We are taking TS Laura very seriously, but its destiny is far from certain

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.

When will we know what Laura is going to do?

Assuming we are between three and four days from a landfall somewhere along the Texas or Louisiana coasts with Laura, historical averages say we should be getting closer to having an accurate forecast. For the National Hurricane Center, the average track position error at 3.5 days before landfall is about 120 miles, which is a little bit greater than the distance between downtown Houston and the Texas-Louisiana border on Interstate 10. In terms of intensity, you would expect the National Hurricane Center forecast for sustained to be accurate to within about 20 mph, plus or minus.

However, we have fairly low confidence in both of these forecasts. First of all, the track forecast is problematic because we have respectable model guidance producing a final landfall location for Laura anywhere from north of Corpus Christi all the way through most of Louisiana, almost all the way to New Orleans. Second, we don’t really know how much (if at all) Cuba will weaken Laura, and then it is just hard to predict when and how much the storm will rapidly intensify over the Gulf of Mexico.

With all that said, I expect confidence in our forecasts to increase steadily over the next 24 hours.

What are the biggest threats from Laura?

As you plan your final hurricane preparations please do not use Hurricane Harvey as a template. Laura is expected to move fairly quickly after the storm makes landfall. This reduces the threat of inland rainfall. However, Laura does have the potential to produce strong-to-devastating winds as well as produce a storm surge, driving water 10 to 15 feet above normal tide levels. The extent of winds and surge will not be determined until we have a better handle on the storm’s forecast.

Should I evacuate?

This is a pertinent question to be asking right now, but we still don’t know enough about the threat to provide a definitive answer. The age-old advice during a hurricane is that you evacuate from a storm surge, but take shelter in your home from wind. Effectively, for the Houston area, this means the closer you are to the coast, the higher your risk for surge. These “zip zone” maps (click here to download medium, and large-sized maps) show the risk in this area by zip codes.

There are other considerations. In the event of a bad windstorm we might expect power outages to last for one to two weeks at some locations. If there is a medical reason why this is unacceptable for you, factor that in. There is also the background complication that we are living through a pandemic, and we offered some suggestions on that earlier this summer with regard to evacuations.  City and county officials are responsible for calling for evacuations, and we recommend heeding their warnings.

The bottom line on evacuations is that now is not necessarily the time to act, it is the time to plan for under what circumstances you would evacuate, and where you would go.

When would Houston start to see effects from Laura?

Most likely we would start to see an increase in winds from Laura sometime on Wednesday, probably during the evening hours. But it is really difficult to say much beyond this without better knowledge of Laura’s track and intensity

Will I lose power?

Again, this is highly dependent upon the storm’s track and intensity. But if you lost power during Hurricane Ike, in 2008, there’s a good chance a Laura landfall near Houston would have similar effects. Hurricane Harvey is not a good analog in terms of power loss. Most of the region retained power because winds were light.

Our next update will be posted no later than 9pm CT.