In brief: Although the coast has largely been spared heavy rainfall for the last two days, it now appears that the axis of strongest storms will shift there on Wednesday and Thursday. Due to this heightened threat for widespread street flooding, we are elevating coastal counties to a Stage 2 flood alert for now through Thursday evening.
Wary of offshore rains
As the Houston region has fallen into a very wet pattern over the last two days, the heaviest rains have fallen north of the city. Some locations in The Woodlands, for example, have received in excess of 9 inches of rainfall, and areas near Kingwood have received 4 to 6 inches. These heaviest rains have been fairly isolated, however, as most of the Houston region has picked up 1 to 2 inches so far.
We have a couple of more days during which the threat of heavy rainfall is high, so what will happen next? The majority of our modeling guidance suggests the threat will shift southward, particularly from southern Brazoria County up the coast through Galveston Island and all the way to Beaumont-Port Arthur. For this reason, we are elevating our flood alert for coastal counties to Stage 2 on our flood scale.
This means that for coastal counties—Brazoria, Galveston, Chambers, Jefferson, and Orange—there is the threat of flash flooding today, tonight, and on Thursday. Under Stage 2 conditions we generally expect widespread street flooding, and the potential for some localized flooding of homes and businesses. For the rest of the Houston metro area, and particularly areas along and inland of Interstate 10, lesser impacts are expected. We are maintaining a Stage 1 flood alert there.
Wednesday
Just before sunrise this morning we are seeing moderate showers across much of the Houston area, and for now these are totally manageable. But there is a line of showers and thunderstorms just off the coast that is more menacing. There is a fairly good chance this line will slowly lift northward into the coast, including Galveston Island, this morning. This will pose a distinct threat to flood streets.
These showers will gradually spread inland today, but based on our latest modeling they should gradually have a reduced impact and weaken some as they do so. Due to widespread showers and mostly cloudy skies, we can expect highs today to top out in the the low- to mid-80s for most locations.
Wednesday night and Thursday
The most likely scenario is that we see a similar pattern tonight. Some time after midnight another line of showers and thunderstorms appears likely to congeal offshore and then push into Galveston, Chambers, and Jefferson counties during the wee hours. This may spark another round of flooding for areas along and near the coast through Thursday morning. These showers should move inland during the daytime, albeit with likely reduced intensity.
All told, most locations south of Interstate 10 should receive at least 2 to 6 inches of rainfall on Wednesday and Thursday. My concern, and the reason for a heightened flood scale alert, is the possibility for some of these storms to dump 10+ inches of rainfall right along the coast. The models are increasingly highlighting this threat for places such as Galveston Island and the Beaumont-Port Arthur area.
Friday, Saturday, and Sunday
The threat of very heavy rainfall should end by Thursday evening or so, but that does not mean our wet pattern will end. Rather, we’ll continue to see a healthy chance of showers through the weekend. We don’t expect to see the kinds of storms that will produce significant flooding, but there look to be fairly widespread showers. If you have outdoor activities planned, especially for Saturday, I would not feel great about them.
Highs for this period will range from the upper 80s to lower 90s, with partly to mostly cloudy skies. There is a chance of some sunshine by Sunday afternoon, however.
Next week
As high pressure starts to build into the area, next week should be hotter. Starting Monday, I expect we’ll reach at least the low-90s, and by midweek I expect Houston to be solidly in the mid-90s with lots of sunshine. We cannot rule out a stray shower here or there along the sea breeze, but these should not result in any serious accumulations.
We will have an addtional update later this afternoon or early evening to keep tabs on the situation.
