St. Johns River Waterspout, June 20, 2010
On, June 20, 2010, widespread convection developed across northeast Florida as a result of outflow and sea breeze mergers over a highly unstable environment with little wind shear. At 5:47 pm, a severe thunderstorm warning was issued for Southeast Clay, Eastern Putnam, Northwest Flagler and Central St. Johns counties due to a high potential of strong wet downbursts with small hail possible (Figure 1). Around 5:50 to 5:55 pm EDT, an outflow boundary from a storm over Clay County merged with an outflow boundary from the severe thunderstorm which was affecting Palatka (Figure 2). By 5:55 pm, the NWS received several reports of funnel clouds and a waterspout over the St. Johns River (Figure 3) from various locations and of various descriptions. The NWS issued a Severe Weather Statement on the severe thunderstorm at 6:07 pm EDT indicating that funnel clouds were reported with the thunderstorm.
There was not a mesocyclone throughout the history of the severe thunderstorm per Doppler radar imagery, and the lowest elevation radar beam over the St. Johns River in the vicinity of the convection was at best 3,500 to 4,100 feet above ground level. Given that there was no obvious rotational signature, it has been determined that the waterspout originated as a result of shallow outflow mergers, then the resulting horizontal rotation was stretched vertically into the approaching thunderstorm updraft (Figure 4). Do to the shallow nature of the rotation the weak vortex was short-lived and decayed likely by 6:10 pm as no more reports were received. The storm itself weakened significantly by 6:30 pm, and the severe thunderstorm warning was expired at 6:41 pm.
Several pictures were taken of a well-defined waterspout, including this one Figure 5.