Month: August 2020

POSTED AT 8:30 PM CT TUESDAY: Good evening, and we come to you with some positive news for once, at least as it relates to Houston.

In a nutshell, we have a growing consensus for Laura to make landfall far enough east of Houston to likely spare us really bad impacts. Just to be clear, you should still be heeding the advice of local officials, and you should remain vigilant in case something changes at the last minute. But from all we’ve seen today, we feel good about our position here in Houston.

The biggest challenge for us in forecasting Laura’s potential impact in Houston has been dealing with the European model and, in particular its ensembles. The overnight run of the Euro (ECMWF) and its ensembles continued stubbornly pushing Laura’s track west to the point that I’ll be honest: I woke up by chance at 3 AM, decided like a good meteorologist and foolish human being to look at my phone to see how the model finished, and basically woke my wife up by belching out an expletive. It had precedent. The Euro had been consistently on the left side of guidance (farther south), and every updated forecast point was coming in south of even that guidance.

 

And since the Euro is generally considered our best performing model, you have to at least grant that some credibility. All along, the models we use specifically for tropical storms and hurricanes have been consistently focused on the Texas/Louisiana border or into southwest Louisiana. Well, wouldn’t you know it but now those verification points above are coming in north of forecast.

Getting questions about track trends/wobbles re: #Laura and #HOUwx implications.

Hurricanes wobble all the time, as you can see by plotting the estimated center each hour from 1-7 PM CDT.

That said, the center is consistently a hair N of EPS forecasts. pic.twitter.com/kzuwTaU11I

— Jack Sillin (@JackSillin) August 26, 2020

In fact, the 18z European operational model takes Laura just over the Louisiana side of the border, in line with tropical models

What does this mean? It means the folks at the National Hurricane Center are pretty <redacted> good at what they do. The latest forecast track for Laura takes the center ashore near the Texas/Louisiana border tomorrow night as a major hurricane.

For us in Houston this explicitly would mean primarily tropical storm impacts instead of hurricane impacts, as tropical storm force winds do extend out over 175 miles east of the center (it will be less to the west). At the coast, that could be different, with slightly stronger wind (perhaps close to hurricane force) and a storm surge of 3 to 5 feet in Galveston to upwards of 6 to 9 feet across the Bolivar Peninsula to High Island.

The caveat to all this? Hurricanes do tend to wobble sometimes. In most cases, the wobbles average themselves out and cancel out. But at times some more distinctive wobbles could yield a track farther southwest or northeast. We will monitor that tonight and tomorrow to see if there are any trends that stand out. This is why it’s important to remain vigilant. We look fortunate now in Houston, but things can sometimes change quickly.

In case you wanted a look at Laura on satellite this evening, here you go.

This is a much healthier looking storm than even 6 hours ago, so we’re likely heading for some impressive strengthening tonight.

While we’re very positive on Houston at the moment, I personally can’t help but feel some sense of despair for folks in the Golden Triangle and southwest Louisiana who have been through the ringer over the last 15 years between Rita, Ike, Harvey, Imelda, and now Laura. Unfortunately, Laura’s storm surge impact into extreme east Texas and southwest Louisiana looks very serious.

Here's the latest ADCIRC estimate of water inundation depth as of 5PM ET (Aug 25). Shows 10+ feet near the landfall spot & feet of water nearing Lake Charles. This could be one of the worst U.S. surge events in recent memory. FYI: 90% of hurricane deaths are due to water. #Laura pic.twitter.com/15wgIOTP4x

— Steve Bowen (@SteveBowenWx) August 26, 2020

While the Houston area gets a lot of air time because we’re the 4th largest city in the country, the folks in Beaumont, Port Arthur, and Lake Charles are sometimes overlooked. So if Laura does indeed spare Houston, we hope we can pay it forward in some way to our neighbors to the east.

Eric will have our next post up no later than 7:30 AM CT Wednesday.

POSTED AT 2:25 PM CT TUESDAY: Ok, everybody. We understand. You’re sick of reading about Hurricane Laura, and trust us, we’re tired of writing about it. (We first mentioned the possibility of Marco and Laura way back on August 16, which seems like several lifetimes ago). So this afternoon, if I can offer one piece of good news, it’s this: Forecast models are starting to cluster a bit more, so confidence in the track is increasing. By tomorrow morning we should probably have it pretty well nailed down. And then by Thursday afternoon it should be all over as Laura pulls away. So in two days we’ll either be starting the clean-up process, or looking to help our friends to the east, in the Beaumont area and Southwestern Louisiana. The unnerving uncertainty, at least, will end.

