Matt Lanza

Helene likely to become a hurricane today, delivering complex, damaging impacts for Florida and much of the Southeast (UPDATED: 2:25 PM ET)

(2:25 PM ET Update): The storm surge forecast has been increased to 12 to 18 feet in the Big Bend, now well above the levels set during Idalia last year. This has potential to be the benchmark event for this region historically.

Storm surge forecast for Florida has increased. (NOAA NHC)

(1:20 ET Update): Hurricane Helene is here, as it has strengthened enough to cross the threshold to hurricane intensity. Winds are 80 mph, and strengthening into a borderline Category 3 or 4 hurricane is expected up to landfall tomorrow night.

Hurricane Helene avoided landfall on the Yucatan and is now set to traverse very, very warm water up to landfall. Helene is a sprawling, large storm. (Weathernerds.org)

Helene will rapidly intensify into a major hurricane tonight or tomorrow. SHIPS model guidance shows a 10 times greater than normal chance of Helene adding 50 mph to its intensity over the next 36 hours, which would place the storm on the cusp of category 4 intensity.

Whatever it becomes at this point may matter little, as the impacts now seem set: Catastrophic storm surge, worse than Idalia for the Big Bend and Nature Coast, severe storm surge in Tampa Bay, significant wind damage from the Big Bend and Panhandle deep into Georgia, and potentially catastrophic flooding in North Georgia and the Carolinas. Among other impacts. For the U.S., Helene appears to be the most significant threat of the 2024 hurricane season.

The surge forecast has changed little from this morning, though the 10 to 15 foot values were nudged a bit west to Carrabelle, FL. Again, this is likely to be much worse than Idalia and over a larger area.

The landfall forecast continues to hold steady. Expected landfall is in or very near Apalachee Bay.

Inland tropical storm watches and warnings have been expanded today and now cover parts of Alabama, all of Georgia, much of South Carolina, and western North Carolina.

Watches and warnings cover a huge swath of the Southeast from the coast to hundreds of miles inland. (Pivotal Weather)

We continue to watch the rainfall outlook very closely. Unfortunately, many areas will be drenched today by a predecessor rain event (PRE) that will exacerbate flooding as Helene itself comes inland tomorrow night. As much as 2 to 5 inches of rain are expected today and tonight across Georgia and into North Carolina.

Heavy rain will fall today from west-central Georgia into western North Carolina, with a high risk of flash flooding. Flooding will worsen tomorrow and tomorrow night as Helene approaches and winds kick up. (Pivotal Weather)

With more rain tomorrow and the storm itself not arriving until tomorrow night and Friday, conditions will steadily deteriorate into Friday in those areas, and the severity of flash flooding will worsen. This will be a prolonged, extremely serious flooding event for North Georgia, Upstate South Carolina, and western North Carolina. Landslides, at least moderate river flooding, and possibly major river flooding is a safe bet in those areas. Current forecasts indicate perhaps as much as 20 inches of rain in some southeast facing mountains in western North Carolina.

We will update again later today.

What’s changed since yesterday

  • Helene’s forecast intensity as it approaches Florida has been increased a bit, with risk for further increase in the intensity forecast today. Folks between Port St. Joe and Cedar Key should be preparing for major hurricane impacts.
  • Hurricane Warnings extend into Georgia, a good bit beyond Valdosta. Tropical Storm Warnings now cover virtually the entire Florida Peninsula. Tropical Storm Watches extend into central Georgia and much of southeastern South Carolina.
  • Helene’s track and surge forecast is relatively unchanged.
  • The interior rainfall forecast has escalated, and there is growing risk of a potentially damaging, catastrophic flash flooding event from northeast Georgia into western North Carolina, including Asheville.
Helene’s forecast to come ashore near Apalachee Bay as a major hurricane. (NOAA NHC)

Not a whole lot has changed since yesterday. It’s nice to have a consistent forecast, but this is certainly turning into quite a serious situation for the eastern Florida Panhandle and Big Bend. Again, the minimum you should expect right now is an Idalia-type impact. For many, if not most places between Apalachee Bay and Tampa, this will probably be a worse impact than Idalia. Current surge forecasts continue to suggest impacts at or above Idalia. This surge forecast is virtually unchanged from 12 hours ago.

