Posting a bit late today as the office is absolutely crazy. I work in Stamford, CT and the big boss (who is also a very nice person... I'm lucky she's my boss) is vacationing out in the Hamptons through next week. I also have family and friends in southeastern New England that I'm trying to pass information along to. So, I'm going nuts here today and running late. But that's ok... a late post means I've caught the 11AM NHC update in here as well as some of the latest afternoon model guidance. So, in that regard my post today will be more up to date and relevant.
The basic headline (errr... kinda my actual diary headline) is that Irene is now a major, Category 3 hurricane and though there has been further eastward shifting of her track, it does seem to be settling down (yesterday's 18Z runs mostly nudged west, then the overnight runs mostly shifted east, followed by mostly west shifts again in the early morning 06Z model runs... if you don't know what "18Z" or "06Z" means, it's the time - in Greenwich Mean Time of that computer model initialization). So, there is increasing confidence, in my own opinion, that Irene will actually make landfall... thought there is some hope, and a real possibility - albeit a fairly low possibility, IMO - that Irene can hook hard enough to avoid any landfall at all. I don't think that happens, but we can certainly hold out hope for that. Ok, let's get to it...
*NOTE: In the interest of time, I did not proofread this. If you notice any glaring stupidity on my part or confusion, please let me know in the comments and I'll correct it. Thanks. And thanks for your understanding of any typos I made.
First a look at things as they stand. NOAA and Air Force reconnaissance data has been invaluable and impressive this morning. Pressures in Hurricane Irene fell rapidly for a short time and winds quickly spun up in response. Occasionally, I might beef with NHC's usage/interpretation of this data (like perhaps they did not downgrade Irene back to a Category 1 quickly enough when she was battling downsloping air coming off of Hispaniola). But they've handled this superbly, not benig too conservative or aggressive with their setting of Irene. The recon data pretty clearly supported a 100kt setting for Irene... no higher, no lower... and that's what the National Hurricane Center has set Irene at. That makes Irene a major, Category 3 hurricane.
Irene's appearance on satellite imagery has been somewhat chaotic this morning... looking extremely impressive at times, and a little ragged at others. Over all though, the impressive appearance has been dominant (thus, the intensification). Here's how Irene is looking as I write this up:
You can see a pretty impressive eye raking across the southeastern Bahamas, with some deep convection (the dark reddish-brown colors) surrounding the eye. It is that deep convection that acts like a chimney (sort of... I struggled to think of a better analogy) and helps lower the pressure inside the storm. This deep, symmetric convection has been supported by a favorable surrounding environment and is the reason for Irene's intensification.
Ok, this intensification isn't good news for anyone in Irene's path, but it's also no surprise... it was in pretty much everyone's forecast and fully anticipated. The real question is... where is Irene headed??? Will she hit North Carolina, or head straight for Long Island, or RI/MA, or simply make a close call and skip on out to sea? Well, here's what the NHC is showing:
Pay close attention to that track and their updates (link to NHC is earlier in the post). They are the "official" word and you should heed their warnings. Moreover, I think their forecast is pretty reasonable. I would maybe only tweak it a bit. And my tweaking is partially the result of an unfair advantage I have... that NHC forecast is from 11AM. Between that time and the time of this posting there's been a little bit of additional model data to come in.
The difficulty I'm having right now is properly interpreting the trends - if any. Due to the initialization scheme in the models (filling in data voids with results from the previous run), these computer models tend to have a "memory". As such, if they are trending in one direction they may continue doing so for several runs in a row. And we've definitely seen that with Irene... first it looked like she might hit Florida, then South Carolina, then North Carolina. Now, she may even avoid landfall in North Carolina (though she should come awfully close) and, instead, hit NY and/or New England. And even that's no sure bet as some models have trended east far enough to keep Irene offshore.
The question I'm stuck with is... Are we done trending east? If not, the U.S. could be thankfully spared a direct strike from this beast (Irene is not only strong, but her wind field is quite large)... something that seemed almost impossible three or four days ago. But if we are done trending, the U.S. will probably still take a direct hit (there are already some models keeping Irene offshore, so that's still a possibility even if the model trending is over... but it's unlikely... many more models have a landfall, and those far eastern solutions are not, historically some of the best models.
Well, I'm concluding that the trending is over (unfortunately). Here's why... check out this trend map from Brian Tang's nice web site.
...this shows the trending of the GFS track over the last several runs. It's a little difficult to decipher the individual runs from the all-too-similarly-colored shades. But that's because there really has been no more trending in the last few runs. Yesterday's late afternoon run bumped west, then the overnight (00Z run) jumped east, followed by today's morning (06Z) run that nudged back west. Furthermore, in the very short term forecast the oldest track on there, which ends up the furthest west at the end, is actually one of the best to verify with the current position. Look at that satellite image again. Irene is moving almost right on the crook of Acklins Island, which is in best agreement with the two most western solutions, including the oldest. Mind you, there is a complex interaction with a couple of weak mid-latitude systems that will mean much more than a simple 10-20mile westward error in the near term. But, the point is, all this adds up to tell me the trending has ceased.
