Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes
General Weather Summary:
New England remains on a road to improving weather for the next few days as a surge of drier and relatively cool air settles southward out of Canada. This new, fresh air comes as the fast jet stream winds high in the sky dip over New England. Serving as both the steering wind for storms across the globe, and an atmospheric thermostat separating cool air to the north from warm to the south, this dip in the jet stream places New England on the cool side of the thermostat for now. At the surface, a large and strong area of high pressure - fair weather - lay at the center of the cool and dry air, and will move southeast over extreme Northern New England, and finally east of Maine. This high pressure center will be a key to the forecast here in New England and for the track of Ernesto, as the core of cool, dry air will protect New England for as long as it's in place.
In the meantime, lingering morning clouds and fog across New England will steadily give way to increasing sunshine as dry air just a few thousand feet off of ground level gradually erodes the cloud deck. The sunshine will certainly help to boost temperatures in many areas except the far North Country, where though temperatures will rise they will be held well below normal thanks to the cool nature of the Canadian air, reinforced by a cool front dropping south through Northern New England. With the passage of the front, an afternoon light shower is possible in the Southern half of New England, though it shouldn't be enough to ruin an otherwise very pleasant afternoon, as the showers would be widely scattered, brief and relatively light. Any clouds will deteriorate after sunset Wednesday evening, and mostly clear skies will allow many communities in Northern and Central New England to drop into the 40s while Southern New England remains in the 50s and deeper valleys of the North drop into the 30s.
With the strong area of high pressure - fair weather - building southeast from Canada and across New England for the middle and end of the week, this drier and pleasant air should gradually turn slightly cooler, but will keep sunshine locked in through the end of the week, and dry conditions into the beginning of the Labor Day weekend.
The future path of Ernesto is becoming a bit more clear, though some uncertainty lingers with regard to the effects upon New England this weekend. In the near-term, the center of Ernesto will re-emerge over the warm waters east of Florida today, after perhaps weakening to a Tropical Depression for a time, and is expected to restrengthen once emerging over water. There is excellent agreement among our guidance products of a landfall in far Southern North Carolina on Thursday, and while most guidance suggests a landfalling system as a strong Tropical Storm, the warm waters of the Gulf Stream certainly may feed this storm enough to develop into a hurricane before landfall. The questions for New England come after that, as the players here are a storm center over the Ohio Valley, a high pressure center building over New England, and the tendency for the jet stream winds to carry Ernesto out to sea. Each of these systems may influence Ernesto, and while the jet stream winds tugging the storm east appear as though they will have minimal influence, the high pressure cell represents fair weather and will protect New England for at least the first part of the holiday weekend, and the Ohio Valley low will pull Ernesto west and inland if the two systems are close enough. The clear trend in our guidance clearly has been to bring that Ohio Valley storm just close enough to pull Ernesto inland over the Mid-Atlantic. Although the interaction between all of these systems is an extremely delicate balance with remaining uncertainty, at this point it seeems reasonable to buy into a track that will keep the center inland over the Eastern United States. As the storm transitions from tropical to non-tropical, however, the wind field will expand away from the center of the storm, and a slug of warm and moist tropical air will launch northward into our cool and dry airmass. This collision of airmasses will probably be enough to generate a band of heavy rain moving toward the northeast, though as this band of rain and wind encounters the powerful area of high pressure east of Maine, it will slow. Questions linger as to how quickly and how far east this band of rain and wind will penetrate, but right now I'd expect to find a mostly dry day Saturday with rain advancing into Connecticut during the day, then this rain expanding over the remainder of New England on Sunday with winds gusting along the coastlines of Southern New England as the rain moves through. If this is indeed how things play out, showers may linger into Labor Day, but I will continue to update you on the future of Ernesto and his interaction with New England.
