Abstract
The national numerical weather prediction system of Vietnam is presented and evaluated. The system is based on three main models, namely, the Japanese Global Spectral Model, the US Global Forecast System, and the US Weather Research and Forecasting (WRF) model. The global forecast products have been received at 0.25- and 0.5-degree horizontal resolution, respectively, and the WRF model has been run locally with 16 km horizontal resolution at the National Center for Hydro-Meteorological Forecasting using lateral conditions from GSM and GFS. The model performance is evaluated by comparing model output against observations of precipitation, wind speed, and temperature at 168 weather stations, with daily data from 2010 to 2014. In general, the global models provide more accurate forecasts than the regional models, probably due to the low horizontal resolution in the regional model. Also, the model performance is poorer for stations with altitudes greater than 500 meters above sea level (masl). For tropical cyclone performance validations, the maximum wind surface forecast from global and regional models is also verified against the best track of Joint Typhoon Warning Center. Finally, the model forecast skill during a recent extreme rain event in northeast Vietnam is evaluated.
Highlights
Vietnam stretches over 15-degree latitude and has a seasonal and relatively predictable weather
The results showed that, for the Southeast Asia region, the root mean square error (RMSE) of Global Forecast System (GFS) is 5–10 mm/day for 24-hour forecast range and large RMSE values were found over the coastal areas of the center and the south of Vietnam: Indonesia and the Philippines
The system is based on available data from two global models (GFS and Global Spectral Model (GSM)) as well as a regional model (WRF) which is run locally with 16 km resolution
Summary
Vietnam stretches over 15-degree latitude and has a seasonal and relatively predictable weather. During the winter or dry season, extending roughly from November to April, the monsoon winds usually blow from the northeast along the China coast and across the Gulf of Tonkin, picking up considerable moisture; the winter season in most parts of the country is dry only by comparison with the rainy or summer season [2]. About 80–90 percent of the precipitation is related to the southwesterly summer monsoon, tropical cyclones from the East Sea of Vietnam, and other tropical disturbances. Seasonal divisions are more clearly marked in the northern half than in the southern half of the country, where, except in some of the highlands, seasonal temperatures vary only by a few degrees, usually in the 21∘C– 28∘C range
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