Potential max storm surge forecasts are as bad or worse than Idalia and unchanged since yesterday. (NOAA NHC)

There’s honestly not a whole lot that needs to be said here with respect to the Florida coast between Cedar Key and Apalachee Bay: This has a decent chance to be worse than Idalia was and you should be closely following the advice of local officials.

The track forecast isn’t entirely locked down, but it’s close to it right now. There are still a handful of model data points suggesting a track slightly farther east than currently shown by the majority of tropical models and the official NHC forecast. This won’t hit Tampa directly, but a track closer to Cedar Key or Steinhatchee is possible, a Nature Coast/Big Bend hit more than an Apalachee Bay hit. This is why we encourage everyone from Port St. Joe to Homosassa or Clearwater to prepare for a significant hurricane hit, be it via surge, wind, or both.

Hurricane force winds are expected to extend deep into Georgia, perhaps north of Tifton and near Albany. Tropical storm force winds will extend possibly into Metro Atlanta and much of South Carolina. (NOAA NWS)

It’s also important to note how deep into Georgia hurricane-force winds are expected to go. That takes them close to Albany, GA and about halfway to Macon. Tropical storm force winds are expected to extend north of Macon to metro Atlanta and into South Carolina. This will almost certainly cause widespread power outages, and folks should be prepared to be without power for at least a few days.

Here is a list of major cities and their maximum wind gust forecasts from the NWS Point and Click forecasts as of Wednesday morning. These are likely to change:

(Editor’s Note: We will update these later today with slightly better data than point & click forecasts)

Florida
Tallahassee: 63 mph
Cedar Key: 80 mph
Apalachicola: 77 mph
Panama City: 54 mph
Clearwater: 60 mph
Tampa: 59 mph
Sarasota: 72 mph
Fort Myers: 57 mph
Naples: 56 mph
Orlando: 49 mph
Jacksonville: 63 mph
Gainesville: 56 mph
Key West: 44 mph

Elsewhere
Valdosta: 57 mph
Albany, GA: 68 mph
Macon: 92 mph
Atlanta: 56 mph
Savannah: 39 mph
Athens: 75 mph
Augusta: 46 mph
Charleston: 37 mph
Columbia: 41 mph
Greenville: 48 mph
Spartanburg: 43 mph
Charlotte: 41 mph
Asheville: 51 mph

A major, potentially catastrophic flooding event possible in the Appalachians

I want to focus on one element of this storm that is now coming into focus and becoming very serious: The risk of significant, possibly catastrophic flash flooding in the Appalachians from north Georgia into North Carolina.

Widespread flash flooding is expected in north Florida and Georgia, but a major, potentially catastrophic flood event is becoming more plausible from northeast Georgia into the western North Carolina mountains, where over a foot of rain is now possible. (NOAA WPC)

A high risk of flooding has been issued for some of those areas by the Weather Prediction Center, which historically has correlated to extensive, significant damage.

A high risk (level 4/4) of flash flooding exists tomorrow north of Metro Atlanta into much of western North Carolina and portions of upstate South Carolina. (NOAA WPC)

This is a historically favorable setup for major rainfall in this region, and there’s no reason to believe this forecast is incorrect. So for anyone in those affected areas and even in the red moderate risk areas surrounding the high risk, it is important to be prepared to take immediate action in the case of flooding or landslides. Please heed the advice of local officials. It is possible that the damage and problems from the inland flooding will be equally as bad as the surge issues at the coast.

Helene is going to be a complex, very difficult storm with multiple different concerns along the way. We’ll keep you posted as best we can through the event, but please also stick with trusted local sources for the latest and most relevant information for your neighborhood. We’ll update this post through the day.

Tropical Storm Helene is beginning to steadily organize in the northwest Caribbean with little forecast change

Changes since this morning

  • PTC 9 became Tropical Storm Helene and its satellite presentation has improved markedly since earlier today.
  • Hurricane Warnings have been issued between Anclote River just north of Clearwater and Mexico Beach in Florida.
  • Storm Surge Warnings have been issued from Flamingo to Indian Pass in Florida, including Tampa Bay and Charlotte Harbor.
  • Tropical Storm Warnings have been issued for the Lower & Middle Florida Keys and the west coast of Florida between Flamingo and the Anclote River, which includes Tampa Bay.
  • Tropical Storm Watches are now posted on the East Coast of Florida and Georgia between the Palm Beach and Martin County line and Savannah River.
(NOAA NHC)

Tropical Storm Helene is slowly getting organized now, as it appears that the wind shear impacting it earlier has leveled off, and it’s feeling the heat of the warm water underneath it. Expect a steady, if not rapid strengthening process to start unfolding soon. SHIPS model guidance indicates rapid intensification risk that is about 8 times climatology over the next 48 hours, not the biggest number we’ve seen in recent years but a very healthy signal that says Helene is going to take off eventually.

