USGS Scientists Work on Four Tropical Cyclones at Once

At the mid-September peak of a very active Atlantic Hurricane Season, with four named storms and three tropical disturbances on the move at the same time, some USGS scientists are responding to multiple storms at once. Their fast-paced work will help emergency managers and coastal planners protect lives and property from coastal erosion and flooding, and will provide scientists with real-world information that can make future storm surge, flood and coastal change forecasts more accurate.

While the USGS Coastal Change Storm Hazards team is forecasting the coastal erosion Hurricane Sally is expected to cause at landfall along the Gulf Coast, the team is simultaneously predicting the impact that far-traveling ocean waves from Hurricane Paulette and Tropical Storm Teddy will have on sandy shorelines in the Mid-Atlantic and Northeastern U.S.

Meanwhile scientists who set out instruments to monitor Hurricane Laura’s storm surge when it made landfall on the Southwest Louisiana-East Texas coast Aug. 27 have had to pause their work recovering those instruments. Instead, they deployed a new set of devices to monitor Hurricane Sally’s expected landfall on the Southeast Louisiana-Mississippi coast.

The situation is not unprecedented for USGS hurricane experts. Between late August and late September 2017, hundreds of USGS staffers were in the field in Puerto Rico, Texas, Florida and the Northeastern U.S. as those regions dealt with flooding, erosion and wind damage caused by Hurricanes Harvey, Irma and Maria and post-tropical cyclone Jose. But this season’s hurricane work is unusually concentrated, with the low-lying central Gulf Coast taking the brunt of four storms, including two hurricanes in quick succession.

“This is one of the busiest seasons we have had, where we have been consistently been working on one storm before another one comes.” said hydrologist John Storm of the Lower Mississippi-Gulf Water Science Center. “We are also preparing for additional storms that are projected to follow.”

Last week USGS scientists from the Lower Mississippi-Gulf Water Science Center, the Wetland and Aquatic Research Center, and the Texas-Oklahoma Water Science Center measured high water marks – telltale lines of weeds, seeds or storm debris that indicate how high storm surges or floodwaters reached – in areas affected by Hurricane Laura, particularly in Southwest Louisiana.

A pair of USGS instruments installed in advance of Hurricane Sally on a pavilion at the Laketown boat launch on Lake Pontchartrain in Kenner, Louisiana on Sunday, Sept. 13. A barometric pressure sensor in the upper right, wrapped in yellow tape, records pressure changes associated with a tropical cyclone’s passage. A storm tide sensor, below, records the weight of water that may pile up above the instrument during the storm. These are some of the sensors installed by USGS scientists at 12 sites in Louisiana, Alabama and Mississippi. Credit: Matt Heartsill, USGS. Public domain.

As Sally approached, USGS scientists and field crews deployed 12 storm-tide sensors along the coast from southeast Louisiana to Mobile Bay, Alabama. The sensors, specialized instruments which record the timing, depth and duration of storm-driven ocean waters striking the shoreline, are attached to structures that are likely to survive the storm. USGS crews normally retrieve them within a few days of a storm’s passage. About 29 storm-tide sensors were deployed before Hurricane Laura made landfall. Field teams have retrieved all of the storm-tide sensors except one, which was unreachable due to Laura’s heavy damage to some roads and bridges.

COVID-19 has also posed new challenges for the USGS teams, who have been taking additional safety measures while out in the field.

“We have the scientists and crews in the field, traveling in trucks individually and maintaining social distancing while they deploy and later collect storm-tide sensors,” said Marie Peppler, the USGS Emergency Management Coordinator. “It will take a little longer and have more complex planning to get the science done, but safety will always come first.”

The USGS Coastal Change Hazards Storm Team, based in St. Petersburg, Florida, is using two different sets of forecasting techniques to predict the likely effects of Hurricane Sally, which is expected to make landfall soon, and Hurricane Paulette and Tropical Storm Teddy, which are far at sea, but are affecting the U.S. Atlantic coast anyway.

The team, in collaboration with NOAA, has developed an experimental, publicly available forecasting tool called the Total Water Level and Coastal Change Forecast Viewer, which predicts water level changes over time along most of the Atlantic coast. The viewer allows members of the public to zero in on a specific section of sandy shoreline and watch water levels rise and fall in that location over several days, as storm waves and tides interact. This information allows emergency planners and coastal residents to understand not only what locations are likely to encounter coastal erosion, but also when peak water levels will occur, and whether abnormally high water levels will return on later tide cycles.

On Monday the viewer’s results showed storm waves generated by Hurricane Paulette are likely to cause erosion at the base of the dunes – called “collision” – along portions of the Atlantic coast from North Carolina to Maine. On a minority of the beaches in North Carolina, Virginia, New Jersey, New York, Massachusetts and Maine, the viewer results show storm-driven water is likely to overwash the tops of the dunes. The erosion is most likely to occur on Tuesday and Wednesday, September 15 and 16, with later effects likely from Tropical Storm Teddy.

“The tropical systems in the Atlantic, though far from the coast, have the potential to cause beach and dune erosion and even overwash along the U.S Atlantic coast from North Carolina through Maine,” said oceanographer Kara Doran, leader of the Coastal Change Hazards Storm Team.   “The swells from these storms are large, long-period waves that elevate water levels at the coast, even though there isn’t any accompanying storm surge. In fact, it could be a beautiful sunny day,  but you wouldn’t want to go to the beach during these dangerous surf conditions.”

 “That’s why these continuously running forecasts of coastal water levels are important,” Doran said. “They can alert people to coastal hazards in all kinds of situations.”

The team’s Coastal Change Forecast Model predicts more than one-third of sandy beaches in Mississippi may be overtopped by storm waves by Hurricane Sally, and more than half of that state’s beaches may have erosion at the base of the dunes. Along the Louisiana coast, where sand dunes are uncommon, about 14% of coastal berms may be overwashed. The forecast will be updated whenever the National Hurricane Center’s surge forecasts are changed. The most current version is always available on the USGS Coastal Change Hazards Portal.

The USGS Coastal Change Hazard Portal predicts Hurricane Sally’s potential erosion effects on Gulf beaches. This map of the September 15, 2020 prediction has an innermost strip showing where erosion is very likely to occur at dunes’ base; a middle strip where dunes are very likely to be overwashed by storm waves; and an outer strip where the dunes are very likely to be inundated, with flooding behind them. “Very likely” is defined as a 90% or better chance. The predictions are updated frequently at https://marine.usgs.gov/coastalchangehazardsportal/    USGS, Public domain.

The USGS coastal change forecast can help local emergency management officials decide which areas to evacuate, where and when to close coastal roads, and where to position clean-up equipment in advance of the storm. The model has been in use since 2011 and is continually being improved. It starts with inputs from the National Hurricane Center’s storm surge predictions and National Oceanic and Atmospheric Administration wave forecast models. It then adds detailed information about the forecasted landfall region’s beach slope and dune height. The predictions define “very likely” effects as those that have at least a 90 percent chance of taking place, based on the storm’s forecast track and intensity.

As the USGS continues to take all appropriate preparedness actions in response to Hurricane Sally, those in the storm’s projected path can visit Ready.gov or Listo.gov for tips on creating emergency plans and putting together an emergency supply kit.

Source: Alerts2