Storm surge estimation due to the incidence of simultaneous tropical cyclones in Mexico

As a result of its geographical location, Mexico is highly vulnerable to the impact of landfalling tropical cyclones. Such extreme events produce severe flooding during and after their occurrence, which may be ascribed to the induced storm surge and/or the resulting torrential rainfall. Very recently, in September 2013, the simultaneous occurrence of two tropical cyclones affecting both basins of the country was recorded. Tropical Storm Manuel in the Pacific and Hurricane Ingrid (category 1) in the Gulf of Mexico, made landfall during a 24 hours period on September 15 and 16, 2013. The systems affected 24 states (i.e. 77% of Mexico was under continuous rain), and produced severe flooding along the rivers discharging to the Pacific Ocean. Their low intensity with regards to the maximum wind speed did not produce a significant storm surge. Although rare, the concurrence of two extreme events poses many questions on the vulnerability of the country to such storms.

This investigation presents an estimation of the storm surge generated by simultaneous events in Mexico. We utilize historic and synthetic hurricane data, from which we estimate the associated water levels in two particular locations on the basins. In the Gulf of Mexico, the city of Tampico is selected, while in the Pacific side of the country, the city of Manzanillo is chosen. The storm surge is derived from a 2D hydrodynamic model, which is forced by historic and synthetic wind fields. The model by Emanuel and Rotunno (2011) was employed for the generation of the wind fields for both data sets, which is based on eye location, maximum wind speeds, radius of maximum winds, minimum and neutral pressure. The hydrodynamic model was used to determine storm surge levels for simultaneous events. We demonstrate that in order to obtain conservative estimates on the storm surge generated by rare simultaneous events, the synthetic hurricanes dataset provides a good alternative to tackle this problem. Based on the synthetic tracks for both locations, a simultaneity analysis was performed to determine the probability of occurrence of high intensity events during the same time frame, as well as the resulting storm surge levels. Although the probability of occurrence of simultaneous high intensity events is low, the latest events in Mexico (Ingrid and Manuel) show that the implications for disaster management makes it essential to consider such scenarios.