Matt Lanza

Good afternoon. Tropical Depression 14 formed late this morning from the disturbance previously dubbed Invest 97L. This is the primary system we will watch over the next few days as it moves toward the Gulf. Here’s a brief rundown of what we know and, more importantly what we don’t know.

Now

Tropical Depression 14 is located east of Honduras and south of Cuba over the western Caribbean Sea.

It’s basically what you would expect from a tropical depression: sort of messy, but with numerous storms both east and west of the center, so it’s not terribly asymmetrical.

The latest forecast from the National Hurricane Center has the system moving into the Gulf and remaining a tropical storm through early next week.

It’s important to note that while a “center line” points this right at Houston, the cone is the cone for a reason. The storm may track well to our east or well to our southwest. Our impacts here in Houston would vary considerably based on that, so this map should not be considered a license to panic or to write it off entirely.

Over the next two days, TD 14 will enter an environment that’s pretty conducive for strengthening. Shear will continue to relax. As it moves toward the Yucatan Peninsula of Mexico, look for this to intensify into a tropical storm and possibly a hurricane. Water temperatures in the western Caribbean are more than supportive of strengthening.

Once it gets to the Yucatan and beyond, the questions begin to mount quickly.

Here is what we know:

We know that TD 14 should move across the northeastern part of the Yucatan Sunday morning. We know it will likely be at least a tropical storm. We know it will be pulled north by a trough over the South and nudged west by the Bermuda high as it expands westward across Florida. We know that if impacts occur in Houston, they would likely begin Monday night or Tuesday.

Here is what we don’t know:

We do not know where TD 14 will ultimately end up and how strong it will be when it gets there. I know this makes you throw your hands up in the air in frustration, but those are the realities.

We do not know how much wind shear TD 14 will encounter over the Gulf. As the trough over the South weakens and pulls out, there will be some wind shear left behind. If that ends up over the Gulf, that will help mitigate TD 14’s ultimate strength. If that wind shear goes north as the storm comes north, then we need to watch for TD 14 to intensify more significantly.

We also don’t even fully know how much land interaction TD 14 will have near Honduras and Mexico. The latest advisory suggests TD 14 is farther south than originally thought, so that is something that could ultimately impact the system.

We don’t know how much rainfall we will see, as it will depend on how organized TD 14 becomes and exactly where it goes.

We don’t know how TD 13 may impact what happens with TD 14, so there’s a good deal of uncertainty there.

More ambiguous things we can say:

A stronger storm would likely go to our east, whereas a weaker one would come closer to us. But weaker does not necessarily mean “weak,” so keep that in mind.

We do not expect a stall/Harvey scenario at this time or even an Imelda one but we are not entirely sure how things will play out. Flooding is possible in any tropical system, so we cannot rule any sort of flooding out right now.

We should be able to narrow the cone a bit in the morning, and we should know a lot more later tomorrow and Saturday morning. So stay tuned.

As we’ve been telling you for essentially weeks now, the tropics are becoming very active. Some of this is just basic math—as we approach late August and September, the tropics usually come alive. But there is more at play this year, with things happening in the background that should allow for basically an “outbreak” of sorts of tropical systems across the Atlantic basin in the days ahead.

Tropical outlook in a sentence

There will be at least two legitimate opportunities for tropical systems to develop and potentially impact some part of the Gulf of Mexico over the next 10 days, and an additional system or two may develop farther out in the Atlantic as well.

Invest 97L: First in line

The system the models are most bullish on is Invest 98L, which we’ll discuss below. But the one we are most concerned with more immediately is Invest 97L, because this is closer to us, and it is the type of system that can sneak up on us and cause some problems.

Invest 97L is currently over the eastern Caribbean Sea. It’s not terribly well organized, and you can see a satellite loop from Tuesday afternoon showing mostly just a “blob” of storms at this point.

Over the next few days, 97L will plod along in the Caribbean, interacting at times with a disturbance over South America. So development is only expected to be slow or gradual. Eventually, it will end up in the western Caribbean, somewhere near the coast of Honduras or the Yucatan. I can hear 75% of our audience now saying, “Wait, that’s how Harvey happened, right?” And the answer is, “Sort of, yes.” It’s the elephant in the room here, obviously, so let’s discuss and compare real quick.

By the time the disturbance gets into the Western Caribbean this weekend, the upper air pattern will be favorable for it to gradually lift north. Here’s a map from the GFS ensemble valid on Saturday afternoon. We’re looking at the 500 mb level, or about 20,000 feet up, basically the large-scale steering pattern for this time.

On Saturday afternoon, 97L should be off the Yucatan or Belize or just north of Honduras. It will be steered to the west by high pressure near Bermuda, while at the same time, a trough of low pressure in the upper atmosphere over the Lower Mississippi Valley is going to try and “pull” Invest 97L to the north. So at this point, the system should be moving to the northwest.

So in that respect, a middling system that gets pulled north and west across the Yucatan and into the Gulf of Mexico, Invest 97L is similar to Harvey. But I’m going to intentionally stop with the similarities there because the potential of what this does is much different from Harvey.

