Good afternoon. Much of Houston is seeing a reprieve from storms after a band of showers moved through the region around noon. It looks as if rain showers will remain somewhat scattered and non-threatening through the late afternoon or early evening hours. The main event is still offshore, and will reach our region later tonight.

Speaking of the main threat, Tropical Storm Nicholas retains 60 mph winds as of 1 pm CT, and continues to move north toward the Texas coast. It likely will make landfall near Matagorda Bay later this evening. The storm covers nearly all of the western Gulf of Mexico this afternoon.

Throughout the day, we’ve been getting our first inputs from high-resolution models about rain accumulations tonight and on Tuesday for the Houston metro area. The early returns suggest that most of Houston may fare pretty OK from rain dropped by Nicholas. We still have some very serious concerns, however. Let’s discuss.

Our confidence is increasing that a line of storms associated with the core of Nicholas will move into our region from the southwest tonight. It looks like these storms will reach Brazoria County around midnight, or shortly thereafter. Then they should progress toward downtown and the I-45 South corridor some time after midnight and before 6am CT on Tuesday. This is a little slower than previously anticipated, and may give Houston residents a few hours after sunset this evening before roadway conditions deteriorate. (Gusty winds will probably also arrive in Harris County around midnight, or after).

The other major shift we’ve seen in some of the model guidance is that the threat for heavy rainfall is becoming more concentrated along the coast, in places like Brazoria, Galveston, and Chambers counties as well as the Clear Lake area of Harris County. If this forecast holds, areas inland of Interstate 10 may see only a couple of inches tonight, whereas the coast will face a higher threat of 5 to 15 inches. One of our big questions right now is whether the heaviest precipitation falls offshore, or along the coast in places like Matagorda, Sargent, Freeport, and Galveston Island.

Matt and I have discussed this quite a bit this afternoon, and for now we’re holding to a Stage 3 flood scale warning for the entire Houston metro area. But that probably oversells the threat to locations north of Interstate 10. We’re going to continue to look at more data and decide whether to reduce our flood scale warning later today. We’ll leave you with this: It’s OK to have some hope about the Nicholas forecast, but we still have a lot of questions and a very explosive, tropical air mass headed this way.

Our next update will come at 6 p.m.

This post will attempt to set expectations for the timing of Nicholas’ rains and winds later today, tonight, and on Tuesday for the greater Houston metro area. Given that there remain some questions about the storm’s precise track and movement speed, these remain estimates, rather than set-in-stone predictions. But we recognize that this information is important for planning purposes, and so we’re giving it our best shot. Thank you for understanding that this is an, uhhh, fluid situation.

The center of Nicholas has been wobbling somewhat this morning, but the National Hurricane Center says the storm is still moving generally northward, and should approach the Texas coast this evening near Matagorda Bay. The storm retains 60 mph winds, and is being hampered by a bit of dry air and wind shear. However, this shear may relax enough to allow Nicholas to strengthen into a Category 1 hurricane before landfall. It will be close. The storm then should move almost directly overhead the Houston area on Tuesday. This post discusses what to expect from this track.

Monday day time

So far, as expected, showers and thunderstorms have been manageable today due to their fairly rapid motion. We should continue to see fast-moving showers traveling from the southeast to northwest throughout the daytime hours. Some of these could be briefly severe, but we don’t anticipate any significant flooding. Winds may also pick up this afternoon, but are unlikely to gust above 30 mph from the east-southeast.

Monday night and Tuesday morning

Based upon our latest data, the period of greatest impact now seems likely to occur between sunset on Monday and about noon on Tuesday. If you want to be perfectly safe, the best plan is to remain off the roads in the Houston area from around 6 pm CT Monday through the middle of Tuesday. However, we realize that this may not be possible for everyone.

In terms of winds, we expect things to start getting breezy by around 10 pm to midnight, particularly along Galveston Island, where gusts may briefly reach hurricane strength. In Harris County, sustained winds may reach 30 to 40 mph, with gusts in the 50s to 60s, especially by midnight or shortly after. This may well lead to some power outages, especially south and west of Houston. I inquired to CenterPoint about their expectations for power losses tonight, but have not heard back. Past experience with such winds suggests there will be isolated to scattered outages due to debris and tree branches that get blown into lines. A storm surge of 2 to 4 feet is likely along the upper Texas coast.