Matt
Matt's Technical Meteorological Discussion: Updated Thursday, August 31 at 7:05 AM
All appears on track from yesterday's discussion regarding Ernesto. He's continuing to organize well over warm water and strengthening should continue gradually until landfall tonight. Expanding wind field bringing wind damage, coastal flooding and flooding rain is still what I'm expecting from the Carolina landfall all the way to NYC, as pressure gradient force with NewEng high pressure center becomes the driving force for winds. Gale force wind gusts likely CT south coast later Sat along with coastal flooding Western end of Long Island Sound. Gale force gusts remainder of Srn NewEng coastline possible Sat Ngt into Sun. More to come later... -Matt
Wednesday's Discussions:
2:30 PM: Dry air continues to erode cloud deck but enuf low level moisture for plenty of Cu and low level convergence along cool frontal boundary will touch off scattered showers in Srn half of NewEng thanks to southward migrating area of 250-750 J/kg surface based CAPE away from stabilizing onshore flow and as a result of falling midlvl temps. Given dry air aloft, however, convection should be low-topped and therefore winds light enuf that we shouldn't have more to concern ourselves with than scattered showers. Clouds expected to diminish after sunset and with Tds falling behind the front, 30s with scattered frost in Northern Valleys with 40s extending into interior Srn NewEng.
Thu and Fri are fairly straightforward but it should be noted that Ci blowoff from Ernesto will race up coastline well in advance of the system and we should already see some into NewEng on Thu, and thicker on Fri even though sfc anticyclone builds over Nrn NewEng.
As for Ernesto, let's review some of the factors we know, and those we ponder. We know: after gaining little additional strength, Ernesto moved into Southern FL where his center of circulation has become more broad, but is still well defined on radar, and feeder bands are quite impressive, especially with deep convection over the warm waters both west and east of Florida. This good radar and decent satellite presentation certainly shows a system whose inner core has not yet been disrputed. We also know that sea surface temperatures from the East Coast of FL, near Cape Canaveral/Daytona Beach, where the storm should come back over water, across the Gulf Stream to the SC/NC state border are running from 28-32 C (82-90 F) which isn't more than 0-1 C above normal but is plenty warm enough to support regeneration of the system. As for atmospheric conditions in the cyclone's environment, it will be entering a corridor of low upper and mid level shear on its trip to the Carolinas, though mid level shear has been noticeably increasing over and along the seaboard from GA to NC. This is important, as it is largely SE shear aloft and SW shear in the midlevels, which is apparent not only on analyses and model forecasts, but also from water vapor imagery. The issue here is that this shear axis to the west of the cyclone's track may provide an opportunity for enhanced outflow jet on the west side of the circulation and has the potential to hasten regeneration and restrengthening of the system, aided further by evident low level convergence just to the ocean-side of this shear axis. The subtropical ridge to the east of Ernesto has broken down somewhat on its western flank in the past 12 hours and as it continues to break down this should lead Ernesto on the track we discussed together here yesterday, which is on the eastern side of the guidance products, to a position near and perhaps just east of the SC/NC border. How strong Ernesto is upon landfall hinges upon the aforementioned factors, but if the deep convection firing well northeast of the center is any indication of what this storm will do in response to the favorable conditions, we should expect a fairly strong ramp-up. There isn't one intensity guidance product that takes Ernesto to over 65 knots, and even that is the SHIP and to a slightly lesser extent the SHF5 model, with the other intensity guidance closer to 40 knots. It's rarely wise to go against millions of dollars of technology but considering QuikScat scans are finding 35 knot winds east of the FL coastline as of 17Z which is supported by CMAN station reports, and given the conditions we've just examined together, I have serious trouble believing this storm will still sit at 40 knots tomorrow. Instead, a rather quick intensification is probable and that SHIPs guidance is probably a lot closer to reality, though the potential really is there to exceed this guidance and see a reintensification to a hurricane, especially tomorrow morning as atmospheric conditions reach their prime.
