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.

Tropical wave with decent chance of development this weekend continues plodding toward the southwest Atlantic

Headlines

  • Slow development of the Atlantic tropical wave is likely this weekend near the Bahamas.
  • The track of the system is highly uncertain with some plausible outcomes ranging between the eastern Gulf and offshore of the East Coast.
  • Interests from Louisiana to Florida to the Carolinas should continue to monitor the progress of this system, even though current expectations are not for a major storm.

It’s a slow go from the Atlantic wave

We continue to track a tropical wave in the open Atlantic this afternoon that the National Hurricane Center continues to gradually beef up development odds on. This afternoon they stand at 60 percent over the next 7 days (near zero the next 2 days).

Development odds in the Atlantic have increased to 60 percent over the next week. (NOAA NHC)

This is a larger, lumbering wave with slowly increasing thunderstorm activity. Larger waves are generally slower to develop, and given how much dry air this thing still has to shed, we likely won’t see any real movement toward organization until this weekend. But compared to Monday it certainly looks better I guess.

The thunderstorms (blue/green) are still few and the dry air (red/orange) still plentiful in and around the tropical wave in the Atlantic. (Weathernerds.org)

We should see a touch more in the way of storminess around this wave tomorrow and again on Thursday. Once we get to Friday or Saturday and this approaches the Bahamas, that’s when we could finally begin to see organization.

From that point, this wave’s future is cloudy. If you dig into the European ensemble’s 51 members, you can actually get a good picture of the possible outcomes. No ensemble spread is perfect, but this gives you a very high level understanding of the generic possibilities that exist with this wave. I’ve broken them into 3 camps below.

Three general possibilities with the upcoming tropical wave as it approaches the Bahamas and Florida. (Weathernerds.org)

On the right, we have the more aggressive solutions, which include the Euro operational and ICON models at present. These quickly strengthen the wave in the Bahamas such that it gets pulled north by a trough, generally remaining offshore, away from land and probably not a huge deal for anyone. This solution seems a bit overaggressive to me, so I’d say odds of this are relatively low. But it’s a possibility.

In the middle, you get the general consensus view of the Euro ensemble which is a storm that only slowly strengthens and organizes, still enough to turn it north, but not before it gets closer to Florida and the Bahamas and potentially close enough to eventually threaten the Carolinas. In this case, you still probably wouldn’t have a particularly strong storm, but you’d have something a little better organized than just a wave or depression. European A.I. modeling also supports a hybrid of this outcome and the previous one, closer to the coast but still offshore.

Then, on the left, you have a small cluster of a couple ensemble members that do not develop the wave at all and allow it to continue west or west-northwest into the eastern Gulf of Mexico. Eventually it would probably still turn north, but because the upper air pattern steering this thing would be fairly convoluted next week, any confidence in where that happens would be quite low. Still, this would likely only gradually organize in this scenario. The GFS operational model supports this outcome at present. Notably, that model also places a little mid-level system ahead of the tropical wave which would probably boost wind shear a bit and could help direct it north a little faster. Maybe. It’s complicated.

What does it all mean? They’re scenarios for a reason. Is one more likely than the other? Well, the middle one seems to have more support among modeling. The GFS is sometimes a bit wonky with these things, so I’m not sure I entirely buy the Gulf scenario. And it’s noteworthy that despite the expected slow organization of this system, between warm water and extremely low wind shear, conditions look pretty good for some strengthening near the Bahamas this weekend.

Wind shear is expected to be minimal over the tropical wave this weekend in the Bahamas, with most meaningful shear well east of it on Saturday. (Tropical Tidbits)

The meteorologist in me favors some combination of the Euro op’s quicker strengthening and the middle majority cluster right now. This would yield minimal direct impacts. But the public communicator in me must tell you that interests from Louisiana through the Carolinas should continue to monitor the progress of this tropical wave. Even if it’s not currently expected to be a significant storm, it will have a few things going for it as it organizes.

In summary:

  • Slow organization is expected this weekend near the Bahamas.
  • The track is uncertain, with some modeling quickly strengthening the wave and turning it out to sea, while other modeling brings it closer to Florida or the Carolinas and even a few not forming it at all, bringing it into the Gulf.
  • At the least, a tropical system should form, but where and when exactly remains to be seen.
  • Interests from Louisiana and the Carolinas should continue monitoring the progress of the wave in the coming days.

I will be out of pocket the next few days for some medical stuff, but Eric has you covered going into the weekend!

