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:
A map of the 4am CT National Hurricane Center track for Marco with two 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:
4am CT Saturday forecast track for Hurricane Laura.
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.
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.
TD 14, which is nearly Marco, is approaching the Yucatan Peninsula. (NOAA)
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.
Hurricane intensity models are not particularly accurate, but there’s now a signal for intensification with Laura. (NCAR)
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.
European model ensemble forecasts for Laura’s location on Wednesday afternoon. (Weather Bell/SCW)
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.
Satellite map at 2:30pm CT on Friday. (NOAA/SCW)
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 #TD14pic.twitter.com/7EjFgSEn0y
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.
European model ensemble forecast for low locations on Monday evening. (Weather Bell)
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.
European model ensemble forecast for low locations on Wednesday morning. (Weather Bell)
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.
Good morning. We’ve got a full rundown on Tropical Depression 14 here today, and we’ll touch on Tropical Depression 13 as well. First, let’s get you through Sunday’s forecast.
Today through Sunday
The next three days have some similarities, and they should be mainly sunny with slight shower chances. The maximum coverage of showers may be today and particularly focused south and west of Houston. Saturday should see a bit less coverage but maybe more of a chance in other parts of the area. As the broader circulation from TD 14 nears on Sunday, we could see offshore winds develop, or at least more of a northeasterly component to them, which would probably shut down rain risks, especially south and east of Houston. Basically, you shouldn’t be expecting rain this weekend, but you shouldn’t be surprised if you see some either, especially Friday and Saturday.
Look for highs in the middle or upper-90s and lows generally in the 70s through Monday morning.
Monday and beyond (or the TD 14 discussion)
Alright, on to the main event. There is good news and bad news today on the Tropical Depression 14 front. The good news is that the storm is not any better organized this morning. The bad news is that because the storm is not any better organized this morning, we remain with more questions than answers.
Let’s start with a satellite loop of the system this morning.
A morning satellite loop of TD 14 shows a broad circulation which masks disorganization a bit, along with limited thunderstorms at the center. (Weathernerds.org)
Most folks will look at that loop and basically see a “swirl,” which is what you expect, even if thunderstorm coverage is a bit sparse. Well, the “swirl” is actually in the mid-levels of the atmosphere, not at the surface. At the surface, which matters greatly for the future of this thing, the National Hurricane Center (NHC) says that satellite passes and earlier reconnaissance aircraft data can’t really hone in on one defined center. Broadly speaking, this means TD 14 is disorganized this morning. That’s a good thing, of course, but it’s also a tricky one because without a defined starting point, you degrade the forecast of your ending point, thus increasing uncertainty in the forecast after a day or two.
Let’s look at the official NHC outlook as of 4 AM CT.
The official forecast brought TD 14 to hurricane strength in the Gulf at 10 PM last night, and it holds there today. Although the rough center line points right at the east side of Galveston Bay, it cannot be emphasized enough that there is a *wide* spread in possible options for a potential landfall point early next week and impacts in the Houston area will vary depending on where that is located. (NOAA)
The NHC track remains pointed right at Houston, and the wrinkle overnight was that it explicitly shows a hurricane in the Gulf as it approaches. How do you interpret the map above? While the forecast shows the track pointed at Houston, by day 5, the reality is that the center could be anywhere from near Matagorda Bay to perhaps near New Orleans. We always say “look at the cone, not a point on a map.” You really need to take that advice with this system, because there is an inordinate amount of uncertainty still today.
We know that TD 14 will emerge in the Gulf on Sunday. It will probably be a tropical storm at that point, but given the current situation off Honduras, that’s not a guarantee. It may be weaker. Over the Gulf, it should find some opportunity to strengthen a bit given very warm water temperatures (as noted yesterday afternoon).
But there are three significant hurdles that will impact how TD 14 may or may not strengthen and track.
1.) Wind shear: We know wind shear is expected to be low as it emerges in the Gulf. But per the NHC, it’s expected to increase in the northern Gulf. According to the SHIPS model, by late Monday or Tuesday, shear is around 15 to 25 knots. That’s not massive, but it’s enough to give a tropical system some problems. Alternatively, there is some risk that the wind shear will lessen or focus more inland. In that case, it may actually help TD 14 to strengthen a bit as it approaches land. This remains a difficult item to pin down, but the going theory is that TD 14 will have to fight some wind shear as it approaches Texas or Louisiana.
