| 29 Jun 2026
Extratropical interactions with the tropical moist margin: a case study and the role of latent heating
Abstract. The tropical moist margin occasionally extends into the extratropics, where it can lead to heavy precipitation in otherwise dry regions. Here, we examine the physical processes involved in these events and their interaction with the extratropical flow. Employing tools such as budget and trajectory analysis, we analyse a case study of an extratropical interaction with the moist margin in January 2018. This event produces a subtropical cyclone and results in damaging winds and precipitation over New Zealand. The event is then simulated with the ACCESS-rAM3 model, highlighting the critical role of latent heating in the development of the cyclone. Overall, the results suggest that interactions between extratropical PV and the moist margin occur in both directions. Deep cyclonic PV anomalies of upstream extratropical origin can result in poleward moisture advection leading to poleward displacement of the moist margin, while convection inside a perturbed moist margin can lead to upper-level ridge building through poleward advection of anticyclonic PV by the divergent wind. These results have implications for the diagnosis and prediction of severe weather, especially for extreme precipitation in the subtropics.
The manuscript by Robinson et al. examines the physical processes associated with the extratropical transition of a tropical-origin low-pressure system that subsequently intensified in the midlatitudes, with particular emphasis on latent heating. The authors describe the synoptic conditions during the cyclone’s intensification and analyze the observed position of the tropical moist margin and the evolution of the upper-level potential vorticity (PV) structure.
However, the analyses and observations presented in the manuscript provide only limited, or indirect, support for the claims made in the abstract, introduction, and conclusions. Moreover, the different components of the analysis are not sufficiently integrated, making it difficult to understand how they collectively address the paper’s central research question.
The manuscript’s key analysis concerns latent heating within cyclones (and warm conveyor belts) and demonstrates its well-established role in cyclone intensification and in modifying upper-level PV structure (Davis et al. 1993, Schemm et al. 2013, Steinfeld et al. 2020, Huaser et al. 2023). This is investigated through numerical experiments with the ACCESS-rAM3 model, using different prescribed latent-heating values. However, this analysis is not convincingly connected to the tropical moist margin. Consequently, the manuscript does not yet establish the specific role of the moist margin in the event or clearly demonstrate the novelty of its central contribution.
Given the potential relevance of this topic to the Weather and Climate Dynamics Journal, the manuscript could be given further consideration if the authors restructure the storyline and either reformulate the key research questions to align with the current analysis or revise the analysis to address the stated questions. Therefore, I recommend a major revision and restructuring.
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