Doing this update in my downtime from work. So, I don't want to dawdle a whole heck of a lot. And please forgive any typos... they are inevitable with my sloppy hands, and in the interest of time, I won't proof-read. Perhaps I'll correct any errors, if I notice any, when I update later in the day. As such, let's just jump right to it, as hurricane Earl continues to pose a threat to the U.S. East Coast...
Hurricane Earl is likely now a major hurricane as I write this, at about 9AM on Monday. It is NOT yet official, and I'm not usurping the National Hurricane Center's authority. Merely making an observation based on current data. An Air Force reconnaissance plane currently investigating Earl clocked winds at thier flight level of 111kts. Based on the height of their flight level that would equate to about 100kts at the surface... putting Earl on the cusp of a Category 3, major hurricane. Here's a current satellite view of Earl:
You can see on this image the eye starting to appear (the reds are deep convection... thunderstorms). An eye has only briefly been visible on Earl. This is about the best that it's appeared, so this is evidence of continued strengthening. However, there is also some dry air around some of the south and eastern outer edges of the core. So, Earl may not undergo any explosive intensification, and could even weaken slightly if this dry air makes its way into the core of the storm. But, on balance, intensification is continuing and should continue over the next 24-48 hours.
The track of Earl and his future potential impact on the East Coast of the U.S. has become more problematic compared to yesterday, rather than coming into better focus. On the one hand, some models have trended even further to the east, which is a very good thing, keeping the East Coast clear of any significant impacts. On the other hand, these are all one "type" of model... all the hurricane-specific models. None of the global models have made such a shift. They've all nudged around a bit... the most recent American model run bumping east slightly, while the European model nudged west a bit. On this shot of the latest track guidance:
... courtesy of Allan Huffman's excellent site... it can be a bit misleading. A sort of "benchmark" for significant impact in southern New England is 40N latitude and 70W longitude. On this plot you see only a couple of models falling on this benchmark and none "inside" (northwest of) the benchmark. This would imply a pretty low threat for any significant impact. However, I say this is "misleading" because this plot contains very limited representation of the "global" models (called "global" because they produce forecast for the entire globe). In fact, not surprisingly, the only real representation is those two lines that touch the benchmark... those are from the American model. Check out the other global models. Here's the UK's global model:
...it pegs Earl right at the benchmark late Friday. How about the European model? ...
...this image doesn't give you the precise track, and some of the in-between time steps I get from proprietary sources that I can't publically distribute. But I can tell you that it moves Earl inside the benchmark, very close to landfall in Cape Cod. And what about the Canadian's model?
...also tough to tell from this one snapshot image whether it moves inside or outside the benchmark. But, no matter, the impacts are significant. The gradient of the black contours on that map will determine the winds; so, you can see it's quite windy throughout all of southeastern New England on Friday. And the shadings are rainfall... that is very heavy rainfall in eastern New England.
On top of that, my focus has been essentially on New England, but these track differences are also very significant for Cape Hatteras, and, to a lesser extent, but not insignificant for the Mid-Atlantic coast. So, what's the right answer?? Honestly, it's impossible to be certain just yet. The National Hurricane Center is basically splitting the difference. Here's their forecast:
...this track is just "outside" (southeast of) the benchmark and would limit impact on New England, but the Cape and Islands would still experience a fair bit of nasty weather. So, the NHC is going east of all of the global models and west of the hurricane models.
Let me be clear that my opinion is just that... mine... and people should closely monitor and follow the NHC's official forecast. That said, here's my opinion... I do think the NHC is pretty close. However, I believe, unfortunately, that Earl will cut closer to the coast than they are advertising (and, in their defense, they do recognize in their latest write-up that their forecast is on the eastern edge of the guidance; here's their quote: "GIVEN THE LARGE SHIFT IN THE MODELS...THE OFFICIAL FORECAST HAS BEEN ADJUSTED TO THE LEFT...OR WEST...BUT STILL LIES ON THE EASTERN EDGE OF THE GUIDANCE SUITE." ...the all-caps is their's... sorry).
Here's why I think Earl will track closer to the coast than they anticipate:
- Earl has been running west of the forecast track his entire life-cycle. That indicates that models are underestimating the influence of a ridge of high pressure to his north. With limited new data for the models to feed on in that area, I would expect this error to continue... though it may wane in time.
