ROANOKE, Va – Two very different tropical systems have brought significant impacts to southwest and central Virginia over the last month.
You may recall in September, the remnants of Hurricane Florence dropped 5-10 inches of rain (isolated higher) across part of the region. Tropical Storm Michael, on a widespread scale, brought half of that. Michael's rains brought record flooding to the Dan River at Danville, and the Roanoke River had its 8th highest crest in Roanoke.
The simple answer as to why Michael was so much worse than Florence? Duration, intensity and location
Florence crawled its way to the U.S. coastline and stalled over the Carolinas before inching its way toward Virginia. Florence's rain was drawn out over a longer period of time.
Michael blew up off of the Yucatan and raced toward the U.S. It was then pulled quickly north by another weather system.
It took days for Florence to reach us. The storm weakened significantly before impacting Virginia. The slow moving nature of the storm was the main reason those significant rain amounts were observed. The wedge was also in play keeping instability down, preventing extreme rainfall rates.
As a result of Michael racing toward Virginia, the storm maintained tropical storm strength well inland. This was forecast, as its center was south of us. Even though Michael moved quicker and dropped less rain overall than Florence did, the rain was much more intense. Rainfall rates eclipsed 2" per hour at times whereas Florence's rates were not nearly as impressive.
With Florence, the most significant rain fell over the Mountain Empire and I-77 corridor.
Michael's heaviest rain was more widespread, rather than focused on one particular area.
The combination of these factors, plus the extremely saturated ground made Michael a much more impactful storm than Florence.