Hurricane forecasters at the federal Climate Prediction Center are sticking with their forecast of an unusually active 2007 Atlantic hurricane season. But their August update has trimmed the upper end of the predictions issued in May.
The forecasters say water and atmospheric conditions in the Atlantic's main hurricane nurseries remain favorable for an above-normal season. The multidecadal conditions that have given rise to unusually active hurricane seasons since 1995 remain in place, they said. And, the chances that a La Nina cycle will arise in the central and eastern tropical Pacific Ocean have increased a bit.
With all that, the forecasters have made few changes in the storm counts released in May. The August update released yesterday predicts 13 to 16 named storms, seven to nine of which will become hurricanes. The May forecast called for 13 to 17 named storms and seven to 10 hurricanes.
The number of hurricanes predicted to reach Category 3 or higher remains unchanged, at three to five.
"Most of the atmospheric and oceanic conditions have developed as expected and are consistent with those predicted in May," said Gerry Bell, lead seasonal hurricane forecaster at the National Oceanic and Atmospheric Administration's Climate Prediction Center in Camp Springs.
The biggest uncertainty was whether La Nina conditions would develop as expected in the Pacific.
La Nina is a periodic cooling of the surface waters in the central and eastern tropical Pacific Ocean. The atmospheric changes that accompany it tend to encourage the development of hurricanes in the Atlantic.
"Today's El Nino/La Nina forecast ... indicates a slightly greater than 50 percent probability that La Nina will form during the peak of the hurricane season," Bell said.
"But more importantly, we are already observing wind patterns similar to those created by La Nina across the tropical Pacific Ocean and Caribbean Sea that encourage tropical cyclone development.
"Conditions are ripe for an above-normal season," he said.
The Atlantic hurricane season typically peaks between Aug. 20 and Oct. 1. So far, three named storms - Andrea, Barry and Chantal - have formed in the Atlantic. None has struck land. NOAA officials said that number is slightly above normal for the season to date.
NOAA's hurricane forecast update comes on the heels of a similar update from Colorado State University storm experts Phil Klotzbach and William Gray. Pointing to "slightly less favorable conditions in the tropical Atlantic," they cut their storm forecast from 17 named storms to 15, nine hurricanes to eight, and five Category 3 storms to four.
Both August forecasts remain well above the long-term averages for the Atlantic: 11 named storms, six hurricanes and two storms reaching Category 3 or higher.