Major Hurricane Isaias

[NorthHillsWx]

This pass will decide if it gets the upgrade. I would be shocked if it didn’t find cat 3-worthy winds 

[beanskip]

Looks like recon quit transmitting data? 

[40/70 Benchmark]

9 minutes ago, NorthHillsWx said:

HAFS-B has gone from a decapitated,  essentially nor Easter, landfall to a cat 3 with eyewall intact as it crosses the coast. Buckle up coastal residents 

It's a tough call because like they said in the statement, a 6-hour delay in the onset of shear could mean 20mph in LF intensity....so they are making the right call hedging more intense. They have to balance the need to disseminate as precise a forecast as possible to the public with the need to convey a sense of urgency commensurate with the worst possible outcome that can be reasonably expected.

[WxWatcher007]

Isaias is on the cusp of becoming a major hurricane this morning, and as you all know by now it is explicitly forecast to become a major shortly. Although not a pristine satellite appearance, Isaias from both satellite and recon is clearly an intensifying hurricane at this hour with an eye, deep convection continuing to wrap upshear in bursts, and rapidly falling pressure in between center fixes as a result. 

While the season has been defined by futility overall, with both Fay and Edouard we had systems that were able to maximize their limited geographic environment to pop, and Isaias is the best example of a system taking advantage of the narrowest of windows for development and intensification this season. If Isaias were moving in any other heading, it would be getting annihilated right now. 

Isaias is the beneficiary of excellent divergence and a relative heading that precludes shear so far from disrupting the increasingly strong inner core. This has also allowed the hurricane to avoid disruption from dry air entrainment. A few days ago, that was a key question for me as the core was establishing itself. Normally a northern Gulf landfall, especially this time of year, features last minute continental air disrupting things, and while that may eventually erode part of the system, that's not happening right now. 

The resilience of Isaias will be tested in the coming hours, and if you're still reading here's the real thrust of the post: the NHC is right to be concerned about a delay in weakening.

I do still think that shear will eventually disrupt Isaias, but it may not happen until landfall is occurring. Operationally, that may mean it's difficult for the NHC to confirm weakening as the center is moving onshore. More importantly, in an expanding wind field, it could be the case that we see the intensification plateau later followed by pressure rises and then winds weakening. For folks along the coast, any lag between the impact of shear and weakening may lead to a C3 landfall.

This is a razor's edge forecast. It seems clear that unlike many of the recent Gulf examples there will not be intensification up to landfall, but weakening may be blunted or delayed. 

The latest HAFS A & B both show more intensification before some weakening--right at landfall. 

Both essentially have a major landfall in the next 12 hours. 

Perhaps more significantly, the GDM, which I've been raving about for two years now and with good reason--it's by far the best hurricane ensemble--shows very little change in intensity until landfall is effectively occurring. Pay less attention to intensity and more to whether there's weakening evident and when. 

At this point, I think folks in the landfall zone should be prepared for a C3 impact. It likely won't be at its peak, which is important from an impacts standpoint (the storms intensifying at landfall tend to "feel" worse than ones weakening at the same intensity), but between surge, rainfall, and a likely significant severe weather threat, this is likely to be a highly impactful hurricane. 

I'm not there for this one, but stay safe to everyone down there. 

 

[olafminesaw]

A nice way to display the impacts (I think a little over cooked on the inland gusts though)

[WxWatcher007]

Latest recon finds 117-120kt FL winds. 959.3mb pressure extrapolated. 960mb dropsonde in the center with a 6kt wind. 

[40/70 Benchmark]

@WxWatcher007It was such a tough call on whether to pull the trigger on major peak or not when I issued the first stab on Wednesday...I'm happy with the forecast overall, but looks like I may have underestimated my 110mph peak a bit. I thought conditions would be hostile by dawn today, so that is the difference. Also happy with the Thursday night hedge for best deepening window.

[PhiEaglesfan712]

21 minutes ago, cptcatz said:

Yep, people seem to only remember the ones that intensified upon landfall. But Idalia in 2023 weakened right before landfall, Delta in 2020 did too, and of course Katrina weakened big time before landfall.

If Idalia didn't get retired, this one probably won't be either. Idalia got up to high end C4 speed, and this one is barely going to be a C3. 

[NorthHillsWx]

Upgrade coming. What a pass. Might be 120

[olafminesaw]

Likely near peak intensity at just over major hurricanes strength right now with pressure leveling off around 960 MB and winds catching up to pressure now supporting a major hurricane around 115-120 at the surface 

[CoastalWx]

1 minute ago, 40/70 Benchmark said:

@WxWatcher007It was such a tough call on whether to pull the trigger on major peak or not when I issued the first stab on Wednesday...I'm happy with the forecast overall, but looks like I may have underestimated my 110mph peak a bit. I thought conditions would be hostile by dawn today,  so that is the difference. Also happy with the Thursday night hedge for best deepening window.

If it weakens right before landfall and the core erodes like some models have, best winds may be found in the convection modeled on the NW side of the center. Would make it more difficult to maximize best winds in that area accounting for forward motion. You really need good mixing to maximize your best winds at the surface. That’s why it makes all the difference when a storm is intensifying as it makes landfall vs weakening. 
 

