Five levels, which were low level, center point, upper level and two axillar points, were considered for each of the factors.
The low level center became exposed for a time, though gales continued.
A low level center began to form as the area moved northwest of Guam.
Strongly sheared tropical cyclones weaken as the upper circulation is blown away from the low level center.
A low level center of circulation developed from a tropical disturbance spawned by this tropical wave midway between the African coast and the Caribbean on September 20.
While most of the mid to upper level moisture associated with the storm got pulled inland by a shortwave trough, the low level center dissipated in the northern Gulf on August 27.
Thunderstorm activity concentrated near its low level center, and the system rapidly moved through the tropical depression stage into the tropical storm stage on August 26, developing an elliptical eye.
A strong and long lived tropical cyclone for December, the initial low level center for the system formed southwest of Ponape on December 4. By December 7, it had moved southwest of Truk without further development.
The system lingered for two days, lacking an organized low level center of circulation until early on the morning of August 21, when advisories were initiated on the tropical depression, 185 miles (298 km) east of Brownsville, Texas.
Hernan turned more to the west as its low level center became separated from its thunderstorm activity and was steering by a surface high-pressure system to its north.
An area of strong thunderstorms formed east of Abby, developing a low level center on August 12 on the western side of the thunderstorm activity, due to westerly vertical wind shear from nearby Abby.
