- If this is more technical than what you're looking for, my video presentation from Monday evening's NECN broadcasts can be found on my Weather Analysis Page
- I've posted some simple, easy, inexpensive preparatory steps we all should consider at this early stage of the game on our NECN Weather Team Blog, WeatherNewEngland.com
Normally, I have a chronological progression to these technical discussions - a big build-up to the final forecast, where we put all of the pieces together. I won't let you down, but want to get a few highlights out in the open first:
- I expect Hurricane Earl to pass very close to New England's benchmark of 40N and 70W.
- If this track verifies, tropical storm force winds and hurricane gusts will be possible in Southeastern New England, particularly the Cape and Islands
- I am encouraging New England residents take easy, cheap, quick preparatory measures at this point. Once uncertainty decreases, more advice will follow.
- This is not a slam-dunk forecast. The typical delicate interactions that govern New England hurricane forecasts are at work again.
With those four major points laid out, let's review what we know...
- The time of greatest impact of Earl on New England will be later Friday through Friday night: The storm will accelerate north, then northeast, after passing the Outer Banks of NC and this should ensure the storm has departed most of New England by Saturday morning. While a slight slowing is possible, it should not be significant enough to jeopardize this timing forecast.
- Waves will increase at the South Coast of New England Thursday, well ahead of Earl. Those waves will bring a return of severe rip currents, and that danger will persist into the weekend.
- Mariners...especially the fishing community...should be back in port by Thursday evening, as seas will continue building on Friday, and wherever the exact track of Earl ends up, ocean conditions will deteriorate quickly on Friday. Getting in trouble on Friday may result in a suspended search operation by Friday night as conditions worsen
- A landfall is extremely unlikely directly on the New England coastline. Though not completely impossible, what seems far more likely is a close pass southeast of Nantucket and Cape Cod.
I say the above points are "what we know" because there would have to be some substantial deviations from the current forecast for these to change. The wave action is fairly straight-forward. The deteriorating marine conditions - particularly for the Southern waters - also seem fairly self-explanatory. The exact acceleration of Earl is dependent upon the mid-level flow between the sub-tropical ridge and the incoming northern stream trough digging across the Great Lakes, but this squeeze will increase later Friday and should serve to provide the classic "New England slingshot" effect (I just made that term up, but it sounds good, eh?).
While we're discussing things we've made up, several years ago, Tim Kelley and I decided to do an historical analysis of storms that made landfall on New England. Our end product was the creation of two critical gates storms that strike New England must pass through - no storm to miss these gates ever hit New England directly. We called these gates the "Kelley-Noyes Wheelhouse" and if Earl continues on his current track, he will pass directly through the first high-risk area of this wheelhouse. That's not a guaranteed direct landfall, rather...a miss seems to be a guaranteed non-landfall. So, historically, landfalling in New England is not off the table according to the Kelley-Noyes Wheelhouse.
Of course, each scenario is different, and a meteorologist must examine the synoptic setup at the time. In this instance, the upper level low that will be deepening and digging across Lake Superior by Friday will be large, and its influence on the jet stream will be pronounced. Also at play is the upper low north of the mouth of the St. Lawrence, up in Newfoundland. The interaction of both upper lows creates a fairly strong southwest flow at 300, 500 and 700 mb that would make it very difficult - in fact, impossible if the forecast mid-level winds are correct - for a hurricane to landfall directly into New England. Rather, that southwest wind should exert a northeast push starting just after the passage east of North Carolina. This is interesting, because some of New England's worst hurricanes, historically, have taken the exact path touted by the 00Z NAM - a due north motion off the Carolina coast. So, historically and speaking from the "Wheelhouse" theory, there is much to be concerned about...but given the forecast mid-level and upper-level winds, it's a very, very difficult case to make, and I think forecasting a recurvature prior to New England is warranted.
