Eric Berger

Good morning. We still are trying to parse details about tropical storms Marco and Laura, and we still don’t have solid information about what will happen. The bottom line is that, from Monday through Friday, the greater Houston region needs to be prepared for the potential of tropical weather—from heavy rainfall, to storm surge and strong winds. None of these are guaranteed, and there is no cause to evacuate now. But you do need to be prepared for rapidly changing forecasts.

Tropical Storm Marco

It appears that Marco has begun to intensify further overnight, and the storm has 50 mph sustained winds. If Marco continues to strengthen further this weekend, up to hurricane strength, it likely will take a more northerly track, toward southeastern Louisiana. However a weaker storm is more likely to move more westward, toward the central or upper Texas coast. Why? Because a stronger storm might have more impetus to barrel into building high pressure over the southeastern United States, whereas a weaker one would be more steerable to the west. Here’s a map showing the National Hurricane Center forecast track (in black) along with a couple of scenarios:

Scenario One, in which Marco never really makes a leftward turn while over the Gulf, would lead to limited impacts for the Houston metro area and the potential for heavy rainfall in southern Louisiana. Scenario Two will bring a decent amount of rainfall to the Houston region—2 to 6 inches, maybe?—along with elevated tides. At this point I would weight these two scenarios equally, in terms of probability.

Because there is so much uncertainty in the track and intensity, projecting other effects such as a storm surge is sort of fruitless. However, probably a worst case scenario is seas about six feet higher than normal along Galveston by late Monday. Peak winds, of tropical storm strength, would likely arrive here by late Monday. All of this is subject to change. All of this.

Tropical Storm Laura

Oh, we have many questions about Laura as well. At present the system is fairly disorganized, and contending with its “center” moving over Puerto Rico. What happens over the next 24 to 48 hours will probably have important implications how how menacing Laura ultimately becomes when it moves into the Gulf of Mexico. Here’s what I mean by that:

Along the current National Hurricane Center track (shown in black) Laura will traverse the mountainous terrain of Hispaniola, followed by the spine of Cuba. If the system is already a struggling tropical storm, it is difficult to see how a particularly organized system emerges into the Gulf of Mexico. Therefore the threat of Laura becoming a hurricane next week diminishes. However, if the storm can find a track just south of the islands, then it has a chance to escape the shredder and move into the Gulf later on Monday poised to intensify.

In terms of track, anything is still possible. Under the “no-shred” track above, Texas would probably be threatened by a hurricane next Wednesday or Thursday. Under the shred track, a weaker system probably comes toward Louisiana. But our confidence in a track remains very low.

We will next update the site by 3pm CT.

Good evening. Much as two tropical systems are swirling around in the Caribbean Sea this evening, forecasters are wallowing around in ignorance as we try to parse what will happen in the days to come as Tropical Depression 14, which is likely to soon be named Marco by the National Hurricane Center, and Tropical Storm Laura will do. (Update: The system was named Marco at 10pm CT). What does seem increasingly clear is that Laura may ultimately pose the bigger threat to interests along the Gulf of Mexico. Let’s start with the nearer storm.

TD 14

This system seems to becoming better organized, and it would not surprise me to see Marco forming tonight or Saturday morning as it nears the Yucatan Peninsula. This system is now likely to only graze the Yucatan as it moves northwest—which would therefore not substantially disrupt its organization—and this may allow for it to intensify through about Sunday, possibly reaching hurricane status over the Central Gulf of Mexico.

A stronger storm would likely to continue to push north or northwest, but it now seems that wind shear and other factors will work to weaken the storm. This probably will allow the system to be driven westward, into the central Texas coast. (We are still not particularly confident in a track, so stay tuned). So far the models are not overly excited about the rainfall potential of this depression as it moves westward, but obviously that is something we’ll have to keep tabs on.

Tropical Storm Laura

We have lots of questions about Laura, but we can be pretty confident that this system will enter the Gulf of Mexico late Sunday or Monday morning, having come near, or across Cuba. As it crosses the central Gulf of Mexico, Laura may find more favorable conditions to intensify. Several models now show it fairly quickly becoming a hurricane by Monday night or Tuesday over the Gulf’s warm waters.

