Matt Lanza

There was nothing inherently special about yesterday. We had some sun, some clouds, some haze from passing wildfire smoke. But we only managed to hit 89° officially at Bush Airport with dew point temperatures in the 60s for the majority of the day.

For August, that is almost as good as it gets around here. We are going to see changes this weekend, and a return to more typical summer weather should be expected over the next few days.

Friday

Today looks like a bit of a transition day. We bring back some humidity. We bring back some temperatures. And we bring back at least a smattering of hit or miss showers, downpours, or thunderstorms. Not everyone will get wet today, but about 30 to 40 percent of the region should see at least something. The highest odds for showers should be south and west of Houston initially, but some areas north and east may see some showers by afternoon. Highs will top off in the low-90s.

Weekend

We’ve had a lot of high clouds and passing moisture overhead this week that’s blocked out the sun at times. We should lose that for the weekend. Expect a return to mainly sunshine, high humidity, and highs in the low to mid-90s and lows in the 70s to near 80 degrees. It will feel like 105° or a bit hotter at times this weekend when you factor in the humidity.

Showers will again be possible both days, but coverage should slack off some, maybe peaking at 20 to 30 percent chances. In other words, if you see some rain, consider yourself lucky. There should be a slight breeze each afternoon but nothing too special.

Next week

There’s nothing particularly interesting about the weather next week as it stands right now. That’s good news in August and September, right? Expect daily chances of thunderstorms to perhaps increase a little each afternoon. But some areas will get drenched while others just hear the distant booms of atmospheric acoustics. Otherwise, expect sun and clouds with highs in the low to mid-90s each day and lows in the 70s, fairly typical for August.

Tropics

It’s tough to make much out of what’s happening in the Atlantic right now. There are a number of possible options for development over the next 5 to 7 days, and maybe one area that’s more clear cut than others (which is assigned a 60 percent chance to develop this morning according to the NHC). We’ll have an update on this Monday and Tuesday. But as of right now, there’s not any model or group of models that’s especially bullish on any one outcome, let alone one that brings it to the Gulf. So we have some time to watch.

Following up on Eric’s post yesterday about NOAA’s seasonal forecast update, Colorado State followed suit on Thursday. They actually reduced their forecast a smidge, though they’re still calling for a season that ends up fairly active in the end. They also released a “subseasonal” outlook, which looks out at the next 2 weeks or so, and it unsurprisingly is calling for a period of above average activity in the Atlantic, something we’ve talked about for a little while now. So we’ll see. The setup in the Atlantic reminds me a bit of what we sometimes see in the western Caribbean or over Central America with what we call a “gyre.” You get a lot of storminess, models hinting at development, but little agreement on which portion of the broader mess becomes dominant. The good news is that it all continues to look mostly sloppy and disorganized for at least several more days.

Lately, I’ve enjoyed opening these posts with a comparison to where we were in 2020 at this time. By August 3rd of last year, we were watching Hurricane Isaias approach the East Coast, and Tropical Depression 10 had recently dissipated. We were actually heading into a lull period, as Josephine would not form for over a week. This year, we remain stuck on Elsa as our last storm. It was great to have a quiet July, but as Eric noted yesterday, we are merely through the easy third of hurricane season. The most likely time for storm impacts here historically is the next 6 to 8 weeks. Of the major hurricanes to strike our region through history (Cat 3+), virtually all have occurred in August or September. The 1909 Velasco Hurricane was an exception, as it occurred in July. So, now is the time to start watching seriously.

Tropical outlook in a sentence

While the noise is going to increase and we are likely to begin to find some disturbances to monitor in the Atlantic over the next week or so, none appear to be overly serious candidates to end up in the Gulf at this time.

Current Atlantic disturbance

The current disturbance outlined by the National Hurricane Center as having a 10 percent chance of developing over the next 5 days is not really much of a concern for us at this point in time. I think we need a little time to start priming the basin, so while this one may make a little noise in the next few days, it seems unlikely to sustain itself.

Most ensemble members of the major models have this thing flailing around for 72 to 96 hours and not doing much. Thereafter, things could change, but that could also be courtesy of another disturbance. Which leads us to…

Next in line

In general, it’s a little noisy in the eastern Atlantic right now, so it’s tough to separate signal from that noise at this early stage in the game, even in modeling. But either the disturbance currently outlined by the NHC or, more likely, another one should begin to try and coalesce from the mess in about 5 to 7 days in the open Atlantic.

At this early juncture, trying to hash out what this does is very uncertain. Right now, the vast majority of ensemble members either kill this disturbance off or have it recurving over the open Atlantic. Few, if any are taking it to the Gulf. We have about 80 different ensemble members between the GFS & European ensemble models, which provides a nice, wide spread of plausible outcomes. But by no means is it a guarantee that we’ll see either of those scenarios (a recurve or a dissipation) play out. But it seems to be the favored outcome at least at this time.

