We’ve got a lot of moving parts in the forecast for the next week or so, with each one helping shape what the next one will do. The first big item is our late week front, which seems to be on track. The second item is the tropical disturbance off Mexico that many of you have expressed interest or concerns in, so we’ll explain how those two interact and what it could mean.
Today
Wednesday should be a sunny, hot day. We should see at least a few showers and storms crop up, perhaps more likely north and west of Houston. But I think most of us will be dry. Look for highs in the low- to mid-90s area-wide.
Thursday
For tomorrow, a disturbance in the upper atmosphere is going to approach southeast Texas. We should see more cloud cover Thursday, and we may even have showers in the area by sunrise. As the day goes on, we’ll call it partly to mostly cloudy with scattered thunderstorms developing. After a morning low in the muggy 70s, look for highs in the low-90s or a touch cooler north and west.
Friday to Sunday and cold front
Last week’s cold front was an “in your face” type of frontal passage, where once the front passed your backyard, you knew it was there. I’m not sure this next front will be quite like that. Look for perhaps some showers Thursday night and Friday morning. They’ll drop south on Friday and any more organized storms should focus south of I-10 to the coast before dissipating late. The front itself will lag a bit, but it is expected to pass the northern half of the area Friday morning and afternoon, and it should eventually reach the coast by Friday night or early Saturday. Instead of a sharp change, we will likely see a gradual drop in humidity and clearing later Friday into Saturday.
Yes, Saturday morning should see low temperatures in the 60s away from the city and the coast. (Weather Bell)
Look for Friday morning lows in the 70s still, followed by highs near 90° Friday afternoon. Then on Saturday, look for morning lows in the 60s in suburbs and outlying parts of the area to around 70 in Houston and mid- to upper-70s along the coast. Sunday morning should be similar.
Both Saturday and Sunday look like fine early autumn or late summer days with ample sunshine. A few morning clouds are possible Saturday south of Houston. We will still see highs in the upper-80s to near 90°, but the humidity will be tolerable.
Can the front fail? It’s plausible that the front doesn’t push quite as aggressively offshore, but trends since yesterday have been toward a slightly stronger push and the front basically dissolving 100 to 200 miles offshore. So we think that this is real.
The Atlantic is full. No room at the inn, folks. We’re fresh out of vacancy. If only that were true. Since our last tropical update last Tuesday, we’ve added <checks notes> three more storms. We’re running about three weeks ahead of 2005’s pace and the last name on the list is Wilfred before we shift over to the Greek alphabet. You can argue all day about how many of the storms have been minimal, but a storm is a storm and 2020 is certainly in a unique place based on our historical records. Incidentally, if you want to look back at an interesting analog year to this one, check out 1971.
This is when it occurred last in September 1971, from Neil Frank. Six active with another about to form. 🙂 pic.twitter.com/yxZSsEze7D
It was also a year full of mostly minor to moderate storms, including Fern in South Texas and Edith near Cameron, LA. But it included six active systems (including Fern & Edith) at once with one additional in the pipeline. Ginger on that map above is noteworthy for being the longest lived modern Atlantic tropical system. It lasted from September 10th through October 7th, before eventually reaching land in North Carolina. That track map is something to behold. Even better, it was drawn by local hurricane legend Neil Frank.
At present, we are monitoring four systems, none of which are a concern for Houston. There are also two “invests,” neither of which are a serious concern for us either. Plus, we have one “untagged” Gulf disturbance.
There are four active storms, two “invest” areas, and one Gulf disturbance that we’re watching in the Atlantic this week. (Weathernerds.org)
We’ll do our best to sift through the morass for you, starting with that current lineup of storms and then talking the hypothetical systems.
Hurricane Sally
Eric covered Sally earlier today, and not much has changed. Sally remains a category 1 storm with 85 mph winds. It is going to meander just offshore of the Gulf for the next day or so before beginning to move along north and northeast. Water trumps wind in terms of greatest threats with Sally, as persistent onshore flow will keep coastal areas inundated for awhile.
Sally is going to slowly advance north and eventually pick up a little speed as it moves inland, but it will deliver severe flooding to parts of the South. (NOAA)
Meanwhile, heavy rainfall will repeatedly pelt southern Mississippi, Alabama, the Florida Panhandle, and eventually Georgia and the Carolinas leading to widespread and potentially severe flash flooding.
Good morning. Tropical Depression 19 was upgraded to Tropical Storm Sally yesterday, and this morning it has 60 mph maximum sustained winds off the west coast of Florida. While we continue to expect no real impacts here in Texas, this will be a problem for the central Gulf Coast.