Of course, the intensity will play a role down the line, not only for those in North Carolina but for the Mid-Atlantic as well. There has been increasing agreement on the evolution of the pattern ahead of Ernesto, with strong indications continuing that the confluent flow off the Northeast seaboard will pull away gradually as the vortex over far Northern NewEng Wed quickly shifts far east to extreme Eastern Canada by Thursday. Still, enough confluent flow remains in place for the surface anticyclone to lodge east of ME for the start of the weekend and SE of Nova Scotia by Sunday. The upper level low over the Mississippi and then Ohio Valley will team with the upper level ridge over SE Canada moving into the Northeast US the nudge Ernesto inland, though after landfalling in NC his track is likely to be north for a bit longer than most guidance - moving thru Central PA, then to Central/Wrn NY. This is in line with the hurricane guidance that has been performing best of the bunch at 96 hours.
I think the biggest resultant problem if my thinking on intensity and track is correct is certainly for the mid-Atlantic coastline, where the combination of a hurricane decaying slowly in the start to an extratropical storm will mean an expanding wind field away from the center, and this will couple with the effects of pressure gradient force to crank winds from North Carolina all the way to NYC, though most intense from the Outer Banks north thru Delmarva and Central Jersey from Friday thru Sat, respectively. Tropical storm force gusts, at least, and likely a not-truly-tropical period of TS sustained should be observed up the coastline in this entire region, and with soft saturated ground, trees will be toppled and - not including damage done from TS or Hurricane force winds in SC/NC at landfall, more damage in dollars may be done along the Outer Banks to NYC than was done in Florida, even though reporters were standing on the coastlines of Florida and won't be as visible since there'll be no validation for an actual TS Watch/Warn farther north!
Here in NewEng, we sit uncomfortably on the fence as the surface anticyclone and upper level ridge will be extending south and providing some protection, but the former will be deteriorating while the latter will be only extending slowly southward. As discussed yesterday, it appears as though the positive height anomalies associated with the upper ridge will build just far enough south to protect NewEng from a direct hit from the storm center which, as mentioned, I'm expecting in Upstate NY. Nonetheless, the same PGF wind maker that moves up the coastline will make its way into NewEng, and winds should gust over 30 mph - though perhaps not to TS force - at the south coast of CT where at least some rain makes it in late Sat or Sat Ngt. I'm aware that these storms often see rain shifting to the west of the track, but with such a cool and dry antecedent airmass, this slug of tropical warmth and moisture should induce sufficient warm and moist advection to bring precip in. Thereafter, the southwestern edge of the sfc high gradually breaks down while Ernesto very well may break into pieces - one of the many scenarios we considered over the past couple of days. The combination of a piece of Ernesto with the ongoing slug of warm and moist advection would bring at least some rain over NewEng on Sunday with a windswept rain at the coastline of Srn NewEng with lingering PGF effects rather than anything directly related to Ernesto, tho closer to the anticyclone in ME it will be more difficult to bring precip in. Periods of rain will probably continue on Mon, tho whether this is directly a result of Ernesto is semantics considering the primary chunk of Ernesto will have already been absorbed into the upper level low over the upper Ohio Valley and a chunk of energy with Ernesto infused moisture will be what's launched east for Labor Day by the way things look now.
I'm going to wrap it up here for today, but please keep in mind what I've been mentioning for a couple of weeks now - that our longwave pattern leaves us extremely vulnerable to tropical systems through the first half of September and a tropical wave should develop over the Atlantic by this weekend, with another on its heels, so we have awhile to go and Ernesto is likely the warning shot for most of the East Coast.
Have a good day - good luck with your forecasting!
