Matt Lanza

Eye on the Tropics: A lull before the peak weeks of hurricane season

Tropical Storm Isaias is bearing down on the Mid-Atlantic and Northeast today, and as that storm exits, we actually look to settle down into a period of calm for a bit in the tropics. All good things must come to an end however, and as we go into the back half of August, we will begin to refocus our attention on the entirety of the Atlantic basin. For now, let’s enjoy the respite.

Tropical outlook in a sentence

No meaningful tropical activity is expected over the next week, although conditions will likely begin to get more active by August 15th or so.

Isaias

Isaias experienced a bit of a renaissance last night, ramping up to a moderately strong category 1 hurricane as it made landfall near Ocean Isle Beach, NC.

Since last evening, Isaias has raced northward and been downgraded to a tropical storm. The center is over the Mid-Atlantic this morning, heading toward Upstate New York or western New England by evening. Along its path will be flooding rains, strong winds, and some tornadoes still to come for places including Philadelphia and New York City.

Behind Isaias

In the Atlantic, we actually have no real disturbances of note behind Isaias. Yes, there is the disturbance dubbed Invest 94L, which is a few hundred miles southwest of Bermuda this morning. That one is unlikely to do much and is certainly not a threat to the U.S. There may be a tropical wave that emerges in the Bay of Campeche this weekend, but that is not expected to develop at this time as it likely moves into Mexico.

Meanwhile, off Africa, we are seeing some waves push across the continent and off the coast that look pretty robust.

The wave train will continue to send waves east to west across Africa and into the Atlantic over the next week or so, though none is considered especially likely to develop. (NOAA)

None of these are expected to develop, but it’s not entirely out of the question that something could develop. Either way, anything emerging off Africa today would be at least 10 to 14 days away from us here, so we couldn’t tell you anything with any specificity anyway. That said, at least for the next week or so, none of these waves appears to be a serious candidate for any kind of meaningful development.

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July to end with a cold front? Really?

In summertime, few things are coveted more in Houston than a cold front, and as we flip the calendar from July to August, we’re going to get just that. Now, don’t get too excited. It is not really going to translate into opening the windows and letting the gloriousness flow.

It’s not going to feel quite this nice this weekend, unfortunately.

Rather, this will probably bring us some rain chances, perhaps some strong storms today, and maybe a tinge less humidity than we’ve had late this week. But beyond that? Not much. We never really, truly cool off. Let’s go through the details

Today & tonight

For the most part, today looks fine. Expect a mix of sun and clouds, along with very hot weather. Look for mid-90s and high humidity. Rain chances in Houston and points south should be confined to primarily just a passing downpour. During the afternoon, we expect showers and storms to fire up between Dallas and Huntsville. Those storms will drop into the northern third of the metro area by late afternoon, with places like Conroe or The Woodlands or northwest Harris County standing the best chance at storms before 5 to 7 PM or so.

The Storm Prediction Center has areas north of Houston in a “marginal” (1/5) risk for severe weather today. Any severe storms should be fairly isolated. (NOAA)

Storms today do have the potential to be strong to severe, but we don’t expect widespread severe weather or anything like that.Strong, gusty winds and hail would be the main risks from the strongest storms.

The front will slip into metro Houston tonight. The strongest storms should begin to ease up a bit after sunset, but we wouldn’t be shocked to see some noisy storms with locally heavy rain moving through the I-10 corridor and just south through late evening and toward midnight. We should see storms generally dissipate after midnight, but if they were to continue going, it would areas south of Houston most likely to see them.

Saturday

With showers and storms generally expected to diminish overnight, we think Saturday will start mostly quiet. However, if there are some morning showers or rumbles of thunder, they would likely be close to the coast or well south of Houston toward Matagorda Bay.

I have to be honest here: Given recent model performance of late, there is still see some uncertainty in exactly how things may transpire tomorrow. But in general, look for some additional showers and storms to fire up along what is left of the cold front south of Houston (Brazoria, Matagorda, Wharton, and Jackson Counties most likely) before it dissipates. Additionally, there could be some storms that fire to the west of Houston Saturday afternoon, perhaps near the Katy area north toward Waller and Grimes Counties.For the city of Houston and points north, much of tomorrow could be a quiet and fairly pleasant summer day. But I would not place rain chances at zero. Highs will be in the low-90s with morning lows in the 70s.

Sunday

Sunday’s forecast is a bit tricky as well. The front should have basically lost any definition and fallen apart by Saturday night and Sunday morning. But there will likely still be enough of a “trigger” for thunderstorms around. However, with atmospheric moisture generally on the wane, we suspect Sunday’s storm coverage and rainfall intensity will be less than we see on Saturday. All that said, I would probably take a more pessimistic stance on Sunday than what models are explicitly showing right now (which isn’t very much in the way of rain). So let’s expect scattered storms and hope for better on Sunday.

Sunday’s high will top off in the low-90s with storms, mid-90s with only a handful of them, and we’ll see morning lows in the 70s.

Rainfall this weekend will be erratic, with some folks seeing little to no rain, others perhaps seeing a couple inches, and many seeing something in between. This map gives you an idea of where the heaviest is currently expected to fall, though that could change. (NWS via Weather Bell)

Total rainfall this weekend? Some may see locally heavy rain that could add up to an inch or two or even more. Others may not see much of any rain at all. And still more of us will see something in between, closer to a tenth or quarter-inch. The map above should just give you a rough idea of where the heaviest rain could fall.

