Back on Friday night and Saturday morning, a low pressure swirl off the coast of our state broke away from a larger low along a frontal boundary and began drifting southward, undergoing a transition that left it in the form of a Tropical Storm by Saturday evening. It was the first named storm of the 2012 season, and of course, ended up forming around a week and a half prior to the official start of the season on June 1st. While about 97% of Atlantic tropical cyclones form between June 1st and November 30th, we do occasionally have early or late storms, with May by far the most likely month for one of those "rogues" to develop.
This time around, Alberto has proven to be a shallow, very small and generally weak tropical storm, and by all indications at this point will apparently have little or no impact on our state beyond perhaps a small increase in surf levels and rip current risk as it moves by well offshore on Tuesday. Many of you may remember the last Alberto, though, which had a much more direct impact on our viewing area. That was a Tropical Storm that formed between the Yucatan Peninsula and western Cuba in June of 2006, moved ashore in northwest Florida and then drifted north through Georgia and South Carolina as it gradually weakened to Tropical Depression status.
As it moved into our stat, there was a stationary frontal boundary in place over North Carolina that helped to focus and enhance rainfall from the system in a band that stretched northeastward from the southern Sandhills up into the northern Coastal Plain. As seen in the map here (produced by the Raleigh NWS office), a sizable swath saw 2-8 inches of rain, and in the Triangle area we generally got 5-8 inches in a fairly short span of time. The result was not only a new daily record rainfall total of 5.2 inches at RDU, but enough rain in a short time to prompt 45 flash flood warnings across the area, and in Wake County alone there were 47 water rescues carried out. If you're interested in more details about that system, there is a nice NWS case study online and I've included a link to that site.
Despite the impacts of that last Alberto, it did not rise to the level of those storms that have their name retired by the World Meteorological Organization, so the 6-year rotation remains in effect, and barring any very unexpected changes in this year's storm of the same name in the next couple of days, we will have another Alberto sometime, somewhere when 2018 rolls around.