FAIRHOPE, Ala. — The Colorado State University hurricane forecast team and the NOAA Climate Prediction Center were on the same page this week. Both are predicting a weak El Niño will form in time for the peak of the 2009 Atlantic Hurricane Season, something that would make conditions less favorable for tropical system formation and development.

CSU researchers on Tuesday predicted a slightly below-average Atlantic basin season based on a cooler-than-normal tropical Atlantic and a greater potential for a weak El Niño to begin developing during the summer.

The report issued by the team suggests 11 named storms will form between June 1 and Nov. 30. Five of the storms are expected to become hurricanes, with two developing into major hurricanes (Saffir-Simpson Scale category 3, 4 or 5) with sustained winds of 111 mph or more.

The CSU April forecast had projected 12 named storms, six hurricanes and two major hurricanes. Long-term averages are 9.6 named storms, 5.9 hurricanes and 2.3 major hurricanes per year.

“We believe that there is a slightly greater chance of a weak El Niño developing this summer/fall than there was in early April,” stated Dr. William Gray, who is beginning his 26th year forecasting hurricanes at Colorado State. “El Niño conditions would likely increase levels of vertical wind shear and decrease Atlantic hurricane activity.”

The CSU team has noted anomalous cooling of sea surface temperatures in the tropical Atlantic over the past few months. Cooler waters are associated with dynamic and thermodynamic factors that are less conducive for hurricane formation.

NOAA seems to agree. The Camp Springs, Md.-based Climate Prediction Center pointed out Thursday that conditions are indeed favorable for a transition from ENSO-neutral to El Niño conditions from June through August.

ENSO-neutral conditions were in force across the equatorial Pacific Ocean during May. But as sea surface temperatures increased there for the fifth consecutive month, surface and subsurface oceanic anomalies were recorded that typically precede the development of El Niño.

According to the NOAA report, “From early 2007 through April 2009, enhanced low-level easterly winds persisted near the Date Line, interrupted only briefly by Madden-Julian Oscillation (MJO) activity. However, during May 2009, both the lower-level equatorial winds were near-average in that region despite the absence of the MJO. Also, suppressed convection expanded westward along the equator from the Date Line to Indonesia. The recent oceanic and atmospheric anomalies are consistent with ENSO-neutral conditions, but also reflect the evolution towards a potential El Niño.”

NOAA officials say all statistical models predict ENSO-neutral conditions will continue for the remainder of 2009. Most dynamical models, however, including the NCEP Climate Forecast System, predict the onset of El Niño during June-August. Current observations, recent trends and the dynamical model forecasts indicate that conditions are favorable for a transition from ENSO-neutral to El Niño conditions, they added.

The CSU forecast team updated its U.S. landfall probabilities in light of the changing conditions. These probabilities are calculated based upon 20th century landfall statistics and then adjusted by the latest seasonal forecast.

“The probability of a major hurricane making landfall along the U.S. coastline is 48 percent compared with the last-century average of 52 percent,” stated Dr. Phil Klotzbach, lead forecaster.

The hurricane forecast team’s probabilities for a major hurricane making landfall on various portions of the U.S. coast:

•A 28 percent chance that a major hurricane will make landfall on the U.S. East Coast, including the Florida peninsula (the long-term average is 31 percent).

•A 28 percent chance that a major hurricane will make landfall on the Gulf Coast from the Florida panhandle west to Brownsville, Texas (the long-term average is 30 percent).

CSU has added landfall probabilities for the Caribbean and Central America. This season, the forecast team expects a 39 percent chance of a major hurricane tracking into the Caribbean, which is slightly lower than the long-term average of 42 percent.

CSU forecasters say the currently observed climate factors are similar to conditions that existed during the 1959, 1960, 1965, 2001 and 2002 seasons. The average of these five seasons had slightly below-average activity, and Klotzbach and Gray predict the 2009 season will have activity in line with the average of these five years.

As a result, the team predicts tropical cyclone activity will be 90 percent of the average season. The 2008 season produced such activity that was around 160 percent of the average season.

Gray and Klotzbach, as well as NOAA, National Hurricane Center and Federal Emergency Management Agency personnel warn coastal residents not to abandon their hurricane preparedness measures simply because of a less active seasonal forecast. They say major hurricanes can devastate coastal communities even in less active seasons.