Weather for New England and the Northeast

Area Forecast Discussion, National Weather Service Boston/Norton MA, 155 PM EDT
Sat Sep 12 2026

**Area Forecast Discussion**

**What has changed**

The Flood Watch has been expanded to include Windham County in eastern Connecticut, southern Worcester County, Norfolk County, and Suffolk County, including Boston. Forecasters are also monitoring a very low chance for waterspouts and a weak tornado along the south coast. The risk for severe thunderstorms remains much smaller than the flooding threat.

**Key Messages**

1. Confidence remains high for a period of torrential rain and a significant flooding risk across much of Rhode Island and southeast Massachusetts.

2. High pressure will bring generally quiet weather next week. A brief period of summer-like warmth and humidity is expected Wednesday through Friday.

**Discussion**

**Heavy rain and flooding**

The main weather concern for the next 48 hours is a disturbance in the upper atmosphere, known as a shortwave, along with a warm front moving through the region from late tonight through much of Sunday.

By around 8 AM EDT Sunday, the region will be near the right entrance region of an 80 to 90 knot jet stream. In plain English, this means strong winds high in the atmosphere will help strengthen the weather system and support heavier rainfall.

The atmosphere will also contain an unusually large amount of moisture. Precipitable water, or PWAT, is expected to rise above 2 inches, which is near the 99th percentile for September 13. In other words, the atmosphere will contain an exceptionally large amount of moisture for this time of year.

The atmosphere will also be nearly saturated, with warm cloud levels around 12,000 to 14,000 feet. These conditions allow rain to develop and fall very efficiently, increasing the potential for torrential rainfall.

Forecast guidance indicates a 40 to 55 percent chance that rainfall over a three-hour period will exceed flash flood guidance, meaning enough rain could fall quickly enough to cause flooding. The area of greatest concern extends from eastern Connecticut across Rhode Island and into southeast Massachusetts.

There is also a 55 to 70 percent chance that precipitation over a 6 to 24 hour period will reach amounts considered unusual for a given location based on the five-year Annual Recurrence Interval, or ARI. There is a 25 to 40 percent chance of exceeding the 10-year ARI. These statistics indicate that some rainfall totals could be unusually high for the area.

The greatest concern for flash flooding is along the urban corridor from Providence to interior southeast Massachusetts. There remains some uncertainty about exactly where the heaviest rain will develop because its placement will depend on the position of a smaller-scale low pressure center.

Current forecast guidance places the heaviest rain anywhere from the south coast to northern Massachusetts. The HREF and RRFS forecast models appear to handle this uncertainty best, placing the highest rainfall totals near the Interstate 95 corridor.

Because of this uncertainty and a northward shift in some forecast guidance, the Flood Watch has been expanded to include Windham County in eastern Connecticut, southern Worcester County, Norfolk County, and Suffolk County, including Boston.

Outside the Flood Watch area, widespread rainfall of 0.50 to 1.50 inches is expected across much of the region. Within the watch area, localized narrow bands of 2 to 4 inches of rain are possible in as little as three hours. The most intense rainfall should move out from west to east between approximately 2 PM and 5 PM Sunday.

**Very low severe weather threat**

Although flooding is the primary concern, there remains a low but non-zero chance for isolated severe weather along coastal Rhode Island and Massachusetts.

Forecast models show a narrow area of atmospheric instability, with MLCAPE approaching 300 to 500 J/kg along the coast. MLCAPE is a measure of how much energy is available to support thunderstorm development.

There will also be around 20 knots of wind shear in the lowest part of the atmosphere, along with curved hodographs. In plain English, this means winds will change in both speed and direction with height, creating a small amount of potential for rotating storms.

As the small low pressure center passes late Sunday morning into the afternoon, there is a very low chance for a brief spin-up tornado or waterspout. However, the atmosphere lacks enough instability and sufficient temperature changes with height to support stronger, deeper thunderstorms. This threat is worth monitoring, but flooding remains the much more important concern.

**Quiet weather next week**

The new work week begins with some lingering showers as the cold front moves offshore. Rain should end after sunrise across western Massachusetts and Connecticut, while showers may continue into the early to middle afternoon across eastern Massachusetts and Rhode Island.

Behind the front, dry northwest winds will bring in dewpoints of around 40 to 50 degrees. Combined with afternoon highs in the lower to middle 70s Monday and Tuesday, this will produce comfortable and seasonable weather.

High pressure will remain in control at the surface through much of the week, keeping conditions generally dry.

As the high pressure system moves offshore Wednesday, winds will turn more southerly. This will bring back warmer and more summer-like temperatures, along with dewpoints rising into the middle 60s and temperatures potentially reaching the upper 70s.

Forecast confidence decreases toward the end of the week and into next weekend. The overall weather pattern remains relatively west-to-east, with the potential for another low pressure system to move near southern New England. It is still uncertain whether that system will remain north of the region or pass directly overhead, but there is a better chance for unsettled weather from late Thursday onward.