Weather

Fast-Moving Storm to Bring Wind, Rain and Surge Impacts to Northern Gulf Coast

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October 18, 2019

As of 1000AM Central Time this morning, a fast-moving storm in the Gulf of Mexico was centered around 230 miles south of the Mississippi River Delta. The National Hurricane Center is calling this system Potential Tropical Cyclone 16, as the storm does not yet have the closed circulation it would need to be classified as a tropical storm and given a name.

On a morning flight, the Hurricane Hunters found that maximum sustained winds in this system had increased to 60 mph, which is well over the threshold for tropical-storm force winds. The National Hurricane Center forecasts a 90% chance that this system will form into a tropical storm before landfall- it would be called Tropical Storm Nestor, and be the 14th named storm of the Atlantic Hurricane Season. Whether or not this storm is named, it will bring wind, rain and storm surge impacts to the Northern Gulf Coast.

The National Hurricane Center forecast track map for Potential Tropical Cyclone 16, as of 1000AM CDT on Fri Oct 18.

This storm is moving to the northeast at 22 mph, which is a faster-than-normal forward motion for storms in the Gulf of Mexico. The average forward motion for a tropical system in this region is approximately 12 mph.

The advantage of fast-moving storms is that they generally pose less flood risk. Heavy rainfall is enhanced from slower-moving storms that stick around, dumping rain over the same locations for extended periods of time. For this reason, we do not expect substantial flooding from this system.

NOAA’s Quantitative Precipitation Forecast map (below) predicts the heaviest rain will fall offshore, with a large swath of rainfall exceeding 1.5 inches possible from the Florida Panhandle through eastern North Carolina, and a localized maximum exceeding 3 inches possible around Florida’s Big Bend. If the forecast holds, these rains will mostly benefit the region, as severe drought has gripped the southeast U.S. in recent weeks.

NOAA’s Quantitative Precipitation Forecast map valid from FRI OCT 18 at 0700AM to SUN OCT 20 0700AM Central Daylight Time.

Coastal flooding from this fast-moving system should generate minimal impacts as well, as the system will move through too rapidly to push extensive salt water onto land. The system also does not have a well-developed core and maximum sustained winds are not strong enough within a broad wind field to generate a large surge.

Although this webcam in Dauphin Island, Alabama, depicted mostly flat water and low waves, storm surge levels are observed between 1-2 feet above normal.

That said, much of the Gulf Coast from Louisiana through southwest Florida has already observed salt water levels at least one foot higher than normal astronomical tides. This includes Dauphin Island, Alabama, shown above on a snapshot from a local beach cam. Maximum storm surge levels could reach 2-3 feet along the eastern Florida Panhandle and potentially 2-4 feet in Apalachee Bay, where storm surge piles up very efficiently.

The map above depicts the highest observed storm surge levels at locations along the Gulf Coast, as well as maximum observed and forecasted wind speeds. We will keep this map updated throughout the storm and you can find the updated version at the U-Surge Project website.

The disadvantage of fast-moving storms is that they can catch us off guard, as they rapidly move to the coastline. Unlike flooding, wind impacts do not need extended time to develop. All we need to experience wind damage is an instantaneous velocity that is strong enough to bring down trees or tear shingles off roofs. Unlike heavy rainfall, just a few minutes of intense winds can produce substantial damage.

Therefore, we should expect the biggest potential impacts from this system to be localized wind damage near the location of landfall in the Florida Panhandle. Tropical storm force winds (39 mph+) are strong enough to bring down tree branches and cause power outages, and 50-knot winds (57 mph), are strong enough to start generating moderate damage to siding and roofs. This storm may be strong enough to inflict such damage along the eastern Florida Panhandle and Florida’s Big Bend region.