Tropical Storm Olga in the Gulf of Mexico October 25-26, 2019

Tropical Storm Olga developed from a tropical wave that propagated from Belize, over the Yucatan Peninsula and into the Bay of Campeche, where it developed into a late season tropical cyclone on October 25. Before making landfall on the southeastern coast of Louisiana it merged with a cold front and became an post-tropical storm that caused a surprising amount of damage. Although it caused more damage on land than at the coast, it did produce a storm surge of 1 m in western Mississippi, and about 0.5-0.6 m in Lakes Bourne and Pontchartrain, which is significant in a region of flat coastal topography. The maximum surge coincided with neap tides, resulting in a smaller surge tide . A seiche with a period of about 3 hrs was set up in Lake Pontchartrain, which lasted approximately 17 hours. Surface currents measured with 25 MHz CODAR SeaSondes in the Mississippi Sound and 5 MHz SeaSondes further offshore in the Mississippi Bight showed a shifting of currents to the west prior to the storm impact as winds were coming from the southeast, then shifting to the north in the Sound when maximum water levels were recorded at the NOAA Bay-Waveland tide gauge. Once currents shifted to coming from the east in the Sound the maximum water levels were recorded at the USGS stations in the western Mississippi Sound, followed by peaks in salinity.