Changes in the Circulation of Tampa Bay Due to Hurricane Frances as Recorded by ADCP Measurements and Reproduced with a Numerical Ocean Model

Hurricane Frances is shown to greatly alter the hydrodynamics within Tampa Bay, Florida, and the exchange of water with the Gulf of Mexico in both observational data and a realistic numerical circulation model of the Tampa Bay estuary. Hurricane Frances hit Tampa Bay on September 5, 2004 with surface winds peaking twice near 22 m s ⁻¹ . There were three stages to the hydrodynamic effect of Frances on Tampa Bay. The first stage included the approach of Frances up to the first wind peak. The winds were to the south and southeast. During this stage sea level was maintained below mean sea level (MSL) and the residual current (demeaned, detided) was weak. The second stage began as the winds turned to the east and northeast, as the eye passed near the bay, and ended as the second wind peak appeared. During this stage the residual currents were strongly positive (into the bay), raising sea level to 1.2 m above MSL at St. Petersburg. The measured residual circulation peaked at over +0.7 m s ⁻¹ near the surface. The model shows this velocity peak yielded a maximum volume flux into the bay of +44,227 m ³ s ⁻¹ , displacing a total volume of 1.5 billion m ³ in just a few hours, about 42% of the bay volume. In the third stage a strong negative flow developed as the wind and sea level relaxed to near normal levels. The ADCP measured a peak outflow of −0.8 m s ⁻¹ during this time. Model results indicate a maximum flux of −37,575 m ³ s ⁻¹ , and that it took about 50 h to drain the extra volume driven into the bay by Hurricane Frances.