Manual surface analyses of pressure and temperature have been completed every six hours from 0000Z 8/31 to 2300Z 9/01 using METAR observations from SC, NC, VA, and (a few) offshore. These analyses were then compared to MSAS 2-D surface frontogenesis and equivalent potential temperature plots to better confirm the frontal location.
Before Ernesto made its second landfall in NC, an MCS developed in NC and VA along the cold front pushing through the SE US on 8/30. Using Galarneau et al.’s (2010) criteria for PREs: 1) Reflectivity ≥ 35 dBZ for at least 6 hours, 2) Rainfall ≥ 100 mm (4”) in 24 hours, 3) Clear separation between PRE and TC rainfall shield, and 4) Deep tropical moisture from TC advected into PRE, it does appear that the MCS on 8/30 met all these criteria. Futhermore, Galarneau et al. (2010) classified the MCS preceding Ernesto as a PRE.
After the MCS dissipated, the cold front stalled along the coast around 0600Z 8/31. As Ernesto approached the coastline, the coastal front strengthened and became entrained into the circulation between 0000Z and 0600Z 9/1. As Ernesto moved inland, it began transitioning into an extratropical cyclone with a split frontal structure developing by 0600Z 9/1:
An occluded front formed by 1800Z 9/1 as the extratropical transition process was nearly complete:
The presence of a frontal boundary provided enhanced forcing for lift, particularly to the east of the TC center where a moist southerly flow was lifted. In the vicinity of frontal lifting nearest the TC center where the circulation and resultant lifting was strongest, a region of enhanced radar reflectivities NE of the TC center led to a swath of extremely heavy rainfall producing storm total accumulations in excess of 10 inches through eastern North Carolina and Virginia.
The next steps will include looking at upper air charts for the presence of any jet features. Additionally, model predictability for this event will be examined. Specifically, can the models replicate the frontal boundary structure and precipitation asymmetries? What model physics, resolution, and initial conditions best represent the boundary structure and precipitation distribution?