Category: Tropical weather

Delta’s path toward Louisiana coming into focus

Posted by Matt Lanza at 2:38 PM

2:35pm CT Wednesday update: Good afternoon, and it’s good to be back. Thanks to Eric for dealing with an absentee site partner for the last couple weeks and getting us from Beta to Delta. I sincerely hope this is the last storm we have to write about for the Gulf this year.

Hurricane Delta is emerging into the Gulf from the Yucatan this afternoon.

Hurricane Delta is back over open water after emerging off the Yucatan this afternoon. (Weathernerds.org)

After being one of the quickest intensifying storms on record, Delta has taken a beating over the last 18-24 hours and, while it’s holding its own, maximum sustained winds of 100 mph may be a bit generous here. Either way, Delta is now back over warm water with relatively low wind shear, so odds favor it beginning to reintensify tonight.

The track forecast has continued to nudge a bit farther west, however that trend appears to be stable or ending now, and I think we’re close to the maximum for how far west Delta will track.

While Delta’s forecast track has nudged west a bit more today, that trend will likely stop or slow going forward, as almost all model guidance now has a landfall between Cameron and the west edge of Vermilion Bay in Louisiana. (NOAA)

The last big holdout, the European model, which had been advertising landfall near the Texas/Louisiana border has shifted east by a good 25 miles or more today, and virtually all reliable model guidance now has Delta’s landfall occurring between Cameron, LA and the western edge of Vermilion Bay, or very close to/slightly east of where Laura made landfall. A word of advice: Don’t focus too closely on every wobble and maneuver Delta makes over the next 24-48 hours. While there is still a small degree of uncertainty on the exact track of Delta, the odds that there would be a significant enough shift to detrimentally impact the Houston area is very, very, very small. We all brace ourselves for The Turn™ during these events, and it will happen.

As far as intensity goes, modeling has been slowly easing up on the excitement since last night. Some of that is likely due to what happened to Delta on approach into the Yucatan and land interaction. But as of this afternoon, virtually all intensity forecasts are for this to not get above a category 3 storm in the Gulf before it weakens on approach to the coast. Wind shear is going to likely increase significantly, and the storm will encounter cooler water as well beginning tomorrow night or Friday morning.

That said, the biggest change with Delta over the next couple days will likely be the expansion of its wind field. Larger storms usually have lower intensity ceilings, but they compensate for that by spreading tropical storm or hurricane force winds out over a larger area. You can see this wind field expansion on the HWRF model by looking at 10 meter winds (winds experienced at ground level will be somewhat lower than shown here). The map at left is this evening’s forecast, while the map at right is for Friday afternoon. Both maps are at the same spatial scale, and you can see how the tropical storm force wind field (green, yellow, red) basically doubles in size as Delta comes north.

The HWRF (and other models) show an impressive expansion of Delta’s wind field as it comes north across the Gulf, so even though Delta may weaken just before landfall, it will be capable of producing strong winds and large surge over a broad area. (Tropical Tidbits)

Hurricane force winds are in purple here also. So despite Delta perhaps being weaker, it will likely have impacts spread over a large swath of Louisiana and perhaps eastern Texas, with a significant surge once again possible along and east of where the center goes.

Speaking of surge, the first National Hurricane Center surge outlook was posted today, showing the potential for as much as 11 feet of surge above ground level if Delta comes ashore at high tide on Friday.

Surge values of 11 feet are possible along and east of the center if Delta comes ashore at high tide. (NOAA)

These surge values are rough, though certainly not quite as catastrophic as those seen in Hurricane Laura. But 11 feet of water is a bad day, and unfortunately, the areas around Vermilion Bay that were hammered during Laura are going to get another significant event with Delta.

Locally in the Galveston Bay area, we expect surge impacts to be more like Laura than Beta, with minor overwash possible near Bolivar and perhaps down Bluewater Highway south of Galveston into Brazoria County. Surge should not be much worse than 1 to 3 feet above normally dry ground. Storm Surge Watches have not been posted in our area, but they are hoisted east of High Island. Tropical Storm Watches have been posted from San Luis Pass to High Island.

Will we see tropical storm force winds in the Houston or Galveston areas? My hunch right now is that we won’t see this in Houston. Galveston always has a chance to briefly get to tropical storm force gusts or even sustained winds at times. But this would be mostly a Friday issue. At this point we don’t expect significant problems from wind in the Houston or Galveston areas.