With regard to rainfall, the heaviest storms associated with the core of Nicholas are likely to approach the southern part of the region, including areas such as Lake Jackson, by around 9 pm. The storms should then move near the central part of the metro area, including the I-10 and I-45 south corridors, around midnight or shortly thereafter. As the core of Nicholas moves near the area, the rains should be just ahead of it, possibly exiting Houston by Tuesday morning, or around Noon.

How much rain is going to fall?

This, as ever, is the difficult question. Our highest resolution models continue to indicate the possibility of very intense rainfall rates of 3 to 5 inches per hour, which will quickly back up streets and bayous. It is not advisable to be out and about when these kinds of storms hit—especially because it will be dark, and driving in these conditions is dangerous.

The good news is that it still appears as though Nicholas will keep moving as it tracks through Houston on Tuesday, and away from the region on Tuesday night. This should help to limit overall rainfall totals for most to 5 to 15 inches of rainfall, with a few isolated areas seeing 15 inches or more. Rains totals will be greatest for coastal counties and the next inland tier, which includes Harris and Fort Bend counties.

What about air travel? Schools? The Harry Styles concert?

We’d love to be able to give you concrete answers on these questions, but we don’t have them. I think airline flights from after about 6 pm today through Noon on Tuesday are a big question mark, and I’d probably at least expect some delays.

Area schools should be closed on Tuesday, period.

As for Harry Styles, man, I don’t know. My daughter has been waiting months for this concert and right now there’s a chance the really heavy rains will hold off until after the show is over. But there’s also a reasonable chance its cats and dogs as the show is letting out of the Toyota Center. If they don’t cancel the concert, I’ll hope to be able to provide some better guidance later this afternoon. The safe thing is not to go, of course.

Our next post will come by 2 pm CT.

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Good morning. Tropical Storm Nicholas has a better defined center of circulation this morning, and it has reformed north of where forecasters believed it to be earlier. This, combined with an expectation that Nicholas will now move a little bit more quickly once inland, have led to some changes in timing and rainfall amounts in the forecast. As a reminder, we’re continuing to predict Stage 3 flood conditions for some parts of the greater Houston area through Wednesday. Some, but not all, of our region will see prolonged heavy rainfall beginning later tonight.

Storm status

Tropical Storm Nicholas has strengthened to have maximum sustained winds of 60 mph this morning, as of 4am CT, and is moving to the north-northwest. The storm will likely make landfall this evening between Corpus Christi and Matagorda Bay.

This will bring tropical storm force winds to the Matagorda Bay region on Monday afternoon, and these could spread up the coast to Galveston Island on Monday evening. Tropical storm force wind gusts will spread inland into portions of Harris, Fort Bend, and Colorado Counties late Monday or early Tuesday before beginning to weaken during the afternoon hours. These winds should not be great enough to produce widespread power outages in the Houston metro area, but some local problems are definitely possible.

Storm surge values of 3 to 5 feet are possible from Port O’Connor to Sargent, and 2 to 4 feet from Sargent to Galveston to High Island. Some significant inundation is possible around Matagorda Bay.

For nearly all of us in the greater Houston metro area the biggest concern, by far, will be rainfall.

How wet will it get, and when?

The Houston region should see scattered to numerous showers on Monday, but the heavier rainfall that is most concerning to us should fall between a 36-hour period from Monday evening into Tuesday night, or Wednesday morning. So this is the time when you should plan for the most significant impacts.

The flood threat is very real, but it is slightly mitigated by the fact that Nicholas is now expected to continue moving to the northeast after it reaches Houston, and seems less likely to slow down. This should, hopefully, bring down rain totals somewhat. To that end, the map below represents an average expectation of the rainfall your location will get from Nicholas. For much of our region, these should be mostly manageable totals.

However, it is important to note that we are most concerned about locally higher amounts, which are likely during a tropical system that produces training thunderstorms with extremely high rainfall rates. Therefore, some locations may see as much as 10 to 20 inches of rainfall from Monday evening through Wednesday morning. While these bullseyes are more likely near the coast, they are definitely possible as far inland as Harris, Montgomery, or Waller counties.

Please note that we have issued a Stage 3 flood alert, on the Space City Weather scale, in expectation of these bullseyes.

