Pilar (2017)

A compact area of low pressure over the eastern Pacific organized into a tropical depression at 1200 UTC on 23 September 2017 about 75 nautical miles south-southwest of Manzanillo, Mexico. The system moved slowly northwestward just offshore of Mexico’s southwestern coast, became Tropical Storm Pilar about 6 hours after formation, reached peak strength on 24 September, and then weakened rapidly as increasing wind shear stripped away its thunderstorms. Pilar became a remnant low by about 1200 UTC 25 September and dissipated over the southern Gulf of California later that day.

Pilar stayed very close to the Mexican coast and affected the Islas Marías and the extreme southwestern mainland, but there were no reports of a formal landfall of the storm’s center on the mainland in the NHC record. Tropical storm warnings were issued for stretches of coast including Manzanillo to El Roblito and the Islas Marías on 23 September, later modified to Playa Perula to El Roblito, and then changed as the system weakened. Warnings were discontinued by 25 September.

The storm’s maximum sustained winds peaked at 45 knots (about 52 mph) at 1200 UTC 24 September, with an estimated minimum central pressure of 1000 mb. That intensity corresponds to a moderate tropical storm; Pilar never reached hurricane strength.

Storm surge impacts were minimal in the official record. Rainfall and wind observations included an automated elevated station at Chamela-Cuixmala in Jalisco (about 45 n mi east of the center) that recorded an offshore sustained wind of 31 kt and a gust to 67 kt at 0740 UTC 24 September. A ship report from Cap Pasley at 0900 UTC 24 September measured pressure 1003.0 mb and a west-northwest wind of 28 kt. The NHC report did not list specific storm-surge heights or large rainfall totals at named cities.

There were no reports of casualties or damage associated with Pilar. The greatest effects were brief periods of locally heavy rain and tropical-storm-force winds along the extreme southwestern coast of Mexico and the Islas Marías.

Noteworthy items: Pilar’s development was slower to be forecast than usual—the disturbance’s formation was not well anticipated in the 48-hour Tropical Weather Outlook—and NHC track forecasts had unusually large right-of-track and slow-motion biases for this short-lived system. Forecasts also did not fully anticipate the sharp increase in wind shear that caused Pilar’s rapid demise.