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Alright, on to the forecast. We’re still really struggling with the evolution of Tropical Storm Laura, and a large part of the uncertainty involves the movement of its center over, or just south of Cuba the next day or so. Laura does not have a particularly well defined center and its interaction with the island may cause the center to re-form. Any of these perturbations could have implications for the storm’s track downstream. This is one reason why the models are struggling with how to handle Laura’s ultimate path.

Another factor is Marco, which we still don’t think will have a sensible effect on weather in the Houston metro area. It seems likely that a “stronger” Marco, maintaining hurricane strength on Monday as it nears the Louisiana coast, would amplify a ridge of high pressure over the southeastern United States. This would push Laura more westward, toward Texas. However, a weaker Marco would probably allow for Laura to follow a more northwest track across the Gulf of Mexico, toward Louisiana. These, and more details, are the reasons why overall confidence in Laura’s track remains low. Because of this uncertainty I thought it might be helpful to outline three scenarios that I think are possible, along with their likelihood of happening.

Scenario One (30 percent)

In this scenario the ridge of high pressure remains strong, and drives Laura toward Matagorda Bay or Galveston Bay very late on Wednesday, or early Thursday. This would allow for maximum time over the warm Gulf of Mexico, and we could see Laura coming ashore as a powerful Category 2, 3, or even 4 hurricane. This obviously would be a very bad deal for Galveston, Houston, and points east in terms of storm surge and winds. This would necessitate coastal evacuations and lead to widespread power outages, among other problems. Rainfall would be less of a concern because we expect Laura to scoot through fairly rapidly.

Scenario Two (50 percent)

In this scenario, which is basically the “skinny black line” on the National Hurricane Center’s forecast, a reasonably strong Category 2 Hurricane comes ashore near the Texas-Louisiana border, or just east of there. In this scenario Houston sees some briefly gnarly winds, possibly gusting to hurricane force on the east side of the city. But beyond some relatively short-lived power outages, conditions should not be too extreme in the metro area. This would, of course, be a bad storm for Beaumont and southwestern Louisiana.

Scenario Three (20 percent)

In this case Laura comes off Cuba and begins moving almost due northwest, toward New Orleans and southeastern Louisiana by late Tuesday night or Wednesday morning. With less time over the Gulf this is a weaker storm. Houston would see almost no significant impacts from such a scenario, but it could cause significant surges or flooding in New Orleans, Mississippi and Alabama.

For the last two runs the deterministic output from the European model has more or less depicted this third scenario, along with the Canadian model. For this reason we can’t entirely discount it.

We hope to have better answers for you tomorrow on all of this, when we’re going to reach the point when final decisions on evacuation and other preparation activities will need to be made for the metro area.

Our next update will be no later than 8:30 am CT.

Good afternoon. There’s a lot of ground to cover in this post, but we wanted to start with this: Tropical Storm Laura remains the region’s primary threat, and you really need to be paying attention. Today, you should be thinking about what you would do if a strong hurricane were to make landfall over the Houston-Galveston metro area on late on Wednesday or Thursday. Let us be clear: We are not saying that is going to happen. But it is well within the realm of possibility, and you should be thinking about what actions you would take, so that you are ready put them into play when the forecast tightens up.

For this post, we will discuss the forecast for Marco, briefly, and Laura. And we will also try to answer some of your basic questions about impacts, evacuations, and more.

Hurricane Marco

Marco became a hurricane today, with 75 mph winds. The storm is moving north-northwest at 14 mph, and this should bring its center very near the Louisiana coast by Monday evening. We still aren’t sure whether this storm will move all the way onshore Louisiana, or remain near the shore, and then start to fall apart as it tracks westward along the Louisiana coast toward Texas. However, because most of the winds and heavy rainfall should remain to the east and north of the center, we do not anticipate severe conditions in the Houston region from Marco.

