Month: September 2021

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.

Good afternoon. The purpose of this post is to emphasize that while we have a pretty good handle on the forecast for Tropical Storm Nicholas over the next 24 to 36 hours, after that many questions remain. And for this reason, we want readers to understand that while Houston may see heavy rain over the next three days, other parts of the state are very much at risk as well.

As of 1pm CT, Nicholas still has 40 mph winds, and it is moving north-northwest across the southern Gulf of Mexico. Winds from the storm may reach South Texas by Monday morning, and the upper Texas coast by around Monday night. It’s possible that Nicholas becomes a Category 1 hurricane, and there will be some effects from this wind and surge. However the greatest threat remains rainfall, so that’s what we’ll now discuss.

I know you’re tired of reading about “uncertainty,” but you’re going to have to bear with us for another 12 to 18 hours on that score. Why? Because Nicholas only now is beginning to develop a reasonably well defined center of circulation, and we’re starting to get better data from reconnaissance airplanes flying into the storm. This improved information will be fed into models. So the computer model outputs after 6pm today will be better, and then models released after midnight tonight should be pretty good. The bottom line: When you wake up on Monday, we should be able to give you a more precise forecast.

In the meantime, it’s important to stress that the greatest threat for heavy rainfall and flooding is not coming on Sunday night Monday, but rather Tuesday and Wednesday as the center of Nicholas moves into the Texas coast. After that, the rains will be largely dependent on the track of the storm—which again we should have a better handle on by tomorrow morning.

Put more explicitly, it is quite possible that some location in Texas inside a triangle from Austin to Corpus Christi to Beaumont sees 20 or more inches of rainfall on Tuesday or Wednesday. (Most areas, of course, will see considerably less). I still probably would favor the Houston, Galveston, or Beaumont regions for the heaviest rainfall, but we just cannot say for sure. So what should you do in the face of this uncertainty? Well, if it helps, you can blame us. But what I would advise is keeping an eye on the forecast, especially tomorrow, when we should have a better handle on things. And then be prepared for the potential of flooding on Tuesday or Wednesday.

Matt will have another update on the situation this evening, before 9pm.

We continue to monitor Invest 94L Potential Tropical Cyclone 14 Tropical Storm Nicholas in the Bay of Campeche, which is likely to become a tropical storm before the day (or possibly the morning) is out. As I write this, hurricane hunters are investigating the storm and they have found tropical storm force winds, and subsequently they have tagged this as a PTC, as it lacks a defined low level center. In other words, it quacks like a duck but it doesn’t yet look like a duck, so we can’t technically call it a duck. But from your perspective, it’s basically a duck. Sorry, Ohio State fans.

Nothing better than writing a bunch of stuff only to have it get blown up. Anyway, we now have Tropical Storm Nicholas. Here’s the forecast track from the National Hurricane Center.

With the formation of Nicholas, we now have Tropical Storm Watches along the coast and in Galveston Bay. The initial read on Nicholas from the NHC is to strengthen it to a moderate to strong tropical storm before making landfall somewhere between Rockport and Sabine Pass. The Matagorda area is favored at this time, but that could always change.

From our vantage point: First, we will be holding this at a Stage 2 flood event. Given the higher end risks and uncertainties involved in this forecast, it’s important to note that this is pretty low confidence. We would continue to skew this as lower risk for a Stage 2 event north and west of Houston and higher risk south and east. In other words, the farther south and east you are in the metro area, the more likely you are to receive heavy rainfall that could produce flash flooding. Or at least that’s our going assumption sitting here today.

Sunday/Monday

Next, let’s talk briefly about today and tomorrow. We are expecting thunderstorms at times, especially along the coast. And those could easily produce 2 to 3 inch per hour rainfall rates which could cause flash flooding eventually. It’s important to note that this rain today and tomorrow is indirectly related to Nicholas, and what we see on Tuesday into perhaps Wednesday would be directly related. In other words, we are expecting multiple rounds of rain and storms between now and Wednesday. If you don’t get rain today or tomorrow, that doesn’t mean you won’t on Tuesday or Wednesday and vice versa.

The Weather Prediction Center arm of NOAA has placed the southeast metro in a slight risk (level 2 of 4) of excessive rainfall today and the bulk of the metro area in that slight risk tomorrow.

