Team BirdCast continues to try to provide some insights on the comings and goings of vagrants in the Bering Sea! The coming days have some great potential for Asian strays to appear in the Alaskan island chains, particularly given pervasive high pressure over the central eastern Pacific that is driving low pressure systems toward and to the North of the Aleutians and into the Bering Sea. Some exciting tales of birding have come forth from the Pribilof Islands of late, including the discovery of this Middendorff’s Grasshopper-Warbler photographed by Doug Gochfeld on St. Paul Island, AK on 16 September 2013.
A substantial low pressure system in the western Bering Sea is followed by high winds wrapping around the low. This system is being pushed by high pressure off the US Pacific Coast to follow a more northerly path before the low is forecast to stall in the Siberian Arctic.
However, as high pressure builds in behind the stalled system and eventually pushes its way East, a new and strong boundary forms to the West and South of the Aleutian Islands by early morning on 20 September between air masses. Some birds migrating in northeastern Asia and over the western Pacific behind this boundary, in favorable conditions associated with a frontal passage, are likely to be entrained behind this now, more substantial front and carried into the Bering Sea.
Presumably, the more southerly islands in the Bering Sea will have a much better chance at Asian strays as the system moves East, given its forecast track over or very close to the Aleutians. Southwesterly and westerly flow becomes westerly and northwesterly flow in these areas as a low reorganizes and moves toward the Alaskan mainland early on 21 September. As the high builds into the area and winds remain strong, birds entrained in the system will seek shelter in any habitat available.
Our friends in the Bering Sea will hope for, among other Asian surprises, another Middendorff’s Grasshopper-Warbler or Asian Brown Flycatcher, like this individual photographed by Doug Gochfeld on St. Paul Island, AK on 9 September 2013. 20-23 September will be an interesting time for vagrant landbirds, and we look forward to more tales and photographs of the vagrants that arrive!