Impact of the Low Wavenumber Structure in the Initial Vortex Wind Analyses on the Prediction of the Intensification of Hurricane Patricia (2015)

Abstract

AbstractEnsemble clustering analysis was performed to explore the role of the initial hurricane vortex‐scale wind structure in the prediction of the intensification of Hurricane Patricia (2015). Convection‐allowing ensemble forecasts were classified into spin‐down (SPD) and spin‐up (SPU) groups. Specifically, 10 members with an intensification rate >0 m/s and 10 members with an intensification rate <0 m/s for the first 6 hr were defined as the SPD and SPU members. The result showed that the tangential winds outside the inner‐core region in the SPD members were weaker compared to the SPU members. Additionally, the SPD members had a weaker inflow near the surface and a weaker outflow between the heights of 8 and 12 km than the SPU members. The SPU members showed more significant azimuthal asymmetry than the SPD members in the surface, tangential and radial winds. Wavenumber analysis showed that the low wavenumber components dominated the differences between the SPD and SPU members. Numerical experiments were conducted to test the hypothesis generated by the clustering analysis. It was found that the storm's maximum wind speed (MWS) intensified during the first 6 hr of the model forecast if only the low wavenumber structure in the SPU members was included in the initial conditions, whereas it decayed during the first 6 hr if only the low wavenumber structure in the SPD members was included. This result confirms that the low wavenumber structure of the initial wind analyses was important in predicting the intensity changes of Hurricane Patricia (2015).