Eric Berger

(9:45 CT Monday Update): We will see PTC classified at the top of the hour. We will have a post before 11 AM CT.

(2 PM CT Update): The disturbance we are going to be tracking is now known as Invest 97L, and there will likely be a bunch of additional data available to us later today.

Headlines

• Confidence is increasing in the formation of a tropical system in the southeastern Gulf of Mexico this week
• Current conditions in the eastern Gulf of Mexico support the possible development of a powerful hurricane by Thursday or Friday
• While confidence in a forecast track is rising, residents of the Gulf coast from southeastern Louisiana all the way to Fort Meyers, Florida should pay heed
• Given the uncertainty of timing, Florida could start to see impacts in as few as four days from this system

System status

We’ve been talking about the potential for a tropical storm to form in the northwest Caribbean Sea for days, and for the time being there’s still not much to look at on satellite. We’re still seeing disorganized showers and thunderstorms in the western Caribbean Sea, in the vicinity of Nicaragua. However, what has changed is that the models we trust the most are now pointing to a more or less similar outcome over the coming week. That is, we expect a tropical system to develop, and then move into the southeastern Gulf of Mexico by around Wednesday. And after that? Well, that’s what the rest of this post will discuss.

Track of this storm

All of our major model guidance now suggests that a tropical system will start to become better organized by Tuesday or Wednesday, with a center of low pressure forming near Cancun, Mexico, or the western tip of the island of Cuba. There is still some discrepancy in the timing and intensity, but we can have pretty high confidence in this outcome.

The timing of this does matter, as a more rapidly developing storm would likely ultimately track further to the east, which is to say toward the west coast of Florida; and a slower developing system has a better chance of going more due north, ultimately making landfall somewhere between the Louisiana delta and Florida panhandle.

If we look at the 06z run of the European ensemble model above, we can get a sense of the most likely locations where the center of this storm could go. Note that this forecast indicates a potential landfall on Friday, but depending on the forward speed of this system, we cannot rule out a tropical storm or hurricane reaching the coast as early as Thursday.

The other global model ensembles are not dissimilar to the European model shown above. Our best high resolution, operational models are starting to coalesce around a landfall somewhere between Destin, Florida, and Cedar Key, Florida. However given that a center of circulation has not formed, overall confidence in where precisely this storm will go about five days from now is necessarily low.

The most important message I want to leave readers with today is that residents of the Gulf coast from southeastern Louisiana all the way to Fort Meyers, Florida, should be keeping tabs on this system over the next couple of days.

As a space guy, I’m also watching closely for impacts to NASA’s Crew-9 launch from Cape Canaveral, Florida, presently scheduled for Thursday afternoon.

What about its intensity?

Forecasting the intensity of a tropical system, of course, often more dicey than a track forecast. Because the storm has not been designated an “area of investigation,” or Invest, we do not have access to a suite of tropical-based models that are used to forecast intensity. So far the global models have been all over the place, ranging from tropical storms to a fairly powerful hurricane. However, these models typically do a poor job with intensity.

From a big picture standpoint, what concerns us here at The Eyewall is that there are no obvious things to slow this storm down. If it does start to develop a low pressure center by around Tuesday or Wednesday, then it would have two full days over the Eastern Gulf of Mexico to intensify, and if conditions are right that offers plenty of time to blow up into a powerful hurricane.

The sea surface temperatures in the vicinity of where this system should track are incredibly warm. This is partly because it is late September, and partly because of the background signal of climate change that has pushed oceanic temperatures, generally, to record highs. In addition, when we look at conditions beneath the surface, oceanic heat content is very high. This means that, as a storm churns north across the Gulf of Mexico, it will not necessarily be bringing cooler water to the surface. Deep oceanic heat is often a precursor to rapid intensification.

Wind shear has been fairly high over the eastern Gulf of Mexico over the last several days, but this shear level is now trending lower. And if this pattern continues as expected, the environment for storm formation and strengthening should be neutral in terms of wind shear, if not even favorable. So we cannot really count on shear for assistance.

Perhaps dry air, particularly on the western flank of the storm, may play a role in inhibiting some development. However, when we stack up the extremely warm surface temperatures in the eastern Gulf of Mexico, and the shear environment, I have to believe that a hurricane is likely to form before landfall late this week. This is another reason for residents of the northern Gulf of Mexico and Florida to keep a close tab on things.

Some final thoughts

It’s still too early to say too much about impacts from this system. However, storm surge, wind damage, and inland flooding from rainfall are all on the table. Where these occur, of course, remains highly dependent upon the track.

Given the current trends, it is unlikely that we see a named storm develop before Tuesday or Wednesday. Waiting for a named storm, therefore, will not leave much time for preparation. Again, this is why we’re advising residents to keep a close eye on things over the next couple of days.