For folks in southwest Louisiana and around the Beaumont/Port Arthur areas, the story is a little less clear. Assuming the wind field does expand as expected, we would likely see tropical storm force gusts and perhaps a period of sustained tropical storm force winds (35-55 mph) in the Beaumont or Port Arthur areas. In Lake Charles, which is still far from recovered from Laura, we expect about an 80 percent chance of sustained tropical storm force winds (greater than or equal to 39 mph) and about a 30 percent chance of sustained hurricane force winds (greater than or equal to 74 mph). This will not be another Laura in Lake Charles by any means whatsoever, however given that many, many structures in the city have not yet been repaired, this does have the potential to produce some considerable damage, particularly the farther west it comes ashore.

As far as rainfall goes, we don’t expect to see much more than perhaps a few outer bands in the Houston and Galveston areas. Rain totals will be manageable and no flooding is expected in our area.

Rain totals should be minimal in Houston and up to 6 or 8 inches in interior Louisiana. (NOAA outlook via Pivotal Weather)

In Louisiana, up to about 6 to 8 inches will be possible along and east of where the center comes ashore, which could cause minor to moderate flooding issues but really isn’t all that bad as far as these storms go. Delta will be a quick mover and out of there by Saturday morning.

Unless something dramatic changes this evening, our next update will be our regularly scheduled update on Thursday morning.

7 am CT Wednesday Update: Good morning. We’ll take a quick look ahead at our forecast for this week and then turn our attention to Hurricane Delta, which made landfall near Puerto Morelos, in the Yucatan Peninsula, around 5:30 am CT today. It had maximum sustained winds of 110 mph. The hurricane will move into the Gulf of Mexico later today.

Wednesday

Today will be warm and sunny, with highs likely climbing into the mid- to upper-80s with light northeasterly winds. We should really start to feel the return of moisture at the surface today, so it will feel a bit more humid, and nighttime temperatures will be a few degrees warmer than Tuesday night, likely not falling below 70 degrees in Houston.

Thursday and Friday

Our weather on both of these days will depend heavily upon how close Hurricane Delta gets to Texas as it moves into the western Gulf of Mexico. In terms of precipitation, for now, we’ll guess (emphasis on guess) the eastern half the region sees perhaps 0.25 to 0.5 inch of rain, with lesser amounts west of Interstate 45. The best rain chances should come on Friday, and partly cloudy skies should help to limit temperatures into the low 80s. Winds may gust up to about 30 mph, or higher, especially on the city’s east side, and along the coast.

NOAA rain accumulation forecast for now through Friday night. (Pivotal Weather)

Saturday, Sunday, and beyond

Some showers may linger into early Saturday, but for the most part, the weekend looks warm and sunny, with highs near 90 degrees. There is the potential for a cold front to arrive on Tuesday or so of next week, but it may get hung up for a few days and not move in until later. Still, we do anticipate more fall-like weather to return in about a week, give or take.

Delta, Delta, Delta

Delta has weakened overnight due to the influence of wind shear at mid-levels of the atmosphere, and it may weaken a little bit further this morning as its center briefly crosses the northeastern corner of the Yucatan Peninsula. As it reaches the southern Gulf of Mexico, the storm should begin to re-intensify tonight, and the National Hurricane Center anticipates Delta briefly pulsing back up to a Category 4 hurricane over the Gulf. (We’ll see).

As the storm moves north it will encounter less favorable conditions and should be on a weakening trend near landfall Friday. Frankly, I have significant questions about how strong Delta will be at landfall, and anything from a Category 1 to Category 3 hurricane seems possible. Most likely, the further east the storm tracks, the stronger it will be.

4am CT Wednesday track forecast for Hurricane Delta. (National Hurricane Center)

In terms of track, our overall thinking has not changed in terms of approaching Texas and then turning north. As you can see in the forecast graphic above, as we get closer to Delta’s Gulf coast landfall, the “cone of uncertainty” in the National Hurricane Center’s official track has narrowed. It now essentially runs from the border between Texas and Louisiana, on the west side, to southeastern Louisiana. This reflects what we’ve been telling you over the last several posts, that the forecast models are generally in quite good agreement on a landfall between the Texas-Louisiana border and Morgan City. Landfall now looks likely to occur some time during the middle of the day on Friday, or during the evening.

Along this track, as noted above, the greater Houston region would only see moderate effects, including increased winds on Thursday and Friday, some decent rain chances, and moderate coastal flooding at high tides. We will need to continue to monitor the storm’s track closely, but the greatest likelihood remains that Delta will be a near-miss for our area.