Tropical Storm Sally looks impressive this morning, but it is still battling a bit of wind shear or dry air. (Weathernerds.org)
On satellite, Sally is quite impressive, but it’s evident that the storm is not yet well-organized. It still seems to be battling some wind shear. That is expected to diminish today, leaving Sally in kind of an ideal space for strengthening. The various weather models we look at are widely varying in terms of how much Sally strengthens over the next day or two as it approaches the central Gulf Coast. The National Hurricane Center (NHC) is forecasting a borderline category 1/2 hurricane at landfall, with maximum sustained winds of 90 mph, but there have been solutions stronger than that and quite a few options that are a good deal weaker than that as well. So suffice to say, there’s a high degree of uncertainty as to whether Sally approaches land as a borderline major hurricane or strong tropical storm. That will have some impact on what central Gulf locations see in terms of wind and surge obviously.
While the intensity forecast is still full of uncertainties, the track forecast is coming into pretty solid agreement on a landfall between about (or just west of) Port Fourchon, LA and central Mississippi.
The official forecast track is into the coast near or just west of New Orleans, and some risks exist west of about Port Fourchon and east to Central Mississippi. (NOAA)
The NHC track takes it ashore just southwest of New Orleans. Tropical models are generally near or east of that forecast. The ECMWF model is generally west of there, closer to or west of Port Fourchon (where have we seen this before?), although the disparity is a bit less glaring this time. So there’s still a bit of uncertainty, which is pretty important, especially when dealing with a place like New Orleans. Timing-wise, impacts should begin late tonight or early tomorrow.
Obviously, the first thing that many people will think of (including me since I’ve been reading a book about it for the last 3-4 weeks) is Hurricane Katrina. Just to be abundantly clear, this is not Katrina. This is an entirely different storm with differences ranging from size to intensity to angle of approach to a newly fortified levee system. So let’s just not even go there.
That being said, this storm is likely to produce a considerable storm surge (in addition to heavy rainfall) that will offer a test of the flood protection infrastructure in southeast Louisiana. The current NHC surge forecast (recall, this product is showing the reasonable worst case scenario of a surge (inundation above ground level) with landfall at high tide outside of levee protected areas) shows some significant values for Mississippi and southeast Louisiana.
A considerable storm surge is becoming possible for southeast Louisiana and the Mississippi coast if the current forecast for Sally holds. (NOAA)
Again, this assumes a high-end category 1 hurricane making landfall at high tide just southwest of New Orleans. There will likely be some modifications to this forecast before landfall depending on exactly how things unfold.
The next hazard is rainfall, and this may be the most significant problem in the end. As Sally approaches the coast, you notice in the NHC track forecast above, it shows the dreaded deceleration and turn. That means that there will be areas dealing with repeating rounds of heavy rainfall in southeast Louisiana, Mississippi, Alabama, and Florida. Sally is likely to become a considerable flooding threat for those areas.
Significant rainfall and widespread flooding are likely along and east of Sally’s track, including southeast Louisiana, Mississippi, Alabama, and Florida. (NOAA)
Total rainfall is likely to be on the order of 5 to 15 inches between the New Orleans area and about Destin, FL. Higher amounts are absolutely possible. As evidence of this, Key West saw 9.37″ of rain on Saturday, which set a new monthly record for September and was the fifth wettest day on record there going back to 1871. So, while the surge and hurricane aspect of this storm are justifiably important and likely to generate a significant amount of attention, the rainfall flooding of Sally may be the most serious problem in the end.
Elsewhere in the tropics, we have Hurricane Paulette heading directly for Bermuda, Tropical Depression Rene dissipating, and Tropical Depression 20 likely to become Teddy over the next day or two. None of these systems are concerns for the Gulf. Another “invest” to the north of TD 20 may develop but stay out at sea. Another weak tropical wave is emerging off Africa and could also develop as it moves west. But for at least the next 10-12 days, we don’t expect any issues in the western Gulf. We continue to see the potential for a cold front next weekend, so as always, there’s a non-zero risk that could pull something unforeseen on us in the Gulf. But no reliable model is implying anything like that at this time. So rest easy here in Houston. We’re good for the time being.
Yesterday was a really interesting day across the broader version of southeast Texas. College Station maxed out at 73° on Thursday, which breaks the record of 77° from 1948 as the coolest maximum temperature recorded there on September 10th. Much of the western half of the Houston metro area saw dewpoints drop into the 60s with cooler temps much of Thursday morning. Hobby Airport never dropped below 79° until late Thursday evening. Galveston saw heat index values approach 110°. Many of us saw some rain, with a narrow strip from about the Texas Medical Center north and east past Mount Houston into Atascocita seeing multiple rounds of storms and anywhere from 1 to 4 inches of rain.
So overall, yesterday was a glorious day for some, a frustrating day for others, and something in between that for others still. We all kind of get back on the same page today and tomorrow.
