Eric Berger

Likely a hurricane at landfall, Harvey approaches a wary Texas

Good morning. Tropical Storm Harvey has shown signs of better organization overnight, and now appears likely to become a Category 1 hurricane before landfall. However, given the warmth of the Gulf of Mexico and lowering wind shear levels, a stronger storm seems possible. As discussed Wednesday, models are increasingly focused on a landfall between Brownsville and Corpus Christi, and the National Hurricane Center has issued hurricane warnings for locations from Port Mansfield to Matagorda, Texas.

Tropical Storm Harvey forecast track. (National Hurricane Center)

This much of the forecast seems clear enough. Over the next two days, before Harvey makes landfall late on Friday or early Saturday, the storm will bring heavy rainfall, storm surge, and possible hurricane conditions to portions of the lower Texas coast. Through Saturday, some areas from South Padre Island through to Matagorda Bay, may receive a dozen inches of rain, or more. Barring a major change in forecast, locations further up the Texas coast, including Houston, will see seas rise 3 to 5 feet above normal levels, gusty winds, and perhaps 2 to 4 inches of rain through Saturday.

The key question for the upper Texas coast, including the Houston region, is what comes next.

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For Houston and Texas, the rains cometh. But where?

As of 2:30pm CT, Harvey remains a depression in the southwestern Gulf of Mexico. We remain most concerned about the potential of this tropical system to drop a prodigious amount of rain from Friday through Tuesday or Wednesday of next week, primarily due to the fact that it will likely stall, or nearly so, once it moves into Texas this weekend. Let’s jump into the forecast.

Harvey track and intensity

The depression remains fairly poorly organized this afternoon, and that’s a good thing, because once it begins to develop a tightly organized circulation, there will be little to inhibit from strengthening further. The official forecast calls for a 75-mph hurricane to make landfall along the Texas coast Friday afternoon. It’s worth noting that the models (including the European forecast system) have shifted a bit to the left, meaning that a landfall between Brownsville and Corpus Christi now seems most probable. That may be good for the Houston region in terms of storm surge, but as we’ll see, it may matter little in terms of rainfall.

The GFS model ensembles are clustered between Brownsville and Corpus Christi. (Weather Bell)

Rainfall, and timing

Please note that the following is speculative, but we’re attempting to affix a time frame to this storm and its effects because we’ve had a lot of travel questions. The following forecast assumes a Friday landfall along the south Texas coast, and therefore the forecast is subject to change. You have been warned.

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Harvey redevelops in southern Gulf, will bring major rains to Texas

Just a quick post to note the official redevelopment of Harvey as a tropical depression in the southern Gulf of Mexico. The forecast track mirrors what we’ve been discussing for a couple of days now—the movement of a tropical storm into the Texas coast, after which its slows down, and drenches the eastern part of the state.

Official forecast track for Tropical Depression Harvey. (National Hurricane Center)

The official forecast predicts Harvey will reach hurricane strength—barely a Category 1 storm with 75mph—before it reaches the Texas coast. Tropical Storm watches are in effect for Galveston and the Galveston Bay area. Hurricane watches are in effect for Brazoria County, and areas southwest of Houston. But the primary concern with this system remains widespread rainfall and inland flooding. The hurricane center’s rain forecast for Harvey reflects this:

(National Hurricane Center)

Our forecast from this morning largely holds up, as it is based on similar model data that made up the National Hurricane Center’s outlook. We will post a more comprehensive update this afternoon, around 2:30pm. In the meantime, here is what Matt and I feel you should bear in mind about the next several days.

  • The rainfall hype is real and serious, and although it’s impossible to specifically forecast it at this time, you need to be aware of the threat.
  • The forecast is going change, and in systems like this trying to pin down who gets maximum rainfall is extraordinarily difficult. Patience required.
  • The rains will be spread out from Friday through Tuesday, but for Houston we continue to expect the heavier rain during the latter half of that period.

 

Harvey to re-form soon, bring flooding to the Texas coast

Houston will see continued warm weather—with highs in the low- to mid-90s—and scattered showers during the next couple of days, but our principal focus remains on the likely redevelopment of Tropical Storm Harvey, and its eventual movement toward Texas. Parts of the state will be be utterly soaked by the end of this weekend, and some flooding seems inevitable.

Tropical Storm Harvey at 6am CT on Wednesday. (Space City Weather/NOAA)

As of 6:30am Wednesday, a reconnaissance aircraft is flying around the large area of disturbed weather in the southern Gulf of Mexico, and may find a tropical depression. Some dry air appears to be slowing development right now, but the Gulf is warm and wind shear manageable, so some intensification is likely as the system moves northwest toward Texas during the next couple of days. While we cannot rule out rapid intensification, a phenomenon which is still relatively poorly understood, it is probable that Harvey will come ashore as a tropical storm or Category 1 hurricane. A landfall between Corpus Christi and Matagorda seems most likely at this time. While we may see some storm surges of 3 to 5 feet with such a storm, and tropical storm-force winds, rainfall is by far the biggest concern.

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