Matt
10:35 AM: More to come later but a quick update on thinking with Ernesto. I'm happy with the increasing agreement on an extreme NC/border SC strike. Impressive banding right now with the storm leaves good potential for growth once back over water. Though this system should remain inland, I'm not surprised to see the tracks gradually shifting east in the early cycle 12Z run...the longwave flow would appear to favor a N/NNW track after NC landfall. My forecast at present is based on the expectation that the high pressure center east of NewEng holds on longer certainly than the GFS is forecasting - good Ensemble agreement on holding deep moisture at bay thru Fri and in most of NewEng thru Sat tho shud see deteriorating conditions into CT by later Sat. Still lots of uncertainty on how long the high can hold on, but at this time I'm bringing a swath of rain in Sat Ngt/Sun. Note that FSU MM5 brings wind swath to SCoast of NewEng as wind field expands with transitioning system and PGF strengthens. More later...
Tuesday's Discussion:
2:10 PM: The fun surprise to the forecast today has been the winds on the Outer Cape and the Islands - especially Nantucket where winds have been gusting to 30 mph! This comes as a wave of low pressure intensifies along the warm front draped south of NewEng after it brought heavy downpours to the Outer Cape early this AM. As the low pressure center pulls away, winds will diminish. Meanwhile, next low brought plenty of isentropic lift ahead of it but that has been intensified even more over Srn NewEng as frontogenesis takes place with cool air sinking S. This same cool air has been dry enuf to erode low level clouds across far Nrn NewEng for some filtered sun.
I expect drizzle, fog and light showers to linger for a time overnight given extremely moist boundary layer and continued northeast flow as next wave moves overhead and departs, but eventually the same drying found in Nrn NewEng today will work south so after midnight the moisture will gradually evaporate, tho fog certainly may linger in valleys. Low cloud deck should start to lift elsewhere after midnight tho mid deck likely to linger into Wed AM before breaking up. Still have the trof axis to come thru later Wed along with a moderate strength shortwave thru Northern NewEng so while models show decent drying I felt it best to keep chc shra in the fcst Wed PM for Srn NewEng where most moisture lingers and orographically favored areas of Nrn NewEng where shortwave will be coming thru with strongest dynamic lift - esp across ME mountains.
Thereafter a straightforward fcst thru the end of the week tho I did cool temps by a couple of degrees thanks to slightly stronger cold air advection and a north-northeast flow ahead of the surface anticyclone.
Of course, as discussed yesterday and as those in tune with the meteorological world are well aware, this anticyclone is one of the key players in the future of Ernesto, and in the effects the storm will or won't have on New England. Rather than re-hashing all of the details (that's why I'm keeping old technical discussions through the entirety of each week...scroll below to see yesterday's) let me key in on what's changed since yesterday:
1) The track guidance and global models have all come significantly west, including the eastern outlying NMM forecast that now brings the storm up the East Coast thru 84 hours. This westward shift has come thanks to the handling of the Ohio Valley upper low, which now digs deeper and does so farther east than initially progged, thereby allowing it to interact with the storm, which stays close to the SE US coastline as it rides the Western periphery of the subtropical Western Atlantic ridge.
2) The vortex over extreme Eastern Canada is much less defined and farther east than it has been in previous cycles, and this allows strong ridging to build in quicker to Eastern Canada and the Northeast US in the northern stream than originally predicted. The result is an upper level ridge axis tilted from the Western Atlantic northwest to a position just east of Hudson Bay, Canada, by 00Z Sat, with only a little eastward shift thereafter.
3) The deeper solution of the Ohio Valley upper low allows positive height anomalies to actually penetrate a bit farther south than originally progged from the northern stream, which is able to exert more of an influence to push the storm farther west.
What we're left with is the major 24 hour forecast track change we've seen, but as explained in the General Weather Summary above, this is still a very delicate balance between a retreating jet stream that urges pushes the storm east and sweeping it out (looking like less of a player given the changes described above), and anticyclone that will block the storm until return flow comes back in, and the Ohio Valley low that will encourage the cyclone westward.
