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An Early Start to the Season?

MAY 9 2007 - 1008AM EDT UPDATE: Get Bryan's update to this developing storm on the front page at

8PM EDT UPDATE: I was just looking at some observations from a buoy that is located about 180 miles east of Cape Hatteras, North Carolina. Winds at this buoy have been above tropical storm strength (>39 mph) throughout the day.

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).

Posted by Adam Moyer | Permalink