Upper-level winds near isles disrupt storms from the east

The downgrading of Tropical Storm Cosme from a hurricane Monday night is quite typical for storms coming across the Pacific Ocean from the east, meteorologists say, because the Hawaiian Islands have a natural barrier to storms from that area.

Despite the warm water surrounding the state and tradewinds from the northeast, it's the strong upper-level winds, predominately from the southwest, that keep the state from suffering more often from tropical storms and hurricanes, said Jim Weyman, director of the Central Pacific Hurricane Center.

Strong upper-level winds, 25,000 to 30,000 feet above sea level, are able to shear off the tops of thunderstorms in tropical systems, disrupting the wrap-around flow and keeping them from getting stronger, Weyman added.

The winds are caused by the tropical upper tropospheric trough, which often sits to the west of the state and causes the southwest flow.

But weather, including hurricanes, has a tendency to buck trends.

The shearing apart of Cosme was actually caused by strong easterly high-level winds, thanks to a high-pressure system currently dominating the northern Pacific Ocean, Weyman said.

The most damaging storms that have hit the islands, however, came from the south and southwest. These storms, which often form during El Nino periods when the tropical upper tropospheric trough moves to a more northerly position, avoid the high winds and come into the warm waters surrounding the islands nearly intact.