Helene’s satellite presentation has improved pretty dramatically today.

The evolution of Helene today from nascent tropical cyclone to organized tropical storm. (College of DuPage)

It now “looks the part” much more than it did earlier. One thing to note is the size of Helene. This is a pretty sprawling storm already, and as it comes north, it will continue to maintain that size, with tropical storm and hurricane force winds extending out farther than we’ve seen with recent Big Bend storms in Florida. According to the NHC’s latest discussion, this storm will be in the 90th percentile of major hurricane size at this latitude. In other words, it’s big, and the winds from Helene will be felt, especially on the east side far away from the center and outside the cone.

An aggressive storm surge forecast continues given the expectation of Helene’s strength and size. (NOAA NHC)

The forecast has changed little since this morning. We still anticipate a major hurricane making landfall in or near the area between the Big Bend and Apalachee Bay in Florida. The size of the storm will complicate the surge potential somewhat on the west coast of Florida, leading to surge values that should be as bad or worse than were experienced in Idalia. We covered that a bit more earlier today.

18z tropical models showing a clustering of weaker outcomes that seem difficult to trust and a clustering of Cat 1 to Cat 3 intensity outcomes. Folks in Florida should be preparing for the higher end to be safe. (Tropical Tidbits)

The intensity forecasts on tropical modeling for Helene have stalled somewhat today, certainly not a bad thing! However, I would be hesitant to read into that too much, as we’ve seen many examples of storms “overachieving” in this part of the Gulf. The biggest question that I have at this point is how close to peak intensity Helene will be when it comes ashore. There is a noteworthy difference between a 115 mph storm making landfall on an upswing versus one that has peaked and is weakening. Idalia was bad enough last year, but it was also past peak and likely less bad than it could have been. Can we pull that off twice? I don’t know, but I know to never trust the Gulf.

More to come tomorrow, and we can hopefully iron out some forecast details farther inland into Georgia and the Carolinas as well.

Helene continues to get itself in order as we focus on the risks to Florida and beyond (UPDATED: 11:40 AM CT)

(11:40 AM CT Update): PTC 9 has been upgraded to Tropical Storm Helene. No big changes have been made to the forecast. According to the National Hurricane Center, there is still a bit of uncertainty on the exact center location, and this means that despite the great model agreement, there is still a bit of uncertainty in the track forecast. Aside from that, everything else appears on track.

The Lower Keys were added to the Tropical Storm Warning with this advisory. Previous post follows.

Headlines

  • PTC 9 continues to fight off a little shear which is slowing its initial organization.
  • As that relaxes, rapid intensification and organization should ensue, with PTC 9 expected to become Major Hurricane Helene by Thursday.
  • Landfall is a little later on Thursday now, likely somewhere between Panama City and Tampa with a focus on Apalachicola through Cedar Key. There is still some uncertainty on this.
  • Storm surge from the Big Bend and Nature Coast through Tampa Bay is expected to be as bad or worse than what occurred during Hurricane Idalia in 2023.
  • Impacts from wind and rain will extend far beyond the landfall point with Georgia and the Carolinas likely to see strong winds and flash flooding.

PTC 9 this morning

PTC 9 continues to lack the ingredients necessary to be a depression just yet, but we continue to edge closer to that point.

PTC 9 continues to slowly organize in the northwest Caribbean. (Weathernerds.org)

What’s holding it back so far? There’s a bit of wind shear mixed in with all this from an upper low over the Yucatan. Tropical systems don’t like wind shear, and as long as that continues, the pace of development will be sluggish. That is not expected to be the case, however, as modeling weakens the shear in the next day or so, allowing PTC 9 to have a less hostile environment over some of the warmest water in the Atlantic basin. That should lead to strengthening and potentially rapid strengthening at that.

PTC 9’s forecast: Angles matter

The overall forecast for PTC 9 has not changed a whole lot since yesterday.

