(System was upgraded by NHC to Tropical Storm Alberto at 5PM EDT)
The NHC gives a 50% chance of tropical development to a low pressure center off the coast of the Carolinas this afternoon, which isn't exactly coming out of left field for us weather geeks. The models have been hinting for a few days at the possibility of some sort of low pressure forming off the coast, and over the last day or two they've shown the distinct possibility of tropical development.
A cold front swept southeastward across the Carolinas earlier in the week, spinning off a low pressure center in the Atlantic Ocean off the coast of South Carolina early yesterday morning. The low has been sitting there for the last day or so slowly gaining strength and organization, until it finally looked like this at 12:15PM EDT:
To me, it looks organized enough to be classified as Tropical Storm Alberto. It has a tight band of convection around the center of the storm, the satellite shows nice spiral banding of clouds around the center of the system, and the Wilmington NC radar is clocking velocities of about 50-55 MPH a few thousand feet off the surface of the ocean within the deepest convection. The storm's radar presentation is also impressive, showing an area of convection wrapped around the center of the storm (with an eye-like feature showing up):
The system is currently sitting in the Gulf Stream, which is probably why it's able to attain tropical characteristics as fast as it is. The models show the storm moving out of the Gulf Stream in a day or so, at which point it should rapidly weaken and fall apart. The image below is a "spaghetti plot" showing all the available model runs on the system. Save for an outlier or two, most of the tracks show a path away from the coast and out to sea.
Anyone living in the Carolinas should keep a close eye on this system. Regardless of development or motion, it's going to bring squally weather to the coastal regions, so even if it's not a named system, it'll be a nuisance for those who like sunny skies.
This system is unusual, but not completely unheard of. If the system does become Tropical Storm Alberto, it'll join 18 other storms in forming in the month of May. Most of the tropical systems that form early in the season (May/June) and late in the season (October/November) form as a result of decaying frontal systems which spin off low pressure systems, which then attain tropical characteristics.
From the NHC's climatology page, here are where all the tropical systems in the month of May have formed, the first image showing May 10-20, and the second image showing May 21-31. Note that they're always in the far western Atlantic, where old cold fronts usually trot out and die.
Is this a harbinger for the upcoming hurricane season? Probably not. Just as the October snowstorm in the northeast wasn't an omen for a terrible winter, this system likely means nothing in the long term. The much-respected forecasters at Colorado State University predict a below-average Atlantic hurricane season due to an El Niño pattern setting in. El Niño patters tend to increase convection in the Pacific, which creates prohibitive wind shear in the Atlantic Basin, slicing off the tall convection in any systems that try to generate.
If anything drastic happens here, I'll post another diary on the system. Otherwise, follow me on Facebook and on my new weather website State of the Skies for updates on this storm and other forecasts and tidbits of weather awesomeness. Yes, I'm not ashamed of the shameless plug.
(Oh, and this post was cross-posted to State of the Skies).
455PM EDT Update: The NHC has upgraded the system to Tropical Storm Alberto with 45 MPH winds. It's expected to drift southward and then race out to sea without much impact to land. However, given its proximity to the South Carolina coast, they say that a Tropical Storm Watch may be needed later on tonight.