Although we are still quite early in the season to discuss the potential for a “slingshot” event that might cause typically southern spring migrants to overshoot their intended destinations along the Atlantic Coast, and although these events are relatively rare each season, team BirdCast would like to highlight some of the conditions along the Atlantic Seaboard that may facilitate such “slingshot” or “southern overshoot” events. Perhaps the best way to highlight these conditions are to consider the prevailing flow where migrants may be flying. Take, for example, the image below: any birds departing from Cuba or portions of the Eastern Greater Antilles and Bahamas tracking warm and moist air parcels might end up displaced far to the East of their intended destination. This flow, largely the result of a substantial frontal boundary advancing across the Gulf of Mexico and forecast to pass across the Florida Peninsula and fairly deep into the Caribbean, is at least one key component for transporting birds from departure to unintended arrival location. Will early migrants, perhaps Protonotary or Yellow-throated Warblers, Northern Parulas, and Indigo Buntings appear in unseasonably early locations along the Atlantic Seaboard? Probably not (but you should look anyway if you live along the Atlantic Seaboard! Or, er, Bermuda!) . . . Is this a useful illustration of at least one of the components that brings about spring overshoots of typically southern breeders along the Atlantic Coast? Probably!
A parcel of air beginning in the Florida Strait is forecast to travel far to the East over the coming 48 hours. Although it is very early in the season for such an event to produce overshoots, and the trajectories do not necessarily bring birds into the best possible position for falling out in New England or the Canadian Maritimes (Bermuda anyone?), the pattern is of interest and worth watching for and waiting for as the spring unfolds.
Another perspective on our air parcel from above – southwesterly winds push the air parcel (and perhaps birds within) over the Atlantic. Following the counter-clockwise rotation around the low pressure center, winds are favorable for any birds to make landfall much further up the coast. Depending on if, when and where birds are entrained within the cyclone, birds may make landfall up to several days after their initial departure.
And . . . a final note on the thread, so to speak. The reflectivity (top) and velocity (bottom) image pair below show primarily light to moderate bird migration over the Florida Straits between Cuba and the US. The blue-gray reflectivities between the Key West radar and the Cuban mainland are presumably mostly birds, moving north toward the radar (green pixels in the velocity image). This pair of images were created at approximately 1030PM EST. Whether any of these birds or others making similar flights become entrained in the circulation of Saturn writ large and end up somewhere far afield up the Atlantic seaboard, whether they fallout in changing wind fields in the Florida Keys on Wednesday morning, or whether they continue moving into more favorable habitat in southern Florida remains to be seen (at least until Wednesday morning . . .).
Posted by Farnsworth and Van Doren
