Tropical Storm Watches Issued for SC Coast

5/19/2012 tropics No Comments

Here's a quick update on Tropical Storm Alberto, which has 50 MPH winds and is slowly drifting off towards the southwest. In about a day or so, a ridge is expected to break and allow the system to move off towards the northeast. However, there is uncertainty in the models and the NHC is making their best guess based on what the most reliable models are saying.

Due to the storm's proximity to the coast and the uncertainty in the track, the NHC has issued a Tropical Storm Watch for the South Carolina coast from the Savannah River northward to the South Santee River. A Tropical Storm Watch means that tropical storm force winds (40-73 MPH) are possible within the next 24-36 hours.

I'll post another update late tomorrow morning or early tomorrow afternoon. If you live on the South Carolina or North Carolina coast, keep an eye on this system.

You can find more information at the National Hurricane Center's website and NWS Charleston's website.

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Tropical Storm Alberto Forms Off SC Coast

5/19/2012 tropics No Comments

Just as I predicted, the first storm of the 2012 Atlantic Hurricane Season, and only the 19th storm ever to form in the month of May, the NHC has declared the low pressure center off the SC coast Tropical Storm Alberto as of 5PM EDT.

The storm has 45 MPH winds and is centered about 145 miles ESE of Charleston SC. The storm is expected to drift southward over the next day or so, then shoot out to sea as it gets picked up by another system. The NHC says that a Tropical Storm Watch may be needed for coastal South Carolina later on tonight.

Here's a satellite view of the storm as of 431PM EDT:

And here's a radar view of the storm from about 445PM EDT from the Wilmington NC radar site:

I'll post an update on the storm later tonight if a watch is issued. Stay tuned to tropical weather using the National Hurricane Center's website.

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Possible Tropical Development off Carolina Coast

5/19/2012 tropics No Comments

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.

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