Hurricane Sandra (2015)

Hurricane Sandra was the latest-forming major hurricane in the northeastern Pacific basin, the strongest Pacific hurricane on record in November, and the record eleventh major hurricane of the 2015 Pacific hurricane season. Originating from a tropical wave, Sandra was first classified as a tropical depression on November 23 well south of Mexico. Environmental conditions, including high sea surface temperatures and low wind shear, were highly conducive to intensification and the storm quickly organized. A small central dense overcast developed atop the storm and Sandra reached hurricane status early on November 25 after the consolidation of an eye. Sandra reached its peak intensity as a Category 4 hurricane on the Saffir–Simpson hurricane wind scale with winds of 150 mph (240 km/h) and a pressure of 934 mbar (hPa; ) early on November 26. Thereafter, increasing shear degraded the hurricane's structure and weakening ensued. Rapid weakening took place on November 27 and Sandra's circulation became devoid of convection as it diminished to a tropical storm that evening. The cyclone degenerated into a remnant low soon thereafter and ultimately dissipated just off the coast of Sinaloa, Mexico, on November 29.

As the precursor to Sandra traversed Central America, it produced unseasonably heavy rainfall that triggered flooding and landslides. Four people died in various incidents related to the system: three in El Salvador and one in Honduras. Initially expecting a landfalling storm, officials in Northwestern Mexico prepared equipment for power outages, closed schools, and evacuated 180 residents. Sandra's effects largely consisted of light to moderate rainfall; some traffic accidents and landslides resulted from this, though the overall impacts were limited.

Meteorological history

On November 6, 2015, a tropical wave emerged off the west coast of Africa into the Atlantic Ocean. Only sporadic convection—shower and thunderstorm activity—accompanied the system as it traveled west for the next ten days. As it reached the southwestern Caribbean on November 17, westerly winds associated with the Intertropical Convergence Zone spurred the development of an area of low pressure and extensive convection. Forecasters at the National Hurricane Center (NHC) noted potential for the system to develop into a tropical cyclone; however, persistent wind shear inhibited this system from consolidating before it reached Central America. The system emerged over the Pacific Ocean near Nicaragua on November 21; once back over water, convection blossomed near the low's center. Convection remained largely disorganized over the following two days as the system progressed westward in response to a subtropical ridge to the north.

A Tehuantepec gap wind event in conjunction with horizontal wind shear spurred development of a vortex within the disturbance and a well-defined low formed by 12:00  UTC on November 23. Six hours later the low acquired sufficient convective organization, including elongated banding features to the north, to be classified Tropical Depression Twenty-Two-E. At this time, the depression was situated 435 mi (705 km) south-southwest of Acapulco, Mexico. Aided by high sea surface temperatures of , ample ocean heat content and low wind shear, the small system quickly intensified into a tropical storm—at which time the NHC assigned it the name ''Sandra''—and developed a central dense overcast. A prominent banding feature with cloud tops below and frequent lightning formed north of the circulation on November 24. By 18:00 UTC, a wide eye became apparent, signaling the onset of rapid intensification.

Throughout November 25, Sandra dramatically strengthened as deep convection blossomed around a tightening and clearing eye. The system achieved hurricane status by 06:00 UTC and major hurricane status—Category 3 or higher on the Saffir–Simpson hurricane wind scale—by 00:00 UTC on November 26. Prominent outflow became established atop the cyclone and further aided the intensification. Throughout the strengthening phase, a mid- to upper-level trough near the west coast of North America created a weakness in the subtropical ridge, prompting Sandra to turn north around the western edge of the high. Sandra reached its peak intensity as a high-end Category 4 hurricane around 06:00 UTC on November 26 with maximum sustained winds of 150 mph (240 km/h) and a barometric pressure of 934 mbar (hPa; ). By this time, the hurricane's eye shrunk to less than 6 mi (10 km) in diameter. Within hours, however, increasing wind shear began to impact the circulation and caused convection to become asymmetric. Concurrently, the system started a turn northeast toward mainland Mexico as it rounded the ridge.

Steadily increasing wind shear gradually unraveled Sandra during the latter part of November 26 and into November 27. The storm's outflow, though prominent to the north, became restricted on the southern side. Sandra briefly regained organization around 00:00 UTC on November 27, with its eye becoming redefined; however, persistent shear prevailed and the system weakened below major hurricane status by 06:00 UTC. The hurricane rapidly deteriorated throughout November 27 as convection became displaced to the northeast of the circulation. The low-level circulation soon decoupled from the mid- to upper-level circulations and Sandra degraded to a tropical storm by 00:00 UTC on November 28. The convectively devoid low-level circulation abruptly turned northwest in response to a shallow ridge. Failing to redevelop convection atop its center, Sandra degenerated into a remnant low by 06:00 UTC. Sustained winds dropped below gale

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