Probably the most significant thing about Marco now is that it seems plausible that the storm will slow down enough to potentially interact with Laura. This would not create some kind of “super storm” but may play some role in the track of Laura. Here’s one possibility:

A note on the 12Z ECMWF:

The rightward track of #Laura into SE Louisiana appears to be due to #Marco falling apart on the model, leaving its remnants in the gulf, which then pivot Laura to the right. Can’t guarantee this doesn’t happen, but so far, Marco is holding together. pic.twitter.com/3f9puGOiFQ

— Levi Cowan (@TropicalTidbits) August 23, 2020

Tropical Storm Laura

This system remains the key threat. Laura has moved across Hispaniola and maintained a reasonable structure. It will now spend Sunday night and most of Monday moving across Cuba before emerging into the Gulf of Mexico on Monday evening. Thereafter Laura will have 48 to 60 hours over warm waters, and an atmosphere favorable to intensification. It is reasonable to expect anything from a Category 1 to Category 4 hurricane to spin up on Tuesday or Wednesday over the open Gulf of Mexico. The situation is further complicated by Marco, which will not be all that far ahead of Laura, and the two systems may interact in ways that are difficult to predict even by the most sophisticated computer models in the world.

We simply have not received much clarity today in regard to a track forecast today. As a result, the National Hurricane Center’s 10am CT forecast track for Laura (shown below) is unlikely to shift much. Because of the broad uncertainty in the global model ensembles we are still reasonably looking at a track anywhere from Matagorda Bay, up through Houston, Beaumont, and across much of the Louisiana coast. For this reason, it’s probably not worth paying much attention to the “skinny black line” right now.

I think the hurricane center’s forecast is about as good as you could get considering all the uncertainties, but the bottom line is that this forecast can and probably will shift rapidly over the next day or so. Sorry, I know you want definitive answers. We don’t have them, and I wouldn’t trust anyone who says they do.

Alright, let’s get to some your most frequently asked questions below.

See full post

Good morning. We’ll run down both storms this morning, though at a high level our concern and interest is primarily focused on Laura at this time.

Marco

Tropical Storm Marco continues to try and become a hurricane this morning in the Gulf.

Marco is expected to continue lifting just west of due north today, and it is aiming for a landfall somewhere in eastern Louisiana before making a fairly hard left turn and basically falling apart over southern Louisiana.

We have seen a model or two bring the remnants more west along the coast, which would increase some storm chances for us and deliver some localized heavy rain on Tuesday, but right now those issues aren’t expected to be too serious.

Rainfall through Tuesday evening is expected to be mostly minor, with the best chance of something heavier along the immediate coast and lesser chances inland. The heaviest rain remains directed into eastern Louisiana.

The brief summary on Marco: Perhaps a small hurricane into southeast Louisiana before it dissipates while shuffling west across southern Louisiana, keeping most heavy rainfall well off to our east.

Laura

Tropical Storm Laura looks impressive this morning, mainly because it’s coming out of the typical nighttime peak in thunderstorms, and because it is doing this while interacting with Hispaniola, which often rips these things apart. Laura is the unfortunate one that actually gets by Hispaniola without a lot of trouble because it was disorganized to begin with.

If you want to provide some criticism of Laura, it’s that the storm is somewhat lopsided. But short of that it has a healthy core of storms, some developing outflow, and it is now exiting the highest hurdle it needed to survive, Hispaniola. Cuba comes next, but the bottom line here is that Laura has the skeleton it needs to become a healthy tropical system when it eventually finds a more hospitable environment for strengthening, likely Tuesday and Wednesday over the Gulf.

Laura’s track has shifted a little to the west since yesterday, but if you read between the lines in the National Hurricane Center’s discussion, there are likely to be more westward shifts to come.

The battle lines right now are between some of the typical global models we use for day to day forecasting, which take Laura farther west, more into Texas and the tropical models we use for situations like this, which have skewed a little farther east, more into western Louisiana. Laura is going to basically work around the periphery of high pressure off to our north and east. Typically, we would expect the global models to have a better handle on the steering situation, so there is a reason to put some trust in them over the hurricane ones for track right now. Once Laura works across Cuba and emerges into the Gulf tomorrow, we will have a better idea of whether Corpus, Houston/Galveston, Port Arthur, or central/eastern Louisiana are most at risk. Right now, all we can tell you is that trends since yesterday have only served to give us more pause about how close Laura may come to southeast Texas. We continue to urge you to pay close attention to this storm and make your preparations today in case they need to be implemented quickly tomorrow and Tuesday.

How strong will Laura be when it gets where it’s going? That’s a great question, and right now, the reliable model intensity guidance ranges from a low-end category 1 storm to a high-end category 3 storm. Given the history of the Gulf, the fact that it’s going to be in a fairly favorable environment for strengthening, and frankly how it has performed so far, we would likely lean toward the higher end of things with respect to intensity right now. The NHC forecast is calling for a category 2 hurricane at max, which is right in the middle of reliable guidance at this time. Hurricane intensity remains a very, very difficult thing to predict and though we are bullish on this storm’s strength right now, there are still risks equally spread that we may be too aggressive or not aggressive enough. More clarity on this should come tomorrow.

