Tropical Storm Hermine continues to churn towards Florida this morning gaining strength as she goes. A Hurricane Warning is posted from Suwanne River to Mexico Beach as the storm is expected to become a Category 1 Hurricane before landfall.
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| NHC 8 AM Advisory/track/warnings for Hermine |
Heavy rain and storm surge will be the biggest threats to Florida. Thankfully Hermine is not as organized as she could be or else a much worse situation would be playing out in Florida. On the other hand the surge and heavy rain will both be on the east side of the system which is atypical. Usually we see heavy rain to the North and west of the center with wind and surge to the east.
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| NOAA GOES Tropical Storm Hermine Infrared rainbow satellite (NHC) |
The reason for the storm surge on the east side of the cyclone is thanks to the counter clockwise motion. The winds drive water on shore and it will be enhanced in this situation thanks to the geometry of the Bay. Those outer rain bands mean business. Here is the southeast regional radar loop.
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| NWS Southeast Regional Radar |
6-10 inches of rain is possible in portions of the Southeast and up into the Carolina's as Hermine makes her trek to the Northeast.
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| NOAA/NWS/NCEP/WPC 1-3 day rainfall forecast |
Now why would Hermine move to the northeast? Well the answer lies in our cold front and rain in Southern New England this morning. An upper level trough is tugging the storm northeast. Take a look at the 500 mb pattern. I've circled the upper trough and note the positive tilt.
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| 12z NAM 500 mb vort Thursday 2 PM (Image NCEP) |
A negative tilt would capture the storm and throw it west into the United States. As a result of this trough we are getting some beneficial rain in Southern New England today. Off and on showers will continue through the afternoon but the steady rain should be coming to an end by 2 PM. The storm is currently moving at 14 MPH and this will continue until Saturday night/Sunday AM when the storm will slow down. Why? Back to 500 mb
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| 12z NAM 500 mb vort 8 AM Sunday (image NCEP) |
The upper trough departs so the storm can't phase with it. At the same time a strong upper ridge develops north of the cyclones keeping it stalled in place. The strength and exact placement of this trough is TBD. That is hugely important because if the ridge is closer to New England the storm will stall south of us and we get no rain and wind and just elevated surf. The bigger impacts would be in the Mid Atlantic.
This is the most likely scenario is the storm stalls south and we get minimal moisture in SNE. That said there is still a chance the rain works into the region Sunday afternoon. Given that we are 72-84 hours out the exact details will have to be worked out. The surf will be elevated most of next week. Anytime you get a storm forecast to move this close it has to be monitored for little wobbles that could cause a lot of headaches.
Don't cancel any plans but think about having a back up in case this thing does move further north.
-Zack Green
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