Let’s begin this morning’s post with a quick look at 24-hour rain totals for the broader southeast Texas region. Imelda moved inland near Freeport on Tuesday, meandered up toward Sugar Land, and is now near, or just west of The Woodlands. Since that time the storm has brought a devastating amount of rainfall to coastal Brazoria County (nearly 20 inches in some locations), and upwards of 8 inches or more for places to the right of the storm’s track near Alvin, Friendswood, Pearland, and Clear Lake.

So what comes next? Imelda’s heaviest rains are continuing well to the south and east of the storm’s center, with much of the most intense rainfall just offshore. (This is good, because an area near Sargent recorded a 5-inch hourly rainfall rate last night).

This intense coastal band is, at present, capturing the deeper flow of Gulf moisture before it can move inland. Long story short, the band highlighted in the radar map below is effectively a shield this morning preventing heavy rainfall over the central Houston area.

Beyond this morning, however, we’re kind of flying blind as to where storms will redevelop later this afternoon and evening. Sometime later today the feeder band shown above should have broken down, and along with some daytime heating we can probably expect storms to re-form over inland areas. But whether that’s over Clear Lake, downtown Houston, or points east is pretty hard to determine. Our short-range modeling does a pretty poor job during these kinds of situations.  If you want my best guess—and this really is a guess—we’ll see some kind of mass of storms form over the central Houston area this afternoon or early evening, and then push into Liberty County later tonight. These could be relatively moderate storms, or quite intense.

For now, at least, Imelda looks to be manageable for all of the region except for the immediate coast, as well as flooding along Clear Creek to the southeast of Houston. More later.

Good morning. For most of the city of Houston and points north and west, overnight rainfall caused few problems and has really only served to saturate soils a bit. Imelda’s dissipation has allowed for one main band to focus this morning well to our south into Matagorda County, which then arcs offshore back inland east of Galveston and Bolivar, aimed primarily at the Beaumont area.

The radar snapshot above from just after 5 AM shows limited heavy rain around Houston, with one narrow band extending from northeast of downtown into Liberty County.

Focusing a little closer on Matagorda County for a moment: This band means business.

Rainfall in the hour prior to my writing this post was over 5 inches (!) in parts of the county. A gauge near Sargent has received over 18 inches of rain in the last 24 hours. Those are extreme rainfall rates that will quickly cause flash flooding in that area. Travel across much of Matagorda County is not advised this morning, and it will likely get a bit worse before it gets better. These beefier rainfall rates will likely push into southern Brazoria County as well, so folks from Lake Jackson and Freeport through Surfside will probably want to use caution this morning as well.

Rest of today

So the million dollar question is: Where is this going? Saving the meteorology lesson for another day, we often see blow ups like this in tropical systems late at night and in the morning. Over the next few hours, this will probably yield areas of heavy rainfall across Matagorda, Brazoria, and Galveston Counties. Given that many of these locations have seen 4 to 9 inches since yesterday, it won’t take much for flash flooding to begin if rainfall rates are intense enough. Rainfall may begin to taper off this afternoon or shift more to the east toward Beaumont or Port Arthur. We do expect some new showers and thunderstorms to develop in and around Houston by later this afternoon. More on that in a moment.

Bottom line: What should you do today? Be cautious, but most of us can go about most of our day as usual (unless you’re down in southern Brazoria and Matagorda Counties as noted above). If you live southeast of Houston, be extra vigilant in case rain rates escalate a bit this morning. Eric will update you on the progress of that a bit later. In Houston and points north and west, I think most daily activities will be fine through 3 to 4 PM, though it will be raining at times. After 3 to 4 PM, things could begin to go downhill a bit. Given all this, if you work daytime shifts and can work your way home a little earlier than usual today, that would not be the worst thing in the world.

