Hurricane Nora was the first tropical cyclone to enter the Continental United States from the Pacific Ocean since Hurricane Lester in 1992. Nora was the fifteenth named tropical cyclone and the seventh hurricane of the 1997 Pacific hurricane season. The September storm formed off the Pacific coast of Mexico, and aided by waters warmed by the 1997–98 El Niño event, eventually peaked at Category 4 intensity on the Saffir–Simpson hurricane scale.
Nora took an unusual path, making landfall twice as a hurricane in the Baja California Peninsula. Weakening quickly after landfall, it lashed the Southwestern United States with tropical storm-force winds, torrential rain, and flooding before becoming a remnant low. The storm was blamed for two direct casualties in Mexico, as well as substantial beach erosion on the Mexican coast, flash flooding in Baja California, and record precipitation in Arizona. It persisted far inland and eventually dissipated near the Arizona–Nevada border.
The system that was to become Hurricane Nora was likely related to a tropical wave, that had moved off the coast of Africa at the end of August 1997 and entered the Pacific Ocean during 12 September. After entering the Pacific Ocean, the wave encountered a favorable environment for tropical cyclogenesis, which caused the system to become better organized and develop into Tropical Storm Nora on 16 September. Over the next couple of days, the system continued to become better organized as it slowly moved north-westwards over the Pacific Ocean away from southwestern Mexico and intensified into a Category 2 hurricane on the Saffir-Simpson hurricane wind scale during 18 September. The steering currents subsequently became weak or balanced over the hurricane which caused the system to become near-stationary and weaken into a Category 1 hurricane.
Nora impacted the majority of Mexico's Pacific-facing coasts including the states of Baja California, Colima, Guerrero, Jalisco, Michoacán, Nayarit, Oaxaca, Sinaloa and Sonora.
Meteorological history
The system that was to become Hurricane Nora was likely related to a tropical wave, that moved off the coast of Africa at the end of August 1997. The wave subsequently moved across the Atlantic Ocean and spawned Hurricane Erika in early September, before it continued to move westwards through the Caribbean Sea and entered the Pacific Ocean during 12 September. After entering the Pacific Ocean, the wave encountered a favorable environment for tropical cyclogenesis, with very warm waters of around and relatively light vertical wind shear. As a result, the system became better organized and developed a closed circulation, before the United States National Hurricane Center (NHC) initiated advisories and designated the disturbance as Tropical Depression Sixteen-E during 16 September. At this time the system was located about to the south of Acapulco, Mexico and had started to be steered towards the west-northwest, as a result of a ridge of high pressure over northern Mexico. During that day, bands of atmospheric convection surrounding the depression increased, before the NHC reported that the system had intensified into a tropical storm and named it Nora. At this time, the NHC noted that they had limited guidance on Nora as a result of various computer problems and that there was considerable uncertainty in the forecast track.
After being named, the system became better organized with atmospheric convection becoming more concentrated near the center, as it slowly moved north-westwards over the Pacific Ocean away from south-western Mexico. During 18 September, after a Dvorak classification that correlated to 1-minute sustained winds of was received from the Tropical Forecast and Analysis Branch, the NHC reported that Nora had become a Category 1 hurricane on the Saffir–Simpson hurricane wind scale. During that day, a large and ragged banding type eye appeared on satellite imagery, which shrank as the system intensified into a Category 2 hurricane with 1-minute sustained wind speeds of . At around this time, steering currents over the system became weak or balanced which caused the hurricane to become near-stationary, while it was located about to the southwest of Acapulco. Over the next couple of days, Nora started to weaken over waters that had been upwelled by its circulation, with atmospheric convection becoming almost non-existent over Nora's eye and north-western semicircle, before it weakened into a Category 1 hurricane.
During 20 September, Nora started to drift north-northwestwards along a ridge of high pressure, into an area of very warm sea-surface temperatures parallel to Mexico's western coast. Over the next day, atmospheric convection surrounding the eye increased and quickly cooled, as the hurricane quickly intensified and ultimately peaked as a Category 4 hurricane with 1-minute sustained windspeeds of . At this time the system was located about to the southeast of Socorro in the Revillagigedo Islands and was starting to move over waters that Hurricane Linda had cooled a few weeks earlier, while it was a Category 5 hurricane. As a result, Nora weakened into a Category 3 hurricane, before it passed within of Socorro in the Revillagigedo Islands during 22 September. Over the next day, the hurricane continued to move over Linda's wake and gradually weaken with the eye becoming ragged, cloud tops warming and its eyewall becoming broken. As a result, the system was classified as a Category 1 hurricane at around 04:00 Pacific Standard Time (12:00 UTC) on 23 September, while it was located about to the southwest of Cabo San Lucas on the Baja California peninsula.
