Prediction of Intensity Changes Subsequent to Concentric Eyewall Events

Concentric eyewall events have been documented in intense tropical cyclones with increasing frequency in the last two decades. Advances in instrumentation on reconnaissance aircraft and polar-orbiting satellites have greatly increased the likelihood of detecting concentric eyewalls. During a concentric eyewall event, a secondary (outer) eyewall forms around the primary (inner) eyewall. Short-term forecasts of intensity for a tropical cyclone exhibiting concentric eyewalls often have low confidence since the resulting structural changes produce fluctuations in intensity. Although a tropical cyclone can intensify (sometimes rapidly) following concentric eyewall formation and dissipation, substantial weakening has also been observed. This paper will examine environmental influences on the structure and intensity of tropical cyclones following the formation of concentric eyewalls.

Concentric eyewall events are identified in the Atlantic and Eastern North Pacific basins during the period 1997-2012. Events are identified by analyzing passive microwave imagery from satellites. The intensity change subsequent to concentric eyewall formation (weakening, steady-state, or intensifying) is identified from the Best Track data. Environmental conditions in which each event occurred are analyzed. Variables of particular interest are sea surface temperature, oceanic heat content, vertical shear of the horizontal wind, outflow environment, mid-level relative humidity, and static stability. Environmental conditions are then compared for events with similar intensity changes to determine which factors appear to influence intensity after concentric eyewall formation.