A very active week of weather ahead with a stalled frontal boundary helping to be the focal point of two distinct periods of heavy rainfall. The first round coming this evening as heavy rainfall begins to break out ahead of a low pressure system traveling along the frontal boundary. Tropical downpours look to break out around 6-7pm and continue through midnight, given the orientation of the frontal boundary and the overall set up, these storms will likely tend to be slow moving and redevelop or “train” over the same areas. Where this occurs and where tropical downpours are most persistent, flash flooding is possible. Rainfall in some locations may exceed 3”.
As of this morning the NAM model has the heaviest rain focused across parts of Orange and Rockland county. This is why flood watches are in effect for our southern most counties. Instability doesn’t look overly impressive so the threat for severe weather appears low and isolated. Please be aware of rapid water rises and localized flash flooding overnight, if you are in an area prone to flash flooding stay alert this evening. We will of course post radar updates as things begin to develop.
Wish we could say that’s it for the flooding potential, but the remnants of Debby look to also interact with a frontal boundary Fri/Sat. This will spread an additional round of heavy rainfall across the region. The biggest concern will be whether or not Debby’s rains will fall over areas impacted the most by tonight’s slow moving downpours as this could lead to more extensive flooding.
A look at the latest GFS and Euro model shows the axis of heavy rainfall across NW parts of the region. These two images above are showing total precipitation between now and Friday, most of the region sees anywhere from 2-6” of rain through this period. If we filter this out, we can isolate the Thur/Fri rainfall amounts below.
Now you can see the NW focus of the Debby rainfall, it has not been exceptional wet vs average across most of the region. With that said, flash flooding is still possible, as are sharp rises on creeks, rivers and streams. The details of where and if widespread flooding could occur is very much tied to where the heaviest rains fall tonight and again at the end of the week. As of now let’s get through tonight’s rainfall and then we will dive even deeper into the second wave. Best to be prepared for a very unsettled weeks of weather and stay tuned for the latest.