Good morning. The primary weather issues we’re watching this week are the approach of Tropical Storm Sally toward the Louisiana and Mississippi coasts, local rain chances, and the potential for a modest cool front to arrive this weekend. The latter should bring slightly cooler temperatures and some welcome drier air.
Monday
The area of low pressure off the Texas coast that drove widespread showers and thunderstorms on Sunday has moved south, and thus the chance for rain today will be less. Some coastal areas, and locations far west of Houston, may still see scattered showers but for the most part we should be dry. High temperatures should otherwise get into the low- to mid-90s with partly sunny skies. Yes, it will be another hot, summer-like day. Winds will be out of the north at about 10 mph—but this isn’t due to a front or anything, it’s because we’ll be on the backside of distant Sally. More on this storm below. Lows tonight will probably drop into the upper 70s.
Summer continues for Southeast Texas on Monday. (Pivotal Weather)
Tuesday and Wednesday
As the region remains on the backside of Sally, we should see a persistent, if light northerly wind. This should help to limit cloud cover during the middle of the week. This, in turn, will allow highs to push into the mid-90s on Tuesday and Wednesday with the potential for only some isolated showers. So yeah, hot.
Thursday and Friday
The end of the work week should see a slightly more perturbed atmosphere, and this could push rain chances into the 40 percent range, or so, for both days. We will expect that partly sunny skies will allow highs to reach 90 degrees, or the low 90s.
National Weather Service forecast for the front — just south of Houston — on Saturday morning. (NCEP)
Saturday and Sunday
It will be a fairly close thing, but for now we generally think a front will reach the coast on Saturday. Our weekend forecast will depend upon the timing and strength of the front, as well as on whether it actually makes it. But overall, we’d anticipate highs somewhere in the upper 80s, with lows of around 70 degrees—areas inland may see 60s but it’s hard to say for sure. The drier air should be noticeable, however, making for pleasant mornings and evenings this weekend. Skies should be partly to mostly sunny.
Tropical Storm Sally
Fortunately we have not seen too much intensification with Sally overnight—this is something we feared might happen. It is now a 65-mph tropical storm. Although Sally still has about a day to intensify, this relative lack of organization means it is mostly likely the system comes ashore as a Category 1 hurricane. The current track, just east of New Orleans, would spare the city the worst in terms of storm surge and winds. Our primary concern remains the potential for very heavy rainfall from southeastern Louisiana through the Mississippi and Alabama coastal areas. Later in the week, the slow-moving Sally could produce very heavy rains across much of the state of Alabama.
NOAA five-day rainfall forecast shows the flooding potential of Sally. (Pivotal Weather)
The tropics remain incredibly active at this time—Tropical Storm Teddy has formed far out to sea, where it will curve north away from the United States—and we’ll continue to watch things closer to home in the Gulf of Mexico where the waters are quite warm.
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.
Although the tropics pose no specific threats to Texas, in the interests of readers of this site all along the Gulf Coast Matt and I will provide updates today and Sunday on the threat posed by Tropical Depression 19.
The system is passing near the southern tip of the Florida peninsula this morning, and will move into the eastern Gulf of Mexico later today. Some time today it probably will become Tropical Storm Sally. One big question is how much wind shear the storm will have to grapple with over the coming days. If shear remains low, the storm will find ideal conditions to strengthen into a Category 1 or Category 2 hurricane over the warm Gulf. Otherwise, it will remain a tropical storm. Regardless, the primary threat is probably heavy rainfall, extending from Southeastern Louisiana along much of the western coast of Florida. For the northern Gulf Coast these heavy rains would likely come some time between Monday night and Wednesday morning.
NOAA rainfall accumulation forecast for now through Wednesday. (Pivotal Weather)
In terms of track, confidence is fairly high that the storm will make landfall somewhere between southeastern Louisiana and the Florida Panhandle—probably on Tuesday. The storm will move mostly westward or northwest until falling under the influence of a trough of low pressure over the continental United States that pulls it northward. Where precisely this happens will determine what part of the northern Gulf coast the storm strikes.
Forecast track map for TD 19 at 4am CT Saturday. (National Hurricane Center)
After this storm, over the open Atlantic Ocean, there are several other tropical waves that are candidates to develop into tropical storms or hurricanes. “Teddy” may therefore soon follow Sally. But at this time we see no specific threats to the Gulf of Mexico. In terms of the tropics, Texas seems to be in a pretty good place at this point.
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.
