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:
Periods of heavy rain will continue to move across New England Tuesday, with the heaviest rain falling Tuesday afternoon in Southern New England. To some extent, this latest disturbance is just another in the parade of disturbances straddling the battlezone between warm and humid southern air and cool, dry Canadian air. This battle continues to be waged right over the Northeastern United States, and this has kept the jet stream winds aloft - that steer our storms and act as a thermostat for the atmosphere - lodged overhead. Tuesday's storm center, however, comes with more tropical moisture than most - similar in scope to Sunday's rainfall - but will remain progressive, giving way to improving weather for the middle and end of the week.
You can follow the rain throughout the day with the radar links at right, but the general trend will be for rain to continue expanding and intensifying across Southern New England from northwest to southeast through the first half of the day Tuesday, yielding periods of heavy rain at times through Tuesday afternoon, and likely resulting in a wet and somewhat difficult evening commute for some of our major metropolitan areas in Southern New England. Remember that this rain falls as the battle of warm and cool air continues, and neither is far away - so close, in fact, that while rain falls heavily enough for locally over two inches of rain in parts of Massachusetts, Connecticut and Rhode Island with localized flooding of streams, streets and low-lying areas, drier and cool Canadian air will settle far enough south to bring breaks of afternoon sunshine to the North Country. Even with the breaks of sun, however, the cool nature of the air will keep most areas below 70 degrees.
Gradually, this drier northern air will penetrate even farther south into New England overnight Tuesday night, bringing lingering drizzle, fog and sprinkles to an end after midnight. Though some clouds will linger in Southern New England on Wednesday morning, the drying trend should breka clouds to sunshine during the day, leaving a pleasant and enjoyable day for most of the six-state region. With a 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.
Of course, Ernesto is still a difficult problem in the extended forecast period, as his track will be so critical to our weather for the latter portion of the holiday weekend. If you're confused about the forecast, you're not alone! Yesterday's official National Hurricane Center forecast took Ernesto southeast of the North Carolina coastline on Saturday, while today's forecast only 24 hours later has shifted so far west that the storm is now predicted to pass into interior Pennsylvania and New York this weekend! So what are we to think of what will REALLY happen? First of all, I think it's important to realize that this dramatic shift in track forecast is a clear statement of how much uncertainty truly exists in the extended period with this storm. 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 will influence Ernesto - the jet stream winds will tug him east, 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 can only pull Ernesto west and inland if the two systems are close enough, and no other system overpowers its influence. At this point, the trend in our guidance has most certainly been to bring that Ohio Valley storm just close enough to pull Ernesto inland over the Mid-Atlantic, but it's so important to understand that the interaction between all of these systems is an extremely delicate balance, which is why we see the shift in track so dramatic. Another shift in track is entirely possible depending upon these interactions, so for now I think the best way to view this for New Englanders is to realize that if Ernesto affects us, it will be Sunday or Monday, but that greater effects are much more likely across the Mid-Atlantic. I'll continue to keep you posted.
Matt
Matt's Technical Meteorological Discussion: Updated Tuesday, August 29 at 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
