. However, it is a fool’s errand to try and make such predictions now as there is a ton of uncertainty about a storm that a) has not yet formed, b) must still traverse the spine of Cuba, and c) may then interact with parts of Florida’s landmass. The bottom line is that residents of Cuba, Florida, and southern Mississippi and Alabama (and maybe even Louisiana) should be tracking the storm’s progress over the coming days.

There is a distinct lack of clarity about where this system is going over the next three to five days. (WeatherNerds.org)

A lack of steering currents

The party doesn’t end early next week, unfortunately. Let’s assume the system moves near the Florida Panhandle by Sunday or Monday. At that point it will run into an atmospheric pattern known as a “col,” not to be confused with the state or military rank. A col, in meteorology, means a place where a trough and ridge intersect. Essentially, due to weak steering currents, this tropical system could spin around and make some wild turns in such an upper air pattern.

For example, the European model brings the center of a very weak tropical system to the Florida Panhandle late next Monday, and then retrogrades the system back over the northern Gulf of Mexico for much of next week. The GFS model brings a strong tropical storm to the coastal bend region of Florida on Sunday, moves it all the way into the Atlantic Ocean off the Carolinas, before bringing it westward all the way back to Destin Florida and then Biloxi, Mississippi, before it finally lifts north on Tuesday, August 13. That’s 12 days from now!

The GFS model has a party with the tropical system given the lack of steering currents. (Weather Bell)

The bottom line is that Florida and the northern Gulf of Mexico coast need to buckle up and be ready for anything over the next week or 10 days. We just don’t know what is going to happen. My biggest concern, for the time being, is the potential for very heavy rainfall along the Florida Panhandle or the west coast of the state. However, as the storm evolves, so will the threats it presents to us.