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updated 6/1/2011 6:48:14 AM ET 2011-06-01T10:48:14

The tough task of guessing what hurricane season will look like could be even more difficult this year for forecasters, who won't be able to rely on the relatively predictable forces known as El Nino and La Nina.

So far, the National Hurricane Center in Miami is predicting that the season that begins on Wednesday will be busier than normal, with as many as 18 named tropical storms, three to six of them major hurricanes.

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El Nino and La Nina — warming and cooling trends in the ocean that can either rev up hurricanes or suppress them — are expected to be essentially neutral, complicating any predictions. The last time temperatures were neutral was 2005, when hurricanes Katrina and Rita hammered the Gulf Coast with lethal results.

"With a strong La Nina or El Nino year, the forecast is much easier," said Dan Kottlowski, senior meteorologist at AccuWeather.com. "Since we don't have a strong signal toward El Nino or La Nina, there's somewhat more uncertainty in trying to determine how strong this season will be."

The La Nina effect is a cooling of Pacific Ocean waters near the equator. It decreases wind shear in the Atlantic and can give storms extra giddyap as they form. It has been linked to above-average hurricane seasons in the Atlantic. But it appears to be weakening.

Interactive: Hurricane facts, figures & preparation (on this page)

The opposite phenomenon, El Nino, warms Pacific waters, increases wind shear and can blow storms apart. But El Nino isn't happening this season.

La Nina helped make last year the third-most active hurricane season on record, said meteorologist Jeff Masters, who writes a popular weather blog. Last year, there were 19 named storms, 12 of which became hurricanes, including Earl, which sideswiped North Carolina just before Labor Day weekend and was the first hurricane to threaten New England since 1991.

The seasonal average is 11 named storms, including six hurricanes, two them major.

Meteorologists say La Nina also contributed to this past winter's barrage of blizzards in the northern United States, heavy summer flooding in Australia and recent tornadoes in the Southeastern U.S. But those events are no indication of what hurricane season might be like.

Even though La Nina's cooling effect is expected to end by June or July, the federal Climate Prediction Center says it could continue to affect weather for months.

Story: Expert: NYC, San Diego overdue for hurricanes

To be sure, there were other important factors that caused last year's tropical storms to form and strengthen: record warm Atlantic waters, low barometric pressure in the Caribbean Sea and favorable winds coming off Africa. Forecasters also looked at something called the "multi decadal signal," or weather patterns that tend to last several decades. Since 1995, the Atlantic basin has been in a pattern of high activity.

Meteorologists use all of these patterns, tools and data to predict the storm season, which runs through Nov. 30.

The National Hurricane Center released its seasonal hurricane forecast May 19, while another prominent group of forecasters from the University of Colorado has already predicted that 2011 will have 16 named storms, nine hurricanes and five major hurricanes.

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The hurricanes could inflict more misery on places like Louisiana and Alabama that have been plagued by flooding and deadly twisters this spring.

Ultimately, experts say, people should take note of the seasonal forecasts but not rely on them. Having an emergency kit and an evacuation plan is important even if the season isn't expected to be active.

Said Kottlowski: "You prepare for the worst, regardless of what the forecast is."

Interactive: Hurricanes: Destructive forces of nature (on this page)

Marshall Gaines, 75, recently moved from Maine to a barrier island on the Gulf of Mexico near St. Petersburg. He visited city hall and was given him a brochure on what to do to prepare for a hurricane — none of which he has done yet.

He said that his top hurricane-season priorities are stockpiling water and batteries, obtaining renter's insurance and determining which shelters or hotels take pets in case he and his two dogs must evacuate.

"I'm not too worried, I guess," he said. "I'm planning on getting the basics. Certainly, hurricanes are a possibility."