There is a chance that the trough remains strong enough to continue in its effort to “capture” Invest 97L, allowing it to come north into the Gulf and toward Louisiana or perhaps the Upper Texas Coast. That scenario can’t be ruled out. There is also a chance that Invest 97L gets “missed” by the trough and ends up stationary without much to steer it over the Gulf of Mexico. While that’s not a huge rainmaker on land, that becomes problematic because there would be a chance Invest 97L could strengthen while sitting offshore. Another possibility is that the Bermuda high continues to expand so much so that it just pushes 97L into Mexico as a weak rainmaker. Harvey was a once in a lifetime storm in terms of rainfall, so we don’t want folks to worry about a “Harvey” type storm right now. There are indeed some similarities in the initial overall big picture, yes. But that’s where it ends right now. What we should be doing (and what Eric and myself will be doing) is making sure we are prepared to take action late this weekend or early next week just in case it becomes clear that 97L will become a problem for us. We will keep you posted.

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Back on Friday, I wrote in our weekend forecast discussion that “if the chance of a shower is about 10 percent Friday and Saturday, maybe it inches up to 15 or 20 percent Sunday.” We pride ourselves on honesty here at Space City Weather, and that will end up likely proving inaccurate. The reality is that compared to Friday, our Monday front is a bit faster and has a burst of upper level support in the atmosphere this afternoon which should allow storms to blossom today.

Radar is quiet as of this writing, but as an upper level disturbance interacts with the ample heat and humidity over our area, it may be just the trigger needed for strong thunderstorms to develop north of Huntsville and Conroe by about 3 or 4 PM. We expect a complex of storms to develop up that way and drop into places like Conroe and The Woodlands between 7 and 9 PM or so.

After that, things do become a little more uncertain. Most modeling does bring those storms into the I-10 corridor and possibly points south after 8 to 9 PM or so. We’ll see if the storms can survive the trip, but the bottom line is a likely dry afternoon for Houston and points south, with storm risks increasing later in the evening.

This does not look like a high-end severe weather outbreak, but storms could certainly become strong to severe as they drop through the region. We are in a “marginal” risk (1/5) of severe weather. Hail is a possibility, but as is often the case in these sorts of setups, strong winds may be the more common problem. With the storms moving at a pretty healthy clip, look for gusty winds ahead of the rain this evening, especially north of I-10.

Storms should dissipate or move offshore overnight, leaving us mostly quiet to start Monday. We can’t rule out more showers and storms tomorrow. The cold front should arrive later tomorrow, ushering in slightly less humid air for midweek, which will be most noticed at night via slightly cooler nighttime lows. Eric will have more on that in the morning and an update on the tropics, which he has already touched on today.

The meteorological phenomenon we call “August” has mostly lived up to its normally unpleasant expectations so far in the Houston area. After hitting 101° on Wednesday, we topped off at 99° yesterday. Overnights have been especially oppressive, with Galveston tying an all-time record warm low temperature on Wednesday and Hobby Airport blowing through its record for most 80 degree mornings in a year already. We will have a post with a lot more on this coming soon. In the meantime, we expect no relief this weekend, but there are signs we should begin to cool off a bit next week. Let’s discuss.

Today through Monday heat

A heat advisory continues for the entire region both today and tomorrow, and we would not be shocked to see it extended into Sunday and/or Monday as well. Expect mostly sunshine with highs near 100, lows in the 70s to near 80°, and heat index values of 105° to 110° or even briefly hotter at times.

Take it slow and easy in the heat this weekend.

Rain chances and a front next week?

As far as rain chances go, we should not see anything other than an isolated pop-up shower or storm today and tomorrow. If the chance of a shower is about 10 percent Friday and Saturday, maybe it inches up to 15 or 20 percent Sunday.

Monday and Tuesday are complicated by a cold front in the area. Don’t expect anything refreshing next week, but we should see a shift to “less hot” weather and a better chance of scattered showers and storms early. Monday would still be hot with scattered showers and storms in the afternoon. The trade off with a cold front possibly pushing through is that rain chances would drop off again behind the front for later Tuesday and Wednesday. Still, we’ve got a few things to work out regarding the timing of the front and just how high rain chances look. We’ll update you Monday.

Behind any sort of front, we would see high temperatures “only” in the mid-90s and less oppressive heat index values. Lows would be more in the 70s for most.

Tropics

Tropical Storm Josephine formed yesterday in the open Atlantic, the earliest 10th or “J” storm on record by almost 10 days.

Josephine will likely begin to get steered to the north as it passes the islands and is no threat to the U.S.

The only other disturbance outlined by the National Hurricane Center (Invest 96L) is a disturbance off the North Carolina coast that will slide out to sea over the next few days. We expect another wave or two to emerge next week as candidates for development, but it’s far too early to speculate on any other details. We just know it’s likely going to get and stay active.

For those of you scoring at home, the earliest eleventh, or “K” storm was Katrina on August 24, 2005. The earliest “L” storm was 1995’s Luis on August 29th, part of a barrage of storms in the Caribbean islands that year.