BATON ROUGE, La. (BRPROUD) — As imagery keeps coming out of Southwest Florida, many, including myself, are heartbroken by what they are seeing. Rescues are ongoing as teams work to survey the area and cleanup begins. Unfortunately, the death toll has increased above 100, breaking into the top 5 deadliest hurricanes in Florida history with the name “Ian” most likely being retired at the end of the season.

Many people in Fort Meyers and the surrounding areas were seemingly caught off guard by Ian’s more southerly track towards the coast. Many did not evacuate for various reasons, including little resources to leave, perception of previous storms, or the thinking that the worst impacts were going somewhere else.

The focus on landfall in the Tampa Bay area was one reason why a more southern path was surprising. From the time Ian was first named a tropical depression up until landfall in Florida, there was uncertainty in the track of the center. This uncertainty made it tough for the forecasters at the National Hurricane Center (NHC) and the emergency managers to prepare.

Ian’s Setup and Track Uncertainty

Many atmospheric factors came into play to influence the forecast of Ian. Once a tropical depression was formed and the NHC issued its first advisory, it seemed likely that a hurricane was headed toward the Gulf Coast of Florida. The question was where along the coast would the storm make landfall.

The Bermuda high over the Western Atlantic helped Ian move westward across the Caribbean. The ridge of high pressure over the Southern U.S. shifted back to the west allowing a break in the pattern for Ian to move north into the Gulf of Mexico. This is when the uncertainty introduces itself.

An upper-level trough was moving over the Great Lakes to the east. This would eventually allow a cold front to push through the Southeast and pick up Ian to steer it northeast into Florida. When and where this would happen was up in the air over three days before landfall.

Some model guidance showed a slower storm and fast-moving trough allowing Ian to trek more west into the Florida Big Bend region. Other guidance showed a faster-moving storm and slower trough to allow a sharper turn northeast into Southwest Florida. Then the strength of the trough was giving models a tough time as a stronger trough would promote a more easterly track and vice verses.

The experts at the NHC take into account all of the guidance and look at the consensus as well as the synoptic (large-scale) patterns to forecast a track. During the weekend before landfall, model guidance was hinting at a more westerly track towards North Florida. Although, two reliable models were in disagreement. The GFS model had a more westerly solution while the ECMWF (Euro) model was more easterly. When looking at weather models, it is important to look at model consensus and the trends between the runs.

When the Saturday (9/24) NHC track had Ian making landfall over the Big Bend region, Ian was expected to weaken. This was due to the fact that if Ian tracked more west and towards North Florida, it would encounter strong wind shear associated with the trough. This would lead to the weakening of the system.

This solution was talked about frequently online and in the media. Unfortunately, some people in Southwest Florida believed the storm was not heading for them and did not take preparations early enough. Once landfall become closer, model guidance came into more of an agreement towards a more easterly solution.

This prompted the NHC to slightly shift the track to the east with each advisory by Sunday (9/25). With a more easterly track, Ian was expected to be a stronger storm at landfall as atmospheric conditions were still favorable.

Another focus was on a worst-case scenario for direct landfall in the Tampa Bay area. This was the forecast for Monday (9/26) into Tuesday (9/27). Again, a different landfall location was still on the table as the NHC noted the high uncertainty in the track. Impacts can also occur well away from the center track. Many people also, unfortunately, thought the worst would now only be in Tampa.

Even with hurricane warnings being issued Monday and Tuesday, evacuations were delayed in parts of the Fort Meyers area. This was the challenge with the track shifting east and delaying warnings.

The most important thing to do when a tropical system threatens near where you live is to keep up with the official forecasts because changes do occur and you need to be prepared in the event that your community now faces heightened impacts.

Understanding the Cone of Uncertainty

The cone of uncertainty graphic is a useful NHC product that forecasts where the center of a tropical cyclone will be up to 5 days out. Unfortunately, it is often misinterpreted.

The NHC will forecast an exact point for the cyclone’s center at 12-hour intervals up to 120 hours (5 days). Then at each point, a circle (not shown on official graphics) is drawn around it with a radius set so 2/3 of forecast errors over the past 5 years fall within the circle. The outside ends of the circles are connected to form the cone.

In other words, the center of the storm can be expected to stay within the cone 60-70% of the time. So there is about a 1/3 chance that the center deviates outside of the cone. The cone and forecast circles become larger the further out in time you go. This is due to the fact that confidence in exact track location decreases over time.

When looking at the cone, it is important to see where you are in relation to the cone, not just the center line, especially more than three days out. If you are in or anywhere near the edges of the cone, it is best to follow the forecast closely.

Cone of Uncertainty from the 5 PM EDT advisory on Saturday, September 24, 2022 || Advisory courtesy: NHC

An important note is that the cone is only used to forecast where the center of the storm may likely go based on historical error. Tropical cyclones are much larger than just a single data point. Impacts including strong winds, heavy rain, and storm surge can occur well outside of the cone. So the cone does good in showing historical track errors, but it does not tell the whole story.

