DAYS 1-5 (SEPTEMBER 24-28)

Blocking pattern takes hold. High pressure, quite strong for this time of year, sits across southeastern Canada. Low pressure evolves to our south and its track / interaction with its upper low, in combination with the high to the north, help determine the details of impact for our region. The pattern and its evolution are already resulting in increased seas / coastal surf now as we’ve had a couple days of a northeasterly fetch, which continues and only gets stronger for a couple to a few more days as the situation evolves. This means we’ll have coastal wave battery and flooding issues, particularly on north-facing and east-facing shores into the start of the weekend, and pending the low’s track, maybe more on south-facing shores with time. I have been favoring a development of low pressure that allows it to peak in intensity south or southeast of New England over the weekend. The key is a loop back to the west – earlier vs. later. Today I lean toward a loop back a little sooner / still pretty far south – i.e., before the center would have a chance to be north of New Jersey’s latitude. As we get to the end of the weekend, just after the low has peaked in intensity, it all starts to shift eastward and a weakening version of the low passes by (or even over southern New England) from west southwest to east northeast. A lot takes place between now and then. Today, we’re dry, with plenty of sun, some low clouds off the ocean in bands, and some high clouds fanning up from the southwest. A gradual increase in cloudiness takes places starting tonight and more so on Friday, though we can still see some sunshine during the morning on Friday, especially the further north and west you are. How I think the rain plays out with the expected low evolution and track is this: Initial swath of rain drifts northwestward out from the developing low into our region from southeast to northwest during late morning through afternoon into early evening, but loses punch due to interaction with dry air. This leaves the region with a more spotty fairly light rain pattern after the initial burst enters the region. A second surge of more showery / convective rainfall comes into the region in bands / clusters during Saturday. The timing on this is still a little uncertain, and there can be areas that see little or no rain for several hours, and other areas that could get under a band of moderate to heavy showers and have several hours of soaking rainfall. At some point a second slot of relatively drier air can work in and limit the rainfall. It remains to be seen if additional rain bands occur – TBD as we watch the storm’s evolution. While winds will be moderate to strong, particularly along the coast and especially over southeastern MA and RI, I think the peak period for wind may take place Saturday night into Sunday as the low just passes peak intensity while looping south of Long Island. This is when the wind direction can become a little more easterly for a time in parts of the region. What happens after this depends on the precise track the low center takes. A rapidly weakening low moving more northeastward would result in a drop off of wind intensity and more variable direction, while a low that holds together and tracks more to the east – staying mostly offshore – would result in a slower diminshment of wind and a more backing of the direction of the wind from east to north. These details will be refined in future updates. We should still be impacted by this system, regardless, into Monday with lingering rainfall. The good news is that if our maximum potential rainfall of 2 to 5 inches is realized in any given area(s), it will take place over a period of days. This reduces rain-related flood potential and continues to reduce the long term deficit we still have. As stated, wind impacts will be greatest toward the coast and further southeast and with still leafed trees this increased the potential for tree damage and of course resultant power outages. Peak period of time for this potential is Saturday afternoon through Sunday, but it’s not out of the question some compromised trees can fail partially or fully prior to that. Use caution when traveling.

TODAY: A lot of sun. Highs 60-67. Wind NE 5-15 MPH inland, 15-25 MPH coast, higher gusts at times.

TONIGHT: Increasing clouds. Lows 45-53. Wind NE 5-15 MPH inland, 15-25 MPH coast, higher gusts.

FRIDAY: Thickening overcast – some early sun especially west and north. Rain chance increase southeast to northwest midday on, but fairly light. Highs 59-66. Wind NE 10-20 MPH inland, 20-30 MPH coast, higher gusts.

FRIDAY NIGHT: Overcast. Periodic rain. Lows 47-54. Wind NE 10-20 MPH inland, 20-30 MPH coast with gusts up to 30 MPH inland and 40 MPH coast.

SATURDAY: Cloudy with potential breaks and even glimpses of sun. Showers likely, some heavy at times. Highs 60-67. Wind NE 15-25 MPH inland, 25-35 MPH coast, gusts 35-55 MPH, strongest Cape Cod & Islands.

SATURDAY NIGHT / SUNDAY: Overcast. Showery rain, heavy at times. Slight chance of thunderstorms. Temperatures generally 56-63. Wind NE (may shift more E at times), 15-30 MPH inland with gusts around 40 MPH, 25-40 MPH coast with gusts 45-55 MPH.

SUNDAY NIGHT / MONDAY: Cloudy. Periodic rain. Lows 53-60. Highs 60-67. Wind variable 10-20 MPH, higher gusts, with potential for higher sustained and gusts (depending on low track).

DAYS 6-10 (SEPTEMBER 29 – OCTOBER 3)

Improving weather with clearing trend September 29 and fair, mild weather September 30 into the first few days of October. More details on this period in coming updates.

DAYS 11-15 (OCTOBER 4-8)

Zonal flow pattern. A couple systems can bring shower threats but overall pattern is dry, seasonable to mild.