As expected, Tropical Storm Arthur will pass well south of New England early Saturday. Virtually no direct impacts from Arthur are expected here. The storm may even pass east of Cape Hatteras as it brushes by North Carolina later this week.
In terms of what we can expect here the much bigger story will be the possibility of strong thunderstorms on Thursday and possibly a period of flooding.
A combination of instability and increasing shear will promote vigorous thunderstorm development during the day Thursday. The strongest storms will be capable of producing strong winds, large hail, and a tornado, while quite unlikely, isn’t out of the realm of possibility.
When tropical storms are lurking to the south frequently a “Predecessor Rain Event” develops well to the north as some of the moisture interacts with the jet stream and a surface cold front. The thunderstorms on Thursday and Thursday night may congeal into a “PRE”. Because of that, there is a threat for flooding but confidence in timing and location is not high. Additionally, it has been quite dry lately and rivers are running low. This will mitigate the flood threat somewhat.
As Arthur pulls away rain will remain possible during the day on Friday not from the tropical storm but from the cold front responsible for Thursday’s storms. A sharpening jet streak (an area of strong winds way up in the jet stream) will put us in a spot that is favorable for lift. Upward vertical motion can be expected in the right entrance region of a jet streak and that will be over New England as Arthur passes to the east.
The good news is the weather looks fantastic for Saturday and Sunday as Arthur pulls away. The sinking air (subsidence) behind tropical systems can provide brilliant blue skies and pleasant dry air for the time of year. This appears to be the case for the weekend.
Bottom line – the weather is going to get pretty crummy here Thursday and Friday. Don’t blame Arthur though – he’s not at fault this time.