Matt Lanza

Tropical Depression 22, what will you do?

We will hop right into things today, beginning with our near-term forecast and then jumping into the latest on Tropical Depression 22.

Friday & Saturday

The cold front is through, and we’re on the way to more comfortable weather. Look for a good bit of cloud cover at times today, with perhaps a slight lean toward more sunshine later in the day. Highs should be in the upper-80s today, perhaps a bit cooler in spots, and you’ll notice a bit less humidity as the day wears on.

Clearing commences tonight, and we’ll have a stellar morning Saturday, with lows mostly in the 60s.Look for full sunshine tomorrow in most of the area with highs again in the upper 80s and tolerable humidity, a very nice late summer day. Winds will be noticeable at 10 to 15 mph, with some higher gusts up closer to 20 mph at times, especially on Saturday.

Sunday & beyond: The TD 22 impact

Alright, let’s talk about Tropical Depression 22. We’ll start with what it’s doing now, and then we’ll run through some track scenarios and what impacts those have for the Houston/Galveston areas south to Matagorda.

Tropical Depression 22 has a formidable area of thunderstorms, but it is not strengthening particularly fast at this time. It will likely become a tropical storm later today. (Weathernerds.org)

If you look at the satellite loop above, you’ll see that while TD22 certainly has a lot of thunderstorm activity, it lacks a lot of organization. Per the National Hurricane Center (NHC), the center of TD22 is fairly elongated and its motion erratic. Basically, this is still a nascent storm.

Over the next 48 hours, the storm will, broadly, track slowly to the north or north-northeast. The center, which is currently about 250 miles east of the coast of Mexico will likely end up about 250 miles off the coast of Corpus Christi by Sunday morning. We have fairly good confidence in this part of the forecast.

The official NHC forecast for TD 22 has it beginning to turn back toward the coast late Saturday and Sunday, before confidence plunges on exactly what it will do. (NOAA)

From there, forecast confidence plummets. But we can again at least make some generalizations. The storm should generally, slowly track toward the coast south of Houston on Sunday, Monday, and Tuesday. The NHC brings it up to category 1 hurricane intensity on Sunday and Monday, but even they admit that is at the “top end” of forecast guidance at this time. Assuming it’s Tropical Storm or Hurricane Beta, it will likely begin to weaken after Monday thanks to dry air from our recent cold front being wrapped into the storm.

The GFS model here shows dry air (in brown) being wrapped into the storm on Sunday and Monday. This should “cap” intensity and may lead to slow weakening. (Tropical Tidbits)

While we should remain vigilant for any sudden changes in intensification, Eric and I (and most others) will be framing TD22/Beta in terms of a water concern more than wind. This is not Laura. With the storm possibly stalling off Corpus Christi for a time, coastal areas south of Freeport may end up seeing lower-end tropical storm winds for a couple days.

Because this is a slow-moving rainstorm, there will also be temptation to compare it to a certain 2017 storm. This is not Harvey. I don’t want to give people a false sense of security; this storm is a serious concern in its own right, but it is a unique storm that will pose different problems for different places than we saw in other past storms.

TD22 or Beta will likely stall off Corpus for a couple days and then begin to drift northeast out of the area. That process may take a couple days itself, and it’s possible we are not done with this storm until next Wednesday or even Thursday.

Eric laid out three scenarios yesterday, and it appears today that some version of scenario B is most likely. We still don’t know if that track will end up bringing it ashore near Corpus and then up the coast or if it will keep it offshore. Either way, we endorse the NHC forecast map above as being about as good as it gets given the information we’re all looking at right now.

Just to give you a sense of why there’s still uncertainty, here’s a look at the tropical “spaghetti” plot.

The wide spread in individual model outcomes beyond day 2 of the forecast is the basis for the uncertainty, specifically in terms of the rainfall forecast. (Tropical Tidbits)

Don’t focus on any individual track here, but the reality is that a number of possibilities exist, each of which could offer a different outcome for the Texas coast. A track to the west approaching the coast near Brownsville will provide a different rainfall outcome than one that comes west closer to Matagorda Bay. And that’s why it’s important to understand that the specific details of this forecast are absolutely subject to potentially considerable change over the next few days.

So what about rainfall? Well, the current forecast is based on the official NHC track. As noted, this can and probably will change for better or worse.

Rain totals will be significant at the coast and likely drop off inland, potentially dramatically. The gradient between lower rainfall totals and problematic ones will be small, meaning there may be considerable differences in impacts over small distances. (Pivotal Weather)

The current rain forecast calls for about 2 to 5 inches for most of the Houston area, escalating to 10 to 15 inches as you get toward Galveston or Freeport. Areas north and west of Houston are currently expected to see 1 to 3″ or so. Spread out over a week, this is probably manageable to some degree for areas south and east of Houston. But much will depend on how intense the rain is and for how long, questions we are unable to answer at this time. But this gives you a good opening bid on what to expect. Again, if the track comes farther north or shifts south, these totals will change.

In addition to the rain, there will be some considerable coastal impacts as well. Days of east or northeast winds and 8 to 15 foot offshore seas will pile water up along the coast, with limited chance for it to drain out substantially. The current expectation is for tides to be 1 to 2 feet higher than those experienced during Laura as early as Sunday. This will cause considerable coastal flooding of low lying roads at high tide, as well as significant beach and dune erosion, especially considering it will likely continue into Monday and Tuesday. Coastal residents should be prepared for issues beginning Sunday and continuing through at least Tuesday. We’ll have more on this as it becomes clearer.

It’s a lot to digest, but hopefully we’ve at least given you a reasonable first call at what to expect here. In terms of timing when the rain will be worst and where we will place this on our flood scale, we’ll try and hammer that out a bit more later today and tomorrow. Right now, expect some rain, possibly heavy each day beginning Sunday and continuing into Wednesday.

Eric will have our next update no later than 2pm CT.

Friday front still on the way, keeping Gulf tropical shenanigans away from us for now

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.

See full post

Eye on the Tropics: No Vacancy

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.

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.

See full post

Tropical Storm Sally sets sights on southeast Louisiana

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.