This study investigates the impact of warm core eddies (WCEs) on the ocean response and intensity of tropical cyclones (TCs) in the Northwest Pacific, focusing on three typhoons in 2018: Jebi, Trami, and Kong-rey. The research uses the Hurricane Weather Research and Forecast (HWRF) model coupled with the MPIPOM-TC ocean model. Idealized WCEs are embedded into the ocean model ahead of each TC. The impacts of WCEs are evaluated by comparing simulations with and without their presence. Uncoupled experiments with the fixed sea surface temperature (SST) serve as a reference for TC maximum potential intensity. To quantitatively assess the impact of WCEs on the SST, enthalpy fluxes, and TC intensity, a Maximum WCE Potential Index (MWPI) is introduced. Our findings indicate that for a WCE with a 200 km radius, the potential to reduce SST cooling ranges from 34 to 37%, while the potential to increase enthalpy fluxes varies between 25 and 39%. The influence of WCEs on TC intensity, as measured by minimum pressure, shows a larger variation from 27% to 48%, depending on the oceanic and atmospheric environmental conditions in each storm. Additional experiments reveal the sensitivity of the MWPI to WCE size, with TC Trami showing less sensitivity due to its slower translational speed. This study underscores the significant role of oceanic thermal conditions, particularly WCEs, in modulating TC intensity.

The Loop Current (LC) and its associated eddies, known as Loop Current Eddies (LCEs), are key oceanic features in the Gulf of Mexico. Using a statistical analysis of 29 years of satellite altimeter data (1993–2021), we show that more than half of the LCEs that detach from the LC reattach within 30 d and that only 42 % truly separate from the LC and move westward in the Gulf. Our observational analysis also shows that (i) before a detachment can occur, the LC needs to extend far enough north in the Gulf to reach the Mississippi fan (∼27.5° N); and (ii) the ratio of separations to reattachments depends on latitude, with detachments being more prone to reattach if they occur south of 25° N and to separate if they occur north of 25° N. In case (iii), cyclonic eddies are consistently present during the detachment process, with one cyclonic eddy on the eastern side of the LC if the LCE is to reattach, and one on each side if the LCE is to separate. When cyclonic eddies occur on both sides of the LC, their co-occurrence in the LC bottleneck zone forms a large cyclonic structure. This large cyclonic structure is often observed during separation events, and when it is absent, LCEs are more likely to reattach, indicating a potential role in modulating the LC extension into the Gulf of Mexico. Sometimes, it can restrict LC growth on time scales of several months. The observed associations between cyclonic eddies and LCE detachments provide a statistical framework that could help anticipate separation events.

It is well recognized that evaporation from the sea surface, primarily within a tropical cyclone (TC) core, provides heat energy required to maintain and intensify the storm. The sea surface temperature (SST) typically decreases within the storm core due to the mixing and upwelling processes in the upper ocean thereby limiting the storm intensity. This negative feedback to the TC intensity depends on the oceanic thermal conditions and salinity stratification ahead of the storm. Upper oceanic heat content (OHC) has become widely accepted as a measure of the ocean energy available to the TCs. Observational and modeling studies note that some TCs rapidly intensify while passing over warm core eddies (WCEs) because of their high OHC. TC intensification is also significantly affected by salinity-induced barrier layers (BLs) formed when a low-salinity is situated near the surface in the upper tropical oceans. When storms pass over the regions with BL, the increased stratification and stability within the layer reduce storm-induced vertical mixing and SST cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, leads to TC intensification. In this study, we applied the Hurricane Weather Research and Forecast (HWRF) v.4.0 system coupled to the Message Passing Interface Princeton Ocean Model (MPIPOM). We conducted the idealized experiments in which the WCE is embedded into the U.S. Navy's Generalized Digital Environmental Model (GDEM) climatology with a specified size using a feature-based initialization procedure. Idealized vertical ocean profiles from Hlywiak and Nolan (2019) are selected to conduct the sensitivity of TC intensity to BL thickness. The goal of this study is to quantify the impact of WCEs and BLs in the upper ocean on TC’s self-induced cooling and subsequent feedback on TC intensity in three TCs in 2018, Jebi, Trami, and Kong-Rey.

The Loop Current (LC) and its associated eddies, known as Loop Current Eddies (LCEs), are key oceanic features in the Gulf of Mexico. Analysis of 29 years of satellite altimeter data (1993-2021) shows that more than half of the LCEs that detach from the LC reattach within 30 days and that only 42\% truly separate from the LC and move westward in the Gulf. We find that i) before a detachment can occur, the LC needs to extend far enough north in the Gulf to reach the Mississippi fan ($\sim$27.5\dg{}); ii) the ratio of separations to reattachments depend on latitude, with detachments being more prone to reattach if they occur south of 25\dg{}N and to separate if they occur north of 25\dg{}N; and iii) cyclonic eddies are always present during the detachment process, with one cyclonic eddy on the eastern side of the LC if the LCE is to reattach and one cyclonic eddy on each side of the LC is the LCE is to separate. In the latter case, the co-occurrence of eastern and western cyclonic eddies in the LC bottleneck zone forms a large cyclonic structure. This structure may hinder the reattachment of newly formed LCEs and, therefore, modulate the extension of the LC into the Gulf of Mexico. Sometimes, it can restrict LC growth on time scales of several months. The results highlight the pivotal role that cyclonic eddies play in detachment events.