Severe Weather & Tropical Storm Henri Coordination Message #1 – Thursday 8/19/21 Severe Weather & Sunday 8/22/21-Monday 8/23/21 Henri Potential Impacts

Hello to all…

..Remnants of Tropical Depression Fred will cause heavy downpours with the possibility of isolated severe thunderstorms through Thursday Afternoon. The greatest threat for heavy rainfall is in Western and Northern Massachusetts and West-Central Connecticut with the potential of urban and poor drainage flooding in some areas..
..The severe weather potential is across Southern New England with isolated strong to damaging winds and the low possibility for an isolated weak tornado due to the tropical air mass in place and the Storm Prediction Center (SPC) has a marginal risk for severe weather across much of Southern New England for Thursday..
..There could be additional thunderstorm chances Friday and Saturday in Southern New England that will have future coordination messages if conditions warrant..
..Tropical Storm Henri must be monitored as we get into the Sunday into Monday timeframe for potential direct impacts to portions of Southern New England. It is too early to speak specific details and a more offshore solution cannot be totally ruled out but given current model runs and consensus, there are enough concerns for direct impacts and now is the time for non-Amateur Radio and Amateur Radio SKYWARN Spotters to monitor the progress of Henri on the region and for all residents of Southern New England to begin preparations for direct impacts from Henri..
..SKYWARN Self-Activation will monitor the flood and severe weather potential for Thursday and will continue to monitor the progress and potential impacts on Tropical Storm Henri..

For Thursday, the remnants of tropical depression Fred is expected to bring the potential for heavy downpours in Western and Northern Massachusetts and West-Central Connecticut and the potential for isolated severe thunderstorms. The headlines depict the current thinking. Key factors include:

1.) There are areas of embedded heavy rainfall on radar with some signs of training particularly in Connecticut and this activity will spread north and east into parts of Western and Central Massachusetts. In those areas, there could be the increased risk of urban and poor drainage flooding.
2.) Any severe weather potential for this morning through late afternoon is contingent on thunderstorm activity being able to tap into stronger winds aloft. Any isolated weak tornado potential would be dependent on thunderstorms being able to become strong enough to tap into the shear and favorable rotation parameters aloft.

There could be some additional thunderstorm chances Friday and Saturday. These will be detailed as needed if they constitute a threat for isolated strong to severe thunderstorms in future messaging.

Attention then turns to Tropical Storm Henri. Henri is expected to change little in strength today as shear over Henri will be offset by very warm Atlantic Ocean waters along Henri’s path will allow it to hold its intensity. In about 24-36 hours, the shear will abate and allow Henri to intensify into a hurricane. Henri will then start to turn Northwest and Northward and head on a path that could bring it over or near the Southern New England coast as we move into Sunday and Monday. This could result in direct impacts from Henri as a strong tropical storm or minimal hurricane. Model consensus has been converging on a solution near or over Southeast New England in latest model updates. The National Hurricane Center in Miami Florida is stating in its advisories that interests in the Northeast United States should monitor the progress of Henri. This wording has necessitated the start of coordination messages on Henri. The key factors over the next several days are as follows:

1.) The track of Henri and whether its near or over the Southern New England coast. The west side of Henri will experience some strong winds with heavy rain as the main threat while closest to the center and on the east side of the system will have the greater potential for damaging winds but less rainfall. The track will also affect which coastal areas will have the greatest risk for coastal storm surge flooding.
2.) The intensity of Henri is another factor. Some models strengthen Henri significantly as it moves northward towards New England. Its peak intensity will also determine how strong the impacts are over the Southern New England coast and Southeast/Eastern New England.
3.) The speed of Henri’s approach to the region. Some models slow Henri’s approach toward Southern New England. Depending on when that slowing occurs and how close it is to the Southern New England coast will determine impacts over the region. Typically, tropical systems accelerate through Southern New England but the setup for Henri may actually have it slow near or over Southern New England. This might allow for more weakening of Henri due to cooler waters but could extend the impacts of the system over a longer duration and where it slows and how close it is to the region when it slows down will determine the extent of Henri’s impacts.

SKYWARN Self-Activation will monitor the flood and severe weather potential for Thursday and will continue to monitor the progress and potential impacts on Tropical Storm Henri. The next coordination message on Henri and any severe weather potential for Friday or Saturday will be posted by 1100 PM Thursday Evening. Below is the NWS Boston/Norton Area Forecast Discussion, Enhanced Hazardous Weather Outlook, SPC Day-1 Convective Outlook and the NHC Tropical Storm Henri advisory package:

NWS Boston/Norton Area Forecast Discussion:

NWS Boston/Norton Enhanced Hazardous Weather Outlook:

SPC Day-1 Convective Outlook:

National Hurricane Center – Miami Florida Information:

Tropical Storm Henri Public Advisory Information:

Tropical Storm Henri Technical Discussion Information:

Tropical Storm Henri Forecast/Advisory Information:

Tropical Storm Henri Wind Speed Probabilities:

Tropical Storm Henri Key Messages:

Tropical Storm Henri Storm Graphics:

Respectfully Submitted,

Robert Macedo (KD1CY)
ARES SKYWARN Coordinator
Eastern Massachusetts ARES Section Emergency Coordinator
Home Phone #: (508) 994-1875 (After 6 PM)
Home/Data #: (508) 997-4503 (After 6 PM)
Work Phone #: 508-346-2929 (8 AM-5 PM)
Email Address:
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