Good evening from Southern Connecticut Weather.
Let's be clear right off the bat: there is still a lot to sort out.
This post is to help provide you with an overview of Tropical Storm Henri, our latest thoughts, and key points that you should take away. This information will change as we get closer to the potential event. Let's dive in.
Overview
Let's be clear right off the bat: there is still a lot to sort out.
This post is to help provide you with an overview of Tropical Storm Henri, our latest thoughts, and key points that you should take away. This information will change as we get closer to the potential event. Let's dive in.
Overview
Above: the latest forecast cone from the National Hurricane Center (NHC). The shift was expected given the consistent signal from guidance of a more westward moving system, but the change in track--some 150 miles on day 5--is a highly unusual change for the NHC.
Below, the latest infrared imagery of Tropical Storm Henri at 9pm, which is officially just below hurricane status. It is a well organized but sheared system that is currently moving toward the US coast in a westward heading that will likely turn to the north by Friday. Image courtesy of the fantastic Tropical Tidbits website.
Below, the latest infrared imagery of Tropical Storm Henri at 9pm, which is officially just below hurricane status. It is a well organized but sheared system that is currently moving toward the US coast in a westward heading that will likely turn to the north by Friday. Image courtesy of the fantastic Tropical Tidbits website.
Henri took a lot of folks by surprise by quickly developing into a tropical depression this weekend. In fact, none of the guidance had development predicted 84 hours before it developed! That's a huge surprise in the era of computer models. Henri has continued to surprise, by developing into a stronger system and moving more and more southward, which has opened the door to potential impacts in New England.
Seemingly the entire time, the computer models have been playing catch up.
Seemingly the entire time, the computer models have been playing catch up.
Latest Thoughts
We are declaring Sunday and Monday a SCW Period of Interest because we believe the steering pattern is looking increasingly conducive for direct impacts (wind, rain, possible coastal flooding) from Henri.
First, let's take a look at the steering pattern. What you will see below are the last two GFS runs looking at the 500mb pattern. Higher heights and ridging (high pressure) will be the red shading and arched lines, and troughing (low pressure) will be the blue shading and sagging lines.
We are declaring Sunday and Monday a SCW Period of Interest because we believe the steering pattern is looking increasingly conducive for direct impacts (wind, rain, possible coastal flooding) from Henri.
First, let's take a look at the steering pattern. What you will see below are the last two GFS runs looking at the 500mb pattern. Higher heights and ridging (high pressure) will be the red shading and arched lines, and troughing (low pressure) will be the blue shading and sagging lines.
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So what's happening here? In the Atlantic you can see Henri. On the left, it becomes a powerful hurricane quickly and on the right it becomes a hurricane, albeit a bit later. Henri travels west tonight and Thursday under the Atlantic ridge we've been talking about all season, and turns north around it on Friday. That's when it is generally believed it starts to intensify.
As it is moving up the coast, a trough swoops in from the Mid-Atlantic. This is critical, because it is oriented to "capture" Henri rather than kick it out to sea. As this happens, Henri turns gets pulled back toward the coast. This is when the final piece comes in. In Canada, you can see a big ridge that develops. This effectively closes off the final escape route for Henri, and the result is clear. On the left, this GFS run portrays a hurricane making landfall just south of Connecticut and slowly moving over the state as it weakens. On the right, the system weakens but hits the Cape Cod portion of New England.
What does this all mean?
There is increasing confidence that the steering pattern will allow for at the very least a close approach by Henri this Sunday or Monday. The devil's in the details however, and it is too early to say whether there will be a direct CT impact or more of a glancing blow. This means it is too early to talk about rainfall, wind, or flooding potential.
What makes this forecast difficult?
Intensity. Intensity forecasting in tropical meteorology is one of the hardest fields in the entire space, and it is critical to this overall forecast. There has been a strong correlation during Henri's life cycle between a stronger system and a further south/west track. This is because a stronger storm is deeper, and more able to feel the push from the ridge toward to the coast. Henri is expected to see a more hostile environment for the next 24 hours, and the stronger this storm is, the more west it is likely to track toward New England.
As it is moving up the coast, a trough swoops in from the Mid-Atlantic. This is critical, because it is oriented to "capture" Henri rather than kick it out to sea. As this happens, Henri turns gets pulled back toward the coast. This is when the final piece comes in. In Canada, you can see a big ridge that develops. This effectively closes off the final escape route for Henri, and the result is clear. On the left, this GFS run portrays a hurricane making landfall just south of Connecticut and slowly moving over the state as it weakens. On the right, the system weakens but hits the Cape Cod portion of New England.
What does this all mean?
There is increasing confidence that the steering pattern will allow for at the very least a close approach by Henri this Sunday or Monday. The devil's in the details however, and it is too early to say whether there will be a direct CT impact or more of a glancing blow. This means it is too early to talk about rainfall, wind, or flooding potential.
What makes this forecast difficult?
Intensity. Intensity forecasting in tropical meteorology is one of the hardest fields in the entire space, and it is critical to this overall forecast. There has been a strong correlation during Henri's life cycle between a stronger system and a further south/west track. This is because a stronger storm is deeper, and more able to feel the push from the ridge toward to the coast. Henri is expected to see a more hostile environment for the next 24 hours, and the stronger this storm is, the more west it is likely to track toward New England.
Above: an animation courtesy of weathermodels.com of the 18z European Ensembles. The Euro/EPS has been furthest behind in modeling this system, but even tonight, we see the most westward shift yet. The stronger lows depicted above, are furthest west. This highlights the sensitivity of the forecast.
Key Takeaways
1) Additional changes to both the track and intensity forecast are likely. The final outcome is highly dependent on small changes in the steering pattern and intensity. For now, it is important to know that a significant event is increasingly likely, but not certain. DO NOT lock into specific computer model runs.
2) This is not a time to panic. Chose preparation. We have been talking about the steering pattern for weeks to prepare you for this potential. Check your preparedness plan and supplies. Tropical Storm watches could be issued as early as Friday.
3) Timing for impacts currently look to be Sunday afternoon and Monday. Plan accordingly, but know that things can still change depending on track.
SCW will be providing updates as we receive additional information that needs to be shared. As we track this system, please understand that we may be much slower to respond than usual.
As always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
Thank you for reading.
-DB
1) Additional changes to both the track and intensity forecast are likely. The final outcome is highly dependent on small changes in the steering pattern and intensity. For now, it is important to know that a significant event is increasingly likely, but not certain. DO NOT lock into specific computer model runs.
2) This is not a time to panic. Chose preparation. We have been talking about the steering pattern for weeks to prepare you for this potential. Check your preparedness plan and supplies. Tropical Storm watches could be issued as early as Friday.
3) Timing for impacts currently look to be Sunday afternoon and Monday. Plan accordingly, but know that things can still change depending on track.
SCW will be providing updates as we receive additional information that needs to be shared. As we track this system, please understand that we may be much slower to respond than usual.
As always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
Thank you for reading.
-DB
