*3.4. Atmospheric Background*

Here, we examine two types of atmospheric systems with different scales and influence regions. One is a cold front that entered the study area around 0000 UTC, 6 January 2014 and left the region around 1800 UTC, 6 January 2014. As shown in Figure 3a,b, the cold front developed from a low-pressure center (1003 hPa), which was located in Indiana. Southwesterly wind was dominating in our study site. As the front moved to the east, air pressure continued to drop to a minimum of 992 hPa. When the front was passing Barataria Bay, the southwesterly wind abruptly changed to northwesterly wind. After the cold front's passage, wind was from the northern quadrants for about two days with a maximum magnitude of 13.5 m/s (Figure 4a). This cold front passage is a typical weather phenomenon between late fall and the following spring ( mostly October to April). During each of the frontal events, wind changes its direction from southern quadrants to northern quadrants when the cold front passages [50].

The other type of weather system studied here is Hurricane Barry. Hurricane Barry was first originated from a mesoscale convective vortex on 2 July 2019. It went into Gulf of Mexico on 10 July and developed into a tropical depression, before being upgraded to Tropical Storm Barry. It made its landfall on 13 July on Marsh Island, Louisiana, 190 km west of Barataria Bay as a Category 1 hurricane with a minimum sea-level pressure of 993 hPa and a maximum wind speed of 33 m/s (Figure 3c,d). The maximum wind speed measured at the Grand Isle station near Barataria Bay reached 14.5 m/s. Before Barry's landfall, northerly wind was dominating, and after the landfall of Barry, wind changed its direction to southerly wind and persisted for at least 4 days. From Figure 4b, one can see that Hurricane Barry had longer influencing period than the cold front mentioned above. Wind magnitude was also larger than that during the cold front.

**Figure 3.** Weather maps during the cold front at 0000 UTC, 01/06 and 1800 UTC, 01/06, and during Hurricane Barry at 0600, 07/11 and 1800, 07/14. (**<sup>a</sup>**,**b**) are the weather maps before and after the cold front passage in January 2014, and (**<sup>c</sup>**,**d**) are weather maps before and after the landfall of Hurricane Barry. Blue lines are contours of air pressure.

**Figure 4.** Wind vectors during cold front event in January 2014 and Hurricane Barry in July 2019. (max wind magnitude: 13.5 m/s and 14.5 m/s). (**<sup>a</sup>**,**b**) show the wind vectors during cold front and hurricane, respectively.