Track

We’ve had a new suite of model guidance come in today, and the big news is that the operational run of the European model has shifted east a bit, bringing it closer in line with the GFS global model, as well as the National Hurricane Center forecast. This is the kind of clustering we would hope to see at this point to increase confidence in a track forecast. Under this scenario, Laura would make landfall near the Texas-Louisiana border, or 10-20 miles west of there, late Wednesday or early Thursday. Along this track, Houston would very narrowly escape the worst of Laura’s winds, waves, and rains—these would impact Beaumont, Port Arthur, and Southwestern Louisiana. This means the most likely scenario is now an event similar to Hurricane Rita, in 2005.

However, and this is very important, this track is far from dialed in. There are still some models that dissent from this scenario, and there remains the potential for Laura to wobble as it moves across the Gulf of Mexico. I think we can safely rule out a landfall near Freeport or the San Luis Pass, which would be the absolute worst case scenario for Houston and Galveston. However, a landfall anywhere from the East End of Galveston Island to the Texas-Louisiana border remains in play. Believe me, I would love nothing more than to close the book on Laura, but we are just not there yet. Maybe by tomorrow morning, maybe not. This is a nail-biter for the Houston and Galveston areas. Please heed mandatory evacuation orders and continue preparations.

Intensity

This remains a very difficult forecast. We have seen little strengthening of Laura through the early afternoon hours, but that’s to be expected. The National Hurricane Center anticipates the storm will undergo most intensification between this evening and Thursday morning. They’re predicting Laura will come ashore as Category 3 hurricane, and that seems reasonable, plus or minus a Category. Strong winds will likely begin reaching the coast by around 6pm CT Wednesday.

Laura should be a large and powerful hurricane at landfall, and it will cause widespread damage. Given the potential for further, modest swings in the track, we’re asking you to hang with us for another day or so. We’ve just really got to keep tabs on this one, Houston.

Matt will have our next update at 8:30 pm CT, or a bit earlier.

POSTED AT 10:30 AM CT TUESDAY: In its 10 am update, the National Hurricane Center has modified its forecast track for Hurricane Laura, and has shifted the storm’s landfall slightly closer to the Houston-Galveston metro area. We remain within the cone of uncertainty, and need to be prepared for the possibility of additional westward shifts in the track this afternoon. We are still in line for anything from a glancing blow to direct major hurricane landfall. Bottom line: This is time for preparedness and action, not panic. This is a very serious situation that all residents should be following closely.

Local effects

The location and intensity will play a major role in the effects Houston sees. Even a track movement of 20 or 30 miles can make a big difference in the effects we see (I discussed this in a post earlier today). Due to the uncertainty, for the discussion below we will provide a forecast for Laura’s effects in Houston based on the current National Hurricane Center track, and those for a reasonable worst-case scenario should Laura track further west and make landfall along Galveston Island.

Winds

At this time winds are our greatest concern. They are likely to be strongest near the storm’s center of circulation, and to its immediate east. The most recent run of the HWRF model depicts a probable wind scenario for Laura should the storm make landfall near the Texas-Louisiana border. As you can see, winds over the Houston area would generally remain near or below Tropical Storm intensity, especially west of Interstate 45.

If the storm makes landfall over Galveston Island, the core of strongest winds would go inland along Interstate 45. This would provide widespread residential damage and knock power out for weeks, for many.

Storm Surge

This is our next biggest concern for the metro area. Laura is smaller than Hurricane Ike, and probably will come in east of its landfall location, so a surge along Galveston Island, and along the bay, probably will be less than the region experienced in 2008 under most scenarios. Here is the hurricane center forecast for surge along the current forecast track:

If the storm tracks further west, it looks like a storm surge of 6 to 10 feet along Galveston and Galveston Bay would be a reasonable estimate.

Inland rainfall

This is a much lower priority due to Laura’s forward speed. As I hope you understand by now, this will not be another Hurricane Harvey. In terms of rainfall, we can probably expect 1 to 3 inches with the current track. Should Laura make landfall further down the coast, we can probably anticipate widespread totals of 6 to 10 inches, with higher isolated amounts.

Should you evacuate?

If you live along the immediate coast and are under a mandatory evacuation order, as Galveston Island is, the answer is yes. You should heed local officials who are making difficult calls.