As a result, I think we're now just bouncing around within an "envelope" of solutions and Irene is likely to end up somewhere within that envelope. Exactly where is still an excrutiatingly tough call - especially since a couple of offshore solutions remain within that envelope. But the point is, I feel, in my opinion, as if there's pretty good confidence that this envelope won't move much more. There won't be any large trending from this point forward. I'll be blunt - I could easily be wrong on that - but that's my assessment. So, some of the most western solutions (like the 06Z GFDL) could jump east, while some of the easternmost (like the Canadian) could shift west. But I don't think we'll see a wholesale eastward or westward shift of all of the models. They'll just jump around within the envelope, possibly leaning one way or the other based on their biases.
So, where is that "envelope". Here's a map of the latest assortment of tracks:
This gives us an envelope for the Carolinas between Morehead City and about 100 miles offshore. And for the Northeast it's anywhere from a New Jersey landfall (rare!) to a track about 100 miles southeast of Cape Cod. And, to be honest, I would shave some of the eastern part of that envelope off (unfortunately). Why? Because they are almost all variants of the same model - and not a particularly well performing one... the NOGAPS. So we can wratchet that back to maybe 50 miles offshore of Cape Hatteras and Cape Cod. Frankly, at these lead times, that's pretty superb agreement. And there are only two worthy models left off this map. The one legitimate statistical model for Irene (the BAMD) which goes from Morehead City, NC to central/eastern Long Island to New London, CT. Then there's the Euro (waiting on the new run as I type this, but here's what the overnight run showed)... barely off of Cape Hatteras (probably by less than 20 miles... the eyewall might even hit Hatteras)... to the exact same points as the BAMD (central/eastern L.I. to New London, CT). Oh, just noticed it's also missing the Canadian. It's old run (new run should be in before I finish writing this) nips Hatteras then goes to Block Island and across southeastern Mass.
...point is, these additional three models all fall right in line with that envelope. So, we've got excellent model agreement. And with such great agreement, my own thinking is to just shoot down the middle and emphasize that there is a small margin of error near Cape Hatteras and a larger margin of error for the Northeastern landfall.
But I'm shooting down a "modified middle"... blending the NOGAPS into one eastern track and adding in the Canadian and Euro models. As such, my expectation is for two landfalls and one close enough (eyewall brush)... like so...
1) Irene scrapes Cape Hatteras as a borderline Category 2/3 Saturday afternoon.
2) Long Island landfall just east of the centerpoint (for those familiar with the island, I'm talking about somewhere around Mastic Beach) as a borderline Category 1/2 hurricane
3) Finally, landfalling just west of New London, CT as a Category 1 hurricane
Further reinforcing this idea, we get to my "cheating" advantage... that I have newer data than NHC had at the time of their update...
The afternoon GFS (American model) run trended west from the overnight run and just a shade west of the morning run. And, as a side note, one worry on the GFS is the extraordinary - very much not normal - wind field on the western side of the storm. Check out this image from Ryan Maue's excellent site:
It's a bit hard to see, but that's an 88kt contour all the way back past NYC when the storm is south of Montauk, and a 114kt peak south of eastern Massachusetts. Now, please notice that's a 900mb wind. You've got to subtract about 20% to get surface winds... and probably 30% on the west side, since that's an over-land wind, running into tremendous friction. Still, that would by 60kts sustained wind in NYC and about 90kts south of eastern Mass. The latter is believable, since Irene could be a Category 2 at that time. But 60kts at NYC with a track that far east?!?!?! To be clear, I do not believe it. But that's what it shows and it's doing it for a reason (starting an extratropical transition, perhaps). So, even this solution is no cakewalk - at least on this model - even well west of the storm center.
Rainfall is also a big issue. There could be significant fresh water (rainfall) flooding with amounts like this:
That's from the GFS. Please note that my own forecast is a little west of this, so you'd need to shift those contours west by about 30 miles.
Note: A new Canadian model is in as well, but shows little change from the previous run, besides being about 12 hours slower. One might think that'd give the trough time to kick the storm out and so this would push the storm further east. But that's not the case. In fact, after landfall in New England the new Canadian actually tracks Irene further west. So, this new run doesn't change things at all.
So, that's the story. I'm leaning a little west of the National Hurricane Center, but not by much. I'm doing so largely on the basis of the consensus being, perhaps, dragged east by too much NOGAPS influence, plus the fact that the GFS has trended west - albeit only barely compared to the morning run. Add in the fact that Irene is currently positioned on the western edge of all of the recent GFS model tracks. And one last point - the new GFS and Canadian runs further reinforce the idea that the eastward trending has ceased.
Any questions, I'll try to hang around in the comments & try to post any updates either in the comments or - if very significant, I'll update the diary.
And as I'm finishing this up the new HWRF is coming in... it was one of the more western solutions in the track plot above. It is now about 6hrs slower and a bit further east (would still landfall on eastern Long Island, though... before landfalling again near New London, CT). This, to me, indicates some convergence... the HWRF was on the western side of consensus and shifted east; the GFS was on the eastern side and nudged west. I think this is very supportive of my forecast, though the HWRF now landfalls on Long Island a little closer to NHC's track than mine. But, honestly, that far out (Day 4), that's splitting hairs - although that difference may be important for folks on the fringe of the significant impacts (like the NYC metro area).