Month: September 2020

11:55 pm Monday: Congratulations, everyone. We survived Monday—although for the southern half of Houston it was a rainy mess. Rainfall estimates show that some areas near the border between Harris County and Fort Bend and Brazoria counties received 6 to 8 inches of rain during the preceding 24 hours, and it has brought some waterways to bankfull. It did not help that the heavy rains on Monday night came just as a high tide was pushing into Galveston Bay, making it more difficult for area bayous to drain. Otherwise, as expected, areas north of Interstate 10 generally received 2 inches of rain or less.

So far, even in the hardest hit areas, this has been a mostly street flooding event. But what happens next? We think the next 24 hours will produce plenty of precipitation as well. This is because although Tropical Storm Beta made landfall at 10 pm CT Monday on the southern end of Matagorda Bay, it’s center should now remain nearly stationary for the next 24 hours or so. This means the Houston region will lay within the storm’s northeast quadrant.

We’re most concerned about the areas that have already received 5 or more inches of rain during the preceding day (pink and reddish hues on the map above). As hoped, showers now moving into this area near midnight are lighter and a bit more scattered than earlier on Monday. The storm’s heaviest rains are now more tightly clustered near its center, further to the southwest of the Houston metro area.

Some of our mesoscale models suggest this clumping of heavier rains could gradually build northeast toward Sugar Land (in a few hours) and Houston and the Interstate 45 corridor by around sunrise on Tuesday. I don’t have great confidence in these models, but it seems as plausible scenario as any. We may also see more feeder bands develop offshore and move inland into metro region during the overnight hours. Additional rainfall amounts of 3 to 6 inches for parts of Houston cannot be ruled out through Tuesday morning.

Our next update will come no later than 7 am CT on Tuesday.

Good evening. Training bands of moderate-to-heavy rainfall from Tropical Storm Beta are continuing to move across the greater Houston area this evening. The heaviest rains from 6 to 9 pm fell generally to the south-southwest of Houston, from Friendswood and Pearland through Sugar Land. A few locations received 4 to 5 inches during this three-hour period and it is starting to back up bayous. Other parts of Houston have largely been spared.

These southern areas appear to have won the Beta lottery this evening with a nearly stationary banding feature that is continuing to feed off moisture from the Gulf of Mexico. The National Weather Service has issued a flood advisory for this general region, suggesting an additional 1 to 2 inches of rainfall may occur over the next several hours. So far, the vast majority of area bayous and creeks remain within their banks. According to Harris County Jeff Lindner, here are the waterways of most concern at the moment:

• Lower Keegans Bayou: overbanks at Roark…flooding is ongoing
• Willow Waterhole: near bankfull at Westbury
• Brays Bayou: water levels are within 2-5 feet of bankfull from Gressner Dr to Rice Blvd
• Clear Creek: Near bankfull along the entire channel and overbanks near I-45
• Turkey Creek: Within 3 ft of bankfull at FM 1959

Waterways aside, these heavy rains have created a dangerous situation on some area roadways. Tonight is not a great night to be out and about.

My read on the radar is that this prolonged banding feature that has been running up the Gulf Freeway for much of today and this evening, and ultimately bending into Sugar Land and now west Houston, is running out of steam. Offshore, the next band appears to be developing slightly to the north and east, and if this happens it should give some of the region’s aforementioned, hardest hit areas a reprieve in an hour or two.

Our next post will come by or before midnight to see whether I have read the radar correctly.

7:55 pm CT Monday: Tropical Storm Beta is limping toward the Texas coast this evening, at a speed of about 5 mph, and will come ashore near Matagorda Bay tonight. It has maintained sustained winds of 45 mph today, but its overall organizational structure is poor. Now that the storm is nearing land, we should start to see some very gradual improvement in coastal flooding over the next two days. The bigger issue is rainfall, particularly a persistent band of showers up the I-45 corridor this evening.

Track

First of all, the most likely track for Beta now is that the storm comes barely inland near Matagorda Bay, and noodles around for pretty much all of Tuesday before beginning to lift to the northeast. Please note it is entirely possible that the center of the storm will slide far enough east that it reemerges over the Gulf of Mexico later on Tuesday or early Wednesday and then scoots up the Texas coast toward Louisiana. If this over-water track happens it will not have much sensible change on our weather in terms of winds and seas. At this point, the near-term track of Beta is almost immaterial—we’ve felt the lash of its winds, and its waves. Now all that’s left is how much rain it puts down over the next two days before exiting stage right.

