Flooding in southern Mexico, tropical cyclone Noel and intense European storms in late October and early November 2007: Linked weather systems?

The purpose of this presentation will be to provide a multiscale overview of the atmospheric processes that contributed to pre-Noel heavy rains in southern Mexico, the slow development of Tropical Cyclone (TC) Noel and its complex extratropical transition (ET), and the resulting post-Noel downstream development and formation of two European storms. The emphasis will be on the likely physical linkages between multiple weather systems in the pre- and post-Noel environment.

Tropical storm (TS) Noel slowly developed out of a broad area of low pressure centered south of eastern Cuba and Hispaniola in late October 2007. To the north of Noel, a persistent low-level easterly flow prevailed south of a strong anticyclone with accompanying significant beach erosion from Florida to the Carolinas. Prior to the development of TS Noel, a surge of cool air plunged southward across the Gulf of Mexico and into the Gulf of Tehuantepec behind a strong cold front. The front crossed the Yucatan peninsular and Florida and then stalled over central Cuba several days before Noel formed. Deep tropical moisture (precipitable water values > 50 mm) was present along and ahead of the frontal boundary from near Honduras north-northeastward to the western Atlantic.

Between 27-29 October the frontal boundary retreated slowly westward into the eastern Gulf of Mexico in response to weak upper-level trough development over the northwestern Gulf of Mexico. The retreat of the frontal boundary was accompanied by low-level warm-air advection and rapid moistening over the Bay of Campeche and central Gulf of Mexico. Pre-existing low-level northerlies strengthened over the Bay of Campeche and southern Mexico as sea level pressures fell (rose) over the Yucatan peninsula (northwestern Gulf of Mexico). The resulting transport of deep tropical moisture from the vicinity of Noel westward and then southwestward into southern Mexico and the associated lift resulted in widespread heavy rains and flooding.

TS/TC Noel moved slowly northward until 2 November. Subsequently, it interacted with a weak upper-level trough over the southeastern US. Over the next few days, Noel accelerated north-northeastward, underwent a rapid ET while retaining some warm core attributes, impacted southeastern New England and Atlantic Canada, and generated a significant diabatically driven downstream upper-level ridge over the North Atlantic which resulted in conditions favorable for downstream development. A second midlatitude disturbance trailing behind Noel further strengthened the upper-level ridge. The resulting downstream trough development over northwest Europe enabled a potential vorticity anomaly to exit the arctic, move southeastward and trigger two significant storms, the first one over northwestern Europe and the second one over southeastern Europe.