After the system had weakened into a category 1 hurricane, a fresh burst of atmospheric convection wrapped around Nora's eye, as the flow from a trough of low pressure that was associated with the remnants of Typhoon David caused the system to turn and accelerate northwards. Warm waters off the west coast of Baja California allowed the system to reintensify slightly and weaken slower than most tropical cyclones in the region, before it made landfall near Punta Eugenia in Baja California Sur at about 22:30 PST on 24 September (06:30 UTC, 25 September). The system subsequently moved over water in the vincinty of the Sebastián Vizcaíno Bay, before it made landfall at about 03:00 PST (11:00 UTC) to the south-southeast of San Fernando in Baja California as a Category 1 hurricane. As Nora moved northwards over the peninsula, atmospheric convection became less organized and the eye disappeared from infrared imagery, which caused the NHC to presume that it had weakened into a tropical storm. Later that day, Nora emerged into the northern Gulf of California and skirted the western coast as it moved northwards, before it made its final landfall near the mouth of the Colorado River to the west of Puerto Penasco, Sonora.
After the system had made its final landfall, Nora continued to move northwards and at around 13:00 PST (21:00 UTC) on 25 September, it entered the United States of America near the border of Arizona and California. This made it the first tropical cyclone to enter the Continental United States from the Pacific Ocean, since Hurricane Lester in 1992. After moving into the Continental United States, the system rapidly weakened and broke up over the mountainous terrain of the southwestern United States, before it degenerated into a tropical depression while it was located in between Blythe and Needles. The system subsequently started to move towards the north-northeast and started to look like a mid-latitude system on radar, before it was last noted at 22:00 PST (06:00 UTC, 26 September), while it was located to the east of Las Vegas, Nevada. Nora's upper-level circulation did not have enough time to wind down and persisted for another couple of days before it dissipated on 28 September, after it had moved through portions of Utah, Colorado, Idaho and Wyoming.
Preparations and impact
Hurricane Nora impacted the majority of Mexico's Pacific-facing coast, as well as parts of the Southwestern United States, including California, Arizona, Utah and New Mexico. Overall the system was responsible for two deaths in Mexico and either three or four fatalities in the United States, as well as at least $150 million in damages.
Mexico Hurricane Nora was the first of four tropical cyclones to impact Mexico during the latter part of the 1997 Pacific hurricane season, with Tropical Storm Olaf, Hurricanes Pauline and Rick impacting southern Mexico later in the season. The system impacted the majority of Mexico's Pacific coast with effects reported in Baja California, Colima, Guerrero, Jalisco, Michoacán, Nayarit, Oaxaca, Sinaloa and Sonora.
Southern Mexico After Nora had become a tropical storm on 16 September, the Servicio Meteorológico Nacional (SMN) issued a hurricane watch for the coast between Lázaro Cárdenas, Michoacán and Cabo Corrientes, Jalisco, as it was feared that the system could make landfall on Mexico's Pacific coast. Later that day, the SMN issued a tropical storm warning for the area between Lázaro Cárdenas, Michoacán and Puntá Maldonado, Guerrero, in addition to the hurricane watch, because of the close proximity of the system to the coast. As a result, authorities set up evacuation centers on higher ground in case evacuations were ordered, while several major ports including Acapulco, Huatulco, Lazaro Cardenas and Zihuatanejo were closed to shipping or restricted to bigger vessels. Over the next couple of days, the tropical storm warning and hurricane watch was canceled and replaced with a flood warnings by the Mexican Government. Despite the system remaining over open waters, parts of Guerrero reported experiencing gusty winds and heavy rain from Nora's outer bands. The system also produced high seas, high surf and waves of up to , which impacted parts of southwestern Mexico. As a result, property along the coastline was damaged, trees were brought down, while substantial beach erosion was reported with the Pie de la Cuesta beach washed away.
During 18 September, radar imagery from Acapulco showed that Nora's outer rain bands had started to impact Mexico's Pacific-facing coast.
Offshore, the strong swells generated by the hurricane caused widespread loss of growing sea lettuce (Ulva lactuca), exacerbating the negative biological effects of the 1997–98 El Niño event.
Oaxaca The port of Huatulco was closed to small craft for at least four days as Nora caused high seas.
Guerrero The ports of Acapulco and Zihuatanejo were closed to shipping for at least three days.
Heavy winds and rain were reported in the state.
High surf caused the beach at Pie de la Cuesta to virtually disappear.
Michoacán The port at Lazaro Cardenas was closed to shipping.
Colima In Colima Nora's storm surge produced waves of up to .
80% of the arbours at the El Paraiso Balneario in Armería were destroyed.
Socorro and the Revillagigedo Islands During 21 September, the Mexican Government issued a hurricane watch for the sparsely populated Revillagigedo Islands, before it was superseded by a hurricane warning later that day. Nora subsequently became the second hurricane in 10 days to pass near or over the island of Socorro, where winds of and a minimum pressure of was reported.
Researchers investigating the maximum potential intensity of tropical cyclones near the island, later found that no useful atmospheric soundings were available to assess Nora's intensity while near the island.
Heavy winds and rain were reported in the states of Jalisco, Nayarit and Sinaloa. A rainfall total of was recorded in La Cruz.
Baja California peninsula