Eric Berger

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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Harvey after dark: What we know after day one

And so it begins … Texas suffered its first major blows from Hurricane Harvey on Friday, as the storm neared the coast and, instead of slowing down, kept moving right along and plowed into the Central Texas coast. It came inland shortly before 10 pm CT as an intense Category 4 hurricane. The early meteorology reports out of Corpus Christi and Rockport are pretty grim. Harvey should now gradually weaken, so long as it remains inland.

What happens now

I understand that some of you appreciate dark humor during these dark times, so I present you with this evening’s spaghetti plot of track models that were initialized at 6pm CT, and came out shortly thereafter. They are nonsensical. I posted them to Twitter with this comment: “Great to see that the latest forecast models are finally getting a good handle on Harvey’s inland track.”

Hurricane Harvey track models. Clear as mud. (Weather Bell)

You have to laugh at times like these, because for a lot of us, the uncertainty, the stress, it can kind of become unbearable. In any case, be glad you’re not a meteorologist trying to make sense of a mess like that. But I am, and so I shall. The first thing to do is simply to ignore that plot.

Secondly, when you look at the major global models, and their ensembles, it seems pretty clear that they think Harvey is going to loop around South Texas, somewhere between Corpus Christi, Victoria, Laredo and South Padre Island, for the next 24 to 48 hours (and dropping prodigious amounts of rain there). After that, the picture becomes more cloudy. When faced with such uncertainty, if you’ve been reading me for any amount of time, you’ll know the way I like to address that is through probability. Let’s revisit last night’s scenarios, shall we?

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