I have a few thoughts to share regarding the model guidance. First, the NMM has represented an eastward bias in each run, and has thus far done horribly with tropical systems this season. Though it has scored some wind with coastal hybrids, the changes implemented to it this spring have made it a relatively useless tropical model thus far, as it's taken a significant step backward from its predecessor versions ETA and NAM. So, I would, at present, not discount the solution entirely but take it with a grain of salt given the recent performance of the model. The GFS is also one of the farther east of the guidance but more importantly to us here in New England, it is the fastest. The model catches the 500 mb vorticity center in the S/SW flow aloft ahead of the Ohio Valley upper low and zips the storm up the coast and even tho it is just inland the storm center appears in MSLP plots to degrade and then just drift east across NewEng. This, of course, looks rather unnatural in how it unfolds. The fast acceleration northward is, of course, something we often see of storms traveling up the coast but not when you have a 1028 mb high moving across NewEng. If this high were farther east, we'd have a better case for this, or as mentioned yesterday, if the positive height anomalies weren't building down over us. But given both of these features are present, I became suspicious of the GFS forecast and decided to dig a little deeper - quite literally. Deeper DOWN in the atmosphere, low level vorticity plots indicate the GFS actually is carrying the low level vortex inland all the way to Buffalo, and develops a new secondary type structure along Delmarva that spins up over NewEng, which is what's indicated in the MSLP plots. I've gambled on this type of low as convective feedback before and dismissed it too quickly so I'm not going to entirely dismiss the possibility of a wave - in fact, that's one of the solutions we looked at here yesterday that Ernesto may break into chunks with some west and some east - but I think the carrying of the low level vorticity to Buffalo in this model is very telling.
So, this leaves us with a storm that will emerge back on the E side of FL over warm water and will attempt to reorganize. SHIP guidance takes the storm back to Cat 1 strength over these waters, though most intensity guidance keeps a tropical storm during this time. I do think it's an important trend that while the shallow hurricane guidance products take the storm into SC with good agreement on Thursday, the global models are favoring a Southern NC landfall, which would give the storm more time over the warm waters. Nonetheless, at this point it's tough to make an argument against a western solution, though the question is how this will affect NewEng.
At this point I'm trusting the Ensemble agreement and my thoughts on the GFS being too fast and keeping Sat dry. Later in the Labor Day weekend, there is very little disagreement among Ensemble members the high center remaining just east of Northern ME. This protects most of NewEng, though admittedly the gradient will tighten on the SW side of the anticyclone, and there is wide variability in the MSLP fcsts for SW NewEng - esp over CT. It's therefore not impossible that a slug of warm and moist advection makes it into parts of SW NewEng along with an increasing sfc gradient wind, tho if the high holds strong this would be focused more in NJ than NewEng. I think this is our biggest potential effect aside from increased ocean swell, and something that certainly bears watching but at this point isn't something I'm ready to spout off about.
That's all for now...I'll be looking forward to the 12Z ECMWF later today.
Matt
Monday's Discussion:
2:35 PM: Inversion is not going to let go easily today with cool air well established under warmer temps even at 900 mb and above - certainly is a very low boundary layer inversion. Nonetheless, drying aloft was able to poke some holes in it and where the sun emerges, temps respond by climbing over 70, then as clouds fill back in temps fall again. This should be the trend thru the remainder of the day, and given the extremely shallow moisture, any light sprinkles or showers will be just that - light! No vertical growth impressive enough to allow for much more.
Next disturbance evident on satellite and radar imagery across the Midwest and once it rounds the ridge over Central Great Lakes, should be a fairly straight and quick shot into NewEng, so I favor the faster timing of the GFS, which has support from the Ensembles and ECMWF run. Quite a bit of precip should crank with this system - a combination of the aforementioned northern stream shortwave and a vort max moving NE across AR as of this writing, supplying an additional shot of moisture. The end result should be for an average 1-3" rainfall across Southern NewEng Tue thru Tue eve. Expecting fast timing and another shot of drying behind the shortwave to taper rain by Tue Ngt, but meteorologists and ameteurs alike should try to avoid hurricane envy and be sure we give credit where credit is due to this upcoming rain event. After flooding through town in Darien, CT, and the shutdown of 95 in Norwalk Sun Ngt, the ground is most certainly saturated and in these areas...along with a few other locales in Central MA, Central/Srn CT, six hour flash flood guidance values are at or below 3" and we should acknowledge the potential for more flooding of streets, streams and low-lying areas.
