Day 243: Complicated East Coast Pattern

Posted by pmarsh on 31 Aug 2010 | 1 comment

Many people are focused on Major Hurricane Earl tonight, wondering what the eventual path will be. The official forecast from the National Hurricane Center (NHC) continues to keep Earl just off the east coast of the United States. However, because of the large size of Earl’s wind field, a hurricane watch has been issued for portions of North Carolina. Even if the eye does not make landfall, it should be close enough that portions of North Carolina will experience some wind and rain.

The eventual path of Earth will be dictated by events that are currently well removed from the hurricane. A strong short-wave trough at 500 mb is forecast to race across the northern plains over the next few days. The southeast shear downstream of the trough axis is forecast to help “steer” Earl to the north and northeast. The speed at which the short-wave trough moves across the northern United States will be impacted by the strength of the ridge over the eastern United States (center denoted by a “N” below).

Rotating around the periphery of the east coast ridge are several mid- or upper-level lows (denoted by small letter “x”). Currently, these upper-level lows are resulting in strong shear (by hurricane standards) across the top of Earl. As these upper-level lows continue to move westward, away from Earl, the shear should decrease allowing for possible strengthening. Might these upper-level lows aid the destruction process of the ridge?

I still don’t think it is wise to rule out a potential North Carolina landfall. Even if Earl does not make direct landfall, it will be close enough to cause significant societal impacts. A second area where landfall is possible is in New England, as hurricane Earl races ahead of the vigorous 500mb short-wave trough.