Copyright 2011 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Interactive: Hurricanes: Destructive forces of nature

Photos: America's worst hurricanes

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  1. Ike

    Galveston and neighbors along the Texas coast saw a direct hit by Hurricane Ike on Sept. 13, 2008. This view was at Crystal Beach, on the Bolivar Peninsula, on Sept. 18. (Eric Gay / AP) Back to slideshow navigation
  2. Ike

    A single home is left standing among the debris of lost homes in Gilchrist, Texas, on Sept. 14, 2008, a day after Ike made landfall. (David J. Phillip / Getty Images) Back to slideshow navigation
  3. Wilma

    Key West, Fla., saw storm surge flooding when Hurricane Wilma made landfall in southwest Florida on Oct. 24, 2005. Wilma roared across the Florida peninsula, pounding Miami, Fort Lauderdale and West Palm Beach. Wilma claimed 5 lives in Florida, 4 in Mexico and 14 in the Caribbean. (Carlos Barria / Reuters) Back to slideshow navigation
  4. Wilma

    Two men sit inside a destroyed mobile home in Fort Lauderdale, Fla. on Oct. 25, 2005, after Hurricane Wilma slammed across the state in about seven hours. Wilma caused $21.5 billion in property losses in the U.S. (Wilfredo Lee / AP) Back to slideshow navigation
  5. Rita

    Tens of thousands fled the Houston, Texas, area on Sept. 22, 2005, as Hurricane Rita neared landfall. (Rick Bowmer / AP) Back to slideshow navigation
  6. Rita

    Residents of Lafite, La., on Sept. 24, 2005, had to deal with waist high flooding as well as a trailer fire after Hurricane Rita passed through the area. Rita caused $11.8 billion in property damages in Louisiana, Texas and Florida. (Kevork Djansezian / AP) Back to slideshow navigation
  7. Katrina

    Survivors of 2005's Hurricane Katrina in New Orleans included this trio: Jennifer Cooper, 33, Otis Brown, 67, and Alber Jean, 50, far left. They fought their way up a highway off-ramp after escaping roof-level flood waters with a larger group aboard a motorboat. (Jim Winn / Vellum Media) Back to slideshow navigation
  8. Katrina

    Hundreds of New Orleans residents were rescued by helicopter and other means in the aftermath of Katrina, which made landfall on Aug. 29, 2005. Some 1,500 people lost their lives due to Katrina, which was the most expensive storm to hit the U.S.: $85 billion in property damage in Louisiana, Mississippi and Florida. (Vincent Laforet / Getty Images) Back to slideshow navigation
  9. Katrina

    Evelyn Turner cries alongside the body of her common-law husband, Xavier Bowie, after he died in New Orleans on Aug. 30, 2005. Bowie and Turner had decided to ride out Katrina when they could not find a way to leave the city. Bowie, who had lung cancer, died when he ran out of bottled oxygen. (Eric Gay / AP) Back to slideshow navigation
  10. Ivan

    The storm surge from Hurricane Ivan cut off this bridge north of Pensacola, Fla., on Sept. 16, 2004. (Rick Wilking / Reuters) Back to slideshow navigation
  11. Ivan

    The owner of this house on Cape San Blas, Fla., kneels to pray after Hurricane Ivan destroyed the property and hundreds more across the coast. U.S. property losses reached $15.5 billion. Ivan also claimed 25 lives in Florida and Alabama. (Phil Coale / AP) Back to slideshow navigation
  12. Frances

    The streets of Titusville and other southeast Florida cities were littered with debris after Hurricane Frances made landfall on Sept. 4, 2004. High winds and rain over several days combined to makeFrances a costly storm, with damages estimated at nearly $10 billion. (Bruce Weaver / AFP/Getty Images) Back to slideshow navigation
  13. Frances

    This mobile home park in Ft. Pierce, Fla., was swamped by storm surge water on Sept. 5, 2004, a day after Hurricane Frances first hit the coast. (Chris Hondros / Getty Images) Back to slideshow navigation
  14. Frances

    Pounding waves and storm surge from Frances left stretches of coastal roads in ruins, including this one in Jensen Beach, Fla. (Chris Hondros / Getty Images) Back to slideshow navigation
  15. Charley