Having said that, the pattern does favor a pass near the 40 degree north, 70 degree west, New England "benchmark." True weather fanatics know this position well - the sweet spot for big winter storms in Southern New England, as this position typically delivers the heaviest wind and snow to the Boston/Providence corridor. With a hurricane, things work a bit differently, but this is still a precarious position to put a storm. Though I have no guarantee this position will be correct, it is extremely close to the NHC track, is a weighted solution toward the global models (hurricane models take the storm farther southeast) which I think is wise given the interaction of northern stream trough with subtropical ridge, and most important of all, was developed by and therefore fits perfectly the synoptic reasoning set forth above.
The first consideration many will have is to question just how substantial a storm passing through this location will be. Afterall, it's common knowledge in the weather world that heaviest wind should stay to the east of the storm track. Remember Ophelia of 2005? Referred to as "No-feel-ya" by Cape Codders and weather nuts, this storm for days looked like it would come across Nantucket. The night prior, NHC posted Tropical Storm Warnings for the Southern New England coast. I'd been beating the drum for TS force winds all that week, and was thrilled to see it was going to pan out. Interestingly, that was a Friday Night/Saturday event, too, and I remember distinctly being on the air both of those periods, able only to show the Doppler velocity plot of the storm center going 25 nautical miles southeast of Nantucket, but no wind whatsoever on the west side. Maximum gust ended up being 21 mph from the west-northwest in Hyannis well after the storm went by, associated with dry and cool advection. It was horrible. Having said that, Earl is not Ophelia. Earl is not a glorified wave named a tropical storm. Earl is a monster. A category 4 and possibly 5 monster with winds that extend hundreds of miles outside of the center. Even a decaying monster is still a force to be reckoned with, and that's what Earl will be when he came by.
Tim Kelley very accurately compared Earl to another E storm from several years ago - Edouard. Edouard was also a monster, and charged northeast, passing southeast of benchmark, even farther away from New England than I currently expect Earl to pass. Edouard brought 90 mph wind gusts to Cape Cod. The stakes are high.
This brings us to the question of just how strong Earl will be when he passes New England, presumably near this 40/70 position. I cannot stress enough that I think Earl's strength is being underforecast by the guidance and therefore by many forecasters - perhaps significantly. It's more than gut that leads me to say this...consider the facts: 1) Waters along the Mid-Atlantic are running between 4 and 9 F warmer than normal, 2) These warm waters have enough heat content to support a CATEGORY FIVE storm as far north as 37.5N if Earl sticks close to his projected path, 3) Though wind shear typically would account for some weakening, once Earl turns northeast, the shear will decrease as acceleration begins, not to mention shear should remain quite limited until about that point. In fact, the forecast is for remarkably low shear, increasing slightly from the southwest when Earl starts his recurvature, but hardly enough to account for the weakening forecast by intensity guidance. The ocean water temperature gradient is just south of the 40/70 benchmark position, and therefore, weakening prompted by ocean cooling won't even begin until Earl approaches his expected closest pass to New England.
If I'm right on this, these factors effectively negate many of the normal alterations storms undergo when they come into northern latitudes - including the transfer of wind to the east side. This should still be a fairly concentric, extremely powerful beast. It's for this reason that I believe at hurricane force gusts - if not sustained - are a distinct possibility on Cape Cod and the Islands, with tropical storm force winds expanding up most of the Eastern MA coastline and perhaps westward to New London along the South Coast.
Given the uncertainty that lingers on precise track - and my desire to find better guidance consensus on my thoughts of a 40/70 position and track - I don't want to put any precise numbers out, and this is also a huge reason why I haven't more definitively hit things hard in my broadcasts - there's still plenty of room for wiggle, as some of 00Z guidance (GFS, GGEM) indicates with a more sea-ward solution. But I think we have plenty to work with in the facts laid out above to introduce the possibility of 74+ mph gusts on Cape (hurricane force) and 39+ mph gusts (tropical storm force) in some of the remainder of the coastal plain, and we can continue to adjust as needed.
It's for all of these reasons that I began suggesting early preps be made in my Monday broadcasts. Everything I suggested were easy, cheap, no-brainer preps that should be done before the season even starts, but few every really do until we have to
This ought to be interesting, to say the least.