Conclusions

Nicholas will soon be here. While conditions across the region should be OK for much of today, they may deteriorate fairly quickly this evening or after midnight. In our next post we will try to provide a firmer time for the onset of heavier rain in the metro area—whether that’s 8 pm, midnight, or later. Our next post will come no later than 10:30 am CT.

Sorry for the delay: Groceries and kids and life get in the way sometimes! Eric and I spoke earlier this evening and agreed that we have enough evidence right now to upgrade to Stage 3 on the SCW Flood Scale.

As we note on the SCW Flood Scale page, a stage 3 event:

Our third stage is probably the most difficult stage to define. These are storms that may be quite memorable for parts of the Houston area but not for the entire area. These are basically larger, more damaging versions of Stage 2 events. You could expect perhaps hundreds of homes flooding in multiple neighborhoods during Stage 3 events.

In this situation, we believe we have enough evidence in model data to support a decent risk for a stage 3 event somewhere in our area or region. We currently believe the highest odds of this type of level being achieved is to the south and east of Houston proper, but the frustrating reality is that flash flooding could occur virtually anywhere in the Houston area. We aren’t much closer this evening than we were earlier today to defining exactly where the highest totals will occur. But we do have some other clarity perhaps.

Tonight & Monday

The rain we see tonight and Monday will be the appetizer to the main event, which should occur on Monday night into Tuesday and possibly Wednesday in our area. Expect scattered to numerous thunderstorms developing overnight and Monday morning along coastal sections, spreading inland tomorrow. Rain amounts by Monday evening will generally be on the order of 1 to 3 inches in Houston proper, lower amounts north of I-10 perhaps and higher amounts possible south of I-10 to the coast. Matagorda County may get into the core of the storm later tomorrow, which could bring additional rain totals in excess of 6 inches there. But for the most part, the rains tomorrow, though locally heavy and with localized flash flooding possible should be manageable.

Tuesday and beyond

I won’t dwell too much on Nicholas’s forecast in terms of tropical impacts, as we discussed that a bit in earlier posts and the flooding threat is of more concern for us. But the track and intensity forecast for Nicholas have remained fairly consistent, though with some risk that it could briefly attain hurricane status before landfall.

Onto the rain forecast. Many of you may have seen the European model today which printed a *lot* of rain for parts of the area. And while that certainly was a bit scary to see, it’s important to note that this model is an outlier, both in terms of track of Nicholas and in terms of the physical amount of rain it’s showing. While we aren’t discounting that model, I think it’s important to focus on the official forecast. Once you get up north of 15 inches of rain possible, it’s a serious flooding event potentially; we don’t need to make it scarier with outliers that show that. I have more issues with where the European model places the heavy rain (in and west of Houston) than how much it shows. With a track likely east of that specific model, I do believe the odds of the highest rain totals are highest east and south of Houston proper, similar to the official NWS rainfall forecast, which also increased today.

As of this evening, the outlook shows basically 5 to 10 inches of rain in the Houston metro area, with 10 to 15 inches in Galveston and Brazoria Counties. That seems reasonable right now, with the one caveat that higher amounts are likely depending on the exact track and speed of Nicholas as it comes through our area. A slow moving but steady outcome like most tropical models and the GFS model show would spread the rain out a bit more, keeping those higher totals somewhat in check. But a very slow, meandering outcome as the European model shows would potentially increase the max totals in spots. We want to see how the Euro goes overnight to see if it trends back to the consensus of tropical models and the GFS, which would further boost our confidence in worrying most about areas south and east of Houston. Regardless, rain will fall at the rate of 2 to 4 inches an hour at times. That can add up quickly.

A personal comment to close with here: This is an extremely difficult forecast because small changes in track outcomes will have big changes in impacts felt across a major metro area. If you live anywhere in the Houston metro area, north, south, east, or west, you should be preparing as if travel will be difficult to perhaps impossible on Monday night, Tuesday, and possibly Wednesday. We will hope for the best possible outcome here, but because of the uncertainty, you need to be ready. Folks east of Houston, particularly in Beaumont, Port Arthur, and Lake Charles: This bullseye could easily shift your way as well, so you need to be paying attention and prepared too.

Eric will have the latest in the morning on the flood threat, as well as tropical impacts from Nicholas, which will be minor in Galveston to moderate in Matagorda.