Sergio (2018)

Hurricane Sergio formed as a well-defined tropical cyclone on 29 September 2018 about 335 nautical miles south of Zihuatanejo, Mexico, and lasted until dissipating over mainland Mexico on 13 October. The storm followed a sinuous path over the eastern Pacific, initially moving westward and then turning west-southwest and northwest under changing steering currents. Sergio underwent periods of rapid strengthening and eyewall replacement cycles, moved generally westward for several days, then turned northeast toward Baja California Sur and mainland Mexico before weakening over cooler waters and terrain.

Sergio made two landfalls on 12 October 2018. The broad circulation first made landfall near Los Castros on the western side of Baja California Sur around 1200 UTC with sustained winds estimated at 45 knots (about 52 mph), a low-end tropical storm. About six hours later the center came ashore on the mainland of Mexico near Reserva Especial de la Biosfera Cajón del Diablo (a Sonoran state park) about 20 nautical miles west-northwest of Guaymas with an intensity near 30 knots (about 35 mph) as a tropical depression.

The storm’s maximum intensity was 120 knots (about 138 mph) with a minimum central pressure of 942 mb, reached near 0600 UTC on 4 October while Sergio was roughly 715 nautical miles southwest of Cabo San Lucas. At that peak it was a Category 4 hurricane on the Saffir–Simpson scale.

Storm surge and rainfall impacts were limited. An offshore elevated station at Roca Alijos recorded 15-minute sustained winds of 60 kt with a peak gust to 78 kt on 12 October, which corresponds to about 55 kt when reduced to 10 m elevation. On land, gusts of tropical-storm force were reported at Guaymas (45 kt) and Santa Rosalía (52 kt). Heavy rains and gusty winds produced flooding and power outages in parts of Baja California Sur and Sonora; no detailed storm-surge heights or large rainfall totals at specific cities were reported in the report.

There were no reported deaths or injuries directly associated with Sergio. Damage was minimal overall, with reports of localized flooding and power outages in Baja California Sur and Sonora. Moisture from Sergio’s remnants indirectly contributed to heavy rainfall and flooding in parts of Arizona and Texas in the week after the Mexican landfalls.

Noteworthy points: Sergio was one of the longest-lived eastern Pacific tropical storms since records began in 1949—about 13.25 named-storm days, the longest in the basin since 1992. Forecast track and intensity guidance for Sergio performed well overall; NHC official track and intensity forecasts had lower-than-average errors, and the European model showed particularly strong long-range track performance.