Highlight: Mid-Atlantic heavy rain event more likely.
Fig. 1: The 12Z GFS trend is much wetter in the Mid-Atlantic States for this weekend.
Discussion: The 12Z GFS develops a low-pressure area well northeast of the Bahamas late tomorrow with steady strengthening as the system moves north and northwest and inland eastern North Carolina Saturday morning. From there, the system weakens while inland drifting slowly to Delaware by Sunday evening. The low-pressure area moves off the coast and eastward on Monday. The low-pressure area forms over the warm Gulf Stream and is likely to become a subtropical or pure tropical storm early this weekend before moving inland. Rainfall amount increases dramatically in the Mid-Atlantic region with widespread several inches expected and high spots exceeding 6 inches (Fig. 1). The 12Z GFS takes a tropical disturbance off West Africa now westward across the tropical North Atlantic over the next week or so and then northward into New England in 10+ days.
Fig. 2: Comparing forecast skill between ECM and GFS for the 16-30-day period for temperature forecasts across North America.
The extended-range forecast verification between ECM and CFS is now available. The 16-30-day temperature anomaly forecast for North America is forecast with better skill by ECM (Fig. 2).
The 12Z GFS maintained a warm Central U.S. forecast in the medium range while each coast was cooler. The U.S. population weight CDD forecast is slightly cooler than 24 hours ago (Table 1).
|Dates||CDD Forecast||12-Hr Change||24-Hr Change||30-Year NML||10-Year NML|
|Sep. 29- Oct. 5|
Table 1: The 12Z GFS U.S. population weight CDD forecast compared to 12 and 24 hours ago.