The forecast for PTC 9 continues mostly in line with what was predicted yesterday. (NOAA NHC)

The cone has narrowed a hair to between Panama City and Tampa. Hurricane Watches are now in effect for the Florida coast, as well as inland in the Panhandle. Tropical Storm Watches including Orlando are now posted as well. Expect some of these watches to expand later today.

On the surface, this looks like a pretty easy forecast: Tropical models are in generally good agreement on a track to the northwest, then north, then north-northeast. The clustering is pretty solid in the modeling in Apalachee Bay or near the Big Bend of Florida. So, simple right? For my college football fans: Not so fast, my friends.

The fundamental problem in predicting storms that turn is the angle at which it all happens. Generally, models handle the concept of this well, and indeed we have very good agreement right now in the models.

Tropical models for PTC 9 are in good agreement on the general track. Florida’s geography poses a unique challenge. (Tropical Tidbits)

Because of Florida’s unique geography with a peninsula jutting out to the south, the exact landfall point gets harder and harder to pin down when a storm comes in from the south or southwest. A shift of 10 to 15 miles out over the Gulf can lead to a shift of 20 to 40 miles with respect to landfall location in Florida. We often talk about not focusing on the exact track, and indeed there’s a reason for that as impacts extend far from the center. But for things like storm surge, that exact landfall point is crucial in determining how things will turn out. It also makes the difference for places even well inland to be on the “dirty” eastern side of the storm or the slightly less menacing western side.

As long as the tropical models are correct, we’re likely to see this chug north-northeast into Apalachee Bay or the Big Bend. However, if the models are not quite grasping the interaction with an upper low over Arkansas properly, well, that could change things a bit. There’s a path to get a storm much closer to Tampa, as we discussed last night and as the ICON model continues to show this morning with a track coming ashore near Cedar Key rather than Apalachee Bay. For now, the most likely window for landfall appears to be Apalachicola to Cedar Key, with lesser bands around that to Panama City on the west and Tampa on the south/east.

The takeaway here is that this is a storm where focusing on the entire cone makes a lot of sense.

In terms of intensity, not much has changed since yesterday. We still struggle with intensity forecasts. One needs to only look at Hurricane John yesterday, which came ashore after 9 PM as a 120 mph category 3 storm in Mexico while initially forecast to be a 70 mph tropical storm at 3 AM. (Credit to the NHC however for constantly stating in their discussions that there were higher risks, and even substantially higher risks than the explicit forecast showed).

But we still expect that PTC will become Hurricane Helene and a major hurricane at that. The National Hurricane Center has this as a category 3 storm at landfall. And model support is generally for a strong storm.

Model forecast intensities for PTC 9 still show a very wide spread in options, but most seem to agree on this becoming at least a category 2 or 3 storm. (Tropical Tidbits)

The takeaway: A powerful hurricane is likely to strike Florida’s coast late Thursday, likely somewhere between Apalachicola and Cedar Key but with risks extending just beyond those goal posts.

Impacts from Helene/PTC 9

We have our first look at storm surge today from the NHC advisory, and it’s not great news.

Storm surge as high as 10 to 15 feet above ground level is possible near and east of where PTC 9/Helene comes ashore in Florida. About 5 to 8 feet of surge is possible in Tampa Bay. (NOAA NHC)

Values of 10 to 15 feet in the Big Bend would be in line with or worse than what occurred in Idalia last summer. A 5 to 8 foot surge in Tampa Bay would also be in line with or worse than Idalia. So for planning purposes, those areas should consider Idalia as a benchmark for minimum impacts, with risk for something worse. The wind field and size of this storm is expected to be somewhat broader than in Idalia, which also is concerning from a potentially worse impact standpoint.

PTC 9’s forward speed is likely to aid in carrying tropical storm and hurricane force winds well inland. The map below shows roughly where, given the current track, tropical storm and hurricane force winds could extend. And that’s a huge area. Things get complicated on Florida’s east coast, including Jacksonville, as well as up toward Savannah where stronger winds are possible than in other inland areas near there.

A rough outline of where tropical storm and hurricane force winds could occur with Helene/PTC 9 as it comes inland. (Weather Bell)

The extension of hurricane force winds inland will depend on the intensity of the storm at landfall and its exact forward speed from there. But suffice to say this has the potential to be a destructive inland wind event too, extending from North Florida into much of Georgia and South Carolina and even parts of North Carolina.