2.) Dry air: If you look at the GFS model on Monday evening at 7 PM, you’ll see TD 14 probably as a moderate tropical storm in the Gulf. If you look at relative humidity on the GFS model, you’ll see the storm is lopsided with the best moisture north and east of the center and a pretty significant amount of dry air south and west.
The GFS model forecast of relative humidity Monday evening shows a substantial amount of dry air close to the center, which could be a significant hurdle to strengthening. (Tropical Tidbits)
We have had some lower humidity than usual lately here, right? You’ve felt that. It’s still plenty hot, but dewpoints (at IAH) have been as low as 59 degrees in recent days! That’s really, really comfortable for Houston in summer. And rare too. That’s the first time that has occurred in August since 2015, and of the 7,180 August hours in the last 10 years, only 20 (0.25%) have had air that dry. Well, dry air is going to linger a bit longer, and it would seem that it will impact TD 14 in some capacity. Could TD 14 fight off dry air? Sure, but it better get its act together quickly if it can become robust enough a storm to accomplish that feat.
3.) Tropical Depression 13: One of the most common questions I’ve seen from people is some variation of “Could TD 14 merge with TD 13 as it comes into the Gulf and create a Category 6 megacane, which would be soooo 2020!?”
Here is the forecast track of TD 13, by the way:
Tropical Depression 13 is also expected to become a hurricane in the Gulf early next week, though uncertainty is equally high with this system. How TD 13 and TD 14 will impact each other’s track, if at all, is still unclear. (NOAA)
The answer to that one is complicated. For the sake of time and simplicity, I’ll be brief here. There is a meteorological process known as the Fujiwhara effect. You can read about it here. In a nutshell, if two tropical systems get within about 800 miles of each other, one can impact the circulation of the other. The diagram below shows this in the case of a much stronger storm. In this case replace Bopha with “TD 14” and Saomai with “TD 13:”
The Fujiwhara effect occurs when two cyclones (tropical systems) get close enough to each other to begin orbiting around one another. (NOAA via Wikipedia)
In an idealized Fujiwhara situation (unlikely), what would likely happen is that TD 13 would move into the Gulf from south of Florida, and as it comes north, TD 14 would probably slow down offshore of Texas or Louisiana, allowing 13 to go inland (likely to our east) and 14 to meander for a day or so offshore before going inland too. Now, to be clear, this is not the base case; it’s not what we expect. However, there could very well be some element of interaction that occurs between TD 14 and TD 13 because of their expected proximity to one another. That would depend on strength, orientation, etc. And since we don’t really know those things right now, it’s difficult to say how that interaction will (or will not) occur. We have also never seen that before in the Gulf. Like, ever. We have had simultaneous systems in the Gulf, but they’ve never been close enough to each other to risk that sort of interaction. In that respect, this is basically unprecedented and there will be unknowns.
So to summarize: It is likely that TD 14 will enter the Gulf Sunday and strengthen, possibly to a hurricane, tracking broadly toward Texas or Louisiana. The Houston area is very much in the cone, and we’d advise folks to continue to prepare as if a hurricane were coming. There are some hurdles for TD 14 and numerous things we do not yet know, however, and impacts could realistically range from hardly anything to a full-blown hurricane in our area. Eric and I will keep you posted through the weekend.
Quick note on rainfall: While we’re trying to figure out the tropical side of this thing, we are obviously sensitive to people’s concerns about rain, flooding, and a Harvey stall type scenario. Right now we do not expect a “stall” situation. No reliable model is hinting at that, and there’s nothing in the data right now that would argue that it’s a serious concern. The storm may slow down a little as it moves through, but slowing down is not equivalent to stalling and the differences are significant. We expect heavy rain, particularly if the storm comes in more to the southwest of Houston, and flooding is always possible in tropical systems. But we are not especially worried about any one possible outcome at this time. We will update you on the rainfall aspect more this weekend as things become clearer.
