Slow preceding motion marked lower next-day wind gain in eastern Pacific tropical cyclones in 1982-2024

We tested whether slow tropical cyclone motion preceded lower wind gain over the next 24 hours. We used fixed IBTrACS v04r01 data for 1982-2024. We selected 8,756 eastern Pacific fixes from 644 storms and 2,283 Atlantic fixes from 245 storms. Each window stayed tropical and more than 200 km from land. Slow motion was below 3 m/s during the preceding six hours. The comparison was 3 to less than 7 m/s. After adjustment for initial wind, position, month and year, the eastern Pacific slow-motion contrast was -2.89 kt, with a storm-cluster 95% interval of -4.47 to -1.30 kt. Within-storm adjustment gave -2.34 kt (-4.16 to -0.52). Adding prior wind gain gave -1.99 kt (-3.55 to -0.44) within storms. The Atlantic primary contrast was -1.89 kt (-4.61 to 0.84). Thus the Atlantic estimate was uncertain. The eastern Pacific sign stayed in all planned checks. The result supplies a test of preceding motion and storm selection. It is consistent with an ocean cooling explanation, but does not test that cause. No ocean temperature, ocean heat content, shear or humidity data were used. Selected surviving windows, wind estimates, model form and pointwise intervals limit the result. Code, input hashes, selected source fields, all estimates, a numerical audit and a figure are included.

tropical cyclone · translation speed · intensification · IBTrACS · storm fixed effects · ocean feedback · null result