Space City Weather

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.

Congratulations, Houston. We’ve made it to the hottest time of year, and Mother Nature has responded right on cue. The high temperature reached 99 degrees at Bush Intercontinental Airport on Monday, tying our hottest day of the year, when the mercury also hit 99 on June 13. We’ll see plenty of more days in the mid- to upper-90s this week. Fortunately, there will also be at least some scattered showers that may break the heat now and then.

Tuesday

For much of the metro area, temperatures have not fallen below 80 degrees this morning. This is due, in part, to mostly cloudy skies and very light winds. Later today we’ll see a mix of sunshine and clouds, with highs likely topping out a couple of degrees cooler than on Monday. Some showers have developed in response to low pressure south of Louisiana, and some rain from this system may eventually work its way into Galveston County later this morning.

The better rain chances—probably about one-in-three for the greater Houston area—will come this afternoon along with daytime heating. This rainfall will probably take the form of a downpour for one area, and nada a mile or two away. The best chances for accumulation are probably inside the Sam Houston Tollway, but rain could really fall anywhere. Storms should continue this evening, before dying off after sunset. Lows tonight may drop into the upper 70s.

Wednesday and Thursday

Expect more of the same with partly to mostly sunny days, highs in the mid- to upper-90s, and about a one-in-three chance of rain at your location. These showers, again, will likely fire up during the afternoon hours and die down as the sun sets.

Friday and Saturday

It looks like high pressure may slide a little bit closer to our region by this weekend, and that could reduce rain chances to “isolated” instead of “scattered.” Basically it means the same thing—it probably won’t rain at your house, but it might. And if it does, rains could briefly be heavy. Highs will remain in the mid- to upper-90s with partly to mostly sunny skies.

Sunday

The second half of the weekend may be a little warmer, with sunny skies and low rain chances. Some locations may come close to 100 degrees.

Next week

I don’t have too much confidence in weather next week, the first full week of August. I will say that right now it does not appear as though we’ll be fully in the grasp of high pressure, which means there’s at least a puncher’s chance of rain most days. But with that said, it will be August. And let’s be honest, August is pretty miserable in the 713.

Tropics

Matt will have a full rundown for you later this morning. Things still look pretty good but we’re just now approaching the time when activity starts to kick in, typically.

The dead of summer is nigh. If you look at the climate “normals” for Houston, the span from July 27 to August 20 is the historically warmest time of year when the average high is 95 degrees, and the average low 75 degrees. This period, a little more than three weeks, is when Houston often sees the hottest weather of the year. And after a somewhat cooler start to July, we’ll definitely experience this in the days ahead.

The overall pattern this week is fairly straight forward. The high pressure ridge that made for a hot and sunny weekend will shift slightly north this week, allowing for some scattered afternoon showers, before shifting southward again in time for next weekend.

Monday

Before the high pressure eases northward, Houston will see a hot and sunny day today a lot like this past weekend. We can expect highs in the upper 90s with only very light west or southwesterly winds. Lows tonight will only fall into the upper 70s.

Tuesday, Wednesday, Thursday, and Friday

Here’s what we know about the mid-week weather for the upper Texas coast. The atmosphere will be a little bit more amenable to rain showers, but rains should still be more “miss” than “hit,” and shower activity will be virtually nil during the overnight and morning hours. So basically these will be mostly sunny days except when they’re not, your daily chance of rain is probably about one-in-three, and highs will likely reach into the mid-90s. Nights should be mostly clear and sultry.

Saturday and Sunday

For now we expect high pressure to build more directly over the region this weekend, which should reduce rain chances. For now, therefore, our expectation is highs in the upper 90s with mostly sunny skies. Since Sunday is the first day of August, that seems appropriate.

Tropics

Overall, the Atlantic tropics remain quiet. A system near the coast of Georgia is increasingly less likely to develop, and across the rest of the Atlantic basin the chance of something else forming this week is low. Matt will have more in a tropics overview tomorrow, but the news for now is favorable. We have about two more months in which we need to watch things closely.

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.