The NHC is monitoring invest area 93L off the Carolina coast this weekend. The low pressure area spun up rather quickly in the wake of a larger storm system that has brought a lot of rain to the region over the last few days. Right now, the NHC is giving the system a 50% chance of becoming a tropical depression or even a tropical storm. Let’s take a look at a couple of things….
First, we do have a very well defined low pressure center at the surface. This is important because it’s the surface low that generates the deep convection – assuming that water temps and other atmospheric ingredients are in place. If the surface low were weak and poorly defined, then this would not warrant nearly the attention that it is currently getting.
Second, sea surface temps in the area (figure 1) are just warm enough to support the amount of energy needed to drive the deep thunderstorm activity, or convection, that is clearly seen on satellite and radar. We typically look for SSTs of around 80 degrees F or about 26 degrees C. The low is currently situated over just marginal temps to allow it to develop to the extent that it has. The question is: will it continue to thrive over the warm water or will the deep thunderstorms not be able to sustain themselves or even grow? This is part of what the NHC will be looking for when determining whether or not to name the feature a depression or a storm (if it is a storm, it would be Alberto).
The SHIPS intensity model, shown in figure 2, is definitely on board with this system becoming a tropical storm. Winds peak out at a healthy 54 knots which equates to about a 65 mph tropical storm. This may be a bit on the high side but a small system, such as 93L, can ramp up quickly given the right conditions. It can also fall apart just as fast if environmental conditions change, even a little. So far, there appear to be enough positive ingredients in place for 93L to have a chance of becoming a tropical storm before the weekend is out.
The steering mechanisms in place are weak for now which will likely mean a slow drift just off the South Carolina coast this weekend. Boating interests need to monitor the situation closely as local seas could get churned up with squally weather. It’s possible that 93L or what ever it eventually becomes, could reach the coast and bring rain and wind to the Carolinas. It will probably not be much more than an interesting topic of conversation and has no bearing on the rest of the up-coming hurricane season. These small low pressure areas are not too uncommon, especially this time of year. It does not mean the hurricane season will be more active than previously thought. The origins of this system are not from tropical sources such as a tropical wave coming from Africa. This is a left over piece of energy from a mid-latitude storm system that just happened to be in the right place at the right time.
I’ll post more about 93L tomorrow and will have short posts on our Facebook and Twitter pages.