October Comes Early: Late September Multi-Hazard Hybrid Storm

[WxWatcher007]

Since it's becoming increasingly likely that a nor'easter or hybrid storm impacts New England, and possibly significantly, I think it's time for a breakout thread. October is usually when we see these kind of systems in New England, but this year we're seeing it early. 

For days, there's been a signal across guidance for some type of storm development off the east coast, and the players are starting to appear on the field. A look over the western Atlantic this morning shows an expansive area of disorganized convection. What's notable here is that in a historically quiet season in the Atlantic, where it has been difficult to get convection to fire, despite the generally hostile basin we have a window for a shallow warm core system to develop out of this. 

As the tropical guy, I'm actually not going to spend too much time over whether this becomes a subtropical storm, because as I noted yesterday, the NHC is highly unlikely to ever designate this, even if it looked ST. Despite not being tagged by the NHC, the guidance does seem to start this out as a warm core system, even if relatively shallow, though the 00z Euro is a bit more aggressive in maintaining a warmer core for longer. 

 

 

While most guidance has kept the storm closer to the coast, the GFS has waffled on whether it scrapes the coast or provides a more solid hit. It's an outlier, so this analysis is based on the current "consensus" across most guidance. Our storm system will gradually take shape, with the convection currently off the coast organizing into a weak low. From there, we see some energy from the tropics--perhaps something that would have been more likely to form in a more favorable Atlantic--get pulled into our developing coastal. From there, we see a faster pace of organization as our low consolidates as it moves up the coast. 

One thing that I'm interested in seeing is if this tropical feature coming up from the south becomes stronger/more organized. The trend on the Euro recently has been yes, as evidenced by the trend gif I'm posting below. Maybe it doesn't matter in the whole scheme of things because it's unlikely to become a tropical cyclone on its own, but it's of some interest to me. 

 

Critically, as energy dives in from the west as well, our newly energized low is blocked from being kicked out to sea, and is forced to hook west and meander until the escape route opens up again. 

This is where we get to impacts. The first thing to analyze is how strong this could get. Pressure falls are modest, and aside from the latest legacy GFS, most guidance gets the low down into the 985-990mb range. I will note that some of the AI GDM and WNV3 ensembles have stronger lows right up under New England on Sunday and given their general performance that may be something to watch as we get into higher resolution range. 

 

Regardless, this is likely to be impactful, especially for coastal areas for a few reasons. First, the pressure gradient between our low and the high to the north will create a persistent flow that likely lasts through the astronomical high tide cycle. That could bring significant coastal flooding. Moderate to major coastal flooding is already predicted for Mid-Atlantic areas. The gradient will also be a wind producer. Each model, regardless of track, has long duration windy conditions, especially in eastern New England. How far inland these winds get will depend on track of course, and how much mixing we can produce with a strong LLJ associated with our storm. 

These are 925mb winds on the 00z Euro

And here's the (wrong) GFS. 

The wind and coastal flooding may be bad enough, but the biggest question IMO is rainfall. I think with a more substantial warm core system we could see higher totals, as we'd likely see a more organized storm with tropical characteristics like banding. The Euro has hinted at big rainfall totals over a few days in eastern NE, and AI guidance has painted a wider area with modest to significant rainfall. In fact, areas up the New England coast are favored for meaningful rainfall--something that folks haven't seen in a while. 

Bottom line: this looks like a pretty significant storm that could impact New England. There's still a lot to sort out on exact track and intensity of the system, and how organized it will be when it reaches out latitude. But the signal for something is growing, and an OTS/low impact track seems increasingly unlikely. 

 

[weatherwiz]

Yeah we can't ignore the rainfall aspect of this. This is a setup in which models (even the more aggressive models) could underplay rainfall totals. As impressive as the Euro is with rainfall totals, it could still be underdone (taking verbatim). That is a continuous fetch of moisture off the Atlantic and the system takes its sweet time occluding. There could be a swath of some substantial rainfall totals. 