- Earl's eventual turn will be largely determined by an incoming cold front late this week. In my view, the global models should handle this much better than the hurricane-specific models. As such, they'll get the turn up off the coast more correctly. In other words, Earl will track very near the benchmark, if not a shade "inside" (closer to the coast), as the global models indicate... not "outside" (east of) the benchmark, as the tropical models show.
- Often times, an approaching hurricane can force a cold front to stall or push backwards a bit as the intense east winds on the north side of the hurricane blast into the front. This then allows the storm to move further to the west. This was a critical factor in allowing the last New England hurricane to make landfall (Hurricane Bob in 1991 would've likely remained offshore had this effect not taken place). That said, models have come a long way since then and handle this effect much better. But, if anything, this should allow for a slightly more west track to Earl.
Given that, I should also add a point I mentioned earlier... with a further west track, I probably shouldn't be isolating my focus to New England. This could also bring Earl dangerously close to Cape Hatteras late Thursday night (or very early Friday). And it could even allow for some minor impacts along the Mid-Atlantic coast (though the shape of the coastline relative to Earl's motion should keep those impacts in check).
The biggest caveat in all of this... remember, impact in Hatteras or New England is three and a half to four days away. Typical forecast errors that far out are on the order of a couple hundred miles. Such an error could either mean actual landfalls or a track out to sea so far that impacts are trivial and inconsequential. I don't mean to lob that out there to make the forecast seem almost useless. Rather, the point is, uncertainty this far out remains a bit high. So, at this timeframe, it is prudent just to keep a close watch one Earl.
I'll try to follow the comments and reply below... and probably even update this as the day goes on. But please bear with me as I'm doing this from work, and I do have some "real" work to do.
UPDATE (11AM EDT) : The National Hurricane Center has upgraded Earl to a 105kt Category 3 hurricane. Note the above discussion supporting a 100kt storm. Since Earl has continued developing, this 105kt setting seems about right. Their track also appears to have nudged to the west slightly. Their discussion isn't out yet, as I write this, so I'm simply basing this on their forecast positions... drawing lines connecting the point... low tech, lol... and it appears to draw Earl slightly closer to Cape Cod. Still it is almost certainly still "outside" the benchmark. So, my thinking remains west of their's, but given their apparent nudge west, honestly... the difference between my thinking and their's on a four day forecast is splitting hairs. No new model data to update right now. Will try to update again later with the new suite of model data.
UPDATE (2PM EDT) : Some new model data has done little to shed any light on Earl's eventual track. The bottom line is that they are encouraging, shifting just a shade eastward away from the Hatteras and Cape Cod coasts. But they do so while establishing an overall pattern more conducive for bringing the storms closer to the coasts or inland. How do these models manage this contradictory result? Simple... timing...
New runs of both the American and Canadian models are in. They both show the same changes in the upper atmospheric guiding winds, with the Canadian showing more significant changes. The changes are all more favorable for getting Earl to the coast. First, the trough digging into the central U.S. is stronger (a trough is the upper system that drives a cold front). Being stronger means it has more south-to-north, rather than southwest-to-northeast flow in advance of it. This more south-to-north flow would draw Earl more straight up the coast. Also (and not unrelated), they are stronger with the ridging in advance of Earl in New England and the NW Atlantic. Basically, Earl moves around this ridge (which is a high pressure aloft)... so being stronger, Earl should get pushed further west... closer to or into the coast. BUT they manage to be LESS threatening, pushing Earl further offshore because of TIMING. They are slower with Earl and, so, even though the pattern would push him further west, that entire pattern is slowly progressing east. So, following through the eastward-shifted pattern, Earl ends up further east.
As I write this, the new HWRF hurricane model is in. It, on the other hand, has trended further west and now brings near-hurricane force winds to both Cape Hatteras and Cape Cod (that is an estimate... it shows winds about 1500ft off the ground... I'm using a standard reduction to obtain a surface wind estimate => that gives something at or just under hurricane force for Cape Hatteras and about the same at Cape Cod). Incidentally, this HWRF track is now over or just inside the benchmark; it also fails to show the hard east turn seen on most models - actually showing landfall near Eastport, Maine on Saturday.
At any rate, the complicated eastward nudge of the global models, combined with the westward shirt of the HWRF leaves things, I'd say, pretty unresolved. At this point, I anticipate no landfall and no majorly damaging impacts, but some significant weather on Cape Hatteras and Cape Cod. But this is definitely not nailed down yet. Stay tuned!