The next couple days are likely to be quite busy in the weather department for Texas. For the sake of simplicity, I’ll keep this blog to the point and try not to get all nerdy. There will be scattered rain chances today through Thursday in association with a weak frontal boundary making southward progress over northern and central parts of Texas. Some storms may be strong with hail and localized high wind gusts. For your specific rain chances please visit www.weather.gov and enter your zip code. This blog will focus on the increasing probability of a tropical cyclone impact on the Texas coast on Friday.
Tuesday Morning Overview on Harvey
Confidence is increasing that Harvey will regain tropical storm or hurricane status in the western Gulf of Mexico on Wednesday, Thursday, and Friday.
Weather model trends over the last 24 hours have also increased the probability that Harvey will pose a direct threat to the Texas coastline.
There is low to moderate confidence that landfall on the Texas coast would be on Friday.
Confidence is low on exactly where Harvey would make landfall on Friday in Texas (where the center will come ashore).
The remnants of Harvey are located over the Yucatan Pensenlya this morning. When ‘Harvey’ emerges into the Bay of Campeche and the southwestern Gulf of Mexico tonight atmospheric conditions will be favorable for it to redevelop into a tropical cyclone. Forecasters at the National Hurricane Center give the system a 90 percent chance of regenerating into a tropical cyclone on Wednesday and Thursday.
Where is it going?
The remnants of Harvey do not have a defined ‘center’ this morning. Without a defined center the downstream track of the system is much more difficult to determine using tropical-specific weather models. Those models start out with a set ‘pinpoint’ on a map and generate downstream forecasts from that starting point. If you move that point north or south 20 miles the downstream solutions in four days could be over a hundred miles offset. We’ll need to wait until tonight until we can start getting specific on potential landfall locations (cities, counties, etc). What does seem fairly likely at this time is that Harvey will make landfall somewhere on the Texas coast on Friday – from the South Texas coast all the way up the Coastal Plains into Southeast Texas.
This one model graphic depicts an ensemble (or multiple models runs with slightly different parameters) for late Friday. You can see that there are a variety of solutions shown with a potential landfall location ranging from near Corpus Christi to just west of Galveston. Again – please don’t get hung up on specific track maps or locations yet. We don’t even have a defined center with Harvey yet today – and we really need that to happen before we can start pinpointing downstream exact locations. Just understand it looks like we’ll have a tropical cyclone – either a tropical storm or hurricane – making landfall somewhere on the Texas coast on Friday or Friday Night.
How strong could Harvey be at landfall?
Seeing as Harvey hasn’t even developed yet this is a problematic forecast as well. Atmospheric conditions and sea surface temperatures near 90 degrees F do support intensification, but that will depend on how quickly Harvey’s inner core can become organized. Tropical storm status (sustained winds of 39-74 MPH) is very likely, but Harvey could strengthen quickly on Thursday and be a hurricane (sustained winds exceeding 74 MPH) before making landfall on Friday. Not to sound like a broken record, but we need to get Harvey into the Gulf of Mexico tonight and Hurricane Hunters into the system to get an inside look at the structure of the system. Not all tropical cyclones are alike – some can strengthen more quickly while others may take their time. Data from the hurricane hunters will be able to give us a clearer look once ‘Harvey’ moves off the Yucatan Peninsula.
The tropical-specific weather models – which should be used with caution until we get a defined ‘center’ on Harvey to form – do ramp the system up quickly once it makes it into the Gulf of Mexico on Wednesday and Thursday. In fact, most of these models ramp it up to a Category 1 hurricane before it makes landfall on Friday. That means hurricane force winds of 75 to 90 MPH would be possible near and in the eastern quadrant of the eyewall at the landfall point – with lesser winds farther out from the eastern or dirty side of the cyclone. I’m getting too technical at this point, but understand Harvey may well be a hurricane before it makes landfall on Friday.
After-Landfall Impacts (AKA Excessive Rain Amounts and High-End Flooding Potential)
While Harvey may bring impacts to the coast, the most worrying aspect of this system could be inland flooding. Various weather models have Harvey moving very slow after it makes landfall – almost to the point of stalling it out. Copious amounts of moisture combined with the lift from Harvey and a remnant frontal boundary would be a near perfect recipe for exceptionally high rainfall totals. No doubt a flooding risk is possible, if not probable – with the possibility of extreme rainfall and significant flooding a concern. We will really need to watch for this possibility since rainfall amounts of 7-15+ inches would be possible where-ever Harvey sits around. This risk looks highest in parts of the Coastal Plains, Southeast Texas, and East Texas this weekend into early next week. However, this will likely change as the eventual location and track of Harvey will dictate the worst impacts. Remember, the ‘dirty side’ of a system is along and east of the track in most cases.
— Jonathan Erdman (@wxjerdman) August 22, 2017
— Tim Heller ABC13 (@HellerWeather) August 22, 2017
What should you be doing?
At this point, we’re in a watch and see mode. If you live on the Texas coast you should always have a hurricane preparedness kit ready to go during the hurricane season. Check with your local municipality’s emergency management office (website, brochure, etc) to see if you’re in an evacuation zone. I’m not saying we’re going to have coastal evacuations from Harvey, but it is always a good idea to check up on these things during hurricane season. Those all along the Texas coast and inland should continue to check back for forecast updates. There will be changes, and we’ll likely be pushing out several blogs a day by Thursday. Harvey’s impacts won’t stop after landfall – and may, in fact, get worse with a serious flooding threat a possibility. We’ve got a Texas Hurricane Resource Center page set up with various resources. We’ll be updating it throughout the week with relevant information for Harvey and other resources that could be helpful.