A modified version of the Holland (1980) gradient wind model for tropical cyclones is presented. This model includes quadrant dependent asymmetry factors for the inner core region of the hurricane as well as the first order asymmetry introduced by translation. Scalar winds calculated above the Marine Boundary Layer (MBL) across a node-centered, motion-oriented grid are adjusted to surface values through application of a transfer coefficient representative of the MBL.
Operationally, the model input parameters are prepared as a forecast track is constructed using the Hurricane Forecasting Interface (HURR). The forecaster interactively executes the model and displays the isotachs at one or more nodes along the track. The primary use of the model is to provide guidance for open ocean wind and wave forecasting in the absence of data observations and real-time, mesoscale model output. In this context, comparisons with Erika (1997) and a re-developed Danny (1997) are presented.