Eric Berger

Tuesday, 7:00pm—It’s over. The weather, that is.

Since Friday, Harvey has moved into Texas, meandered around the area between Corpus Christi and Houston, moved offshore, and is now moving steadily to the east. It’s taking its godforsaken rain with it. The meteorological event has now ended, but unfortunately this is only the end of the beginning. Now comes the hard part, putting our city back together. We’ll have much more on that later.

For now, we’re exhausted, just like everyone else. We’re sick and tired of the rain, just like everyone else. So this will be a quick forecast.

Light rain has been falling across Brazoria, Galveston, and eastern Harris County late this afternoon and evening, but rates have been easily manageable at 0.10 inch per hour—this is less than 50 times the rainfall rates seen during the peak of Harvey. Overnight this western periphery of Harvey’s rains should continue to move east, hopefully pushing through Liberty and Chambers counties by or before sunrise.

For Wednesday, we can’t rule out some rain showers (the southwestern edge of Harvey) rotating through the area, but we don’t anticipate any widespread flooding from these problems. In fact, on Tuesday night and Wednesday, in absence of heavy rainfall, we should see fairly rapid falls in most area bayous.

Mostly sunny conditions should prevail from Thursday through Saturday, with highs in the low 90s, during which Houston can get to work on cleaning itself up. There is much to be done. Can’t rule out some showers, but there won’t be anything too concerning.

We’ve seen some concerns about the GFS model showing the development of a low-pressure system over the Gulf of Mexico next week, and blowing up some potentially heavy rain over the eastern half of Houston by late Monday or Tuesday of next week. While there’s a chance for the return of some heavier showers, we’re not too concerned about this. We’ll have more on that in the morning.

For now when you go to bed tonight, wherever you are, enjoy the thought of not waking up to thunder, pulsating rain, or tornado alarms. Finally.

Tuesday, 11am CT—There is some good news in the latest update from the National Hurricane Center on Harvey’s position and movement—the storm is off the coast to the southeast of Galveston, and it is moving a bit faster (5 mph) to the east northeast. This means it is definitively moving away from the greater Houston area, and the rains are going to end. But we’re not across the finish line yet. This post will also take a quick look at some area waterways, and address rumors about “another hurricane.”

Forecast

Steady moderate to heavy rains are falling over the eastern half of the Houston area, especially for coastal areas including Galveston and Texas City. These should continue throughout the day, on and off, as Harvey slowly lifts away from the region. This updated rainfall forecast map from the National Weather Service shows that, from this point forward Harvey is far more likely to affect the eastern half of the region (3 to 8 inches more) than the western half of the region (1 to 3 inches at the most).

We are probably about 24 hours away from a general cessation of rainfall, including for most of the eastern half of the Houston area. It’s been an absolutely miserable four or five days, but it’s almost over

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Monday, 6:15pm CT—It’s been a wet day across an already waterlogged Houston, and unfortunately we can probably expect similar conditions to continue through the night. During the day we have seen a lot of dry enter into Harvey’s circulation along its eastern side, but unfortunately this has yet to substantially affect the convection on Harvey’s northwest side—which just happens to be continuously dumping rainfall on Houston.

This pattern has allowed Harvey to drop 3 to 8 inches of rain across most of the Houston metro area during daylight hours today, with the heaviest rains in northern Brazoria County and Southern Harris County.

Because Harvey is only moving to the east-southeast very slowly, about at the pace of a slow walk, we can probably expect this pattern to continue for tonight, and into Tuesday morning. For the most part these aren’t excessively heavy rains, but even rainfall rates of 1 inch an hour will cause bayous and floodwaters to rise if they persist long enough. Therefore, while we don’t expect floodwaters to rise rapidly tonight, steady, moderate rains could cause slow rises in bayous. This is about exactly what the Houston region doesn’t need right now.

As far as accumulations, the National Weather Service predicts that the following areas of Houston could get as much rainfall as the amounts shown in this graphic during the next 24 hours, through 7pm Tuesday. I’m hoping these totals are little high, but we can’t rule them out.

Looking for some good news? We have a little bit of that. The favorable area for tornado formation is moving to the east, so we should have fewer tornado warnings tonight, and then fewer to none on Tuesday. Also, we feel fairly confident that the potential for prolonged, heavy rainfall will end sometime on Wednesday, during the afternoon or evening hours.

Matt will have another update later tonight.

Posted by Eric at 6:15pm CT on Monday

Monday, 1pm CT—Houston remains in the midst of Hurricane Harvey’s devastating aftermath, and we are weeks if not months away from a full accounting of its toll on the fourth largest city in the United States. And while a definitive account of its epic proportions will have to wait, we can at least begin to make some preliminary assessments.

In this post we will discuss how Harvey compares to other major flood storms in US history, and also how it stacks up to the region’s previous flooding event of record, Tropical Storm Allison. (Spoiler alert: Allison had a good run, but Harvey has forever dethroned her).

Mississippi discharges

The Texas state climatologist, John Nielsen-Gammon, has been closely tracking Harvey and its attendant flooding. To gauge the overall impact of a rain event, he uses a metric that defines a target zone of 20,000 square miles (about the size of West Virginia, or about 30 times the size of the city of Houston), and then measures the rainfall rate over a 120-hour period in comparison to the discharge rate of the Mississippi River. Here are the top 10 Gulf Coast flood events, as measured in “Mississippi River discharges” over that time:

• 3.6 Hurricane Harvey 2017 (estimate)
• 3.4 Hurricane Beulah, 1967
• 3.1 Brazos River flooding, 1899
• 2.8 Hurricane Georges, 1998
• 2.6 Southeast Texas flooding, 1994
• 2.5 Louisiana floods, June 1940
• 2.4 Tropical Storm Alberto, 1994
• 2.3 November Texas floods, 1940
• 2.3 Louisiana floods, 1953
• 2.3 Tropical Storm Allison, 2001

Note that the initial estimate for Harvey may be too low. As of Monday morning, Neilsen-Gammon’s hand estimate for Harvey to date was 3.1, but more heavy rains were falling in the target area and a full five days not reached. Already, for 72 hours, Nielsen-Gammon said Harvey is the greatest event over this shorter time scale.

Under this metric of rainfall over a large area, then, Harvey will very likely produce the greatest total amount of rainfall in the United States from any single storm, at least during the last 120 years. (the Gulf coast is by far the most susceptible US regions to such events due to its proximity to the warm, humid body of tropical water).

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