DAYS 1-5 (SEPTEMBER 23-27)
Autumn arrived at 2:50 a.m. with the equinox occurring, and our new season will get underway with something familiar – an unsettled weekend. However, today is not going to be a washed-out day for a good part of the WHW forecast area, and the reason is one that was outline previously as this tough forecast was being formulated over the last handful of days. Coming to pass is the source of dry air at mid levels born of “confluent flow” between high pressure in east central Canada and a low pressure trough to its east. This drying effect is pronounced in northeastern New England, i.e., Maine, with that dry air being transported southward into southern New England just as a rain shield, far in advance of Ophelia (a named system set to make landfall in NC). Basically, the forecast for “part 1” of the event today is the same: Rain shield to the South Coast early morning, then slowly advancing northward as the day goes along, but struggling to do so against dry air. The most solid rain shield will remain south of I-90 and the steadiest rain will indeed be closer to the South Coast. Once you get north of I-90, as the rain tries to move in there, it will be eroded by the dry air being supplied from Maine (a-yeahp), and once you are around the MA/NH border, you may not see anything more than sprinkly very light rain which struggles to even dampen the ground. By the time it even gets up there, the dry air still holding on and the tailing off of the initial rain plume will just clear the region of any rainfall this evening, with just patchy drizzle becoming more likely due to a persistent northeast flow from the Atlantic. Even that will take all day to get its act together, so I’m not expecting a lot in the way of low clouds/drizzle until after dark, and first closer to the eastern coastal areas before it can penetrate inland. Meanwhile, Ophelia will have gone inland in the Southeast and the low will rapidly weaken and start to dissipate, also losing any tropical characteristics. The remnant low will then emerge off the Mid Atlantic Coast and travel south of New England later Sunday and early Monday, when we have our best chance of rainfall across the region. When this is all done, I expect 1 to 2 inch rainfall amounts along the South Coast, dropping off to around 1/2 inch in the I-90 belt and less as you go north from there, again with a good amount of that coming in part 2, especially northern areas. High pressure from Canada will push the wet weather out of here during Monday, though I’m not sure how much clearing we might see later Monday. Will revisit and refine that tomorrow. Also, we still have an upper disturbance that has to swing through the region Tuesday which may also result in a fair amount of cloud cover, but only a remote chance of a light shower, remote enough that I still don’t have it in my forecast. Finally, dry, bright, cool weather arrives by Wednesday as the high pressure area in southern Canada takes full control.
TODAY: Cloudy. Rain South Coast all day, advancing northward with time. Highs 60-67, coolest eastern coast. Wind NE 5-15 MPH, higher gusts likely especially Cape Cod.
TONIGHT: 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. Highs 57-64, 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 morning with periods of rain, best chance south and east. Partial sun may develop afternoon. Highs 60-67. Wind N 10-20 MPH.
MONDAY NIGHT: Variably cloudy. Lows 50-57. Wind N 5-15 MPH and gusty.
TUESDAY: Lots of clouds – intervals of sun. Highs 60-67. Wind N 10-20 MPH and gusty.
TUESDAY NIGHT: Clearing. Lows 46-53. Wind N 5-15 MPH.
WEDNESDAY: Mostly sunny. Highs 60-67. Wind N 5-15 MPH.
DAYS 6-10 (SEPTEMBER 28 – OCTOBER 2)
High pressure will provide fair weather for the final 3 days of September as we see a gradual temperature moderation. The end of the period may see low pressure trying to push back toward our region from the south, introducing the possibility of unsettled weather, but this is a low confidence outlook at this point.
DAYS 11-15 (OCTOBER 3-7)
Potentially unsettled start to the period followed by a drier trend again. Temperatures near to slightly above normal.