As of 11 AM EDT Tuesday, Idalia has strengthened into a category 1 hurricane and is situated northwest of Cuba. Despite less than favorable conditions for Idalia to strengthen yesterday, warm Gulf of Mexico waters are expected to lead to rapid intensification in the next 12 to 36 hours.

As Idalia tracks north toward the Gulf Coast tomorrow, it will encounter even warmer water than it’s been in over the last few days. Hurricane Idalia is expected to make landfall along the northern Gulf Coast of Florida Wednesday morning, though impacts are already being felt in the southern part of the state. 

The image above shows the current water temperatures in the Gulf of Mexico and Atlantic Ocean.

Warm ocean water acts as a heat reservoir, providing the energy and moisture needed to fuel the storm’s growth and development. 

It is not surprising to see that these warmer waters closer to the US coastline are above normal for this time of year, and more above normal than farther south where the storm began developing over the last few days.

The image above shows the current water temperatures in the Gulf of Mexico compared to normal.

Further, the depth of the heat in the Gulf of Mexico is impressive. Compared to the Gulf of Mexico prior to Hurricane Michael in 2018, which took a similar path through the region, the current depth of the heat in the water provides nearly 2 to 3 times the tropical cyclone heat potential.

Tropical cyclone heat potential is a measure of the heat content in the ocean, which supplies the energy for the development and intensification of tropical storms. The depth of the heat currently in the Gulf of Mexico is around 40 - 50 meters, and combined with the anomalous warmth of this water, produces an environment conducive to rapid intensification. 

The image above shows the current tropical cyclone heat potential in the Gulf of Mexico.

The National Hurricane Center (NHC) expects Idalia to develop into a major category 3 hurricane prior to landfall, with dangerous winds, heavy rain, and catastrophic life-threatening storm surge.

Hurricane-force winds sustained up to 125 mph are possible along Flordia’s Gulf Coast, with higher gusts and devastating damage likely. The latest guidance from the NHC, shown below, has the most severe impacts between Tampa Bay and Indian Pass on the panhandle. As we get closer to landfall, the area expecting the worst winds will be narrowed down.

Idalia will produce significant rainfall as well with the potential for flooding over a large area. The latest rain projections from the NHC, shown below, reveal a wide swath of 6 to 10 inches of rain in northern Florida. Parts of Georgia, North and South Carolina could see 6 to 10 inches of rain as well, with a large area of these states seeing 4 to 6 inches.

Perhaps the most dangerous and significant concern with Idalia is the storm surge. During a tropical cyclone, storm surge occurs when strong winds cause ocean waters to inundate coastal areas, causing a rapid and often dramatic rise in sea levels. 

Several factors contribute to the formation and severity of a storm surge, including wind, low pressure, forward speed, shape, and depth of the sea floor, angle of approach, size, and the shape of the coastline. 

The strong winds associated with tropical storms collect water and push it toward the coastline, as shown below.

Low air pressure at the center of a hurricane causes the sea level to rise, increasing the storm surge, which is shown in the figure above as well.

The forward speed, or speed at which the hurricane is moving, can impact the magnitude and inland penetration of the surge. Slower storms typically produce a more relentless surge over a large area that pushes farther inland. 

The shape and depth of the sea floor (continental shelf) play a key role in the impact of the storm surge as well. A wide, shallow continental shelf will result in a higher surge, acting like a gentle ramp for the water to be pushed up. A narrow, steep shelf, with deep water close to the shoreline, results in a lower surge, as the shelf acts like a wall.

The image above how the shape of the continental shelf impacts storm surge.

The angle of the storm’s approach can affect the storm surge, with a direct impact producing a greater surge. The size of a tropical storm is a factor too, as a larger storm will typically have a greater wind field and thus more water to move. 

The shape of a coastline, and whether it includes naturally concave areas, such as bays, sounds, and inlets, help determine how severe the storm surge will be. Low-lying areas are at greater risk, while water is funneled in and trapped by naturally concave areas. 

Finally, if the surge occurs during a natural high tide, the impacts can be much more severe. 

With respect to Idalia and the Florida Gulf Coast, several of these factors are concerning. Generally, this area has a wide and shallow continental shelf. Tampa Bay, Crystal River, and Cedar Key are just a few examples of where the shape of the coastline will worsen the storm surge. Strong category 3 winds will push huge amounts of water toward the coastline. The size, angle of approach, speed, and tides are elements that remain unknown at this time.

Still, the NHC is forecasting the following surge for the region, with a large stretch of coastline expecting a 10 to 15-foot surge above ground level, and several other areas up to 7 feet. Even the coast of Georgia and South Carolina could see a 2 to 4-foot storm surge.

The image above shows the expected storm surge with Hurricane Idalia as it approaches Florida.

As mentioned, the track will determine where the most severe storm surge will occur. At this time, nearly all residents along the Florida Gulf Coast need to stay informed and heed the advice of the authorities. 

It is important to note that a category 3 or stronger hurricane has never made landfall in Apalachee Bay. This is a potentially unprecedented event, as NWS Tallahassee explains below  

Below are the links to the most up-to-date information regarding Hurricane Idalia. You can follow along for updates as the storm approaches. 

Storm Track Cone

Expected Rainfall

Storm Surge Projection

Luke Stone
Forecaster, OpenSnow