Mean cyclone motion changes stayed uncertain after latitude, month and wind adjustment in two basins in 1982-2024

We compared tropical cyclone motion in 1982-2002 and 2003-2024 in the North Atlantic and eastern Pacific. We used IBTrACS v04r01 and six-hour segments in June-November at 10 to less than 35 degrees N, with tropical winds of at least 34 kt. We split mean changes into changes within latitude, month and wind groups and changes in the group mix. The common groups had 7,749 Atlantic and 11,509 Pacific segments. Within-group mean speed changes were -0.502 and -0.447 km/h. Nominal 97.5% marginal block intervals were -1.665 to 0.764 and -1.551 to 0.693 km/h. Both include zero. The group mix accounted for -0.086 and -0.183 km/h of the raw changes. All planned checks also gave uncertain within-group changes. Thus, this test does not resolve a change in mean motion in either selected basin sample. The intervals are conditional on the selected groups and on bootstrap draws that cover all groups. Sparse groups, 43 seasons, revised tracks and missing physical drivers limit inference. This is a descriptive motion benchmark, not a rainfall estimate or climate attribution. Code, fixed source subsets, source hashes, cell evidence, resampling output and an independent audit are included.

tropical cyclone · translation speed · composition adjustment · IBTrACS · null result · sampling