    Volunteer Buddy Shipp sits in the destroyed Peace River Church of Christ in Punta Gorda, Fla., on August 22, 2004. The church's roof was blown off by Hurricane Charley but church members vowed to rebuild. Property damage from Charley reached $16.3 billion. (Mario Tama / Getty Images) Back to slideshow navigation
  16. Charley

    The roof of a garage is blown onto sheriff's cruisers in Punta Gorda, Fla., on Aug. 13, 2004. (Scott Martin / AP) Back to slideshow navigation
  17. Andrew

    Tens of thousands were made homeless by Hurricane Andrew, including Janny Vancedarfield of Florida City, Fla., seen here on Sept. 1, 1992, in front of debris that was once his house. Andrew was the second most expensive storm in U.S. history with property damage of $48 billion. (Lynn Sladky / AP) Back to slideshow navigation
  18. Andrew

    A tornado spawned by Hurricane Andrew destroyed this home on Aug. 26, 1992. (Paul J. Richards / AFP-Getty Images) Back to slideshow navigation
  19. Hugo

    Shrimp boats lie wrecked on the beach in McClellanville, S.C., on Sept. 26, 1989, after Hurricane Hugo hit. The storm caused $13.5 billion in property damage. (Jeff Amberg / Associated Press) Back to slideshow navigation
  20. Hugo

    This bridge on Sullivan's Island, S.C., was knocked out by Hurricane Hugo. The main span of a swing bridge was wrenched off its foundation during Hurricane Hugo's 135 mph winds. (Wade Spees / AP) Back to slideshow navigation
  21. Agnes

    Senior citizens are rescued in Wilkes Barre, Pa., on June 23, 1972, after Hurricane Agnes made the Susquehanna River overflow its banks. Property damage from the storm was estimated at $12.4 billion. (Phil Butler / Scranton Times via AP) Back to slideshow navigation
  22. Agnes

    Floodwaters triggered by rain from Agnes submerge homes in Pottstown, Pa., on June 23, 1972. Agnes was blamed for 122 deaths. (AP) Back to slideshow navigation
  23. Agnes

    Residents of Harrisburg, Pa., flee floodwaters from Agnes on June 23, 1972. (Paul Vathis / AP) Back to slideshow navigation
  24. Camille

    A boy takes a break after returning to the remains of his home in Buras, La., on Aug. 22, 1969, four days after Hurricane Camille hit the Gulf Coast and caused nearly $10 billion in property damage. (Jack Thornell / AP) Back to slideshow navigation
  25. Camille

    An 85-foot boat slumps in a Biloxi, Miss., yard after Camille's storm surge carried it more than 100 yards from its moorage. (Joe Holloway Jr. / AP) Back to slideshow navigation
  26. Betsy

    U.S. Highway 90 at Biloxi, Miss., went under several feet of water as powerful Hurricane Betsy slammed into the coast on Sept. 10, 1965. Betsy was responsible for 75 deaths and $11.9 billion in property damages. (AP) Back to slideshow navigation
  27. Audrey

    Crowds gather graveside for unidentified seaman killed during Hurricane Audrey, which made landfall on June 27, 1957, near the Texas-Louisiana border. The storm was the seventh deadliest in the U.S., claiming at least 416 lives. (Robert W. Kelley / Time & Life Pictures via Getty Image) Back to slideshow navigation
  28. Audrey

    Louisiana residents clean up wreckage in the aftermath of Audrey, which ripped through the southwest part of the state as well as eastern Texas. (Shel Hershorn / Getty Images) Back to slideshow navigation
  29. Galveston

    A large part of of Galveston, Texas, was reduced to rubble after being hit by a hurricane on Sept. 8, 1900. Between 8,000 and 12,000 people were killed and 10,000 left homeless from the storm, the worst natural disaster in U.S. history. (AP) Back to slideshow navigation
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