Published: May 9,2015
Highlights
- Ana transitioned from a subtropical storm to a tropical storm on Saturday morning. It's the first named storm of the 2015 Atlantic hurricane season.
- A tropical storm warning has been posted from South Santee River, South Carolina, to Cape Lookout, North Carolina.
- A tropical storm watch is in effect south of the warning from south of South Santee River to Edisto Beach, South Carolina.
- The center of Tropical Storm Ana is meandering about 115 miles south-southeast of Myrtle Beach, South Carolina.
- Bands of rain continue to wrap into parts of the eastern Carolinas.
- A slow crawl toward the coastal Carolinas is likely into the weekend where the most direct impacts are expected (bands of locally heavy rain, some strong wind gusts, minor coastal flooding and isolated beach erosion).
- High surf, rip currents possible along parts of Florida's Atlantic beaches and the Georgia coast.
Latest Status
Infrared Satellite: Tropical Storm Ana
Current Watches/Warnings
Projected Path
The Latest
Ana originally formed as a subtropical storm off the coast of the Carolinas late Thursday night. For more on what a "subtropical" cyclone is, scroll down the page a bit.Early Saturday morning, the National Hurricane Center said that Ana had made a complete transition from a subtropical storm to a full tropical storm. This was based on the fact that shower and thunderstorm activity was now more collocated with the center of circulation, which is a characteristic of tropical storms.
Though the center of Ana has been well offshore, bands of rain from the storm have been wrapping into the coastal Carolinas since Thursday.
(INTERACTIVE: Coastal Carolinas Radar Loop)
Winds have gusted up to 30 mph or higher since Thursday in Wilmington, North Carolina, and a few coastal Carolina locations have seen gusts over 20 mph. A wind gust to 56 mph was reported at a buoy off the coast of southern North Carolina early Saturday.
Where's Ana Headed?
Ana's center of circulation is expected to drift toward the northwest, finally crossing the coast near the North Carolina and South Carolina border on Sunday.The reason for this slow forward speed is the steering flow in the upper atmosphere will be very weak through early Monday. The northern, or polar jet stream will remain far to the north, while any upper-level high pressure will remain rather weak and centered far to the east.
Bands of rain and some strong wind gusts will pester parts of the Carolinas through the weekend.
Ana's landfall won't be that noteworthy Sunday, compared to a hurricane landfall with intense eyewall winds and storm surge.
While slowly weakening after landfall later Sunday into Monday, onshore gusty winds will continue along the southern coast of North Carolina, spreading northward into the Outer Banks and Virginia Tidewater Monday.
By Monday night, a southward dip in the polar jet stream will catch hold of what's left of Ana and finally whisk it away into the Atlantic.
Incidentally, Ana has become the earliest subtropical or tropical cyclone to produce direct effects in the United States (excluding a tropical storm that made landfall in Florida on Groundhog Day in 1952), according to Stu Ostro.
Rainfall Potential
Potential Impacts
Rain/flood threat: Bands of rain continue to move into parts of eastern Carolinas. Areas of rain may linger in the eastern Carolinas through Monday, eventually spreading into parts of Virginia through Monday. The greatest potential for locally heavy rain and flash flooding is in far eastern North Carolina and northeast South Carolina.
- Winds: Gusty winds pick up in coastal North Carolina (especially south of Hatteras) and coastal South Carolina Saturday, continuing Sunday, before spreading from coastal North Carolina to southeast Virginia Monday. Some gusts over 40 mph are likely, at times beginning later Saturday. Some downed tree limbs and sporadic power outages are possible, but the threat of widespread damaging winds and numerous power outages appears low.
- High Surf/Rip Currents/Coastal flooding: High surf, rip currents, some coastal flooding and beach erosion from the northern South Carolina coast to the southern North Carolina coast (Hatteras south) continues possibly through Monday, particularly in areas where onshore flow persists the longest (southern North Carolina coast). The combination of storm surge plus normal tides may lead to water levels 1-2 feet above ground near high tide from the southern Outer Banks to South Carolina. High surf, rip currents may also persist along parts of the Georgia and northeast Florida coasts the next day or so.
(FORECASTS: Myrtle Beach | Charleston | Wilmington | Hatteras)
If you have plans or live in the coastal Carolinas, keep checking back with us at weather.com and The Weather Channel for the latest.
Water
vapor satellite image of Subtropical Storm Andrea in early May 2007.
Green shading generally corresponds to areas of convection, with
Andrea's center of circulation located in the gray hole surrounded in
some distance, by the convection.Tropical or Not?
The low started out not as a typical low-pressure system with fronts you may see over, say, the Plains states. Nor was it a tropical depression or storm like you see in the Atlantic or Pacific Oceans in summer. It was a combination of those, called a subtropical cyclone.Our friends at Weather Underground have a full explanation of subtropical cyclones. Basically, a subtropical depression or storm exhibits features of both tropical and non-tropical systems, with a broad wind field, no cold or warm fronts, and generally low-topped thunderstorms spaced some distance from the center.
Subtropical cyclones typically are associated with upper-level lows and have colder temperatures aloft, whereas tropical cyclones are fully warm-core, and upper-level high-pressure systems overhead help facilitate their intensification.
Because of this hybrid nature, the National Hurricane Center still issues advisories and forecasts (i.e. projected path) for subtropical depressions and storms and assigns a number or name much like a regular tropical depression or tropical storm.
Occasionally, if thunderstorms cluster close enough and persist near the center, latent heat given off aloft from the thunderstorms can warm the air enough to make the storm a fully tropical storm. As mentioned before, this is the case with Ana.
When that happens, the wind field will tighten closer to the center. Of course, this would also open the door to further intensification.
It's Happened Recently
Some recent Atlantic hurricane seasons have jumped the June 1 starting gun.(MORE: When Hurricane Season Starts Early)
Most recently, in May 2012, a pair of tropical storms, Alberto and Beryl, both formed off the coast of the Carolinas, Georgia and north Florida.
Beryl washed out the Memorial Day weekend, and was the strongest tropical cyclone to make a U.S. landfall before June 1 on record, with 70 mph maximum sustained winds.
In fact, Beryl made the transition from a subtropical to tropical storm prior to landfall, exhibiting an eye and eyewall on radar, according to Ostro.
Five years earlier, a cut-off low-pressure system off the Southeast coast morphed into Subtropical Storm Andrea. Before officially gaining the subtropical designation, the wrapped-up low was responsible for a 2-3 foot storm surge in St. Johns and Flagler Counties in Florida. A surfer and four crew members of a sailing vessel lost their lives in high surf from Andrea.
There was even an Atlantic tropical storm in late April 2003, ironically also named Ana.
Since 1950, eight subtropical depressions or storms have formed before May 7th, according to Dr. Matt Sitkowski, science and weather content coordinator.
In all, there have been 39 Atlantic tropical or subtropical cyclones that have formed before June 1 since 1851, according to hurricane specialist Michael Lowry. Thus, you can expect one of these pre-June 1 systems once every four years, or so, on average.
More importantly, there's no link between an early start and an active season. Lowry says only 38 percent of early-starting Atlantic hurricane seasons ended up with above-average numbers of named storms.
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