10(b). Northeasterly and easterly winds continued to blow up to 16:00 and 17:00 UTC (Fig. 10(d) and (e)) when the water from both the northern Bay and the continental shelf converged making the surge elevation reach to its maximum. Directly after 17:00 UTC on the same day, as the eye of the hurricane swept over the Bay mouth, the winds changed to a northwesterly direction with a maximum speed of 23.4 m s−1 (not shown), which elevated the water level specifically along the Eastern Shore of Virginia. From 18:00 UTC on, consistent large outflows from the Bay

to the ocean were observed and the surge height started to decrease, as shown in Fig. 10(f), (g), and (h). For Hurricane Isabel, time sequences of the elevation and sub-tidal depth-integrated flows were plotted in Fig. 11. (It should be noted Z-VAD-FMK solubility dmso that different background color

scales was used for Figs. 10 and 11). There were initially a seaward outflow driven by northeasterly winds (Fig. 11(a)), but from 15:00 UTC, 18 September, the seaward outflow along the Bay mouth started to decrease and selleckchem changed to an inflow. As the remote northeasterly and easterly winds strengthened up to 23 m/s during the period from 15:00 to 21:00 UTC, September 18, it generated very strong landward inflows from the continental shelf into the Bay as shown in Fig. 11(c) and (d). Over the period from 01:00 UTC to 03:00 UTC on 19 September, as Hurricane Isabel made the landfall PRKD3 and moved inland on a northwest track, the trailing edge of the cyclonic, local winds (i.e., southeasterly and southerly winds) became dominant. This pattern of wind is very persistent and efficient in intensifying the

northward inflows and set up against the head of the upper Bay (Fig. 11(d), (e), and (f)). During this period, the peak surge height gradually built up in the upper Bay (not shown). In the end, the pressure gradient created by the sea level slope from the north to the south drove the water in an opposite direction to that of the wind, as shown in Fig. 11(h). From the comparison of the Bay’s water level response to hurricanes, it was found that the storm surge in the Bay has two distinct stages: an initial stage setup by the remote winds and the second stage induced by the local winds. For the initial stage, the remote wind was setup by both hurricanes initiated in the coastal ocean resulting in the similar influx of storm surge; but for the second surge, the responses of the Bay to the two hurricanes were significantly different. Hurricane Floyd was followed by down-Bay winds that canceled the initial setup and caused a set-down from the upper Bay. Hurricane Isabel, on the other hand, was followed by up-Bay winds, which reinforced the initial setup and continued to increase the water level against the head of the Bay. Longitudinal distributions of 25-h tidally averaged velocity and salinity during the hurricanes are plotted in Fig. 12(a) and (b) for Hurricanes Floyd and Isabel, respectively.