Extended Abstract (696K)3C.2
Intensity change and eyewall replacement in Hurricane Floyd (1999)
Joseph E. Tenerelli, RSMAS/University of Miami, Miami, FL; and S. S. Chen
Over the last a few decades hurricane track forecasts have improved significantly, whereas relatively little progress made in hurricane intensity forecasts. The lack of skill in the intensity forecasting may be attributed to insufficient spatial resolution to resolve the hurricane inner-core structure and inadequate representation of physical processes in hurricane prediction models. Though axisymmetric models can resolve the inner-core of the hurricane vortex, they cannot explicitly treat the effects of asymmetries on hurricane intensity. It is observed that hurricane intensity changes are often associated with eyewall contraction and replacement. However, the mechanisms responsible for the development of secondary wind maxima and eyewall replacement processes are not well understood. Here we examine simulations of Hurricane Floyd (1999) using a nonhydrostatic full physics model that explicitly resolves the dynamics and microphysics near the vortex center through use of a 1.67 km mesh that follows the vortex. We show that the model is able to reproduce observed storm structure and evolution, including track, intensity, and the spatial pattern of precipitation. Additionally, the model produces a contracting ring of high reflectivity and corresponding maximum in the swirling wind profile outside of the innermost eyewall, similar to what is observed in the aircraft flight-level data. As observed, the innermost eyewall in the model dissipates over the period of several hours and is replaced by a single ring of high wind speed and rain rate at a radius larger than that of the original eyewall. Focusing on this concentric eyewall structure, we examine the evolution of the horizontal structure of the storm's wind and precipitation fields in relation to the evolution of its intensity, and we perform several sensitivity experiments in order to isolate physical mechanisms responsible for the secondary maxima in rain rate and swirling wind speed.
Session 3C, Tropical Cyclone Intensity Change II (Parallel with Sessions 3A, 3B, & 3D)
Monday, 29 April 2002, 4:00 PM-5:30 PM
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