But, let’s focus on the overall pattern as forecast by the GFS and European ensemble models beginning around day 10 to see if there are any clues. Let me start by showing you wind shear. Both the GFS and European ensembles show a fair amount of wind shear setup over the Central Atlantic — for days.

This makes sense at a high level, and this seems to lend some credibility to the idea that whatever does develop may have some challenges in front of it as it moves across the ocean. Closer to home, the shear relaxes a bit, but until we see a disturbance heading that way, it’s not too concerning.

So where will it track? Great question. If we compare the GFS ensemble & European ensemble forecast maps at the 500 mb level (about 20,000 feet overhead) on day 10, I’ve annotated the maps with some notes.

There is a fairly strong high pressure in the upper atmosphere over the ocean. It’s not overly strong, but it may be enough to allow a weaker system to get kicked westward a little farther than perhaps models currently say. The general rule of thumb with Atlantic and Caribbean systems is that a stronger storm will gain latitude faster and a weaker disturbance will be subject to being “bullied” by high pressure and shoved west a little farther. Of course, if this fails to coalesce into a system at all, the point is moot and all the better.

So at this point it’s nothing to worry about because even through day 15, hardly any reliable model guidance has anything of note looking like it will enter the Gulf. But, given the calendar and trajectory of the disturbances out there, Eric and I will be keeping tabs on things, though not talking much unless it becomes apparent that we’re going to have something legitimate to watch.

Beyond this day 10+ stuff in the Atlantic, there will likely be continued background signal support for further disturbances through August 15th to the 25th or so. There may be some signs of less supportive conditions arriving later in the month, and when you factor in some lag time, that could start to assert itself in September. But I’d rather not get my hopes too high just yet. This concerns the “velocity potential” maps we discussed last week. A colleague and PhD candidate at Florida State, Jake Carstens, wrote a great piece on those maps and how they’ve been used to help sniff out this upcoming active period. He did a great job explaining how those maps work and it’s worth your time if you’d like to really get more into some serious meteorological analysis.

Anyway, enough for this week. We’ll see where things stand when we check back in on the tropics next week!

Not a whole lot to cover in this morning’s post, which is good news for most of us. But there are a couple things we’ll dig in on, mainly heat index values this weekend and rain chances with the cold front next week.

Today through Sunday

All of the next few days look fairly similar in nature, with sunshine, some clouds, and at least a smattering of afternoon downpours across the region. Exactly how numerous those are will likely vary from day to day, with today seeing the best odds of a downpour (still probably no worse than about 30 percent coverage) and tomorrow or Sunday probably seeing the lowest odds. Areas along and south of I-10 probably have the highest odds of seeing a shower play out, while areas north of Houston likely have the lowest odds.

The other weather issue you’ll contend with this weekend is heat. Look for highs in the mid to upper-90s today through Sunday with nighttime lows in the 70s to around 80 degrees.

It will feel more like 104° to 108° each afternoon when you factor in the humidity, with some places possibly even sneaking up close to 110° at times. It’s a good idea to take it easy outdoors this weekend and drink lots of water.

Monday

Consider Monday our transition day, albeit late. We will start off like the weekend, with ample heat and humidity. Look for 70s to near 80° in the morning again and daytime highs in the mid to upper-90s as well. The front will arrive sometime Monday night or early Tuesday it appears. As Eric has noted, August fronts don’t usually arrive with a ton of fanfare in the temperature department, so you probably won’t realize when it gets here. But, storms are possible by Monday evening.

Tuesday through Thursday

With the front overhead or just offshore, it will serve as a focal point, in concert with the sea breeze each day for showers and thunderstorms. Because we’ll have more clouds and higher rain chances, we can expect cooler temperatures. Highs will likely be in the upper-80s to low-90s with lows in the 70s. You may walk outside one morning and comment, “Hey, this isn’t all that bad.” But short of that, this looks like it will remain a fairly warm and humid period.

How much rain should we expect with all this next week? I think it depends on exactly how far offshore the front gets. Today that means probably an inch or two for some areas, a bit less in others.

Some higher amounts will be possible in isolated areas, but honestly this doesn’t look like too menacing a period, and it will probably just be mostly a nuisance couple of days for us. Rain chances should peak Tuesday and Wednesday and probably begin to tail off a little by Thursday. There is still some uncertainty on these details, so you’ll want to check back with us on Monday to see what has changed over the weekend.

Tropics

All remains quiet right now and probably for at least the next 5 to 7 days. There are some hints that activity may begin to pick up again the week of August 9th. But as of now, there is nothing specific we can hone in on anywhere in the Atlantic basin, so that’s purely speculation, albeit speculation rooted in meteorology. We shall see. But nothing to worry about for now at least!

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.