We will have to wait and see how the steering pattern in the atmosphere evolves before we know what will happen with what is probably going to be the first tropical storm of the season. Before we get in to that in more detail, let’s look at what we know for sure.
First of all, what does “91L” mean? This is the designation given to a system that is in the development stage. The numbers 90-99 plus the letter “L” for Atlantic are used to signify an area of interest before it becomes a tropical depression or stronger. It helps with computer models, recon, satellite assets, etc. Once we get to 99L, we start over with 90L and so on. Got it? Ok, let’s move on.
As of early this afternoon, 91L continues to deal with some dry air to the north that is limiting its ability to push up deep, tropical thunderstorms. The process of convection is what helps to lower the air pressure and start the chain reaction going to spin up a tropical cyclone. The NHC mentions that it may not be until Wednesday before conditions truly allow for development.
So far, the weak low has moved southward to about the latitude of Jacksonville, Florida. We may see it begin to push westward some early in the week before it turns north again ahead of an approaching trough in the atmosphere. This trough is the key to where what will probably be TS Arthur ends up.
To put it in simple terms, if the trough is not fast enough or strong enough, then the would-be storm could track more north than east. This would mean a track closer to the North Carolina coast later this week. It is also possible that the trough swings by and misses the system completely- not likely, but not impossible.
The latest computer guidance suggests that the pattern will be just right to kick the system out to the northeast enough to keep it away from the coast, minimizing impacts to places like the Outer Banks. However, we are talking about four to five days or more in to the future and even the slightest changes in the pattern could lead to some serious forecast challenges.
What about intensity? This is almost impossible to speculate on right now. We do not even have a tropical depression yet so I do not feel comfortable pretending to know how strong this system could get. The obvious signs are there: warm water, more favorable conditions, etc. but this tells me nothing about how well organized the storm would be later in the week. Let’s wait for it to develop and go from there. I think we all know by now how tough intensity forecasting is, no need to spend time worrying about that at this point in time.
I realize that this potential threat comes at perhaps the most critical time of the year for beach interests. Hard to believe we’re looking at a possible tropical storm threat for the Fourth of July along the Southeast coast. For this reason, I think it is especially important to be aware of the impacts that this system will bring. A lot of people will be heading to the beach in the coming days from the Carolinas to Georgia, Florida and on up the rest of the East Coast. Even the lesser-talked about impacts such as rip currents and ocean swells need to be addressed. Careful explanation of the hazards is important so that people are not afraid to keep their plans but are aware of things such as rip currents or large, breaking waves.
I will keep posting updates here at least once per day. I’ll also have frequent posts on Twitter and our Facebook page. Social media is a great tool to utilize for weather information. This blog, as well as Twitter and FB posts, all feed in to our iOS/Android app, Hurricane Impact. I also add a daily, detailed video discussion exclusive to the app. It’s a great way to stay connected even if you’re on the go. Search Hurricane Impact in the App Store or on Google Play. I’ll have more here tomorrow morning around 9am ET.
M. Sudduth 1:40 PM ET June 29