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:
Note: Discussions will resume Tuesday, September 5, after the Labor Day holiday.
Tropical Storm Ernesto made landfall just before midnight Thursday night in North Carolina as a very strong tropical storm - just a few miles an hour shy of the 74 needed to be classified as a hurricane. As Ernesto races north near the Interstate 95 corridor of the Mid-Atlantic, he will eventually be deflected to the northwest - sending the center well west of New England - as he encounters a strong, expansive and protective area of high pressure over New England. It is, however, this same high pressure that will create problems for the Mid-Atlantic, and will eventually break down enough to allow a weakened chunk of Ernesto into New England during the Labor Day weekend.
High altitude cirrus clouds are riding over New England again today, this time the result of Tropical Storm Ernesto, whose moisture tens of thousands of feet in the sky is being carried northward on fast winds racing up the coastline and over New England. The good news for New Englanders is that the overall steering flow in the atmosphere will not favor tracking Ernesto into New England, but rather to our west this weekend. Nonetheless, this doesn't mean we'll emerge from the Labor Day weekend entirely unscathed.
As Ernesto tracks north on Friday, not far from Interstate 95, heavy flooding rains and strong winds will continue spreading up the Mid-Atlantic coastline, with up to a foot of rain falling in parts of the Appalachian Mountain chain, and tropical storm force wind gusts spreading throughout the Mid-Atlantic coastline from the Carolinas to New York City. In some of these areas - especially from Virginia to New Jersey, recent rains have made the ground soft and trees will topple along with powerlines, ensuring that even without factoring in the damage done at landfall in the Carolinas, Mid-Atlantic damage will surpass what was witnessed in in Florida. Though the center of Ernesto won't be passing over these areas directly on its northwest track, it's the squeeze play between our area of high pressure (fair weather) and Tropical Storm Ernesto that will force onshore winds to increase throughout the Mid-Atlantic, which also will bring areas of coastal flooding.
Here in New England, protected by our large area of high pressure, it will take awhile longer for the rain and wind to move in, and it will make its move in significantly weakened form. Nonetheless, I'm expecting the leading edge to the band of rain now over New Jersey to gradually ride northward, entering extreme southern Connecticut on Saturday morning. Watching this rainband on radar Friday, it's become quite apparent that the rain truly has been nearly halted in its tracks by the influence of our fair weather center, so even as it finally creeps northward into extreme Southern New England on Saturday morning, it will take most of the day to cross from southwest to northeast across Connecticut, eventually falling from Southern Vermont through Western Massachusetts and most of Connecticut by late afternoon or early evening. Elsewhere, our dry air should hold rain at bay for most of the remainder of New England through the day Saturday for a day of thickening clouds, but little or no rain. Nonetheless, you can always check to make sure the forecast still looks good this weekend by clicking on the radar links at right and following the rain for yourself. Of course, rain isn't the only problem, as the aforementioned corridor of wind will be snaking up the Eastern Seaboard, and winds will increase through especially Southern Connecticut Saturday afternoon into the evening, with gusts to over 40 mph possible at the State's south coast and perhaps in the elevated terrain of Western Connecticut, as well. Winds of this magnitude would do little damage, though may bring a few small tree branches down, resulting in isolated power outages. The other concern with increasing east-southeast winds is for water to pile up in the Western end of Long Island Sound, where coastal flooding is possible near the 7 PM high tide on the South Coast of Connecticut and on parts of Long Island.
As our protective area of high pressure shifts from Northern Maine to Nova Scotia heading into Saturday night and Sunday, rains will spread northeast over most of New England - probably as far east as Western Maine - overnight Saturday night into Sunday morning. The relaxation of our fair-weather cell will also allow the winds to pick up across New England the southwestern half of New England by Saturday night, and gale force wind gusts from the southeast look possible on most of Southern New England's coastlines Saturday night into early Sunday. Periods of rain, heavy at times, should continue to fall into Sunday with breezy conditions, though rains may taper to showers later in the day. For those in Eastern Maine, even a part of Sunday will be dry before late day showers finally advance. By Labor Day, I'm hopeful that a slug of dry air will provide for at least some sunshine, especially in Central and Southern New England, though a new disturbance will swing through New England, keeping at least scattered showers and downpours in the forecast - nonetheless, at this relatively early stage I'm optimistic that we'll be able to salvage some of Labor Day for outdoor activities. By Tuesday, deep moisture should shift southeast of New England for at least a day or two, before a midweek rainstorm is likely in the making for Wednesday or Thursday.
It's important to note that for the next few weeks - at least through the first half of September - the weather pattern will be quite favorable for transporting tropical systems into New England. The shots of cool Canadian air will abate, a deep southerly and southwesterly flow of air will establish in the atmosphere, and any storm that can make it as far west as the Leeward Islands would have a good chance of moving in on the Eastern Seaboard. The bottom line here is that now is a good time to check that everything is in order should we need to prepare for a storm strike in New England over the next couple of weeks.
Have a wonderful weekend.
Matt
Matt's Technical Meteorological Discussion: Updated Friday, September 1 at 10:05 AM
Note: Discussions will resume Tuesday, September 5, after the Labor Day holiday.
