Eric Berger

WANTED: Fall-like weather. Last seen in Houston sometime around April. Suspect is known to bring crisp mornings, low humidity, and open-window weather. Reward offered for immediate return. No questions asked.

Fall Day, where art thou?

Here at Space City Weather we are as desperate (if not more so!) than most of our readers for a real taste of fall. The definition we’ve settled on for “fall” over the years is a low temperature of 65 degrees, which we then declare to be the Houston holiday of “Fall Day.” It is a great and glorious day. Now such a temperature is not cold, by any means. But after a long, hot summer it can be considered pleasantly cool evening.

So far this season our “coolest” night came on September 26, when the low dropped to 69 degrees. Our first “taste” of fall is running late this year. Very late, in fact. Dating back to 1900, the average date of Houston’s first 65-degree (or lower) temperature after August 1 in a calendar year is September 15. Not this year. In fact, only nine years have had a later “Fall Day” than this year. The latest 65-degree day in Houston, since 1900, came in 1904 when poor Houstonians had to wait until October 13. That’s next Tuesday.

It is possible that we’ll see a 65-degree reading at Bush Intercontinental Airport on Friday or Saturday morning this weekend, with drier air helping to cool down nights some. It will be close, but also fleeting with muggy nights returning next week. I do have some hope for a stronger front about 8 to 10 days from now. More on that below.

Thursday

It is warm and rather humid this morning, with temperatures only falling to the lower 70s. Highs today will climb into the lower 90s, with sunny skies. Rain chances are near zero. However, falling on the back side of Hurricane Isaias, Houston will start to see a more northerly flow later today, and that will usher in some drier air. As a result lows for much of the region, outside of the urban core, should see temperatures fall into the mid- to upper-60s tonight.

A word for my fellow runners. If you’re training for the Houston Marathon this year—and the event keeps getting more popular, having sold out in July—we finally have some decent weather for longer runs. Temperatures won’t be cold by any means, but I’m hopeful that both Friday and Saturday mornings will see dewpoints in the upper 50s across most of Houston. If you’re out running before, at, or just after sunrise you should be able to escape summer-like humidity. It should, dare I say it, feel almost pleasant? Anyway, best of luck with your training.

Friday and Saturday

As mentioned we’ll see an influx of drier air on both of these days. Expect highs ranging from the upper 80s to about 90 degrees, and cooler nights in the 60s for most locations. In concert with modestly lower humidity, these will be nicer days, with pretty great mornings and evenings. Rain chances remain very low, perhaps in the 10 percent range.

Sunday

Humidity will be a bit higher on Sunday, with highs of around 90 degrees and mostly sunny skies. Overnight lows may warm a little bit as a result.

Next week

Muggier conditions return. Most of next week should bring mostly sunny skies, with highs in the lower 90s and lows in the mid-70s. This is pretty warm for October, but I continue to have some hope that by Friday (or thereabouts) we could see the arrival of a genuine fall front. This could also bring some rain with it. I don’t want to offer any details or false confidence, but I am hopeful we’ll see a meaningful pattern change by next weekend.

Hurricane Isaias

We have our first Atlantic hurricane of the season, with Isaias forming on Wednesday evening in the Gulf. The storm is moving toward the east-northeast, and will likely make landfall in southern Alabama or the Florida Panhandle as a Category 2 or Category 3 hurricane on Friday night. There are no real implications for Texas (aside from the drier air discussed above), but all of the typical hurricane threats are in play for parts of the southern United States. Matt has much more on those implications over at The Eyewall.

In brief: Tropical Storm Isaias has formed in the southern Gulf, and it has a really good chance to become the season’s first hurricane. It is bound for the northern Gulf coast. This should usher in a few days of drier air into Houston this weekend.

A Gulf hurricane?

In the modern record, an era dating back to World War II when there has been aircraft reconnaissance and later continuous satellite coverage, there has never been an Atlantic season without a hurricane. Prior to this there have been two years, 1907 and 1914, in which no hurricanes were recorded. However, that does not definitively mean there were no hurricanes. Before aircraft flew across the Atlantic, our records almost certainly missed hurricanes over the open ocean.

So far this year, with El Niño reaching historic strength, the Atlantic has produced several tropical storms but no systems that have reached hurricane strength. But with the formation of Isaias in the southern Gulf that is likely to change. There is a high likelihood that Isaias will become a hurricane, and possibly a major hurricane over the warm Gulf waters before tracking north toward a landfall somewhere between southeastern Louisiana and the Florida Panhandle late Friday or early Saturday.

Be sure to check The Eyewall for full and ongoing coverage of Isaias. Along the upper Texas coast we may see tides running a foot or two higher, and some rough seas offshore. But mostly we should see some modestly drier on Thursday, Friday, and Saturday.

