Calvin — 2023

Calvin formed as a tropical cyclone on 11 July 2023 about 390 nautical miles south-southwest of Zihuatanejo, Mexico after a low-pressure area and convective burst organized into a well-defined center. It moved generally westward under a subtropical ridge, became a hurricane on 13 July, rapidly intensified to peak strength on 14 July, then weakened as it moved over cooler water and drier air. Calvin crossed into the central Pacific as a tropical storm on 17 July, passed about 60 n mi south of the Big Island of Hawaii on 19 July, and became a post-tropical remnant low later that day before dissipating. Calvin did not make a direct landfall as a hurricane. Its closest approach to land was shortly after 0600 UTC 19 July when the center passed about 60 n mi south of the island of Hawaii (the Big Island) while it was a weakening tropical storm (near 40–50 kt). Tropical storm watches and warnings were issued for the Island of Hawaii from 17–19 July; the Tropical Storm Warning for the Big Island was discontinued on 19 July at 2100 UTC. The storm’s maximum sustained winds at peak were 110 knots (about 126 mph), with an estimated minimum central pressure of 953 mb, making Calvin a Category 3 major hurricane at its strongest on 14 July 2023. The peak was short-lived: winds fell quickly as the cyclone moved into less favorable conditions. Storm surge impacts reported in official observations were limited. Heavy rainfall affected the Hawaiian Islands as Calvin passed south of the chain on 18–19 July, with totals generally of 4 to 8 inches across the Big Island. Stream and gage reports on the Big Island recorded elevated water levels at locations such as Honolii Stream (about 7.24 in reported at that site in the data table) and several Hydrometeorological Automated Data System (HADS) sites reported 5–7 inch totals at places like Hakalau and Kulani NWR. There were no reports of casualties or storm-related damage attributable to Calvin. Periods of heavy rain caused flooding across much of the main Hawaiian Islands on 18–19 July and prompted brief road closures on the Big Island on the morning and early afternoon of 19 July. Forecasts of Calvin’s formation and track were generally accurate; genesis was anticipated more than five days in advance and official track and intensity forecasts performed better than or near recent averages despite the storm’s rapid intensification period.