The TC Diurnal Cycle: The Landfall Before the Landfall

The TC diurnal cycle is characterized by a dramatic radial expansion of the TC cloud field (i.e. diurnal pulse or wave) that begins propagating away from the storm around local sunset each day, eventually reaching areas hundreds of kilometers from the storm by the following afternoon. Observations and model simulations are now suggesting that diurnal pulses/waves likely involve a deep vertical layer of the troposphere and are often characterized by marked changes in TC structure as they propagate away from the storm with squall line-like behaviors. For landfalling TCs, diurnal pulses/waves can arrive onshore several hours before the 34 kt tropical storm force winds reach the coast and appear on radar as rapidly propagating, narrow bands of high reflectivity. These features are often referred to as “outer bands”, but in many instances, may actually be highly predictable radially propagating TC diurnal pulses/waves that can bring tropical storm force conditions and heavy precipitation to the coastline well in advance of the actual landfall. This presentation will use GOES satellite imagery, P-3 lower fuselage (LF) and tail Doppler radar data, WSR-88D data, and land-based surface observations to examine several TC diurnal pulses/waves from 2014 Hurricane Edouard and select landfalling TCs from 2017.