Gulf Stream Sea Surface Temperature Anomalies Associated With the Extratropical Transition of North Atlantic Tropical Cyclones.

This study investigates Gulf Stream (GS) sea surface temperature (SST) anomalies associated with the extratropical transition (ET) of tropical cyclones (TCs) in the North Atlantic. Composites of western North Atlantic TCs indicate that GS SSTs are warmer, and both large‐ and fine‐scale SST gradients are weaker than average, for TCs that begin the ET process but do not complete it, compared with TCs that do. Further analysis suggests that the associated fine‐scale GS SST gradient anomalies are related to atmospheric processes but not the same as those that are typically associated with the onset of ET. As sensible heat flux gradients and surface diabatic frontogenesis are shown to generally scale with the local SST gradient strength, these results suggest that knowledge of the fine‐scale GS SST gradient in the weeks prior to the arrival of a TC might potentially provide additional information regarding the likelihood of that system completing ET. Plain Language Summary: Tropical cyclones can undergo a process known as extratropical transition as they move toward higher latitudes. The resultant weather systems can cause extensive damage and can be difficult to forecast. This study discusses how knowledge of the Gulf Stream sea surface temperature gradients in the week prior to the passage of a tropical cyclone may provide additional insight into whether that tropical cyclone will complete extratropical transition in the region. In particular, we discuss how fine‐scale sea‐surface temperature gradients can modulate the gradient in heat exchange between the ocean and the atmosphere, and in turn influence how favorable the lower atmosphere is to the development of sharp atmospheric temperature gradients. Key Points: Gulf Stream sea surface temperature anomalies are statistically related to the completion of tropical cyclone extratropical transitionFine‐scale sea surface temperature gradients present do not come from an atmospheric setup conducive to extratropical transition completionThe associated sensible heat flux gradients may potentially influence extratropical transition by impacting frontogenesis in the region [ABSTRACT FROM AUTHOR]