Yes, it’s rainy again, but better weather is on the horizon

People walked in light rain on Stuart Street in Boston.Pat Greenhouse/Globe Staff

A flood watch is back in effect for the eastern half of Southern New England through the middle of this evening. Low pressure will move from Cape Cod up to the Gulf of Maine over the next 12 hours, bringing periods of showers, some of them heavy, and even the outside chance of a thunderstorm.

With all the rain of the past month there could be some urban street flooding as well as some small-stream flooding depending on where the heaviest elements of rain end up.

The National Weather Service In Norton has issued flood watch for Monday.NOAA

The good news with this current bout of rainfall is the whole system is what we call progressive, in other words it is moving quickly. This will set us up for a gorgeous stretch of weather beginning Tuesday and likely lasting into the start of the weekend.

I’m expecting plenty of sunshine, warm temperatures, and comfortable sleeping weather the rest of the week.

This map show the percentage of cloud cover Tuesday morning. Notice much of southern New England is forecast to have no cloud cover!WeatherBELL

The humidity levels will be typical for September. What I’m not looking at is any chilly air, which could definitely start to play into the forecast in the next few weeks.

Rainfall will continue into the evening Monday, but will be gone before sunrise Tuesday.WeatherBELL

The autumnal equinox will arrive on Saturday just before 3:00 a.m. in the morning. The actual moment when fall arrives astronomically actually changes year to year, though. It’s more commonly on the 22nd of the month but sometimes it falls on the 23rd.

Starting tomorrow we have the nine days with the fastest daylight loss of the entire year. Along the way we are going to see the gap between sunrise and sunset be shorter than the one between sunset and sunrise as darkness continues to grow.

Daylight continues to rapidly decrease with the largest light loss of the year this week.TimeandDate.com

In addition to daylight, average temperatures are quickly falling. Although we haven’t had a lot of crisp, cool air as of yet, it’s only a matter of time. By the final week of this month, average highs are back to the 60s and will drop another 10 more degrees next month.

Average temperatures fall quite precipitously in September as the sun angle decreases quickly.NOAA

Heading into the first weekend of astronomical autumn I’m going to be watching an area of tropical moisture trying to move northward.

Depending on the upper-level pattern somewhat higher humidity and more rainfall is likely to arrive for the second half of the weekend. How quickly the system moves will determine whether or not Sunday is wet or if we luck out and any new moisture doesn’t get here until Sunday night or early Monday.

Low pressure with more rain will located along the southeast coast this weekend and likely impact New England late in the weekend.Tropical Tidbits