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Hurricanes and Severe Storms
Introduction
El Niño historically tends to suppress Atlantic hurricane activity. Fewer hurricanes than normal form in the Atlantic during August to October, the peak of Atlantic hurricane season. During El Niño conditions, upper-level air flow is dominated by west-to-east flow, which is not favorable to the movement of large tropical storms into the warm waters of the western Atlantic. However, the pool of warm water in the eastern Pacific (Pathfinder SST data) favors the formation of more hurricanes than normal off the coast of Mexico, Central America and northwest South America. The reverse is true during non-El Niño years.
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El Niño Storm Tracks |
Hurricane Mitch in Perspective |
La Niña Storm Tracks |
La Niña Storms
The ENSO cycle can effect micro- to mesoscale events, like tornadoes and their parent thunderstorms (TRMM LIS data). It has observed that tornadoes during an ENSO cold phase (La Niña) are stronger and remain on the ground longer than do warm phase (El Niño) tornadoes. A study of the top 15 tornadic outbreaks (at least 40 tornadoes) showed that only 1 outbreak occurred during an El Niño event. Six occurred during a La Niña event, while the remaining eight occurred during neutral ENSO years. During the spring, the southern plains have statistically significant decreases in activity during El Niño. The Ohio River Valley and Deep South contain a region of statistically significant increased tornadic activity during La Niña.
The 1998 (La Niña) hurricane season was one of the deadliest Atlantic hurricane seasons in the past 2 centuries. A total of 14 named storms formed, 10 of which evolved into hurricanes. Hurricane Georges first made landfall in the Leeward Islands, followed by landfalls in the Virgin Islands, Puerto Rico, the Dominican Republic, Cuba, and finally the United States (near New Orleans) and was responsible for an enormous amount of damage and a large number of fatalities. Hurricane Mitch produced one of the worst weather disasters ever in the Western Hemisphere when it stalled over Central America and poured an enormous amount of rain (TOVS rain data) (TRMM TMI rain data) over the Yucatan Peninsula, Honduras, and Nicaragua. A minimum of 11,000 people died due to floods and landslides. Also, central Florida was ravaged by a series of seemingly random twisters, which some people blamed on the impact of El Niño conditions on the jet stream.
The 1999 (La Niña) severe weather season started early with a record-setting number of tornadoes, mostly in the southeastern United States. In January, 169 twisters occurred in 6 southern states. Back in 1974 (another La Niña year), 148 tornadoes crossed some 2,500 miles of countryside from Ohio to Alabama in 1 day; 49 tornadoes were killers and 6 reached F5 intensity (winds greater than 260 mph). Tornadoes usually strike along the Gulf Coast in winter, but these were farther north and more violent than usual. The 1999 hurricane season started with the category 4 Bret. During La Niña conditions, U.S. weather is more unstable; colliding air masses set the stage for more tornadoes.
El Niño Storms
Despite a early warning, which allowed residents of Los Angeles to band together to clear flood channels, bolster levees, and distribute sandbags to areas subject to flooding, El Niño storms lashed California for months on end and damaged or destroyed more than 1,400 homes. Estimates indicated over $550 million in damages for the state, and 17 storm-related deaths for the winter. Thirty-five counties were declared federal disaster areas. Clear Lake in northern California reached its highest level since 1909, flooding portions of Lakeport.
During the sprng of 1998, smoke-laden air masses from forest fires in northern Mexico crossed into Texas and moved as far north as Minnesota and Canada. Natural cloud-to-ground lightning in thunderstorms matched with smoke-contaminated air tripled the climatological norm. These thumderstorms also produced abnormally high numbers of mesospheric optical sprites. (SCIENCE Vol. 282, 2 Oct. 1998, p. 78)
The strong ENSO event was well underway at the time of tropical cyclone Paka's formation north of the equator. When the typhoon crossed the island of Guam, the duration of typhoon force winds (NSCAT wind data) was greater than 8 hours across some populated regions. This long period of strong winds and the wind direction shifts (> 180°) that occurred as the typhoon's eyewall moved over the island likely contributed to much of the damage, including the loss of all official wind recording equipment on the northern portion of Guam.
Jump to 'Hurricanes and Severe Storms' List of Web Sites
Disclaimer: NASA offers these suggested sites for additional information regarding effects of El Niño and La Niña teleconnection events. Web access is required to reach these sites. Link existence and contents are not under the control of the EOSDIS Science Operations Office.
Hurricanes and Severe Storms Web Sites
