Warning Issued: Possible Heavy Rains and Flooding Through Monday Night [Update]

Update 12:45 p.m.:

The National Weather Service's latest forecast for Norwalk, posted at 12:28 p.m., now says showers this afternoon are only "likely," with the chance at 60 percent. There will be patchy fog before 4 p.m. and a high temperature of 48 degrees, forecasters say.

Expect winds from the south at 14 to 16 mph, but gusts of up to 33 mph, according to the forecast.

A "Flood Watch" and "Hazardous Weather Outlook" are both still in effect.

Update 9:48 a.m.:

Winds of up to 45 mph may accompany a "strong thunderstorm" now over Norwalk, according to a "Special Weather Statement" issued at 9:12 a.m. by the National Weather Service.

"Cloud-to-ground" lightning is also expected.

Update 9:42 a.m.:

With a rainy day and evening ahead and possible thunderstorms in the afternoon, the National Weather Service has issued an updated "Flood Watch" advisory for the New York metropolitan area and coastal counties of Connecticut, and now says the watch is in effect from 10 a.m. today through late tonight.

The 5:15 a.m. update states that the flood watch is in effect from 10 a.m. through this evening. Up to an inch of rain may fall in much of the region, with locally higher amounts possible, the weather service says.

According to the seven-day forecast specifically for Norwalk, issued by the weather service at 7:43 a.m., rainfall of half an inch to three quarters of an inch is possible. There may be afternoon thunderstorms accompanied by heavy rain. The temperature should reach a high of 49 degrees, and winds of 14 to 16 mph will be accompanied by gusts, which could reach 33 mph.

Showers are also likely tonight (with a 70 percent probability of precipitation overnight), with another quarter of an inch to half an inch of rain possible. There's a chance of a thunderstorm before midnight. After that, there's a "slight chance" of rain showers between midnight and 1 a.m. Winds of 13 to 20 mph may be accompanied by gusts of as much as 38 mph.

Tuesday should be sunny, with a high temperature of 41 degrees. Winds of between 9 and 16 mph will be accompanied by gusts that may reach 36 mph. No more rain is in the seven-day forecast until Saturday, when there's a "chance of showers," according to the weather service.

Original article:

The National Weather Service has issued a "Flood Watch" from early Monday through late Monday night for the New York metropolitan area and the coastal counties of Connecticut, including Norwalk, with possible periods of heavy rain leading to potential flooding.

"Total rainfall amounts of 1 to 2 inches, with locally higher amounts, are possible across the Tri-State area on Monday," weather service forecasters said in a statement released at 4:21 p.m. Sunday.

As it normally does when it issues a "watch" or "warning" statement for a region, the weather service continues to provide parallel forecasts for specific locations, and these may differ from the regional forecast. A National Weather Service meteoroligist has told Norwalk Patch that in cases where the forecasts differ, the more specific local forecast should be given more weight.

Norwalk's forecast

The seven-day forecast for Norwalk, issued at 3:18 p.m. Sunday, said the chance of showers overnight was 50 percent, with rain mainly after 3 a.m. and temperatures as low as 32 degrees. New rainfall of less than a tenth of an inch is possible. Winds are expected to be light: between 3 and 6 mph.

On Monday morning expect rain, and fog in patches is possible before 10 a.m. Thunderstorms are also possible after 1 p.m., although the forecast also states that the chance of precipitation sometime during the day is "100 percent". New rainfall of half an inch to three quarters of an inch is possible.

Monday night, there may be showers and a possible thunderstorm before midnight, then possible showers from midnight to 2 a.m. The chance of precipitation is 80 percent, and anywhere from a quarter of an inch to half an inch of new rainfall is expected. The temperature is expected to reach a low of 31 degrees (just under freezing) and the winds are expected to be 9 to 17 mph.

Tuesday is expected to be sunny, with a high temperature of 42 degrees. No further rain is in the forecast until Wednesday afternoon, when the forecasters expect a "slight chance of showers."

More from the Flood Watch statement

The Flood Watch forecast calls for rain after midnight early Monday, continuing into the early afternoon. In the afternoon and early Monday evening a second wave of rain with scattered thunderstorms is expected to come from the southwest.

"This rainfall, combined with the nearly saturated grounds from the 1 to 2 inches of rainfall that fell on Friday will exacerbate the flood threat," forecasters said in the 4:21 p.m. statement.

Recent mild weather has allowed ice jams to form in rivers and streams, forecasters said. "The buildup of water behind these ice jams can result in flooding upstream as well as downstream if they give way. ...  Those living in areas prone to flooding should be prepared to take action should flooding develop."