Late post today. My schedule is really eating into my ability to post these updates. :(
Boy did this hurricane season flip the switch. From dead calm to a three-storm setup in the Atlantic. As we jump below the fold, I'll take a look at all three of these storms. But, as you'll see, I've decided to focus mostly on Bill. It is not the most threatening storm (Claudette is, as it is about to make landfall in the Florida Panhandle), but it is the most relevant storm (IMO) from a forecasting point of view. So, let's get to it...
First, kudos to reader EdlinUser for the comment in yesterday's thread picking up on the development off of Florida. This was not entirely tropical yesterday, being instigated by cool air aloft from a nearby upper level low. But convection had flared up and there was evidence of some developing circulation (esp. on radar... harder to tell on satellite). And, indeed, this system continued to develop, became Tropical Depression #4 and is now Tropical Storm Claudette.
So, now, after a slow start to the season, we're all of a sudden faced with three tropical storms roaming the Atlantic. On the plus side, it looks - right now - as though none of them will pose a serious threat to land. TS Ana will run across the Caribbean and eventually it should run aground somewhere in the U.S. However, Ana has struggled mightily - again - over the last 24 hours. I would not be at all surprised if it gets downgraded to a depression soon. So, this is not an impressive storm system, and the models do not project it to become a major storm. Bill, meanwhile, is expected to be just the opposite... it should become a major storm, but is unlikely to hit land. To be clear, there is a complex evolution of the upper level steering flow which will take place over the Eastern U.S. late this week, and it may allow Bill to sneak into New England. But, right now, all model guidance indicates that the flow will not back (that is, turn more out of the southeast, to let Bill move west of due north) quite enough to push Bill into New England... instead, the storm should curl out to sea. Finally, there's Claudette. This storm will hit land... it has no escape from the Gulf without hitting land... and it will do so soon. It should come ashore in the Florida Panhandle late tonight. So, Claudette will certainly have an impact; however, this brief time over water will severely limit development. So, the storm should come ashore as only a tropical storm. That's not to say there will be no impact. Heavy rain could cause some flooding, and the gusty winds could take down a tree or two in the saturated ground.
Hmmm.... this is a tricky write-up to try to handle. I'm not going to go on ad nauseam, so I'd like to focus on the most critical system of the bunch. But which is it? Claudette is a guaranteed impact, but there's not much to forecast there with landfall impending. Ana is the most likely to landfall, and far enough out in time to make it a good issue to deal with forecasting-wise. But Ana is so close to falling apart again that it hardly seems like an issue. Finally, Bill is almost assured of being the most impressive of the bunch, but it is the one least likely to reach land.
Well, I'm going to focus on Bill. Tropical storms, unless they stall over land and cause massive flooding, rarely yield a major impact. They can be somewhat disruptive, but are not a big issue (unless, again, they stall out... I reiterate that because it's an important point - some tropical storms have caused massive damage by stalling out over one area and creating large scale damage). So, Claudette and Ana should not be major problems (though there will almost certainly be some localized flooding in Florida and the Southeast from Claudette). Bill probably won't be a problem either, as it remains offshore, but it has a window of opportunity to edge back into New England. And since it will probably be of considerable strength, it seems like the right storm to focus on.
So, here's what Tropical Storm Bill is looking like in recent satellite imagery:
...a nice spiral look to it and some deep convection near the center (known as a central dense overcast... or CDO); but this CDO feature is rather new. So, we'll need to see if it persists. If it does, Bill may be off to the races intensity-wise. For now, though, this nice structure, offset by oscillating convection, leaves Bill as a moderate tropical storm, probably in the 45-55kt range. Officially, in their brand new update, the National Hurricane Center puts Bill at 55kts. This is on the high side of what I'd estimate, but, no matter, if Bill isn't actually at 55kts, it'll get there - and beyond - quickly if that central convection persists.
Conditions around him are generally favorable - though there could be some shear down the line for him. So, general intensification is expected. Here's how the model intensity forecasts stack up:
The most reliable of these models are the GFDL, HWRF and related models, as those are the only ones built to handle the dynamics within a hurricane. By the end of the forecast period (5 days out) they have Bill in the 100-120kt range. In deference to the possible developing shear the NHC tops Bill out in the lower end of that range... at 105kts. That seems quite reasonable to me, unless Bill can undergo a rapid intensification cycle, which would allow him to peak higher, sooner.
But, thankfully, all of this intensification that's expected may well not lead to any consequences (except perhaps for some shipping interests). Here's where the model guidance takes Bill over the next five days:
All except the UK's model (EGR2) keep Bill well north of the Caribbean islands over the next five days. Keep in mind, the worst of a westward moving storm is on the north side. So, even if Bill were large enough for the outer fringes to reach the northernmost Lesser Antilles, they'd be on the weak side - merely brushed by a few showers with some gusty winds. And beyond that, as far as a U.S. threat, check out the GFS Ensemble spread (the GFS Ensemble is the American long range model run several times with some minor perturbations to the initial conditions):
...note that this keeps Bill clear of the U.S. East Coast. Now, be mindful, even though this is an ensemble with lots of perturbations, it does not necessarily cover the entire gamut of possibilities. Each ensemble "member" is still running the same basic model. So, if it contains any systematic errors or biases which could impact the track of Bill, all members will reflect that. However, both the European and Canadian models show a similar track, keeping Bill offshore.
Nonetheless, New England can't let its guard down just yet. This is a long way off and long range hurricane forecasts are prone to significant errors. Moreover, this is a complex pattern evolution which will lead to a window of opportunity for Bill. There are two "troughs" (dips in the jet stream) that come along to impact Bill. One pulls the storm north, but misses it; the next catch Bill and kicks it out to sea to the north and northeast. But, that second one is far enough west when it is trying to capture Bill that the "ridging" in between the two troughs may build enough for Bill to nose back to the north or northnorthwest for a while. And this could bring the storm dangerously close to New England.
To illustrate what I mean, here's the upper level flow in seven days:
...Bill is the "ball" well east of New Jersey. The ridge is the bubble to Bill's east, and the trough is the big "dip" with the yellow shading in the middle of it out near Michigan and the Ohio Valley. The wind barbs roughly show the steering flow and, note, that they are parallel to the black contour lines. So, if that trough is a little sharper and tilted more due north-to-south, and/or the northwestern part of that ridge noses up more to the northwest, Bill could get pulled more northnorthwestward towards New England. Is this likely? No. None of the model guidance shows this. However, model biases tend towards the weak side with systems in the longer range. As such, there is certainly at least an outside possibility that both that trough and ridge are a little sharper, allowing Bill to come closer to New England.
So... at this point, Bill should be a non-event... just creating some heavy surf along the Atlantic Seaboard. But it is too early to discard the possibility entirely of a landfall along the New England coast. So, we do need to keep monitoring Bill very closely.
As a side note, as I'm finishing this up, the 5PM EDT NHC updates have all come out. Claudette is already closing in on landfall on the FL Panhandle as a 45kt tropical storm. With winds like that I'll reiterate that Claudette will not do significant damage in terms of wind or storm surge. But there may be some flooding due to heavy rainfall. Meanwhile, Ana - not surprisingly - has been downgraded back to a depression. So, I think it is correct to downplay this system. It looks terrible and may well not even be a depression any more (NHC acknowledges this as an Air Force reconaissance aircraft had trouble even finding a circulation center). So, Bill is the focus right now, with a preliminary expectation that it remains offshore throughout its life cycle.