[WxWatcher007]

1 minute ago, weatherwiz said:

Yeah we can't ignore the rainfall aspect of this. This is a setup in which models (even the more aggressive models) could underplay rainfall totals. As impressive as the Euro is with rainfall totals, it could still be underdone (taking verbatim). That is a continuous fetch of moisture off the Atlantic and the system takes its sweet time occluding. There could be a swath of some substantial rainfall totals. 

Yeah, as we get into high-res range, we may see some big totals forecasted. A more organized system meandering west with dynamic bands could create some serious localized flash flood issues. 

[weatherwiz]

1 minute ago, WxWatcher007 said:

Yeah, as we get into high-res range, we may see some big totals forecasted. A more organized system meandering west with dynamic bands could create some serious localized flash flood issues. 

I think there is also some potential this could become a deeper storm than what is being advertised now, especially given it starts warm core and how it may take its time transitioning to more of a cold core. Another factor in this too is how the upper-level wind field evolves. At least on the Euro, look at how the structure of the ULJ evolves...that is very favorable for enhanced diffluence aloft which would further factor into the strengthening of the storm and wind fields. Lots of interesting processes will be undergoing with this thing. Sexy science at work 

[WxWatcher007]

If the Euro and others are right about the track, there could be some serious coastal erosion. 

[CT Rain]

I posted this in the other thread but these soundings off the Euro are certainly problematic. 

[WxWatcher007]

Oof, yeah that would be a problem. 

[ineedsnow]

NAMMY trying to go wild

[Damage In Tolland]

30 minutes ago, WxWatcher007 said:

Oof, yeah that would be a problem. 

As boring as the last several years have been we are long overdue for a widespread infrastructural kind of big boy storm. Fingers crossed this is finally it.

[Bostonseminole]

Anxiously awaiting the ICON

[Damage In Tolland]

Margusiry gets it 

[ineedsnow]

16 minutes ago, Bostonseminole said:

Anxiously awaiting the ICON

going wild down to 981 mb at hr 102

[ineedsnow]

ICON is a beast! that would do some damage 

[Masswx]

Icon gone wild at 114

[ineedsnow]

[ineedsnow]

@Damage In Tolland will like this run

[Damage In Tolland]

Just now, ineedsnow said:

@Damage In Tolland will like this run

Yes and Liam Likes !

[ineedsnow]

perfect track and strength for a damaging SNE storm.. hopefully we can ramp this up even more 

[CoastalWx]

4 minutes ago, Masswx said:

Icon gone wild at 114

Phones off at school 

[kdxken]

5 minutes ago, ineedsnow said:

ICON is a beast! that would do some damage 

[Damage In Tolland]

3 minutes ago, CoastalWx said:

Phones off at school 

Pants off at home?

[ineedsnow]

3 minutes ago, CoastalWx said:

Phones off at school 

oh please if you were at school still you would be doing the same thing 

[Prismshine Productions]

Nothing but heavy rain here in Townshend off that, not even strong winds

Sent from my SM-S176V using Tapatalk

[Brian5671]

2 minutes ago, ineedsnow said:

oh please if you were at school still you would be doing the same thing 

my sons have to put them in a magnetic locking pouch now when they walk in the door.   

[ScituateWX]

1 hour ago, WxWatcher007 said:

If the Euro and others are right about the track, there could be some serious coastal erosion. 

Interested to see how it pans out.  Usually when you have a storm that can last over multiple tide cycles is when we have our biggest issues on the South Shore.  Looking at it for Scituate you have tides of

9.8 Friday PM

9.7 Saturday PM

9.8 Sunday PM

10.0 Monday PM

If the winds are more out of the ENE then that is when historically the flooding has been more significant specifically in Scituate.  Not to say that NE is a cake walk but the more northerly component there is it is more like a big bowl of jello sloshing around.

[ineedsnow]

Full moon Saturday should make coastal flooding worse

[Brian5671]

GFS correcting west now

[ineedsnow]

12z GFS starting to get a clue but not there yet

[WxWatcher007]

Eastern SNE gets hit good up to Maine. Not much elsewhere. But it is further west from earlier runs. 

[Sey-Mour Snow]

I like to compare 12z to 00z, Gfs is a bit east of 00z and less impactful, but well west of the 6z east outlier.  All options still on the table.