Birders in coastal areas of the West, particularly in the Pacific Northwest, should watch coastal migrant traps, as light but incrasingly northeasterly winds aloft should bring some migrant songbird concentrations to these areas. The remainder of the region will see primarily scattered light movements in precipitation free areas, as light winds aloft are mostly marginal for larger movements to occur. This pattern continues through the weekend and into the middle of next week. However, the Desert Southwest and Four Corners region will see increasing threat for local precipitation, which will shut down migration where and when it occurs.
Light and variable winds aloft spawn moderate migration in rain free areas to begin the weekend. Birders in the border states should watch for heavier migration in northerly winds and for potential fallouts as these migrants interact with rain in the Dakotas and Minnesota on the weekend. In the southern plains Isaac’s influence will shut down movements near its path, but spawn movements in rain free areas to the North and West of its center of circulation. Slightly more favorable conditions begin the week in many areas, and migration will be moderate to heavy in many areas after several days of unfavorable conditions. Tuesday and Wednesday look to be potentially heavy migration nights as conditions become favorable with the exit of low pressure and Isaac to the east. After this large flight conditions become more marginal and numbers of migrants will decrease to end the week, with moderate movements scattered through the region.
Upper Midwest and Northeast
Isaac’s remnants affect the region early in the weekend, and unfavorable conditions prevail over much of the Mississippi River valley. However, high pressure over the western Great Lakes facilitates moderate to heavy movements from the eastern Great Lakes east through the Appalachians and even to the Atlantic coast. As Isaac’s remnants and the high pressure center move east, western areas continue to see unfavorable conditions for much movement, whereas eastern areas from New York through New England should see continued moderate to heavy movements. Conditions reverse as the week begins – widespread rain will shut down movements in eastern and coastal areas, while favorable northerly and westerly flow will spawn widespread moderate and locally heavy movements in western areas. Birders in the Great Lakes should watch for fallouts in and around bodies of water early in the week. Conditions improve by midweek for widespread moderate and heavy movements from the Mississippi to the Atlantic as precipitation exits and high pressure builds into the southern Appalachians. High diversity of Neotropical migrant songbirds should be apparent in many of these movements, particularly warblers.
Gulf Coast and Southeast
Isaac dominates the scene in western areas to begin the weekend, and generally southerly flow across Texas and the western Gulf continues even after Isaac departs. Scattered light to moderate movements will occur in many of these areas, however, assuming many birds will be ready to depart after days of unfavorable conditions. A different story evolves east of the Appalachians, where more widespread moderate and even heavy movements are likely early in the weekend. Conditions deteriorate through the end of the weekend as Isaac’s remnants move east, but areas free of rain will experience moderate to heavy flights, particularly along the immediate coasts. Westerly flow and scattered precipitation prevail early in the week, and moderate to heavy movements may occur in areas free of rain. By midweek, moderate to heavy movements in northerly winds occur from the Mississippi to the Appalachians and Carolinas, while Florida will see mostly unfavorable conditions are any movements. At the end of the week, birders in the Carolinas and Georgia should watch for fallouts in coastal habitat, as northerly winds and rain may co-occur.
New York City Region
Westerly and northerly winds spawn moderate to heavy nocturnal movements in the greater New York area for much of the weekend. Diurnal movements should be apparent on Saturday and Sunday mornings. The beginning of the week will be increasingly less favorable for migration, as southerly winds and precipitation move into the region. As this weather associated with the remains of Isaac exits, conditions will improve – this is forecast to occur on Tuesday night, suggesting the potential for migrants to fly into poor visibility conditions, a scenario that frequently spawns fallouts in the city’s parks. As winds shift North and West on Wednesday, conditions for viewing diurnal and nocturnal migration are favorable, and moderate to heavy movements should be apparent on Wednesday through the end of the week. Expect high diversity of species in the city parks during this week, including 20+ species of warbler; diurnal movements should include Ospreys, the first pulses of Broad-winged Hawks, small numbers of Ruby-throated Hummingbirds and southbound Double-crested Cormorants. Additionally, depending on timing of low pressure passage, it is likely that morning flight will occur on Wednesday or Thursday morning.