Vortex Initialization in the NCEP Operational Hurricane Models

This paper describes the vortex initialization (VI) currently used in NCEP operational hurricane models (HWRF and HMON, and possibly HAFS in the future). The VI corrects the background fields for hurricane models: it consists of vortex relocation, and size and intensity corrections. The VI creates an improved background field for the data assimilation and thereby produces an improved analysis for the operational hurricane forecast. The background field after VI can be used as an initial field (as in the HMON model, without data assimilation) or a background field for data assimilation (as in HWRF model).

Satellite Microwave TC Warm-core Retrieval for a 4D-Var Vortex Initialization Using a Nonhydrostatic Axisymmetric Model with Convection Accounted for

<p>A recently further refined hurricane warm core retrieval algorithm is applied to the NOAA-20 and S-NPP Advance Microwave Temperature Sounder (ATMS), the Advanced Microwave Sounding Unit-A (AMSU-A) and the Fengyun-3D (FY-3D) microwave temperature sounding instrument (MWTS) brightness temperature observations within and around Hurricanes and incorporated into A four-dimensional variational (4D-Var) vortex initialization (VI) system is developed for a nonhydrostatic axisymmetric numerical model with convection accounted for (the RE87 model). It is shown that the temporal evolution of the ATMS and AMSU-A derived maximum warm core temperature anomalies follow more closely with that of the minimum mean sea level pressure and slightly less closely with the maximum sustained wind, and the radii of the ATMS derived warm cores at 4 and 6 K compared favorably with the 34 kt and 50 kt wind radii during the entire life span of Hurricane Irma in 2017. The vertical extend of the warm core toward the lower levels increases with increasing intensity when Irma experiences a strong intensification due to an enhanced latent heat release associated with diabatic processes. The multi-polar-orbiting operational meteorological satellites can well capture the TC inner cores’ diurnal cycle with a maximum around midnight. A model fit to satellite microwave retrievals of tropical cyclone (TC) warm-core temperatures from the above mentioned three polar-orbiting satellites and and total precipitable water (TPW) Global Change Observation Mission <sup> </sup>– Water Satellite 1 produced a significantly improved intensity forecast of Hurricane Florence (2018) and Typhoon Mangkhut (2018), with more realistic vertical structures of all model state variables (e.g., temperature, water vapor mixing ratio, liquid water content mixing ratio, tangential and radial wind components, and vertical velocity) are obtained when compared with a parallel run initialized simply by the European Centre for Medium-Range Weather Forecasts ERA5 reanalysis.</p>

A New Vortex Initialization Scheme Coupled with WRF-ARW

The ability of numerical simulations to predict typhoons has been improved in recent decades. Although the track prediction is satisfactory, the intensity prediction is still far from adequate. Vortex initialization is an efficient method to improve the estimations of the initial conditions for typhoon forecasting. In this paper, a new vortex initialization scheme is developed and evaluated. The scheme requires only observational data of the radius of maximum wind and the max wind speed in addition to the global analysis data. This scheme can also satisfy the vortex boundary conditions, which means that the vortex is continuously merged into the background environment. The scheme has a low computational cost and has the flexibility to adjust the vortex structure. It was evaluated with 3 metrics: track, center sea-level pressure (CSLP), and maximum surface wind speed (MWSP). Simulations were conducted using the WRF-ARW numerical weather prediction model. Super and severe typhoon cases with insufficiently strong initial MWSP were simulated without and with the vortex initialization scheme. The simulation results were compared with the 6-hourly observational data from Hong Kong Observatory (HKO). The vortex initialization scheme improved the intensity (CSLP and MWSP) prediction results. The scheme was also compared with other initialization methods and schemes.