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Eye on the Tropics: Watching the next wave closely, though it has hurdles ahead

With Hurricane Hanna behind us, the obvious question is, “What’s next?” We have one system at present to watch, and then the situation gets a little trickier to figure out.

Tropical outlook in a sentence

The disturbance just dubbed “Potential Tropical Cyclone 9” by the National Hurricane Center is the one we are watching for development this week. Although we do not expect an especially strong system, it is still far too early in the game to dismiss any scenario or track.

PTC #9

The road forward on where Potential Tropical Cyclone 9 goes and what it does is a long one, and we are still at the beginning. Possibilities range from no impact at all on the United States to an impact on the Gulf, US East Coast, or something in between. Basically, everything. That’s a less than helpful forecast, but it’s the only realistic one that can be offered right now. The National Hurricane Center’s designation of this disturbance as a “potential tropical cyclone” means it has confidence a depression or storm will develop and impact land soon. They will initiate advisories on this system this morning, which will allow for watches and warnings to be issued for Caribbean islands. Their first forecast is below.

The National Hurricane Center’s opening forecast for Potential Tropical Cyclone 9. There is *very* high uncertainty on details later in the forecast. (NOAA)

From their technical discussion, it’s worth noting that there is a very high degree of uncertainty. As they note:

It cannot be stressed enough that since the system is still in the formative stage, greater than average uncertainty exists regarding both the short-term and longer-term track and intensity forecasts.

PTC 9 has some hurdles ahead. A look at the satellite image from this morning shows a lot of “stuff,” but not a lot of healthy organization right now.

Potential Tropical Cyclone 9 has a lot of thunderstorms associated with it as of this morning, but it remains mostly disorganized. (Weathernerds.org)

That shouldn’t minimize it as something to watch, but given how things have gone in recent years, it’s nice to see a disturbance struggling to organize. One of PTC 9’s problems is that it has a large size. It’s a lot easier to spin up a smaller system that grows, but this one covers a large chunk of real estate already, so to get it started requires some effort. The other problem is that there are multiple clusters of thunderstorms within the broader circulation, any of which could become dominant. That obviously has implications on the long-term track.

The disturbance is also surrounded by a lot of dust and dry air.

PTC 9 has dust or dry air to content with on its west, north, and east flanks. (University of Wisconsin CIMSS)

The problem here from a forecast standpoint is that since we don’t know where in this broad circulation the thunderstorms will consolidate to help develop a defined tropical depression or storm. we cannot quite give you a definitive starting point. Without a solid starting point, forecast accuracy 3, 5, or 7 days from now will obviously suffer.

What we can tell you is that PTC 9 has hurdles in front of it. Between the dry air, a likely encounter with a weak trough in the Bahamas Friday, and another, stronger trough over the Southern U.S. next week, as well as any land interaction on its way west, it will need to overcome some challenges and insulate itself from these threats or else it will struggle to develop.

That said, anything from where the system consolidates to how strong these troughs and other features actually are (compared to what they’re currently forecast to be) could impact where PTC 9 goes and how strong it is. For now, the best advice with this system is to not worry about it (we’re certainly not), but check back in on it every day or two to see what has changed.

And for those of you wondering, if we do get a storm out of this one, it will be named Isaias, and pronounced:

Beyond Isaias

Things get complicated beyond PTC 9/Isaias. Intriguingly, there are no other systems showing up on the models with any frequency or confidence right now. This is implying that we may enter a quiet stretch for a time again. There’s some background support for this as a feature that typically helps suppress storm development should move through the Atlantic Basin this week. On the flip side, the 2020 M.O. has been for random stuff to flare up seemingly out of nowhere. So in that sense, it’s tough to argue a quiet period.

Whatever the case, I do think we will have a slightly quieter stretch post-Isaias, with the risk of a more significant ramp up in activity by the middle or late portion of August.

Major flooding in the Rio Grande Valley as Hanna moves into Mexico

Good morning. We’re here to offer up a brief update on Hanna as the storm works its way into Mexico this morning.

Houston area

Things are quiet this morning in Houston. There are some showers south and west of us and another batch moving across the coast of western Louisiana. As some of this works into Texas, we should see showers and storms become scattered across the area.

Showers and storms in Louisiana will likely work toward our area today, bringing at least scattered rains, some heavy, to the Houston area. (College of DuPage)

Some folks won’t see much, but others may see a couple inches of rain in an hour or two this afternoon. An isolated severe storm is also possible. More typical scattered showers and storms will continue to be possible tomorrow and Tuesday, as onshore flow continues.

Rio Grande Valley

Hanna has moved into Mexico this morning, but the storm’s rains continue in the Valley. Mission has probably been the hardest hit of any of the cities in that area, and a flash flood emergency is posted for that area through late morning, as upwards of 10″ of rain has fallen, with more coming.

The heaviest rain as this is being written is falling east of Mission and just west of Harlingen. Several more inches of rain is likely to fall today and tonight as Hanna dissipates inland in Mexico.

Totals are impressive, especially just north of the Valley.

Areas in purple on this map of estimated rainfall are likely to have seen 9 to 10 inches or more of rain so far. (NOAA NSSL)

You can just make Mission out as the western-most purple area on the map, with upwards of 9 to 10 inches of rain. Other hard hit areas include Weslaco and Harlingen. The area just northeast of there with maximum totals is estimated to have received close to 20 inches of rain.This is right on the Arroyo Colorado near Arroyo City on the Cameron/Willacy County line.

Conditions should improve in that area tomorrow with more scattered showers and storms, but flooding could worsen in spots still today before subsiding. We will have the latest on the rest of this upcoming week tomorrow morning.