Matt Lanza

The last time we had a tropics post was back on July 13th, and since then zero storms have formed. By July 30, 2020 Isaias had formed. We’re still stuck on Elsa this year, and I hope no one is complaining. It would seem that the next week or two, broadly, will continue on this quiet trajectory. Today, we will look into perhaps why things have been so different this month compared to a year ago.

Tropical outlook in a sentence

While one can never rule out a rogue “homegrown” system this time of year from a disturbance over the Gulf or off the Southeast coast, there is no sign of any organized activity in the Atlantic over at least the next 7 to 10 days.

2021 vs. 2020

So the obvious question here is “what gives?” Why has 2021 behaved so differently from last season? Well, for one 2020 was not “the norm.” At all.

We had 30 named storms last year. The defeatist in me really did expect this season to also be very busy by now, even if it lagged 2020 by a bit. That has not yet happened thankfully, and ultimately I think it mostly comes down to a law of averages in some sense. Of course, that doesn’t explain things scientifically. Let’s look at a couple things.

First, sea surface temperature. How warm is the Atlantic Basin right now? Well, if we look at a snapshot of recent water temperature anomalies, you’ll be able to see that we’re still a bit above normal in most of the Atlantic.

Now, granted, the water temps off the Southeast coast and in the eastern Caribbean and central Atlantic aren’t impressive. And indeed, this is notable, particularly when you look at how late July compares in 2021 versus last year. The map below shows water temperatures for the week of July 18th through July 24, 2021 minus the same week in 2020.

In some cases, we’re running 1 to 2 degrees cooler than a year ago, at least for late July. So that may be one reason why this year has lacked some of last year’s firepower to date.

Let’s go into the meteorological weeds a bit. If we look at a metric called “velocity potential,” or “VP,” we can see a very interesting year over year difference in the Atlantic basin. Without getting too deep into things, think of negative velocity potential values as being favorable for tropical development and positive ones as being unfavorable. This is especially true if those values are over the eastern half of the Atlantic basin. Negative VP will promote more rising air & thunderstorm activity in the background, while positive VP will promote more sinking air and fewer robust tropical waves. It’s much more complex than this, but at a very high level, that explains some of the basics.

In a nutshell, the deep purples on the map above indicated a lot of smoke on the water in 2020, which ultimately meant a number of tropical systems. Edouard, Fay, Gonzalo, Hannah, Isaias, and a bonus tropical depression all formed in July of 2020. This July is likely to finish with just one storm, Elsa. Looking at the map labeled 2021 above, you can see the reds and oranges in western two-thirds of the Atlantic basin, Caribbean, and Gulf, along with much less blue and purple over Africa and the eastern basin. Thus, the background state this July has been less favorable than it was a year ago and subsequently, it’s been a fairly quiet month.

The obvious question is whether that will change. In general, based on most modeling I’ve seen, this is expected to change a bit in August to a pattern not as robust as 2020 but at least something more like it perhaps. So in addition to climatology favoring our typical ramp in tropical activity in August and September, we may get a subtle addition from the overall background state too. My gut feeling is that August will start quiet, but as the month wears on, we will have systems to watch closely, as we typically would in any hurricane season. I don’t think it will be quite at the frenetic levels of 2020 or even 2017, but to be sure, it won’t stay this quiet forever. My advice? Enjoy what we have left of the quieter conditions, and make sure you’ve got your plans and kits together for the August and September gauntlet.

While it hasn’t exactly been chilly this summer, at least July has been running a couple degrees below average for Houston. We’re now set to, in the words of Emeril Lagasse, “kick it up a notch” this weekend. Let’s rock and roll.

Today

High pressure is going to begin to exert its will on southeast Texas today. The amount of moisture in the atmosphere is going to drop precipitously, allowing for a reduction in rain chances this afternoon. The faucet isn’t going to shut off completely, but it’s likely going to scale back to a slow drip. Call it maybe 20 percent coverage of rain this afternoon. And that may even be generous.

More importantly, the heat is going to ramp up. We topped out at 93° at both Bush & Hobby Airports yesterday. Look for about 95-96° today officially, with a few places hotter and coastal areas a little less hot but quite humid.