Tonight

All along, it appeared tonight would be the “main event” so to speak for the Houston area. Look for storms to begin to show up around 3 to 4 PM or so in and around Houston. Some of the storms will be heavy with impressive rainfall rates. As we work through the evening, I think the general trend will allow for those storms to slowly lift north and east, while becoming more numerous. For Houston, the hope is that the storms will lift out quickly enough to limit significant problems. We would then see the heaviest rain tonight up into Liberty County or point northeast from there. There is still a good deal of uncertainty regarding tonight’s forecast, so be sure to check back with us later today for an update when we should hopefully know more. It could get a bit rough this evening, but we’re hoping for the best possible outcome right now.

We still see rain becoming more scattered tomorrow and Friday, with a mostly dry weekend expected. Eric has you covered a little later this morning.

Tropical Storm Imelda has begun its transformation into a significant “blob” of rain over Southeast Texas this evening. Let us walk you through what we are expecting through Wednesday morning.

Now

Imelda is now classified as a tropical depression, and if I’m reading the radar correctly, the center as of 7:45 PM was located just west of Pearland and becoming more diffuse.

You can see from the radar loop above that Imelda has 2 or 3 areas of main concern, as it relates to rainfall. There is the main “core” of the storm over Brazoria County. This will be the primary rain producer this evening. As the center crawls north, that will come with it. This is what we are concerned about for the bulk of the Houston Metro.

The second area is a feeder band to the east of Baytown. That is aimed at parts of Galveston Island and north toward Chambers and Liberty Counties. That is not expected to move much, and within this region, expect heavy rain and potentially localized flooding overnight.

The third area is a band well to our east, aimed at the Beaumont/Port Arthur area or just west. That will be capable of some heavy rainfall tonight as well. But it may weaken a bit as this band near Baytown takes over.

So a lot happening here.

Overnight

I mentioned above that Imelda’s center is becoming more diffuse. That means that more erratic behavior of the storm track could occur. So expect that heavy rain currently located over Brazoria, Galveston, and southeast Harris Counties to lift north into the bulk of the Houston metro area. At nighttime, tropical systems can sometimes see rains intensify a bit. So I fully expect heavy rain at times in Houston and points south and east. At a minimum we would expect 2 to 5 inches of additional rain in these areas by sunrise on Wednesday. We could see some spots pick up as much as 5 to 8 inches or even more, however, and those would be the areas we’re most concerned with in terms of flooding. Again, that would be most likely from Downtown Houston south and east.

For those north and west of Downtown Houston, we expect periods of rain overnight, locally heavy. While we will monitor those areas for flooding risks, we do not think it is quite as serious as south and east. But given that there is still a degree of uncertainty with this system, the entire region should monitor the progress of the rain, both before bed and when you wake up. Do not assume tomorrow that you’ll be able to get to the airport or to work without issues, so make sure to check in on what has transpired overnight in the morning.

Wednesday daytime

We should see rains continue off and on through the day Wednesday. We could see a bit of a lull in the activity for a time during the afternoon hours before heavy rain sets back up late. Again, we have some uncertainty around exactly how tomorrow will unfold. Eric will have an update later this evening, and I will update you more on Wednesday’s outlook in the morning.

Wednesday evening and beyond

We expect another round of heavy rain tomorrow night, again in multiple areas. We’ll likely see the “core” of the storm reignite tomorrow night with heavy rain gradually lifting north of Houston. We aren’t entirely sure if that will be aligned over the center of the city or more to the east. We also will likely see another significant “feeder” type band east of Houston, though we’re not quite certain where that will be aimed. Check with us tomorrow for the latest on these aspects of the storm. We could see some very heavy rain from this, and with the grounds certainly saturated by then, we would expect a good amount of flooding risks, potentially significant to develop. We continue to expect event totals to be on the order of 5 to 10 inches on average, with isolated smaller areas seeing as much 20 inches or more.

Eric and I will continue with a Stage 3 flooding event expectation for Imelda’s rains tonight, tomorrow, and Thursday. This remains an evolving situation though, and it would be best to check back for the latest several times through the event. Eric will have an update around midnight.