In the example of Hurricane Ian, the cone from the Sunday night (9/25) NHC advisory stretched from Fort Meyers to Destin (red dots below) along Florida’s western coastline. This shows the inherent uncertainty based on historical errors in the cone. What the cone does not show is that impacts can absolutely occur well outside the cone. At this point in time, all of Florida had a chance to see some impacts associated with Ian.

Cone of Uncertainty from the 11 PM EDT advisory on Sunday, September 25, 2022 || Advisory courtesy: NHC

Potential Threats and Other Important NHC Products

In addition to the cone of uncertainty, which only forecasts the center point of the storm, the NHC also produces many other impact-based graphics. Possible impacts on your location are the most important thing to focus on when a storm rolls your way. These products can be found on the official NHC website and they are typically shared on their social media pages.

Winds
NHC produces probability graphics for the chance a certain location sees winds of certain speeds. Different graphics are for tropical-force winds (39 mph), 58 mph winds, and hurricane-force winds (74 mph). Paired with these graphics is a timed-out approach to the most likely arrival time of said winds as well as the earliest reasonable time of arrival.

The NHC explains that the earliest reasonable time graphic shows the “time before which there is no more than a 1-in-10 (10 percent) chance of seeing the onset of sustained tropical-storm-force winds” for a specific location. This graphic is useful to make sure preparations are in place before tropical-storm-force winds could begin.

Usually overlaid onto the cone of uncertainty graphic are the tropical storm/hurricane watches and warnings as well as the current wind field extent. This shows how far out tropical storm force winds (orange) and hurricane force winds (brown) extend from the center as of the issuing advisory. This also showcases that winds and impacts affect areas well outside of the cone.

Storm Surge
One of the biggest threats is in fact storm surge during the storm. Storm surge is the abnormal rise in the sea level over the astronomical tide levels due to a landfalling hurricane that can cause devastating flooding, especially in coastal communities. Not only is the height of the water that is dangerous, but the force of the water being pushed in by the winds is also strong enough to float cars away and push down weak structures. Debris and wastewater can find their way into the surge which also presents a threat.

To communicate the risk of storm surge, the NHC issues watches, and warnings when impacts are possible and expected, respectively. Potential inundation maps are also produced with their forecasts for storm surge heights. Your local county or parish should have evacuation zones based on the forecasted threat related to storm surge. It is important to know what zone you live in.

Tornados
To help the NHC with severe threats, the Storm Prediction Center (SPC) produces convective outlooks and tornado probability maps. Tornados can be a threat in the northeastern quadrant (relative to the storm motion) embedded in the feeder bands of the system. Below are maps produced on Tuesday (9/27), the day before the landfall of the center. Southeastern Florida had 9 reports of tornados that day. This showcases that impacts can be felt far from the storm’s center.

Flooding
Heavy, prolonged rainfall during tropical systems brings the threat of flooding to areas far away from the coast where surge is an issue. Flooding is a great concern with storms that have a slow forward speed during landfall, like Hurricane Ian. The Weather Prediction Center (WPC) will help the NHC with rainfall graphics such as the excessive rainfall outlook and rainfall forecasts.

The excessive rainfall outlook (bottom left) shows the risk of flash flood guidance being exceeded by rainfall within 25 miles of a point. Below is the outlook on Thursday (9/29) as Ian was moving through the Florida Peninsula which shows a high probability (above 70 percent).

The rainfall forecast (bottom right), or quantitative precipitation forecast (QPF), is a product issued typically over 2 or 3-day periods for the expected rainfall totals in inches. The image below shows over 10 inches expected in areas near the center of the storm and over 3 inches for parts of Florida including the Southeastern part of the state.

Other
On top of the other graphics, the NHC will condense the most important points about the storm and what impacts could be felt in a single product. These key messages will include relevant graphics to showcase the point. Below is an example from Ian that mentions the threat of surge, hurricane-force winds, and heavy rains.

Hurricane Ian key messages. || Courtesy: NHC

Bottom Line

When tropical systems threaten your community, it is important to have all the information from official sources to best assess your risk. The most important thing you can look at are graphics that communicate the risk that impacts from the storm will affect your area in addition to where the storm is going. Impacts, such as the aforementioned ones above can, and usually do occur well away from the center of the storm.

As learned from Ian, it is not wise to compare an incoming storm to previous storms, as tropical cyclones can be drastically different from each other. Also, keep in mind that certain forecasts can have uncertainty in regards to track location which could be a difference maker in who sees the worst of the storm. Keep updated on the forecasts in real-time and be prepared in the event you are told to evacuate.

To find resources to prepare and be safe, the NHC has some great pages to explore. Hurricane safety can be found here, and preparedness tips can be found here.