With the humidity, it’s likely to feel like 105 to 110° at times, which is right about when Heat Advisories should be issued by the National Weather Service. So, don’t be shocked to see at least a couple of those in the days ahead. It may turn a bit hazy as the day goes on and a cloud of Saharan dust arrives from the Gulf, but that will be more noticeable tomorrow I think. High summer’s here folks.

Weekend

This weekend should feature similar weather on both Saturday and Sunday. I’d expect highs to be 96 to 98° officially, with a few places possibly coming in near 100° and coastal locales in the lower 90s. Lows will likely be in the 70s to low 80s. Heat index values each afternoon will again likely exceed 105° in many spots. Rain chances are about as close to zero as it gets for this time of year.

You will notice a good bit of Saharan dust in the air this weekend from that dust cloud overhead. I think Saturday may look more acrid than Sunday. Either way, those of you with respiratory sensitivity to dust events should be ready for some discomfort this weekend. Sunrises and sunsets may be a bit more alluring than usual at least.

Next week

Yesterday, Eric wondered if I might be able to provide some clarity on next week’s rain chances. I can’t tell you too much new, but based on what I see in the weather models, I suspect we’ll see another hot, mostly dry day Monday, followed by a slightly less hot, slightly less dry Tuesday. On Tuesday, Wednesday, and Thursday, the center of the ridge shifts back into Colorado, which should be enough to open the Gulf back up for daytime, sea breeze-driven thunderstorms.

By later Thursday and into next weekend, it appears that the ridge will actually slide back southeast again toward Texas, which means we might recycle hotter, drier weather for several days late next week and into the weekend. I don’t think it will be quite like this weekend, but it may not be too far off.

Tropics

The National Hurricane Center is highlighting a disturbance that is emerging off the Southeast coast today. It has a low chance of possibly developing over the weekend, but at this time it is not expected to turn west into the Gulf.

We’ve had quite a 12 hours of storms across the region, particularly from just north of I-10 south to the coast, with some impressive lightning and heavy rainfall. The highest 24 hour total I can find on the Harris County Food Control website is just a hair over 3 inches of rain near Dickinson. Radar estimated rainfall from the last 24 hours is shown here.

This morning’s radar snapshot below shows the bulk of the rainfall hugging the immediate coast, with the heaviest mostly offshore at this time.

So, what’s next?

Today

Often, when we see this sort of cluster of rain offshore, it helps to cut off moisture inflow from the Gulf of Mexico. In other words, significant moisture is involved with the offshore rain, and it could help reduce rain chances on land a bit, especially the first half of today. That doesn’t mean it will be totally dry, but showers should be very isolated this morning for the most part.

As the day wears on and daytime heating takes over and presumably we see offshore rains weaken a bit, look for a few more storms over Houston and other inland locations. But today’s rain and storms will probably be more hit and miss than widespread, and odds may favor you avoiding rain. We’ll see how that goes. As someone flying to Houston in just a bit, I am okay with this.

Other than rain chances, expect clouds and sun. Highs will probably approach 90 degrees.

Wednesday and Thursday

Look for afternoon showers and thunderstorms, driven mostly by daytime heating and the sea breeze for the middle of the week. Not everyone will see storms, but those that do could easily see an inch or two of rain between both days. The overall pattern will stay pretty unsettled on both days, but it’s tough to get too cute with details today. We will know more tomorrow morning. Highs should be in the upper-80s with lows in the 70s.

Friday and weekend

The storm system in the upper atmosphere that will help the midweek period be so unsettled will continue working back to the west Friday, into West Texas. By Sunday, it ends up in Arizona (good news for the drought plagued West), so things should begin to really settle down around here this weekend. With more sun, that means more heat, and high temperatures should go from the low to mid-90s to mid to upper-90s as the weekend progresses. Rain chances are never zero in summer here, but they look to be quite low. We’re coming up on our hottest time of the year, so this isn’t too surprising. But still, be ready.

In addition to all that, it’s likely we’ll be seeing another blast of Saharan dust this weekend.

It’s going to look, feel, and taste like high summer around Southeast Texas.

There are signs this very hot, drier weather will continue well into next week. If you’ve managed to keep the sprinklers off most of this summer, that may change next week.

Due to travel and work for both Eric and myself, we’ll be foregoing our tropical post today, but there’s honestly not much to discuss right now. The tropics remain quiet, and that should continue for at least another week or so. Things may change heading into August, as they often do, but for now we have nothing in particular to discuss. We will let you know when that changes.