As we await the Atlantic’s awakening, a tropical wave without thunderstorms is what we’re watching

Headlines

  • The tropical wave in the Atlantic is unlikely to develop before at least Friday.
  • Development after Friday should be slow as it moves toward the Bahamas.
  • From there, numerous questions about which will determine if this system can up in the eastern Gulf or turn north off the Florida coast and where it goes from there.
  • Interests between eastern Louisiana and the Carolinas should check in on this again in a day or two.

A dry tropical wave for now

You hear the term “tropical wave” tossed around by meteorologists and others all hurricane season long. But what is it, exactly? By definition, a tropical wave is “an inverted trough (an elongated area of relatively low pressure) or cyclonic curvature maximum moving east to west across the tropics.” Nothing in that definition says thunderstorms or rain or anything like that. So, yes, in theory some tropical waves can be dry.

When we look at the central Atlantic today on the traditional satellite imagery, we don’t see a whole lot that’s perceptible. There’s a wave there, sure; you can see some cyclonic curvature. When you look at water vapor satellite imagery, you can see it even a bit better, but where you see browns, reds, and oranges, that indicates the presence of a lot of dry air. Use the slider below to toggle between a visible and water vapor image of the central Atlantic wave this afternoon.

Visible satellite imagery in black and white, and water vapor imagery with lots of red, orange, and brown indicating the presence of dry air in the central Atlantic. (weathernerds.org)

What does this tell us? It says that the tropical wave in the Atlantic is not going to develop anytime soon into a formal tropical entity. However, the presence of a tropical wave indicates that once it can shed some of this dry air, perhaps then we could see slow development. That may not be til Friday or the weekend.

Modeling continues to indicate the potential that the slow development noted above could occur as the wave comes west northwest toward the Bahamas or Turks and Caicos late this week or weekend. Clearly, it’s dealing with dry air and Saharan dust right now, but once it gets to the west, north of Puerto Rico by Thursday morning it will begin to likely increase moisture presence.

The overnight run of the European model shows this tropical wave adding moisture by the time we get to Thursday morning when its north of Puerto Rico. (Tropical Tidbits)

For the Lesser Antilles, Virgin Islands, and Puerto Rico, this system is unlikely to cause much heartburn. After Thursday, the system will continue to the west-northwest into the Bahamas. The overall atmospheric setup by Saturday as forecast by the European model is fairly complex, and as usual the ultimate path of this wave, depression, storm, whatever it is will be contingent on its strength as well as the exact location of these features. But at this point, I can count three big players: High pressure in the Atlantic, high pressure over Texas and the Plains, and a sharp trough of low pressure digging into the Ohio Valley and Appalachia.

Tropical wave over the Bahamas on Saturday will be steered west and northwest around high pressure in the Atlantic, tugged north by a sharp trough in the Eastern U.S., and likely slowed a bit by high pressure over Texas and the Plains. (Pivotal Weather)

The interplay that the Euro is “seeing” here right now appears to be that the wave slows on approach to Florida. It is being steered by the high to the east, but it slows as it runs into the influence of high pressure over Texas (the arrow pointing down) and also as it “feels” the trough over the Eastern U.S. trying to pull it north. It’s tough to speculate much on exactly what happens here. A weaker system would probably keep drifting west into the Gulf, whereas a stronger one would be more apt to turn northward in the Bahamas and possibly stay off the Florida coast. Most European ensemble members have supported this stronger idea, and you can see today’s 12z probabilities of a tropical depression from the ensemble favoring the “off the East Coast of Florida” idea.

The bulk of the European ensemble model guidance seems to favor a track of the tropical wave east of Florida, but sketchy beyond that as it comes north. (Weather Bell)

Beyond Florida, even in a faster turn scenario, all bets are off because the upper pattern may get a bit convoluted next week. An out to sea turn is not inevitable by any means in that scenario. Likewise, if a weaker storm sneaks under the trough and ends up in the eastern Gulf of Mexico, interests between Louisiana and the Florida Big Bend may be on notice too.

So, to summarize:

  • Tropical development is not expected before Thursday or Friday at the earliest.
  • Development is likely to be slow, though with exceptionally warm waters, any risk of development should be treated with respect.
  • The best guidance we use favors a slowing in the Bahamas, followed by a turn north near or off the coast of Florida.
  • However, given the very high uncertainty with regard to the speed of development and the precise location of steering features, any track forecast is low confidence and interests between Louisiana and the Carolinas should continue to monitor this system’s progress.

Elsewhere, no further tropical development is expected before mid to late next week, but we continue to look toward mid-August as the Atlantic inflection point, and activity may begin apace by then.