After that, it’s really a personal decision for you and your family. How high is your risk tolerance? Are you willing to spend several very intense, and yes, scary hours in the middle of a hurricane? Do you have a safe place in your home to shelter within? Can you survive without power for several days? 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.

All evacuations should be completed by Wednesday, at noon. This is about the earliest reasonable times that winds would arrive in the Houston metro area.

We will update again by 2:30pm CT.

POSTED AT 6:40 AM CT TUESDAY: Unfortunately we don’t have great news to report this morning. The overnight trends with Laura are not good and everyone in the greater Houston and Galveston metro area needs to be making final preparations for a potential hurricane landfall. After moving off Cuba overnight, the storm made a slight westward jog, and this has had the effect of nudging several model runs west. This is likely to bring the center of the storm closer to Houston, and this is not good.

Track forecast

It now seems highly likely that Laura will make landfall somewhere between Freeport and Southwestern Louisiana—with the most probable location between Galveston Bay and the Texas-Louisiana border on Wednesday night shortly before midnight, or early Thursday morning. This forecast is a worst-case scenario for the Beaumont area, and a mandatory evacuation order is in effect for Jefferson County. The situation is not much better for the Houston area. Please note: The official forecast track shown below will likely be adjusted westward, toward Houston, at 10am CT this morning.

Now that Laura is over the open Gulf of Mexico and strengthening, confidence in the track should increase later today. Further changes will certainly be possible due to wobbles or other factors in the storm’s movement, however.

It is very important to really understand where this storm will go. Hurricanes have effects over a large area, but their strongest winds are generally clustered tightly around the core, or to its northeast. And storm surge is significantly greater to the right of a land-falling center. For this reason, track really matters (see section below on Hurricane Ike).

Intensity forecast

As ever, this remains problematic. The storm will now spend nearly two days over the warm waters of the Gulf of Mexico. Laura is actually over the most explosively warm waters right now. One of the best measures of the potential for intensification is “Tropical Cyclone Heat Potential,” and anything above a value of 80 is considered fertile for rapid strengthening. Here is the most recent map of heat potential, with Laura’s track overlaid.

Unfortunately, Laura is going to miss the less explosive “blue” water to its north. (This feature actually predates Tropical Storm Marco). However, it also will not have the very deep pool of warm water that some past hurricanes have had to draw upon. A final consideration is that due to Laura’s relatively fast forward motion, presently 17 miles to the west-northwest, the storm will not be as effected by heat potential as a more slow moving system. Bottom line: The Gulf is conducive to strengthening, but it is not as quite explosive as it could be.

Another factor in intensity is wind shear, and unfortunately that is expected to remain on the low side until Laura nears shore. Add this all up, and the National Hurricane Center now forecasts Laura to come ashore with 115-mph winds, as a Category 3 hurricane. This is a pretty reasonable estimate, but it is only that. Laura could well be stronger, or a bit weaker.

Hurricane Ike

If you’re looking for an analog for what to expect in Houston from Laura, probably the best recent storm is Hurricane Ike. This storm made landfall on the east end of Galveston Island in September, 2008, and followed a track up the western side of Galveston Bay. It had maximum sustained winds of 110 mph.

It is not a perfect comparison, as Laura probably will be more intense as it comes ashore with more damaging winds; and Ike was a larger storm so it produced a significantly more powerful storm surge we will probably see with Laura. But the reason I want to show the graphic below is that, very roughly, it provides a way to set expectations for Houston and Galveston.

If Laura’s track ultimately is east of this line—which for now seems likely, but is not guaranteed—effects in Houston ultimately will probably be less significant than Ike. If the storm tracks along, or west of this line, winds and potentially even surge in Houston will be worse. It might not be too strong to say “unimaginably worse,” because Houston has not really experienced an intense wind storm since Hurricane Carla in 1961. This would require sheltering in a safe place. If you’re looking for a worst case scenario for Houston, it would be a landfall near Freeport or San Luis Pass.

For those who did not live here at the time, Hurricane Ike caused $30 billion in damages in Texas, mostly due to storm surge. This report provides a good analysis of the storm’s winds. It can be summarized as: one-to-two weeks of power outages, lots of downed trees, and roof damages. So like we said, a storm east of the line above would probably result in less of that. West, and all bets are off.

We will update again by 10:30 am CT. By then we probably can begin to talk realistically about what most of Houston will experience in terms of winds, waves, and rain; and when to expect it.