Headlines

• As of 7 pm CT, Francine has become a hurricane in the Gulf of Mexico with 75 mph sustained winds
• The storm will likely make landfall as a Category 1 or Category 2 hurricane on Wednesday afternoon near Morgan City or Houma
• The center of the storm will likely pass between Baton Rouge and New Orleans, bringing its strongest core of winds there and to the east
• New Orleans should fall on the right side of the storm, facing the most significant storm surge from Francine

Francine status

At 7 pm CT Tuesday evening, Francine was moving to the northeast at 10 mph. The hurricane has seen both its winds increase as well as its central pressure fall to 982 millibars. The later pressure fall is an indication that further strengthening is possible during the next 16 to 20 hours before Francine reaches the Louisiana coastline.

Confidence is high in the track forecast for Francine, with all of our best available models in agreement that the center will come ashore and then likely split the difference between Baton Rouge and New Orleans. While some minor track changes are possible, at this late hour they are likely to be modest. In terms of intensity, most of our guidance points to a Category 1 or 2 hurricane. However, our confidence in intensity at landfall is lower than the track forecast.

Given all of this, a hurricane warning is in effect for the Louisiana coast from Cameron eastward to Grand Isle. A hurricane watch is in effect for Lake Maurepas and Lake Pontchartrain, including the New Orleans metro area.

Francine impacts

The hurricane will bring all three major components of storm damage to southern Louisiana: high winds, inland rainfall, and storm surge. Staring with winds, it is likely that the core of strongest winds will now pass near, or even directly over the New Orleans area. This map of maximum wind gusts from this evening’s run of the European model gives an indication of where the strongest winds will occur.

In terms of rainfall, the heavier rains may fall a bit west of New Orleans, which would help with flooding issues in the city. Nevertheless, predicting precisely where the most intense rainfall will occur during a hurricane is an impossible task. The only good news I can offer is that Francine will have a healthy forward motion, and will be exiting the area to the north by late Wednesday night. This should help provide an upper limit on inland rainfall and associated flooding.

The following storm surge map is based on the National Hurricane Center’s forecast, issued at 4 pm CT on Monday. I would expect the surge levels for the Mouth of the Mississippi River and Lake Maurepas and Lake Pontchartrain to increase a bit in subsequent forecasts. However, these do not appear to be surge levels that will promote catastrophic flooding in the New Orleans metro area.

In summary, this certainly will not be the worst hurricane to ever strike the Louisiana coast. However, even Category 1 storms are unpleasant. Wednesday and Wednesday night will be a time to take shelter in the region.

We will have a comprehensive update on Hurricane Francine early Wednesday morning.

Headlines

• All eyes are on a system in the tropical Atlantic
• It is not clear whether this system will ultimately develop as it tracks toward the Caribbean Sea
• Elsewhere the tropics are quiet, but there are hints this could change in a week or so

Focusing today on the Central Atlantic

The most likely candidate for the Atlantic basin’s next named storm—it would be Francine—remains a tropical wave over the Central Atlantic Ocean. As of Thursday afternoon, the National Hurricane Center continues to pin a 40 percent chance on this system becoming a tropical depression or storm in the next seven days.

Honestly, we have a lot more questions about this system than answers. And if you’re wondering what impacts this will have after it gets into the Caribbean Sea, or downrange to the United States or Mexico, the short answer is stay tuned. It could never get off the ground, or it could eventually become a tropical system that moves into the Gulf of Mexico. We don’t know, and that’s the bottom line.

So the rest of this update will focus on what we do know. As it presently exists the system is a disorganized mass of showers and thunderstorms. However, over the next several days, it should find supportive atmospheric conditions as it approaches the Caribbean Sea. Once it passes the Leeward Islands, some development is possible. It probably would be slow.

Will it develop?

So will it? I like the National Hurricane Center odds of about 40 percent. Not all of our operational models bring the system to depression or tropical storm strength over the next week, and although there is some support in the ensembles, it is not super robust. For example, here is what the 12z ensemble forecast of the European model looks like from today. Some of the members show development, but this is far from a consensus.

If we look at the GFS ensemble forecast for the same time period, there is even less support for anything beyond a very weak tropical storm.

So why are we paying so much attention to this system? It is because we’re now at the end of August, with September on the horizon; and the Atlantic seas are blazing hot. If a storm like this gets going, it will be difficult to stop, in terms of intensification. So yes, any tropical system moving toward the Caribbean Sea is going to catch our eye at this time of year. Especially when there’s not much else happening in the tropics unless we really squint.

In this case, we just need to watch and see what happens over the next couple of days. This system could develop and become Francine, or it could fizzle out. If it does form, it might eventually move toward the Gulf of Mexico, or turn northward before hand. We just don’t know, and won’t know, for awhile now.

There continues to be hints in the models that, regardless of what happens with this system, the tropics are going to start lighting up quite a bit in about a week or so. For now, we’re going to have to sit back and see what happens.

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.

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.

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.

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.

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.