Then, there is the question of track. Laura’s path will depend upon the extent of a ridge of high pressure building over the Southeastern United States. Some guidance depicts this ridge weak enough by Tuesday or Wednesday to allow Laura to bend northward toward Louisiana. However, the latest (18z) run of the European model finds nearly all of its ensemble members driving Laura westward, toward Texas, with some kind of land-falling system on Thursday. We will have to see whether this trend holds in subsequent runs, and whether other models follow the European on a more western track. We may know more tomorrow.

So where does this leave us on a Friday night? Besides at home and in need of a glass of wine, that is? We’re still left with the need to watch two tropical systems. For now, it appears that TD 14/Marco may be somewhat benign as it moves toward Texas early next week, but that is far from guaranteed. Interests in Texas and Louisiana should also keep more than a wary eye on Laura, which appears to have better potential to develop into a hurricane, and possibly a powerful one, next week.

Our next update will come on Saturday morning before 9 am CT.

Oh, my friends. We hear you. You’re tired of us saying, “There are a lot of uncertainties” when it comes to forecasting Tropical Depression #14 and Tropical Storm Laura. But the fact of the matter is that the latest model guidance is giving us less clarity, rather than more. I’m going to discuss the realm of possibilities, but first I want to start with this:

The overall probability of the Houston region, including Galveston, seeing significant, sustained effects from one or both of these storms remains fairly low. What do I mean by this? At present, the odds of Galveston seeing hurricane force winds in the next week is under 10 percent. The odds of the Houston region seeing 5 inches or more of rainfall, total, is probably less than 10 percent too. We’re not saying Houston will not experience severe weather in the next week. What we’re saying is that given the spread of possibilities, the overall chances are fairly low. It’s our job to let you know if that changes. And we will.

Now, onto the forecast. As the National Hurricane Center predicts, both TD 14 and Laura are likely to move into the Gulf of Mexico. The depression will come first, on Sunday, after moving across the Yucatan Peninsula. Laura will follow, likely traveling near or over Cuba. Because of these land interactions, both systems may only be weak tropical storms, or depressions, upon entering the Gulf of Mexico.

Normally we’d be scared pants-less when a low pressure system enters the Gulf, with its warm water, in August. But the combination of these land interactions, as well as less than ideal wind shear and dry air over the Gulf, suggest neither of these systems are locks to become hurricanes; and if they do, there is no signal whatsoever they will become major ones.

The big question is track, and the forecast models are all over the place. For TD 14, most of them have made significant shifts over the last 12 hours. Some, but not all, have shifted their landfall predictions from the Houston region, down the Texas coast, more toward Corpus Christi. (Update: The National Hurricane Center’s 4pm CT track forecast for TD 14 has shifted significantly south). Given this wide variability, we have very low confidence in TD 14’s track.

One thing to note is that, should TD 14 go more toward the central Texas coast rather than a more northward track, this may open up a lane for Laura to follow a more westerly track across the Gulf. Instead of moving into the Florida Panhandle, therefore, it may eventually threaten Louisiana or even Texas. The following plot of the UK model shows how this might work. If you look closely, you can see the Fujiwhara Effect at the end of the run, as TD 14 dips southwest, and TS Laura jumps north.

12z UKMET shows #Laura quite a bit south of previous runs and takes the weak system right into Hispaniola. Intensity forecast thereafter would be extremely difficult as it would rely on the organization of both #Laura and #TD14 pic.twitter.com/7EjFgSEn0y

— Steve Copertino (@TheSteveCop) August 21, 2020

We always talk about the ensemble models, so here’s the forecast for “low locations” from the European model that has just been run. The first image shows low locations on Monday night, when we can see a bunch of weak TD 14s or TS Marcos moving toward Texas. (Note, sea level pressure is 1013 millibars, so numbers from 1000 to 1005 represent very weak storms). The point here is that, even for a forecast less than four days from now, there is very little agreement on track.

Now let’s jump ahead to Wednesday morning. This is just 36 hours later in the forecast period, and we’re taking a look at the same plot. TD 14 has gone poof, and in its wake “Laura” has moved westward, toward Texas or Louisiana. Some of ensemble members have developed a slightly deeper and stronger system, but most are still tropical storms.

So yeah, it’s pretty much chaos. There are so many forecast challenges here it’s hard to know where to begin. Bottom line: We’ve got to watch out for TD 14, and potentially Laura as well. But as for specific threats, we’re a ways from saying anything intelligible. We’ll continue to track the madness, that we can promise.