As far as rainfall goes? That is always a concern, but Laura is expected to keep moving and no models indicate a slowing or stalling. For all intents and purposes, we are viewing this a tropical threat (storm surge, wind) first and foremost and a rainfall flooding threat secondarily. Again, please stay aware and ready to act.

Eric will have our next update posted no later than 3 PM today.

Good evening. Eric’s update from this afternoon has most of the situation covered. I’m here to just refresh what’s going on, and I also want to talk a little bit about Laura.

Marco

As of this evening, Marco has moved past the Yucatan channel and into the southern Gulf of Mexico.

Marco still has maximum sustained winds of 65 mph and is still moving just slightly west of due north around 10 to 15 mph. I put a tropical storm icon on the satellite image above to indicate where Marco was located. It’s worth noting how lopsided Marco’s thunderstorms are, with basically everything north and east of the center. This has implications on the rainfall forecast for Marco after landfall.

There has been little to no change in terms of expected track with Marco relative to what we thought most of the day.

The National Hurricane Center’s forecast track takes Marco broadly toward eastern Louisiana. The storm is expected to become a hurricane, and it could maintain hurricane intensity up to landfall. Marco is compact, so any hurricane-force winds will only extend out a few miles from the center, mainly to the east of where it tracks.

As far as rainfall goes, we feel the bulk of it will end up well into Louisiana, Mississippi, and Alabama. The map of rainfall below (through Tuesday evening) will look a little odd because it’s a composite of various National Weather Service offices putting together their own forecasts, so some may be older or newer and not smoothed out. But it shows that the heaviest rain is expected to be closer to New Orleans than Houston.

If for some reason Marco starts to weaken tonight and ends up falling into disarray tomorrow, there is some chance it could drift back west of the forecast cone. We feel that possibility is highly unlikely however, and we are not going to worry about significant rainfall from Marco in our area. Marco should fall apart after coming onshore, drifting into northwest Louisiana, Arkansas, or northeast Texas as a remnant low with isolated pockets of heavy rainfall. We should be able to close the books on Marco by Tuesday night or Wednesday morning.

Laura

Let’s talk about Tropical Storm Laura. I’m going to be really honest about this one: We do not know who is most likely to see landfall from Laura when it gets to the Gulf. There is a plausible risk that it could go toward the Florida Panhandle, the central Gulf, Louisiana, southeast Texas, or even Matagorda, Corpus Christi, or Brownsville. So quite literally no one (save maybe the Florida Peninsula) can let their guard down with respect to Laura. We really want folks in Southeast Texas to be prepared in case this does come this way. There will likely be some element of “Well, y’all were fired up about Marco and look what it’s gonna do” from some people out there. With Marco, we laid out scenarios because we knew there was no answer key (til today). With Laura, we’re in that same scenario phase right now, and there is no clear model or forecast that is able to see Laura’s future clearly at this point.

We have laid out some of the factors involved with Laura’s interaction with Hispaniola through the day today. As of this evening, it appears Laura may be choosing to set itself up on the south side of Hispaniola.

This and other such interactions with Hispaniola and Cuba are critical to Laura’s future. They are also unpredictable. The current NHC forecast takes Laura generally off to the west or west-northwest.

But each shift like this, with a center possibly forming farther south keeps the storm disorganized and following the bottom or left side of the cone.

The rule of thumb: As with Marco, the weaker the storm is, the more likely it will come farther west before turning northward. So if Laura continues to struggle in the islands and remains weak, there’s a pretty good chance it will follow the bottom of the cone more than the top of it, which puts it farther south to start in the Gulf and gives it a much easier route to get as far west as Texas. A stronger storm will be more apt to lurch poleward and help limit the impact of high pressure over the Southeast, meaning it would likely turn well before it gets to Texas, either near Louisiana or east of there. As of Saturday evening the weaker option is winning out, which is why it’s important to continue to stay tuned in tomorrow and Monday. We are going to still have questions tomorrow, but I predict that by Monday, we’re going to have a good idea if this is an ominous threat to Texas or another miss to our east. Stay tuned.

Our next update will be posted no later than 9 AM on Sunday.