Rainfall

For the most part Beta’s rainfall has been moderate today, and the good news is that most of the storms that have moved through have produced rainfall rates of 0.5 to 1.0 inch per hour. This is within the capacity of our streets and bayous the handle. The one problem area is roughly the Interstate-45 corridor between Galveston and Pearland. Some communities along and adjacent to the freeway have seen in excess of 5 inches today as storms have basically trained over the area since around noon. Even at relatively moderate rainfall rates, these totals add up over time. As a result the National Weather Service has issued a flash flood warning for this area through 8:30pm.

So what happens this evening and overnight? This I-45 band has slowly been lifting north, so the areas “under the gun” will hopefully get a reprieve later this evening, and we’d expect the heaviest rains to probably fall a little to the east of where they occurred today. However, if the band does not move it could lead to rises on Clear Creek, Chigger Creek, Cowart Creek, and Mary’s Creek—all of which remain comfortably within their banks for now.

At 7:45 pm another area of heavy rainfall just north of Pearland was pushing into Sugar Land and West Houston. Most of these areas, except for Sugar Land, have generally only see 1 to 2 inches of precipitation so far today, so they can handle the additional rainfall. But these will be strong storms as they push through and need to be monitored for additional development.

The high resolution models do not have a great handle on trends during the overnight hours, and I want to see what happens with these banding features before hazarding a prediction beyond the next hour or two. Therefore I will update again by about 10 pm CT tonight.

Baby Lanza update

Tropical Storm Beta has brought some wind, some rain, some coastal flooding, and Theodore Kelvin Lanza who arrived a little earlier than we had expected on Sunday night! Mama and baby are doing great. Thanks to all for well wishes and messages. pic.twitter.com/Rld5VBIJ6Y

— Matt Lanza (@mattlanza) September 21, 2020

1:45pm CT Monday: Tropical Storm Beta continues to slog toward the Texas coast this afternoon. In its 1pm update, the National Hurricane Center said the storm has weakened this morning, with sustained winds dropping from 50 to 45 mph, and a rise in the storm’s central pressure from 996 to 999 mb. This is another indication of a system losing some of its organization. Beta is still moving toward Texas with a landfall tonight near or south of Matagorda Bay.

Although Beta is weakening—a very welcome trend for a cyclone nearing landfall—it is nonetheless creating some unfortunate impacts on our region’s weather. Let’s talk about coastal surge and rainfall, and then take a look at the forecast for the rest of today.

Coastal surge

There are reports of water covering low-lying areas along the coast, and inland along waterways connected to the Gulf of Mexico, such as Galveston Bay and Clear Lake. Based upon the latest modeling, we believe this morning’s high tide was the worst of the surge our region will see, with this evening’s tide perhaps half a foot lower than conditions observed Monday morning. Conditions should slowly improve on Tuesday and Wednesday.

Rainfall

We have begun to see some bands of moderate to heavy rainfall move into the coast today, particularly in southern Brazoria and Galveston counties. Fortunately, most of these storms have been producing rain at rates of 0.5 to 1.5 inches per hour. (Rates above 2 inches per hour will generally flood streets). The heaviest band of these training storms is now lifting into the Houston metro area, and will be the focus of activity this afternoon. Currently, it looks like these storms may produce 2 to 3 inches of rain total as they slowly progress northward, so it could impact the afternoon and evening commute home. We don’t anticipate more than some street flooding at this point, but please do take care. Should the situation warrant, we will update the site.

Another threat today is tornadoes. NOAA’s Storm Prediction Center says a few “brief” tornadoes are possible this afternoon and evening, although it is holding off issuing a tornado watch for now. Overall, the environment is not strongly supportive of tornadoes, but we do often see a few in the northeast quadrant of a landfalling storm. Earlier, the National Weather Service issued a tornado warning for an area near Texas City, but a tornado was not confirmed on the ground.

This evening

We will have to continue to watch the progression of Beta’s rain bands this afternoon and evening as the storm moves closer to the Texas coast. However, we do not expect continual rainfall at this time across the area.

Our next update will be posted no later than 8:30 pm CT.