The end of the week looks rather tranquil here in NewEng, tho I am holding onto a shower Wed in Srn NewEng with a bit of hesitancy for the trof axis to swing thru completely and cleanly, but otherwise we're looking good right into the upcoming holiday weekend.
Of course, it would be a joy to stop writing now, pack up and head home, but this is where the challenges continue from a forecasting perspective. While there are still hairs to split over track in the short-term, certainly the overwhelming guidance brings the center of Ernesto over the Southern Tip of FL Tue Ngt, then back off the ECentral Florida coast. Of course, the connundrum is where to go from there. The trick here is that the jet stream is finally lifting over us and continuing north as ridging moves into Hudson Bay, Canada, and heights rise across the Northeastern US with a vortex over extreme Eastern Canada. This this transition occurs as Ernesto moves off the Carolina coastline midweek, and a large surface anticyclone is progged to shift SE across NewEng mid to late week. Meanwhile, the shortwave currently closing off across the Midwest meanders eastward across the Ohio Valley. So the questions revolve around the interaction of Ernesto with a) the confluent flow to our east on the south side of the vortex, and b) the Ohio Valley upper low. As for the surface anticyclone, I think it's fairly clear that it will serve as a blocking high to keep Ernesto south of NewEng thru the end of the week, so this isn't a factor at first, but will become a big player later if Ernesto is still around. First, some of the guidance is trying to interact the Ohio Valley low with Ernesto early in the game, with the GFDL leading the charge by dragging Ernesto far inland, and the UKMET of a similar scenario. Given the lingering confluent flow across the Mid-Atlantic at midweek, and the rather fast breakdown of the Western Atlantic ridge along the SE US coastline, this far western solution is likely in error, as negative height anomalies along the Eastern Seaboard will be tugging Ernesto north and northeast. The challenge here comes as the confluent flow shifts even farther east, and the heights rise, leaving the fast Westerlies flowing south around the Eastern Canada vortex to move well north of Ernesto, which may leave him behind. In fact, the trend in the guidance most certainly is to build heights and keep Ernesto in a rather light steering flow off the Carolina/Virginia coastline in what may be a stalling/looping fashion at the end of the week. Of course, the game isn't up there as the waters are warm and the surface anticyclone is building in, which will prohibit a northward run of the coastline by the storm early on. This means Ernesto may sit and spin off the Mid-Atlantic coast for a couple of days, and though there is certainly the potential that the expansive anticyclone nudges Ernesto west into the coastline where he rains out, breaks into pieces and is then dispersed into chunks between Ohio low and chunks that shoot east, it's hard to nudge a tropical cyclone west based on surface flow alone, and 500 mb height anomalies suggest above normal anomalies will not build far enough south to interact with the storm, which leads me to believe we won't have enough to nudge this storm inland. In fact, I'd expect it to initially feel the pull eastward but as confluent flow shifts away from the storm, it should be left behind to mull around over the Gulf Stream, where waters are running in the 80s. If that is the scenario, the storm would be left to sit on the southern periphery of the high until the high shifts eastward, at which point whatever is left of Ernesto could move north or northeast in the return flow, helped along by the counter-clockwise flow ahead of the new Ohio Valley upper low.
While Ernesto still is far from written and we'll wait anxiously for additional guidance and to see how the longwave pattern establishes, the next wave coming off Africa is well agreed upon to develop, and as discussed last week, the longwave pattern keeps NewEng vulnerable for the first half of September at least. The end result is that even if Ernesto doesn't come our way - or if he does - we still are quite susceptible to tropical systems for the next couple of weeks and there will be another coming down the pike.
That's all for today.
Matt
