There is a lot of weather to talk about as we wrap up astronomical summer and enter autumn. The autumnal equinox will occur at 9:04 p.m. Thursday, marking the official change of seasons. First, we have leftover low level moisture behind yesterday’s departing low pressure system. We haven’t had a strong advection of drier air into the region behind this system, so the clearing has not been quick to occur. The drizzle is gone though, and the clouds are breaking in some areas as of sunrise, and while many areas start with a grey sky, we’ll end up with intervals of clouds and sun – sun becoming more dominant – as the day goes on, and really a nice final full day of summer. Appropriately, the day we transition from summer to autumn will also be a transition day for our weather. A strong cold front will be moving across the region. I once thought this system would whistle through from northwest to southeast during the early morning hours, but Hurricane Fiona (we’ll get to her shortly) has had enough impact on the pattern already, just enough, to slow the front down by a handful of hours. This means that a lot of the shower activity will take place from Thursday morning to mid afternoon with a slightly slower-moving frontal boundary. But it will push through, and almost as if somebody planned it, we’ll know that a new air mass has arrived – cool air on a gusty northwest wind – as we get to evening and fall officially begins with the occurrence of the equinox. Friday through Sunday will be dry days for us here in the WHW forecast area, with an October-like day for the first full day of autumn on Friday – very dry air, a gusty breeze, and some locations that struggle to make 60. The cool breeze will continue Friday night into Saturday, and that combined with the very dry air will be the reasons that some interior portions of southern New England don’t see their first frost of the season as the temperature probably won’t be able to drop low enough due to wind-mixed air. Anyway the air might just simply be too dry for dew or frost to form. Regardless, if you’re an early riser, get ready for a chilly Saturday morning, even with a bit of “wind chill” in areas that keep the breeze going. We will see a nice temperature recovery back to the 60s that day with sun. Sunday will further warm up, back to 70+ territory for much of the region, although our sun may become filtered to limited in advance of an approaching warm front by later in the day, although it does look rain-free. So our first weekend of autumn does indeed look like quite a nice one. However, if you have plans taking you to the coastline then, even before then (South Coast already today and tomorrow, all areas Friday-Sunday), watch for rough surf and large ocean swells stirred up by Hurricane Fiona. The storm itself, now a major hurricane moving into open waters northeast of the Bahamas, will be taking a track fairly close to by west of Bermuda late Thursday / early Friday. I do believe it will be far enough west to spare that island the worst of the storm, but they will still get a gusty rain event. This is kind of a best-case scenario for Bermuda and the US East Coast for a storm this far west and this strong – moving between the two with minimal and manageable impact. This may not be the case for southeastern Canada, a large portion of which will be whacked by the post-tropical but still-powerful storm with lots of wind, rain, and even some snow over interior areas where it will be just cold enough, while we’re enjoying our nice weekend. Oh how the weather can be vastly different over not-too-great a distance.
TODAY: Clouds break for intervals of clouds and sun – more sun with time. Highs 69-76. Wind NW up to 10 MPH shifting to SW by late in the day.
TONIGHT: Clouds return west to east. Scattered showers arrive west to east overnight but may favor areas north of I-90, especially southern NH. Lows 59-66. Wind SW 5-15 MPH, a few higher gusts especially South Coast.
THURSDAY: Mainly cloudy through mid afternoon with scattered showers early, then numerous to widespread showers and possible embedded thunderstorms, which will then end from west to east by later in the day. Breaking clouds and intervals of sunshine from west to east by late day. Highs 67-74. Wind SW 5-15 MPH with higher gusts, shifting to NW 10-20 MPH with higher gusts by late in the day from west to east across the area.
THURSDAY NIGHT: Partly cloudy early, then clear. Lows 45-52. Wind NW 5-15 MPH, higher gusts.
FRIDAY: Sun and passing clouds. Highs 58-65, coolest in higher elevations. Wind NW 10-20 MPH, higher gusts possible.
FRIDAY NIGHT: Clear. Lows 44-51. Wind NW 5-15 MPH, higher gusts.
SATURDAY: Mostly sunny. Highs 63-70. Wind NW 5-15 MPH.
SATURDAY NIGHT: Clear. Patchy ground fog may form in interior low elevations. Lows 45-52, slightly cooler some interior lower elevations. Wind variable up to 10 MPH.
SUNDAY: Partly sunny. Highs 67-74. Wind SW 5-15 MPH.
DAYS 6-10 (SEPTEMBER 26-30)
More weather changes as we head through the final 5 days of September… Low pressure trough and frontal system moves through September 26 to early September 27 with a shower threat – more details to come later. Generally fair weather and another shot of cool air to follow this system as Canadian high pressure moves in, then a little warmer weather be the end of the period as high pressure shifts to the east of the region.
DAYS 11-15 (OCTOBER 1-5)
There is a fair amount of uncertainty in the forecast for the early days of October. A tropical wave approaching the southern windward islands, typical for this time of year, is getting more organized and has a good chance of becoming the next tropical storm (eventually possible / probable hurricane). I don’t often mention names too far in advance because of uncertainty, but we already have TS Gaston in the open Atlantic, and with no other systems of concern at the moment the disturbance heading for the Caribbean would likely end up with the name Hermine, so let’s assume for a moment that this is what happens. Again, noting that model guidance for tropical systems is to be taken with grains of salt due to their limited performance ability with such systems, the medium range models are in agreement at this time that this new system would move through the Caribbean and be in a much better position to impact at least the southeastern US (not sure where yet – too soon to know) eventually. After that the guidance takes the remains (or weakened version of the system) at least part way up the US East Coast as a significant rain system. Again it’s too soon to sound like I’m grabbing onto any details – we’re really just talking models at this point. But at this time of year you monitor. In our case, we monitor for any typical issues a storm like that might bring, but also monitor somewhat in hopes that moisture from a system like this could help us majorly reduce our still-ongoing drought. So as you can see there is a lot to consider in the medium range, and while we never should jump to conclusions we must be aware of all of the possibilities. These will be kept track of as always, and refined and fine-tuned as we get closer to this period of time. For now, I’d lean toward dry weather to start October, a milder spell, and then the chance of rain at some point, pending future movement of that tropical system and any mid latitude disturbance that may approach the region too.