Tropical Storm Henri is expected to strengthen into a Hurricane tonight or tomorrow before impacting the Northeast US with strong winds, flooding rain, and storm surge on Sunday. It may become the first Hurricane to make landfall in Long Island or Southern New England since Bob in 1991, but in reality there isn't much difference between a 70 MPH Tropical Storm and 75 MPH Hurricane. Ultimately, the exact forecast track will determine who sees flooding rain vs strong wind. In this blog I'll discuss the possible tracks and what kind of impacts that would have in Southeastern New England.
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| National Hurricane Center Forecast Cone |
Big Picture
As of 5 PM Friday Evening, Henri is a 70 MPH Tropical Storm with a 994 minimum pressure. The storm has started its move to the North. Although convection remains impressive, the northerly shear is continuing to displace the center of the storm. If you look carefully at the visible satellite, you can see a swirl in top left of the storm. Until this co-locates under the deepest convection, the storm is going to have trouble getting stronger.
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| GOES-16 Visible Satellite 4-6 PM (image credit- College of Dupage Weather Center) |
The shear is expected to relax tonight and there are already signs of increased organization. Henri will be moving over the Gulf Stream, so intensification is likely as the storm moves northward. That heat starts to run out around 38 N, but it doesn't go away completely until 40 N. So the storm should begin to weaken as it approaches Southern New England and Long Island, but it won't have enough time to lose all its strength.
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| Tropical Cyclone Heat Potential (image credit- WeatherModels.com) |
Henri is expect to move slowly, which is unusual for a Northeast tropical cyclone. The legendary Hurricane of 1938 was moving close to 50 MPH. That is why I am skeptical that Henri breaks the 30 year Hurricane drought, but it won't really matter. This storm will have a high impact on millions of people. The slow movement gives it more time to weaken, but it also allows for more rain. I don't need to tell anyone in Southern New England just how unwelcome that is.
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| National Weather Service Flash Flood Guidance for 3 Hour Precip (Image Credit- WeatherModels.com) |
This map says that it will only take 1.9 inches of rain in 3 hours for flash flooding to occur in Worcester. It will take 3 inches in Springfield and 2.1 inches in Boston. Tropical cyclones produce tremendous rainfall as we have seen locally with Elsa and Fred already this summer. The Weather Prediction Center is highlighting a slight to moderate risk of flash flooding across SNE on Sunday and Monday. Flash flooding can literally happen in a minutes (flash)- for reference see what happened on Route 20 in Worcester yesterday. Water started to rise rapidly, stranding several motorists. Turn around, don't drown!
It can also cause ordinarily calm streams to rise rapidly so please consider creating an evacuation plan in the event that your local stream decides to go crazy. Unfortunately, that happened in Western North Carolina as Fred moved through this week. As of today, there are at least 4 confirmed dead and at least 20 more missing.
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| WPC Excessive Rainfall outlook (source) |
Soggy ground makes healthy trees susceptible to strong winds. Normally 50-60 MPH does not get the attention of New Englanders. 50-60 MPH cold season winds out of the NW do not generally cause damage to healthy trees. Sure, rotted trees and some branches come down but its not generally a big deal. Southeast winds on the other hand are trouble makers in Southern New England. Add in the moist soil and uprooted trees is a big concern with any winds over 40 MPH. Eversource is estimated 300-600K outages for an Eastern CT landfall and over a 1 million if it makes landfall in Western CT. That doesn't include National Grid so you can imagine the potential for long service disruptions.
The other concern will be storm surge flooding. There is an astronomical high tide this weekend, which will enhance the threat. Add waves on top of the surge along the South Coast of MA, RI, CT, both sides of Long Island, New York City, and the Jersey Shore and there will be moderate to major coastal flooding.
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| National Hurricane Center Peak Surge (source) |
Scenario's In Southern New England
As currently forecasted, Henri would make landfall in Long Island and South Central Connecticut before moving into Western Massachusetts. That track would bring 6-10 inches of rain to parts of CT and W MA. A general 1-3" would fall in Worcester County with even less in Eastern MA. All of that rain could potentially come in 1-2 bands, so flash flooding would still be possible, but the odds of it occurring would decrease across Central and Eastern MA. These bands would also be capable of producing tornadoes. There were 2 confirmed tornadoes in the area yesterday as Fred moved through. They tend to be brief, but can cause localized destruction, similar to the twisters that moved through Douglas, Uxbridge, Northbridge, and Upton in 2018.
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| Weather Prediction Center Forecast Precipitation though Wednesday 8/25 (source) |
The trade off would be stronger and more frequent damaging wind gusts. This track would lead to widespread tree and power line damage in Central MA with scattered tree and power line damage in Greater Boston. This track would largely spare the Merrimack Valley, Eastern NH and Maine. It would be similar to Hurricane Irene from late August 2011. Irene weakened to a Tropical Storm but it still knocked out power to millions in the Northeast. Irene caused tremendous flooding and was also a slow moving Northeast Tropical Cyclone. A lot of people are comparing this to Hurricane Sandy's left hook turn, but Irene is a stronger comparison.
Another potential outcome for Worcester County would be a landfall around Montauk to New London, CT, gradually bending west through Hartford to Springfield. This would bring stronger wind AND heavier rain to Providence and Worcester plus more coastal flooding in Buzzards Bay/Cape and Islands. There is some computer model support for this scenario
NOTE- IMAGE NOT A FORECAST
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| 18z HWRF HENRI Composite Reflectivity Sunday 4 PM (Image Credit- Tropical Tidbits) |
The next question is how strong will it be when it gets here. I think at best, it will be a low end Category 1 Hurricane. If it really blows up tomorrow, maybe the storm would be at 80 MPH at landfall. On the other hand, at worst I see it coming in with 60 MPH winds. I'm taking 70 MPH.
Timing
We have all day Saturday to prepare, although I do expect some showers and thunderstorms tomorrow. The atmosphere will feel noticeably tropical. The first bands will arrive well ahead of the storm early Sunday AM. The first impactful bands will approach the Providence, Boston, and Worcester corridor after 5 AM and the significant bands moving in after 7 AM. The worst of the storm will be mid afternoon as the center, perhaps eye? of Henri makes its closest pass to Central and Eastern MA. Precip will pause in Central and Eastern MA around 8 PM as the center slowly drifts into the Berkshires, where the rainfall "jackpot" will be.
Some guidance is insisting that the low will loop around and trigger additional rainfall on Monday. We will have a better handle on that tomorrow.
Conclusion
My advice is to prepare for power to be out for 1 week. Not everyone will lose power for one week, but some people will. If you live near the coast or by a river, have an evacuation plan. Storms like this are rare in the Northeast and its best to prepare for the worst and hope for the best. Mother Nature did not do us any favors this summer and a tropical system is the last thing we needed. More details tomorrow. Have a good night and thanks for reading.
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