Slowly but surely, the guidance has been focusing the forecast for Tropical Storm Henri, and unfortunately, the result has been the increased chance of a high impact event for Connecticut.
This is the SCW first call forecast for Henri. It will provide details on potential conditions, impacts, and timing. As this is a first call, remember that things are likely to change a bit, though we are writing now because we have higher confidence in the bigger details of the forecast.
Let's begin once more by providing an overview of the storm so far.
In fact, the guidance has continued to trend west, illustrating the strength of the steering pattern. This is not going out to sea. Here is a 500mb GFS depiction of the next few days. This general idea is supported across all reliable guidance, though the difference in details creates the spread we see in ensemble forecasts.
Saturday looks fine. The period of interest is Sunday morning into Monday. The start time looks to be between 6-8am from starting in southern CT and working its way north as rain bands from Henri overspread the state. According to the National Hurricane Center (NHC) forecast, tropical storm winds are likely to begin around 8am on Sunday. All preparations should be completed by then. The image below shows the NHC forecast, and the percent chance of tropical storm force winds. This will increase the closer Henri gets.
One of the key pieces of this forecast is the prediction that Henri slows down. That means that instead of the usual 6-12 hour event, we will see a longer duration period of wind and rain. There are still questions over what this means for the track, but for the purposes of this forecast, expect wind to pick up Sunday morning with the worst taking place Sunday afternoon and night, with things beginning to let up on Monday morning.
How long Henri sticks around is subject to change as guidance figures out final track.
This is a very difficult part of the forecast still, though we have narrowed down where we believe landfall (where the center crosses) will occur. Currently, we think that Henri makes landfall between New Haven, CT and Westerly, RI. Note of course that if it hits a place like New Haven, it will cross Long Island first.
What does this mean? Coastal areas in this zone can expect to see the strongest winds. For Connecticut as a whole, if you are on the west side of the storm you will likely see more rain, and if you are on the eastern side of the storm you are likely to see more wind and a potential tornado threat.
Below is the operational GFS. For the first time, we are actually showing you the surface depiction to give you a sense of what a track like the GFS could look like. West side has the heavy rain, east side has the highest winds.
We expect the intensity of Henri to be 75mph at landfall, but we think it could reasonably be between 65 mph and 85 mph at landfall. At 75 mph, Henri would be the first New England hurricane since 1991 (Bob) and first CT hurricane landfall since Gloria in 1985.
The first impact we write about we have the least confidence in. We believe that based on a track in our landfall zone, we see the following during the worst part of the storm:
- Coastal areas: Sustained winds of 55-65 mph with gusts between 70-80 mph. Some isolated areas in SE CT may see slightly higher gusts.
- Inland areas: Sustained winds of 30-50 mph (higher the further south/closer to center you are) with gusts between 55-65 mph.
Now, the exact track matters here. Unlike other tropical systems, the wind field will not be as large and it will not be as strong as Henri is expected to be weakening on final approach. The closer you are to the center the more likely you see damaging wind, especially along the shoreline. These winds are on par with Tropical Storm Isaias, which hit the state last year.
Coastal Hazards: High Impact
Unfortunately, we expect significant impacts at the coast. By coastal hazards we mean storm surge and beach erosion. The push north by Henri will push water into Long Island Sound, bringing 2-4 feet of storm surge. That will cause significant problems, enhanced by the full moon expected this weekend. We do not expect the kind of surge we saw in Sandy, as Sandy was a stronger and much larger storm that was able to push incredible amounts of water onshore.
However, with a landfall, we expect the combination of wind, rain, waves, and surge to cause major beach erosion. Be aware if you are along the immediate shoreline. Below is the NHC peak surge forecast.
Note that not every inch of coastline will see this kind of water rise, but if you have ever been unlucky enough to experience it, you know what kind of damage can be done with just a few feet of flooding.
As mentioned earlier, the eastern side of a tropical system tends to see severe weather in the form of tornadoes. These generally are quick and relatively weak spin ups. This is something we will be watching on the eastern side of the system depending on where it makes landfall. We do not expect severe weather for most of the state. This would likely be isolated to eastern CT.
Rainfall: High to Extreme Impact
We believe when the dust settles it will be the rain that is the story of Henri. This is an area of very high concern for us. First some context. Last month was the third wettest on record. We saw multiple flash flood events.
Just yesterday, central and eastern Connecticut saw 3-5 inches of rain, causing major flash flooding. The prospect of a slow moving tropical storm or hurricane has us taking the rare step of calling for a potentially extreme impact somewhere in Connecticut.
We believe a general 4-10 inches of rain will occur with higher totals possible in isolated spots, especially within the path of the center of Henri. That means central CT is in the crosshairs.
Flash flooding on the order of what could happen is a bona fide life threatening event, especially if you are on the roads and driving through flooded roads. I cannot emphasize enough that if you encounter flooded roads do not drive through them. River flooding will need to be watched as well.
Not everyone will see dramatic rain totals. This is highly dependent upon banding and center track, but this is something to pay very close attention to, especially on the west side of the center.
Below are two images. The first is the WPC prediction for rainfall and the second is the moderate risk for flash flooding that has been issued at a long lead time, suggesting high confidence.
I know we went through this last year, but expect widespread and long duration power outages if this forecast comes to pass. The combination of wind, significant rain, and long duration nature of the storm is a recipe for a potentially historic power outage event as saturated soils give way during wind gusts.
Hopefully the recent storms that took out large trees makes this less likely, but we doubt it.
A storm need not be the Great 1938 Hurricane to have a major impact. If this storm comes in as a strong long duration event at either category one hurricane or strong tropical storm, we expect a high impact across the state. Travel will be hazardous Sunday morning through Monday morning.
The impacts will vary depending on location and track (wind at the shore, rain in central and western CT) but this looks to be on par with some of the high impact events we've seen in the past. One area of possible concern is the intensity forecast. Although we believe there are no surprises coming with intensity one way or the other, intensity is very hard to predict, and we will watch in case Henri end up stronger or weaker than anticipated.
Bottom line: this will be a big and slow moving storm. Make sure you are prepared for whatever comes.
SCW will be providing constant updates as we receive additional information. As we track this system, please understand that we will be much slower to respond than usual.
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Thank you for reading.
-SCW Team (written by DB)