Rosa (2012)

A small tropical cyclone formed from a disturbance well southwest of the southern tip of the Baja California peninsula. A well-defined surface low developed late on 29 October 2012, and the system became a tropical depression around 0600 UTC on 30 October about 610 nautical miles south‑southwest of southern Baja. It strengthened to Tropical Storm Rosa by 1200 UTC that day and moved slowly west‑northwestward and then westward before drifting southwest and south‑southwest into early November. Rosa weakened as increasing westerly wind shear displaced its thunderstorms, became a depression by 1200 UTC on 3 November, degenerated to a remnant low about 6 hours later, and dissipated by 1200 UTC on 5 November about 900 n mi southwest of southern Baja.

Rosa did not make any landfalls. The entire life cycle occurred over the eastern North Pacific well away from land, and no center of circulation crossed the Baja California peninsula or mainland Mexico.

The maximum intensity reached 45 knots (about 52 mph) with a minimum central pressure of 1001 mb, equivalent to a moderate tropical storm (below hurricane strength). Peak winds occurred early on 31 October and were maintained through 1 November before gradual weakening.

Because Rosa stayed far offshore, observed storm surge impacts are not reported in the NHC record. There were also no ship reports of tropical‑storm‑force winds. The official report lists no rainfall totals at specific cities or counties associated with Rosa, and no flood or surge measurements were recorded for populated locations.

There were no reported deaths, injuries, or damage associated with Rosa. The storm had minimal societal impact because it remained over open water for its entire existence.

Noteworthy items include that Rosa formed late in the season from a breakdown of the Intertropical Convergence Zone linked to the Madden‑Julian Oscillation, and that NHC intensity forecasts performed well — official intensity forecasts had smaller errors than recent 5‑year means. Track forecasts showed a persistent northward bias in many models, and official track errors were larger than the recent 5‑year means at most lead times.