Month: September 2020

2pm CT Saturday: Tropical Storm Beta made its expected turn west earlier today and is now crawling toward the Texas coast at 2 mph, according to the National Hurricane Center. Its maximum sustained winds are 60 mph. Our overall forecast for the Houston metro area has not changed at this time: We still anticipate Stage 2 flood conditions south of Interstate 10, and Stage 1 for areas north of Interstate 10. Bottom line: We have not seen anything today that makes us any more concerned.

I want to start with a satellite image of the Gulf of Mexico this afternoon that illustrates water vapor—a good proxy for convection. When you look at this image there are a couple of important things to notice. One, the precipitation associated with Beta is strongest near its core and well to its east. Second, the reddish hues across Texas indicate dry air. Some of this dry air is wrapping into the circulation of Beta, which is helping to hamper its intensification. Finally, it’s clear that until Beta moves further west the bulk of its precipitation is going to fall over the Gulf, or southern Louisiana.

In this afternoon post I want to discuss the timing of what to expect after today, and when. The usual caveats apply, this is a dynamic weather system, so forecasts will change. But this is our best guess as of 1:30pm Saturday afternoon.

Sunday

Beginning fairly early on Sunday we could see some outer rain bands from Beta moving into the Texas coast. Most likely these will be light to moderate, at least during the daytime hours. Coastal areas may see upwards of 1 to 2 inches of rain, but inland areas will likely see less. All in all, this should not be too disruptive. Coastal areas may see tides 3 to 4 feet above high tide levels, particularly on Sunday evening, and Monday morning. Tropical Storm force winds may arrive along the coast, from Matagorda Bay to Galveston by Sunday evening or during the overnight hours.

Monday

Most of the best available model guidance suggests we will see similar conditions on Monday as the storm’s center nears the Texas coastline, probably near Matagorda Bay. I should note that overall confidence in this track remains somewhat low, and that a northward jog in the track would bring more serious winds and surge into Galveston Bay. However, we don’t expect that right now. Beta will likely will be a high-end tropical storm or a low-end Category 1 hurricane at this time. Winds will probably increase across the Houston area, although I’m not sure they will reach Tropical Storm-force.

Tuesday and Wednesday

These are the days when we can probably expect the heaviest rainfall, although amounts are still to be determined. This is the period when we expect Beta (or the remains of Beta) to begin lifting to the north and then northeast, perhaps bringing its circulation near the Houston metro area. By Thursday we should see improving conditions across Texas.

So really, how much rain?

If you remember the satellite image at the top of this post, almost all of the convection and strong storms lay to the east of the storm’s center. We think that the most likely scenario is that this pattern continues during the coming week, and we end up with a situation where most of the Texas coast north of Corpus Christi sees 4 to 12 inches of rain over the next week, with lesser amounts inland. This is very general, ballpark value. The key thing to remember is that this scenario would not lead to widespread, catastrophic flooding.

However, we cannot discount the possibility of Beta really getting its act together over the next day or two, and becoming a prodigious rainmaker over Texas. In this reasonable worst-case scenario, areas from Matagorda Bay to Galveston to Beaumont are at risk for 20 inches or more of rain, with 10-plus inches for parts of Houston. That is the high-end risk. But again we do not favor that scenario right now; and if our view changes we will let you know post-haste with a hasty post.

Our next update will come no later than 8pm CT this evening.

Good Saturday morning! We’ll be with you here all weekend on Space City Weather to track the progress of Tropical Storm Beta, and its effects on Houston, Texas, and Louisiana. Broadly speaking our forecast has not changed a whole lot. For now, on our Flood Scale, we are still calling for a Stage 2 flood for areas south of Interstate 10, and a Stage 1 flood for areas north of Interstate 10.

With this system we are most concerned about the potential for heavy rainfall next week, and then rising seas along the coast due to a prolonged period of winds from the east-northeast. Probably the most important thing we can tell you this morning is that there is still a lot of uncertainty in the track forecast for Beta, and where the storm’s heaviest rains will fall. We suspect this storm will have some surprises in store.

Track

As anticipated, Tropical Storm Beta has moved north overnight, and now lies nearly 300 miles due east of the mouth of the Rio Grande River. Pretty soon we expect the storm will run into a ridge of high pressure and take a westward turn, gradually moving toward Texas. We are reasonably confident that the storm will then approach the Texas coast somewhere between Corpus Christi and Matagorda Bay on Monday, potentially as a strong tropical storm or a Category 1 hurricane. Through Monday this track should keep most of the heaviest rainfall just along, or off the coast. So far, so good.

The problem is that, after this point, we’re not really sure what will happen. The National Hurricane Center’s official track brings the storm to the northeast on Tuesday, along the Texas coast, as weakening high pressure allows for an exit. However, it also seems possible the storm could move 50, or even 100 miles inland before making this turn, or remain 100 miles offshore. I know what you’re thinking, slow-moving storm, landfall near Corpus, moving inland—Eric, that sure sounds a lot like Hurricane Harvey. Well, I’ll agree, but there are some key differences here. Most significantly, Beta lacks Harvey’s organization, and will be fighting dry air as it moves toward Texas. This may help to limit inland rainfall. Moreover, the storm really should move away by Tuesday or Wednesday, so we are probably not looking at a four- or five-day heavy rainfall event.

Rainfall

So how much is it going to rain next week? The global models have trended slightly downward in terms of rainfall accumulation during recent runs, and I think a good general expectation is 2 to 8 inches across much of the Houston metro area, with coastal areas potentially seeing 6 to 12 inches between later Sunday and Thursday. That much rain over four days is manageable, so our concerns are very high rainfall rates—which tropical storms produce—and higher than anticipated totals. We can’t rule out some 20-inch bullseyes, but so far there’s not much support for this in our best models. I think the bottom line is that we need to prepare for heavy rainfall through Wednesday or so of next week, and the possibility of flash flooding. But it may not come to that.

