At this hour, Tropical Storm Isaias is gradually becoming better organized as it make its final approach toward the Carolina coast. Tonight it will make landfall and rapidly accelerate toward New England. Since last night, we have reviewed additional computer model data and the overall environment to provide you with this final call forecast. This is a moderate confidence forecast.
We believe that this will be a moderate to high impact event with a variety of hazards.
- The biggest hazard looks like a brief period of strong wind gusts that will pass through the state tomorrow afternoon or evening. This is likely to cause scattered to widespread power outages.
- For western and central Connecticut, heavy rain on the order of 1-3 inches brings the risk of flash flooding. This will not be a typical stratiform rain, but rather bands of rain that will have torrential downpours to get you to your total.
- For all of Connecticut, there is a tornado risk in the bands that will rotate over the state. Tropical systems are notorious for producing quick spin ups, and that is something to watch closely.
Below is our final call wind gust map. Note that not everyone will see the highest end of this range, or see this kind of wind at all times. In fact, most likely won't. We believe this is a reasonable forecast on what the strongest wind gusts will be.
Tomorrow we should begin to see some of the far flung rain bands move in during the morning hours. They may not amount to a whole lot for most, but strong winds and heavy rain are possible. There is a severe threat there as well with a quick spin up possible. The best chance of rain early on will be in western CT.
Over the course of the day, rain bands will increase in coverage, especially in western and central Connecticut. Less is expected in eastern CT, but even one or two bands could bring quick and significant rain.
The strongest wind is likely to occur during the afternoon, likely between 3pm and 10pm. The range is wide, but most will see their highest wind gusts in a 1-3 hour period during that time. The shoreline will see the strongest winds first and that will progress north. That is a fast moving storm, which helps reduce the possible damage to trees and power lines, but as you will see below, the winds are likely to pack a punch.
The heaviest rain and wind should depart during those overnight hours beginning in southern areas and heading north. Wednesday should be a fine day.
Wind & Power Outages
Although it is the fastest hitting impact, wind looks like the main show here. As mentioned earlier, most will only see 1-3 hours of the strongest gusts, though weaker (but still strong) gusts are likely through the day. Why are we looking at potentially damaging wind? As Isaias accelerates northeast, normally we would see a weakening storm. However, my second scenario from last night is playing out. This will not weaken much because of the interaction with the trough to the west. That interaction will enhance the rain to our west and the wind right over us. There are hurricane force winds just off the surface that are likely to be over us, but in order for big wind gusts, those winds need to "mix down". Today's guidance has shown an almost unanimous move toward better mixing to bring strong winds tomorrow. Not all of that wind aloft, but a lot of it.
As you saw in the graphic, we expect the following:
- Maximum wind gusts of 50-65 mph along the shoreline. There may be some isolated gusts above 65 mph. Widespread power outages are expected. Note that because of the ongoing pandemic, it may take longer for power to be restored.
- Maximum wind gusts of 40-55 mph for inland areas. There may be some isolated gusts above 55 mph. Scattered to widespread power outages are expected.
Tomorrow also has the possibility to be a severe weather day. The main hazard would be quick tornadoes that spin up along the bands that enter the state. Keep an eye to the radar tomorrow. The Storm Prediction Center has placed us in a slight risk category.
Rainfall & Flash Flooding
Rainfall looks like less of a threat with a slightly further west track, but the rain that falls will likely be heavy at times. The forecast from tomorrow still works, but I am upping the maximum rain potential for central Connecticut. Because of the quick rainfall threat, watch for basement flooding.
We expect the following:
- .50" to 1.5" of rain in eastern Connecticut. There is a low flash flooding risk.
- 1" to 3" of rain in central Connecticut. There is a moderate flash flooding risk which is dependent on the banding your location receives.
- 1" to 3" of rain in western Connecticut. There is a higher flash flooding risk here, especially in NW CT, because this location has the greatest chance of seeing the higher end of those rain totals.
We are not expecting significant coastal flooding, but residents in flood prone spots should definitely have heightened awareness.
This is likely to be a moderate to high impact event. We expect the strongest winds along the shoreline, but significant and potentially damaging winds are possible inland as well. This will be a fast mover.
This is not the worst storm we've ever seen, but this is something to take seriously. We will survive this. We will be fine. But let's make good decisions. Do not run your generator in your home or garage. Do not go near downed power lines. Stay away from rooms with large trees outside (especially near the shoreline). Try to stay off the roads during the worst of the weather, and if you have to drive, watch out for debris and falling tree branches.
We will be on tomorrow to provide continuous updates.
Thank you for reading and trusting SCW.