My energy today was devoted to the General Weather Summary above. The technical thoughts laid out here yesterday seem to be holding and my concerns/thoughts haven't changed. Should see very slow progression of rain band across NewEng on Sat and I think the GFS is still too fast and NAM not penetrating the high enough - trusting Canadian and GFS Ensemble mean solution more. Some of this meant an educated guess on winds here in NewEng as the corridor of fast wind will be diminishing, but I don't expect winds to get much over 40 even in CT where the strongest will blow. Some coastal flooding Western LI sound at 7 PM high tide Sat. Otherwise, we look on target, tho timing of midweek rain for next week may end up being delayed by a day depending on how long it takes to clean out the OH valley energy. Have a great weekend. -Matt
Thursday's Discussion:
1:45 PM: I certainly could go on and on about Ernesto but we did that together in this discussion yesterday and I think the thoughts presented here are panning out well today, so I'll reference you to yesterday's discussion below for the foundation and just add some extra thoughts here. Ernesto looks fantastic on radar and satellite presentation and both are indicating he's closing off an eyewall. IR satellite shows this eyewall has generated thru the course of the morning and is about 3/4 complete as of this writing. Radar presentation shows the closed and tightening center with new convection firing in the eyewall gap, all of which indicates continued strengthening. There has been a bit of dry air entrainment to the system which decreased convection a bit just after midday though should be overcome rather quickly over the course of the afternoon. Quikscat passes have shown steady intensification, as well, and buoy reports have consistent 33-36 kt gusts well removed from the tightening center. As discussed here yesterday, the shear axis to the W and NW of the storm has aided in outflow and will continue to as the system nears the Southern NC coastline. All of this suggests a storm that will continue strengthening and we're likely to have a minimal hurricane at landfall.
Track forecast has gained some degree of certainty with continuing excellent guidance agreement, though water vapor imagery supports a track somewhat east of the model guidance mean through 48 hours, which is similar to the track we examined yesterday based on low level vorticity progs, and would take the center northward until Nrn VA or MD before starting the more NNW and then finally NW trek. This is important because it will serve to further increase winds for the Mid-Atlantic. I laid out most of my thinking on this yesterday but the bottom line is that we're in for a doozy of a wind storm from landfall northward all the way to New York City, as the pressure gradient between the Northern NewEng high and Ernesto will be fierce. Continued gusts to over 30 mph have already been occurring along Virginia's coastline, and this is far removed from Ernesto - in fact, it's north of a lower wind speed zone so it's most definitely outside of the storm's envelope and is an early affirmation of the power of the pressure gradient. This also is going to prime the seas prior to the arrival of Ernesto's effects, as we're already seeing buoy reports of 5-7 foot seas on 7 second periods. The result will be at least hurricane force gusts in the Carolinas, then a corridor of wind that will lift north up the Mid-Atlantic coastline all the way thru Nrn NJ producing 60+ mph gusts as it goes. Not all locales will record these gusts, but I'm willing to bet we'll find at least scattered gusts to this level thru that entire area, and in places from Srn NJ to Virginia where antecedent conditions have been wet and the ground is soft, trees will be uprooted and widespread power outages will occur. As mentioned yesterday, the media may be blindsided by this because there is no name and due to the extratropical nature of the forces driving it, we're looking at a scenario where no tropical watches or warnings will probably come up. Would be nice to see high wind watches instead but reading the products from local issuing offices down there the special statements are reflecting a forecast for far less wind, so I'm not sure we'll see these either. I know there is some amount of blind faith with this forecast for meteorologists along the Mid-Atlantic, but even those who need convincing should turn to both the NMM and GFS, both of which actually STRENGTHEN the wind at 850 and 925 mb thru this corridor AFTER Ernesto makes landfall, with the GFS ripping 850 winds at over 60 kts. Part of the reason for the strengthening is that the models aren't accurately portraying the increasing strength of the cyclone at present, but this still should be a flashing red alert that something non-tropical is leading the guidance to spin up the wind along the Eastern Seaboard. Important to note that given the seas already churned up as described above, coastal flooding is likely in many areas up the Eastern Seaboard and New England won't be entirely immune to that either.
Speaking of New England, I've kept my timing of a late Saturday advancement of precip - hanging out in CT and perhaps Wrn MA for awhile on Sat before advancing farther NE, as the southwest periphery of the surface anticyclone breaks down enough to allow these SW NewEng areas to transition into the rain and wind soonest. In fact, some coastal flooding seems like a good bet during the Saturday high tide in the western end of Long Island Sound at the south coast of CT, and again Sat Ngt. Gusts to over 40 mph are possible in Srn CT later Sat. By the time the high breaks down enuf to allow all of this to shift east, the PGF should be weakening, Ernesto will begin his absorption into the upper low over the upper Ohio Valley, and though gusts should be to gale force on Srn NewEng coastlines Sat Ngt into early Sun, should be below damaging criteria. This leaves us with windswept periods of rain on Sun, especially early.
Guidance has been in decent agreement of bringing a slug of very dry air in at 800 mb and above to start Labor Day as NewEng transitions into a warm sector that would be full of tropical modified air. If we do see sunshine early on Labor Day, a little would go a long way in this airmass and temps would climb nicely. The trick here is a departing slow wave of low pressure over SE NewEng waters early in the day, and approaching front late, and uncertainty as to how much the low levels really will allow things to break up in between these two features. Played a bit optimistic for now, but will tone down the optimism tomorrow if that seems necessary.
As new Canadian energy enters the dumbbelling vorticies over the Lower Great Lakes and Upper Ohio Valley early next week, this energy will help to once again dig the trough to our west while Western Atlantic ridging expands westward over the Eastern Seaboard. The result will be to increase SW flow aloft over the Eastern 1/3 of the US, which will usher a combination of Gulf moisture and entrained remaining Ernesto moisture up the Appalachian mountains and into NewEng for a midweek rainstorm with heavy rain before somewhat drier weather returns with temperatures near...then above normal as the Western Atlantic ridge hold troffing at bay to the west.
This above normal temperature structure comes along with the vulnerable tropical pattern we've been looking at together in these discussions for quite some time.
Enjoy your Thursday.
Matt
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
