“Hurricane” Hal Needham is a storm surge scientist who specializes in data-driven storm surge analysis. He is the founder and president of Marine Weather and Climate.
The U-Surge Project has launched a community storm surge website for Cedar Key, Fla., as Tropical Cyclone Colin approaches. The website contains the first comprehensive data archive of coastal flood events at Cedar Key, a small village 80 miles north of Tampa.
U-Surge selected Cedar Key as a partner community thanks to extensive weather records in this historic location and its strategic location near Apalachee Bay. The physical features of this region, like shallow water and the concave shape of the bay, efficiently create large surges. Fortunately, this region infrequently observes hurricane landfalls, at least compared to locations farther west and south along Florida’s Gulf Coast.
The historic record for Cedar Key contains 30 tropical surges, the highest of which reached 8.5 feet in Hurricane Alma of 1966. When these observations are converted to a common datum, or reference line, Alma’s water level drops to 8.11 feet above the North American Vertical Datum of 1988 (NAVD88), but still retains first place.
Tropical Storm Colin is forecast to track northeast before making landfall near Apalachee Bay Monday evening. Although Colin has strengthened slightly overnight, the storm is rather disorganized, as the most intense convection is offset from the center of circulation. This is good news for residents of coastal Florida, as disorganized storms lack the broad shield of powerful winds for generating large surges.
Colin’s timing, however, makes things a bit more interesting. The storm is arriving just one day after the new moon, in a time of the lunar cycle in which tidal ranges increase. Fortunately, Colin is forecast to make landfall this evening, several hours after high tide. Therefore, expect the worst flooding impacts to occur around the time of this afternoon’s high tide, which is around 3:00 p.m. local time at Cedar Key.
I’m predicting that storm surge levels at that time will be around 2.5 feet above normal astronomical tides, creating a total water level of around 4.72 feet above NAVD88. Due to the high astronomical tides at that time, Colin’s total water level would rank ninth in the list of historic storm tides from tropical systems. Sea level rise helps boost Colin into the top 10, as storm tides are measures of total water levels, and sea levels have risen around 8 inches over the last century near Cedar Key.
A storm tide of 4.72 feet above NAVD88 would top the water level produced by Tropical Storm Debby in 2012 by several inches near Cedar Key. Debby splashed water over flood defenses, flooded roads, and inflicted some property damage, as seen in the video below, which is also posted on the U-Surge webpage for Cedar Key. The U-Surge project helps residents compare current and past events, as water levels are converted to the same datum.
In general, Colin’s biggest impact should be heavy rain, as the heaviest convection is displaced to the east of the center of circulation and is already impacting Florida. Heavy rainfall compounded with higher-than-normal storm tides will cause minor flooding in coastal communities from Tampa north to Apalachee Bay.
This originally appeared on Hurricane Hal's Storm Surge Blog.