The Eyewall

Isaias is one of those storms that is classic autumn hurricane. While working through the various pieces of this forecast this week, I kept coming back to Hurricane Delta back in 2020. And this is partially why I never really thought to downplay this storm as hype.

Much like Isaias, Delta, six years ago to this day, was a storm that had been a major hurricane, turning north, and beginning to weaken in the face of considerable wind shear.

The shear facing Delta was less intense than that of Isaias, but the end result seems to be similar. A look at the radar images of the two storms just past landfall tells that story fairly well.

Both storms lacked much action south of the center. Both storms saw the wind field expand at landfall and shift to the west side of the storm. And both storms produced impressive wind gusts over a broad area.

Why does this happen? One possible explanation of this is the dry air we talked about in the run up to the storm’s development. We did note that Isaias could wrap in drier air off the western Gulf Coast, causing it to weaken. This can also help enhance wind gusts (through stronger downdrafts) simultaneous to weakening the storm overall.

A similar thing happened during Hurricane Delta in 2020 as well:

We also typically see this type of expanding wind effect on all sides of a storm as it begins to lose tropical characteristics. We are passing the threshold of deep warm core (tropical) and more into moderate warm core now, eventually transitioning to cold core (extratropical) by tomorrow afternoon.

So that is a simplistic explanation of what’s happening here, and it’s similar to what happened six years ago today in Texas and Louisiana. The combination of a robust inner core of a storm that held intensity, wind shear both hurting it and helping it, dry air both hurting it and helping it, and a transition to an extratropical storm has led Isaias to come ashore swinging away unlike some other past storms that have made landfall in a weakening state.

In the meantime, the poweroutage.us page says that over a half-million customers are without power nationally, most of them in Florida and Alabama. As the night wears on, the winds will continue to expand north, and this will lead to another escalation in power outages overnight toward Birmingham, Huntsville, and Atlanta. We also continue to expect a decent side helping of tornado warnings tomorrow, so folks in Georgia and the Carolinas should have ways to receive warnings tomorrow.

In brief: We have the latest on Isaias, which will make landfall this evening near Destin, FL as a borderline major hurricane. We also talk more in depth about flooding concerns and wind concerns inland from Isaias. Also, the San Diego area is under a Tropical Storm Watch for Rachel. We explain how that scenario should unfold on Sunday.

Hurricane Isaias

The storm remains a major hurricane this evening as it’s rapidly approaching the Gulf Coast.

Maximum sustained winds are reported to be 115 mph, and the core of Isaias is resilient as anything I’ve seen. It’s currently estimated to be fending off 30 to 40 knots of wind shear. The center is currently about 90 miles south of the Panhandle, and it’s moving north at over 15 mph. A little back of the napkin math suggests landfall is roughly 4 to 5 hours away, so about 9 PM ET/8 PM CT, give or take.

On the current trajectory, Isaias will make landfall very near Destin or Fort Walton Beach. Surge and wind impacts will likely be worst there and just east of there. Indeed, conditions are deteriorating already.

Wind gusts have been as high as 56 mph at Pensacola Naval Air Station so far, along with a 63 mph gust west of the center, about 50 miles south of Gulf Shores. So even on the west side of the storm, we’re likely to see some decently strong winds.

The surge forecast and general wind forecast remains mostly unchanged. As the storm progresses inland, the wind field is going to expand and spread out across the region. This will likely cause power outages and the like, perhaps as far inland as Birmingham or Atlanta. Charge your phones tonight.

The tornado threat continues to be elevated on the eastern flank of the storm, and we’ve already discussed that in more detail in our most recent post.

Bottom line: Hurricane Isaias will make landfall before midnight near major hurricane intensity, with significant impacts on the Florida Panhandle, spreading inland overnight.

One last thing, the rainfall forecast. Watch for localized instances of more significant flash flooding potentially in the mountains of North Carolina Upstate South Carolina. We aren’t talking Helene type stuff here, but still a meaningful impact. A moderate risk (3/4) is in effect for flash flooding tomorrow in those areas south into Georgia.

