WASHINGTON - Summer may be behind us, but it is autumn that can sometimes bring the worst that hurricane season has to offer. Before Gabrielle became just the second hurricane of the season last week, we had nearly three weeks of no activity at all during the very peak of the season. All indications are that September will not close as quietly as it started though, with Humberto being named on Wednesday, and Imelda likely to be named in the days ahead.
Current storms
What we know:
As of 8 p. m. Thursday, there is currently only one storm named in the Atlantic. Humberto, which is a strengthening tropical storm in the southwestern Atlantic Ocean. Humberto is forecast to become the season’s next major hurricane by the weekend, with the National Hurricane Center (NHC) forecasting it to become at least a Category 3 storm with winds of 120 mph by Sunday.
The other hurricane that was in the northern Atlantic much of this week, Gabrielle, was officially downgraded to post-tropical cyclone status this afternoon. Her remnants are forecast to impact parts of Portugal and Spain this weekend.
Potential Imelda
Why you should care:
What is making headlines is not so much Humberto though, but another area of thunderstorm activity centered near Hispaniola. This cluster of storms likely has the potential — up to 90% in the latest update from the NHC as of Thursday evening — to become the next named system. The strength of the system and exactly how it could track are up for some major debate though. The vast majority of computer guidance out there does take the system northward through the Bahamas over the next couple of days, when it begins to strengthen. It is beyond that point where models really start to diverge.
Landfall or no landfall?
It is almost funny how models seem to have a "fork in the road" type of scenario setting up with the system, which will be named Imelda if it gets strong enough to get a name. How intense the system gets (models range from just a tropical storm to a strong hurricane) and how fast its forward speed is will be absolutely key to whether or not the system takes the route that pulls it into the southeastern United States, or if it takes a turn to the left.
The key to whether or not we will see a United States impact or not depends not just on the likely Imelda, but also, and almost equally key will be what her neighbor, Humberto does...
Fujiwhara Effect: Dance of hurricanes
So how would one hurricane effect the track of another storm? Well, it is due to something known as the Fujiwhara Effect, essentially how the strength of one zone of low pressure can influence the track of another.
Essentially, if the storm that will likely become Imelda stays weaker than Humberto, and the centers of the two storms come within a relatively close proximity to one another (~1,200 miles), the strength of the wind field and the twisting of the atmosphere (vorticity) around Humberto will start to influence the track of the weaker system, in this case what would be Imelda. So Humberto could in a way "tug" at the weaker storm, and effectively pull it to the east as Humberto pulls away.
The issue with this is it is all about timing, positioning, speed, and strength of both systems...not just one. You can see the image above how chaotic the appropriately named spaghetti model plot, you can see how chaotic it looks. The more things that need to happen for a certain scenario to come true, the more weather computer models are going to struggle with its outcome. It is a chaotic dance between two storms, and that makes the forecast an extremely low confidence one for the next several days. At least until the cluster of thunderstorms has organized enough to actually become Imelda, and that may not happen until Sunday.
How could these storms affect DC?
Local perspective:
So of course impacts on our immediate area will heavily dependent on the final track of the storm. If Humberto is a little weaker, and takes a more easterly track through the Atlantic while Imelda picks up speed and pushes into the Carolinas, rainfall from the system could reach the DC region by as early as Monday night. Rainfall would likely be heavy in some areas, though the truth is much of our region could benefit from rainfall it would bring. Since this scenario would keep the storm’s center well to the south of DC, our region likely would not have to worry about much impact from severe weather or wind.
Should Humberto be stronger, take a more westerly track, and start to influence a slower moving Imelda, it would likely pull the center of the storm westward so that it stays off the coastline. Both systems working together would likely pull down some much heavier, drier air from the north, and it’s very possible that the DC area could get through with absolutely no impacts at all, while the beaches get high surf and rip currents.
This is a forecast where so many factors are going into it that it absolutely could change on a dime. The FOX 5 Weather Team will be watching this system closely in the days ahead, and keep you updated on any changes as the picture becomes clearer.
The Source: Information in this story is from the National Hurricane Center.