Wednesday and Thursday

Today and Thursday will be warm (hot?) and sunny days, with high temperatures in the lower 90s for most of the region, away from the coast. Rain chances are essentially zero. Nights will be warm, with lows generally in the low- to mid-70s. On Thursday afternoon we should start to see modestly stronger winds from the northeast (on the backside of Isaias), and this will bring us some moderately drier air for a few days.

Friday and Saturday

These will be mostly sunny days with a slightly cooler northeasterly flow. Highs will be in the upper 80s to lower 90s. For areas along and south of I-10 there will be a slight chance of showers on Friday afternoon, but probably only in the 10 to 20 percent range. Nights will be pleasant, with lows around 70 degrees in Houston, and in the 60s for outlying areas.

Sunday and Monday

The second half of the weekend, and Columbus Day, will see continued mostly sunny skies and highs around 90 degrees. Humidity levels will recover a bit, so our nighttime temperatures will rebound into the mid-70s.

Rest of next week

With the return of the onshore flow we could see some decent rain chances as early as Monday or Tuesday of next week, and I think we’ll see a healthy 30 percent chance (or so) on a daily basis on most days. Highs will continue in the vicinity of the upper 80s to lower 90s. I’m still looking at the possibility of a stronger fall front later next week, but this is no sure thing so don’t bring out your box of sweaters just yet.

In brief: In today’s post we discuss the increasing potential for a tropical storm form in the Gulf this week, and what that will mean for Houston’s weather as the system stays away from the Texas coast.

Will Isaias form?

The big news this week is that we actually have some tropical action in the Gulf, and even though it is early October seas there are plenty warm for intensification to occur. However, as Matt as discussed over on The Eyewall, there are a number of factors to consider. But the bottom line is that, more likely than not, Tropical Storm Isaias will form during the next couple of days. There is a chance, perhaps about 1-in-3, that it eventually becomes a hurricane.

To be clear, the storm is not coming to Texas. The system should eventually move to the northeast (slowly) before coming ashore on Friday or Saturday somewhere between Louisiana and the Florida Panhandle. It is likely to be a prolific rainmaker for some (still to be specified) areas along the northern Gulf coast. As for what happens in Texas, and more specifically the greater Houston region, we are likely to see tides elevated by a foot or two later this week. And since we are going to be on the backside of the system, it should amplify a northerly flow into Houston on Friday and Saturday.

Tuesday and Wednesday

These will be mostly sunny and warm days, with moderate humidity. We can expect highs in the upper 80s to lower 90s, with moderate northeasterly winds. With dewpoints in the mid- to upper-60s or thereabouts, it is going to feel moderately humid, but not oppressively so. Nighttime lows will be in the lower 70s. Rain chances are very low, perhaps 10 percent.

Thursday, Friday, and Saturday

Skies will again be partly to mostly sunny during this period, but we should see a slightly drier flow due to the Gulf system. Highs will still be in the vicinity of 90 degrees, but nights should drop into the upper 60s to 70 degree range in Houston, with even cooler conditions possible further inland. Humidity should also be a touch lower, especially on Friday and maybe Saturday. Daily rain chances remain on the order of 10 to 20 percent daily.

Sunday and the early part of next week

By Sunday, or so, a more southerly flow should return, and this probably will bring a few more clouds into the forecast. Highs are likely to remain somewhere in the upper 80s to 90 degrees, with fairly warm nights in the mid-70s. Rain chances should increase by Monday or Tuesday of next week, but the details are still pretty fuzzy.

A real front?

We have yet to receive a real fall cold front that knocks nighttime temperatures down into the lower 60s, or even 50s, and really whacks humidity down. I’m not guaranteeing that will happen next week, but it does seem possible toward the next of next week, in the Thursday to Saturday time frame. We’ll keep an eye on things, because at some point it would be nice to step outside and say, “Ahhhhh.”

In brief: The weekend has started off calmly, in terms of rainfall. Most likely we will see that start to change later this afternoon or on Saturday evening, with scattered to widespread showers and thunderstorms.

Setting expectations for the rest of the weekend

So far, today, moderate to heavy rainfall has remained offshore in proximity to low pressure over the northern Gulf. This has given us a quiet start to Saturday. The question is, does that mean the threat of rainfall is over for the Houston region?

I do not think it is. We are seeing daytime heating over much of the area, and this should help provide a spark for some shower development over land later this afternoon and evening. Predicting exactly where remains a challenge, but some of our guidance is pointing again to areas just north and west of central Houston, which were hard hit by showers on Thursday night.

Broadly speaking I expect fairly widespread showers to develop over our region from mid-afternoon onwards, perhaps lasting through most of the evening. For the immediate coast, the threat may persist a little longer. For most of us, this is likely to bring 0.5 inch of rain, or less, so more of a nuisance than anything consequential. But we could definitely see some bullseyes with 2 to 4 inches in isolated areas, leading to street flooding.

Showers remain possible on Sunday, but should be more scattered in nature. Drier air starts filtering in on Monday, leading to somewhat lower humidity and basically ending our rain chances for the time being.