Those dates, adopted by convention, describe the period in which most subtropical or tropical cyclogenesis occurs in the Pacific Ocean.
The National Hurricane Center (NHC) will begin issuing routine Tropical Weather Outlooks for east of 140ºW on May 15, 2025, and the Central Pacific Hurricane Center will begin issuing routine Tropical Weather Outlooks for west of 140ºW and east of 180º on June 1, 2025, both on the same date as the seasons starting dates.
Broadly speaking, ACE is the measure of the power of a tropical or subtropical cyclone multiplied by the length of time it existed.
ACE is only calculated for full advisories on specific tropical or subtropical cyclones reaching wind speeds of 39 mph (63 km/h) or higher.
For storms that form in the North Pacific from 140°W to the International Date Line, the names come from a series of four rotating lists.