DAYS 1-5 (SEPTEMBER 22-26)
High pressure remains in control with another day of very nice weather for the final full day of astronomical summer. Autumn arrives at 2:50 a.m. Saturday with the vernal equinox (the moment the sun is directly over the equator on its journey to the southern hemisphere, where its their first day of spring). For the weekend, we turn our attention to a moisture plume associated with low pressure well to our south. While this low center, which may acquire enough tropical characteristics to be named, drifts to the coast of NC where it moves onshore there, its associated moisture plume elongates northward in a southerly flow aloft and makes a charge at southern New England. At the same time, an amplified higher latitude pattern with a high pressure ridge in east central Canada and a deepening low pressure trough further east in Canada will create a road block of sorts for the moisture / storm to the south. One surface high (the one governing today’s weather) will slide to the southeast and leave a little weakness in the pressure field to aid in the rain’s northward progress as we get to early Saturday, but as this is happening a second surface high to the northwest of it will begin pushing toward New England. So now you see the set-up for a tough day 2 forecast – just how fast and how far north does the rain push before it gets obliterated by dry air supplied by the systems to our north? Earlier onset / best chance of steadiest rain and most amounts will be the South Coast region, while the further north you go the onset time, ability to maintain steady rain, and ability to generate measurable rain drops off quickly, as well as the amount of time this can occur, because by Saturday evening the dry air to the north should already be in the process of slicing right into the rain area. On regional radar it will look somewhat like the rain splits in two with one area drifting into NY while another peels off to the east off Cape Cod. Either way you see it, we have a dry interlude where it rained, and continued dryness in any areas the rain never quite reaches. The greatest chance for the latter are places from around the MA/NH border into NH where it may only sprinkle lightly or not rain at all from the initial push of rain. All during this, with high pressure to the north and low pressure well south southwest of our region, we’ll set up a cool northeasterly air flow with below normal temperatures for the weekend. Patches of drizzle can evolve eventually, favoring the east-facing coastal communities where the wind will be directly off the ocean. This is most likely to happen later Saturday night into Sunday. During Sunday and Sunday night, and into early Monday, what remains from the low to the south will make its way northward through the Mid Atlantic, and then as a remnant low into the waters south of New England. It’s during this time when our region can see additional periods of rain along with continued areas of drizzle and some developing fog, though the gusty wind that had developed especially along the South Coast during Saturday will ease off some, because low pressure will be much weaker. Eventually, the stronger features to our north will push that remnant low away later Monday, but we still have to wait for upper level low pressure to cross the region through Tuesday. This means Monday would probably remain generally cloudy even if it starts to dry out in terms of rain chances, and Tuesday would be day that if any sun was to shine, it would help trigger lots of clouds, but I think the air would be dry enough to prevent much shower activity from developing. Those days will also feature a continuation of below normal temperatures for the early days of autumn. Also, the wind that had eased off a little Sunday would pick back up again as the pressure gradient tightened up behind now-regorganizing low pressure and the high to the north and west.
TODAY: Sunshine becomes filtered through an increasing shield of high clouds. Highs 66-73, coolest coast. Wind variable becoming E up to 10 MPH.
TONIGHT: High overcast. Low elevation ground fog patches. Lows 47-54. Wind E under 10 MPH, calm in some low elevations.
SATURDAY: Overcast may be thin enough for some sun in the morning-midday especially north of I-90 otherwise thickening overcast with time. Rain likely South Coast, tries to push north but very slowly and may struggle to get to areas north of I-90 doing so only as patchy and light. Highs 61-68 with a cool-down to under 60 especially near east-facing shores by late in the day. Wind E to NE 5-15 MPH but 15-25 MPH South Coast including late-day higher gusts around Cape Cod.
SATURDAY NIGHT: Cloudy. Any lingering rain ends / dissipates. Areas of drizzle/fog overnight favoring eastern coastal locations. Lows 52-59. Wind NE 5-15 MPH, higher gusts near the South Coast.
SUNDAY: Cloudy. Areas of drizzle and fog. Periods of rain, favoring the South Coast to I-90 region. Chance of rain at times further to the north. Highs 58-65, coolest eastern coastal areas. Wind NE 5-15 MPH.
SUNDAY NIGHT: Cloudy. Areas of drizzle and fog. Periods of rain, again favoring southern areas. Lows 50-57. Wind NE-N 5-15 MPH.
MONDAY: Mainly cloudy. Best chance of rain southeastern areas morning. Highs 60-67. Wind N 10-20 MPH, a few higher gusts possible.
MONDAY NIGHT: Breaking clouds. Lows 50-57. Wind N 5-15 MPH and gusty.
TUESDAY: Lots of clouds – intervals of sun. Highs 60-67. Wind NW 10-20 MPH and gusty.
DAYS 6-10 (SEPTEMBER 27 – OCTOBER 1)
High pressure builds in from Canada with a stretch of dry weather from mid week to at last the start of the weekend (September 30), but may have to watch to our south once again for low pressure threatening the region with rain by the end of the period (October 1).
DAYS 11-15 (OCTOBER 2-6)
General pattern should feature high pressure to our north and the tendency for additional low pressure to our south, leaving our region somewhat vulnerable to battle zone unsettled weather, but my continued leaning is that high pressure to the north will be close enough / strong enough to keep us drier more often than wet.