Potential changes applying the pseudo-global warming (PGW) approach in the relationship between tropical cyclones (TC) and the Caribbean Low-Level Jet (CLLJ).

Tropical cyclone (TC) activity in the Caribbean Sea from May to October is related to the structure and dynamics of the Caribbean- Low-Level jet (CLLJ), which has great temporal variability and a maximum of 15 m/s during July, at 15°N, 75°W and 925 hPa. The vertical shear generated by this CLLJ has great seasonal and interannual variability and modulates the inhibition of tropical cyclones, whose vertical movement is essential for their development.

To estimate the potential changes associated with pseudo global warming (PGW) conditions of both TC and the CLLJ, as well as their relationship, analysis of regional numerical simulations was applied using both dynamical and statistical methods to identify local atmospheric structures and processes associated with TC and the CLLJ.

The application of this regional dynamical analysis to evaluate simulations for the Caribbean is analyzed, this under the hypothesis that in active (inactive) years associated to TC, the CLLJ is weak (intense), due to weak (strong) vertical shear in the core of the jet. The dynamical methodology in which this hypothesis will be explained is by correlating the convergence of momentum associated with perturbations and how these perturbations contribute to the acceleration of this low-level jet between of May and July and how this jet contributes to the intensification of cyclones between August and September.

To evaluate the interannual variability of TC on seasonal and interannual scales and their impacts on precipitation, numerical simulations were carried out (control simulations) using the RegCM model in the convection permitting mode with a resolution of 4.5 km and 41 vertical levels from 1 June - 31 October for the years: 1980, 1988, 1995, 1996, 1998, 2004, 2005, 2007, 2008, 2017, years with greater TC activity in the Caribbean Sea. To apply this analysis, two numerical experiments were evaluated, the first one is a control period driven by ERA5 data and the second one a pseudo global warming approach (PGW), based on 19 CMIP5 RCP8.5 models. This is an evaluation of how well a regional numerical model can reproduce the interaction of processes of different spatial and temporal scales in the tropics.

The results of the analysis indicate that the RegCM model adequately reproduces the structure of the CLLJ and its seasonal variability, as well as the TC activity through the kinetic energy associated with perturbations (PKE) between 3 and 9 days of period.

Under PGW conditions there is an increase in the CLLJ (compared to the control simulations) and a decrease in the PKE, this being associated with the increase in vertical shear in the region close to the core of the CLLJ.

The implications of the inverse relationship between TC and CLLJ are discussed in terms of impacts on precipitation in Central America and southern Mexico.