Today
The cold front is essentially dead at this point. But! The air mass over us is notably drier, yes, and you will probably notice that the humidity today isn’t as oppressive as, say, Wednesday (or even yesterday for folks south and east of Houston that largely missed any tangible impact of the front on Thursday). But it will still feel like late summer in many spots. Those of you that experienced an autumn preview yesterday will probably see upper-80s to around 90° today. Most of the rest of the Houston area will see lower-90s. But again, with humidity down it may not feel super terrible.
In terms of rain chances, look for a few showers or storms this afternoon, especially south and due east of Houston with slowly diminishing chances as you go north and west.
Tropics & weekend
I wasn’t quite sure how to go about breaking up sections today, but given the complexity, I feel just hitting it all at once would be best. We’re watching two disturbances today, one in the Gulf and one over the Bahamas.
There are two tropical disturbances to watch, a weaker one in the eastern Gulf and a more robust one in the Bahamas (Weathernerds.org)
Clearly, one looks healthier than the other. The Bahamas one is now dubbed Invest 96L, and the National Hurricane Center is giving it a 60 percent chance of development over the next five days (40% over the next two days).
The NHC is giving the first Gulf disturbance a 30% chance of organizing over the next 5 days and the second disturbance a 60% chance over the next 5 days. (NOAA)
But we have to get through the lead disturbance first. This one has odds of 30 percent to develop over the next five days, but it seems that if it were to form, it likely wouldn’t happen until it gets south of our area toward Mexico. So why are we watching that lead disturbance? Well, it’s close enough to the coast that it will likely send a surge of moisture this way beginning tomorrow. This should be enough to generate numerous showers and storms offshore, along the coast and/or just inland on both Saturday and especially Sunday. If storms do blow up offshore significantly, it is possible that coastal areas may only see a little rain. Areas north and west of Houston may not see much rain at all this weekend.
Averaging together rain chances through Sunday gives the highest totals along the coast, with lesser amounts inland. (Weather Bell)
Total rainfall from Friday into this weekend will probably average under a quarter inch north and west of Houston and closer to a half-inch near the coast. Some areas will likely see higher amounts up over an inch, and others may see no rain at all. Flooding, other than the typical ponding or minor street flooding we see in heavy downpours is not expected this weekend.
After a morning low in the 70s Saturday, we’ll see humidity inch up all day, and with highs in the 90s, expect heat index values to surpass 100° once more. Back to late summer we go. On Sunday we’ll see similar temperatures or a little cooler weather due to more cloud cover. Humidity will remain high. Watch for some choppy conditions over the bays and in the Gulf with slightly increased winds (~15 mph) with onshore flow.
Tropics & next week
The second system will not impact us, if it does at all, until at least Wednesday or Thursday. So to start the week on Monday, look for scattered to numerous showers and storms, perhaps chances push a bit farther inland than the weekend. This pattern may continue Tuesday. By Wednesday, we could see a brief break before that second system gets involved Thursday.
Simple discussion: The next tropical wave is going to slowly work west across Florida and through the Gulf the next few days, possibly developing as it does so but likely coming ashore to our east. Regardless of any of that, it will increase our rain chances by Thursday or Friday.
More technical stuff: There’s a really high degree of uncertainty at the moment with respect to that Bahamas system. One the one hand, I looked at a bunch of weather models, even the speculative ones we constantly tell people not to bother looking at for tropical systems (I need a shower now), and I don’t see a single one developing it much past where it is now; maybe one or two get to depression level. But when you look at satellite above, it looks a lot better than I would have expected today. Additionally, it’s going to be over the Gulf for a time, and it will be in a low shear environment. Realistically, this has a better shot at development than any model gives it credit for right now. The only thing I can come up with to explain why the models don’t particularly care for it, is that a good chunk of its low-level vorticity or the most “spin” associated with the system ends up along the immediate Gulf Coast or, as the European model suggests, just inland. So the models likely sense this is too close to the coast to develop. Given how far south it appears to be right now, I think the Euro may be a bit off-kilter here, and although we’d still expect a general track toward southeast Louisiana, it’s worth continuing to watch.
What does it mean for us? Right now, we’ll just call for an increase in rain chances later next week and perhaps some choppy conditions offshore with some slightly gustier winds. At this time, we do not expect significant impacts to our area (or to Hurricane Laura damaged areas) beyond increasing rain chances and slightly higher tides. But again, given the disturbance’s location and the time of year, it would be foolish to write it off completely, so we’ll keep watching.
We will also watch for maybe, possibly a new chance to see cold front by next weekend. That’s literally all I’m going to say about that for now, and if it’s still there Monday, we’ll tell you about it.
