From concentric eyewall to annular hurricane: A numerical study with the cloud-resolved WRF model

Observations show that concentric eyewalls may lead to the formation of an annular hurricane (AH), but available radar and satellite images provide very limited information. By using the cloud-resolved Weather Research and Forecasting (WRF) model, the transformation from a nonAH to an AH through a concentric eyewall replacement cycle is simulated under a resting environment. The simulated hurricane experiences three distinct stages: the formation of a secondary eyewall, the eyewall replacement and the formation of an AH. The simulated eyewall succession and accompanying intensity change are qualitatively consistent with observations. The bottom-up mixing of the elevated PV in the concentric eyewalls leads to the formation of an AH. The time of the transition from concentric eyewalls to the AH is less than 24 hours, suggesting that the concentric eyewall replacement is an efficient route to AH formation. The results demonstrate potential capability of the WRF model to predict concentric eyewall cycles, the formation of AHs and associated intensity changes.