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August 2 – Isaias impact Tuesday night

Tropical Storm Isaias may briefly become a hurricane on Monday before making landfall late Monday along the South Carolina or North Carolina coast. It will be a tropical storm transitioning to a post-tropical cyclone when it passes by New England Tuesday night.

The storm will not to cause tremendous destruction in Southern New England. If it hangs together as it moves through the Mid-Atlantic it could bring a few inches of rain to western Connecticut, and isolated wind gusts over 50 mph to the coast of Southern New England. If it’s completely falling apart, then peak wind gusts will likely be in the 30-40 mph range causing little, if any, damage. A notable storm surge is unlikely. The center of the storm will likely be far enough west and passing by near low tide to limit the coastal flooding potential. Here are the impacts in a nutshell:

Rain potential

This is the Weather Prediction Center (NWS) forecast for rain in the next 5 days over Southern New England. Keep in mind, this includes the rain from any thunderstorms on Sunday. It’s possible western CT picks up more than 4″ of rain between the two events. Some river/stream flooding cannot be ruled out if there is more than 4″ rain in the next 72 hours.
I expect areas outside of western Connecticut to get less than 1″ of rain from Isaias. I think the rain forecast for eastern CT and RI is too high, and I expect 0.4-0.8″ from Isaias over RI. These areas will likely be on the drier and windier side of the storm as it passes by.

Wind Impact

Isaias will be carrying the stronger wind gusts on the east side of the storm. This projection from the American GFS model shows widespread peak gusts over 50 mph from eastern CT through RI and SE MA. These gusts may be 5-15 mph too strong if the storm really struggles as it moves north over the next 24 hours. If it’s a hurricane when it reaches the Carolina coast, there’s a good chance these peak gusts will be in the ballpark of what the storm brings to SNE. Notice the lower winds where the rain is expected to be heaviest.

Coastal Impacts

As mentioned above, the coastal impacts should be limited from this storm. It is not a huge storm, and it will be moving quickly when it races by. The passage of the storm’s center is not expected to coincide with high tide. It looks like a splashover to minor coastal flooding event for south facing shorelines.

Timing

Showers are possible ahead of the system on Tuesday, but I do not expect steady rain until Tuesday night – and that’s mainly along and west of the storm’s track. It will be showery throughout to the east of the storm track, which includes most of RI and all of SE MA. The heaviest rain in western CT is likely Tuesday night.

The strongest winds are likely from late Tuesday evening until before dawn on Wednesday.

The storm will be moving quickly, so you can expect dry skies by dawn on Wednesday. It will be partly sunny day with pop-up showers possible.

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Fred Campagna

President and Chief Meteorologist - Right Weather LLC AMS Certified Broadcast Meteorologist

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