This means that there is at least some chance that we get enough rain to produce flash flooding in spots today or tomorrow. Rain will likely fall at the rate of 1 to 3 inches per hour in the heaviest storms, and any storms that linger awhile or “train” repeatedly over the same areas could begin to produce some street flooding. This would be most likely at the coast or just inland today and tomorrow, but some risk exists farther inland as well tomorrow.

How much rain do we expect today and tomorrow? Well, here’s the official NWS outlook for rainfall through Tuesday morning.

We would expect to see about 3 to 5 inches of rain along the immediate coast with 1 to 3 inches inland. There will likely be isolated higher amounts in here — through late Monday night or Tuesday morning.

Beyond Monday night

Here’s where forecast confidence drops a good bit. When we have tropical storms we often tell you not to focus on the center line because impacts will extend far from the center. That’s as true as always with this storm, but the reality is that: Because of the angle at which this is coming up the Texas coast, that track actually really matters in terms of what we experience in the Houston area and coast on Tuesday into Wednesday. Why is this? We can look at two goal posts here to get a sense of why this is important.

Last night’s GFS model took the storm into Cameron Parish, Louisiana and because it spent a lot of time over water, it basically intensified it into a hurricane. But! Because it tracked offshore, the bulk of the tropical storm and hurricane force winds stayed offshore, and Galveston saw just moderate tropical storm conditions. The Euro brings the system inland over Matagorda and because that’s far enough south Galveston again just saw moderate tropical storm conditions on that run. But from a rainfall perspective, the farther east GFS directs most of it into Louisiana, while the west tracking Euro brings it more into the Houston metro area.

The final track of Nicholas will be dictated by where exactly the low level center forms. So in terms of Houston rainfall, a solution like the GFS provides minimal impacts Tuesday and Wednesday, whereas the Euro implies significant risk of flash flooding. It’s important to note that both solutions imply heavy rainfall risk is likely along the immediate coast, so for places like Galveston, you should expect at least another period or two of heavy rain Tuesday into Wednesday regardless of the exact track.

The good news is that with a defined tropical storm now and hurricane hunters continuously investigating, and better data going into our models, we should have some clarity on this by tonight, or so that’s the hope!

In terms of tropical impacts: Based on the track above. Winds will likely approach 30 to 40 mph at times beginning late Monday night or early Tuesday along the coast. Winds will likely be sustained at 30 to 45 mph on the coast Tuesday, with gusts of 45 to 55 mph possible. Higher winds are possible with a stronger storm or one that splits the model difference right now and comes ashore near Galveston. A storm tracking farther east would likely result in slightly less wind at Galveston and more impacts to Port Arthur or Cameron, LA. Inland winds should remain below tropical storm force, but it would likely be a breezy day at times on Tuesday, especially south and east of Houston. This doesn’t appear to be a major power outage risk event for the majority of the Houston area, but coastal areas could have a few issues.

Tides are going to approach levels of about 3 to 5 feet above mean low lower water (MLLW). This may lead to impacts close to what you may have experienced during Tropical Storm Beta almost exactly one year ago. This is mostly minor coastal flooding. If Nicholas does intensify beyond current expectations or come ashore closer to Galveston, tides could be a bit higher and flooding would become more of a concern along the bay communities as well as in Galveston, Surfside, and Bolivar.

So just to summarize:

• Periods of heavy rain, indirectly associated with Nicholas are likely today and tomorrow, with the highest amounts likely closer to the coast. Flash flooding is possible with those storms.
• An additional period of heavy rain is likely on Tuesday into Wednesday, contingent on the exact track of Nicholas. That is where we have significant forecast uncertainty still. Additional, possibly more significant flash flooding is possible then.
• Tropical storm conditions are becoming more likely along the immediate coast, with Galveston likely to experience tropical storm conditions on Tuesday. At this time, we don’t expect inland locations, including the city of Houston to see significant wind, though it will be a bit breezy Tuesday.
• Minor coastal flooding is likely, with impacts possibly similar to what was seen during 2020’s TS Beta. A stronger storm or a storm closer to Galveston would likely yield slightly worse impacts, but a storm passing east of our area may reduce impacts some.
• We expect better model data this afternoon and evening to hopefully help boost some forecast confidence.

Eric will have the latest based on morning model data around 2 P.M. today, and we’ll have another post this evening as well.