The mountains north and east of Atlanta will also be under this moderate risk.

Tropical Storm Rachel

Watches have been issued for the San Diego area for tropical storm conditions possible this Sunday as Tropical Storm Rachel pushes that way. This last occurred in 2023 with Hilary. Most forecasts are currently keeping that intensity of wind out of San Diego, but with landfall not terribly far to the south, it’s not out of the question that we if the track shifts at all between today and Sunday we see those winds lift north.

Rachel is expected to make landfall between Ensenada and Lázaro Cárdenas in Baja California, Mexico. Tropical storm force winds will spread north as it also moves north, and this could bring those conditions into the mountains of San Diego County or southeast California, as well as into Arizona. Either way, Sunday looks like a windy day across the desert, with gusts of 35 to 55 mph across Arizona, southeast Nevada, and southern Utah.

In addition to the wind, we’ll see rain as well impacting the region, with areas of flash flooding possible. A large area is under a moderate risk of excessive rainfall and flash flooding Sunday in Arizona, California, Utah, and Nevada.

Worth noting that enhanced moisture will spread north and linger in Utah into Monday and Tuesday as well, which could trigger additional issues.

There’s a lot going on out there folks. Stay safe.

In brief: A morning update on Hurricane Isaias, now the season’s first major hurricane. The exact intensity remains a little challenging for landfall, but at this point, the western Florida Panhandle should be preparing for a major hurricane to make landfall tonight.

I just want to get a quick morning update out on Hurricane Isaias.

Over the last 12 hours or so, Isaias has steadily strengthening, with its core incubated from the disruptive wind shear that surrounds it. What this has led to is an environment over exceptionally warm water where the storm can thrive. Certainly, it’s not without flaws, but this is a bonafide major hurricane over the Gulf.

The track forecast is basically unchanged, with a western Florida Panhandle focus for a probable landfall tonight.

In terms of what it comes in as? Well, we’ve been warning you all along that this storm is likely to weaken toward landfall, but the margin of error was a little too close for comfort. That remains the case this morning. Isaias is probably going to get another 6 to 8 hours of time to strengthen before it can’t keep back the shear any further. By that time, we expect Isaias to be 100 to 150 miles south of the Florida Panhandle, meaning it will have only that long under a hostile shear environment to weaken.

Whether it actually happens or not, folks from Gulf Shores through about Panama City should be preparing for a major hurricane to make landfall by midnight.

The only other notable changes have been that the surge forecast has been bumped up some, and the tornado risk tomorrow expanded a bit into South Carolina.

The surge is now a bit higher near and east of the landfall point, and it is correspondingly a bit lower in Mobile Bay and on the Alabama coast.

In terms of the tornado risk tomorrow, a yellow slight risk (2/5) extends from the Panhandle into southeast Georgia and South Carolina.

The SPC did consider adding in a more substantial tornado intensity risk contour but held off for now. So at this point, while this is the risk, there is a slight chance we could see this get nudged up some before tomorrow. Either way, scattered instances of tornado warnings seem likely tomorrow in the yellow or dark green shaded areas above.

That’s all for now. We’ll be back with another update this afternoon.

In brief: Hurricane Isaias is a category 2 storm this evening, with the forecast basically on track as expected. Landfall will occur tomorrow night, likely between Mobile and Fort Walton Beach, FL as a formidable hurricane. We discuss the latest. We also take a look at the West, where the Desert will be impacted by two (2) remnant tropical storms over the next week.

I don’t want to bury the Isaias coverage here, so scroll through for some thoughts on Tropical Storm Rachel’s Southwest U.S. impact.

Isaias

Hurricane Isaias has been fascinating to watch today. It started off looking ok. Then, we saw some “under the hood” elements that suggested it was gearing up to intensify. Its satellite presentation actually degraded a bit this afternoon, and after about 3 PM ET, we have seen what appears to be steady intensification ongoing.

