Hurricane Hernan (2002)

Hurricane Hernan was the second of three Category 5 hurricanes during the 2002 Pacific hurricane season. The twelfth tropical cyclone, tenth named storm and sixth hurricane of the season, Hernan originated from a tropical wave that formed in the Atlantic Ocean and crossed to the Pacific Ocean. The wave spawned a low-pressure area which organized into a tropical depression on August 30, a tropical storm on August 31 and a hurricane later that day. Hernan rapidly intensified and reached peak intensity as a Category 5 storm on the Saffir–Simpson hurricane scale. Proceeding northwest, it maintained this strength for eight hours, but on September 2 it entered cooler waters and began to weaken. By September 6 it had degenerated into a remnant area of low pressure.

Hernan was the second most intense hurricane of the season, and it maintained Category 5 status for the second-longest time of the season, behind Hurricane Kenna. Although Hernan remained far from land, swells of 15–20 feet (4–6 meters) caused minor beach erosion along the coast of Mexico. In addition, an associated remnant plume of moisture generated light shower activity in southern California as it tracked just offshore.

Meteorological history
On August 16, a tropical wave left the coast of Africa. It traveled westward across the Atlantic Ocean, crossing over Central America and emerging in the eastern Pacific, where it merged with a pre-existing Intertropical Convergence Zone disturbance. The system gradually developed moderate convection, and on August 30 it had developed sufficient convection to be designated Tropical Depression 10-E. The depression produced persistent strong thunderstorms, primarily in two areas of deep convection located to the northeast and west of the center of circulation. Although the center was elongated, wind shear over the system remained light and outflow was good, which led forecasters to predict modest intensification. On the afternoon of August 30, banding features became evident, and the depression was upgraded to Tropical Storm Hernan with sustained winds of 45 mph. Further organization occurred, and the center of circulation became encircled by convective thunderstorms. On August 31, the storm was upgraded to Hurricane Hernan as it moved northwestward about 400 mi southwest of Acapulco.

Light wind shear and favorable ocean temperatures led to steady intensification of the storm, and satellite images indicated that an eye had developed late on August 31. The storm quickly reached Category 3 major hurricane intensity on the Saffir–Simpson scale. As Hernan continued strengthening, its eye became ragged, while its lateral movement to the northwest rose to 17 mph around the southern periphery of a strong deep-layer ridge over the United States. By September 1, the hurricane reached its peak intensity as a Category 5 hurricane, with 1-minute sustained winds of 160 mph and a minimum pressure of 921 mb (hPa).

On September 2, Hernan began weakening after its cloud tops had warmed slightly. Soon after, an eyewall replacement cycle began, causing the storm to be downgraded to Category 3 status, just before it turned slightly to the west later in the day. The storm underwent another eyewall replacement cycle as winds decreased further. As the storm entered cooler waters, it quickly weakened below major hurricane intensity. Soon Hernan was downgraded to a Category 1 hurricane, and its eye became cloud-filled. On September 5, Hernan was downgraded to a tropical storm as the storm rapidly decayed despite developing a new band of convection. Later in the day, the system was downgraded to a tropical depression as it began to lose its tropical characteristics. Strong wind shear developed, weakening the depression further. On September 6, the system degenerated into a remnant low-pressure system, which spawned a remnant plume of moisture that meandered off the coast of California, producing light showers.

Intensity
When Hernan intensified from a tropical storm into a Category 5 hurricane, it intensified at a rate of 1.73 mbar (hPa) per hour, just under the threshold for "rapid intensification". However, for a 12-hour period from August 31 to September 1, it deepened at 2.58 mbar (hPa) per hour, within the range of "explosive deepening" due to favorable conditions including light wind shear and warm water.

Impact
Hurricane Hernan remained far from shore and caused little damage to land. It brought light wind to Socorro Island off the coast of Mexico. Rough surf caused minor impact; in the open waters near the center of Hernan, waves generated by the storm were unofficially estimated to exceed 70 ft. However, official buoys reported swells of 57 ft. Along the coast of Mexico, waves reached 15 –, causing minor beach erosion. A portion of Hernan's remnant moisture off the southern California coast produced light rainfall and slippery roads.