Rapid Intensification as Seen in the WRF-JONR Hurricane Nature Runs

Abstract:

Two numerical simulations that depict the entire life cycles of Atlantic hurricanes were recently developed and produced for use as "nature runs" in observing system simulation experiments. These hurricanes are down-scaled, high-resolution depictions of Atlantic cyclones simulated in the global nature run previously produced by ECMWF. By comparions to composited observations, the structural evolutions of the simulated storms were shown to be quite realistic. Both cases have periods of rapid intensification (RI), which is typically defined as 30 knots of surface wind speed increase in a 24 hour period. However, the modes of RI are quite different: RI in the first storm (NRH1) occurs over the open ocean after a significant decrease in wind shear, while RI in the second storm (NRH2) occurs after it moves off of Cuba and into the Florida Straits. This study will compare and contrast these two modes of RI to each other and to available observations from real hurricanes. During RI, NRH1 has a series of convective bursts that lead to a brief period of "overshooting tops" on the inside edge of the eyewall. The RI of NRH2 is much more asymmetric, with mesovortices generated on the downshear-leftquadrant of the eyewall that spiral into the center. The relative roles of diabatic heating and surface friction to intensification and contraction of the inner-core wind fields will also be discussed.