In addition to the wind will be heavy rainfall, and that’s expected to cover a massive area of the Southeast.

While these aren’t the most extreme rain totals we’ve seen in recent years, the coverage and intensity of this rain is likely to contribute to widespread flash flooding in the Southeast. (NOAA WPC)

We’ve seen worse rain events, but spatially, this is going to put a lot of places at risk of flash flooding.

Obviously, isolated tornadoes are a possibility along and to the right/east of where this storm goes.

The takeaway: Significant impacts from PTC 9/Helene are expected to extend well inland from the coast.

We will update this post today as we can if anything changes. We’ll aim to have another post out early this evening with the latest.

A Monday evening update on PTC 9/Helene and a word about Tampa

Headlines

  • No major forecast changes with PTC 9/future Helene this evening.
  • A major hurricane is now explicitly forecast by the National Hurricane Center.
  • Watches now extend up to the Florida Keys.
  • Impacts in Tampa are expected to include tropical storm force winds and some degree of storm surge. This post examines how bad that could theoretically get and how that might happen.

Helene/PTC 9 forecast update

The overall forecast is generally steady this evening versus this morning, so not a whole lot has changed. The NHC is now explicitly forecasting Helene to become a major (category 3+) hurricane on approach to the Florida Panhandle.

PTC 9’s forecast is mostly unchanged this evening, except now showing a cat 3 major hurricane on approach to Florida. (Tomer Burg)

The current forecast track takes it to the west side of Apalachee Bay, which would likely produce a substantial, very bad surge in Apalachee Bay and points east around the Big Bend and Nature Coast. With some models indicating this could get even stronger, that surge risk is going to be extremely bad. I need to underscore that for folks in Florida’s Big Bend, we know you have been through several storms in recent years. This one has a higher ceiling than those it would appear, meaning the surge impacts could be as bad or worse than anything you’ve experienced in the last several years. Just keep that in mind.

The timing is mostly unchanged today, and we’re looking for a Thursday evening landfall in Florida right now. The cone extends from about Destin through Tampa. It’s important to recognize that 72 hour forecast errors are significant enough usually that storms can deviate considerably. Just ask Houstonians how Beryl’s expected track into Corpus Christi and South Texas changed this year. So if I lived in Tampa right now, I would be taking this as seriously as anyone on the Panhandle or Big Bend.

Let’s talk about Tampa Bay risks

Assuming a track as forecast by the NHC, tropical storm force winds are likely in Tampa, and there is some potential for hurricane-force winds on the immediate coast in Pinellas or Pasco Counties.

Current wind threat map from NWS for the Tampa-St. Pete and Sarasota areas. (NOAA NWS)

The issue is that if this shifts any farther east, which is something the ICON model hints at with a landfall more in the Big Bend than in Apalachee Bay, then the risks increase drastically in Tampa both from a wind and surge standpoint.

Speaking of surge, the NHC publishes storm surge inundation maps that show reasonable worst-case scenario outcomes. These maps are not the *likely* case, but they are the outcome that could occur in a worst-case, something that has about a 1-in-10 chance of occurring. For Tampa, this would sort of like if the ICON model came to pass, and the storm made landfall just up the coast rather than in the Panhandle.

Reasonable worst-case scenario flood inundation map for Tampa Bay if the storm track presumably comes much closer/stronger than is currently forecast. (NOAA NHC)

The map suggests some rather significant inundation potential in and around Tampa Bay in this worst case outcome. This is one reason why I want to just make sure that folks in Tampa take this very, very seriously. As noted, this probably won’t happen, especially if the current forecast remains unchanged, however there is still enough uncertainty out there that it’s not a scenario I would be willing to discount at this point.

Anyway, this is one of many different storylines we need to follow with this storm, including the coastal impacts in Florida at landfall, the inland impacts in Georgia and South Carolina and elsewhere from wind and rain, the east coast impacts, and so on.

Currently, Hurricane Watches are posted between Cabo Catoche and Tulum on the Yucatan and Pinar del Rio in Cuba. Tropical Storm Warnings are in effect for Grand Cayman, much of the eastern Yucatan, and Artemsia, Pinar del Rio, and the Isle of Youth in Cuba. Tropical Storm Watches are in effect for the Keys. Those will be expanded northward later.

We’ll have more for you in the morning.