I’m not minimizing this, just stating what we know with these storms. 

[WxWatcher007]

7:20 AM CDT Fri Oct 09
Location: 27.0°N 87.6°W
Moving: NNE at 15 mph
Min pressure: 959 mb
Max sustained: 120 mph

[NorthHillsWx]

1 minute ago, WxWatcher007 said:

7:20 AM CDT Fri Oct 09
Location: 27.0°N 87.6°W
Moving: NNE at 15 mph
Min pressure: 959 mb
Max sustained: 120 mph

Fully supported by recon data. That’s why NHC waited at 8 am knowing they had a plane heading straight for the money pass. Great job hurricane hunters. This might peak at cat 4

[CoastalWx]

If there is a time for further strengthening it’s now through 18z or so. Definitely good venting helping out. 

[WxWatcher007]

5 minutes ago, 40/70 Benchmark said:

@WxWatcher007It was such a tough call on whether to pull the trigger on major peak or not when I issued the first stab on Wednesday...I'm happy with the forecast overall, but looks like I may have underestimated my 110mph peak a bit. I thought conditions would be hostile by dawn today, so that is the difference. Also happy with the Thursday night hedge for best deepening window.

Yeah, very tough call. Just a few hours made the difference here, though it's incredibly impressive how well GDM has been through the entirety of this one. Like you said in another post, it was easy to hedge east for this one, and GDM never backed down on a higher end peak. 

4 minutes ago, PhiEaglesfan712 said:

If Idalia didn't get retired, this one probably won't be either. Idalia got up to high end C4 speed, and this one is barely going to be a C3. 

Well, keep in mind that Idalia hit one of the least populated areas of the state. Idalia's eyewall was legit, but less damage=less need for retirement. That won't be the case with this one, even if it's weakening at the end, because it's hitting real population centers.

Not to mention the yet to be seen inland impacts in the south. 

1 minute ago, CoastalWx said:

If it weakens right before landfall and the core erodes like some models have, best winds may be found in the convection modeled on the NW side of the center. Would make it more difficult to maximize best winds in that area accounting for forward motion. You really need good mixing to maximize your best winds at the surface. That’s why it makes all the difference when a storm is intensifying as it makes landfall vs weakening. 
 

I’m not minimizing this, just stating what we know with these storms. 

Agree with this too. There's going to be a line of discussion here tonight about why we're not seeing G125 across the landfall zone and it'll be because 1) that's not how things work lol and 2) the strongest winds in a decaying core may be concentrated in a few spots. Still bad to be clear with other impacts and with wind itself, but as I've found, eyewall dynamics and impacts are more mesoscale than people tend to realize. 

[TriPol]

Isaias now a major hurricane. 

[TriPol]

https://pbs.twimg.com/media/HUMGXpaXQAAwuKb?format=jpg&name=medium

[olafminesaw]

Another convective tower trying to wrap around the eye as it fights some intense shear on the West side. Wish we had one more pass to see if pressure drops or holds steady

[lee59]

Latest pressure went up so slightly from 958 to 959. Maybe a sign that it has maxed out and some weakening could start happening during the day.

[Buddy1987]

I cannot believe what I am seeing. Thing should be getting shredded like it hit the Hispaniola mountains yet the west side of the storm is enveloped with -60 tops.

[40/70 Benchmark]

13 minutes ago, CoastalWx said:

If there is a time for further strengthening it’s now through 18z or so. Definitely good venting helping out. 

Yes, I though this window was going to close about 12 hrs early than it is.

Nice from a met standpoint, not so nice for the Gulf coast.

[hawkeye_wx]

Models accurately forecasted the 10-15 mb drop as it traversed the loop current eddy overnight.

[suzook]

34 minutes ago, olafminesaw said:

A nice way to display the impacts (I think a little over cooked on the inland gusts though)

65 to 80 mph gusts as far inland as la grange GA???? That definitely seems overdone.

[WxWatcher007]

17 minutes ago, olafminesaw said:

Another convective tower trying to wrap around the eye as it fights some intense shear on the West side. Wish we had one more pass to see if pressure drops or holds steady

Recon is heading in for another pass. 

[ROOSTA]

I feel like that guy who does those Dos Equis commercials. ISSY once took on 60kt. shear and became a CAT3.
When your wrong, your wrong and admit it. 
Surprised but not shocked.
"Stay thirsty my friends." LOL  

[HKY_WX]

Google DM brings this in around 7 to 8PM. Majority of the models have the pressure bottoming out around 1PM. That give us about a 6 hour window to weaken before landfall. Not much time there to work with at all. Better hope it doesn't strengthen much more this Morning.

[WxWatcher007]

First light

[NorthHillsWx]

1 minute ago, HKY_WX said:

Google DM brings this in around 7 to 8PM. Majority of the models have the pressure bottoming out around 1PM. That give is about a 6 hour window to weaken before landfall. Not much time there to work with at all. Better hope it doesn't strengthen much more this Morning.

It might be earlier than that. Keeps bumping up landfall time each run. We’re not working with a ton of time for this to fall apart and it doesn’t matter when the center crosses because that eyewall is obviously out ahead of it. Dangerous situation saw they increased max surge from 7 to 9 feet, not insignificant at all especially with the population center this is plowing into