Sensitivity of Numerical Simulations of Hurricane Joaquin (2015) to Cumulus Parameterization Schemes: Implications for the Process Controlling Hairpin Turn in the Track

A notable hurricane, Joaquin, in 2015 is studied with emphasis to its unique hairpin turn that it underwent between 2100 1 Oct – 0600 2 Oct. A series of high-resolution mesoscale numerical simulations are performed with an advanced research version of the Weather Research and Forecasting (WRF-ARW) model. Specifically, since there is considerable uncertainty in the Hurricane Joaquin NWP track forecast, five groups of sensitivity experiments with different cumulus, boundary layer and microphysical schemes, as well as different initial and boundary conditions and initial times in WRF simulations, are performed to investigate the large-scale environment and hurricane inner-core structures related to the best-track simulation of Joaquin. It is found that the track of Hurricane Joaquin is highly sensitive to the use of cumulus schemes. Further diagnosis found that the middle- and upper-level steering flows and the thermal structure of the hurricane core region, including diabatic heating and azimuthally averaged vertical velocity and relative humidity, are crucial for track and intensity forecasts. Finally, we performed various simulations in which the vertical levels of the KF scheme are increased. We found that, while not substantial, increasing the vertical levels within the KF scheme from 37 to 62 levels reduced track error by approximately 12 km during the hairpin turn of Joaquin.