Eric Berger

In brief: Unfortunately, we are celebrating Father’s Day by issuing a flood alert for the Houston area. There won’t be any issues today, or likely on Monday. But the period of Tuesday and Wednesday is likely to experience heavy rainfall that could lead to flooding. Some of this flooding, especially for areas south of Interstate 10, could be significant.

We are continuing to track the threat of surging tropical moisture this week, loosely associated with a tropical low over the Southern Gulf of Mexico. While there remain major details to parse, the threat of heavy rainfall in the greater Houston metro area is sufficient to put a Stage 2 flood alert into place for the entire region—including Harris and all surrounding counties.

A Stage 2 flood alert signifies the potential for flash flooding. Events falling into this category may cause significant, widespread street flooding across large swaths of the area, flooding numerous cars. Some limited home flooding is also possible, but this is not widespread during a Stage 2 event.

In terms of expectations for flooding this week, for areas along and north of Interstate 10, a Stage 2 flood is likely to be a worst case scenario. However, for areas south of Interstate 10, and especially coastal counties, we may have to escalate to a Stage 3 flood alert depending on how the forecast evolves over the next few days. We’ll be monitoring this closely.

What to expect this week

We have no concerns about weather conditions today. Skies will be partly to mostly sunny, with high temperatures in the low 90s, and only a few, isolated showers. Conditions will be similar tonight. Showers will become more widespread and numerous on Monday, but again rain totals should be manageable for most.

However, the period from Tuesday morning through Wednesday night will see a surge a tropical moisture, and bring the best rain chances into the region. With this kind of tropical moisture we can see high rainfall rates that quickly backup streets, and flood yards. For any plans you have on Tuesday, Tuesday night, and Wednesday, you’ll need to be weather aware. Rain will remain possible for Thursday onward, but the threat of heaviest rainfall should diminish after Wednesday.

In terms of accumulations, I think most areas north of Interstate 10 will see 2 to 6 inches of rainfall, with higher localized amounts. However for areas south of the freeway, and especially closer to the coast and near Galveston and Matagorda Bays, there is the potential for 6 to 12 inches of rain, with higher bullseyes. Some uncertainty remains. Our forecast modeling remains a bit split as to whether the heaviest rain will fall near Galveston, or further south closer to the Coastal Bend. However, the clear message is that we need to be prepared for the possibility of flooding in Houston. (If you’re wondering about impacts for the entire state of Texas, Matt has you covered on The Eyewall).

In addition to the rains, we’ll see the breeze picking up from the Gulf of Mexico on Tuesday, with onshore winds of 20 to 30 mph, and higher gusts. These winds will be strongest right along the coast. With these winds tides will push a couple of feet higher, potentially flooding low-lying coastal areas such as parts of Bolivar Peninsula.

I do want to be clear that there is a difference between tropical rains and the types of violent wind storms we saw earlier this spring. Straight-line winds and hail are unlikely with this kind of system. The primary threat for most of is going to be heavy rainfall and accompanying flooding.

We’ll have full coverage for you all week.

In brief: We’re continuing to follow the possibility of heavy rainfall next week in the greater Houston area, especially for coastal areas. We’re still far from having all of the details, but we know enough to take the threat seriously.

Weekend outlook

Happy Saturday, everyone. If sunshine and heat are your jam, you’re in luck this weekend. Today, especially, will bring brilliant blue skies and temperatures in the mid-90s. There may be a few clouds tomorrow, but I still expect mostly sunny skies on Sunday, with high temperatures in the low- to mid-90s. It’s possible we’ll see a few isolated showers and thunderstorms during the afternoon and evening hours on Sunday, but most of us will simply be sunny and warm.

And then it won’t be.

Next week

The overall pattern appears unsettled for most of next week, with a very healthy chance of showers each day, and the middle of the week especially concerning. A low pressure system over the southern Gulf of Mexico will help push a large plume of tropical moisture into Texas and Louisiana. This threat of heavy rainfall next week will materialize whether the low in the southern Gulf becomes a tropical depression or storm. In fact, it doesn’t really matter. The table is set, regardless.

Over the last 24 hours some of our guidance has been showing excessive amounts of rainfall along the Gulf coast, but whether these bullseyes occur over Matagorda Bay, Galveston Bay, Port Arthur, or Southern Louisiana is something we cannot say. In terms of timing, the greatest threat of heavy rainfall likely will come during a period from Tuesday evening through Thursday morning.

So what does this all mean? If you live inland of Interstate 10, the overall risk is lower. Most of these areas are likely to pick up 2 to 4 inches between Monday and Friday. However, areas along and south of Interstate 10 are likely to see 4 to 6 inches of rainfall next week. Our concern is that some localized areas may see 10 inches or more of rainfall next week given the tropical nature of this rainfall. The expected level of moisture in the atmosphere—a value known as precipitable water—is very high, and such levels are capable of producing high rainfall rates that can quickly flood streets. We don’t know for sure whether this kind of pattern will establish itself over the Houston area, but it is a distinct possibility.

I’m writing all of this on a Saturday morning not to scare you, but rather to prepare you for the possibility of heavy rainfall next week. We will continue to watch this closely, and update this weekend as warranted.

