Sep 25th: Watching 94L for Potential US Impacts

All of a sudden, the Atlantic Basin is busier than its been all season, with three separate systems being monitored: 

Gabrielle will bring hurricane conditions to the Azores tonight through Early Friday and isn't a worry for anyone in the US. Humberto and 94L are what we need to discuss, especially since Humberto could play a role in both the track and intensity of 94L.

Yesterday, 94L maintained good convection, bringing squally weather to the Virgin Islands and Puerto Rico. Our station on the British Virgin Islands had nearly 3" of rain and a wind gust to 45 mph:

While models started to trend to a US landfall overnight, this is by no means a slam dunk forecast. First of all let's look at the deterministic (operational) runs of our two main global models, the GFS and Euro. Both of these models are in good agreement that a landfall somewhere along the southeast coast is likely early next week. 

Below are the Euro model trends the last 5 runs valid 8 am on Monday. You can see that the model is locking in on a storm just off the South Carolina coast. 

Similarly, the last few runs of the GFS have shown the same thing:

Both models are now in really good agreement that landfall will occur somewhere along the South Carolina to North Carolina coast late Monday or early Tuesday:

This is far from a decided solution however. There are still ensemble members of both the GFS, Euro, and Google AI that turn potential Imelda out to sea due to interaction between the trough over the Southeast US and Humberto:

The intensity forecasts also have uncertainty due to Humberto's proximity but most models bring 94L at least to tropical storm strength if not a hurricane:

It is forecast to track over the warm waters of the Bahamas and there should be little shear over it:

We know what most people want is to talk impacts and we can generally discuss what we think will happen at this point. Remember, there are large errors in forecasts when a system hasn't developed yet but we are now less than 5 days away so we feel comfortable talking a little about potential impacts.

1. Wind impacts: Residents along the Southeast coast should prepare for the possibility of strong gusty winds as early as Monday afternoon. Right now that would mean 60+ mph winds near where the system makes landfall:
   
   
2.  Rain impacts: We mentioned in yesterday's blog post about how regardless of a landfalling system, moisture will be transported into the Southeast between the upper low and the tropical systems. Rain totals through Sunday night before the tropical system even arrives will likely been the 2-3" rain across the Carolinas. The region has been dry lately, but have a wet ground right before a tropical system is never good:
   
3. Surge and Wave Impacts: Exact amounts aren't available yet, but the highest surge values will be north and east of where the storm makes landfall. Waves and rip current risk will also be elevated, especially with the addition of Humberto just to the east. Waves could reach over 20 - 25 ft:
   
   The bottom line is that residents of the NE Florida, Georgia, and Carolina coasts should be paying close attention to this storm. We will be posting regular updates.