The role of low-level flow direction on tropical cyclone intensity changes in a moderate-sheared environment

The background flow profiles are constructed by varying the LLF direction with the same moderate deep-layer shear. When the maximum surface wind speed of the simulation without background flow reaches 70 kt (36 m s(-1)), the background flow profiles are imposed.

After a weakening period in the first 12 h, the members with upshear-left-pointing LLF (fast-intensifying group) intensify faster between 12 and 24 h than those members (slow-intensifying group) with downshear-right-pointing LLF. The fast-intensifying group experiences earlier development of inner-core structures after 12 h, such as potential vorticity below the midtroposphere, upper-level warm core, eyewall axisymmetrization, and radial moist entropy gradient, while the inner-core features of the slow-intensifying group remain relatively weak and asymmetric.