The Challenges of Surveying Tornado Damage after a Major Hurricane

After major weather events, such as flooding, hurricanes and tornadoes, the National Weather Service (NWS) conducts storm surveys, in coordination with local officials, to assess damage and gage the magnitude of the event. Hurricane Michael made landfall in the Florida Panhandle in October, 2018, causing extensive damage to the infrastructure, structures, and vegetation from the Gulf Coast into Southwest Georgia. The NWS documented much of the damage during the post-event surveys. On March 3, 2019, a tornado outbreak occurred across portions of the same area. In fact, five out of the twelve tornadoes impacted areas that had pre-existing severe to catastrophic tree damage from Hurricane Michael.

Typical storm surveys produce a variety of challenges on their own, including timely documentation of damage prior to it being disturbed, examining the nature of damage to distinguish straight line from tornadic winds, and assigning the correct damage indicator to measure intensity. Following the March outbreak, much of the hurricane and tornado damage was juxtaposed. Several techniques for discriminating the source of damage will be discussed, including both in-situ and remote sensing methodologies. For example, trees were examined for indications of past damage and how they were felled, particularly in relation to the hurricane’s track at a single point. In one dramatic case, dozens of trees were felled pointing to the northeast due to hurricane winds, while several trees across the street were felled in the opposite direction due to tornadic winds. In addition, given the weakened state of the trees due to the hurricane, careful consideration had to be given to the assigned wind speeds, often leading to the lower end of the scale for particular Degrees of Damage. This presentation will examine the long term challenges associated with damage assessments in hurricane impacted areas, with the goal of improving such assessments.