Before we get into the nitty-gritty forecast details I want to take a moment to help calm some nerves.
A personal note…
Many folks on the coast or in adjacent inland regions are going to be nervous whenever they hear about some tropical mischief in the Gulf of Mexico. This upcoming system is not a ‘Harvey’. This is not an Allison or Ike. We’re not expecting it to attain hurricane status, not to even mention attaining major hurricane status.
We’re not expecting two to five feet of rain. Whenever folks ask if this is going to be like Harvey the common answer will usually be ‘no’. That was a historic storm with an unprecedented amount of rain. With that said – if your home floods in an event, it’ll be ‘your Harvey’ event. Understand that I’m not here posting weather information to scare anyone.
This system looks like it’ll be on the ‘minor’ event list versus something higher-end. Impacts should be localized, but again, if you happen to have the one house or one car that gets flooded, it’s a big-time event for you. By sharing information we hope we can help minimize any impacts you may experience and to keep you informed. Use us as one of several sources for accurate weather information. Your local National Weather Service office and preferred television meteorologist are great resources to get weather information from as well.
What’s Invest 95L up to this morning?
A trough of low pressure is located over the southern Gulf of Mexico this morning. Satellite imagery confirms that this system has not become any better organized since yesterday afternoon. There are no signs of a well-defined circulation (the definition of a tropical cyclone). We didn’t expect any organization this morning as wind shear remains strong. We’ll probably have to wait until late today or Thursday before wind shear weakens enough to permit some development.
Tropical Cyclone Development Chances & Intensity Guidance
The National Hurricane Center continues to give Invest 95L a high probability of becoming a tropical depression on Thursday or Friday. This system is moving northwest toward the western Gulf of Mexico. The longer the system takes to organize means the less time it will have to strengthen once it develops. I do believe this will attain tropical depression status at some point, but tropical storm status is more questionable. Even if this system can become a tropical storm before landfall the impacts from wind and storm surge should remain low. I can’t absolutely rule out a more rapid intensification, but even if that low-probability event occurs, it would probably only result in a 50-55 MPH tropical storm. Those winds would be limited to a small area and probably not even make it on-shore.
Another more probable possibility is that Invest 95L never becomes a tropical depression. In that case, we’d still have to deal with some heavier rains on Friday, Saturday, and Sunday. That aspect of the forecast would not change much.
Where is 95L going?
Without a well-defined surface circulation, the track of Invest 95L is somewhat uncertain. We’re confident it will move into/landfall in Texas sometime on Friday. However, where it makes landfall and eventually moves is still questionable. Yesterday most model data indicated the system would make landfall near or south of Corpus Christi, moving west/northwest toward Laredo. This solution would have the heaviest rains across the Middle Texas Coast and South Texas. Overnight model data shifted that a bit north toward the Middle Coast. That farther north solution wouldn’t really change the forecast too much, but the rain chances would extend up into South-Central Texas.
Frankly, we’re going to have lower confidence than average in the track of the storm (and thus the axis of heaviest rainfall) until this thing actually develops that well-defined surface circulation or gets closer to the coast. It doesn’t do much good to put a pin on a map, run models from that point, only to have that ‘pin’ end up being off by 30-50 miles. Remember, if something is off by 30-50 miles at the get-go, that’s a good 100+ mile difference down the road. Confidence is moderate to high that rain chances will increase on Friday and Saturday across parts of South Texas and the Middle Texas Coast, but the heaviest rain axis may not be more than a few counties wide. Rain chances continue today and Thursday in association with a stalled frontal boundary that is unrelated to this potential tropical system.
Above are the rainfall total forecasts for Friday, Saturday, and Sunday from the Weather Prediction Center (WPC). Keep in mind that the heaviest axis of rain along with rainfall totals will probably change some as we get a better idea of the overall organization of our tropical system. The concern of localized flooding isn’t necessarily because we’re expecting super high rain totals, but because we’ve already had heavy rains over the last two weeks.
Three-hour flash flood guidance numbers across South-Central Texas, South Texas, and the Middle Texas Coast range from 1.8 to around 3 inches. That means it would take between 2 and 3 inches of rain in a 3 hour period to cause flash flooding. Since a tropical system in a tropical airmass could dump that much rain in an hour in localized spots, that is where the concern over some new flooding exists. 2 to 4 inches of rain over 6-12 hours might not cause too many issues. 2 to 4 inches of rain in 1 to 3 hours will cause some issues.
Anyway, we’ll refine the rainfall numbers today and on Thursday. The rainfall aspect of this system is likely to occur regardless of it becoming a tropical depression, tropical storm, or just remaining a tropical wave/upper-level storm system.