Direct tropical impacts are relatively rare in Connecticut, and tonight for the second time this season, coastal Connecticut is under a Tropical Storm Watch as we track a tropical storm move toward the region.
Unlike Fay, which missed to the west with a landfall in New Jersey, Connecticut is likely to see a direct impact from a weakened Isaias, which is currently a 70 mph tropical storm off the coast of Florida. We have waited until now to make our first call first because there is significant uncertainty about the details of the impact. In this first call forecast, we will outline where we stand currently, the possible scenarios, and our current forecast.
I am going to give it to you straight and let you know what I don't know. This is not likely to be the worst storm we've ever seen, but this is a storm to take seriously. Let's begin.
Currently, Tropical Storm Isaias is moving along the coast of Florida. It is moving slowly along a ridge of high pressure, which is steering it toward the coast. A weakness in that ridge is coming, as a deep trough over the US approaches. This ridge/trough interaction will force Isaias to turn northeast and toward the Carolina coast tomorrow. From there, it will begin to move rapidly up the east coast, as illustrated in the NHC track, on a heading to Connecticut. There is high confidence in a direct impact.
As a result, the odds of the state seeing tropical storm force winds have increased.
1) Final Track--As you will see above, even though CT is in the cone of uncertainty, the center can still go to our west or east. The way this storm will evolve will force the heaviest rain, but less wind, to the west of the center. The strongest winds and tornado threat, but less rain, will be to the east of the center. With CT in the middle ground, that creates a forecasting headache, and as we saw with Fay, just a few miles makes all the difference in impacts.
2) Intensity--Intensity is the thing that may keep me up. Although the NHC does not explicitly forecast additional strengthening, the potential is there for this to become a hurricane again. While it is disorganized now in the face of drier air and wind shear, it is holding its own and this may be the most hostile environment this storm will see over the next few days.
To be clear, it will weaken and it is highly unlikely to become a strong hurricane. There is not a lot of time over water left and as it makes landfall over the Carolina coast, this will begin to decay.
But if it is stronger than expected by that Carolina landfall, it will take longer to wind down and that means we could see bigger impacts here. Forecasting tropical cyclone intensity is one of the hardest fields in all of meteorology.
We do not need to panic or assume that a high end solution is coming, but we need to be prepared if this storm take advantage of an increasingly favorable development environment and arrives as a stronger tropical storm.
If you recall when I last wrote, I mentioned three possible scenarios. Now that there is high confidence in direct impacts we have honed in on the possible scenarios we think are viable.
Scenario 1: Weaker but closer to CT
Not much different than before. Under this scenario, the current National Hurricane Center forecast more or less pans out. Isaias weakens in the Carolinas and Mid-Atlantic as it is over land, but makes a direct landfall on CT or passes just to the west. This would bring the heavier rain over New York and maybe NW CT, but the rain would be less and more banded in nature. That would also bring stronger winds, especially along the coast, and a tornado threat. This would be an impactful event, especially in SE CT and places where rain bands set up. This is currently the favorite, but there is enough uncertainty to bring down the 65% odds it had before.
Chance of occurrence: 55%.
Scenario 2: Stronger but impacts extremely dependent on track
Under this scenario, Isaias is modestly stronger than anticipated after making a landfall in the Carolinas. Again, this could happen in two ways. First, the storm could intensify more than expected tonight and tomorrow, and ends up hitting land stronger. This would mean that the system takes longer to weaken. The second way would be that the system while over land is enhanced by the trough that it is interacting with. The truth is that the strongest scenario would require a little bit of both, with a track very close to the coast but just offshore.
The result here would likely mean that the system is further east, and brings more rainfall, but it also means that the wind threat would be higher, perhaps significantly so, for central and eastern Connecticut depending on the exact track. To the east of the center, a tornado threat would exist as well. There is additional forecast risk in this solution, though. Too far east, and this would become a rain threat almost exclusively. This is not the favored outcome currently, but a stronger system has a legitimate shot of happening due to the current development environment off the southeast coast and current mid-level center pulling the storm more northward in the short term.
Chance of occurrence: 45%
Alright, now that I have laid out where things stand and the possibilities, the actual forecast. The forecast below is a moderate confidence forecast, but keep in mind that depending on the track and intensity of Isaias this can change tomorrow to bring more impact or less.
- Tropical Storm Isaias becomes a hurricane tomorrow off the Carolina coast and make a landfall in between Georgetown, SC and Wilmington, NC.
- Isaias weakens while over land, but hugs the Mid-Atlantic coast on its approach toward Connecticut.
- Rainfall begins Tuesday morning and afternoon as the storm moves up the coast. The worst occurs during Tuesday afternoon and during the overnight period. The worst part will be closest to the center with most of the day having relatively lighter rain and winds while furthest away from the center.
- Tropical storm Isaias makes landfall along western/central Long Island and the southern Connecticut coastline on Tuesday night. It rapidly moves through the state.
- Tropical storm Isaias brings moderate impacts over Connecticut, with the highest impacts in SE CT.
- Rainfall: Rain will be banded, which means there will be different totals depending on location. Expect .5"-1.5" of rain in eastern CT, 1-2 inches in central CT, and 1-3 inches in western CT. Flash flooding and basement flooding will be possible.
- Wind: Expect the highest winds along the shoreline and in SE CT. In those areas, the highest wind gusts will be between 40-60 mph. This does not mean that everyone will see the highest end gusts. Most gusts are likely to remain in the 40-50 mph range. For inland CT, expect the highest wind gusts to be between 30-40 mph with isolated gusts that are a little higher in eastern CT.
- Tornadoes: Expect a low tornado risk across the state, but especially in eastern CT.
- Power Outages: Expect scattered power outages, with outages closest to the shoreline and in SE CT.
- Coastal Flooding: There may be some coastal flooding, but we are expecting relatively minor flooding. This could change as we get closer.
Overall, this first call forecast foresees a moderate impact event. The biggest threat is rainfall in western CT and power outages due to wind gusts in coastal and SE CT.
Again, this isn't the worst we've ever seen, but it is worthy of serious attention because of the current projected track and intensity on closest approach.
Stay tuned and remember preparation over panic. We will be back with a final forecast tomorrow.
Thank you for reading and trusting SCW.