September 23, 2021

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Flash Flood Watch As Ida’s Remnants Likely To Bring Up To 5+ Inches Of Rain Overnight – CBS Boston

3 min read

BOSTON (CBS) – Here we go again. For the fourth time this year a tropical system or its remnants are set to move right over southern New England.

Elsa, Fred, Henri and now Ida – it’s been that kind of summer.

Believe it or not, for some areas, the Ida leftovers may deliver the biggest punch of all. While it will be moving quickly, we are in for some torrential downpours overnight, some of the heaviest rain we have seen all summer. Add that to an already saturated ground (Boston has received 17 inches of rain in the past two months and had the third wettest summer on record) and you have a recipe for all kinds of flooding issues.


For the rest of the day on Wednesday, light to moderate rain will spread over southern New England from the southwest. We’re not expecting any serious flooding issues through this evening as most of our area will have less than an inch of rainfall through 8 p.m.

After 8 p.m. some elements of heavier rain will start to migrate eastward and we will have pockets of downpours.

(WBZ-TV graphic)

The peak of the storm really occurs after 11 p.m. Between 11 p.m. and 7 a.m., waves of torrential rain will blanket the area. The rain will be coming down in buckets, at times at rates of 1-to-3 inches per hour. Storm drains will be unable to keep up. Areas receiving 3 or more inches in a 3 hour span will be at risk for significant flash flooding.

(WBZ-TV graphic)

In fact, some models are indicating the potential for a high end flood event in parts of our area, something on the rarity of 1 in 10 years. This would mean not only urban and small stream flooding but also some river flooding as well. Basements prone to water and roads that are prone to washing out could easily flood overnight.

(WBZ-TV graphic)

If you live in a flood prone area or have issues when heavy rain comes through, this could be a long night.


While it initially appeared as though the highest rainfall totals would be over extreme southern New England, including the Cape and Islands, this forecast has changed a bit.

The center of the remnants of Ida are now forecast to come up over southeast Mass. (a few days ago it appeared they would slide south of our region). With this change in track, areas along and north of the Mass Pike are now at greatest risk of receiving the higher end rainfall totals. This includes parts of southern New Hampshire, Vermont and Maine as well.


It looks like just about all of southern New England is in line for 2.5 to 5 inches of rainfall overnight. The worst case scenario for some isolated areas would be as much as 6-to-7 inches of rain. This is about what we normally get in about 2 months – all coming in about 6-to-10 hours.

(WBZ-TV graphic)

The Cape and Islands may end up with a bit less, somewhere in the neighborhood of 1-to-2 inches of rain, as they will likely be on the south side of the track. Precipitation there will come more in the form of scattered convection (thunderstorms) and be much more variable from place to place.


Most of our area will not need to be concerned about severe thunderstorms, however, there is a high probability of severe weather down across the Mid-Atlantic states. This higher risk area extends offshore and just clips the South Coast of New England. So, given this, we cannot completely rule out a severe thunderstorm or two or a spin-up tornado over the South Coast, Cape and Islands overnight.


Most of the winds from this storm will stay aloft (above ground level), however there is a fairly high risk of wind gusts between 30-to-45 mph along the east coast and southeast coastal areas of Massachusetts overnight into early Thursday. Typically winds of this strength wouldn’t cause much concern along our coast, but given the amount of rainfall saturating the ground, some trees will likely come down and some scattered power outages are likely in this area.

As always we urge you stay tuned to updates on WBZ-TV, and CBSN Boston before, during and after the storm has passed.

Follow Terry on Twitter @TerryWBZ
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