SR/SSD 97-32 7-1-97

Technical Attachment

Potential Effects of Strong El Niño on Southern States

Prepared by

Scientific Services Division

NWS Southern Region Headquarters

Fort Worth, Texas

Satellite and other observations have revealed that unusually strong El Niño conditions are developing over the tropical Pacific Ocean. The El Niño is an abnormal state of the ocean-atmosphere system that develops every few years. It involves warming of surface waters, and it can have important consequences for weather around the globe. It appears this developing El Niño will be the strongest one since the fall and spring of 1982/1983. Likely effects for the coming November through March are cooler and wetter weather for the southern half of the United States, while the northern half of the country may likely have warmer than normal weather.

The 1982/83 El Niño was the greatest ocean-atmosphere disturbance ever recorded, and its effects were especially felt in the Gulf Coast states, where heavy rains and flooding were blamed for $1.2 billion in losses to property and agriculture between December 1982 and May 1983. At least 50 deaths also resulted from flooding. In every state in the Southern Region, from New Mexico to Florida, flooding occurred at some time between November 1982 and October 1983, and much of it was attributed to weather systems triggered by the unusually strong El Niño.

Numerous rainfall and all-time flood records were set. Florida had its wettest February on record, and records in abundance were eclipsed in Louisiana where the drenchings persisted for months. Heavy rains in December boosted the 1982 total for parts of Louisiana to nearly 90 inches, over 1 times the normal rainfall. During the year severe major flooding also struck Mississippi, Arkansas, Oklahoma, Texas, and even normally arid New Mexico, where rains in excess of 5 inches fell in October. Rains and snowmelt from across the entire Mississippi River Valley produced one of the major Mississippi River floods of this century.

An unprecedented number of low pressure systems formed in the Gulf of Mexico during the winter of 1982/83. These resulted in frequent gales over the Gulf and heavy rains over south Florida. At the same time, winter cold air outbreaks from the north were suppressed by the El Niño conditions, so although the winter in the South was wet, it was generally mild.

The effect of El Niño on hurricanes and tropical storms is less well established, because the influences are inconsistent. In 1982 only five named storms developed in the Atlantic and Gulf of Mexico, and there were only four in the 1983 hurricane season -- the lowest number since 1930. Even so, hurricane Alicia flooded South Texas in August 1983 with over 12 inches of rain, and the remnants of Pacific tropical storm Tico spread heavy rain as far as Oklahoma in October, covering over half of that state with rains of up to 15 inches. There are indications that the years during and after the El Niño see fewer--but no less severe--tropical storms, while a major increase in storms may be seen 2-4 years following an El Niño. There were 12 named storms in 1984 and 11 in 1985.

More detailed information can be found on NOAA's "El Niño Theme Page" at http://www.pmel.noaa.gov/toga-tao/el-nino/home.html. That Web site contains information about what El Niño is, impacts, and charts and graphs which describe past trends and this year's developing El Niño. It also provides links to the NWS/NCEP Climate Prediction Center, where forecasters are keeping a close eye on developments. The NWS Southern Region Headquarters homepage (http://www.srh.noaa.gov) provides additional information concerning conditions in the southern U.S., including access to Web sites at forecast offices in each of the ten Southern Region states and Puerto Rico.