In the 25 years since the Hebert-Poteat technique for estimating the intensity of North Atlantic subtropical cyclones was developed, no known formal verification study has been conducted. This is likely due to the relatively infrequent occurrence of subtropical cyclones, lack of in-situ observations from the systems, and ambiguity regarding the definition of a subtropical cyclone. Nevertheless, subtropical cyclones are significant due to the facts that many eventually become tropical cyclones, present a hazard to shipping interests and, in some cases, threaten land areas. For example, Hurricane Karen in October 2001 evolved from a subtropical cyclone which affected Bermuda with near hurricane-force winds.

During the 2000 and 2001 hurricane seasons, nine subtropical cyclones were classified by the Tropical Prediction Center using the Hebert-Poteat satellite classification technique. This study will verify the Hebert-Poteat intensity estimates against ground-truth data from ships, buoys, and reconnaissance aircraft..