Storm surge

The other issue we’re going to face is storm surge as Beta produces strong easterly winds over the area. For now, Hurricane Laura’s water levels, plus one or two feet, is probably a good guide for what to expect from Beta along Galveston Island, Bolivar Peninsula, and Galveston Bay. However, this part of the forecast remains very much subject to change, given Beta’s track and intensity.

Winds

Winds will begin to increase across the area on Sunday and Monday, and there is a 30 to 40 percent chance that the Houston metro area will see tropical-storm force winds next week, with higher chances along the coast. This forecast, too, is very dependent on track and intensity so winds are a work in progress. But right now the expectation is that wind should not be too disruptive in terms of power outages across Houston.

Our next update will be posted no later than 2pm CT today.

Apologies for being a few minutes late: Toddler life.

So Eric’s post from earlier this afternoon tackled a number of things, including track risks, our flood scale update, and the coastal impacts expected from now Tropical Storm Beta. In this update, I am going to focus primarily on the now and next couple days. We will close with a quick bigger picture update.

Tropical Depression 22 was upgraded to Tropical Storm Beta with the 4 PM advisory package from the National Hurricane Center (NHC). One of their key points, something that seems to be further backed up by the reconnaissance aircraft flying in Beta as I write this, is that the center is both somewhat elongated and seems to be perhaps a bit to the east of where it initially was expected. It’s important that we make note of how these changes in the specific location of the center impact the models over the next 12 to 24 hours. So, a satellite loop of Beta shows a storm that’s more like a “blob” of thunderstorms than a well-defined tropical storm

But if you look at the data from the Hurricane Hunters in the storm, there are pockets of winds supportive of a moderate tropical storm already. Winds will likely be increased this evening during the 10 PM update to at least 55 or 60 mph. So despite the “blobby” nature of Beta, it’s already fairly formidable. With us heading into the typical nighttime ramp in tropical thunderstorms, we would expect additional gradual strengthening of Beta tonight.

As we go into Saturday, a number of things may happen with Beta’s center. It may come a bit to the north. It may meander not far from where it sits currently, or it may even reform in another section of the storm. It’s for these reasons that the storm track and rainfall impacts beyond the weekend are extra uncertain. We know that at some point tomorrow, Beta will begin to feel the influence of the strong area of high pressure to our north, which will be responsible for the glorious weather we have tomorrow morning.

As that happens, Beta will basically screech to a halt and begin to drift west. And that will be Beta’s M.O through Monday: A slow drift west.

So what does that mean for our weekend? One strategy I have found in the many slow moving storms we’ve had around here in recent years is that it makes the most sense to focus most on what we know, the next 36 to 48 hours, and then touch base at a high level on the future. So let’s do that.

Saturday should start off sunny and pleasant. Look for clouds to gradually filter in during the afternoon, particularly south and east of Houston. A shower or two is possible by evening toward Galveston, Freeport, or Matagorda. No serious weather expected.

On Saturday night, we could begin to see some of the northern outer bands from Beta creep toward the coast, so I wouldn’t rule out a couple periods of showers or storms after midnight for coastal adjacent communities.

As we go through Sunday, look for this chance of storms continue at the coast and gradually spread inland. The way things are lining up right now, I would think we see outer bands on the coast off and on throughout the day. Inland areas may see some scattered storms, and perhaps a more organized, heavier single band of activity pivots across the region east to west through the morning and afternoon. Overall, conditions through Sunday evening should be manageable across the entire area.

Rain totals by Sunday evening will likely be 1 inch or so on average at the coast, with risk for perhaps up to 2 inches or so between Freeport and Matagorda, right up along the coast. For the Houston metro, we probably range from minimal rain north and west to a quarter or half-inch in the city to perhaps three-quarters of an inch south and east of the city. Again, these are average amounts. Some will see less, some a bit more.

Coastal areas will begin to notice the rough surf and stiff, steady breeze pick up, and coastal flooding is likely to commence by Sunday’s high tide cycles (see Eric’s earlier post for more on that).

Sunday night into next week

Beyond Sunday evening, we expect Beta to approach the coast near Corpus Christi Monday and stall out for a time by Tuesday. This will keep continued periods of rain and storms in our area with breaks likely, but the heaviest rain will stay to our south and west. There is also a chance that heavier rain event could break out well out ahead of Beta. This would be from about central Louisiana into North Texas, away from the Houston area.

A plume of deep tropical moisture straight out of the Pacific, with perhaps some additional contribution from the southwest Atlantic is going to basically converge on Louisiana. You can see this on the GFS forecast of precipitable water for midnight Monday night/Tuesday.

This has been a more pronounced model wrinkle today that seems to suggest heavy rain will break out east of the Houston area and possibly east of the Beaumont area also. This would direct heavy rain into Louisiana that may perhaps expand and arc north and west into northeast Texas maybe north central Texas as well. The heaviest rain in that situation would stay both to our southwest and east on Monday and Tuesday. I don’t want to say that’s the “likely” scenario here, because a lot can change depending on how Beta is oriented at that time. If the storm is farther inland, that plume could end up much closer to Houston. If Beta is more offshore, we remain on the fringe of the heavier rain chances. So a lot of uncertainty here. We will keep you posted. Beta should begin to exit Wednesday and Thursday. But details are very much TBD at this time.

Eric will have our next update by 9 am CT on Saturday.