Deep thunderstorms started to pop on the western eyewall and then began to wrap around and expand into the evening, and as of this writing, Isaias looks like a reasonably healthy hurricane, despite enduring about 25 knots of wind shear near the center. Be thankful for this wind shear because without it, Isaias would be on the way to elite hurricane status I think. It’s sitting over water temperatures that are over 2 degrees Celsius warmer than normal, which is surely helping, and it’s also passing near the healthiest ocean heat content in the Gulf of Mexico.

Isaias may be able to fight the intense shear around it off for another 18 hours or so. The center appears to be somewhat incubated from the worst of the shear. By tomorrow afternoon or evening, it may become too much to hold off, and Isaias will begin to shed some intensity in the few hours before landfall. Notably, over 95 percent of Google’s 1,000 member ensemble brings Isaias over 115 mph tonight or tomorrow. This model has been absolutely steadfast and resolute in suggesting that Isaias would make a run at major hurricane intensity over the open Gulf before weakening on approach.

So what does this mean for the folks in the path of the storm? It means you need to prepare for a significant hurricane impact. Even if Isaias does weaken some before landfall, it may not appreciably change the surge and wind outcomes on the immediate coast. It may also allow for the wind field to expand farther north and east, so the inland areas under tropical storm watches and warnings will also need to assume there will be power outages and the like as the storm presses inland. Charge your phones tomorrow and tomorrow night.

Notably, the surge forecast has pretty much held since yesterday, with a 5 to 7 foot peak surge expected, especially near and east of where the center comes in. I would be most concerned about surge in the western Florida Panhandle right now and watch it cautiously around Mobile Bay. Tides will run up elsewhere along the Gulf Coast, as far west as Louisiana and as far east as the Nature Coast.

Rainfall continues to be mostly an asterisk on this storm. I don’t want to minimize rainfall at all. As someone who spent 14 years in Houston, boy do I know. While there will be instances of flash flooding likely all over the Southeast, these should hopefully not be the worst you’ve seen in recent years and hopefully mostly scattered or isolated in nature. Still, respect the water.

The other element is severe weather. As the wind field expands in a high shear environment, Isaias is likely to spawn tornadoes. This seems most likely in the pocket east of where the center comes in, potentially well east across Florida and southern Georgia.

Based on what I’m seeing on some of the other modeling, this tracks, and I would watch for isolated tornadoes in these areas tomorrow night and/or Saturday morning. There may also be a secondary area that shows up north of here on Saturday evening closer to coastal South Carolina. As Isaias weakens through the day Saturday, aside from those areas, the threats and hazards from the storm will diminish.

So, the bottom line with Isaias is that not much has changed. A hurricane will make landfall, probably somewhere between Mobile and Fort Walton Beach, FL tomorrow night. While it will probably be weakening on approach, it will likely come in as a formidable hurricane with an expanding wind field, meaning storm surge and winds near the coast, as well as inland will be impactful. The threat of severe weather and isolated tornadoes will also potentially be impactful in North Florida and southeast Georgia.

More in the morning.

Pacific Tropical Storms Rachel & Simon

Let’s shift from the Gulf into the Pacific, where Tropical Storm Rachel is this evening.

Modeling has Rachel coming ashore late Saturday somewhere between northern Baja and San Diego. While Rachel will be weakening, it will likely still have some degree of tropical storm force winds with it as it moves ashore, meaning that strong winds interacting with the terrain of northwest Mexico and/or California and Arizona will produce locally powerful wind gusts.

In addition to the wind gusts (and some coastal flooding and rough surf in California), locally heavy rain may occur in parts of the Southwest. Not only that, the remnants of what should become Hurricane Simon in central Mexico will also push into the Southwest next week, likely leading to another round of heavier rain. The heaviest rain from Rachel Sunday and Monday will occur in Arizona and Utah. The heaviest rain from Simon later next week will occur in New Mexico and Colorado (and parts of west Texas).

Areas of flash flooding risk should begin to pop up with Rachel this weekend and Simon next week.

It has been quite busy across the Pacific this year.