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1999 Atlantic hurricane season

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Through El Niño–Southern Oscillation, Cuba and Atlantic Ocean

The most significant storm of the season was Hurricane Floyd, a strong Category 4 hurricane that caused devastating flooding along the East Coast of the United States, especially in North Carolina. Damage from the storm totaled approximately $6.5 billion (1999 USD) and there were at least 77 fatalities, making it the deadliest hurricane in the United States since Hurricane Agnes in 1972. Flooding from Floyd in North Carolina followed Hurricane Dennis, a slow and erratic–moving storm that dropped heavy rainfall in the eastern portion of the state. Tropical Depression Eleven in October contributed to extreme flooding in Mexico, which left 636 people dead and caused $491.3 million in damage, though impact could not be distinguished from the storm itself. Hurricane Irene caused extensive flooding in Cuba and Florida, with lesser effects in the Bahamas and North Carolina. Irene was the second–costliest storm of the season, with about $800 million in damage. Hurricane Lenny was an unusual eastward–moving storm in the Caribbean Sea and a strong late–season storm. It caused extensive damage in the Lesser Antilles in the month of November. Collectively, the storms of the 1999 Atlantic hurricane season caused at least 775 fatalities and $8.78 billion in losses.

Seasonal forecasts

Ahead of and during each hurricane season, various national meteorological services, scientific agencies, and noted hurricane experts issue forecasts of hurricane activity. These include forecasters from the United States National Oceanic and Atmospheric Administration (NOAA)'s National Hurricane and Climate Prediction Center's, William M. Gray and his associates at Colorado State University (CSU), as well as Weather Research Center (WRC) and Tropical Storm Risk (TSR), then known as TSUNAMI. The forecasts include weekly or monthly assessments of the significant factors that help determine the number of tropical storms, hurricanes, and major hurricanes within a particular year.

Gray and his team at CSU issued their initial season outlook on December 4, 1998, predicting fourteen named storms, nine hurricanes, and four major hurricanes. The three main factors for this above average season forecast cited included a continuation of abnormally warm sea surface temperatures, the probability that La Niña conditions would remain, and that the quasi-biennial oscillation (QBO) winds would be in a westerly phase. Early in 1999, WRC issued its forecast for the season, projecting ten named storms and six hurricanes, but no prediction on the number of major hurricanes. In subsequent outlooks from Gray and his associates in April, June, and August, the predictions were unchanged.

On April 7, CSU noted that the probability of a major hurricane landfall in the United States was 72%, including a 54% chance on the East Coast and a 40% likelihood on the Gulf Coast. In their outlook on May 27, experts at NOAA noted that an above average season was a strong possibility. An addition to a La Niña, vertical wind shear would be decreased across much of the Caribbean Sea and tropical Atlantic Ocean, and a favorable jet pattern for tropical waves to develop into tropical cyclones. On June 1, TSR predicted that there would be 12 named storms, 7 hurricanes, and 2 major hurricanes.

As stated by NOAA and CSU, an average Atlantic hurricane season between 1981 and –2010 contains roughly 12 tropical storms, 6 hurricanes, 3 major hurricanes, and an accumulated cyclone energy (ACE) Index of 66–103 units. NOAA typically categorizes a season as either above-average, average, of below-average based on the cumulative ACE Index; however, the number of tropical storms, hurricanes, and major hurricanes within a hurricane season is considered occasionally as well.

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