Abstract
On 4–5 September 2013, a relatively shallow layer of northerly dry airflow was observed just west of the core deep convection associated with the low-level center of the pre-Gabrielle (2013) tropical disturbance. Shortly thereafter, the core deep convection of the disturbance collapsed after having persisted for well over 24 h. The present study provides an in-depth analysis of the interaction between this dry airflow layer and the pre-Gabrielle disturbance core deep convection using a combination of observations, reanalysis fields, and idealized simulations. Based on the analysis, we conclude that the dry airflow layer played an important role in the collapse of the core deep convection in the pre-Gabrielle disturbance. Furthermore, we found that the presence of storm-relative flow was critical to the inhibitive effects of the dry airflow layer on deep convection. The mechanism by which the dry airflow layer inhibited deep convection was found to be enhanced dry air entrainment.
Significance Statement
A persistent region of deep convection near the core of a tropical disturbance is critical to tropical cyclone formation. The sudden collapse of this deep convection is often poorly anticipated and can result in large forecast errors. Here we perform a careful analysis of observations of a tropical disturbance that experienced such a collapse in order to understand the roles of environmental moisture and wind variations in the sudden collapse of the convection. Our findings suggest that the collapse can be explained by the transport of dry air into this region of deep convection. These findings emphasize the importance of examining full profiles of moisture and wind when determining if a disturbance environment is favorable for tropical cyclone formation.
Helms’s current affiliations: NASA Goddard Space Flight Center, Greenbelt, and Universities Space Research Association, Columbia, Maryland.
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This article is included in the NASA Hurricane Severe Storm Sentinel (HS3) special collection.
