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. This post will discuss our rain chances toward the end of the week, a modest cool front this weekend, and also dig into Hurricane Sally, which is nearing the northern Gulf of Mexico coast and will bring devastating flood impacts there.
Tuesday
Today is going to be just plain hot. Most (but not all, I know) readers are dearly looking forward to the end of summer. But we’re not going to find it today, with clear skies and high temperatures pushing up into the mid-90s. We’ll see slight northerly winds on the back side of Sally’s circulation, but it’s going to be just plain humid and summer-like. Overnight temperatures will likely push into the upper 70s across the metro area to low 80s right on the coast. There is a slight chance, perhaps 20 percent, of some afternoon and evening showers to provide some relief.
Wednesday
Wednesday should be a lot like Tuesday—hot, mostly sunny, and with only a slight chance of afternoon showers. If you like summer in Houston, you’re in luck!
Thursday and Friday
The overall pattern begins to change by Wednesday night or so, as an atmospheric disturbance nears the area. This should allow for the development of some clouds in the sky, and a healthy chance of rain showers. It appears as though rain chances will be highest on the western side of Houston—some areas may see on the order of half an inch of rain, maybe? Temperatures should moderate slightly, into the low 90s, and overnight lows will drop a few degrees as well.
This European model forecast for dewpoints shows the forecast for Friday morning (left) versus Sunday morning. The latter should be quite pleasant. (Weather Bell)
Saturday and Sunday
We’re now pretty confident that some sort of front will push into Houston on Friday night or Saturday morning, but we still don’t have great confidence in the details. At this point it’s probably best to temper expectations. Yes, we’ll see some noticeably drier air. Yes, this should shave a few points of high and low temperatures. But no, at least right now, we can’t definitely say it will feel like fall in Houston. However, the good news is that we don’t expect to go back to highs in the mid-90s and lows near 80 after this front passes. Summer’s days are numbered as we should see more fronts after this one.
Hurricane Sally
Matt will have all the details on an incredibly action-packed tropics in a post later this morning, and you’ll want to be sure and check that out. Regarding Sally, the good news is that the storm not intensified over night, and remains a Category 1 hurricane with 85 mph winds. As wind shear begins to increase, Sally should not get a whole lot stronger over the next 24 hours before it makes landfall. But that’s where the good news ends.
NOAA five-day rainfall outlook for Hurricane Sally. (Pivotal Weather)
Sally is only moving to the northwest at 2 mph. At present the storm remains a few dozen miles east of the mouth of the Mississippi River. Two days from now, on Thursday morning, it should still be over southern Alabama. As anyone who lives in Houston knows, this is a recipe for extremely heavy rainfall. This will occur primarily over southern Mississippi, Alabama, and the Florida Panhandle over the next several days, with isolated totals of 20 inches or more possible. A large swath of heavy rain will then traverse Alabama and northern Georgia along Sally’s eventual track. This will of course lead to devastating flooding.
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.
