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Abstract This study quantifies tropical cyclone (TC) error statistics from the Hurricane Analysis and Forecast System (HAFS) across different environmental conditions (e.g., vertical wind shear) and inner-core structural metrics. A particular focus is the evolution of poorly understood aspects of internal TC structure, including vortex tilt, and their impact on forecast errors. Although previous studies have demonstrated that vortex tilt, vertical wind shear, and precipitation processes impact TC intensity and track, this is the first known study to stratify these cooperative interactions to gain insights into their relationships with forecast errors. A 3-yr retrospective sample of forecasts in the North Atlantic basin from two HAFS configurations (HAFS-A and HAFS-B) demonstrates that TCs with larger tilt magnitudes have larger forecast track errors on average than smaller tilt TCs. Smaller tilt magnitudes have larger absolute intensity errors in short-range forecasts, whereas larger tilt magnitudes tend to have larger negative intensity biases at medium range. TCs with a tilted vortex are shown to have both left-of-shear [maximizing downshear left (DSL)] and left-of-tilt-oriented positional track biases. Furthermore, those cases with greater downshear biases tend to have more convection and larger positive intensity biases, highlighting the importance of the interplay between inner-core characteristics and forecast errors. 

Abstract This study uses a recently developed airborne Doppler radar database to explore how vortex misalignment is related to tropical cyclone (TC) precipitation structure and intensity change. It is found that for relatively weak TCs, defined here as storms with a peak 10-m wind of 65 kt (1 kt = 0.51 m s⁻¹) or less, the magnitude of vortex tilt is closely linked to the rate of subsequent TC intensity change, especially over the next 12–36 h. In strong TCs, defined as storms with a peak 10-m wind greater than 65 kt, vortex tilt magnitude is only weakly correlated with TC intensity change. Based on these findings, this study focuses on how vortex tilt is related to TC precipitation structure and intensity change in weak TCs. To illustrate how the TC precipitation structure is related to the magnitude of vortex misalignment, weak TCs are divided into two groups: small-tilt and large-tilt TCs. In large-tilt TCs, storms display a relatively large radius of maximum wind, the precipitation structure is asymmetric, and convection occurs more frequently near the midtropospheric TC center than the lower-tropospheric TC center. Alternatively, small-tilt TCs exhibit a greater areal coverage of precipitation inward of a relatively small radius of maximum wind. Greater rates of TC intensification, including rapid intensification, are shown to occur preferentially for TCs with greater vertical alignment and storms in relatively favorable environments. Significance StatementAccurately predicting tropical cyclone (TC) intensity change is challenging. This is particularly true for storms that undergo rapid intensity changes. Recent numerical modeling studies have suggested that vortex vertical alignment commonly precedes the onset of rapid intensification; however, this consensus is not unanimous. Until now, there has not been a systematic observational analysis of the relationship between vortex misalignment and TC intensity change. This study addresses this gap using a recently developed airborne radar database. We show that the degree of vortex misalignment is a useful predictor for TC intensity change, but primarily for weak storms. In these cases, more aligned TCs exhibit precipitation patterns that favor greater intensification rates. Future work should explore the causes of changes in vortex alignment.