Development of an Advance Research WRF-Based Operational Forecast System for Forcing Ocean Models and Evaluation of Its Winds Using Buoys in the Indian Ocean

This paper presents the development of a high-resolution mesoscale atmospheric numerical model Advanced Research version of WRF (ARW 3.7, henceforth ARW)-based operational forecast system and evaluation of its surface wind forecasts using buoys and satellite data in the Indian Ocean. This was set up as part of the ocean-state forecasting system to force the operational ocean models at the Indian National Centre for Ocean Information Services (INCOIS). Evaluation of winds is carried out by comparing the ARW forecasts with ocean buoys and scatterometer observations during 2016. The analysis is conducted separately with coastal and open ocean buoys, revealing marginally better performance in the open ocean simulations. The comparison of ARW forecasted winds against offshore buoy winds shows mean differences for wind speed and direction of- 0.1 m s-1 and- 3.3 degrees, with root-mean-square errors (RMSEs) of 2.1 m s-1 and 39.0 degrees degrees and correlations of 0.75 and 0.42, respectively. At coastal regimes, the mean differences for wind speed and direction are 0.6 m s-1 and 2.6 degrees, degrees, with RMSEs of 2.2 m s-1 and 57 degrees degrees and correlations of 0.63 and 0.60, respectively. The ARW model performs reasonably well compared to the National Centre for Medium-Range Weather Forecasting (NCMRWF) model in capturing wind speed variability in the Arabian Sea compared to the Bay of Bengal. Particularly during the Very Severe Cyclonic Storm (VSCS) Vardah, the ARW model provided more accurate forecasts (high skill score 80%-90%) compared to the NCMRWF model. These results indicate the efficacy fi cacy of the WRF-based forecast system in predicting surface wind fi elds in the Indian Ocean region, particularly in the coastal areas, thus endorsing its use for an effective operational ocean forecasting at INCOIS.