The interesting thing to me though are the wave heights. Operationally, NHC warns of a 12-ft wave height radius for named systems, that is how far from the center of the storm does one find 12-ft high waves. Have a look below at the wave heights generated by this system. Pretty impressive.
Alas, looking at the latest model runs, this is most likely the height of the storm's intensity, so if NHC has not upgraded the system yet, it most likely will not. Still, this storm will be a significant rain/wind/surge event for the Southeast Coast, with hurricane force wind warnings posted off the South Carolina coast. If anything else happens with the storm, we'll try to get it posted here.
Wave height at buoy 41001 180 miles to the east of Cape Hatteras, NC. A strong low pressure system has formed off the East Coast of the United States (Figure 1). This system has developed central thunderstorm activity while remaining over the warmish waters of the Gulf Stream. Sea surface temperatures underneath the area of activity are below the usual threshold of 26C, however, upper level temperatures are cold enough that the storm could develop some tropical characteristics.
The forecast track moves it southwestward over the next few days. I'm showing the UKMET model here because it has been the most consistent and best forecast for this storm (Figure 2). To my eye, this looks like classical subtropical development.
Figure 1. Visible (top) and infrared (bottom) satellite images of the area of interest off the East Coast (Courtesy NHC).
Figure 2. Track forecast for the area of interest off the East Coast. The "C" indicates the current position of the low, the "A" indicates where the low originally formed, and the "Z" indicates the final position for the low. Sea-surface temperatures are underlayed on the figure. The color and placement of the circles shows the intensity and position forecasts respectively (Courtesy Bob Hart at Florida State). Shear values above the area of interest are quite low for this time of year (Figure 3), with values as low as 10 knots. If the convection continues to build, and this is a big if, it is possible that we will have our first named storm of the 2007 season in the second week of May.
I'm not sure whether NHC would name the storm as a subtropical storm (because the storm is still cold core at the upper levels) or as a tropical storm, but if it does get named, it will be christened Andrea.
Figure 3. Values of vertical wind shear across the Northwest Atlantic. The white circle encompasses the area of interest (Courtesy UW-CIMSS).
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ndMIAMI (AP) - The first named storm of the year formed Wednesday off the southeastern U.S. coast, more than three weeks before the official start of the Atlantic hurricane season, forecasters said.
Subtropical Storm Andrea had top sustained winds around 45 mph Wednesday morning and didn't appear to be much of a threat, the National Hurricane Center in Miami said. Still, a tropical storm watch was issued for parts of Georgia and Florida, meaning tropical storm conditions are possible within 36 hours.
"We're not looking at this system strengthening significantly," said Richard Pasch, a senior hurricane specialist at the center. "We're not viewing this as a major threat."
At 11 a.m. EDT, Andrea was centered about 140 miles southeast of Savannah, Ga., and about 150 miles northeast of Daytona Beach. The storm was moving west at about 3 mph.
Forecasters said no significant rain from the storm was expected to fall over land through at least Thursday morning. But wind-driven waves have been causing beach erosion in South Carolina, Georgia and Florida and the ocean has lapped at beachfront homes and condominiums.
Subtropical systems are hybrid weather formations that are usually weaker than hurricanes and tropical storms. They are kind of a half-breed, sharing characteristics of tropical systems, which get their power from warm ocean water at their centers, and more typical bad weather that forms when warm and cold fronts collide, Pasch said.
Forecasters said Andrea has the warm center characteristic of tropical storms but its core is not particularly well defined. In addition, its winds are farther out from the center than they would be in a tropical storm.
Typically about one subtropical storm forms each year, but they often turn into tropical storms. That doesn't appear to be the case with Andrea, senior hurricane specialist Jack Beven said. It only has a small area of warmer water to draw energy from and is also facing dry winds.
He said it wasn't unusual for the storm to form in May, outside the hurricane season that starts June 1 and end Nov. 30.
"What we call the hurricane season is a totally manmade creation. Nature doesn't always pay attention to that," Beven said.
Eighteen tropical storms and four hurricanes have been recorded in that month since 1851, and none of the hurricanes made landfall in the U.S. The earliest hurricane to strike the U.S. was Alma in northwest Florida on June 9, 1966.
Private and university forecasters have predicted that the 2007 season will be especially active, producing up to 17 tropical storms and hurricanes and a "well above average" possibility of at least one striking the U.S. The federal government plans to release its predictions May 22.
The Atlantic basin has been in a busy period for hurricanes since 1995. Some federal forecasters believe this is part of a natural cycle. But the Intergovernmental Panel on Climate Change, a U.N.-sponsored group, says global warming caused by humans has led to an increase in stronger hurricanes.
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