Marty (2021)

Tropical Storm Marty formed from the remnants of Atlantic Hurricane Grace. The mid-level circulation of Grace crossed Mexico and reached the southwestern coast of Mexico on 22 August 2021. Convection organized over the offshore waters and a broad surface low formed late on 22 August, with Marty becoming a tropical storm just after 0000 UTC 23 August about 200 nautical miles south-southeast of the southern tip of the Baja California peninsula. Marty moved generally west-northwestward and then westward, weakening quickly as wind shear, drier air, and cooler water disrupted its convection. The system degenerated to a remnant low by 0600 UTC 24 August and later opened into a trough by 0700 UTC 27 August about 1,100 nautical miles west-southwest of the southern tip of Baja California.

Marty did not make any landfalls. It remained well offshore of mainland Mexico and the Baja California peninsula for the duration of its life as a tropical cyclone.

The storm’s peak intensity was 40 knots (approximately 46 mph) with an estimated minimum central pressure of 1002 millibars, reached around 1200 UTC 23 August 2021. At peak it was a minimal tropical storm and never reached hurricane strength.

Measured storm surge values were not reported in association with Marty, and there were no ship reports of tropical-storm-force winds. Rainfall totals tied to Marty were not reported in the post-storm observations. The report contains no specific surge heights or station rainfall amounts for cities or counties.

There were no reports of damage or casualties linked to Marty. The regions closest to the storm—southwestern coastal Mexico and the southern Baja California offshore waters—did not report impacts from the system.

One noteworthy point is that the storm’s formation was well anticipated: NHC first mentioned the potential for eastern Pacific development from Grace’s remnants in the Tropical Weather Outlook about 102 hours before genesis, and the probabilities of formation were raised to high well before Marty formed. Because Marty existed as a tropical storm for only about a day, the official forecast sample was very small, but the limited official intensity forecasts had lower-than-average errors for the short period.