The Eyewall

Remnants of Isaias

The remnants of Hurricane Isaias are moving inland this morning after spewing wind across the South overnight. Wind gusts hit 49 mph in Birmingham, 45 mph in Atlanta, 68 mph in Macon, and 54 mph at Auburn, Wind damn Eagle.

Wind gusts are still in the 35 to 45 mph range over a wide area moving north. Power outages sit around 900,000.

Rain totals were highest near where the storm came ashore, but you can see how rain totals thus far have triggered some flash flood warnings in metro Atlanta. The worst of the rain should stay north and east of there for the remainder of the day.

So what about the rest of the day? We have two primary concerns remaining with Isaias: Rain and tornadoes. So far, the tornado threat has generally failed to materialize in any real serious way. But much of South Carolina and a chunk of East Georgia are under a slight risk (level 2/5) for severe weather with a risk for tornadoes today.

We’ll see that risk shift north a bit tomorrow into eastern North Carolina and southeast Virginia and perhaps up through Delmarva. In addition to the severe weather, heavy rain will overspread most of the Eastern Seaboard over the next day or two, with widespread 1 to 3 inch totals.

There may be a bit of a drier slot between the Triad and Outer Banks in North Carolina and in parts of southeast Virgina. The mountains will see locally meaningful flash flooding in North Carolina (again, nothing remotely close to Helene). Those higher rain totals continue up the Appalachians into the Blue Ridge and Shenandoah.

So, still a bit to go before we can close the book on Isaias.

Tropical Storm Rachel

Rachel has already helped to unleash some havoc in Southern California. Parts of Orange County, specifically around Newport Beach were hit pretty severely yesterday by coastal flooding. The combination of swells from Rachel, higher tides, El Niño vulnerability, and a much ballyhooed oceanic Kelvin wave seem to be multi-faceted, nuanced contributors. We’re coming into another high tide as I write this. We’ll see if that causes as many issues.

Rachel is still expected to track into Baja tonight, right around midnight local time. The storm will track into Arizona from there, spreading wind and rain across the region. The strongest wind gusts tomorrow will be in the higher terrain east of San Diego and across Arizona. The rain, however, will be a little more widespread, with pockets of heavier rainfall likely in the higher terrain, as well across Utah and parts of Nevada and northern Arizona. Flash flooding is likely in some areas.

We could even see some higher terrain snow in parts of the San Bernardino Mountains, the Sierra, and the Uinta Mountains in Utah (and the Wasatch to a much lesser extent). Snow totals won’t be significant (except perhaps in the Uintas) but it’s a reminder of the season to come.

Wind gusts from Rachel will be on the order of 30 to 50 mph with higher gusts in some of that higher terrain.

We should then hopefully see a quieter stretch of tropical weather.

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.