In brief: Houston will see a few more isolated to scattered showers and thunderstorms today, but overall our pattern will turn sunnier and a bit hotter through Saturday. After that the focus turns to the Gulf of Mexico, where a tropical disturbance is likely to develop. Local rain chances start to increase on Sunday, but at this point we expect the heaviest rain associated with this system to remain south of the Houston metro area.

Thursday

As high pressure expands over the Southern United States, we’ll see decreased rain chances today, perhaps on the order of 20 percent. Like in recent days, any showers and thunderstorms will develop during the late morning, afternoon, and early evening hours with daytime heating. A few areas may see accumulations of 1 inch or greater, but much of the area will see nothing. Skies, otherwise, should be partly to mostly sunny today with high temperatures in the low 90s. Winds will be light. Lows tonight will fall into the upper 70s for most locations.

Friday and Saturday

With high pressure reaching is broadest expanse into our area, skies will be mostly sunny on both of these days with temperatures in the low- to -mid-90s. Since we are very near to the summer solstice now, please know the Sun is almost directly overhead (an altitude of 84 degrees) during the midday hours. This will burn your skin quickly, so please take precautions. Afternoon dewpoints will be slightly lower on Friday and Saturday so it won’t feel as hot as it will later this summer. Rain chances on both days is 10 percent, or less.

Sunday and beyond

By Sunday our attention will turn toward the Gulf of Mexico. As we’ve been discussing for several days, a tropical disturbance is likely to form in the Bay of Campeche early next week. (The National Hurricane Center now gives the system a 40 percent chance of becoming a tropical depression or tropical storm during the next seven days).

At this point I am fairly confident that high pressure over the southern United States will help to keep this system penned up in the southern Gulf of Mexico, and eventually steer it westward into Mexico (most likely) or South Texas. Although some organization is possible, the main threat from this tropical system is very likely to be heavy rainfall.

Due to the overall steering that we’re expecting, I think rainfall accumulations for the Houston area next week are likely to be manageable. Totals are likely to be highest along the coast, with the potential for 3 to 5 inches, with lesser amounts likely for inland areas. Greater accumulations than this are possible for locations further south, such as the Brownsville area, but uncertainty remains.

In the greater Houston area we’re also likely to see stronger onshore winds, perhaps 10 to 20 mph, with higher gusts, associated with the system. Tides may also run 1 to 2 feet higher with a persistent onshore wind. All of this forecast is subject to change if the tropical system evolves differently, but as for now I anticipate our localized effects to be mostly modest.

The bottom line is that much of next week, beginning Sunday, is likely to bring at least partly cloudy skies into the region with the chance for intermittent heavy rainfall. This pattern should help to keep high temperatures in the vicinity of 90 degrees, so a bit cooler than normal. Matt and I will be watching this closely and update as warranted if the forecast substantially changes.

In brief: After one more day with storm-o-clock weather this afternoon, Houston will see a sunnier and hotter pattern set in through the first half of the weekend. We’re not going to get super-hot, but it will feel like June out there. By Sunday our attention turns to the Gulf of Mexico, and the potential for tropical rainfall much of next week.

Wednesday

We’re going to see one more day with the potential for scattered to widespread showers and thunderstorms. Conditions will be similar to what we’ve seen on Monday and Tuesday, with storms firing up during the late morning, afternoon, and early evening hours due to a combination of plenty of moisture in the atmosphere, the sea breeze, and an overall perturbed atmosphere. Similar to the last couple of days, a few locations may see accumulations of 1 to 2 inches of rain, whereas most of the area sees considerably less.

Skies will be partly to mostly sunny when it’s not raining, with high temperatures reaching the low 90s for much of Houston. Outside of thunderstorms, winds will be light, around 5 mph from the northwest. Lows tonight will drop into the mid-70s.

Thursday

This will be a bit of a transition day as high pressure builds into our area from the northeast. I can’t rule out some isolated showers and thunderstorms, but most of us will see sunny skies with high temperatures in the low- to mid-90s. Lows will drop into the mid-70s.

Friday and Saturday

These will be sunny and hot days, with highs in the low-to-mid 90s. However, dewpoints will be a bit lower than a classic Houston summer, especially on Friday. This will take some of the sting out of the daytime highs, and make evenings a little more comfortable. Lows on Friday night could drop into the low 70s for much of Houston. Rain chances for both of these days are less than 10 percent.

Sunday and beyond

Starting on Sunday, our attention will need turn to the Southern Gulf of Mexico, where we could see some sort of tropical disturbance develop. Right now I don’t anticipate anything too organized—i.e. with strong, hurricane-force winds. However, whatever does develop is likely to be an efficient conveyor belt to bring Gulf moisture onshore, and therefore serve as a source of moderate to heavy tropical rainfall.

Our best forecast models are split on the evolution of this system, and how far north it moves (this will depend on the strength of high pressure over the southern United States). What I can say is that, beginning Sunday and especially from Monday through Thursday, there will be the potential for heavy rainfall along the Texas coast, including the greater Houston area.

It is a folly to try and predict rainfall totals because there are still so many uncertainties about a forecast for 5 to 10 days from now. But this is the kind of thing where our area could see 1 inch of rainfall, or 10 next week. In any case, most of next week should see a cloudier pattern, and this should help to limit highs in the upper 80s. Matt and I will be keeping a close eye on this, and when we know something, you will.