In terms of Louisiana, Delta’s effects will depend heavily upon its intensity. It does seem really, really cruel that this storm will probably make landfall not too far from where Hurricane Laura did so in August. However, we do think Delta’s winds will probably be less at landfall than Laura, and surge as well. Because the storm is expected to be moving fairly quickly to the north-northeast, rainfall amounts should generally be less than 8 inches for most areas.

Our next post will come no later than 2:45 pm CT.

7:40 pm CT Update: Just a quick post this evening on Hurricane Delta. The storm has intensified further since this afternoon, reaching maximum sustained winds of 145 mph at 7pm. However some wind shear in the mid-levels of the atmosphere has lately begun to affect Delta and may prevent further strengthening tonight, or even weaken the storm.

Regardless, Delta will bring devastating winds and storm surge to the Yucatan Peninsula later tonight and on Wednesday. After this time it will enter the Gulf and track west-northwest across the Gulf of Mexico. In terms of what happens after that, not much has changed with respect to the track forecast, which turns Delta north and brings a hurricane to the Gulf coast Friday evening or early Saturday—about three days from now. It seems the most likely location for this landfall will lie somewhere between the Texas-Louisiana border, on the western side, and Morgan City, on the eastern side. Even though we are within three days of landfall, some uncertainty remains, and this is reflected within the National Hurricane Center’s forecast cone.

4pm CT track forecast for Hurricane Delta. (National Hurricane Center)

By tomorrow morning we should have a pretty good sense of the ultimate track forecast for Delta, as the overnight model runs ingest data from today’s aircraft reconnaissance missions as well as supplemental weather balloons to sample the atmosphere helping to control the steering flow for this system. The odds still strongly favor a landfall in southwest or south-central Louisiana, but there is enough uncertainty that we’re going to need to continue to watch Delta closely along the upper Texas coast.

That’s just what we’ll do, of course. In tomorrow morning’s post, which will go up no later than 7:30am, we’ll have the latest on track and potential impacts along the upper Texas coast later this week, as well as Louisiana.

 

2:10pm CT Tuesday: We’re talking about Hurricane Delta this afternoon, which has undergone rapid intensification and is now a powerful Category 4 hurricane with 140 mph winds. (It was only named Delta 30 hours ago.) The storm will approach the Yucatan Peninsula tonight, and likely make landfall somewhere near Cancún early on Wednesday. This will be a dangerous hurricane for that area. By Wednesday evening the storm will be back out over the Gulf of Mexico, moving to the northwest.

Track

Overall, the track forecast remains largely unchanged. The 12z models are beginning to show a tighter cluster of solutions in which Delta moves to the west-northwest, or northwest for most of Wednesday and Thursday. Then, when Delta is a few hundred miles offshore from South Padre Island, it should begin a pretty sharp turn to the north. All of the best available guidance now shows a final landfall between the Texas-Louisiana border—very near where the devastating Hurricane Laura came ashore in August—and further east, around Morgan City and Houma. This tighter clustering of models is consistent with the National Hurricane Center forecast track, and increases our confidence in where Delta is going to go.

National Hurricane Center forecast track for Hurricane Delta at 10am CT.

With that said, we are still roughly three-and-a-half days away from landfall, so the average track error is about 120 miles, and we also have to account for the possibility of wobbles. The bottom line with Delta’s track is that right now every available bit of evidence we have suggests this storm is going to turn toward Louisiana—but its future path is not 100 percent locked down.

Intensity

Delta has had near ideal conditions for strengthening over the last 24 hours, including very warm waters not just at the surface, but also below. This is important because, as the storm moves across the ocean it churns up seas from below, a process known as upwelling, which can bring cooler water to the surface. One measurement of an ocean’s depth of warm waters is its “Tropical Cyclone Heat Potential,” and basically any value of 80 or higher is conducive for intensification. As you can see from a recent map of this potential, the waters in the northwestern Caribbean Sea are explosively warm.

Plot of Tropical Cyclone Heat Potential. (NOAA/AOML)

This will begin to change as Delta moves away from the Southern Gulf of Mexico, at which time the storm also should begin to encounter more wind shear. These factors should help to limit the intensity of Delta as it moves toward the northern Gulf of Mexico, but it remains possible that this system could be a major hurricane at landfall.

Houston effects

Along this track Houston is likely to experience only very mild effects from Delta—perhaps some rain showers on Thursday, Friday or Saturday. Seas will reach their maximum on Friday, but should be below the levels the region experienced during Hurricane Laura.

Needless to say all of this depends upon the storm’s track, and if that changes significantly, so will our local forecast.

Our next update will come no later than 8:30 pm CT.