[Weather] NWS Boston EM Briefing: Potential for Flash Flooding Friday/Saturday

[BOX Operations - NOAA Service Account]

Good morning everyone,

We are monitoring the potential for a tropical cyclone developing which
should track north along the coast or remain just offshore. The NHC has
increased the chance of formation to 80%. Regardless of its development, *the
main concern with this system in southern New England will be the potential
for flash flooding from heavy rainfall Friday into Saturday, especially in
more urbanized areas. *The only substantial change with this email is to
add the mention for an isolated severe thunderstorm which may spawn a
tornado or two.

Here are the key points:


*Track/Strength Uncertainty: High*
It is unknown how the system will develop and where it will eventually
track. This will have a big impact on who sees the heaviest rainfall.

*Main Threats:*


*Flash Flooding:* We are most confident in the potential for heavy rainfall
Friday night into Saturday morning. Rainfall of 1 to 2 inches is likely
with locally higher amounts. Minor urban flooding is likely but more
significant urban and small stream flooding is possible depending on where
the heaviest rain falls, which is unknown at this time.


*Severe/Tornado:* There is the threat for an isolated severe thunderstorm,
and with that a tornado or two is possible.


*Wind:* We are less confident in wind impacts due to high uncertainty as to
how the system develops and eventually tracks. It’s quite possible stronger
wind gusts (more than 30-40 mph) remain offshore southeast of Cape Cod and
the Islands or don’t materialize at all. Prevailing direction of any of the
stronger wind gusts should be from the south or southeast.

*Seas:* We are also less confident in how much seas will build given
uncertainty in the wind forecast. Highest seas approaching 10 feet may
affect waters south and east of Cape Cod and the Islands.

*Coastal Flooding:* We are highly confident that the threat is low on both
coasts as tides are relatively low through the weekend.

*Rip Currents:* We have low confidence due to uncertainty in the wind
forecast, but there is the potential for moderate rip currents Friday and
Saturday, possibly into Sunday, mainly at the south coastal beaches.

Thanks,

Bryce Williams and Hayden Frank

If you have any questions or would like more information, don't hesitate to
contact us via this email address, on NWSChat <https://nwschat.weather.gov/>,
or at the following:

National Weather Service Boston/Norton, MA
46 Commerce Way
Norton, MA 02766
508.622.3280
Website <http://www.weather.gov/boston> | Facebook
<http://www.facebook.com/NWSBoston> | Twitter
<http://www.twitter.com/NWSBoston>
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