Saturday was the day to be outside, and the forecast delivered: mid 70s and sun, with Chelsea Day’s festival and fireworks inside the dry window. Sunday is the day to stay in. The National Weather Service has a flood watch on Suffolk County from 5 a.m. to 6 p.m., and the rain it is watching for is the sudden kind that puts water in basements and closes the low spots every Chelsea driver already knows.
The forecast
A line of showers with embedded thunderstorms crosses the region from west to east between about 5 and 10 a.m. Sunday. Behind it, steadier rain through midday, ending from west to east between 2 and 5 p.m. The Weather Service expects half an inch to two inches most places, with narrow bands where two to four inches can fall in three hours. Those bands are what the watch is about. The chance of true flash flooding is rated low, and the greater concern is south of the Massachusetts Turnpike, but “flooding may occur in poor drainage and urban areas” is the operative sentence, and Chelsea is an urban area with poor drainage.
No wind of note. No coastal flooding in the watch. High near 72. By late afternoon some brightening, which is why the Red Sox pushed Sunday’s first pitch from 1:35 to 3:05.
What that means here
Chelsea Day’s rain date was Sunday and will not be needed. Revere Beach’s art festival was Saturday. Winthrop’s Music on the Landing is scheduled for Sunday 1 to 4 at the Town Landing, with the Deane Winthrop House as the fallback. The Orange Line’s Forest Hills to Back Bay shutdown, already running on shuttle buses, gets slower in the rain. And the underpasses that flood in every heavy storm will do it again.
Everett is in Middlesex County and is not formally in the watch area, which is a quirk of how the Weather Service draws its zones, not a forecast that the rain will stop at the Chelsea line.
For the water quality minded: by Save the Harbor’s rule of thumb, this much rain means no swimming at Revere Beach or Constitution Beach until at least Monday afternoon. Nobody will post a sign; the season’s signs came down on Labor Day.
Before it starts
Clear the catch basin in front of your house tonight if there are leaves on it. The city cannot get to all of them and a blocked grate is the difference between a wet gutter and a wet cellar. Move anything valuable off the basement floor. If you have a sump pump, test it. If you park on a street that floods, you know which streets those are; move the car Saturday night.
The watch may be upgraded to a warning Sunday morning if the heavy bands set up over the city. Warnings go out through the Weather Service, through the city’s alert system, and, if past storms are a guide, through the Chelsea scanner account before anyone official.