Although numerous studies have demonstrated that increasing model spatial resolution in free forecasts can

potentially improve tropical cyclone (TC) intensity forecasts, studies on the impact of model resolution during data assimilation

(DA) on TC prediction are lacking. In this study, using the ensemble-variational DA system for the Hurricane

Weather Research and Forecasting (HWRF) Model, we investigated the individual impact of increasing the model resolution

of first guess (FG) and background ensemble (BE) forecasts during DA on initial analyses and subsequent forecasts

of Hurricane Patricia (2015). The impacts were compared between horizontal and vertical resolutions and also between the

tropical storm (TS) and hurricane assimilation during Patricia. The results show that increasing the horizontal or vertical

resolution in FG has a larger impact than increasing the resolution in BE on improving the analyzed TC intensity and

structure for the hurricane stage. The result is reversed for the TS stage. These results are attributed to the effectiveness of

increasing the FG resolution in intensifying the background vortex for the hurricane stage relative to the TS stage.

Increasing the BE resolution contributes to improving the analyzed intensity through the better-resolved background

correlation structure for both the hurricane and TS stages. Increasing horizontal resolution has an overall larger effect than

increasing vertical resolution in improving the analysis at the hurricane stage and their effects are close for the analysis at the

TS stage. Additionally, the more accurately analyzed primary circulation, secondary circulation, and warm-core structures

via the increased resolution in DA lead to improved TC intensity forecasts.