Wednesday September 20 2023 Forecast (7:24AM)

84 Comments

DAYS 1-5 (SEPTEMBER 20-24)

The next 3 days (through Friday) will be dominated by high pressure with fair weather with mild days and cool nights. Late in the week we’ll be watching the development of a low pressure area near the US Southeast Coast. Most guidance tries to push this low somewhat to the north over the weekend, but takes its rain shield more vigorously north, now early enough to arrive sometime on Saturday. But that’s not necessarily my forecast just yet. I’ve seen a very similar set-up be handled incorrectly by medium range guidance before, with the computer simulation taking the rain shield too quickly and too solidly north, when in reality the high pressure area holds stronger and dry air associated with it gives the rain area a buzz cut, and a deflection. I’m leaning toward this scenario at the moment, which if it is the case, we’ll salvage Saturday mainly dry around the region, despite increased cloud cover, and then Sunday would be the day with a higher rain chance as the low pressure area, now weakening, got closer to the region. Fine-tuning of this outlook will take place as needed through the week. One thing that is not uncertain – fall arrives at 2:50 a.m. Saturday with the occurrence of the autumnal equinox.

TODAY: Mostly sunny. Highs 69-76. Wind NW-N up to 10 MPH, turning NE in some eastern coastal areas.

TONIGHT: Clear. Ground fog patches low elevations. Lows 47-54, coolest low elevations inland. Wind N under 10 MPH.

THURSDAY: Sunny. Highs 68-75, coolest coast. Wind NE up to 10 MPH.

THURSDAY NIGHT: Mostly clear. Ground fog patches low elevations. Lows 48-55. Wind variable under 10 MPH.

FRIDAY: Mostly sunny. Highs 67-74, coolest coast. Wind variable up to 10 MPH with coastal sea breezes.

FRIDAY NIGHT: High clouds increase. Ground fog patches low elevations. Lows 48-55. Wind calm.

SATURDAY: High overcast, may thicken up enough for some rain near the South Coast or Cape Cod. Highs 66-73. Wind E 5-15 MPH.

SATURDAY NIGHT: Mostly cloudy. Patchy fog. Lows 53-60. Wind E up to 10 MPH.

SUNDAY: Cloudy. Chance of rain, favoring the South Coast. Highs 62-69. Wind E 5-15 MPH.

DAYS 6-10 (SEPTEMBER 25-29)

If my scenario works out as expected, high pressure to the north pushes surface low pressure to the southeast of our area but an upper low means lots of clouds and maybe a few showers around on September 25 before the high pressure area takes over with another stretch of dry weather. Temperatures would cool down early period and warm up again later.

DAYS 11-15 (SEPTEMBER 30 – OCTOBER 4)

Guidance is divergent out this far, but the general pattern to me looks weak hybrid – a bit of a zonal (west to east) flow over our region but still a tendency to see high pressure to the north of the region and low pressure to the south of the region, which can always set up potential battle zones. Leaning toward a drier pattern with no major temperatures swings to end September and begin October.

84 thoughts on “Wednesday September 20 2023 Forecast (7:24AM)”

    1. When I watch those storms pop, I think that something as simple as the outflow boundaries from that initial convection could play a huge role in the eventual development and future path of low pressure. These are things that medium range guidance can’t “know” when those simulations are run. So many things contribute to model error, and part of my A.M.E. method is trying to figure out some of those, and a lot of that is based on things I have seen before. 🙂 It can work, as long as you don’t rely on it too much!

  2. TK, thanks for the update. Saw some TV mets, but not all, expressing uncertainty about Saturday’s potential rain arrival and the location of heaviest rain. Still a day or two away I guess before it can be firmed up.

    Noticed Nigel (remnants) being carried by the Gulf and North Atlantic streams sort of near Iceland. Led me to wonder if Iceland has ever experienced a “tropical” event. Good homework for me today.

    1. The closest a tropical system has ever come to Iceland is Tropical Storm Hope in September of 1978, which was declared extratropical about 225 miles southwest of Iceland.

  8. In the FWIW department, the 6z GFS, 12Z HRRR and 12z NAM are now at or below (and in the 6z GFS’ case, well below) 1,000 mb for this mid latitude low, possibly evolving into a hybrid system.

    Seemingly 2 wind fields. One close to the low/hybrid low, particularly on its western side and a separate one, about half way btwn the low and the high to its north, near the best pressure gradient.

    1. That flow in SE Canada, east of Hudson Bay, I believe is the key.

      If its further south, we rain less.

