Eric Berger

Why we’re worried about the rest of tonight in Houston

A major rain band has slammed Houston this evening beginning on the west and southwest side, progressing through central Houston, and now it is approaching a line from The Woodlands to Baytown to League City. It has produced tropical-storm-esque rainfall rates of 4 inches per hour (and higher), which has backed up bayous. The National Weather Service issued a rare flash flood emergency, indicative of the dire state of affairs.

As a result of this, Houston on the cusp of a major, widespread flood event of that could affect thousands of homes. Only the fact that this main band has progressed slowly to the north-northeast has saved the region from greater flooding. So far, this has mostly been a street flooding issue. (Mostly). And while some bayous are teetering on the edge or overtopping their banks, for the most part the region’s bayou systems are holding. So the critical question is, what comes next? Is this it? Or will one or two more bands fire up before Sunday morning and push through Houston.

So, as of 10:30pm CT, here is what we are worrying about.

1. Will further rain bands from Harvey exacerbate a bad situation? Another rain band pushing into Houston from the west within the next several hours, of similar intensity to the first band, (Band 1 in the graphic below) would likely push bayous out of their banks, and turn a major street flooding problem into a major structure flooding problem.

Harvey’s radar appearance at 10:30pm CT Saturday. (Intellicast/Space City Weather)

2. Will Band 1 slow down as it moves toward a line from, say, Humble to Seabrook, or along the Gulf Freeway? There are some meteorological reasons to think it might, and this could potentially become a devastating event for the east side of Houston. A nearly stationary line of showers producing 4 inches of rain per hour does not take long to flood structures.

3. What comes next? Tropical Storm Harvey may be weakening, but its rainmaking potential isn’t going anywhere. The latest forecast track from the National Hurricane Center suggests this. We might hope that some of its ability to produce such massive, powerful rainbands diminishes over the next couple of days. But still, it’s going to be there in some form or fashion. Alas, we’ll have to worry about this one tomorrow.

10pm CT Saturday official forecast track for Tropical Storm Harvey. (National Hurricane Center)

We will continue updating tonight as warranted. Or as long as the beer here at Space City Weather HQ holds out.

Posted by Eric at 10:45pm CT on Saturday

Flooding begins as worst of TS Harvey’s moisture moves into Houston

Earlier, Matt called attention to the potential for very heavy rainfall tonight from Tropical Storm Harvey, which is drifting east-northeast between San Antonio and Houston. Unfortunately this is exactly what is happening in the Houston metro area. Now is the time to get off the roads, get to your residence, and wait out a potentially long night of flooding.

Before jumping to the forecast, we’ve had some questions about why Harvey can maintain its strength and rainfall generating potential a full 24 hours after making landfall along the Texas coast. The following satellite photo, taken by NOAA’s GOES-16 satellite at sunset tonight, tells the story. We have a vigorous low-pressure center inland, but it remains near enough to the Gulf of Mexico to pull copious amounts of moisture into the state.

Satellite image of Harvey at sunset. (NOAA)

Rainfall rates

Beginning at about 7:00 pm a large feeder band began moving into the Houston area, and it has brought an impressive amount of rainfall in a short period of time. Some areas near Waller, northwest of Houston, and Stafford, southwest of Houston, have seen rainfall rates of 4 inches per hour during the last hour. That is about twice the carrying capacity of most bayous in the Houston area, and we have started to see flooding along some nearby bayous. We are already seeing deep street flooding in parts of western central Harris County, near Interstate 10 and the Sam Houston Tollway.

Here’s a look at the rainfall band’s position at around 9pm tonight. You will note the main feeder band extends over the Gulf of Mexico, from which it is pulling moisture into Houston. Additionally, a second rain band near El Campo and Bay City appears to be strengthening, and will move through Houston later this evening.

