Subseasonal Tropical Cyclone Prediction in the Navy Earth System Model

The Madden-Julian Oscillation (MJO) and El Niño Southern Oscillation (ENSO) are major sources of predictability for tropical cyclone (TC) formation and intensity at subseasonal time scales. In the Navy Earth System Model (NESM), the NAVy Global Environmental Model (NAVGEM) is coupled to the Global Ocean Forecast System (GOFS), which consists of the HYbrid Coordinate Ocean Model (HYCOM) and the Los Alamos Community Ice CodE (CICE). Reforecasts out to 45 d initialized 4x weekly from 1999-2015 were performed for the Subseasonal eXperiment (SubX). We examine the ability of the NESM and other models in the seasonal-to-subseasonal (S2S) database to predict variations in the TC environment and TC genesis and intensity at subseasonal time scales.

Wavenumber-frequency filtering is applied to forecasts and observations of fields relevant to TCs (e.g., shear, mid-level humidity, and low-level vorticity). Variations in mid-level humidity and low-level vorticity associated with the MJO are concentrated within the MJO convective envelope while shear variability is tied to the global wind response to the MJO. The ability of the NESM and other S2S models to predict subseasonal variations in the TC environment and TC genesis and intensity are strongly related to their ability to predict the MJO. Regional biases in easterly wave activity are observed in the NESM and several other models and related to model drift away from the observed mean state. We also examine the ability of the models to predict easterly wave variability associated with the MJO and ENSO at subseasonal time-scales and how this is related to downstream TC prediction.