      If its further north, well ……. that’s going to be a lot of rain.

      https://www.pivotalweather.com/model.php?m=ecmwf_full&p=500wh&rh=2023092000&fh=96

      Euro, a little less rain, that eastern Canada flow gets down towards northern New England

      https://www.pivotalweather.com/model.php?m=nam&p=500wh&rh=2023092000&fh=84

      NAM, further west, that eastern Canada flow stays well north of northern New England.

  12. I think the development in the 12z runs so far, is a stronger low or hybrid low or eventual tropical low.

    The [projected pressures are coming in lower today.

    Nothing to say that this can’t reverse in future runs.

  22. So, what are we to believe???

    Honestly, at this point I would take a GFS/EURO blend and TOSS all the others. 🙂 🙂

  23. What TK said earlier in the blog post:

    when in reality the high pressure area holds stronger and dry air associated with it gives the rain area a buzz cut, and a deflection.

  24. I was in Star Market earlier and there was this big display of Hostess PUMPKIN SPICE Twinkees and Cupcakes!

    Y-U-C-K!!!!!!!!!!!!!!!!

    Is there anything NOT made of pumpkin spice these days????

      1. I think you’re onto something. How about a Pumpkin Spice fuel additive so that we can all smell it everywhere? It could segue right into the Christmas scents.

        1. HAHA sure! And some cinnamon and apple, yes. How about a nice pine for the holiday season?

          I mean why stop there? Lilac in May!

  25. ECMWF is showing the closest to what I think the solution will be for the weekend. Not quite there, but getting there.

    GFS at 12z started a correction, but it will take several runs to do this (if I am right in my thoughts about it as stated in the today’s discussion).

    Canadian model – forget it. Overdevelops the low and moves it far too aggressively.

    NAM is outside its reliable range at this point.

    1. I’m asking this question not under the stance of not believing you.

      I’m asking from the meteorology point of view.

      Do we go with the euro on this one because the storm doesn’t begin as a tropical system and it’s better equipped to handle a mid latitude low ?

      We just saw how much the euro is struggling at least with a tropical feature.

      1. Not definitively, but that is a slight factor in my leaning.

        The models are far too complex for a yes and this, no on that to work all the time. So I lean toward the ECMWF right now, but with less than solid confidence. 🙂

          1. No problem. 🙂

            How’s the Marshfield football team doing so far?

            Woburn is 2-0. Longmeadow & Burlington have been our first 2 opponents. Next up: Boston College High School.

            1. 0 – 2.

              They lost at home to St John’s prep and at Methuen.

              The coach likes to open the season with a tough non-conference handful of games and that has, in the past, proved beneficial when they played their conference schedule.

              My wife and I go to all the home games because our daughter is on the dance team.

              Good start for Woburn and good luck to them for the rest of the season !!

              1. I remember seeing her on the team last year. Awesome she’s still doing it! Good luck to Marshfield! I’m sure they will bounce back after the early speed bumps. Not sure if we’ll meet again this year. Never seem to know how those playoff games are going to line up. 🙂

  27. Thanks, TK.

    There’s been some drying yesterday and today but at 1pm there were still several small puddles on the pedestrian paths – on both the Cambridge side of the river and Boston – and even a few on the bike paths. They’ll be gone by late tomorrow but will be replaced soon enough. The ground is clearly oversaturated.

  30. COVID situation is starting to get worse. I hope this is a blip as opposed to a slow rise through the holidays. I now know 10 people with COVID right now including my sons teacher.

    1. I have not heard a lot and know we should be. Thanks, Ace. And boy do I hope you are right about a blip. Prayers that your kids stay negative

  31. Part of me agrees with TK – a big high to the north will usually win out, and most of the region will stay dry, except near the South Coast.

    Part of me thinks that everytime there’s been the slightest chance for rain this summer, we’ve gotten a lot of it.

    It’s the irresistible force vs the immovable object. Which wins? Stay tuned…..

    1. Yeah, the second point has me nervous. We’ll see…
      Still early, and we’ve seen a model trend several days out before only to see it reverse…

  34. im curious to see if the gfs continues its insistence of a hurricane in the northeast caribbean or if it loses it. I am hoping it loses it and goes to what the EURO/CMC/ICON/UKMET are all saying.

    I am hoping that the weather is good for Wednesday of next week up in Mass, thats when my Mom goes to the hospital for her surgery.

  36. Whereas the last few days had thunderstorms off the SE US coast, I think this morning, the upper low can be seen and perhaps there’s a mid level or mid latitude sfc low developing a couple hundred miles out over the ocean.

    Tropical, hybrid or not, the eastern Carolinas have a decent strength system coming for them.

      1. Stronger high than modeled in east central Canada = deeper trough to its east = suppressed confluent zone = rain area peels off more to the east, also gets chewed up by dry air anyway.

Comments are closed.