Radar image of Tropical Storm Harvey at 9pm CT Saturday. (Space City Weather/Intellicast)

High resolution models (which are run frequently) continue to show high rainfall totals tonight and into Sunday morning, with widespread accumulations of 3 to 6 inches, and some locations receiving in excess of 10 inches. On top of the rainfall, we continue to see indications of tornadoes on the radar. As Matt suggested, now would be a good time to make sure you have your mobile device emergency alerts notification set to “On” tonight.

We remain concerned about the potential for flooding in the Houston region tonight, and will do our best to keep you apprised of the situation.

Posted by Eric at 9:10pm CT on Saturday

The big question: Where will Harvey and its rains go?

This afternoon’s post will focus on now-Tropical Storm Harvey’s inland track. Where the center goes from here is going to make a big difference in terms of whether Houston sees widespread flooding—or not. Unfortunately, the track forecast has remained something of a mess.

But before that discussion, just a quick update on the state of rains in Houston. The heavy band we were concerned about this morning has slowly moved north-northeast of the central Houston area, and this has allowed the city and its bayous to dry out a bit. This is good, because we expect more rain bands to move into the area later today and especially tonight. For now travel is mostly safe, but try to stay off the roads unless you really need to go out, and complete any trips before dark. Also, if you’re wandering around outside, be careful of wildlife. It, too, is looking for shelter from rising waters.

Look what we found in League City, near Clear Creek, this afternoon. (Space City Weather)

Harvey’s track

The big question is where Harvey’s center (and its outer rain bands) will go over the next few days. While 10 to 15 inches over three or four days is a lot of rain, for most of Houston it is manageable. However, 20 inches or more will cause widespread problems.

What I think I know today is that there’s a chance the Houston region escapes catastrophic flooding. I feel better than I did yesterday at this time, when the forecast was almost completely grim. Let me explain why.

Both the GFS and European model runs have Harvey wobbling around south Texas, and the central-Texas coast today through Monday, and then they bring the center back out into the Gulf of Mexico near the point where it made landfall late Friday night. But neither model keeps it offshore for long, and at this time I don’t think significant re-intensification is a major threat. No, the long-term worry for Houston, the Texas coast, and much of southern and southeast Texas remains rainfall.

GFS ensemble model forecasts for Thursday morning. (Weather Bell/Space City Weather)

By Wednesday night and Thursday morning the GFS model ensemble solutions (shown above) start to diverge, with a slight majority dragging Harvey toward the Rio Grande and ultimately toward lower pressures over northern Mexico. This is a good scenario (Dying in the Rio) for Houston because it ultimately limits rainfall potential over the area. The remainder bring the storm north toward Houston (The Wandering 59 special). This results in more rainfall for Houston during the middle of next week, when we certainly will already be waterlogged.

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Harvey weakening, but sending its strongest rains into Houston

This post will provide a brief update on Hurricane Harvey’s official forecast track, and discuss what we’ve seen so far from the storm’s rains in Houston, and what to expect for the rest of the day. We’re still at the “manageable” stage in terms of rainfall, but it won’t take too much to push us into unmanageable.

Harvey

In its 10am CT update, the National Hurricane Center says Harvey remains a hurricane—but only barely so with 75mph winds. It is weakening, but in the process it has thrashed the central Texas coast, from Corpus Christi to Freeport, and inland areas such as Victoria for most of the last day.

From here on out, the official forecast track is basically summarized as follows: ¯\_(ツ)_/¯

Official National Hurricane Center track forecast at 10am CT on Saturday.

In their discussion, forecasters at the hurricane center wrote, “Based on this pattern, Harvey could easily meander for the next 4 to 5 days over southeast Texas as indicated in the NHC forecast. The only agreement among the track guidance is that Harvey is certainly not going anywhere fast.”

We discussed several scenarios for Harvey’s evolution in a post last night, and that thinking more or less holds up (here the National Hurricane Center is following “The Wandering 59 special”) But theirs is, frankly, a low-confidence track forecast. We will provide a comprehensive update on what we can say about Harvey’s track, and its implications for Texas rainfall early next week, by around 2pm CT today. Basically, our weather for Sunday and beyond depends on where Harvey goes.

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