Abstract
The early evolution of a coastal front that formed off the southeast coast of the United States on 24 January 1986 is examined. Satellite and radar imagery together with the intensive surface, upper0air, and aircraft observations available during GALE are combined in an analysis highlighting the low-level mesoscale features associated with the front. The main fonrtal surface appears to form as separate narrow precipitating bands of convection slowly propagate from the east and consolidate near the western edge of the Gulf Stream. The frontal zone to the west is characterized at low levels by alternate axes of convergence and divergence extending roughly parallel to the coast. The role of these semipermanent features in the evolution of the front is discussed and compared with the classical frontal, model. Analysis of the diagnostic frontogenesis terms shows that while confluence reinforces the thermal gradient locally along confluent axes, the differential in diabatic heating, arising principally from differences the underlying surface, promotes the westward displacement of the northern half of the frontal zone. The subsequent inland propagation of the front is found to be complex. The northernmost section of the frontal boundary initially moves steadily inland, leaving a small frontal remnant at the coast, then the entire northern half of the front jumps inland discontinuously. By 1800 UTC on 25 January, the norther portion of the front has become a broad zone established over 200 km inland, while the southern portion has maintained a very sharp boundary offshore, coincident with an oceanic thermal discontinuity.
