The poleward movement of a decaying tropical cyclone often results in a rapidly moving and explosively deepening midlatitude cyclone. The reintensification of the remnant tropical cyclone as an extratropical cyclone depends on the phasing between the decaying tropical cyclone and a midlatitude environment that is favorable for re-intensification. Because of the typical rapid translation speed of the decaying tropical cyclone, accurate extended range prediction of the phasing between the remnant tropical circulation and midlatitude environment into which it is moving is critical. However, the complex physical interactions that occur with the structural changes associated with the extratropical transition (ET) of the decaying tropical cyclone often contribute to large errors in numerical forecasts from operational global forecast models. Furthermore, forecast errors associated with the ET may propagate rapidly downstream and upstream of the ET location.

In this study, measures of the relative predictability in global numerical weather forecasts during ET events are computed based on ensemble prediction systems. Often, a poleward-moving tropical cyclone is related to an increase in variability among ensemble members, which implies a decrease in predictability. Ensemble prediction systems are utilized in a framework defined relative to the poleward-moving tropical cyclone. The impact of the increased standard deviation in ensemble members due to the tropical cyclone on the midlatitude circulation is measured as is propagates downstream and upstream of the ET location. The impact of the ET event on overall forecast predictability is defined relative to various paradigms of the ET process (i.e., tropical and barcoclinic types over the North Atlantic and northeast and northwest types over the western North Pacific).